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

Results 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.Unbiased 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.The role of genetic deterioration in the extinction of endangered species or populations has long been controversial. For over 20 years, several authors have proposed that most populations go extinct for environmental or demographic reasons before genetic deterioration will affect them [1,2]. Yet, 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 [6-8] and the important role of genetic deterioration processes in population declines and extinctions has been demonstrated by empirical evidence [9,10] and extensive analyses [11]. In spite of these lines of evidences, the weight of genetic deterioration mechanisms in limiting population viability remains difficult to evaluate, mainly because the classical approaches used to assess the "demographic" and "genetic viabilities" are different and neglect the interactions between demograph