Why Big Islands Feed More Predators: New Theory Links Food Webs to Biodiversity Hotspots

Our theoretical models reveal how food web structure influences species-area relationships on islands and isolated habitats. We built mathematical models based on neutral theory and food web dynamics to predict how species richness at different trophic levels should vary with habitat area, testing scenarios from simple food chains to complex webs.

We found a clear pattern: species at higher trophic levels consistently showed steeper species-area relationships than those below them. When we modeled food chains with specialized predator-prey relationships, this effect became even more pronounced—the species-area relationship became progressively steeper moving up each level of the food chain. Our mathematics showed that predators, being less abundant and more dependent on their prey, are disproportionately affected by area loss.

What we found most robust was how consistent this pattern remained across different model assumptions. Even when relaxing strict neutral assumptions and allowing species to interact in more realistic ways, the fundamental pattern held. Systems with generalist predators that can feed on multiple prey species show different area-scaling patterns than specialist-dominated systems.

This work matters because most conservation strategies focus on protecting individual species rather than entire food webs. Our models suggest that habitat fragmentation hits top predators hardest, not just because they're naturally rare, but because of fundamental mathematical relationships governing how trophic interactions scale with space.

Understanding how food web interactions scale with area could help predict which species are most vulnerable to habitat fragmentation and guide conservation strategies for maintaining entire ecological communities, not just individual species.

Citation

Holt, Robert D.; Gravel, Dominique; Stier, Adrian; Rosindell, James (2021). On the Interface of Food Webs and Spatial Ecology: The Trophic Dimension of Species–Area Relationships. **.

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