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Growth, reproduction, and production dynamics of a littoral microcrustacean, Eurycercus vernalis (Chydoridae), from a southeastern wetland, USA
Abstract
Population and production dynamics of the chydorid Eurycercus vernalis were studied in the laboratory and in a small wetland during a 2-y period. Laboratory growth studies were conducted to measure the effects of temperature on E. vernalis growth and reproduction and to develop a multiple-regression equation that used temperature and mass-specific growth rates to estimate secondary production in the field population. Density, biomass, and production were estimated from benthic, water-column, and Nymphaea odorata leaf habitats within vegetated (Nymphaea) and nonvegetated (open-water) areas using monthly samples from the wetland. Eurycercus vernalis exhibited optimal growth, reproductive output, and net reproductive rate when reared at temperatures between 15 and 20°C. Reproductive age and egg development time decreased with increasing temperature, and these decreases led to increased innate capacity of population increase and decreased generation time with increasing temperature. In the field studies, annual density, biomass, and production were significantly higher in the Nymphaea zone than the open-water zone during both years. Eurycercus vernalis populations developed during the fall from oversummering resting eggs and reached maximum density, biomass, and daily production in mid to late spring when water temperatures reached 18 to 21°C. Mean annual density and biomass for the wetland pond were 2134/m2 and 42.2 mg dry mass (DM)/m2 in year 1 (1993), and 1122/m2 and 19.0 mg DM/m2 in year 2 (1994–1995). Annual production and the production/biomass ratio were 2138 mg DM m−2 y−1 and 50.7/y in year 1, and 1111 mg DM m−2 y−1 and 58.5/y in year 2. High production values suggested that E. vernalis is an important component of the microcrustacean community in the Nymphaea zone, especially during winter when production of most microcrustacean species is low.
... In spite of life tables and production analyses having much in common, the vast majority of studies incorporate only one approach, with no recognition of the other. Nonetheless, a small number of investigators have applied both approaches to the same population(s); e.g., hydropsychid caddisflies (Willis and Hendricks 1992), damselflies (Duffy 1994), microcrustaceans (Hall et al. 1970, Lemke andBenke 2004), crayfish (Momot and Gowing 1983), salamanders (Spight 1967), land snails (Staikou et al. 1990, Lazaridou-Dimitriadou andKattoulas 1991), and aquatic snails (Eleutheriadis and Lazaridou-Dimitriadou 2001). Production estimates in these papers may have arisen directly from the life tables or may have been an independent calculation, but these authors recognized that the simultaneous application of both approaches provided a more complete picture of population dynamics than either alone. ...
... However, the task certainly is not impossible, as demonstrated by simultaneous life-table-production studies of Willis and Hendricks (1992) on caddisflies and Duffy (1994) on damselflies. Life-table-production analyses should be somewhat easier for taxa such as crayfish (Momot and Gowing 1983), some microcrustaceans (Lemke and Benke 2004), and some aquatic beetles (Wallace andO'Hop 1985, Stagliano and, whose immature and adult stages coexist in the same habitats. Snails may be among the most amenable to such simultaneous analyses, as has been demonstrated for both terrestrial and aquatic species in Greece (Staikou et al. 1990, Lazaridou-Dimitriadou and Kattoulas 1991, Eleutheriadis and Lazaridou-Dimitriadou 2001. ...
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... Finally, the utilization of the mixing model provided evidence that Eurycercus was mostly feeding on epiphyton. This is consistent with the fact that this genus, often associated with macrophytes-rich habitats (Balayla and Moss 2003;Lemke and Benke 2004), is known to be a scraper. We are aware that the use of only one isotope and three food sources in our mixing model may have decreased the accuracy of assessing diet sources and that the use of another isotope would have provided more detailed information. ...
... The high nutritional quality of epiphyton reported in our study suggests that this feeding ground likely plays a key role in littoral food webs, as it can represent half of the food assimilated by some zooplankton species. Its potential high nutritional quality could be one of the factors accounting for the high density of microcrustaceans in littoral macrophytes zones (Lemke and Benke 2004;Walseng et al. 2006). ...
The maintenance of species diversity in a given environment is strongly linked to resource partitioning. Littoral macrophyte zones are heterogeneous environments with high microcrustacean diversity, where zooplankton have dietary access to seston as well as organisms growing on macrophytic surfaces (epiphyton). We conducted a field study in a macrophyte-rich backwater of the river Allier to examine how seston and epiphyton were used as potential food sources by four dominant cladoceran species. Fatty acids were analyzed in these two food sources to assess how their differential uptake affects the trophic trajectory of essential compounds from these resources to cladocerans. Our results showed resource partitioning among the four cladocerans studied; while Eurycercus fed mostly on epiphyton, Daphnia mostly consumed phytoplankton, and Ceriodaphnia and Simocephalus were able to forage on sestonic and epiphytic resources. Based on their polyunsaturated fatty acid (PUFA) content, it was evident that epiphyton was of higher food quality than seston in this macrophyte-rich backwater system. Variability of PUFA compositions of seston and epiphyton, and diversity of foraging strategies of cladoceran species, which represent the major link between microorganisms and consumers at higher trophic levels, affect dietary energy pathways and point to a variable PUFA transfer efficiency in backwater food webs.
... E. lamellatus, with its feeding strategy that allows it to feed on a resource not available to other microcrustaceans, is probably very competitive in such an environment. Lemke and Benke (2004) reported a higher density of Eurycercus vernalis in the Nympheae zone in mid to late spring. Phytoplanktonic species are often not well developed at this time of year (Sommer et al., 1986), but Eurycercus probably found in the Nympheae zone a periphytic resource allowing the establishment of a dense population. ...
The high species richness of zooplankton communities in macrophytes littoral zones could result from the diversity of potential trophic niches found in such environment. In macrophytes littoral zones, in addition to phytoplankton, neustonic, benthic and epiphytic biofilms can also be potential components of the microcrustacean diet. Here, we investigated the ability of three large cladocerans: Daphnia longispina, Simocephalus vetulus and Eurycercus lamellatus, to develop on periphyton as their only food source or as a complement to a phytoplankton resource in scarce supply. D. longispina exhibited a very low growth and reproduction rates on the periphytic resource and as S. vetulus seems unable to scrape on periphyton. In contrast, E. lamellatus could not grow on phytoplankton, and appears to be an obligatory periphyton scraper. This latter finding contrasts with previous studies suggesting that E. lamellatus could be able to scrap periphyton as well as filter-feed on suspended matter. These differences in feeding strategy probably reflect the different trophic niches occupied by these three species in macrophytes littoral zones, and may explain at least in part their ability to coexist in the same environment.
... We identified diet items to various taxonomic levels, typically order or family for benthic macroinvertebrates and genus for zooplankton. To estimate biomass of different invertebrates in sediment samples and trout-perch diets, we photographed up to 20 individuals of each prey type using a dissecting microscope and 318CU Micrometrics camera, measured prey items (±0.01 mm) with Image J software (Rasband 2009), and calculated dry biomass using published length-weight regressions (Dumont et al., 1975;Nalepa and Quigley, 1980;Smock, 1980;Culver et al., 1985;Makarewicz and Jones, 1990;Haugen and Rygg, 1996;Benke et al., 1999;Lemke and Benke, 2004;Soetaert et al., 2009; Riseng C. and Eaton L., University of Michigan, unpublished data). Whenever possible, we measured whole prey items; however, for some partially digested items we had to resort to measuring head capsule width or length. ...
Trout-perch are abundant in many North American aquatic systems, but the ecological roles of trout-perch as predators, competitors and prey remain relatively understudied. To elucidate the ecological role of trout-perch in Saginaw Bay (Lake Huron, North America), the spatial and temporal diet composition was quantified and the frequency of occurrence of trout-perch in diets of piscivorous walleye and yellow perch was evaluated. From May through November 2009–2010, trout-perch and their potential predators and prey were collected monthly from five sites in Saginaw Bay using bottom-trawls. Trout-perch were abundant components of the Saginaw Bay fish community, and in 2009, represented 13.5% of fish collected in trawls, with only yellow perch (38%) and rainbow smelt (19.1%) being more common. Trout-perch primarily consumed Chironomidae (84.0% of diet biomass) and exhibited strong, positive selection for Chironomidae and Amphipoda, suggesting that their diet preferences overlap with the economically important yellow perch and juvenile walleye. Energy content of trout-perch averaged 4795 J g−1 wet and was similar to yellow perch (4662 J g−1 wet) and round goby (3740 J g−1 wet). Thus, they may provide a comparable food source for larger piscivorous fish. However, despite their high energy density, abundance, and spatial overlap with other fish prey species, trout-perch were very rare in diets of piscivorous walleye and yellow perch in Saginaw Bay, indicating that trout-perch are a weak conduit of energy transfer to higher trophic levels.
