Distinct responses of antagonistic and mutualistic networks to agricultural intensification

Abstract

Species interaction networks, which govern the maintenance of biodiversity and ecosystem processes within ecological communities, are being rapidly altered by anthropogenic activities worldwide. Studies on the response of species interaction networks to anthropogenic disturbance have almost exclusively focused on one interaction type at a time, such as mutualistic or antagonistic interactions, making it challenging to decipher how networks of different interaction types respond to the same anthropogenic disturbance. Moreover, few studies have simultaneously focused on the two main components of network structure: network topology (i.e., architecture) and network ecology (i.e., species identities and interaction turnover), thereby limiting our understanding of the ecological drivers underlying changes in network topology in response to anthropogenic disturbance. Here, we used 16,400 plant-pollinator and plant-herbivore interaction observations from 16 sites along an agricultural intensification gradient to compare changes in network topology and ecology between mutualistic and antagonistic networks. We measured two aspects of network topology-nestedness and modularity-and found that although the mutualistic networks were consistently more nested than antagonistic networks and antagonistic networks were consistently more modular, the rate of change in nestedness and modularity along the gradient was comparable between the two network types. Change in network ecology, however, was distinct between mutualistic and antagonistic networks, with partner switching making a significantly larger contribution to interaction turnover in the mutualistic networks than in the antagonistic networks, and species turnover being a strong contributor to interaction turnover in the antagonistic networks. The ecological and topological changes we observed in the antagonistic and mutualistic networks have different implications for pollinator and herbivore communities in agricultural landscapes, and support the idea that pollinators are more labile in their interaction partner choice, whereas herbivores form more reciprocally specialized, and therefore more vulnerable, interactions. Our results also demonstrate that studying both topological and ecological network structure can help to elucidate the effects of anthropogenic disturbance on ecological communities, with applications for conservation and restoration of species interactions and the ecosystem processes they maintain.

A dearth of data: fitting parasitoids into ecological networks

“…There is empirical evidence to support this assertion; Bastolla et al (2009) showed that integrating competition between pollinators in plant-pollinator networks predicts overall species richness better than only considering the mutualistic interaction between pollinators and plants [60]. Data also suggest that anthropogenic land-use change or management interventions have divergent effects on different interaction networks [61], implying that decisions made to enhance, for example, pollination, may inhibit pest control or vice versa.…”

Importance of interaction rewiring in determining spatial and temporal turnover of tritrophic (Piper‐caterpillar‐parasitoid) metanetworks in the Yucatán Península, México

“…Overall, interaction turnover across sites and seasons exhibited high values and less variable dissimilarity (β wn = 0.87-0.95) compared to species turnover (β s = 0.59-0.99), which reflects the prevalence of interaction rewiring across space and time. A high degree of interaction turnover is common among interaction networks, and similar magnitudes and ranges have been reported primarily for mutualistic, but also antagonistic networks, across spatial (Carstensen et al, 2014;Kemp et al, 2017), temporal (CaraDonna et al, 2017Lepesqueur et al, 2018;Olesen et al, 2011), and land-use gradients (Morrison & Dirzo, 2020). Interaction turnover in plant-herbivore networks has mixed results, Kemp et al (2017) showed that species composition influenced interaction turnover across spatial gradients, while Lepesqueur et al (2018) showed that interaction rewiring is the primary driver of interaction turnover across seasons.…”

Pathways for Novel Epidemiology: Plant–Pollinator–Pathogen Networks and Global Change

“…There are several nestedness indices, of which nestedness metric based on overlap and decreasing fill (NODF) is considered the most robust [117]. expect that pathogen spread within a pollinator population or interspecific spillover may be reduced or exacerbated by: (i) invasions by novel species or subspecies [17] (Figure 1C); (ii) the extirpation of pre-existing populations or species [62] (Figure 1C); (iii) modification of the relative abundance of species and dominant interactions [63] (Figure 1D); (iv) disruption of species' phenology [64,65] (Figure 1D); (v) shifting species distributions at landscape, regional, or global levels [62]; or (vi) changing species physiology, altering disease resistance, infectivity, or virulence [17,66] (Figure 1E). While scientific and policy awareness of pressures on wild pollinators has increased and led to regulations at various levels protecting pollinators and their habitats, less regulatory…”

“…Use of herbicides, fertiliser, and destruction of seminatural elements reduce richness and abundance of floral resources providing nectar and pollen [1], which can lead to network generalism [100]. Consequently, plant-pollinator networks in intensively farmed areas tend to be generalised with low modularity and nestedness and high connectance [59,63]. Such a network architecture can either limit or propagate community-wide pathogen transmission (Box 1).…”