Habitat Fragmentation Effects on Birds in Grasslands and Wetlands: A Critique of Our Knowledge
Figures
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| Figure 1. The incidence function describes
the proportion of habitat patches in a size class that contain a given
species. Increasing incidence functions are frequently interpreted as
evidence of area sensitivity in habitat selection by a species, but
the functions are confounded with the commonness of the species. |
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| Figure 2. Simulated distribution of points,
representing birds, randomly distributed across some region of uniform
habitat, to demonstrate why the incidence function cannot distinguish
between area sensitivity and regional abundance. The left figures represent
an uncommon species; the right figures represent a very common species.
The squares represent habitat patches; A and B show three large patches,
and C and D show 18 small patches. The rare species, shown as dots in
A and C, is more likely to be sampled on the large (A) than on the small
(C) patches compared to the more common species shown as dots on the
large (B) and small (D) habitat patches. The incidence function for
the very common species (upper line in Fig.1)
shows little effect of patch size: the species occurred in 89% of the
small patches and 100% of the large patches. In contrast, the incidence
function for the rare species suggests a patch-size effect: the species
occurred in only 5.6% of the small patches versus 75% of the large patches
(Fig.1). But no patch-size sensitivity
was involved in the simulations; the apparent sensitivity is an artifact
of the species' rarity |