... We know that E. longirostris s.str. is widely distributed through whole U.S.A. and southern Canada (Hann & Karrow 1984;Chengalath 1987;Lemke & Benke 2004) and present even in Churchill (Manitoba, Canada) (Jeffery 2011) and the Yukon Territories (our data). But more Canadian populations need to be studied to further assess species diversity. ...
Frey (1975) subdivided the genus Eurycercus Baird, 1843 (Cladocera: Eurycercidae) into three subgenera: E. (Eurycer-cus) s.str., E. (Bullatifrons) Frey, 1975 and E. (Teretifrons) Frey, 1975. We conducted a revision of the subgenera Eurycer-cus (Eurycercus) and E. (Bullatifrons) in the Holarctic based on the morphology of parthenogenetic females and a phylogeny of cytochrome c oxidase subunit I (COI ) sequences. The following six species are found to be valid: E. lamel-latus (O. F. Müller, 1776); E. macracanthus Frey, 1973; E. pompholygodes Frey, 1975; E. microdontus Frey, 1978; E. lon-girostris Hann, 1982; E. nipponica Tanaka & Fujuta, 2002. The separation of E. vernalis Hann, 1982 from E. longirostris lacks morphological and genetic justification, so E. vernalis is a junior synonym of E. longirostris. A new species, E. ber-ingi sp. nov., was found in several localities in Alaska, U.S.A. Its characters are intermediate between two subgenera sensu Frey (1975): a median keel is expressed, but only in the posterior portion of the carapace dorsum (while it is absent in E. (Bullatifrons) and passes through all the dorsum in Eurycercus s.str.); the dorsal head pores are located on the bubble-like projection (a character of the subgenus E (Bullatifrons), but the latter is sitting on a prominent transverse fold (character of the subgenus Eurycercus s.str.). The COI tree also does not support separation of the subgenus E. (Bullatifrons) from E. (Eu-rycercus), while separation of E. (Teretifrons) is well-supported. So, we propose to avoid a separation of E. (Bullatifrons) and regard all the species previously placed there as belonging to the subgenus E. (Eurycercus) emend. nov. We also demonstrat-ed that E. macracanthus, E. pompholigodes, E. longirostris and E. nipponica have much broader distributional ranges than previously known.
... tenebrosus: g AFDM = 0.000006 ocular carapace length [mm] 3.693 , R 2 = 0.98; O. australis: g AFDM = 0.00003 ocular carapace length [mm] 3.175 , R 2 = 0.96; MPV, unpublished data). We estimated DM of all other macroinvertebrates with linear regression equations developed by Leeper and Taylor (1998), Benke et al. (1999), Lemke and Benke (2004), and A. D. Huryn (University of Alabama, unpublished data). ...
Detrital inputs into ecosystems vary in quantity and quality (e.g., plant litter vs carrion). Variability in detrital quantity and quality potentially affects consumer biomass and rates of organic matter (OM) breakdown. We used cave streams to test 2 linked hypotheses regarding the influence of total detrital inputs on consumer biomass and the breakdown of high-quality carrion detritus. First, we hypothesized that cave systems with higher total OM availability would support a higher biomass of consumers. Second, we predicted that higher consumer biomass would cause faster carrion breakdown rates. To test these hypotheses, we quantified macroinvertebrate biomass and breakdown rates (k, d−1) of carrion (mouse carcasses, Mus musculus) in 4 cave streams in northeastern Alabama and southeastern Tennessee (USA) that varied in total OM storage. We estimated carrion breakdown rates in coarse- and fine-mesh packs (10-mm and 500-µm mesh size) to isolate the influence of scavenging by crayfish. Macroinvertebrate biomass (excluding crayfish) in carrion packs was positively correlated with OM storage, but neither macroinvertebrate biomass (excluding crayfish) nor OM storage were strong predictors of carrion breakdown rates. Crayfish biomass was not correlated with total OM storage but was positively correlated with coarse-mesh breakdown rates. Our study illustrates the influence of community structure and consumer biomass on detrital breakdown rates in cave ecosystems. However, determining how detrital inputs structure cave communities will require further study.
... Somatic growth rates of both cladocerans were positively affected by increasing temperature. This result is in line with other studies on zooplankton and particularly on cladocerans (Dawidowicz and Loose 1992;Lemke and Benke 2004), although growth rates can vary among species. As for all poikilotherms, reduced metabolic rates are generally induced by decreasing temperature and account for slower somatic growth (Angilletta et al. 2004). ...
We investigated the effect of food quality on somatic growth and reproduction of zooplankton at different temperatures (12°C, 15°C, 20°C, and 25°C). Standardized growth experiments of two cladocerans, Daphnia magna and Simocephulus vetulus, were performed on (1) high-quality food (Cryptomonas sp.), (2) relatively low-quality food (Scenedesmus obliquus), and (3) intermediate-quality food (Cryptomonas : Scenedesmus mixture). Food quality constraints on somatic growth and reproduction of the two cladocerans decreased with increasing temperature. For D. magna and for S. vetulus, differences between clutch size and growth rate of individuals fed on the three food sources were highly pronounced when they were reared at 12°C and 15°C; however, such differences decreased at 20°C and were negligible at 25°C Variations in food quality constraints with temperature can be explained by the variability of dietary polyunsaturated fatty acids, such as eicosapentaenoic acid and stearidonic acid requirements of these cladocerans. We conclude that dietary constraints exerted by food quality for zooplankton development vary as a function of different temperature conditions. © 2009, by the American Society of Limnology and Oceanography, Inc.
... Invertebrates removed from stomachs and benthic samples were identified to the lowest taxonomic level possible (Thorp & Covich, 2001;Merritt, Cummins & Berg, 2008), and their lengths were measured to the nearest 0.5 mm using 1-mm transparent graph paper placed on a dissecting microscope stage. Dry mass was estimated using regression equations from Leeper & Taylor (1998), Benke et al. (1999), Lemke & Benke (2004), and A. D. Huryn (unpubl. data). ...
1. Surface ecosystems provide the primary source of organic matter to many cave communities. Variation in the strength of connectivity to the surface suggests that some caves may be more resource-limited than others. To test this, we examined diet, prey availability and production of an obligate cave salamander Gyrinophilus palleucus (Plethodontidae), a top predator, in two south-eastern U.S.A. caves with different levels of organic matter (Tony Sinks cave, 165 g AFDM m−2; Bluff River cave, 62 g AFDM m−2).
2. We quantified density, biomass, growth rate, production and diet of G. palleucus monthly for 21 months. Diet composition, differences in prey communities and seasonal patterns in prey consumption were also analysed.
3. Salamander density, biomass and secondary production were significantly greater in the high organic matter cave (0.10 m−2, 0.18 g AFDM m−2, 0.12 g AFDM m−2 year−1) than in the low organic matter cave (0.03 m−2, 0.03 g AFDM m−2, 0.01 g AFDM m−2 year−1). Although growth rates were not statistically different between the two cave salamander populations, low recaptures probably influenced this result.
4. Isopoda prey were the major contributor to salamander production in the high organic matter cave (69%). In the low organic matter cave, production was provided by isopods (41%) and oligochaetes (20%). The lower number of prey taxa contributing to salamander production in the high organic matter cave suggests the ability to forage more selectively.
5. The differences in foraging strategy, density, biomass and secondary production were probably related to differences in the strength of surface connectivity, which controls organic matter supply. Links between basal resource level and top predator performance show the importance of bottom-up limitation in the food webs of caves and other detritus-based ecosystems.
... Production is a comprehensive representation of a population's 'success' because it is a composite of several other components: density, biomass, individual growth rate, reproduction, survivorship , and development time (Benke, 1993 ). Furthermore , secondary production analysis provides an estimate of the energy available for transmission from one trophic level to the next and, consequently, is a measure of the functional role of a population in an ecosystem (Waters, 1977; Lemke & Benke, 2004). Sigara (Halicorixa) selecta (Fieber, 1848) is a euryhaline species that is abundant in brackish and saline lagoons, with a wide range of salinity, normally up to 30 g L )1 (Scudder, 1976; Krebs, 1982). ...
1. This is the first study on the life cycle, growth and production of Sigara selecta, a Palearctic corixid species typical of brackish and saline waters, at the warmest limit of its European distributional range. The study combines field and laboratory approaches.
