Decoupling the effects of logging and hunting on an Afrotropical animal community

Abstract

Abstract. In tropical forests, hunting nearly always accompanies logging. The entangled nature of these disturbances complicates our ability to resolve applied questions, such as whether secondary and degraded forest can sustain populations of tropical animals. With the expansion of logging in central Africa, conservation depends on knowledge of the individual and combined impacts of logging and hunting on animal populations. Our goals were (1) to decouple the effects of selective logging and hunting on densities of animal guilds, including apes, duikers, monkeys, elephant, pigs, squirrels, and large frugivorous and insectivorous birds and (2) to compare the relative importance of these disturbances to the effects of local-scale variation in forest structure and fruit abundance. In northern Republic of Congo, we surveyed animals along 30 transects positioned in forest disturbed by logging and hunting, logging alone, and neither logging nor hunting. While sampling transects twice per month for two years, we observed 47 179 animals of 19 species and eight guilds in 1154 passages (2861 km). Species densities varied by as much as 480% among forest areas perturbed by logging and/or hunting, demonstrating the strong effects of these disturbances on populations of some species. Densities of animal guilds varied more strongly with disturbance type than with variation in forest structure, canopy cover, and fruit abundance. Independently, logging and hunting decreased density of some guilds and increased density of others: densities varied from 44% lower (pigs) to 90% higher (insectivorous birds) between logged and unlogged forest and from 61% lower (apes) to 77% higher (frugivorous birds) between hunted and unhunted forest. Their combined impacts exacerbated decreases in populations of some guilds (ape, duiker, monkey, and pig), but counteracted one another for others (squirrels, insectivorous and frugivorous birds). Together, logging and hunting shifted the relative abundance of the animal community away from large mammals toward squirrels and birds. Logged forest, even in the absence of hunting, does not maintain similar densities as unlogged forest for most animal guilds. To balance conservation with the need for economic development and wild meat in tropical countries, landscapes should be spatially managed to include protected areas, community hunting zones, and production forest.

Hunting-induced defaunation drives increased seed predation and decreased seedling establishment of commercially important tree species in an Afrotropical forest

“…The combination of uneven harvest rates of wildlife species and compensatory ecological responses may lead to increased rodent abundance with hunting, despite a decline in total animal biomass (Effiom et al, 2013;Galetti et al, 2015c;Happold, 1995;Laurance et al, 2006;Phillips, 1997;Poulsen et al, 2011;Wright, 2003). For our region in Gabon, two recent studies have documented community-level increases in rodent biomass with hunting pressure (Koerner et al, 2016;Markham, 2015).…”

“…Human hunting disrupts these interactions when it causes defaunation of larger species, resulting in trophic cascades that can reduce plant diversity (Camargo-Sanabria et al, 2014;Harrison et al, 2013) and carbon storage (Kurten et al, 2015;Osuri et al, 2016;Poulsen et al, 2013), and may be detrimental to the regeneration of commercially important timber species (Rosin, 2014). As hunting is widespread in timber concessions (Auzel and Wilkie, 2000;Fimbel et al, 2001;Robinson et al, 1999) and can affect animal abundance more strongly than the direct effects of logging (Bello et al, 2015;Poulsen et al, 2011;van Vliet and Nasi, 2008), understanding the consequences of defaunation is a priority for both forestry and conservation. Most studies of defaunation have focused on the reduction of large-bodied seed dispersers and the loss or modification of their services (e.g.…”

Ecological erosion of an Afrotropical forest and potential consequences for tree recruitment and forest biomass

“…Defaunation generally occurs in size-based increments, with hunters first taking the largest species, and then working down to lower size classes of animals (Peres and Palacios, 2007;Poulsen et al, 2011 ); most Central African forests are located somewhere between the extremes of complete defaunation and a fully intact vertebrate community. Hunting therefore initiates a process we call ecologica l erosion -the incremental deterioration or alteration of ecological communities and processes .…”

Apparent environmental synergism drives the dynamics of Amazonian forest fragments

“…Strictly speaking, this term implies that the net impact of two or more stressors is greater than the sum of each acting individually (Zala and Penn 2004), but it is often used simply to indicate that simultaneous stressors are 5 E-mail: bill.laurance@jcu.edu.au operating roughly in concert or that one stressor facilitates another (e.g., Myers 1986, Laurance andUseche 2009). Two notable synergisms in the tropics are those between habitat fragmentation and fire (Cochrane and Laurance 2002), and between selective logging and hunting (Poulsen et al 2011). Here we extend current knowledge by describing an apparent synergism between habitat fragmentation and global or regional-scale drivers affecting Amazonian forests.…”