Site-level variation in field of view is associated with altered anti-predator responses in farming damselfish.

Abstract

The three-dimensional (3D) structure of habitats influences how prey detect and respond to predators, but the specific roles of different aspects of structural complexity remain poorly understood, particularly in coral reef ecosystems. We used 3D models of 3 Caribbean reef sites to quantify 3 structural metrics at site level: field of view (the extent of observable area), refuge density (density of holes), and rugosity (reef surface roughness). We then observed the anti-predator behavior of damselfish, parrotfish, and wrasses at each site. Territorial damselfish showed species-specific responses to habitat structure, especially in relation to field of view. Stegastes adustus, for example, exhibited shorter flight initiation distances (FIDs) at the site with the highest field of view, consistent with expectations from optimal escape theory. In contrast, wrasse and parrotfish species showed little variation in behavior across sites, though larger individuals tended to have longer FIDs and flight distances. Refuge density was similar across sites, likely reflecting long-term regional loss of fine-scale complexity in the Caribbean. While rugosity is widely used as a proxy for reef complexity, our results suggest that field of view may be more strongly associated with differences in anti-predator behavior, particularly in damselfish. These findings highlight the need to assess multiple dimensions of habitat structure, as even closely related species may exhibit distinct behavioral adaptations to their 3D environment.