Matching habitat choice: it's not for everyone

Matching habitat choice is a habitat preference mechanism based on self-assessment of local performance, such that individuals settle in the habitats that are best suited to their phenotypes, promoting local adaptation. Despite the important evolutionary implications of matching habitat choice, examples from natural populations are rare. One possible reason for this apparent rarity is that phenotype-matching habitat choice might be manifest only in those population segments for which the cost of a phenotype–environment mismatch is high, although this hypothesis remains to be tested. Here, we test for matching habitat choice in a breeding population of sockeye salmon Oncorhynchus nerka where the strength of performance tradeoffs across environments, and therefore the costs of mischoosing, can be evaluated in meaningful discrete groups (e.g. male versus females, and ocean-age 2 versus ocean-age 3). Consistent with matching habitat choice, salmon of similar ocean-age and size tended to cluster together in sites of similar water depth. However, matching habitat choice was only favored (longer life span) in 3-ocean females – the segment of the population most vulnerable to bear predation. Our findings support the hypothesis that matching habitat choice is more likely to be evident in those segments of a population that suffer a major cost of mischoosing, leading to ‘partial matching habitat choice’.