Local and landscape environmental heterogeneity drive ant community structure in temperate semi-natural upland grasslands

Environmental heterogeneity is an important driver of ecological
communities. Here, we assessed the effects of local and landscape spatial
environmental heterogeneity on ant community structure in temperate
semi-natural upland grasslands of Central Germany. We surveyed 33
grassland sites representing a gradient in elevation and landscape
composition. Local environmental heterogeneity was measured in terms of
variability of temperature and moisture within and between grassland
sites. Grassland management type (pasture vs. meadows) was additionally
included as a local environmental heterogeneity measure. The complexity of
habitat types in the surroundings of grassland sites was used as a measure
of landscape environmental heterogeneity. As descriptors of ant community
structure, we considered species composition, community evenness, and
functional response traits. We found that extensively grazed pastures and
within-site heterogeneity in soil moisture at local scale, and a high
diversity of land cover types at the landscape scale affected ant species
composition by promoting nest densities. Ant community evenness was high
in wetter grasslands with low within-site variability in soil moisture and
surrounded by a less diverse landscape. Fourth-corner models revealed that
ant community structure response to environmental heterogeneity was
mediated mainly by worker size, colony size, and life history traits
related with colony reproduction and foundation. We discuss how withinsite
local variability in soil moisture and low-intensity grazing promote ant
species densities, and highlight the role of habitat temperature and
humidity in affecting community evenness. We hypothesize that a higher
diversity of land cover types in a forest-dominated landscape buffers less
favorable environmental conditions for ant species establishment and
dispersal between grasslands. We conclude that spatial environmental
heterogeneity at local and landscape scales plays an important role as a
deterministic force in filtering ant species and, along with neutral
processes (e.g. stochastic colonization), in shaping ant community
structure in temperate semi-natural upland grasslands.