On the adaptational significance of migration under resource regeneration

Abstract Community adaptation to locally variable environments is modeled, where the environments provide density- and capacity-regulated resources for reproduction of self-replicating genetic types. Adaptational success or failure is assessed in terms of community persistence. A community's adaptational strategy to its environments is specified by reproductive responses of genotypes (reproduction norms) to and migration among environments. It is adaptationally successful only to the degree to which it guarantees sustainable utilization of the environmental resources. Combined analytical and numerical evaluation of the model, and its special approach to the notion of adaptation, allow several unconventional insights into the interplay between selection and migration. Analysis of scenarios of habitat choice (genetic types differ in migrational preferences for environments) and habitat fragmentation (local isolation through constrained migration) help demonstrate the relevance of the findings. Among these are: $\bullet$~migration can reverse selection effects, and density regulation can reverse adaptational tendencies, and this is rather the rule than the exception, $\bullet$~strategies for avoidance of over-exploitation rely on mutual immigration of less reproductive genotypes (establishing mutual selection-immigration balances between environments/locations), $\bullet$~genetic variation among environments can thus aid in reducing over-exploitation and by this support adaptation, $\bullet$~if selection-immigration balances fail and resource depletion proceeds, local extinction risks can be reduced by adjusting the local emigration rates that determine stationary reproduction, $\bullet$~the greatest challenges to adaptational strategies are posed by weak density regulation, while strong regulation challenges adaptational perfection rather than facilitating adaptational failure, $\bullet$~extinction risks can be more readily compensated under local than under global density regulation. These findings help substantiate several common concepts of (evolutionary) adaptation, including evolutionary rescue and suicide as the results of success or failure in establishing sustainable resource utilization.