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Semelhante a MVP and Effective Population Size in Conservation Biology
Semelhante a MVP and Effective Population Size in Conservation Biology (20)
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MVP and Effective Population Size in Conservation Biology
- 1. Minimum Viable Population and Effective Population Size Conservation Biology
- 2. Minimum Viable Population A minimum viable population size (MVP) can be defined as the smallest size required for a population or species to have a predetermined probability of persistence for a given length of time
- 3. The probability for long-term persistence of a species depends on whether the species can avoid the erosion of genetic variability that can occur in small populations. When genetic variation is reduced, the ability of a species to adapt to environmental change may become restricted.
- 4. In these cases, genetic variability can be substantially reduced through inbreeding (mating between close relatives) and genetic drift (random changes in gene frequencies). Inbreeding and genetic drift both can result in an increased chance for the transmission of harmful traits to subsequent generations, which ultimately affects population and species viability.
- 5. Genetic bottlenecks When the individuals are genetically weak, in any case of disease they can not survive because of interbreeding and having no resistance to diseases. This is known as genetic bottlenecks.
- 6. Franklin Rule One of the earliest attempts to define a minimum lower threshold that would prevent the loss of genetic variability in a species was made in 1980 by Australian geneticist Ian Franklin and American biologist Michael Soulé. They created the “50/500” rule, which suggested that a minimum population size of 50 was necessary to combat inbreeding and a minimum of 500 individuals was needed to reduce genetic drift. Management agencies tended to use the 50/500 rule under the assumption that it was applicable to species generally.
- 7. In general, the results of Population Viability Analysis modeling indicate that species with high reproductive capacities, such as arthropods and rodents, can accommodate lower MVPs than species with lower reproductive capacities, such as redwood trees and large mammals and some birds.
- 8. Demographic Stochasticity The PVA ( Population Viabilty Analysis) model also incorporates environmental and demographic stochasticity. Demographically stochastic events are random fluctuations in population variables, such as sex ratios and number of births or deaths.
- 9. Environmentally Stochasticity Environmentally stochastic events are random events, such as severe weather, floods, fires, and other ecological disturbances.
- 10. Depicting such events with PVA has the effect of increasing the model’s MVP estimate, because both types of phenomena have the potential for reducing population size, either by increasing the death rate or increasing the annual variability with respect to the birth rate.
- 11. Estimating MVP with PVA allows scientists to determine which biological parameters (e.g., hunting pressure, disease, habitat loss, inbreeding) will have the greatest impact on the extinction probability of a given species. This information can provide environmental managers with a set of quantitative targets for the minimum critical area required to support a viable population.
- 12. One major limitation of PVA is that it requires large amounts of data to make realistic predictions. Therefore, some researchers argue that using a single, universal MVP (such as the 50/500 rule) would streamline conservation efforts. Others, however, maintain that MVPs must be carried out in a case-by-case fashion, because the circumstances that characterize extinction risk differ among species.
- 13. Effective Population Size The effective population size is the number of individuals that can contribute to the next generation. It is denoted by Ne. Over aged are not included. Adults that can not increase progeny not included.
- 14. Factors which affect the Ne Unequal sex ratio can affect the effective population size. For say, we have 1:4 of female and male in case one. 2:7 of female and male in case two. 5:9 of female and male in case three. So we have all different ratios. When sex ratios are not equal or near to equal the population size can not defined as effective population size.
- 15. Reproductive Output of females The reproductive output of female can affect the population size. For example, A goat can give birth to 3 baby goats On the other hand, second goat can give birth to only one. So, when reproductive output is different a population size can affect.
- 16. Population Fluctuation Many individuals can migrate from one populated are to another populated group so, population number and size could be affected by their immigration or emigration.