Sampling bias affects the relationship between structural importance and species body mass in frugivore-plant interaction networks

Abstract

Within a community, body mass variation among frugivore species is associated with: a) animal's ecological, physiological and functional traits; b) community-level biogeographic/climatic variables; c) anthropogenic factors, and methodological approaches. Furthermore, frugivore-plant relationships are highly context dependent; thus, variation in species attributes at the community level might determine interaction patterns. An interaction network approach is a useful tool to analyze the relationship between species attributes and species role in maintaining the network connectivity patterns (species structural importance). Particularly, the relationship between species body mass and interspecific interaction patterns could be determined by differences in the community properties and the environmental context of the network's geographic location. We tested the hypotheses that: i) the relationship between frugivore species body mass and its structural importance in the network is determined by the frugivore species body mass coefficient of variation (COV) in the community, and ii) frugivore body mass COV depends on the network context in terms of the local climate variables, level of human impact, and taxa considered within the sampling. We evaluated the relationship between species structural importance and its body mass in 28 frugivore-plant interaction networks from different parts of the world. Species structural importance was calculated as a general measure of centrality, which quantifies the generalization level of the species, the proximity of a species to other species in the network, and the importance of a species as a connector between different parts of the network. A meta-analysis approach was applied to evaluate the influence of local climate and community variables associated with each network on the relationship between species structural importance and its body mass. The relationship between centrality and species body mass was highly fluctuating between networks, and frugivore body mass COV was the variable that best explained this heterogeneity. Moreover, networks with both bird and mammal species showed the highest COV values. Our results show that when there is sufficient body mass variability among species in the community, the largest species take important roles in maintaining the network connectivity patterns. This suggests that the bias towards small species in networks studies may impact the magnitude of the frugivore species body mass COV and, therefore, conceal the importance to larger species in network topologies. Future research in frugivore-plant interaction networks should include the highest possible number of interacting species without limiting the samples to species within a particular body size or taxonomic group.