The cost of reproduction: differential resource specialization in female and male California sea otters

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Intraspecific variation in behavior and diet can have important consequences for population and ecosystem dynamics. Here, we examine how differences in reproductive investment and spatial ecology influence individual diet specialization in male and female southern sea otters (Enhydra lutris nereis). We hypothesize that greater reproductive constraints and smaller home ranges of females lead to more pronounced intraspecific competition and increased specialization. We integrate stable carbon (δ13C) and nitrogen (δ15N) isotope analysis of sea otter vibrissae with long-term observational studies of five subpopulations in California. We define individual diet specialization as low ratios of within-individual variation (WIC) to total population niche width (TNW). We compare isotopic and observational based metrics of WIC/TNW for males and females to data on population densities, and movement patterns using both general linear and linear mixed-effects models. Consistent with our hypothesis, increasing population density is associated with increased individual diet specialization by females but not by males. Additionally, we find the amount of coastline in a sea otter’s home range positively related with individual dietary variability, with increased range span resulting in weaker specialization for both males and females. We attribute our results to sex-based differences in movement, with females needing to specialize in their small ranges to maximize energy gain, and posit that the paradigm of individual prey specialization in sea otters with increased intraspecific competition may be a pattern driven largely by females. Our work highlights a potentially broader role of sex in the mechanistic pressures promoting and maintaining diet specialization.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title The cost of reproduction: differential resource specialization in female and male California sea otters
Series title Oecologia
DOI 10.1007/s00442-014-3206-1
Volume 178
Issue 1
Year Published 2015
Language English
Publisher Springer
Contributing office(s) Western Ecological Research Center
Description 13 p.
First page 17
Last page 29
Country United States
State California
Online Only (Y/N) N
Additional Online Files (Y/N) N
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