Multiple determinants of the structure of plant-animal mutualistic networks

CAGNOLO, LUCIANO; VÁZQUEZ, DIEGO; CHACOFF, NATACHA

Congreso; XXIII Congresso Brasileiro de Entomologia (CBE); 2010

Species Interaction networks are becoming increasingly used as a framework to study plant–animal mutualisms within their ecological context. Although such focus on networks has brought about important insights into the structure of these interactions, relatively little is known about the mechanisms behind these patterns. Networks involving mutualistic interactions between species show regularities such as the skewed distribution of links per species, the nested organization of the interaction matrix and the frequent occurrence of asymmetric interactions. The structure of these networks is likely to result from the simultaneous influence of neutrality and the constraints imposed by complementarities in species phenotypes, phenologies, spatial distributions, phylogenetic relationships, and sampling artefacts. We develop a conceptual and methodological framework to evaluate the relative contributions of these potential determinants. Applying this approach to the analysis of a plant–pollinator network, we show that information on relative abundance and phenology suffices to predict several aggregate network properties (connectance, nestedness, interaction evenness, and interaction asymmetry). However, such information falls short of predicting the detailed network structure (the frequency of pairwise interactions), leaving a large amount of variation unexplained. Taken together, our results suggest that both relative species abundance and complementarities in spatiotemporal distribution contribute substantially to generate observed network patterns, but that this information is by no means sufficient to predict the occurrence and frequency of pairwise interactions. Future studies could use our methodological framework to evaluate the generality of our findings in a representative sample of study systems with contrasting ecological conditions.