The influence of imperfect matching habitat choice on evolution in source-sink environments

Studies of evolution in source-sink environments can illuminate when to expect niche conservatism, versus niche evolution. A species can persist in habitats outside its ecological niche (sinks, where mean fitness < 1), given recurrent immigration from source habitats within the niche. Persistence of this demographic asymmetry among habitats over many generations (despite recurrent exposure of a species to the sink habitat) is tantamount to niche conservatism. We have previously shown that given genetic variation in a trait determining fitness in both source and sink, perfect phenotype-specific habitat choice substantially speeds up adaptation to the sink. (With perfect habitat choice, individuals disperse out of the source if and only if expected fitness in the sink is greater.) However, we observed that sometimes imperfect matching habitat choice could hamper sink adaptation. We explore this observation in more detail, using individual-based simulations for evolution of a single quantitative trait. With imperfect habitat choice and one-way adult dispersal (source to sink), adaptation in the sink can be slowed, relative to phenotype-independent dispersal. This counterintuitive result reflects directional effects of emigration on the source genetic distribution, which shifts in a way that hampers sink adaptive evolution. However, with bidirectional juvenile dispersal, imperfect habitat choice caused a strong increase in sink adaptation. Thus, the likelihood of niche conservatism or evolution may depend in a sensitive way on factors such as the life history stage, directionality, and imperfection of non-random dispersal. More broadly, our results (along with other recent results) illustrate that non-random dispersal can profoundly influence evolution via how it molds the pool of genetic variation available for selection.