Generalized linear mixed models can detect unimodal species-environment relationships

Tahira Jamil, C.J.F. ter Braak

Research output: Contribution to journalArticleAcademicpeer-review

13 Citations (Scopus)


Niche theory predicts that species occurrence and abundance show non-linear, unimodal relationships with respect to environmental gradients. Unimodal models, such as the Gaussian (logistic) model, are however more difficult to fit to data than linear ones, particularly in a multi-species context in ordination, with trait modulated response and when species phylogeny and species traits must be taken into account. Adding squared terms to a linear model is a possibility but gives uninterpretable parameters. This paper explains why and when generalized linear mixed models, even without squared terms, can effectively analyse unimodal data and also presents a graphical tool and statistical test to test for unimodal response while fitting just the generalized linear mixed model. The R-code for this is supplied in Supplemental Information 1
Original languageEnglish
Article numbere95
Number of pages14
Publication statusPublished - 2013

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