Differential responses of insect communities to habitat mixing in a dynamic marsh-mangrove ecotone

Along many coastlines worldwide, the boundary between tropical and temperate areas is marked by a habitat gradient between mangrove forests (tropical) and salt marshes (temperate). These gradients, or ecotones, are dynamic: their location and extent are impacted by climate trends, extreme weather events, and biotic interactions. In areas such as the Southeastern United States, mangrove-marsh ecotones are changing as mangroves expand their ranges poleward due to a historical trend of increasingly mild winters. These shifting mangrove-marsh ecotones provide a significant research opportunity, allowing us to ask questions about how climate-related range expansions affect the structure and function of ecological communities, while simultaneously gaining a better understanding of two threatened, economically important habitats.

In the present study, we sampled insect communities along the mangrove-marsh ecotone on the Atlantic coast of Florida, USA. We compared insect community structure and diversity 1) between mangrove patches inside the ecotone and in mangrove forests south of the ecotone 2) between patches of marsh vegetation inside the ecotone and in mangrove-free marshes north of the ecotone, and 3) between mangrove and marsh patches inside the ecotone. Insect communities on mangroves were distinct from those in marsh patches, regardless of surrounding landscape type (ecotone or not). Diversity was greater in marsh patches located in ecotone landscapes compared to patches in northern marshes, while diversity did not differ between mangrove trees in the ecotone vs. trees in southern mangrove forests. However, community structure significantly differed between patches inside vs. beyond the ecotone for both mangroves and marsh plants.