Niche partitioning within a population of seasnakes is constrained by ambient thermal homogeneity and small prey size

<p>In many populations of terrestrial snakes, an individual's phenotype (e.g. body size, sex, colour) affects its habitat use. One cause for that link is gape-limitation, which can result in larger snakes eating prey that are found in different habitats. A second factor involves thermoregulatory opportunities, whereby individuals select habitats based upon thermal conditions. These ideas predict minimal intraspecific variation in habitat use in a species that eats small prey and lives in a thermally uniform habitat – such as the seasnake <i>Emydocephalus annulatus</i>, that feeds on tiny fish eggs and lives in inshore coral-reefs. To test that prediction, we gathered data on water depths and substrate attributes for 1475 sightings of 128 free-ranging <i>E. annulatus</i> in a bay near Noumea, New Caledonia. Habitat selection varied among individuals, but with a preference for coral-dominated substrates. A snake's body size and reproductive state affected its detectability in deep water, but overall habitat use was not linked to snake body size, colour morph, sex, or pregnancy. A lack of ontogenetic shifts in habitat use allows extreme philopatry in <i>E. annulatus</i>, thereby reducing gene flow among populations and potentially, delaying recolonization after local extirpation events.</p>