2. The S. selecta population studied was multivoltine, producing four asynchronous cohorts from early spring to December and overwintering in the adult state. Development time from egg to first adult ranged from 2 to 3 months. A minimum temperature threshold of 10 °C and diel amplitude of ≥10 °C were observed for reproduction and oviposition.
3. Maximum density and biomass were reached in mid spring and early autumn. The sex ratio was unbalanced, females dominating during most of the year, except in spring, when the sex ratio was balanced or dominated by males during the first adult emergence.
4. Laboratory rearing experiments at constant temperatures (18, 22 and 26 °C) pointed to a significant effect of temperature on egg development and nymphal growth. In the range of temperatures tested, both egg and nymphal instar duration decreased with increasing temperature. Mean nymphal development time varied from 43 days at 26 °C to 71 days at 18 °C, with a mean of 57 days. Survivorship was independent of temperature.
5. A reduction in nymphal and adult length was observed with increasing temperature.
6. Growth rates decreased with increasing body mass and increased as temperature increased. The first nymphal instar had the highest length increments and growth rates in all temperature treatments.
7. Satisfactory agreement was found between the field and laboratory degree-days required for complete development from egg to first adult. At constant and variable thermal regimes, degree-days decreased with increasing temperature.
8. Rate of growth in the field could be predicted with reasonable accuracy from a simple model obtained as a function of body mass. The model explained 67% of the variability in growth rates.
9. Annual production and production/biomass ratio (P/B) of S. selecta estimated by the Instantaneous Growth method were 1.28 g m−2 year−1 and 13.71, respectively. Spring and autumn cohorts contributed 32% and 54%, respectively, of total annual production. Maximum production corresponded to intermediate temperature periods, although summer production may have been underestimated because of the longer sampling interval relative to cohort interval production. The Size Frequency method underestimated production by at least 18% with respect to the Instantaneous Growth method.
... Chydoridae are typically associated with vegetation (Smith 2001), and are typically more abundant in structurally complex habitats where macrophyte coverage is around 40% (Tremel et al. 2000). Lemke and Benke (2004) also found that a species of Chydoridae had significantly greater abundances, biomass, and production in vegetation than in areas devoid of vegetation. I also found high abundances of several fishes that can decimate zooplankton populations and can also cause zooplankton to avoid the area due to increased predation risk (Burks et al. 2001;Romare et al. 2004). ...
A large scale habitat manipulation was conducted to assess the effects of establishing an emergent macrophyte, American water willow Justicia americana, on littoral reservoir communities. Coves in three large (>1,800 ha) Kansas impoundments were chosen and half planted with water willow. Sampling was conducted during the summer from 2001 to 2004. I found that water willow coves had more complex habitat as well as higher abundance and diversity of fishes, macroinvertebrates, and zooplankton than control coves. However, strong temporal variation in water levels influenced the amount of inundated water willow available in these systems. The effects of water willow on density, growth, condition, and diet of age-0 largemouth bass Micropterus salmoides were assessed. Significantly higher densities of age-0 largemouth bass were found in water willow coves, but growth, condition, and diet did not differ between water willow and control coves. Therefore, water willow was able to support higher abundances of age-0 largemouth bass than control coves without affecting growth, condition, or diet. Characteristics of age-0 largemouth bass from the water willow coves were compared to those from two small impoundments (<80 ha) with abundant macrophyte and healthy largemouth bass populations. Small impoundments had higher densities of age-0 largemouth bass than water willow coves in the three large impoundments, but individuals on average also had lower growth, condition, and fewer fish in their diet. Thus, largemouth bass populations in small impoundments may be more regulated by density dependent factors than populations in large impoundments. Overall, water willow is beneficial to littoral areas, supporting an increase in both abundance and diversity of assemblages. Finally, I used a field experiment to test the inundation and desiccation tolerance of water willow for different depths and durations. Water willow was susceptible to inundation, but resistant to desiccation. My findings provide information that can be used to select candidate reservoirs for water willow establishment based on expected water-level fluctuations. Funding and support was provided by the Kansas Department of Wildlife and Parks; KSU Division of Biology; Kansas State University; U. S. Geological Survey; The Wildlife Management Institute; Federal Aid in Sport Fish Restoration Act. Additional support has been provided by Terry C. Johnson Center for Basic Cancer Research; American Fisheries Society including the Kansas Chapter and North Central Division. Doctor of Philosophy Doctoral Department of Biology Keith B. Gido
Background
Chydoridae is the most diverse family of cladocerans but information about their biology or life cycles is still limited, perhaps because of the hard task that their taxonomy involves or that culture in optimal conditions are not described for several species.
Goals
This study examined the effects of culture conditions (algal concentration, algal species, and temperature) on the demography of Alona guttata (Sars, 1862) to obtained their maximal growth rates.
Methods
Life table analysis with the chydorid A. guttata were performed as follows: five females per cohort (six replicas) were fed on either Chlorella vulgaris (Beijerinck, 1890) or Nannochloropsis oculata (Hibberd, 1981) at 0.5×10⁶ or 2×10⁶ cells/mL, reared at 20ºC or 25ºC and photoperiod 16:8 h (light: dark). Media was supplemented with an artificial substrate. Then, daily fertility and survival were assessed to estimate the demographic parameters: average lifespan (ALS), life expectancy at birth (LEB), generation time (GT), gross reproductive rate (GRR), longevity, net reproductive rate (NRR), and the intrinsic rate of population increase (r).
Results
Significant effects were observed due to the three factors tested and their interactions. Increasing algal concentrations of either C. vulgaris or N. oculata promoted higher fertility and longer survival. Lower temperature extended the ALS and LEB when organisms were fed on the highest algal concentration. The highest r values were observed when Alona was fed on N. oculata at 2×10⁶ cells/mL.
Conclusions
The best culture conditions, in terms of the population growth rates of A. guttata, were provided by N. oculata at 2×10⁶ cells/mL at 25°C with the supplementation of artificial substrate.
Processes that regulate common carp (Cyprinus carpio) recruitment (i.e. survival of eggs, larvae and juveniles) are largely unknown. In interconnected lake-marsh systems of Minnesota, young of year (YOY) carp are generally found in marshes that winterkill and lack bluegill sunfish (Lepomis macrochirus), an abundant native predator. This suggests that bluegills might function as a biocontrol agent for carp. Further, whereas YOY carp are commonly found in winterkill marshes of south-central Minnesota, they are not found in similar systems in northern Minnesota where lake productivity is much lower, suggesting an aquatic productivity bottleneck on carp recruitment. Finally, in marshes where carp recruit (productive and bluegill-free), YOY must disperse into adjacent lakes to drive high population abundance. In this study, I conducted three experiments to test 1) the effect of bluegills on carp recruitment; 2) the effect of aquatic productivity on larval carp survival, growth and diet; 3) natural dispersal tendencies of YOY carp from a marsh into an adjacent lake. The first experiment employed four (20 m diameter) impermeable enclosures from 2011-2014. Each year, enclosures were stocked with carp eggs and every other one was stocked with bluegills. Backpack electrofishing surveys conducted five weeks later showed that carp catch per unit of effort (CPUE) was over 10-fold lower in the enclosures stocked with bluegills than in the controls. The second experiment, conducted in 2014 and 2015 used aquaria stocked with carp larvae and supplied with zooplankton densities and community structures from lakes of three different trophic states (oligo-, meso-, and eutrophic). It showed that carp larvae selectively consumed macrozooplankton (> 200 μm) and their growth rates were highest in the eutrophic lake and lowest in the oligotrophic lake. Survival, however, was high in all treatments. The third study was conducted in a natural lake-marsh system and utilized passive integrated transponder (PIT) tags to quantify the outmigration of YOY carp from the marsh to the lake. It showed that < 6% YOY carp outmigrated to the lake, supporting previous indirect estimates. The results of these three studies are important to understanding recruitment dynamics of carp in lake-marsh systems in Minnesota.
