Ecological consequences of defaunation in the Anthropocene

Humans are one of the major drivers in structuring vertebrate communities, altering food webs, with unprecedented consequences for ecosystem function. For instance, in tropical terrestrial ecosystems, hunters remove a large proportion of the standing mammalian biomass reducing population densities by 60-100%. Most of these vertebrates are large-bodied species in distinct trophic levels. Theoretical and empirical studies have found that apex consumers play a fundamental role in food web structure and stability in temperate biomes. Large-bodied forest dwelling vertebrates comprise important top predators, seed dispersers and herbivores, and their loss may lead to trophic cascades. Therefore, defaunation is likely to erode key ecosystem processes with far-reaching consequences.

Consequences of defaunation

Current ecological knowledge indicates that apex consumers are fundamental in the maintenance of biodiversity and ecosystem functions. Human hunting in key elements of the food web may lead to trophic cascades, yet we lack information from non-fragmented tropical ecosystems. The Atlantic rainforest have more than 80% of the woody plant species dispersed by vertebrates and it is estimated that 88% of its area is under trophic cascade due to the extinction of apex consumers. Most of our understanding of trophic cascades is based on temperate biomes or fragmented landscapes, which cannot be easily extrapolated to larger scales. In this proposal, we seek to understand long-term effects of defaunation on trophic cascades, particularly in plant composition, and examine functional changes in forest dynamics and composition (diversity, functional organization and carbon stock).

Testing ecosystem functions of invasive plants and frugivores

feral pig Sus scrofa

Introduction and invasion of exotic species has been particularly studied by the negative point of view of what they result to natural ecosystems. Invasive species might compete, predate and transmit disease to native species, driving many of them to extinction. However, in biologically impoverished environments, invasive species can provide food resources or ecosystem functions lost by fragmentation or defaunation. Frugivores and fleshy fruit plants are a good study model to test the potential effects in such biologically impoverished ecosystems. This project is divided in 3 subprojects: (a) create and analyze a data base of interactions between frugivores and exotic plants in Atlantic Forest; (b) understand the factors that favors the biological invasion of an invasive palm (Archontophoenix cunninghamiana) mediated by birds and its role in maintaining frugivore birds; (c) evaluate the role of the megafrugivore feral pig (Sus scrofa) in dispersing seeds, trampling and rooting in defaunated forest remnants. Through field experiments and naturalistic observations, we will be able to understand how these species are affecting the ecosystems in which they are interacting, either positively or negatively.

Patterns and determinants of pollen, seed and gene dispersal

Patterns of pollination and dispersal

Pollen, seed and gene dispersal by animals are non-random processes that depend on the pollinator and frugivore assemblage and how they interact with the environment. These processes help shape the spatial distribution and genetic diversity of plants at fine scales and are key to the connectivity among populations and genetic structure across modified landscapes. Therefore, our overarching goal is to disentangle the relative importance of multiple factors ranging from population characteristics, microhabitat and landscape features on dispersal to understand how populations respond to environmental deterioration. Our research focuses on plants with disparate life history traits, from highly generalist, pioneer trees (e.g. Cecropia hololeuca) to large, slow growing species (e.g. Hymenaea courbaril). Our main study system comprises the juçara palm Euterpe edulis and its avian dispersers in the Atlantic Rainforest. Euterpe edulis is a paramount food source for several animal species but it is endangered due to the large scale harvesting of the heart of palm. Likewise, most of the large fruit-eating birds (toucans, toucanets and bellbirds) are functionally extinct from small remnants and heavily defaunated reserves. The ecological roles provided by the different frugivore assemblages across the fragmentation gradient will most likely generate a spatial and genetic signature with unknown consequences for the long term persistence of plant populations in highly impacted areas.