Data from: Phenotype-dependent selection underlies patterns of sorting across habitats: the case of stream-fishes

Spatial and temporal heterogeneity within landscapes influences the
distribution and phenotypic diversity of individuals both within and
across populations. Phenotype-habitat correlations arise either through
phenotypes within an environment altering through the process of natural
selection or plasticity, or phenotypes remaining constant but individuals
altering their distribution across environments. The mechanisms of
non-random movement and phenotype-dependent habitat choice may account for
associations within highly heterogeneous systems, such as streams, where
local adaptation may be negated, plasticity too costly and movement is
particularly important. Despite growing attention, however, few empirical
tests have yet to be conducted. Here we provide a test of
phenotype-dependent habitat choice and ask: 1) if individuals collected
from a single habitat type continue to select original habitat; 2) if
decisions are phenotype-dependent and functionally related to habitat
requirements; and 3) if phenotypic-sorting continues despite increasing
population density. To do so we both conducted experimental trials
manipulating the density of four stream-fish species collected from either
a single riffle or pool and developed a game-theoretical model exploring
the influence of individuals’ growth rate, sampling and competitive
abilities as well as interference on distribution across two habitats as a
function of density. Our experimental trials show individuals selecting
original versus alternative habitats differed in their morphologies, that
morphologies were functionally related to habitat-type swimming demands,
and that phenotypic-sorting remained significant (although decreased) as
density increased. According to our model this only occurs when phenotypes
have contrasting habitat preferences and only one phenotype disperses
(i.e. selects alternatives) in response to density pressures. This
supports our explanation that empirical habitat selection was due to a
combination of collecting a fraction of mobile individuals with different
habitat preferences and the exclusion of individuals via scramble
competition at increased densities. Phenotype-dependent habitat choice can
thereby account for observed patterns of natural stream-fish distribution.