Areas with littoral macrophytes play an important functional role in freshwater systems. In addition to the high productivity recorded in such areas, they also shelter a high diversity of organisms. However, possible links between spatial heterogeneity, biodiversity and energy pathways are still poorly known. As they constitute the major link between microorganisms and species higher in the food web, microcrustaceans play a key role in the transfer of polyunsaturated fatty acids (PUFA) to organisms at higher trophic levels. In this study, we wanted to assess if microcrustaceans diversity encountered in macrophytes littoral zones would lead to a variability of PUFA transfer in the food web. This work combined controlled conditions experiment and studies run in natural environments in order to help the interpretation of results from lipid analysis, isotopic analysis and fatty acid isotope analysis. Our results indicate that there are no differences of PUFA concentrations between cladocerans from a macrophyte littoral zone when they were exposed to the same pool of dietary PUFA. Hence, in heterogeneous feeding habitats such as macrophytes zones where these cladocerans often co-exist, foraging behavior of cladoceran species more than differences of metabolism may be crucial for determining PUFA transfer to upper trophic levels. In addition to seston, our study shows indeed that some cladoceran species are able to forage on the epiphytic and neustonic compartments. Lipid analyses highlight moreover that the diversity of trophic compartments lead to a variability of PUFA inputs to primary consumers. In our study, the epiphytic compartment is indeed significantly more concentrated in PUFA than seston. At the air-water interface, neuston is moreover characterized by important allochthonous organic matter accumulation. During a pollen rain, this organic matter represents an important source of carbon and PUFA for some microcrustacean species. In macrophytes littoral zones, cladocerans complementarity leads to a more complete use of PUFA sources. The association of trophic compartment diversity and microcrustacean diversity probably allows an optimization of PUFA transfer to higher trophic levels.
Dietary niches of fishes have traditionally been evaluated at the population level, with diet pattern central tendencies compared spatio-temporally among habitats and populations. More recently, however, studies have emphasised the importance of within-population diet variation and niche partitioning. Several studies have examined diets of young yellow perch (Perca flavescens) at the population level and have described an ontogenetic transition from zooplankton to benthic prey during the first year of life. However, independent of ontogenetic diet shifts, intrapopulation variation of young yellow perch diets remains largely unexplored. We quantified patterns of diet composition in age-0 yellow perch collected from Saginaw Bay, Lake Huron, USA during July–October, 2009 and 2010. We observed substantial variation in diet composition among individuals across and within sites, but found relatively weak evidence indicating an ontogenetic diet shift. Zooplankton were the dominant prey for age-0 yellow perch on most occasions, and individual diets were composed primarily of either zooplankton (e.g. Daphnia spp., Calanoida) or benthic (i.e. Chironomidae larvae, Chydoridae) prey. These patterns were not simply attributable to differences in prey availability and ontogenetic diet shifts, because a) not only diet composition, but also prey selectivity (Chesson's α) varied among sites and b) individual and spatial diet differences were evident independent of ontogeny. Within-cohort differences in diet composition may be an important, but often overlooked, phenomenon with implications for cumulative trophic interactions and intracohort growth and survival among young fish.
The life table is a well known approach for understanding populations and has appeared in general ecology textbooks for >60 y. Secondary production is associated with energy flow, but methods rarely appear in texts. Our objectives were to: 1) demonstrate conceptual/analytical relationships between secondary production and life tables, 2) use a real example of pond-breeding salamanders to illustrate how the 2 approaches can be integrated, and 3) use publication frequency analysis to determine trends and biases for each approach within ecological (particularly aquatic) subdisciplines. The example illustrated that both approaches incorporate age- or stage-specific survivorship. The main difference is that life tables are used to calculate production of offspring with age-specific fecundity, and production analyses are used to calculate production of biomass with mass-specific increments. Publication frequency analysis over 12 y demonstrated that 78% more papers used life tables (698) than production (393) overall, but 50% more papers used production (353) than life tables (236) in basic research. Furthermore, production was studied primarily in aquatic (98%), mostly benthic (77%), environments. Life tables were used primarily in terrestrial environments (65%). Recognizing the relatedness of these concepts and usage biases may explain philosophical differences and help bridge gaps between terrestrial–aquatic and population–ecosystem ecologists.
Invertebrate secondary production, or the formation of invertebrate biomass through time, has been estimated in many freshwater benthic habitats. It has been a major research theme for the North American Benthological Society (NABS), and many of its members have made significant contributions to the subject, both before and during the existence of J-NABS. Although some benthic production work occurred before 1960, the major methods were developed primarily during the 1960s and 1970s. Most of these methods also were applied in terrestrial and marine environments. The main focus of our paper is how secondary production has been used as an essential variable in facilitating answers to a wide variety of ecological questions. Benthic freshwater production studies before the inception of J-NABS were primarily related to life history, interpopulation comparisons, niche overlap/competition, predator–prey relationships, differences in production/biomass (P/B), energy flow, the trophic basis of production, habitat-specific microdistributions, effects of pollution and dams, and quantification of aquatic–terrestrial linkages. Since that time, new applications have been related to habitat-specific macrodistributions, quantitative food webs, experimental and tracer-based studies of trophic resources, chemical flows/stoichiometric relationships, diversity/function relationships, influence of nonnative species and landuse changes, implications of metabolic theory, and the importance of meiofauna vs macrofauna. J-NABS has been a major outlet for many of these applications, has probably included a higher fraction of papers incorporating secondary production analysis than any other journal, and probably will continue to be a leader in this area.
The high species richness of zooplankton communities in macrophytes littoral zones could result from the diversity of potential trophic niches found in such environment. In macrophytes littoral zones, in addition to phytoplankton, neustonic, benthic and epiphytic biofilms can also be potential components of the microcrustacean diet. Here, we investigated the ability of three large cladocerans: Daphnia longispina, Simocephalus vetulus and Eurycercus lamellatus, to develop on periphyton as their only food source or as a complement to a phytoplankton resource in scarce supply. D. longispina exhibited a very low growth and reproduction rates on the periphytic resource and as S. vetulus seems to be able to feed mainly on suspended particles. In contrast, E. lamellatus could not grow on phytoplankton, and appears to be an obligatory periphyton scraper. This latter finding contrasts with previous studies suggesting that E. lamellatus could be able to scrape periphyton as well as filter-feed on suspended matter. These differences in feeding strategy probably reflect the different trophic niches occupied by these three species in macrophytes littoral zones, and may explain at least in part their ability to coexist in the same environment.
Cumulative incorporation of radiolabeled algal (NaH14CO 3) and bacterial (14C-acetate) carbon associated with benthic organic matter (BOM) was measured at timed intervals to determine the relative importance of algal, bacterial, and detrital components of BOM to the growth and reproduction of Eurycercus vernalis (Chydoridae). Five times more algal than bacterial carbon was incorporated, which corresponded to relative amounts of algal and bacterial carbon quantified from the BOM. Algal and bacterial carbon provided 38% and 8% of the carbon required for Eurycercus growth and reproduction, respectively. Approximately 54% of the carbon required for Eurycercus growth was presumably provided by nonlabeled microbes (e.g., fungi, protists) or detritus. Parallel studies were conducted to measure the growth and reproduction for Eurycercus fed diets varying in amounts of algae, bacteria, and detritus. Effects of diet were especially noticeable in early instar growth and reproduction. Individuals fed diets with high algal and bacterial biomass relative to detrital content exhibited higher maximum somatic growth rates (75-89% d-1) than those fed aggregate and particulate detritus (51-60%). Egg production and net reproductive rate were highest for females fed nutrient-supplemented algae and corresponded to increased survivorship, early reproduction, and larger clutches. Survivorship was highest for females fed aggregate detritus; however, the percentage of total growth allocated toward egg production was similar for individuals fed aggregate detritus and cultured algae (67-82%). Relative trophic importance of algae and bacteria as constituents of BOM likely depends on their relative abundance, but the two in combination can be substantially more important than the detritus alone. © 2007, by the American Society of Limnology and Oceanography, Inc.
1. In contrast to extensive studies of zooplankton in lakes, the role of microcrustaceans in wetlands is not well studied. In this study, spatial and temporal patterns of microcrustacean assemblage structure and secondary production were quantified over a 2-year period in a southeastern U.S.A. wetland.
2. Thirty-two species, including 19 cladocerans, 10 copepods and three ostracods, generated different temporal patterns of density and production between vegetated (Nymphaea) and non-vegetated (open-water) zones reflecting species-specific differences in life histories.
3. Summer assemblages were dominated by small, planktonic filter-feeders, typified by high annual production/biomass (P/B) and daily production. In contrast, winter assemblages were dominated by larger, epibenthic detritivores with low P/B and high biomass. Seasonal shifts in the relative importance of planktonic species in the warmer months to benthic and epiphytic species in the cooler months suggest that energy flow pathways through microcrustaceans may vary seasonally.
4. Total annual production was higher during both years in the Nymphaea zone (13.0 g and 13.6 g DM m−2 year−1) than the open-water (8.2 and 6.3 g DM m−2 year−1), and was similar between years for the entire wetland pond (12.3 and 12.2 g DM m−2 year−1).
5. Although wetland ecosystems have been the subject of considerable ecological research in the past 20 years, our study is one of the few to demonstrate a highly diverse and relatively productive microcrustacean assemblage. Such comprehensive production studies can be used to quantify the ecological importance of microcrustaceans in freshwater wetland ecosystems.
