Obstruction of biodiversity conservation by minimum patch size criteria

Abstract

Minimum patch size criteria for habitat protection reflect the conservation principle that a single large (SL) patch of habitat has higher biodiversity than several small (SS) patches of the same total area (SL > SS). Nonetheless, this principle is often incorrect, and biodiversity conservation requires placing more emphasis on protection of large numbers of small patches (SS > SL). We used a global database reporting the abundances of species across hundreds of patches to assess the SL > SS principle in systems where small patches are much smaller than the typical minimum patch size criteria applied for biodiversity conservation (i.e., ∼85% of patches <100 ha). The 76 metacommunities we examined included 4401 species in 1190 patches. From each metacommunity, we resampled species–area accumulation curves to evaluate how biodiversity responded to habitat existing as a few large patches or as many small patches. Counter to the SL > SS principle and consistent with previous syntheses, species richness accumulated more rapidly when adding several small patches (45.2% SS > SL vs. 19.9% SL > SS) to reach the same cumulative area, even for the very small patches in our data set. Responses of taxa to habitat fragmentation differed, which suggests 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. Because minimum patch size criteria often require larger patches than the small patches we examined, our results suggest that such criteria hinder efforts to protect biodiversity.

Positive effects of fragmentation per se on the most iconic metapopulation

“…Our results challenge the idea that fragmentation per se has largely negative effects on species persistence. Indeed, the positive response of the ÅGFB to fragmentation per se adds to other work suggesting that small patches often have disproportionately high conservation value relative to their areas (Riva & Fahrig, 2022; Wintle et al., 2019), including very small patches (Arroyo‐Rodríguez et al., 2022; Riva & Fahrig, 2023b). We found this same result for a species that is thought to epitomize sensitivity to habitat fragmentation, which indicates that a paradigm shift in conservation is needed.…”

“…We found this same result for a species that is thought to epitomize sensitivity to habitat fragmentation, which indicates that a paradigm shift in conservation is needed. In particular, we see the need for a shift away from policies that place lower limits on the sizes of conserved areas (Riva & Fahrig, 2023b) or that emphasize “defragmenting” landscapes. Past and current lack of protection for small patches of habitat has real consequences.…”

Habitat functionality: Integrating environmental and geographic space in niche modeling for conservation planning

“…From a theoretical perspective, the framework builds on metapopulation theory, including more flexible assumptions and broadening its applicability. By integrating the effects of both habitat degradation and loss of connectivity or fragmentation into a quantitative metric (Rubio & Saura, 2012), the habitat functionality framework goes beyond simplistic dichotomies that might hinder conservation practice (whether to manage single large or several small habitat patches; Riva & Fahrig, 2023; Szangolies et al, 2022) and has great potential to guide sustainable land planning. This makes the framework ideally suitable for assessing the cumulative impacts of anthropogenic activities, including infrastructure development, land‐use changes and climatic changes (Dorber et al, 2023).…”

Effects of Habitat Fragmentation of a Mediterranean Marine Reef on the Associated Fish Community: Insights from Biological Traits Analysis

“…Historically, empirical studies have always suggested that HF has negative direct and indirect effects on biodiversity [50,51]; however, more recently, these theories have been the subject of renewed discussion [4] since a multitude of studies have yielded contrasting…”

“…Its community-shaping action has been demonstrated across all ecosystems, from terrestrial to aquatic ones [2]. HF is at the core of a long debate that started with MacArthur and Wilson's [3] theory of island biogeography and that extended over the successive six decades up to the recent work by Riva and Fahrig [4]. Riva and Fahrig hypothesised that the ecological role played by patchiness, although raising a number of questions, is addressed within a considerable body of literature confirming that the assessment of HF is a complex exercise [5].…”