Consequences of defaunation for a tropical tree community

Abstract

Hunting affects a considerably greater area of the tropical forest biome than deforestation and logging combined. Often even large remote protected areas are depleted of a substantial proportion of their vertebrate fauna. However, understanding of the long-term ecological consequences of defaunation in tropical forests remains poor. Using tree census data from a large-scale plot monitored over a 15-year period since the approximate onset of intense hunting, we provide a comprehensive assessment of the immediate consequences of defaunation for a tropical tree community. Our data strongly suggest that over-hunting has engendered pervasive changes in tree population spatial structure and dynamics, leading to a consistent decline in local tree diversity over time. However, we do not find any support for suggestions that over-hunting reduces above-ground biomass or biomass accumulation rate in this forest. To maintain critical ecosystem processes in tropical forests increased efforts are required to protect and restore wildlife populations.

Loss of animal seed dispersal increases extinction risk in a tropical tree species due to pervasive negative density dependence across life stages

“…Without animal-mediated seed dispersal, conspecific spatial aggregation (V) increases by a factor of four (figure 4), and the probability of extinction increases by more than an order of magnitude. These results suggest that NDD throughout the life cycle is probably a demographic mechanism underlying observed declines in abundance of animal-dispersed tree species after extirpation of seed dispersers [12,49]. More generally, these results demonstrate the pervasive impact of seed dispersal for dynamics of all tree life stages, not just seeds and seedlings.…”

“…Comparisons between hunted and non-hunted sites generally reveal lower rates of seed dispersal and lower seedling abundance of animal-dispersed tree species in hunted sites [8][9][10][11]. The most comprehensive study to date tracked changes in a tree community as hunting increased over a 15-year period and found increased spatial aggregation and decreased sapling recruitment for animaldispersed tree species, leading to an overall decline in sapling biodiversity [12]. While these empirical studies provide convincing evidence of short-term negative impacts of overhunting on tree populations, there is a discrepancy between these empirical results and the general finding of demographic studies that in long-lived plants, population dynamics are minimally sensitive to changes in recruitment [13][14][15].…”

The value of trophic interactions for ecosystem function: dung beetle communities influence seed burial and seedling recruitment in tropical forests

“…This adds weight to suggestions that large-seeded trees are most affected by the extinction of animal-plant interactions as a result of human pressures (cf. [16]). …”

“…We therefore have a poor understanding of direct effects of diversity within higher trophic levels or the indirect, cascading effects of biodiversity loss across tropic levels (but see [14]). There is mounting evidence that changes in forest vertebrate communities can lead to direct top-down consequences for plant demography, community composition and diversity [15][16][17][18][19][20][21][22], with knock-on effects for forest services and resilience [23,24]. However, because the indirect, multitrophic consequences of changing mammal communities are rarely experimentally tested, we have limited understanding of the ecosystem-wide consequences of anthropogenic impacts on tropical forests.…”

Medium and large-sized mammals of the Reserva Ecológica de Guapiaçú, Cachoeiras de Macacu, RJ

“…Cullen et al 2005, Soisalo & Cavalcanti 2006, their large area requirements (Sanderson et al 2002b, Cullen et al 2005 and also because they are preferential targets to hunters (Redford 1992, Peres 1996, Cullen et al 2001, Travassos 2011. These factors has conducted to the loss of these animals in tropical forests, promoting profound transformations in forest dynamics and threaten the maintenance of these ecosystems (Stoner et al 2007, Jorge et al 2013, Kurten 2013, Harrison et al 2013). …”