Generalists are more specialized in low-resource habitats, increasing stability of ecological network structure

Abstract

Linking mechanistic processes to the stability of ecological networks is a key frontier in ecology. In trophic networks, “modules”—groups of species that interact more with each other than with other members of the community—confer stability, mitigating effects of species loss or perturbation. Modularity, in turn, is shaped by the interplay between species’ diet breadth traits and environmental influences, which together dictate interaction structure. Despite the importance of network modularity, variation in this emergent property is poorly understood in complex natural systems. Using two years of field data, we quantified interactions between a rich community of lepidopteran herbivores and their host plants across a mosaic of low-resource serpentine and high-resource nonserpentine soils. We used literature and our own observations to categorize herbivore species as generalists (feeding on more than one plant family) or specialists (feeding on one plant family). In both years, the plant-herbivore network was more modular on serpentine than on nonserpentine soils—despite large differences in herbivore assemblage size across years. This structural outcome was primarily driven by reduction in the breadth of host plant use by generalist species, rather than by changes in the composition of species with different fundamental diet breadths. Greater modularity—and thus greater stability—reflects environmental conditions and plastic responses by generalist herbivores to low host plant quality. By considering the dual roles of species traits and ecological processes, we provide a deeper mechanistic understanding of network modularity, and suggest a role for resource availability in shaping network persistence.

High fidelity defines the temporal consistency of host-parasite interactions in a tropical coastal ecosystem

“…S1). Taken as a whole, these findings reinforce the prevalence of cohesive and stable nucleus of interacting species, a pattern commonly described for mutualistic networks 66,67 , but barely explored in antagonistic systems 29,42 . www.nature.com/scientificreports/ For the first time, we revealed a constant turnover of avian hosts and haemosporidian parasites over time, even under the influence of migrant hosts.…”

“…S1 ). Taken as a whole, these findings reinforce the prevalence of cohesive and stable nucleus of interacting species, a pattern commonly described for mutualistic networks 66 , 67 , but barely explored in antagonistic systems 29 , 42 .…”

“…Modularity in host-parasite networks suggests that certain groups of parasites tend to infect specific hosts groups, increasing system compartmentalization and specialization 56 . This network propriety thus, is directly related to the ecological and/or evolutionary proximity among species pairs 41 , a pattern already documented for avian malaria 37 and other antagonistic systems, such as fish-endoparasite 40,57 , reptile-endoparasite 58 , mammal-ectoparasite 59 , and lepidopteran herbivores-plants networks 29 .…”

“…As follows, it seems that modularity in interactions networks, i.e. a structure that emerges when cohesive subgroups of species interacts among themselves in higher frequency than with the remaining network 38 , is an important property that provides stability in antagonistic systems 29 .…”

“…After all, we must comprehend the dynamism of these interactions through time, as the causes and consequences of any such dynamic patterns. Nevertheless, to unveil how interaction networks change over time is important to understand the assembly and disassembly of biological interactions and their persistence under ecological and evolutionary unpredictability 29,48 .…”