The Role of Urbanness, Vegetation Structure, and Scale in Shaping Puerto Rico’s Acoustically Active Mangrove Fauna Communities

Abstract

The mangroves of Puerto Rico occupy a gradient of urbanization that offers a chance to test hypotheses on urban faunal communities. These hypotheses state that urban avifaunal communities have greater representation by generalists and that certain mangrove specialists can utilize urban landscapes. Much of this is said to be driven by food resources, with frugivores and nectarivores benefiting from abundant residential flowers and fruits, while insectivores are driven away by low food resources. This study used passive acoustic monitoring to identify the audible anuran and avifaunal species in mangroves across an urban gradient of Puerto Rico. Five anurans and thirty-one avian species were detected across all sites, with twenty-three species found at the most species rich site, and eight at the least rich site. Analyses on urban effects were conducted at an island-wide scale as well as a local scale with different results between the two. Island wide, the most urban faunal communities were more similar to each other in species composition relative to the least urban communities, and there was a significant difference in the community composition between the two. However, there were no differences in avian or anuran species richness between the least and most urban sites. Minimum canopy height was the strongest predictor of overall avian richness and avian invertivore richness, while the extent of mixed forest cover was the strongest predictor for increasing anuran richness. Some urban metrics, such as street density and the percent of surrounding urban and developed open space were strong predictors of certain avian feeding guilds and distribution groups. At the local scale, sites of maximum urbanness held 2–3 more bird species on average than corresponding sites of minimum urbanness at the same location, although there was no difference in anuran species and no differences in avian or anuran community composition between the two. Further, avian richness did increase significantly from the minimum to maximum urbanness site at six of the nine locations. These findings highlight that higher mangrove canopies are the strongest predictor of higher avian richness, but depending on the scale of observations, urbanness also plays a limited role in shaping mangrove faunal communities.