Frugivores at higher risk of extinction are the key elements of a mutualistic network

Abstract

Most tree species rely on vertebrates for seed dispersal, and many vertebrates use fruits as food resources in tropical forests. Therefore, plant-frugivore interactions affect population dynamics and persistence in ecological communities. Plant-frugivore interactions often involve many species, forming networks of interacting plants and animals that play different roles in determining network organization. The network organization is the way interactions are structured in the community, which may have consequences for its ecological and evolutionary dynamics. Some species have greater influences on network organization and may be particularly important to species persistence. We identified the frugivores most important to the organization of networks of plants and frugivorous birds in three contiguous Atlantic forest sites in southeastern Brazil. We found that the species that contributed most to network organization were at higher risk of extinction. Among the main contributors to network organization were two cotingas and a toucan, large-bodied species that disperse seeds from many plants and are particularly vulnerable to habitat loss and hunting. As a consequence, ongoing extinctions may significantly affect the organization of plant-frugivore interactions in the studied system. We hypothesize that the crucial role of some threatened frugivores may occur in other seed dispersal systems in tropical communities, although the association between structural importance and degree of threat may be contingent on peculiarities of local communities and disturbances.

Unravelling Darwin's entangled bank: architecture and robustness of mutualistic networks with multiple interaction types

“…These species and their interactions play disproportionately important roles in the community either through many direct or indirect links to other species that help guarantee the persistence of a mutualistic community rich in species [42,43]. The loss of keystone mutualists has important consequences for the ecological and evolutionary dynamics of the system, because the extinction of these highly connected species can lead to co-extinctions of other species and reduce the long-term overall species persistence [23,25].…”

“…See electronic supplementary material, appendix S2 for details on methods of calculation for all metrics, descriptors and null model. Additionally, we used a principal component analysis (PCA) on the correlation matrix among k i (number of interactions), c i (among-module connectivity), z i (standardized within-module degree) and cn i (contribution to nestedness) values to synthesize the species' contributions to connectivity, nestedness and modularity according to Vidal et al [25]. The first principal component (PC1) was used as a new descriptor summarizing species' contribution to network structure, and the higher scores assigned to each species indicate greater contributions to all analysed structural aspects described above.…”

Ecological Responses to Climate Change at Biogeographical Boundaries

“…However, the extinction of less-connected specialized species presumably does not lead to the collapse of the whole network in contrast with the decline of the central super-generalist species. Similar networks are located in the Atlantic Forest in Brazil as well which are also threatened by extinction [46]. The authors' results suggest that generalist species play an important role in the ecosystem functions.…”

Producing Diversity: Agroforests Sustain Avian Richness and Abundance in India's Western Ghats

“…Populations of sensitive, large-bodied frugivorous species such as hornbills and pigeons are most affected by areca and rubber agroforests. This in turn destabilizes crucial mutualistic plant-frugivore networks and ecosystem functioning (Vidal et al, 2014). Coffee agroforests also supported highest densities of low, mid-high and high canopy habitat guilds.…”