Epigeic spiders as ecological indicators of conservation value for peat bogs

Raised and basin bogs are in serious decline throughout the western Palaearctic. There is a need for a monitoring protocol that would signal changes in the habitat and the biota it supports. Spiders (Araneae) are a group of predators containing many bog specialist species, some of which are of Red Data Book status. Twelve-month continuous trapping in 11 basin bogs in Cheshire (western England) established the species present, their phenology, and relative abundance. Data were combined with those from another 21 lowland bogs obtained from the literature and a number of common statistical descriptors calculated. Some of these were of little value, but the number of spider bog indicator species is shown to be a surrogate for the conservation value of the total invertebrate fauna of bogs in the study area. A model short-survey protocol is devised and tested. Using this protocol and suggested stopping rules, it appears that adequate indication of good peatland sites can be assumed when the naturalness index exceeds 0.5, the species quality index is ⩾1.8, and the indicator species–area relationship gives a datum point on or above the trend line derived from the full data set.