The jungle brothers: peccaries and tapirs structure tropical forest diversity (Part 1)

The Journal of Ecology has recently published new research by Villar et al. “The cryptic regulation of diversity by functionally complementary large tropical forest herbivores.”

Read more about their work in this post & Part 2, written by authors Nacho Villar & Mauro Galetti.

The empty forest

The “empty forest” syndrome described by Redford (1992) portrays a sad reality: the local extinction of large vertebrate populations due to overhunting and habitat destruction, in many tropical forests across the world. The Anthropocene long shadow has left a gloomy track of relentless extinction of megafauna, from some of the Earth’s most hyperdiverse ecosystems. Ecologists have been busy documenting defaunation of tropical forests, but have paid less attention to studying the functional and ecosystem-level consequences of this process in a structured way. Rigorous, empirical-based research is necessary to underpin the mechanisms involved.

The white-lipped peccary: a large herbivore from the tropical forests of South America. Peccaries live in large groups and feed on plant seeds and seedlings. Although their feeding habits reduce the number of plants found at the forest floor, when living alongside tapirs they have a net positive effect on plant diversity. Photograph by João Paulo Krajewski.

Most of what we know about the ecological functions of large vertebrates in tropical systems comes from a very limited number of exclusion experiments scattered across the world (e.g. Cocha Cashu in Peru, Barro Colorado in Panama, Los Tuxtlas in Mexico, La Selva in Costa Rica, and several others in Congo and Borneo, to mention just a few). These studies have provided phenomenal insights into the ecology of large tropical vertebrates, but few of them to date have been able to provide solid evidence about the ecological roles played by different large vertebrate types. We know that spider monkeys disperse seeds by eating fruits, and forest elephants have a strong impact on plant recruitment through trampling and browsing – but what about different species with apparently more similar ecology? How complementary or redundant are the functions provided by, say, a brocket deer and a tapir? If we compare our current knowledge of the ecological functions of large vertebrate species in savanna or grassland ecosystems with those in tropical forests, the latter is lagging eons behind.

One of a kind

In 2009, we established an ambitious experiment in the hyper-diverse Atlantic Forest of Brazil, in order to disentangle the ecological functions of two key, large tropical herbivores of conservation concern: the white-lipped-peccary (WLP, Tayassu pecari) and the lowland tapir (Tapirus terrestris). This long-term project is supported by the BIOTA Program from the São Paulo Research Foundation FAPESP. The tapir, weighing 250 kg, is the largest remaining megafauna species in these forests. Whilst the WLP (25-40 kg) is the most abundant, representing about 80% of the biomass for large terrestrial herbivores. Many tropical ecologists consider these species “ecosystem engineers”, but in reality there is no sound conclusive experimental evidence of this. Interestingly, these species have divergent ecological traits: tapirs are solitary browsers and frugivores, whilst peccaries are voracious seed and seedling predators, living in large extended families often exceeding a hundred individuals. Furthermore, as tapirs are seed dispersers and peccaries are seed predators the experiment provides a unique but powerful insight into the complementary ecological role of two fundamental types of consumer-resource outcomes: mutualism and antagonism.

*Our long-term multi-site experiment in the Atlantic Forest of Brazil. See Figure 1 of our article for further details.*

Our experiment comprises 86 exclosure-control paired plots, located at four different regions – where tapirs and WLPs occur either in isolation, in combination, or where both are simultaneously absent. Since 2009, we have been monitoring plant demography and identifying seedlings every 6 months, with an accumulated dataset of more than 8000 seedlings. Honestly, to maintain a locally funded experiment of this magnitude in a challenging location is a logistical nightmare, but the results are starting to pay-off!

Nacho Villar, Universidade Estadual Paulista (UNESP), Brazil
Mauro Galetti, Universidade Estadual Paulista (UNESP), Brazil & University of Miami, USA

Read the full paper online: The cryptic regulation of diversity by functionally complementary large tropical forest herbivores (free to view for a limited time)

Read the press release from São Paulo State University (UNESP): https://www.britishecologicalsociety.org/large-herbivores-increase-biodiversity-tropical-forests/