Species interactions regulate the collapse of biodiversity and ecosystem function in tropical forest fragments

Abstract

Abstract. Competitive interactions among species with similar ecological niches are known to regulate the assembly of biological communities. However, it is not clear whether such forms of competition can predict the collapse of communities and associated shifts in ecosystem function in the face of environmental change. Here, we use phylogenetic and functional trait data to test whether communities of two ecologically important guilds of tropical birds (frugivores and insectivores) are structured by species interactions in a fragmented Amazonian forest landscape. In both guilds, we found that forest patch size, quality, and degree of isolation influence the phylogenetic and functional trait structure of communities, with small, degraded, or isolated forest patches having an increased signature of competition (i.e., phylogenetic and functional trait overdispersion in relation to null models). These results suggest that local extinctions in the context of fragmentation are nonrandom, with a consistent bias toward more densely occupied regions of niche space. We conclude that the loss of biodiversity in fragmented landscapes is mediated by niche-based competitive interactions among species, with potentially far-reaching implications for key ecosystem processes, including seed dispersal and plant damage by phytophagous insects.

Causes and Consequences of Behavioral Interference between Species

“…In these cases, behavioral interference can determine which species are lost or gained after land-use change. For example, two species might co-occur in larger patches of habitat, but when these patches shrink one of the species might be driven to extinction by elevated competition associated with spatial constraints and a dwindling pool of resources [86]. More information about how behavioral interference is mediated by frequency dependence, dominance asymmetries, and other mechanisms that reduce the fitness of one or both species will help us to predict the rate and order of local extinctions in response to land-use change.…”

Using avian functional traits to assess the impact of land-cover change on ecosystem processes linked to resilience in tropical forests

“…To prevent these correlations biasing analyses towards detecting only processes associated with body size, we used ordination techniques to derive independent trait axes. Specifically, we generated three trait axes related to different ecological characteristics by applying a two-step principal component analysis (PCA) on morphological trait data, following previous studies [25,28]. Initially, separate PCAs were undertaken on locomotory (tarsus : tail/wing ratio) and trophic traits (beak shape).…”

“…For instance, most previous studies of functional diversity pool all functional groups (e.g. dietary groups) together within total communities, making it difficult to draw conclusions about any specific process [20,25], particularly as the impacts of land-cover change vary across such groups [26,27]. Likewise, most previous studies are unidimensional in that they pool together multiple functional traits despite contrasting functions (e.g.…”

The Interplay Between Landscape Structure and Biotic Interactions

“…For instance, interspecific competition among birds in tropical forests was most intense in small forest patches, but also varied in intensity depending on trophic specialization [98]. Interactions can also weaken with decreasing patch size.…”