The spatial distribution of termites in shortgrass steppe: a geostatistical approach

The broad-scale distribution of subterranean termites (Reticulitermestibialis) was studied in a shortgrass-steppe ecosystem in northern Colorado, United States. Termite occurrence and abundance was measured over 4 months at 10-m intervals along a 900-m transect that spanned a topographic gradient. Geostatistics were used to model the probability of termite occurrence along the transect, and to identify the distributional extent and potential roles of termites in shortgrass steppe. Semivariance was calculated between sample pairs of differing distances and kriging was used to interpolate the probability of termite occurrence along the transect. The semivariogram showed spatial dependence in termite distribution between samples 10-330 m apart and converged on the population variance at distances >330 m, which suggested that spatial dependence explained much of the broad-scale variation in termite distribution. A relatively large nugget variance, however, indicated there was spatial dependence below the 10-m sampling resolution. Termites were most frequently found on a south-facing slope and in a lowland swale. Four-wing saltbush (Atriplexcanescens) was also common in these areas and is important in the production of woody litter. The distribution of termites was significantly associated with proximity to saltbush, which showed a strong spatial dependence at scales <500 m. Kriged probabilities of occurrence and cross-correlation between termites and shrubs showed that peak termite occurrence was shifted upslope 100 m from areas of closest shrub proximity. Other factors, such as soil temperature, texture, or organic matter, are therefore likely to influence termite distributions in shortgrass steppe. The geostatistical approach used here provides a basis for further study on termites in shortgrass steppe, where their roles in decomposition and nutrient cycling are unknown. Geostatistics could also be used to describe distribution patterns on other soil arthropods sampled from traps or soil cores along transects that span topographic or land-use changes.