Obstruction of biodiversity conservation by minimum patch size criteria.

Many habitat protection policies contain minimum patch sizes below which habitat is not eligible for protection. Such minimum patch size criteria reflect the conservation principle that a large patch of habitat has higher biodiversity than several small patches of the same total area (SL > SS). Nonetheless, evidence suggests that this principle is often incorrect, and that instead, biodiversity conservation requires placing more emphasis on protection of large numbers of small patches (SS > SL). We use a recently compiled, global database to conduct a new assessment of the SL > SS principle in systems where the small patches are much smaller than the typical minimum patch size criteria applied for biodiversity conservation (i.e., ∼ 85% of patches smaller than 100 ha). The analysis includes 76 metacommunities, with 4401 species in 1190 patches. Counter to the SL > SS principle and consistent with previous tests, species richness accumulated more rapidly when adding several small patches (45.2% SS > SL vs 19.9% SL > SS), even for the very small patches in our dataset. Differential responses to habitat fragmentation across taxa suggest that, when a given total area of habitat is to be protected, overall biodiversity conservation will be most effective if that habitat is composed of as many small patches as possible, plus a few large ones. Critically, since minimum patch size criteria often require larger patch sizes than the small patches in our analysis, our results suggest that such criteria hinder efforts to protect biodiversity. This article is protected by copyright. All rights reserved.