Modeling the consequences of the demise and potential recovery of a keystone-species: wild rabbits and avian scavengers in Mediterranean landscapes.

Ainara Cortés-Avizanda,Antoni Margalida,Olga Ceballos,Maria Àngels Colomer,José Antonio Donázar

doi:10.1038/srep17033

Abstract

Restoration of demised keystone-species populations is an overriding concern in conservation biology. However, since no population is independent of its environment, progress is needed in predicting the efficacy of restoration in unstable ecological contexts. Here, by means of Population Dynamics P-system Models (PDP), we studied long-term changes in the population size of Egyptian vultures (Neophron percnopterus) inhabiting a Natural Park, northern Spain, to changes in the numbers of wild rabbits (Oryctolagus cuniculus), a keystone-species of Mediterranean ecosystems that have suffered >90% population decline after a hemorrhagic disease outbreak. Low availability of rabbit carcasses leads Egyptian vultures to extend their foraging activities to unprotected areas with higher non-natural mortality whereas growing numbers of griffon vultures (Gyps fulvus), a dominant competitor, progressively monopolize trophic resources resulting in a focal population decrease. Modeling shows that, even if keystone-species populations recover in core protected areas, the return to the original studied population size may be unfeasible, due to both the high non-natural mortality rates in humanized areas and long-term changes in the scavenger guild structure. Policy decisions aimed to restore keystone-species should rely on holistic approaches integrating the effects of spatial heterogeneity on both producer and consumer populations as well as within-guild processes.

Highlights

Overall for the structure and functioning of food webs, communities and ecosystems
Our results show that even if the populations of wild rabbit recover, non-natural mortality of Egyptian vultures associated with the alternative exploitation of humanized landscapes would heavily condition the future viability of its population
The modeling procedures show that the long-term changes in the composition of the scavenger guild may play a determinant role: if the population of the dominant griffon vulture continues to increase, it would consume a significant part of the trophic resources to the detriment of the more threatened and less competitive scavenger

Summary

Introduction

Overall for the structure and functioning of food webs, communities and ecosystems (see[3,4]). Our specific goals were to: i) determine the long-term viability of the population of the focal species; and to examine how Egyptian vulture population dynamics would evolve given changes in ii) wild rabbit abundance; iii) non-natural mortality in humanized areas; and iv) long-term population-trends of direct competitors (griffon vultures). To examine these issues we used Population Dynamics P-system Models (PDP)[31]. There is a close parallelism between the functioning of cells and ecosystems making P-systems an increasingly useful tool in many different research lines including animal behavior, invasion processes and conservation planning[33,34,35,36]

Methods

Results

Conclusion