Ecological Archives A021-081-A6

Taal Levi, Glenn H. Shepard, Jr., Julia Ohl-Schacherer, Christopher C. Wilmers, Carlos A. Peres, and Douglas W. Yu. 2011. Spatial tools for modeling the sustainability of subsistence hunting in tropical forests. Ecological Applications 21:1802–1818.

Appendix F. How sustainability indices work and why we need better methods.

Sustainability Indices

  1. A hunting zone "catchment area" around a settlement is chosen arbitrarily.
  2. The maximum production of this area is calculated using a sustainability index.
  3. Field data are gathered on actual harvests, H, and compared to maximum production, P.
  4. If H > P, hunting is unsustainable, but P increases with area so this conclusion is sensitive to catchment area. Additionally, H < P may mean either that hunting is sustainable or that the hunted population is already depleted, causing the encounter rate between hunters and game to be low.

Being spatially explicit is important

Wildlife populations grow most rapidly when below carrying capacity. Given this, consider the following 2 examples, treating a catchment area disk centered on a human settlement:

  1. The catchment area has uniform density
  2. The catchment area has density increasing with distance from the community center

In example 1, the entire disk is growing at the maximum rate, but in example 2, only a small portion of the area contains a population growing near the maximum rate, and the remaining area is growing more slowly because the density is either above or below . Existing sustainability indices incorrectly assume a uniformly depleted catchment area.

Advantages of the biodemographic method

  1. Large and expensive field projects are not required, which allows the method to be widely used.
  2. Conclusions are not binary and are not sensitive to arbitrary choices in catchment area.
  3. Spatial distributions of game are predicted.
  4. Multiple settlements can be incorporated, new settlements can be created, and scenarios can be projected.
  5. Diffusion of game into the hunting zone can be incorporated.

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