Foraging ecology

By: , and 
Edited by: M. Tim TinkerJames A. EstesKatherine RallsTerrie M. WilliamsDavid A. Jessup, and Daniel P. Costa

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Abstract

  1. Longitudinal foraging data collected from 60 sea otters implanted with VHF radio transmitters at two study sites in Central California over a three-year period demonstrated even greater individual dietary specialization than in previous studies, with only 54% dietary overlap between individuals and the population.
  2. Multivariate statistical analyses indicated that individual diets could be grouped into three general "diet types" representing distinct foraging specializations. Type 1 specialists consumed large size prey but had low dive efficiency, Type 2 specialists consumed small to medium size prey with high dive efficiency, and Type 3 specialists consumed very small prey (mainly snails) with very high dive efficiency.
  3. The mean rate of energy gain for the population as a whole was low when compared to other sea otter populations in Alaska but showed a high degree of within- and betweenindividual variation, much of which was accounted for by the three foraging strategies. Type 1 specialists had the highest mean energy gain but also the highest withinindividual variance in energy gain. Type 2 specialists had the lowest mean energy gain but also the lowest variance. Type 3 specialists had an intermediate mean and variance. All three strategies resulted in very similar probabilities of exceeding a critical rate of energy gain on any given day.
  4. Correlational selection may help maintain multiple foraging strategies in the population: a fitness surface (using mean rate of energy gain as a proxy for fitness) fit to the first two principal components of foraging behavior suggested that the three foraging strategies occupy separate fitness peaks.
  5. Food limitation is likely an important ultimate factor restricting population growth in the center of the population’s range in California, although the existence of alternative foraging strategies results in different impacts of food limitation on individuals and thus may obscure expected patterns of density dependence.

Additional publication details

Publication type Book chapter
Publication Subtype Book Chapter
Title Foraging ecology
Chapter 5
Year Published 2006
Language English
Publisher U.S. Department of the Interior: Minerals Management Service, Pacific OCS Region
Contributing office(s) Alaska Science Center
Description 27 p.
Larger Work Type Report
Larger Work Subtype Federal Government Series
Larger Work Title Population dynamics and biology of the California sea otter (Enhydra lutris nereis) at the southern end of its range
First page 103
Last page 129
Public Comments OCS Study MMS 2006-007; MMS Cooperative Agreement Number 14-35-0001-31063