Pioneer palm tree as an ecosystem engineer: Effects on ant community structure

AbstractEcosystem engineer species can affect the assembly and maintenance of biological communities by altering local environmental conditions. Several palm tree species play this role in changing the surrounding environment mainly through the fall of entire rachis and the formation of a thick and homogeneous leaf litter layer beneath the canopy. However, their impact on soil animal communities remains unclear. In particular, soil organisms (e.g. ants) can be negatively affected by palm‐driven local changes, since they are especially susceptible to leaf litter changes. Our objective was to test if the presence of palm trees reduces alpha and beta diversities of ant communities at taxonomic and morphometric levels. We also tested if palm tree understory mound (debris pile just below the canopy) area and population density reduce ant community alpha and beta diversities (at the taxonomic and morphometric levels) in tropical rainforests. To do so, we described taxonomic and morphometric diversity patterns of ant communities in a relictual landscape of the Atlantic Rainforest (northeastern Brazil) using Hill's numbers approach in two habitats: understory mounds surrounding the palm tree species Acrocomia intumescens, and forest understory without A. intumescens (non‐palm understory). Our main findings were: (1) Taxonomic and morphometric alpha diversity were similar between A. intumescens understory mound and non‐palm understory; (2) Ant communities in non‐palm understory presented higher beta diversity than communities from A. intumescens understory mounds considering both rare species and morphometric traits; (3) A. intumescens understory mound area negatively affected common and dominant ant species; and (4) the interaction between understory mound area and the population density of A. intumescens affected dominant ant species in complex ways and the outcomes depend on the balance between both predictors. Our findings point to an important role of palm trees as ecosystem engineers in reducing ant biodiversity and changing the functional signature of human‐modified tropical rainforests.