Predicting the consequences of disperser extinction: richness matters the most when abundance is low

Abstract

Summary The ongoing biodiversity crisis entails the concomitant loss of species and the ecological services they provide. Global defaunation, and particularly the loss of frugivores, may negatively affect the seed dispersal of fleshy‐fruited plant species, with predictable stronger impacts in simplified communities such as those on oceanic islands. However, logistical difficulties have hindered the experimental and theoretical need to disentangle the roles of species identity, richness (i.e. number of species) and abundance. Consequently, studies to date have focused exclusively on the loss of species richness leaving us largely ignorant regarding how species identity and abundance affect the loss of ecosystem functions. Here, we applied a network approach to disentangle the effects of disperser abundance, richness and identity on the seed dispersal service provided by frugivores to the Galapagos plant community. We found that both abundance and richness of the dispersers significantly affect the function of seed dispersal and that richness becomes increasingly important as disperser abundance declines. Extinction simulations revealed that the order of species loss has profound implications to the plant community. On the one hand, abundant generalist dispersers like the Galapagos lizards, can mitigate the loss of specialized dispersers. On the other hand, specific threats affecting key dispersers can lead to the rapid collapse of the community‐level dispersal services. Our results suggest that the identity of the disperser species lost can have a large effect on the number of plant species dispersed, and generalist species are essential to the persistence of the community dispersal service. Both abundance and species richness of seed dispersers are key and synergistic drivers of the number of plant species dispersed. Consequently, the coupled negative effect of population declines and species extinctions in frugivore assemblages may lead to an accelerated loss of the seed dispersal function. http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12897/suppinfo is available for this article.

Moving from frugivory to seed dispersal: Incorporating the functional outcomes of interactions in plant–frugivore networks

“…Resilience can increase despite plant species having fewer partners on average if the removal of interactions changed the animal removal sequence or if non‐mutualistic interactions constituted a large proportion of a species’ interaction frequency in the original networks. Therefore, we conclude that, while most estimates of resilience are relatively unchanged by incorporating natural history information, some plant species underwent more major changes, revealing them as more susceptible to global change pressures, including climate change (Schleuning et al., ) or disperser extinction (Rumeu et al., ).…”

Seed‐dispersal networks are more specialized in the Neotropics than in the Afrotropics

“…Carvalho et al () documented that defaunation of large frugivores can lead to microevolutionary changes in a Brazilian Atlantic Forest palm ( Euterpe edulis ) through the loss of dispersal functions from large seed dispersers, which can even result in a decrease in seed size in defaunated habitats (Galetti et al, ). Functional consequences of the loss of generalist seed dispersers have been shown to be particularly severe, because these species help to stabilize seed‐dispersal functions against the loss of specialists (Rumeu et al, ), although specialist seed dispersers cannot always be replaced by generalists (Guaraldo, Boeni, & Pizo, ). Species loss could be buffered further by species that switch their preference to compensate for lost interactions (Timóteo, Albino Ramos, Vaughan, & Memmott, ).…”

Contribution by vertebrates to seed dispersal effectiveness in the Galápagos Islands: a community‐wide approach

“…() who reported a similar result for the Canary Islands. Those asymmetrical relationships of plant species depending on just one frugivore that disperse many plant species are very vulnerable against disperser extinctions (Rumeu et al ). Such a fragile interaction profile is common on islands, e.g., Calvaria major in Mauritius (Witmer ), Neochamaelea pulverulenta in the Canaries (Valido , Pérez‐Méndez et al.…”