Habitat connectivity and regional heterogeneity represent two factors likely to affect biodiversity across different spatial scales. We performed a 3 × 2 factorial design experiment to investigate the effects of connectivity, heterogeneity, and their interaction on artificial pond communities of freshwater invertebrates at the local (α), among-community (β), and regional (γ) scales. Despite expectations that the effects of connectivity would depend on levels of regional heterogeneity, no significant interactions were found for any diversity index investigated at any spatial scale. While observed responses of biodiversity to connectivity and heterogeneity depended to some extent on the diversity index and spatial partitioning formula used, the general pattern shows that these factors largely act at the β scale, as opposed to the α or γ scales. We conclude that the major role of connectivity in aquatic invertebrate communities is to act as a homogenizing force with relatively little effect on diversity at the α or γ levels. Conversely, heterogeneity acts as a force maintaining differences between communities.
Many reservoirs in arid regions experience highly variable water levels caused by seasonal inflow fluctuations and designated outflow requirements. At Shasta Lake, California, managers plant cereal-grain grassbeds on exposed drawdown shorelines to increase juvenile fish habitat, localize productivity, and increase invertebrate fish prey. To determine the efficacy of these plantings, the abundance of juvenile black basses Micropterus spp. (20–55 mm standard length) and the amount of periphyton and macroinvertebrate prey were compared among three treatment types: (1) planted grassbeds of cereal barley Hordeum vulgare; (2) artificial rope grassbeds, which eliminated physical deterioration and nutrient release; and (3) nonplanted control sites with predominately sand and gravel substrates. In comparison with control areas, juvenile black bass abundance averaged 54 times higher in planted grassbeds and 230 times higher in artificial grassbeds. Periphyton (chlorophyll a) and benthic invertebrate biomass did not differ significantly between planted grassbeds and control sites. In artificial grassbeds, periphyton was more than two times the control levels, and benthic invertebrate biomass was more than 12 times the control levels. We conclude that the long-term availability of physical structure, rather than nutrient release associated with decomposition of grassbed materials, drives use and effectiveness of grassbed treatments. Future management decisions in drawdown reservoirs should emphasize increasing long-term availability and integrity of physical habitat for juvenile fishes in the littoral zone.
SUMMARY 1. Growth, reproduction and life-history parameters were measured for three cladoceran species from a small south-eastern wetland, U.S.A. Simocephalus serrulatus, Diaphanosoma brachyurum and Scapholeberis mucronata juveniles were reared at temperatures between 10 and 25 °C on natural food resources.
2. Growth rate increased with temperature and decreased with individual size for all three species. Maximum somatic growth rate was higher for Simocephalus (49–72% day−1) and Diaphanosoma (21–91% day−1) than for Scapholeberis (11–45% day−1). Multiple regression equations were developed which predict temperature- and mass-specific growth rates for each species.
3. Scapholeberis egg production was positively related to temperature; however, maximum egg production occurred at intermediate temperatures for Simocephalus and Diaphanosoma. Mean cumulative egg production was higher for Scapholeberis (28–92 eggs per female) than for Simocephalus (18–25 eggs per female) and Diaphanosoma (1–41 eggs per female), and was related to differences in reproductive strategy and survival.
4. Survival was inversely related to temperature in most cases. For all three cladocerans, the intrinsic rate of increase (r) and net reproductive rate (R0) increased with temperature, whereas generation time (G) decreased. Greater egg production by Scapholeberis compared with the other two cladocerans was consistent with higher R0 values for Scapholeberis at any given temperature. Although r was very similar among species, G was typically longer for Scapholeberis than for Simocephalus and Diaphanosoma.
5. This analysis provides basic information about the population parameters of these coexisting wetland species, and the growth rate models can be applied to field data to determine production dynamics.
To study experimentally the relation between zooplankton and phytoplankton, laboratory cultures of Daphnia hyalina Leydig were set up. The combined influence of food quality and quantity on growth, birth-rate and longevity was measured. The effect of seven different food regimes was tested. Natural unfiltered lake water from the eutrophic lake Tjeukemeer was used in one regime. The food value of the natural unfiltered lake water appeared to be relatively low, which was most likely caused by the abundance of large sized algae in the lake water.
A computer simulation was used to investigate the relative effects of changes in net fecundity and development time on population growth rate (r). Increases in net fecundity had the largest effect on r when net fecundity is small. Conversely, decreases in developmental time had the largest effect on r when net fecundity was large. The intersection point where similar changes in developmental time, and net fecundity had equivalent effects on r was also investigated in four organisms with very different life histories. Cases were considered where changes in net fecundity and developmental time are correlated and different results were obtained.
The mean carapace lengths of first instar and primiparous females were 356 ± 27 μm (SD, n = 1225) and 721 ± 62 μm (n = 346), respectively. Females maturing in an early instar were smaller than those maturing later. Duration of juvenile and adult instars decreased at higher temperatures. Juveniles molted more frequently and had a shorter instar duration than adults. The rates of embryonic and postembryonic development increased and the duration of development decreased at higher temperatures. The duration of development in the laboratory was shorter than that determined at comparable temperatures in the field. The duration of embryonic development was a function of temperature, whereas the duration of postembryonic development was a function of both temperature and nutrition. The mean longevity of laboratory animals at 10°C was 102 d (17 instars) for females and 78 d (13 instars) for males. The mean longevity of field D. ambigua tended to decrease with increase of temperature. At comparable temperatures, the much shorter life-span of field Daphnia compared to laboratory animals was attributed to lower nutrition in the field. Growth rate was comparatively rapid in young animals and progressively decreased as animals aged. Within the range of temperatures (5-30°C) studied, growth rates generally increased with increasing temperature. The growth rate of field D. ambigua was affected by both temperature and food. The lower growth rates of field animals compared to laboratory animals probably resulted from lower food availability in the field. For laboratory animals, the mean number of young produced per brood tended to increase progressively during the early stage of adult life and decreased toward the end of the life-span. High temperature increased the frequency of reproduction; high food concentration increased the number of young per brood and the total number of young produced during a life-span. Female Daphnia grown in the field lived a significantly shorter time, had smaller clutch sizes, and produced fewer broods and fewer total young than laboratory females. Although reproduction is affected by temperature, light, food, oxygen, and other factors, food probably was the main factor which regulated the number of young produced in the field. /// Средняя длина панциря у самок 1 возраста и впервые размножающеихся, составляла соответственно 356±27 мкм ( SD n= 1225)и 721±62 мкм (n = 346). Самки, созревающеие в раннем возрасте, мельче чем самцы, созревающие позднее. Продолжительность развития ювенильных и имагинальных стадий снижается при более высоких температурах. Ювенильные особи линяют чаще и имеют меньшую продолжительность отдельных стадий, чем имаго. Скорость змбрионального и постзмринального развития повышается, а продолжительность развития снижается при повьшении температуры. Длительность развития влабораторных условиях короче, чем при сходных температурных усповиях в природе. Продолжительность змбрионального развития - функция температуры, в то время как продолжительность постзмбрионального развития - функция и темпервтуры и питания. Средняя продолжительность жизни у лабораторных животных при 10°C - 102 дня (17 возрастов) у самок и 78 дней (13 возрастов) у самцов. Средняя продолжительность жизни у полевых D. ambigua снижается при повьшении температуы. При сравнимых температурах более короткая продолжительность жизни у дафний из природных местоовитаний в сравнении с лабораторной популяций, определяется более низким у повнем пищевой активности. Скорость роста относительно высока у молодых животных и снижается у более взрослых в прогрессивной зависимости. В исследованном интерале температур скорость роста в целом повьшается при повьшении температуры. у D. ambigua из прироцных местообитаний скорость роста определяятся и температурой и пищеной активностью. Низкая скорость роста у животных из природных популяций, в сравнении с лабораторными, очевидно, результат меньшей доступности пищи в приподных местообитниях. Для лабораторных животных среднее количество молодых особей на 1 самку прогрессивно возрастает в течение ранней стадии имагинальной жизни и снижается к концу жизни. Высокая температура увеличивает честоту размножения: высокая концентрация пищи повьшает плодовитость и общее количество потомства от одной самки в течение жизни. Самки дафний, выросшие в природных условиях, имеют меньшую продолжительность жизни, более низкую численность выводков и дают меньше потомства, чем самки лабораторной популяции. Хотя активность размножения зависит от температуры, освещенности, пищи, кислорода и других факторов, пища - основной фактор, регулирующий численность нового поколения в природных местообитаниях.
