Aspects of the ecology of some invertebrates on limestone outcrops in Moorland
In 1984-5 the carabids and staphylinids on ten isolated limestone outcrops and intervening blanket peat within the Moor House Reserve, Cumbria, were investigated. In 1986 a subsidiary study on similar habitats was made at Tailbridge Hill, Cumbria. Pitfall and window traps sampled beetles from the ground and air respectively. Numbers and alpha diversities of carabids and staphylinids were higher on the Moor House limestone outcrops than on the blanket peat. The outcrops acted as isolates to many species, but also suffered considerable contamination by adjacent peat faunas. Limestone species taken on outcrops exhibited a positive species: area relationship consistent with island biogeographical theory. Peat species taken on outcrops showed a negative species: area relationship. Overall, species of staphylinid were positively, and carabid, negatively, correlated with outcrop size. Dispersal of species between habitats was influenced by body size, degree of hygrophily and flight activity. Flight by carabids was negligible, but most staphylinids could fly. Weather conditions were probably the primary cause of this difference between taxa. Flight by staphylinids was related to the stability of the habitat or resources involved. All Nomadic species could fly whereas flight by Peat species was negligible. Limestone species showed relatively high levels of flight activity attributable to the need of many rarer species for regular dispersal between outcrops to spread the risk of extinction. The aerial fauna at Moor House had three components, with species deriving from the immediate habitat, moorland habitats nearby, or regions beyond the Reserve. A considerable influx of staphylinids (and aphids) onto the Reserve occurred in July-October as aerial plankton was carried in from the west by prevailing winds. The applicability of island biogeography theory to the Moor House system, and to 'habitat islands' in general, is discussed.