Invariant antagonistic network structure despite high spatial and temporal turnover of interactions

Abstract

Recent work has suggested that emergent ecological network structure exhibits very little spatial or temporal variance despite changes in community composition. However, the changes in network interactions associated with turnover in community composition have seldom been assessed. Here we examine whether changes in ecological networks are best detected by standard emergent network metrics or by assessing internal network changes (i.e. interaction and composition turnover). To eliminate possible spatial or phylogenetic effects, that in large‐scale studies may obscure mechanisms structuring networks and interactions, we sampled multiple antagonistic (plant–herbivore) networks for a single diverse plant family (the Restionaceae) in the hyperdiverse Cape Floristic Region. These are the first plant–herbivore networks constructed for this global biodiversity hotspot. We found invariant emergent network structure despite considerable changes in insect and plant composition across communities over time and space. In contrast, there was high interaction turnover between networks. Seasonally, this was driven by turnover in insect species and insect host switching. Spatially, this was driven by simultaneous turnover in plant and insect species, suggesting that many insects are host specific or that both groups exhibit parallel responses to environmental gradients. Spatial interaction turnover was also driven by turnover in plants, showing that many insects can utilise multiple (possibly closely related) hosts and this may create divergent selection gradients that promote insect speciation. Thus we show highly variable interaction fidelity, despite invariant emergent network structure. We suggest that evaluating internal network changes may be more effective at elucidating the processes structuring networks, and many fine‐scale changes may be obscured when only calculating emergent network metrics.

Significant Local-Scale Plant-Insect Species Richness Relationship Independent of Abiotic Effects in the Temperate Cape Floristic Region Biodiversity Hotspot

“…This is further supported by plant richness being a better predictor of insect richness than plant phylogenetic diversity. Similar results were found by Kemp et al [60] where plant-herbivore interactions in the CFR showed high levels of fidelity at the species-level. Our results contrast with Procheş et al [28] who found plant genera and plant phylogenetic diversity to be the strongest predictors of insect diversity in the CFR, and the taxonomic level at which insects specialise may thus vary between plant groups in the CFR.…”

Effects of species traits, motif profiles, and environment on spatial variation in multi‐trophic antagonistic networks

“…Here, we find substantial interaction turnover across lakes with a larger contribution of interaction rewiring than previous bipartite food web studies (Novotny , Kemp et al. ), but with the contribution of species turnover still as the primary driver. In addition, we find that most environmental variables were poor predictors of spatial interaction turnover and that the ecological drivers we considered were inadequate predictors of species‐specific interactions per lake.…”

“…, Kemp et al. , Saavedra et al. ) systems leaving a gap, to our knowledge, in the study of spatial interaction turnover in multi‐trophic, antagonistic (i.e., unipartite) networks.…”

Climate warming alters the structure of farmland tritrophic ecological networks and reduces crop yield

“…Third, we only examined the effects of treatment over a single growing season. Further temporal replicates would determine whether the response observed is year‐dependent and the extent of interaction turnover (Kemp, Evans, Augustyn, & Ellis, ). Fourth, we did not consider other organisms potentially affecting the plant–aphid–parasitoid networks, such as ants interacting with aphids or predators consuming both aphids and parasitoids (Barton & Ives, ; Raso et al., ; Traugott, Bell, Raso, Sint, & Symondson, ).…”