Species richness gradients are usually studied on large spatial scales, but regional analyses can be equally informative and can be used to generate fine-scale maps of species distributions. In a previous study we examined ant species richness in bogs and surrounding forests across three degrees of latitude in northern and central New England, and we found that latitudinal patterns of species richness at this regional scale paralleled continental-scale, temperate-tropical gradients observed throughout the western hemisphere. Here, we ask whether similar patterns in ant species richness are observable at even smaller geographic scales, but among a much wider range of habitats. In summer of 2007, we sampled ant nests and workers in litter samples in standardized plot censuses in three habitats in each of 35 sites representing all ecoregions and vegetation community types in Massachusetts. Sites were chosen to give an even spatial coverage across the state, and represented both common and rare community types in properties owned by Massachusetts Audubon, The Trustees of Reservations, and the State of Massachusetts.
Results/Conclusions
In total, we accumulated 2482 ant occurrence records, each representing a single nest (85% of records) or an individual worker retrieved in litter samples (15% of records). As in studies conducted at coarse geographic scales, species richness and density decreased with increasing elevation and latitude. Species richness increased with (modeled) growing degree days but was not significantly associated with sites that have been continuously forested since European settlement. Species composition was more similar within vegetation community types than within sites, indicating habitat specialization among many taxa. As a result, there was only a small amount of spatial turnover in species richness as measured by a partitioning of alpha, beta, and gamma diversity. Thermophilic species (e.g., Camponotus chromaoides, Prenolepis imparis) are represented by only a few occurrences in the Cape Cod region and the southeastern part of the state, whereas boreal species (e.g., Camponotus herculeanus) are restricted to higher elevation sites in the north-central and north-western part of the state. The ranges of these species are likely to respond most sensitively to projected regional increases in temperature, and could be early indicators of the signature of global climate change.
