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| This study analyses the effect of resource availability (i.e. sheep dung) on dung
beetle communities in an arid region of Central Spain, both at regional and at local
scales. A total of 18 sites within 600 km
2
were sampled for the regional analysis and
16 sites within the 30 km
2
of an Iberian municipality were sampled for the local analysis.
Spatial and environmental characteristics of sampling sites were also compiled
at both scales, including measures of grazing activity (livestock density at regional
scale, and two counts of rabbit and sheep dung at local scale). At a regional scale, any
environmental or spatial variable can help to explain the variation in abundance.
However, species richness was related to summer precipitation and composition was
related to elevation. At local scale, abundance is not significantly related to any of
the environmental variables, but species richness was related to the local amount of
sheep dung (27% of variance). The amount of dung in a 2-km buffer around the site
accounts for 27–32% of variance in abundance and 60–65% of variance in species
richness. The presence of the flock with the highest sheep density explains 53% of
abundance variability and 73% of species richness variance. A cluster analysis of
localities identified two main groups, one characterized by a lower abundance and
species richness that can be considered a nested subsample of the species-rich group.
The mean and maximum amount of sheep dung in the sites separated by less than
2 km are the only significant explanatory variables able to discriminate both groups.
These results suggest that grazing intensity (and the associated increase in the
amount of trophic resources) is a key factor in determining local variation in the
diversity and composition of dung beetle assemblages. However, dung beetle assemblages
are not spatially independent at the analysed resolution, and the amount of
dung in the surroundings seems to be more important for locally collected species
than the dung effectively found in the site. Although differences in the availability
and quantity of trophic resources among nearby sites could be affecting the population
dynamics and dispersion of dung beetles within a locality, sites with larger populations,
and greater species numbers would not be able to exercise enough influence
as to bring about a complete local faunistic homogenization. | |
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