Mario Blanco-Sánchez, Marina Ramos-Muñoz, Beatriz Pías, José Alberto Ramírez-Valiente, Laura Díaz-Guerra, Adrián Escudero, Silvia Matesanz

This is a plain language summary of a Functional Ecology research article that can be found here.

Natural selection is the main process driving adaptive evolution. For a trait to be under selection, there must be differences in the ecophysiological characteristics of individuals (i.e., traits) associated with differences in their reproduction or survival (i.e., fitness). Therefore, identifying adaptive traits (i.e., those influencing individual fitness) is key for unveiling successful plant strategies in stressful and heterogeneous environments such as Mediterranean ecosystems.

Although a conservative use of resources has been hypothesized to be adaptive in Mediterranean taxa, the functional strategies to cope with abiotic stress and, importantly, how differences among individuals in their traits affect fitness, is unknown for most Mediterranean plants. In natural semiarid conditions in the Iberian Peninsula, we assessed the relationship between 20 ecophysiological traits and two fitness components (reproduction and survival) in individuals of two gypsum endemic species—Centaurea hyssopifolia and Helianthemum squamatum. Plants were measured in environments with contrasting abiotic conditions (south- and north-facing slopes of gypsum hills) during two climatically contrasting years (dry and mesic), thus allowing the identification of adaptive traits and strategies at different spatiotemporal scales.

Our results showed that the reproductive output of individuals was consistently associated with an acquisitive use of resources. Specifically, individuals that flowered earlier were water spenders, and, those that had larger leaves with higher leaf nitrogen content showed higher fecundity across slopes and years in both species. Furthermore, plants did not reproduce less under higher abiotic stress in either species. In contrast, survival was similar across environmental conditions and was not affected by any particular trait—neither by plant size nor the reproductive output of individuals. Contrary to our expectations, natural selection via reproductive fitness consistently favoured an acquisitive use of resources to escape from drought in Mediterranean semiarid plants—rather than the predicted strategy of conservative use of resources—even under conditions of higher abiotic stress. Such acquisitive strategies could allow rapid development by maximizing resource assimilation and reproduction before the most limiting climatic conditions of mid-late summer. Our results provide insights on future responses to environmental change in Mediterranean plant species.