Habitat area but not habitat age determines wild bee richness in limestone quarries

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Abstract
Summary: Within highly modified European landscapes, limestone quarries can act as important secondary habitats for a range of endangered wild bee species. However, the relative influence of quarry habitat area, habitat age and within‐habitat diversity on the conservation value of these secondary habitats is mainly unknown. We assessed species richness and abundance of wild bees by variable transect walks in 24 limestone quarries ranging in size from 0·01 to 21·2 ha. Species traits such as social status, resource specialization and nesting substrate were used to define functional guilds of bees. In total, 41% of all wild bee species known from southern Lower Saxony, Germany, were found in the studied quarries. Total species richness increased with habitat area but, in contrast to our expectations, not with habitat age, although we tested an age gradient of over 120 years. Solitary species were more strongly affected by decreasing habitat area than social species but response did not differ with respect to habitat age. Hierarchical partitioning analyses revealed that habitat area per se, within‐habitat diversity and sampling effort were of similar importance in explaining species richness patterns. Synthesis and applications. Even newly created limestone quarries provide an important secondary habitat for wild bees. Therefore, maintenance and management of secondary succession of these sites should be given high priority in species conservation plans. Landscape management schemes involving filling or flooding such quarries should be prevented.