MEASURING INDIVIDUAL-LEVEL RESOURCE SPECIALIZATION

Many apparently generalized species are in fact composed of individual specialists that use a small subset of the population's resource distribution. Niche variation is usually established by testing the null hypothesis that individuals draw from a common resource distribution. This approach encourages a publication bias in which negative results are rarely reported, and obscures variation in the degree of individual specialization, limiting our ability to carry out comparative studies of the causes or consequences of niche variation. To facilitate studies of the degree of individual specialization, this paper outlines four quantitative indices of intrapopulation variation in resource use. Traditionally, such variation has been measured by partitioning the population's total niche width into within- and between-individual, sex, or phenotype components. We suggest two alternative measures that quantify the mean resource overlap between an individual and its population, and we discuss the advantages and disadvantages of all four measures. The utility of all indices depends on the quality of the empirical data. If resources are measured in a coarse-grained manner, individuals may falsely appear generalized. Alternatively, specialization may be overestimated by cross-sectional sampling schemes where diet variation can reflect a patchy environment. Isotope ratios, parasites, or diet-morphology correlations can complement cross-sectional data to establish temporal consistency of individual specialization.

[1]  Lani West.  Prey Selection by the Tropical Snail Thais Melones: A Study of Interindividual Variation , 1988 .

[2]  L. V. Valen,et al.  MORPHOLOGICAL VARIATION AND WIDTH OF ECOLOGICAL NICHE , 1965 .

[3]  P. Feinsinger,et al.  A Simple Measure of Niche Breadth , 1981 .

[4]  S. E. A. Durell.  Individual feeding specialisation in shorebirds: population consequences and conservation implications , 2000 .

[5]  R. Svanbäck,et al.  Effects of habitat and food resources on morphology and ontogenetic growth trajectories in perch , 2002, Oecologia.

[6]  T. Schoener.  The Anolis Lizards of Bimini: Resource Partitioning in a Complex Fauna , 1968 .

[7]  K. Warburton,et al.  Generalists as sequential specialists: diets and prey switching in juvenile silver perch , 2004, Environmental Biology of Fishes.

[8]  E. R. Keeley,et al.  Allometric and environmental correlates of territory size in juvenile Atlantic salmon (Salmo salar) , 1995 .

[9]  D. Macdonald,et al.  Individual feeding specialization in the European mink, Mustela lutreola and the American mink, M. vison in north-eastern Belarus , 2001 .

[10]  S. Konovalov.  Parasites as indicators of biological processes, with special reference to sockeye salmon (Oncorhynchus nerka) , 1995 .

[11]  B. Gu,et al.  INTRAPOPULATION FEEDING DIVERSITY IN BLUE TILAPIA: EVIDENCE FROM STABLE-ISOTOPE ANALYSES , 1997 .

[12]  W. Sutherland,et al.  The Criteria Determining the Selection of Mussels Mytilus Edulis By Oystercatchers Haematopus Ostralegus , 1987 .

[13]  Marco A. Rodríguez,et al.  Individual variations in habitat use and morphology in brook charr , 1997 .

[14]  B. Fry,et al.  Rapid 13C/12C turnover during growth of brown shrimp (Penaeus aztecus) , 1982, Oecologia.

[15]  P. Petraitis,et al.  Likelihood Measures of Niche Breadth and Overlap , 1979 .

[16]  T. Sherry,et al.  Behavioral feeding specialization in Pinaroloxias inornata, the "Darwin's Finch" of Cocos Island, Costa Rica. , 1987, Proceedings of the National Academy of Sciences of the United States of America.

[17]  Parasitological evidence for specialized foraging behavior in lake-resident Arctic char (Salvelinus alpinus) , 1995 .

[18]  B. Ebenman,et al.  Components of Niche Width in a Territorial Bird Species: Habitat Utilization in Males and Females of the Chaffinch (Fringilla coelebs) on Islands and Mainland , 1982, The American Naturalist.

[19]  T. Ehlinger.  Habitat Choice and Phenotype‐Limited Feeding Efficiency in Bluegill: Individual Differences and Trophic Polymorphism , 1990 .

[20]  E. Prepas,et al.  Individual specialization and trophic adaptability of northern pike (Esox lucius): an isotope and dietary analysis , 1999, Oecologia.

[21]  D. Schindler,et al.  Density-dependent changes in individual foraging specialization of largemouth bass , 1997, Oecologia.

[22]  P. Wainwright.  Ecological Explanation through Functional Morphology: The Feeding Biology of Sunfishes , 1996 .

[23]  D. Wilson,et al.  Parasites, morphology, and habitat use in a bluegill sunfish (Lepomis macrochirus) population , 1996 .

[24]  Jonathan Roughgarden,et al.  Evolution of Niche Width , 1972, The American Naturalist.

[25]  B. Lister.  THE NATURE OF NICHE EXPANSION IN WEST INDIAN ANOLIS LIZARDS II: EVOLUTIONARY COMPONENTS , 1976, Evolution; international journal of organic evolution.

[26]  J. Roughgarden.  Theory of Population Genetics and Evolutionary Ecology: An Introduction , 1995 .

[27]  S. Hurlbert.  The Measurement of Niche Overlap and Some Relatives , 1978 .

[28]  Lani West.  Interindividual Variation in Prey Selection by the Snail Nucella (= Thais) Emarginata , 1986 .

[29]  E. Smith.  C188. On the asymptotic variance of socransky's proportional similarity index , 1984 .

[30]  J. E. Bryan,et al.  Food Specialization By Individual Trout , 1972 .

[31]  D. Wilson,et al.  Trade-Offs of Ecological Specialization: An Intraspecific Comparison of Pumpkinseed Sunfish Phenotypes , 1996 .