Emergence of aquatic insects from freshwater systems can provide information that is useful from both taxon-specific and ecosystem perspectives. Although numerous studies of emergence have been conducted in high-latitudes systems, relatively few studies have been done in warm-water systems, particularly in wetlands, where multiple generations and long emergence periods are likely. We used emergence traps in a small beaver-impounded wetland in the southeastern USA to measure density and biomass of emerging insects, and deposition basins to measure adult return and potential export from the system. We focused on 2 major habitats of the wetland: a shallow (0-1.0 m) vegetated zone dominated by the white water-lily Nymphaea odorata and a deeper (>1 m) open-water zone. Insects (primarily Chironomidae) emerged from the Nymphaea zone throughout the year, but peaked in April at 205 individuals·m -2·d -1 and then declined from mid June to November to 20-50·m -2·d -1. Emergence from November through January was <10·m 2·d 1. Insects (primarily Chironomidae) did not begin emerging from the open-water zone until late March, but continued emerging through November. Annual emergence in the Nymphaea zone of 16,128 individuals/m 2 and 2.39 g dry mass/m 2 was significantly higher than 4374/m 2 and 0.59 g/m 2 in the open-water zone. Tanytarsini (primarily Tanytarsus) chironomids accounted for >33% of the emergent biomass in the Nymphaea zone, whereas Chaoborus punctipennis and Cladopelma sp. accounted for 19% and 21% of the emergent biomass, respectively, from the open-water zone. The emerging densities and biomasses of at least 6 taxa were significantly higher in the Nymphaea zone that in the open-water zone, and only Chaoborus was higher in the open water. Depositional trapping showed that deposition of adult insects in the aquatic environment averaged 25% of emerging numbers and biomass. The mayfly Caenis diminuta was common in deposition traps (1253 individuals·m(·2)·y 1), but avoided emergence traps. Both emergent and depositional trapping appeared necessary to quantify terrestrial activities of aquatic insects. Future comparisons of emergence and deposition data with larval production in the wetland will enable us to determine the fraction of production that is represented by emergence and the fraction that returns to the aquatic environment.
The life history, population dynamics, and secondary production of Hyalella azteca (Amphipoda) were studied in a small southeastern wetland pond. Habitat-specific sampling was used to estimate density, biomass, and production in each of 3 habitats (benthic, Nymphaea odorata leaves, and submerged wood). Laboratory experiments at different temperatures (10, 15, 20, 25, and 30 degrees C) provided predictive equations for estimating growth rate and egg development times that could be applied to field populations. Size-frequency data from field sampling suggested that H. azteca had 2 major cohorts per year, but reproduction was continuous from spring through fall. Mean annual density and biomass were 904/ m(2) and 85 mg dry mass (DM)/m(2). Daily growth rate was a function of both individual mass and temperature. Annual production of somatic tissues as estimated by the instantaneous growth method (675 mg DM . m(-2). y(-1)) agreed well with that using the size-frequency method (714 mg DM . m(-2). y(-1)). Egg production (252 mg DM . m(-2). y(-1)) represented 27% of total production (927 mg DM . m(-2). y(-1)). Annual production:biomass (P/B) was 7.8 without eggs and 9.8 with eggs. Habitat-specific estimates of density, biomass, and production were highest in the benthic habitat. The contribution of somatic production from Nymphaea leaves to total amphipod production was low (6.2%), but temporal patterns of production followed trends in leaf abundance. Production on leaves reached 29% in September when leaves were most abundant. Contributions of animals from submerged wood were consistently low (2.9%). Monthly densities and production peaked in May at the start of the summer cohort, decreased throughout summer, and showed a small increase in October at the start of the winter cohort. Although egg production and birth rates were highest in summer months, high death rates were responsible for the late-summer declines in density and production. These temporal trends in production suggest heavy predation or environmental stress, or both, during summer months.
Correlations were determined between growth/body condition of centrarchids age 0+ to 1+ and abundance of specific taxa of zooplankton in the littoral zone of three lakes in piedmont North Carolina over a period of eight months. Stomach analyses were conducted, and electivity indices calculated to provide comparative data. Significant differences were found in body condition, growth rate, and zooplankton abundance between lakes (P < 0.05, ANOVA). First year growth and changes in body condition of age 0+ Lepomis, Pomoxis and Micropterus species were positively correlated with the abundance of copepod nauplii and copepodids in each lake (mean r s=0.898, P < 0.01). The abundance of adult copepods was also frequently correlated with growth and body condition, but at a lower level of probability (mean r s=0.713, P < 0.05). The number of significant correlations dropped sharply as fish age increased to 1+ years. Significant associations could not be generated using data for Rotifera, Protozoa or Ostracoda, and were quite infrequent for Cladocera. The correlations suggest that copepod nauplii and copepodids are primary food during the critical period when larval centrarchids switch from endogenous to exogenous nutrition. The correlation data were supported by stomach analyses and electivity indices which indicated 0+ fishes to be mainly utilizing copepods, supplemented with cladocerans, insect larvae, and fishes in the more piscivorous species. The mean prey size for larval bluegill and largemouth bass (≤15 mm total length) was found to be 0.48 mouth gape and 0.60 mouth gape respectively, which translates to prey sizes of 0.11 mm to 0.35 mm during the larval stage. Due to mouth size during the period of first feeding, most adult copepods and cladocerans are too large to be ingested even if prey could be handled with dimensions approaching 0.99 mouth gape. The relative insignificance of Cladocera in the diet of post-larval fishes appears to be due to negative selection rather than to influences of seasonal abundance or encounter probability. It is evident that in these North Carolina lakes, cladocerans are not so universally important in the diet of age 0+ centrarchids as studies on northern and midwestern lakes would indicate. Correlations, stomach analyses, and electivity indices can be integrated into a multiple factor approach to diet studies, allowing consideration of several environmental and population variables and yielding more meaningful results than by using one method alone. Potential impacts of aquatic pollution on food organisms required during the first weeks of feeding should place additional priority on diet studies and ecological relationships between centrarchids and the littoral zone.
Microcrustaceans are common in the meiobenthos of many freshwater habitats including wetlands. Quantification of their functional roles, including determination of secondary production, has lagged behind our understanding of macrobenthos because microcrustaceans are small animals with nearly continuous reproduction and often short generation times. Such noncohort populations necessitate independent estimates of growth to quantify secondary production. Growth rates of 3 benthic microcrustaceans from a forested floodplain swamp in Alabama were measured on a diet of natural food at temperatures of 10, 15, 20, and 25°C, which span much of the annual range. For Chydorus brevilabris (Cladocera:Chydoridae), somatic growth rates were as high as 20%/d at all temperatures, and total growth rate (including egg production) was roughly twice the somatic growth rate in the larger size classes. For reproductive-sized individuals, eggs represented >60% of the growth within an instar and >60% of an individual's lifetime production. Multiple regression using individual size and temperature as independent variables explained 76% of the variation in somatic growth rates and 49% of the variation in total growth rates. Somatic growth rates were also measured for Physocypria pustulosa (Ostracoda:Cyprididae) and Cypridopsis vidua (Ostracoda:Cypridopsidae). The ostracod species had lower somatic growth rates than the chydorid, but growth rates of all 3 taxa increased with temperature and decreased with increasing size. Somatic growth rates for ostracods were <20%/d in most size classes, and multiple regressions, using individual mass and temperature as independent variables, explained 50% of the variation in somatic growth for Cypridopsis vidua and 33% for Physocypria pustulosa. Growth rates measured in this study under natural conditions suggest that freshwater meiofauna can have higher annual turnover rates (i.e., >15) than is generally assumed.
