The influence of edge contrast on the diversity and composition of ground beetle (Coleoptera: Carabidae) functional traits in a lowland heterogeneous landscape.

Abstract

Understanding the effects that habitat fragmentation has on biodiversity is of vital importance for both the discipline and implementation of nature conservation. Ecological edges are transitional zones or boundaries that occur naturally between two adjacent land cover types or landscape patches. Edge effects are known to modify habitat quality within fragments, which will in turn affect the composition of species via habitat preferences. Functional diversity is now appearing as a factor of crucial importance in the determination of ecosystem processes. The functional diversity of invertebrates is directly relevant to the functioning of ecosystems. The gaining of information from functional traits can be useful in providing an insight into the mechanisms which influences the response of arthropods to changes in the environment. Carabids (ground beetles) are well suited to studies of edge effects. Edge contrast, or the harshness of an edge, plays a vital role in explaining the distribution patterns of carabid beetles belonging to different habitat affinity groupings at forest edges. In order to research the influence of edge contrast on the functional diversity of forest carabids, 3 types of edge were defined via the stages of succession: mature forest-young forest (soft), mature forest-shrub (intermediate) and mature forest-grass (hard). Overall, 9 sites were set up (3 soft, 3 intermediate and 3 hard edges) in Ringwood Forest, Hampshire, with 9 pitfall traps per site: 3 traps set at 5 m apart at the forest edge, 3 traps set at 5 m apart at 30 m into the forest and 3 traps set at 5 m apart at 60 m into the forest. Canopy cover, soil moisture, leaf litter depth and ground vegetation type were also collected as environmental variables. Kruskal-Wallis tests and linear mixed-effects models were used to identify the influence of both edge contrast and environmental variables on the functional diversity and Shannon diversity of carabids. It was found that carabid functional diversity and Shannon diversity follow the edge effect hypothesis, whereby diversity is greatest at the habitat edge. It was also found that the Shannon diversity of carabids was shown to be influenced by edge contrast by both the linear mixed-effects model and the Kruskal- Wallis test. Finally, it was also found that edge contrast, edge distance and the environmental variables which were tested for did not have an influence on the functional diversity of carabids.