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Comparing species interaction networks along environmental gradients
Author(s) -
Pellissier Loïc,
Albouy Camille,
Bascompte Jordi,
Farwig Nina,
Graham Catherine,
Loreau Michel,
Maglianesi Maria Alejandra,
Melián Carlos J.,
Pitteloud Camille,
Roslin Tomas,
Rohr Rudolf,
Saavedra Serguei,
Thuiller Wilfried,
Woodward Guy,
Zimmermann Niklaus E.,
Gravel Dominique
Publication year - 2018
Publication title -
biological reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.993
H-Index - 165
eISSN - 1469-185X
pISSN - 1464-7931
DOI - 10.1111/brv.12366
Subject(s) - modularity (biology) , variation (astronomy) , null model , trait , ecological network , nestedness , ecology , matching (statistics) , abiotic component , standardization , computer science , biology , species richness , evolutionary biology , ecosystem , mathematics , statistics , physics , astrophysics , programming language , operating system
Knowledge of species composition and their interactions, in the form of interaction networks, is required to understand processes shaping their distribution over time and space. As such, comparing ecological networks along environmental gradients represents a promising new research avenue to understand the organization of life. Variation in the position and intensity of links within networks along environmental gradients may be driven by turnover in species composition, by variation in species abundances and by abiotic influences on species interactions. While investigating changes in species composition has a long tradition, so far only a limited number of studies have examined changes in species interactions between networks, often with differing approaches. Here, we review studies investigating variation in network structures along environmental gradients, highlighting how methodological decisions about standardization can influence their conclusions. Due to their complexity, variation among ecological networks is frequently studied using properties that summarize the distribution or topology of interactions such as number of links, connectance, or modularity. These properties can either be compared directly or using a procedure of standardization. While measures of network structure can be directly related to changes along environmental gradients, standardization is frequently used to facilitate interpretation of variation in network properties by controlling for some co‐variables, or via null models. Null models allow comparing the deviation of empirical networks from random expectations and are expected to provide a more mechanistic understanding of the factors shaping ecological networks when they are coupled with functional traits. As an illustration, we compare approaches to quantify the role of trait matching in driving the structure of plant–hummingbird mutualistic networks, i.e. a direct comparison, standardized by null models and hypothesis‐based metaweb. Overall, our analysis warns against a comparison of studies that rely on distinct forms of standardization, as they are likely to highlight different signals. Fostering a better understanding of the analytical tools available and the signal they detect will help produce deeper insights into how and why ecological networks vary along environmental gradients.

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