Cazelle, K., Araujo, M.B., Mouquet N., and Gravel, D. (2016).

Theoretical Ecology, 9, 039-048, doi:10.1007/s12080-015-0281-9

Key message : We argue that a theory of species co-occurrence in ecological networks is needed to better inform interpretation of co-occurrence data, to formulate hypotheses for different community assembly mechanisms, and to extend the analysis of species distributions currently focused on the relationship between occurrences and abiotic factors. The main objective of this paper is to provide the first building blocks of a general theory for species co-occurrences. We formalize the problem with definitions of the different probabilities that are studied in the context of co-occurrence analyses. We analyze three species interactions modules and conduct multi-species simulations in order to document five principles influencing the associations between species within an ecological network: (i) direct interactions impact pairwise co-occurrence, (ii) indirect interactions impact pairwise co-occurrence, (iii) pairwise co-occurrence rarely are symmetric, (iv) the strength of an association decreases with the length of the shortest path between two species, and (v) the strength of an association decreases with the number of interactions a species is experiencing. Our analyses reveal the difficulty of the interpretation of species interactions from co-occurrence data. We discuss whether the inference of the structure of interaction networks is feasible from co-occurrence data. We also argue that species distributions models could benefit from incorporating conditional probabilities of interactions within the models as an attempt to take into account the contribution of biotic interactions to shaping individual distributions of species.

Co-occurrence in multi-species networks. A The disparity between observed co-occurrence (Pi,j ) and independent co-occurrence (Pi,j ;IND) decreases with the path length between nodes (species). The envelopes are drawn around the 5 and 95 % quantiles of all of the data, from 100 replicated simulations for every species richness value (5 to 100 species). B The strength of co-occurrence (log(Pi,j /Pi,j ;IND)) decreases with the number of interactions of a species i (i.e., the degree of a node). Points represent the mean for a particular degree of node value (1 to 60). The solid line represents the overall trends and the grey envelop reflects the variance associated. At least 3000 values were used for each point.

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OTHER TOPICS: Aesthetics of Biodiversity, Biodiversity & Ecosystem Functioning, Biogeography, Macroecology & Ecophylogenetics, Experimental Evolution, Functional Biogeography, Functional Rarity, Metacommunities, Metaecosystems, Reviews and Synthesis, Trophic Biogeography & Metaweb