Dung-visiting beetle diversity is mainly affected by land use, while community specialization is driven by climate

Abstract

Dung beetles are important actors in the self-regulation of ecosystems by driving nutrient cycling, bioturbation, and pest suppression. Urbanization and the sprawl of agricultural areas, however, destroy natural habitats and may threaten dung beetle diversity. In addition, climate change may cause shifts in geographical distribution and community composition. We used a space-for-time approach to test the effects of land use and climate on α-diversity, local community specialization (H ₂') on dung resources, and γ-diversity of dung-visiting beetles. For this, we used pitfall traps baited with four different dung types at 115 study sites, distributed over a spatial extent of 300 km × 300 km and 1000 m in elevation. Study sites were established in four local land-use types: forests, grasslands, arable sites, and settlements, embedded in near-natural, agricultural, or urban landscapes. Our results show that abundance and species density of dung-visiting beetles were negatively affected by agricultural land use at both spatial scales, whereas γ-diversity at the local scale was negatively affected by settlements and on a landscape scale equally by agricultural and urban land use. Increasing precipitation diminished dung-visiting beetle abundance, and higher temperatures reduced community specialization on dung types and γ-diversity. These results indicate that intensive land use and high temperatures may cause a loss in dung-visiting beetle diversity and alter community networks. A decrease in dung-visiting beetle diversity may disturb decomposition processes at both local and landscape scales and alter ecosystem functioning, which may lead to drastic ecological and economic damage.

Keywords: coleoptera; coprophagous beetles; decomposition; global change; hill numbers; network analysis.

FIGURE 1

Rank abundance curve depicting the number of individuals of all recorded beetle species on a logarithmic scale

FIGURE 2

Scatterplot of observed H ₂′ (red dots) and randomized H ₂′ values (gray dots) along a mean multi‐annual temperature gradient. Dashed horizontal line indicates H ₂′ = 0.5. A null model calculated randomized H ₂′ values with 1000 simulations (in 87% of the networks, the observed H ₂′ was significantly higher than in random assemblages).

FIGURE 3

Linear regression showing the degree of specialization (d′) on individual dung resources along the temperature gradient. Gray dots depict individual d′ values; colored lines represent regression lines of each dung type. Dashed line indicates d′= 0.5.

FIGURE 4

Sample size‐based rarefaction curves of rare, common, and dominant dung beetles for Hill numbers (q = 0, 1, and 2) across habitats, landscapes, and climate zones. Solid lines depict the interpolated number of sampling units (rarefaction), while dashed lines depict the extrapolation of sampling units. Shaded areas indicate the 95% confidence interval. Nonoverlapping confidence intervals indicate significant differences in γ‐diversity between treatments.