Structure in plant–animal interaction assemblages

Abstract

We present a comprehensive approach to detect pattern in assemblages of plant and animal species linked by interactions such as pollination, frugivory or herbivory. Simple structural models produce gradient, compartmented or nested patterns of interaction; intermediate patterns between a gradient and compartments are possible, and nesting within compartments produces a combined model. Interaction patterns can be visualized and analyzed either as matrices, as bipartite networks or as multivariate sets through correspondence analysis. We argue that differences among patterns represent outcomes of distinct evolutionary and ecological processes in these highly diversified assemblages. Instead of choosing one model a priori, assemblages should be probed for a suite of patterns. A plant Á /pollinator assemblage exemplifies a simple nested pattern, whereas a plant Á / herbivore assemblage illustrates a compound pattern with nested structures within compartments. Compartmentation should reflect coevolutionary histories and constraints, whereas differences in species abundance or dispersal may generate nestedness.

Interaction intimacy organizes networks of antagonistic interactions in different ways

“…A long-lasting notion is that high modularity and low nestedness characterize antagonistic ecological networks [7,23]. Here, we show antagonisms can give rise to nested networks when interactions have a low degree of intimacy.…”

“…We did not use entire food webs because they often include different types of interactions varying in their degree of intimacy [16]. Conversely in two-mode networks all links represent the same kind of ecological interaction and thus are presumably subjected to similar ecological and evolutionary processes [23]. Moreover, we did not analyse networks in which a considerable proportion of nodes ('species') are actually sets of species that are assumed to be ecologically similar because two species sharing similar resources or consumers may differ strongly in their degree of intimacy.…”

Components of Phylogenetic Signal in Antagonistic and Mutualistic Networks

“…Now, if we assume that the matching traits are aggregated in clusters, as we can see in figure 1c, the modular structure appears in the diagonal. Thus, the matching centrality model is very flexible and can infer networks whose architecture is a mixture between nestedness and modularity, as illustrated by figure 1d (see also Lewinsohn et al 2006). This is an important property for a candidate model to fit both food webs and mutualistic networks.…”

Build-up mechanisms determining the topology of mutualistic networks

“…In the network formalism, species are represented by nodes, and interactions between species are described by links (reviewed by Pimm, 2002). The network approach is helping to describe community-level patterns of interspecific interactions and understanding how interactions coevolve in species-rich assemblages Guimara˜es et al, 2006;Jordano et al, 2003;Lewinsohn et al, 2006;Montoya et al, 2006;Prado and Lewinsohn, 2004). Our major challenge, however, is to infer what are the ecological and evolutionary factors that generate the observed community-level structure of ecological networks (Fig.…”

“…1A). In this context, community-level patterns of interactions are likely to uncover the importance of different ecological factors and coevolutionary processes (Lewinsohn et al, 2006;Olesen and Jordano, 2002;Thompson, 2005Thompson, , 2006.…”