ABSTRACT
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 seminatural 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 grasslands 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 in terms of nest density, 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 higher nest densities of some species. 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 within-site local variability in soil moisture and low-intensity grazing promote ant species densities and highlight the role of habitat temperature and humidity 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 scale plays an important role as deterministic force in filtering ant species and, along with neutral processes (e.g., stochastic colonization), in shaping ant community structure in temperate seminatural upland grasslands.
ABSTRACT
Analysing how seasonality shapes abundance patterns fosters understanding of the processes related to amphibian community assemblies. In this study we analyse the relationship between local seasonal patterns of abundance within the anuran community of the Monte Zerpa Cloud Forest, Mérida Mountain Range (Cordillera de Mérida), in the Venezuelan Andes. We hypothesized that variation in precipitation, temperature, and relative humidity affects the temporal abundance patterns of anurans. Data collection was performed through nocturnal biweekly inspections from 2002 to 2003. Air temperature, relative humidity, and monthly precipitation were considered as variables of climatic seasonality. Generalized linear models were used to evaluate the effect of climatic variables on anuran abundance across seasons. Overall, 542 individuals and four anuran species were recorded in stream tributaries only. The local anuran community was comprised of Hyalinobatrachium duranti, Hyloscirtus platydactylus, Hyloscirtus jahni, and Pristimantis vanadisae. The most abundant species were H. duranti (288 individuals) and H. platydactylus (145 individuals), representing 53% and 27% of the total anuran abundance, respectively. Differences in abundance between species were observed. Although the total abundance of anurans was higher during the low precipitation season, no significant differences between the two seasons were detected. The variation in anuran abundance was explained by relative humidity and temperature. Our results suggest that the highest abundance of anurans can be expected when temperatures reach favourable levels (15- 17°C), relative humidity increases, and precipitation remains constant.
