Effects of subsistence hunting on vertebrate community structure in Amazonian forests

Subsistence hunting affects vast tracts of tropical wilderness that otherwi se remain structurally unaltered, yet distinguishing hunted from nonhunted tropical forests presents a difficult problem because this diffuse form of resource extraction leaves few visible signs of its occurrence. I used a st andardized series of line-transect censuses conducted over a 10-year period to examine the effects of subsistence game harvest on the structure of ver tebrate communities in 25 Amazonian forest sites subjected to varying level s of hunting pressure. Crude vertebrate biomass, which was highly correlate d with hunting pressure, gradually declined from nearly 1200 kg km(-2) at n onhunted sites to less than 200 kg km(-2) at heavily hunted sites. Hunting had a negative effect on the total biomass and relative abundance of verteb rate species in different size classes at these forest sites, but it did no t affect their overall density. In particular, persistent hunting markedly reduced the density of large-bodied game species (>5 kg), which contributed a large proportion of the overall community biomass at nonhunted sites (65 -78%) and lightly hunted sites (55-71%). Nutrient-rich floodplain forests c ontained a consistently greater game biomass than nutrient-poor unflooded f orests, once I controlled for the effects of hunting pressure. Conservative estimates of game yields indicate that as many as 23.5 million game verteb rates, equivalent to 89.224 tons of bushmeat with a market value of US$190. 7 million, are consumed each year by the rural population of Brazilian Amaz onia, which illustrates the enormous socioeconomic value of game resources in the region. My cross-site comparison documents the staggering effect of subsistence hunters on tropical forest vertebrate communities and highlight s the importance of considering forest types and forest productivity in gam e management programs.