Structure of trophic and mutualistic networks across broad environmental gradients

Abstract

This study aims to understand how inherent ecological network structures of nestedness and modularity vary over large geographic scales with implications for community stability. Bipartite networks from previous research from 68 locations globally were analyzed. Using a meta-analysis approach, we examine relationships between the structure of 22 trophic and 46 mutualistic bipartite networks in response to extensive gradients of temperature and precipitation. Network structures varied significantly across temperature gradients. Trophic networks showed decreasing modularity with increasing variation in temperature within years. Nestedness of mutualistic networks decreased with increasing temperature variability between years. Mean annual precipitation and variability of precipitation were not found to have significant influence on the structure of either trophic or mutualistic networks. By examining changes in ecological networks across large-scale abiotic gradients, this study identifies temperature variability as a potential environmental mediator of community stability. Understanding these relationships contributes to our ability to predict responses of biodiversity to climate change at the community level.

Moderation is best: effects of grazing intensity on plant-flower visitor networks in Mediterranean communities

“…Different studies have shown contrasting relationships between network size and nestedness (e.g., Okuyama and Holland 2008, Bastolla et al 2009, James et al 2012, Dalsgaard et al 2013, Welti and Joern 2015, and therefore, we did not have a clear prediction about how intermediate grazing intensity might affect nestedness. Vanbergen et al (2014) found grazing to affect nestedness in opposite directions, depending on whether the networks were standardized or not, which suggests that if an effect of grazing on networks exists, it may be complex.…”

“…On the other hand, it is still not clear how species richness relates to nestedness, i.e., the tendency of specialist species to only interact with generalist species. Some studies indicate positive relationships between network complexity and nestedness (Bascompte et al 2003, Okuyama and Holland 2008, Bastolla et al 2009), while others indicate negative relationships (James et al 2012, Dalsgaard et al 2013, Welti and Joern 2015.…”

Fire, grazing and climate shape plant–grasshopper interactions in a tallgrass prairie

“…Modularity and generalism of herbivore diet are hypothesized to be important structural property stabilizing bipartite plant–herbivore networks (Montoya et al, ; Thébault & Fontaine, ). While few previous studies have compared trophic networks within the same system, comparisons across datasets have shown an increase in generality with species richness across producer–consumer network comparisons, whereas the relationship between modularity and species richness is less clear (Morris, Gripenberg, Lewis, & Roslin, ; Welti & Joern, ). However, while larger ecological networks themselves may be more stable, modularity, generality and robustness provide predictions for responses to future species loss.…”

“…Ascertaining plant–herbivore network composition is challenging as it requires identification of both species and diet interactions (Novotny & Basset, ). Moreover, recent efforts have only begun to examine how habitat and climatic conditions shape network structural properties (Dalsgaard et al, ; López‐Carretero, Díaz‐Castelazo, Boege, & Rico‐Gray, ; Rezende, Albert, Fortuna, & Bascompte, ; Welti & Joern, ).…”

A distributed experiment demonstrates widespread sodium limitation in grassland food webs

“…Climate and soil nutrients such as nitrogen and phosphorus can control abundance, diversity, and food web complexity (Meserve et al. , Welti and Joern , Lind et al. ).…”