MATCHING HABITAT CHOICE IS NOT COMMON, OR IS IT?Submitted by editor on 21 March 2020.Get the paper!
Written by: Carlos Camacho
"Matching habitat choice: it's not for everyone" by Camacho & Hendry (2020)
No one gets to decide where they are born, but if one is lucky, they can choose where to settle. Matching habitat choice offers individuals a means to escape maladaptation and optimize the match of phenotype to the environment through phenotype-dependent dispersal and habitat selection. This particular form of habitat choice has attracted considerable research attention over the last decade and a number of simulation-based studies suggest that many of the patterns that have been historically assumed to result from natural selection or adaptive phenotypic plasticity might not always involve these mechanisms. However, matching habitat choice seems to be much less common in nature than one would expect on the basis of its great advantages in terms of increased local adaptation. Why so rare?
Here we suggest that, in addition to the scarcity of field tests and the difficulty in distinguishing this mechanism from other forms of habitat selection (e.g. direct genetic preference and imprinting), one major reason for the apparent rarity of matching habitat choice is inter-individual variation in the costs of mischoosing. Or, stated another way, matching habitat choice would not be expected for segments of a population where the cost of making a “mistake” is minimal.
To test the idea of “partial matching habitat choice”, Prof. Andrew Hendry kindly dusted off an amazing data set collected some 25 years ago in a breeding population of sockeye salmon (Oncorhynchus nerka) exposed to size-dependent predation risk by bears. Breeding sockeye salmon of similar age and size cluster together in stream sites of similar water depth, a pattern that might well be explained as an outcome of matching habitat choice. However, the uniqueness of this mechanism lies in the assessment of local performance and, therefore, the occurrence of matching habitat choice depends on the strength of performance trade-offs across different environments. Bear preference for larger fish, especially in shallow water, translated into a performance trade-off that sockeye salmon could use to guide their settlement decisions. However, using reproductive life span as a measure of individual performance of male and female salmon, our findings revealed that only one segment of the population (3-ocean females) suffered major costs of mischoosing, supporting the notion that “partial matching habitat choice” might constrain the occurrence of matching habitat choice at the level of the entire population.
Our study illustrates the unequal relevance of matching habitat choice to different segments of a population. Hence, it is possible that, due to “partial matching habitat choice”, past population-level analyses failed to detect this mechanism, resulting in an underestimation of its actual prevalence in nature.