1. The occurrence of thirty-six species of Cladocera in Hampton Court Long Water during the course of four years is recorded. Two of the species, Scapholeberis aurita and Pleuroxus denticulatus, have been recorded only once previously in Britain. 2. The period of maximum abundance of the oligochaete Chaetogaster diaphanus coincided with the maximum abundance of Chydorus sphaericus which formed the main food of the oligochaete. 3. Simocephalus vetulus normally remained active and reproduced parthenogenetically throughout the winter. This species produced very few resting eggs in the Long Water. 4. Chydorus sphaericus also reproduced parthenogenetically throughout the winter and reached a maximum of abundance in the early spring. 5. Scapholeberis mucronata and Polyphemus pediculus overwintered as resting eggs and emerged to begin parthenogenetic reproduction in March and April. Both species produced large numbers of resting eggs in October and November, but then reverted to parthenogenesis for a short period before dying. 6. Sida crystallina overwintered as resting eggs, and emerged in March or April. During October the females changed from parthenogenetic reproduction to the production of resting eggs and might persist until January before the active population died. The period of production of resting eggs was not followed by any reversion to parthenogenesis. 7. Low temperatures (2-7 degrees C) restricted the production of eggs by Simocephalus vetulus, even when food was abundant. 8. The low numbers of eggs per female of S. vetulus in summer were caused by a combination of factors, but the dominant factor was the small size of adult females at temperatures above 18 degrees C. 9. In S. vetulus and Scapholeberis mucronata the number of eggs produced by a female was directly proportional to her size. This relation was modified in populations from different latitudes. Arctic populations, from Greenland, produced fewer and larger eggs at a given body size. A population of S. mucronata from Italy produced more but smaller eggs than British and Danish specimens of the same size. Eurycercus lamellatus in Britain produced smaller eggs than E. glacialis in Greenland. 10. The sizes of the parthenogenetic eggs of Simocephalus vetulus and Scapholeberis mucronata varied seasonally. This variation was governed largely by an inverse relationship with the temperature of the water. 11. The size of a cladoceran egg is partially determined by the differing advantages given at different temperatures. In cold water a large egg ensures that the neonate has a maximum chance of reaching maturity and reaches this state after fewer instars. In warm water the greater number of smaller eggs ensured a greater rate of population growth.
The chydorid populations of Lake Itasca, Minnesota, were monitored over a 2.5-yr period by pattern sampling. Of the 24 species collected, 15 were sufficiently abundant to allow analysis of population trends. Chydorid species have two basic patterns of abundance. One group of species exhibits only a summer density peak. The second group shows one abundance peak in summer and a second peak in fall or winter. All species experience a precipitous decline in density following the summer peak. Population growth in chydorids is limited by different factors during different times of the year. During periods of ice cover most species are apparently limited by a reduction in primary productivity due to reduced light penetration rather than by water temperature. Spring chydorid populations are limited by temperature. Summer populations, at least for abundant species, are limited by predation. Chydorid species are distributed patchily within Chara beds. Patchiness is moderate in spring, declines to low levels during summer, and peaks in the fall for most species. Patchiness remained about constant during the summer decline in density. Experimentation showed that heterogeneity of the physical habitat is not a necessary cause of patchiness. A Bray-Curtis-type ordination was performed on data from a complete year of monitoring. The primary component of variation extracted from the data matrix is due to temporal differences in abundance among species. The second major source of variation is due to spatial differences in abundance (habitat preference). The most abundant chydorid species tent to have similar habitats and temporal patterns of abundance.
Populations of four chydorids in the littoral of Lawrence Lake, Michigan, were studied through an entire year. Three species appeared in spring after a winter absence. Their population sizes were smallest in summer and greatest in late summer or fall. Numbers of the fourth species, Chydorus sphaericus, peaked in spring and dropped to a low level in the summer, then rose through fall to a winter plateau. Rates of population processes were estimated with the egg-ratio technique. This required monitoring littoral temperature and determining developmental times of chydorid eggs over a range of temperatures. Predicted rates of birth were higher during summer when rates of observed change fluctuated considerably. A probabilistic method, based on reproductive potential, showed relatively large probabilities for changes observed from late fall to early spring in populations of Chydorus. Most population changes in the other three species, and in Chydorus during the summer, had zero probability. Birth alone could explain few population changes. Most population loss appears to be predatory; emigration and "natural" mortality are not important.
Population dynamics of chyorids from Elk Lake, Minnesota, were followed from May through October 1971 by means of three collecting methods. Emphasis was placed on data obtained by use of artificial substrate. This method was found to collect most species of chydorids living in the underlying substrate. A second method, funnel trapping, collected animals that migrated 10-20 cm vertically from their substrate into the funnel traps. Funnel trapping was found to be not very efficient at collecting all chydorid species, but to be useful for following overall population trends and for exploring the vertical movements of some species. A third method, called pattern sampling, was tried experimentally. It appears to collect most chydorid species, and also shows the mocro-distributions (or spatial arrangements) associated with population densities. Most chydorid species increase in population numbers during spring and fall, and decrease during midsummer. Chydoris have clumped or contagious patterns that fit the negative binomial distribution. A log/log relationship exists between estimates of the mean and variance over the sampling interval, May--October; this relationship establishes a relatively constant structural arrangement of patterns as reflected by the exponent k of the negative binominal, and by b of Taylor's power law. There are several possible explanations for chydorid clumping--heterogeneous habitat, aggregation about food sources, predation, lack of dispersal, and behavior. Future studies will be directed at evaluating the relationships between spatial patterns and population densities.
Ishnura verticalis naiads (Odonata: Zygoptera) were reared among simulated aquatic plants in eight large pools. Simocephalus serrulatus (Crustacea: Cladocera) was the principle prey. The intensity of damselfly predation on Simocephalus was estimated using two independent procedures: (1) a mathematical model predicating the potential density of prey at the end of successive 4-day intervals, and (2) exclosure nets which permit random samples of the prey population to grow, free from predation, during each 4-day interval. Potential densities minus observed density yield estimates of Simocephalus mortality during each interval. These estimates fluctuate dramatically, suggesting an intermittent influence of the predators. Peaks in prey mortality tend to follow periods during which large number of naiads molted. It is hypothesized that changes in feeding behavior associated with developmental phenomena are responsible for fluctuations in the intensity of predation by damselfly naiads.
Pattern sampling (Whiteside and Williams 1975) was employed to study the population changes, habitats and spatial arrangements (pattern) of littoral cladocera in Lake Itasca, Minnesota during 1974. Population dynamics of the 19 most abundant species of chydorids had changes similar to other populations studied in north-temperate lakes. All species had either spring or fall maxima, or both, a mid-summer low in numbers. Population trends were the same for vegetative and mud habitats. In a comparison of Chara vs. mud habitat we found Chydorus piger, Leydigia leydigi, Alona quadrangularis, Pleuroxus aduncus, and Alona circumfibriata to live mainly in littoral mud. Kruzia latissima, Camptocerus rectirostris and Chydorus faviformis were most restricted to the vegetative habitat, while other species were more ubiquitous. Pielou's (1974) terms describing pattern, phase, mosaic, grain, and intensity are discussed. We redefined intensity as describing the visual effect of density. The changes of intensity accompanying changes in density typified 1974 patterns, while no changes in the other parameters were evident. Preliminary experiments exploring the behavior of chydorids suggest that visual stimuli are very important in directing movements, followed by tactile and chemical clues.
Spatial and temporal distribution, abundance and production of the floodplain macroinvertebrate communities of two low‐gradient headwater streams in Virginia, U.S.A., were studied over 1 year.
Spatial and temporal distribution patterns of invertebrates were affected by inundation patterns. Numbers, biomass and production were higher in low than high floodplain areas and on a floodplain continuously inundated over 9 months compared with a floodplain completely flooded only occasionally during storms.
The predominant species in terms of numbers and production on both floodplains was the harpacticoid copepod Attheyella illinoisensis Forbes. Other species with relatively high production were the sphaeriid clam Pisidium sp., the leptophlebiid mayfly Leptophlebia sp., the isopod Caecidotea racovitzai (Williams), and the chironomids Paratendipes sp. and Polypedilum spp.
Annual invertebrate production (dry weight) on the floodplain continuously inundated over 9 months was 6.1 g m ⁻² ; production on the periodically inundated floodplain was 1.7 g m ⁻² . Collector‐gatherers accounted for 58–61%, and predators 19–25%, of the production.
Annual invertebrate production on the floodplains, calculated on the basis of a linear metre of channel length, was 84–490 gm ⁻¹ , or about one to two orders of magnitude greater than probable production in the channels, suggesting the significance of floodplain invertebrates to stream system trophic dynamics.
Synopsis
Outstanding structural features related to habits of life in the chydorid cladoceran Eurycercus lamellatus are described. Crawling is as important as swimming in this deposit-feeding species. The nature of the food, its collection and subsequent manipulation, are described. Both cephalic and trunk appendages are involved in this process. Their structure and mode of action are described and illustrated in detail. Many hitherto unknown structural features are described and the functional significance of these and other morphological peculiarities is explained.
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The measurement of production is being employed as an indicator of the health of an ecosystem, assessing the effect of environmental pollution or other disturbance. Additionally, secondary production is of vital interest to natural resource administrators responsible for the management of wild populations utilized for both food and recreation and in inland waters, particularly for vertebrate fisheries. This chapter discusses a selected portion of aquatic production biology, secondary production in inland waters. The chapter focuses on three groups, fishes, zoobenthos, and zooplankton, which have received most attention, for which methodology has been best worked out, and which are of most immediate concern to man. The production of other secondary producers, including heterotrophic algae, bacteria and fungi, protozoans, amphibians, reptiles, and other aquatic vertebrates, such as some birds and mammals more commonly associated with the terrestrial environment, must await further advances and reviews by other specialists. The energy flow through these other groups may be extremely important.
