Sex and occupation time influence niche space of a recovering keystone predator

Predators exert strong effects on ecological communities, particularly when they re-occupy areas after decades of extirpation. Within species, such effects can vary over time and by sex, and cascade across trophic levels. We used a space-for-time substitution to make foraging observations of sea otters (Enhydra lutris) across a gradient of re-occupation (1–30 yrs), and nMDS analysis to ask if 1) sea otter niche space varies as a function of occupation time, and 2) if niche space varies by sex. We found that niche space varied among areas of different occupation times. Dietary niches at short occupation times were dominated by urchins (Mesocentrotus and Strongylocentrotus spp; > 60 % of diets) in open habitats at 10–40 m depths. At longer occupation times niches were dominated by small clams (Veneroida; > 30% diet), mussels (Mytilus spp; > 20% diet), and crab (Decapoda; > 10% diet) in shallow (< 10 m) kelp habitats. Diet diversity was lowest (H’ = 1.46) but energy-rich (~3...捕食者对生态群落具有强烈的调控作用，尤其在其经局部灭绝数十年后重新占据的区域中。就同一物种而言，这类调控效应会随时间推移和性别差异而变化，并沿营养级联产生级联效应。我们采用空间替代时间法（space-for-time substitution），对不同重新定居时长（1至30年）的海獭（Enhydra lutris）进行觅食行为观测，并通过非度量多维标度分析（non-metric Multidimensional Scaling，nMDS）探究两个科学问题：1）海獭的生态位空间是否随定居时长发生变化；2）海獭的生态位空间是否存在性别差异。研究结果显示，不同定居时长区域内的海獭生态位空间存在显著差异。定居时长较短的区域，其海獭食物生态位以10至40米水深开阔生境中的海胆（Mesocentrotus属和Strongylocentrotus属；占食物组成的60%以上）为主；而定居时长较长的区域，其食物生态位则以水深小于10米的浅海海带生境中的小型蛤蜊（Veneroida目；占食物组成的30%以上）、贻贝（Mytilus属；占20%以上）和蟹类（十足目；占10%以上）为主。该种群的食物多样性最低（香农指数H’=1.46）但能量密度较高（约3……