Community-Wide Weakening of the Species-Area Relationship for Coral Reef Fishes Following a Multi-Decade Period of Increasing Stressors

Positive species-area relationships are widely documented characteristics of faunal communities in terrestrial, freshwater and marine environments.  While limited but relatively clear evidence exists for a weakening of the species-area relationship for coral reef fish due to an anthropogenic stressor (fishing), no studies in any system, of which we are aware, have assessed stressor-related changes in the species-area relationship for a community-wide suite of functional guilds.  We assessed changes in the species-area relationship for all species combined and for seven trophic guilds of coral reef fish in Biscayne National Park, FL, between two periods (historical and recent) separated by ~25 years of increasing anthropogenic stressors.  For all species combined and for all trophic guilds, the slope of the species-area relationship decreased or reversed between the historical and recent period.  Additionally, the variation in species richness attributed to reef area declined for all species combined and for six of seven trophic guilds.  These results provide the first evidence of which we are aware, spanning terrestrial, freshwater and marine ecosystems, of the weakening of a widely established characteristic of natural communities – a positive species-area relationship – across functional groups within a faunal community.