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Not single large, not several small: the Requirement Estimation Based on Species Ecological Needs (REBSEN) is the best conceptual model to define conservation strategies in severely fragmented landscapes
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DOI：10.1007/s10980-026-02394-z.png)
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Abstract
En 中文
The “Single Large or Several Small” (SLOSS) debate, rooted in island biogeography theory and proposed in the 1970s, continues to influence conservation strategies in fragmented landscapes. However, its binary perspective oversimplifies the complex ecological dynamics of species in highly degraded ecosystems. We tested the validity of the SLOSS framework by evaluating how fragment size, habitat quality, and heterogeneity affect amphibian communities in Brazil’s Atlantic Forest—one of the world’s most fragmented and biodiverse ecosystems. Using anurans as model organisms, the most threatened vertebrate group globally, we combined satellite imagery, historical land-use analysis, and field surveys to assess species richness, abundance, and composition across forest fragments of varying sizes. We applied a guild-based ecological classification to capture species-specific habitat requirements and dispersal limitations. Our results indicate that the Single Large or Several Small debate is inadequate for severely fragmented landscapes because it overlooks key ecological drivers such as habitat quality, habitat heterogeneity, dispersal capacity, and species-specific landscape use. Nearly six decades after its introduction, this debate must move toward greater ecological realism, particularly in tropical biodiversity hotspots where conservation urgency is greatest. We propose the Requirement Estimation Based on Species Ecological Needs (REBSEN) model as a more robust alternative. By integrating species-specific ecological requirements and dispersal capacities, REBSEN provides a more realistic basis for conservation planning in fragmented landscapes. Our findings show that Nestedness was not structured by fragment size alone, but emerged across multiple patch dimensions, including habitat quality and vegetation heterogeneity, indicating ordered forest-species loss under degradation. This pattern was accompanied by generalist-taxa turnover along gradients of patch environmental quality across the landscape. When species’ ecological habits are considered, our results reject the idea that forest fragmentation can be beneficial to any degree. At the same time, small fragments (< 20 ha) with high vegetation quality and structural heterogeneity can support rich and often endemic amphibian assemblages. We therefore conclude that conservation strategies should move beyond simplistic area-based approaches and prioritize species’ ecological needs, which, in severely fragmented biomes, requires zero-deforestation policies, habitat restoration, and the maintenance of habitat quality and heterogeneity.
Keywords:
Amphibians
Conservation
Community ecology
Fragmented landscape
Habitat fragmentation thresholds
Island biogeography
Landscape ecology
Metapopulation dynamics
Spatial planning
Trait-based conservation
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