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

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 Emydocephalus annulatus, 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 E. annulatus 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 E. annulatus, thereby reducing gene flow among populations and potentially, delaying recolonization after local extirpation events.

在众多陆地蛇类的种群中，个体的表型（例如体型、性别、颜色）对其栖息地利用具有显著影响。此现象的成因之一为张口限制，导致大型蛇类食用存在于不同栖息地的猎物。另一因素涉及体温调节的机会，个体基于热环境条件选择栖息地。这些观点预测，在一种以小型猎物为食且生活在热环境均一化的物种中，栖息地利用的种内变异将最小——例如以微小鱼卵为食、栖息于近岸珊瑚礁的蛇类 Emydocephalus annulatus。为了验证这一预测，我们在新喀里多尼亚的努美阿附近海湾收集了128只自由活动的 E. annulatus 的1475次观测数据，包括水深和底质属性。个体的栖息地选择存在差异，但偏好以珊瑚为主的底质。蛇的体型和生殖状态影响了其在深水中的可检测性，但总体而言，栖息地利用与蛇的体型、颜色形态、性别或妊娠状态无关。栖息地利用的个体发育阶段无显著变化，使得 E. annulatus 具有极端的亲缘性，从而减少了种群间的基因流动，并可能在局部灭绝事件后延缓重新定居。