The nested assembly of individual-resource networks

Abstract

Summary1. Much of the current understanding of ecological systems is based on theory that does not explicitly take into account individual variation within natural populations. However, individuals may show substantial variation in resource use. This variation in turn may be translated into topological properties of networks that depict interactions among individuals and the food resources they consume (individual-resource networks). 2. Different models derived from optimal diet theory (ODT) predict highly distinct patterns of trophic interactions at the individual level that should translate into distinct network topologies. As a consequence, individual-resource networks can be useful tools in revealing the incidence of different patterns of resource use by individuals and suggesting their mechanistic basis. 3. In the present study, using data from several dietary studies, we assembled individual-resource networks of 10 vertebrate species, previously reported to show interindividual diet variation, and used a network-based approach to investigate their structure. 4. We found significant nestedness, but no modularity, in all empirical networks, indicating that (i) these populations are composed of both opportunistic and selective individuals and (ii) the diets of the latter are ordered as predictable subsets of the diets of the more opportunistic individuals. 5. Nested patterns are a common feature of species networks, and our results extend its generality to trophic interactions at the individual level. This pattern is consistent with a recently proposed ODT model, in which individuals show similar rank preferences but differ in their acceptance rate for alternative resources. Our findings therefore suggest a common mechanism underlying interindividual variation in resource use in disparate taxa.

Interindividual variations in fruit preferences of the yellow-shouldered bat Sturnira lilium (Chiroptera: Phyllostomidae) in a cafeteria experiment

“…Sometimes, individuals with a narrower diet feed on a subset of the items consumed by individuals with a broader diet, what could be interpreted as evidence of an optimal diet (Howell andHartl 1980, Pyke 1984), as the items in the population's diet could be ranked according to their cost-benefit relationship from preferred to occasional. The most important items would be present in the diets of most individuals, while the least consumed items would appear only in the diet of the most generalistic individuals (see, for instance, Pires et al 2011).…”

Complex-to-Predict Generational Shift between Nested and Clustered Organization of Individual Prey Networks in Digger Wasps

“…Previous studies have demonstrated that the use of network analysis can be a powerful tool to find out patterns of individual resource use [23], [35], [36], having the potential to elucidate which factors may promote different network topologies [34]. In this study, the assessment of the network-based inter-individual variation parameter is used as a starting point that may allow a subsequent in-depth analysis of the network properties.…”

“…A population would be organized in clusters when different groups of individuals specialize on different subsets of resources, in such a way that individuals within a group strongly compete with the rest of the members of that group, but show little competition with the individuals belonging to other clusters [34]. Nestedness, on its part, appears when individuals with both narrow (specialist individuals) and broad (generalist individuals) niches are found in a population, in such a way that the resources consumed by the specialists are ordered and predictable subsets of the resources used by the generalists [23], [35], [37]. Additionally, anti-nested patterns could emerge if the nestedness is lower than expected by chance [38], as happens in checkerboard patterns, in which pairs of prey species that never co-occur can be found [39].…”

The evolution and ecology of individual specializations amongst a group of dietary generalists.

“…5a, b). Like many other studies, at sites with greater conspecific density, individuals are forced to specialize on underutilized prey (Svanbäck and Bolnick 2005;Tinker et al 2012;Pires et al 2011). However, all the true frogs had a negative relationship between conspecific density and IS.…”

“…Individuals can differ in their rank order of less preferred prey items or can have the same rank order of prey but differ in when they switch to those alternative prey types depending on the frequency of the top ranked prey (Svanbäck and Bolnick 2005). Network analysis has demonstrated that both types of expansion are possible in natural populations (Araújo et al 2008;Pires et al 2011;Tinker et al 2012). However, intraspecific competition may not always be a diversifying force.…”