Find the weakest link. A comparison between demographic, genetic and demo-genetic metapopulation extinction times

Alexandre Robert

doi:10.1186/1471-2148-11-260

Abstract

BackgroundWhile the ultimate causes of most species extinctions are environmental, environmental constraints have various secondary consequences on evolutionary and ecological processes. The roles of demographic, genetic mechanisms and their interactions in limiting the viabilities of species or populations have stirred much debate and remain difficult to evaluate in the absence of demography-genetics conceptual and technical framework. Here, I computed projected times to metapopulation extinction using (1) a model focusing on the effects of species properties, habitat quality, quantity and temporal variability on the time to demographic extinction; (2) a genetic model focusing on the dynamics of the drift and inbreeding loads under the same species and habitat constraints; (3) a demo-genetic model accounting for demographic-genetic processes and feedbacks.ResultsResults indicate that a given population may have a high demographic, but low genetic viability or vice versa; and whether genetic or demographic aspects will be the most limiting to overall viability depends on the constraints faced by the species (e.g., reduction of habitat quantity or quality). As a consequence, depending on metapopulation or species characteristics, incorporating genetic considerations to demographically-based viability assessments may either moderately or severely reduce the persistence time. On the other hand, purely genetically-based estimates of species viability may either underestimate (by neglecting demo-genetic interactions) or overestimate (by neglecting the demographic resilience) true viability.ConclusionUnbiased assessments of the viabilities of species may only be obtained by identifying and considering the most limiting processes (i.e., demography or genetics), or, preferentially, by integrating them.

Highlights

While the ultimate causes of most species extinctions are environmental, environmental constraints have various secondary consequences on evolutionary and ecological processes
Insights on the “genetic viability” of species or populations use generic data and come from two main categories of studies: (i) genetically determined minimum viable population sizes (MVPs), corresponding to the size necessary to compensate the loss of quantitative genetic variation by gains through mutations [13]; (ii) theoretical, metapopulation scale studies focusing on the dynamics of deleterious mutations and their effects on fitness [14]
A hierarchical partitioning (HP) indicated that TG was mainly related to metapopulation size and fragmentation (Kt, R2 = 51%; N, R2 = 18%) while TD mostly depended on the basic growth rate and the perturbation regime (F, R2 = 28%; P, R2 = 17%) (All detailed results are provided in Additional file 1)

Summary

Introduction

While the ultimate causes of most species extinctions are environmental, environmental constraints have various secondary consequences on evolutionary and ecological processes. Theories predict that the properties of most threatened populations (reduced size, isolation, fragmentation) should lead to inbreeding depression [3], mutation accumulation [4] and loss of evolutionary potential [5] All these expectations have been empirically verified [6,7,8] and the important role of genetic deterioration processes in population declines and extinctions has. Besides the fundamental importance of understanding how ecological and evolutionary proximal factors limit species viability (e.g., the need of theoretical arguments to solve the debate on the role of genetic deterioration referred above), a general assessment of the conditions under which ecological or genetic factors are the most critical to viability might have considerable applications in the definition of species or population conservation status [21]. Recent demo-genetic study on Centaurea corymbosa, a narrow-endemic plant, provided guidelines for future reintroductions of the species regarding the number of seeds required and their initial distribution in space to limit the demographic effects of genetic self-incompatibility [28]

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Results

Discussion

Conclusion