Pervasive Defaunation of Forest Remnants in a Tropical Biodiversity Hotspot

Abstract

Tropical deforestation and forest fragmentation are among the most important biodiversity conservation issues worldwide, yet local extinctions of millions of animal and plant populations stranded in unprotected forest remnants remain poorly explained. Here, we report unprecedented rates of local extinctions of medium to large-bodied mammals in one of the world's most important tropical biodiversity hotspots. We scrutinized 8,846 person-years of local knowledge to derive patch occupancy data for 18 mammal species within 196 forest patches across a 252,669-km2 study region of the Brazilian Atlantic Forest. We uncovered a staggering rate of local extinctions in the mammal fauna, with only 767 from a possible 3,528 populations still persisting. On average, forest patches retained 3.9 out of 18 potential species occupancies, and geographic ranges had contracted to 0–14.4% of their former distributions, including five large-bodied species that had been extirpated at a regional scale. Forest fragments were highly accessible to hunters and exposed to edge effects and fires, thereby severely diminishing the predictive power of species-area relationships, with the power model explaining only ∼9% of the variation in species richness per patch. Hence, conventional species-area curves provided over-optimistic estimates of species persistence in that most forest fragments had lost species at a much faster rate than predicted by habitat loss alone.

Species–fragmented area relationship

“…Canale et al (42) have examined the presence of 18 species of forest-inhabiting mammals in forest fragments in four The results for two values of 1/α, the average dispersal distance, 10 and 3 lattice cells, respectively (Fig. S1).…”

“…In general, much of the Atlantic forest region in Brazil, one of the major biodiversity hotspots on Earth, is already so highly fragmented (45) that using the conventional SAR at the landscape level would almost certainly severely underestimate extinctions (see ref. 42). Given the rates of habitat conversion in many biomes (46,47), the Atlantic forest biome may represent a model system of what will happen in many other biomes as well as highlight the importance of taking fragmentation effects into account in our analyses.…”

“…Our results demonstrate that, in the case of highly fragmented landscapes, it is not sufficient to consider only the total area of habitat, because fragmentation may cause a severe reduction of biodiversity for a given total habitat area. The fragmentation effects include high risk of extinction of small populations and reduced dispersal to isolated habitat fragments, but also factors such as hunting, wildfires, and various other anthropogenic impacts that may become elevated in fragmented landscapes (42). The SFAR model allows one to incorporate the fragmentation effects into a quantitative assessment of the threat that habitat loss and fragmentation pose to biodiversity.…”

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

“…Both species are habitat generalists, occurring both in preserved and anthropized areas (Dickson et al 2005, Andrade-Nuñ ez & Aide 2010, Mazzoli 2010, Canale et al 2012. The large home range sizes of P. concolor (100--220 Km 2 , Mazzoli 2010) and the difficulty of differentiate individuals , however, can have contributed to their elevated number of records.…”

“…In this scenario, large (. 100 ha), protected remnants are responsible to maintain the diversity of medium and largesized mammals (Canale et al 2012).…”