Hunting both animals and plants

Many people are aware of the negative effects of hunting on the species that are being hunted, especially on large-bodied, slow-reproducing forest vertebrates, but have you ever considered the knock-on effects on the plant community in those same ecosystems? The latest issue of Biotropica (vol. 39, no. 3) features a special section on the ‘Pervasive consequences of hunting for tropical forests’, which looks at the consequences of hunting on seed dispersal and plant species composition.

Hunting levels have been increasing, especially over the last 50 years when the importance of hunting for subsistence has been increasingly outweighed by hunting for the market. Drs Carlos Peres and Erwin Palacios report that "The total extent of partially defaunated, but otherwise "pristine" tropical forests, is often severely underestimated. For example, subsistence hunters have access to most areas of lowland Amazonia, affecting even the core of many relatively remote nature and indigenous reserves". Several factors are contributing to the overexploitation of forest game. Dr Joseph Wright and his colleagues write "The weak economies of many tropical countries fail to provide sufficient jobs for their growing populations, while land-use change, improved infrastructure, and new technology facilitate commercial hunting." Land-use change, often resulting in fragmentation, brings hunters and their markets closer to previously remote forests, while improved infrastructure, for example building of roads for timber and mineral extraction, provides access to forest interiors and to distant urban markets. All of this leads to an increase in the return for time spent hunting.

So what affect does this have on the plant community? Dr Richard Corlett of the University of Hong Kong reports that “All the major dispersal agents of large fruits in the Oriental region – large birds, primates, large fruit bats, civets, and terrestrial herbivores – are hunted… The only mammalian frugivores that thrive in human-dominated landscapes are some small fruit bats… Birds cannot compensate for the loss of mammals in such landscapes, even for fruit species consumed by both groups, because only small-gaped bird species survive.” Wright and colleagues sum up the research presented in the special section papers pointing out that “hunting has pervasive effects on tropical forest plant communities altering levels of predispersal seed predation, primary and secondary seed dispersal, and postdispersal seed predation, which, in turn, alter seedling and sapling species composition… A discouraging possibility is that plant species composition might shift to a new steady state with crucial plant species absent or at such low numbers that animals fail to recover.”

The abstracts of the Biotropica special section papers will be appearing soon on CAB Abstracts.

References:

  • Peres, C. A.; Palacios, E. (2007) Basin-Wide Effects of Game Harvest on Vertebrate Population Densities in Amazonian Forests: Implications for Animal-Mediated Seed Dispersal. Biotropica 39 (3), 304-315.
  • Wright, S. J.; Stoner, K. E.; Beckman, N.; Corlett, R. T.; Dirzo, R.; Muller-Landau, H. C.; Nuñez-Iturri, G.; Peres, C. A.; Wang, B. C. (2007) The Plight of Large Animals in Tropical Forests and the Consequences for Plant Regeneration. Biotropica 39 (3), 289-291.
  • Corlett, R. T. (2007) The Impact of Hunting on the Mammalian Fauna of Tropical Asian Forests. Biotropica 39 (3), 292-303.

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