1.1. Six of eight life-history traits related to growth and reproduction were significantly affected by temperature-photoperiod regimes.2.2. A temperature-photoperiod interaction was the most significant factor affecting life-history traits.3.3. Temperature probably significantly affected length of life, age at first brood, mean carapace length at first brood, length of time between broods, and number of young per day of adult life independent of the temperature-photoperiod interactions.4.4. Photoperiod probably did not significantly affect any of the life-history traits independent of the temperature-photoperiod interactions.
Microcrustaceans are abundant in many freshwater wetlands, including forested floodplain swamps, but little has been done to assess their secondary production and functional role in these systems. Since standard cohort approaches to estimating secondary production are impossible with continuously growing and reproducing microcrustaceans, it is necessary to obtain independent determinations of their growth and reproductive characteristics under environmental conditions encountered in their natural habitat throughout the year. The growth and reproduction of Ceriodaphnia dubia fed natural swamp seston were measured at 10, 15, 20, and 25"C-temperatures which span much of the annual temperature range in southeastern floodplain swamps. Somatic biomass growth rates were as high as 61% d-r. Total growth rates (somatic tissue and egg mass) reached 95% d-r. Both somatic growth rates and total growth rates could be described as functions of individual size and temperature. High egg production, particularly in the larger instars, resulted in individuals maintaining high total growth rates (>20% d-l at most tem- peratures) over the lifespan. Lifetime egg production accounted for ~50% of biomass produced by individuals at all temperatures and > 80% for temperatures 120°C. Somatic growth rates for C. dubia fed swamp seston were within the range of literature estimates for other species of Ceriodaphnia under various food conditions.
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Three models of egg hatching in zooplankton populations gave significant differences depending on whether egg mortality was included. The differences were due to the effect of adult mortality on reducing the probability that eggs survive from the time of laying until they are released as live young. Adult mortality results in a population of eggs disproportionately dominated by younger stages, with resulting recruitment rates being lower than expected from development times alone.
A technique based on the relative duration of various developmental stages was used to determine the age of eggs from two natural populations during periods of decline. The observed tendency for the age distribution of eggs to be dominated by younger eggs was as expected from models of egg hatching which included mortality but was not as expected from models of declining populations which did not incorporate egg mortality.
Littoral populations of chydorid Cladocera were studied in 1968 and 1969 at 3 collection areas in Lake Lacawac, Pennsylvania. The station on the sandy leeward margin of the lake had peak populations in spring, the one on the detritus rich windward shore peaked in late summer and fall, and the one at the interface between the sandy and detritus‐rich shores had peak populations in both spring and fall. At all areas the chydorids were least abundant in summer.
There appeared to be ample food available in summer; chydorids were still able to reproduce after water temperatures had reached the summer maximum; and potential competitor species did not increase as chydorids decreased. Observations indicated that the summer population minimum was largely caused by predaceous tanypodine midges. The midges were most common, and the number of chydorids in their guts increased, just before major chydorid population declines. The midges were rare or absent in spring and fall when chydorids were most abundant.
Eight species of tanypodines were found in the lake. Three were common from mid‐May to June; the others occurred in July. The first pulse of midges in June devastated the chydorid populations. The second pulse appeared only after the chydorids had recovered and began to develop large populations.
Microcrustacean community and biomass dynamics were studied for two years in a Nymphaea-Eriocaulon macrophyte marsh and a nearby shallow lake which lacked macrophytes in the Okefenokee Swamp. In this blackwater, acidic wetland, microcrustacean diversity and biomass were similar to other circumneutral lakes and littoral areas, contributing to a productive fish assemblage. In the lake, the annual biomass pattern (15–1627 μg 1⁻¹) was unimodal and was dominated by the crustaceans Diaptomus sinuatus and Eubosmina tubicen. Rotifers were occasionally important, constituting up to 55% of total biomass. Over the long term, mean annual biomass in this post-drought study are higher than in pre-drought years. In the marsh, biomass (11–777 μg 1⁻¹) fluctuated biomodally with late winter depressions corresponding to low temperatures and midsummer declines indicative of increasing fish predation. Summer dominance shifted between years from Macrothricidae in 1982 to Sididae in 1983. Variation in biomass correlated most strongly with algal chlorophyll in the marsh and with bacterial density in the lake.
Previous authors have used simple models to investigate the relative importance to population increase of variations in the total and age-specific reproductive rates. But while acknowledging that the latter were the product of the age specific birth and death rates, they have used their models only to investigate changes in total or age-specific birth rates and have not been concerned with variations in death rates. This paper extends the use of Lewontin's (1965) model, to a wide range of values of r, the exponential rate of population increase. It shows how the relative importance of changes in certain life-history features can change with r and be reversed when r is near to zero. It is also shown that variations in mortality rate are not necessarily best expressed in analogous terms to variations in birth rate. If more suitable terms are used it is seen that changes in mortality rate can be of varying importance depending on the existing mortality rate. They can be overwhelmingly important when the mortality rate is high.
Data on generation time, length of life, instar duration and frequency of moulting at a range of constant temperatures are given for eight species of epiphytic Cladocera from the River Thames. For each species each of the above events was inversely related to temperature. The number of juvenile instars was constant for a particular species, but varied between species; large species tending to have more juvenile instars than small species. A similar size relationship was found for generation time. Juveniles moulted more frequently than adults. The duration of an adult instar was the same as the duration of egg development, except at low temperatures. The data are compared with published data on daphniids, and possible reasons for the basic differences discussed.Regression analysis of the relationships between the various dependent variables and temperature required a logarithmic transformation. A reciprocal transformation was statistically inadequate for describing the relationship.
Seasonal species abundance and community structure of the littoralmicrocrustacean community (Cladocera, Copepoda) in two areas of DeltaMarsh were investigated over the open-water season. Cladoceranabundance in Crescent Pond, with no fish, only invertebrate predatorswas considerably higher than in Blind Channel, with both fish andinvertebrate predators, and where cyclopoid copepods were thedominant microcrustaceans. In both areas, a small number of speciesof planktonic cladocerans characterized the community in spring andearly summer, whereas a diverse array of species of phytophilouscladocerans comprised the community throughout the summer. Daphnia rosea was the most abundant species in the planktoniccommunity in Crescent Pond for the first half of the summer, and Ceriodaphnia dubia was most abundant in the last half. In contrast,no single planktonic cladoceran species was consistently mostabundant in Blind Channel. The sequence of dominant phytophilouscladoceran species observed in Crescent Pond through the season wasChydorus sp. 2, Simocephalus vetulus, Pleuroxusdenticulatus, and Ceriodaphnia dubia, and in Blind Channel,Alona circumfimbriata, Simocephalus vetulus, and Ceriodaphnia dubia. Dominant planktonic and phytophilous copepods inboth areas were Diacyclops thomasi, Acanthocyclops vernalis,Eucyclops agilis, and Macrocyclops albidus. Canonicalcorrespondence analysis revealed differences in community structurebetween areas of the marsh related to turbidity, phytoplanktonbiomass, and soluble reactive phosphorus concentration.
We measured aquatic invertebrate abundance, standing stock biomass, and community production in three types of wetlands on
Noxubee National Wildlife Refuge from December 1987 through April 1988. Together,Orthocyclops modestus andDaphnia pulex were the most abundant organisms collected in all habitats during both winter and spring, but each contributed little to
total standing stock biomass or production.Caecidotea communis andPristina osborni made up ≥47% of the total standing stock biomass at each site during both winter (December–February) and spring (March–May).Crangonyx gracilis, Chironomus spp.,Chaoborus punctipennis, andEclipidrilus spp. each contributed ≥5% of the total biomass at one or more wetland habitats. Estimates of aquatic invertebrate community
production ranged from 930 to 1,578 mg dry weight/m2 among wetland types during winter and from 3,306 to 5,421 mg dry weight/m2 among wetland types during spring.Caecidotea communis andPristina osborni contributed most to community production during both seasons, but particularly in beaver ponds during spring. Other taxa
made up substantial portions of the community production in one or two wetland habitats.
Two new species of Eurycercus (Bullatifrons) from eastern North America (Chydoridae, Cladocera). Taxonomy, ontogeny, and biology
- B J Hann