NDLI: Evaluating δ15N–body size relationships across taxonomic levels using hierarchical models

Content Provider	Springer Nature Link
Author	Reum, Jonathan C. P. Marshall, Kristin N.
Copyright Year	2013
Abstract	Ecologists routinely set out to estimate the trophic position of individuals, populations, and species composing food webs, and nitrogen stable isotopes (δ15N) are a widely used proxy for trophic position. Although δ15N values are often sampled at the level of individuals, estimates and confidence intervals are frequently sought for aggregations of individuals. If individual δ15N values are correlated as an artifact of sampling design (e.g., clustering of samples in space or time) or due to intrinsic groupings (e.g., life history stages, social groups, taxonomy), such estimates may be biased and exhibit overly optimistic confidence intervals. However, these issues can be accommodated using hierarchical modeling methods. Here, we demonstrate how hierarchical models offer an additional quantitative tool for investigating δ15N variability and we explicitly evaluate how δ15N varies with body size at successively higher levels of taxonomic aggregation in a diverse fish assemblage. The models take advantage of all available data, better account for uncertainty in parameters estimates, may improve inferences on coefficients corresponding to groups with small to moderate sample sizes, and partition variation across model levels, which provides convenient summaries of the ‘importance’ of each level in terms of unexplained heterogeneity in the data. These methods can easily be applied to diet-based studies of trophic position. Although hierarchical models are well-understood and established tools, their benefits have yet to be fully reaped by stable isotope and food web ecologists. We suggest that hierarchical models can provide a robust framework for conceptualizing and statistically modeling trophic position at multiple levels of aggregation.
Starting Page	1159
Ending Page	1168
Page Count	10
File Format	PDF
ISSN	00298549
Journal	Oecologia
Volume Number	173
Issue Number	4
e-ISSN	14321939
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2013-06-29
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Nitrogen stable isotopes Mixed effects model Multilevel models Biomass spectra Food web Puget Sound Ecology Plant Sciences
Content Type	Text
Resource Type	Article
Subject	Ecology, Evolution, Behavior and Systematics

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