Seeing halos: Spatial and consumer-resource constraints to landscape of fear patterns

Abstract

Coral halos are algae-free space surrounding coral patches linked to the landscape of fear hypothesis, where risk-averse herbivores avoid grazing too far from coral shelter. Halo patterns thus provide insight into the state of overfished predator populations on reefs. However, halos are absent in some protected reefs and their sizes are uncorrelated with predator abundance. Here, we show that these observations are consistent with the landscape of fear hypothesis. When coral are dispersed, herbivores have more even shelter from predators across the seascape, allowing herbivores to overgraze and halos to oscillate. When coral are clustered, shelter is limited and halos can stabilize, but reducing herbivore limitation drives critical transitions to cycles that are difficult to recover from. Discordance between theory and observations may, therefore, arise from differences in underlying coral spatial distributions, with broad implications for how the landscape of fear influences pattern formation and ecological resilience in patchy ecosystems.