Résumé
1. Inbreeding is common in nature, and many laboratory studies have
documented that inbreeding depression can reduce the fitness of
individuals. Demonstrating the consequences of inbreeding depression on
the growth and persistence of populations is more challenging because
populations are often regulated by density- or frequency-dependent
selection and influenced by demographic and environmental stochasticity. A
few empirical studies have shown that inbreeding depression can increase
extinction risk of local populations. The importance of inbreeding
depression at the metapopulation level has been conjectured based on
population-level studies but has not been evaluated. 2. We quantified the
impact of inbreeding depression affecting the fitness of individuals on
metapopulation persistence in heterogeneous habitat networks of different
sizes and habitat configuration in a context of natural butterfly
metapopulations. 3. We developed a spatial individual-based simulation
model of metapopulations with explicit genetics. We used Approximate
Bayesian Computation to fit the model to extensive demographic, genetic,
and life-history data available for the well-studied Glanville fritillary
butterfly (Melitaea cinxia) metapopulations in the Åland islands in SW
Finland. We compared 18 semi-independent habitat networks differing in
size and fragmentation. 4. The results show that inbreeding is more
frequent in small habitat networks, and consequently, inbreeding
depression elevates extinction risks in small metapopulations.
Metapopulation persistence and neutral genetic diversity maintained in the
metapopulations increase with the total habitat amount in and mean patch
size of habitat networks. Dispersal and mating behavior interact with
landscape structure to determine how likely it is to encounter kin while
looking for mates. 5. Inbreeding depression can decrease the viability of
small metapopulations even when they are strongly influenced by stochastic
extinction-colonization dynamics and density-dependent selection. The
findings from this study support that genetic factors, in addition to
demographic factors, can contribute to extinctions of small local
populations and also of metapopulations.