Why small cold-blooded insects pose different conservation problems to birds in modern landscapes

Butterflies and other insects have declined more rapidly than birds over parts of southwest Europe this century, and early attempts to conserve them often failed. Failure occurred mainly because reserve managers did not cater for three differences in their needs compared with those of vertebrates: (1) Many insects occupy very narrow specific niches within their biotopes, often associated with an ephemeral successional stage; (2) although an insect population can sometimes be supported by a small (<1 ha) patch of its specific habitat, an individual habitat patch may remain suitable for no more than 3–10 years and (3) several insect species are too sedentary to colonize new patches of habitat that arise farther than 300 m-1 km from old ones during the period that each remains suitable for breeding. Further complications arise from the dependency of some insects on narrow temperature bands, especially in northwest Europe where many species reach their edges of range and are locked into warm, anthropogenic habitats. The same species have broader or different niches farther south, and their habitats may require very different management across geographical ranges. Despite these problems, conservationists have had considerable success in maintaining populations of threatened insects within nature reserves, once knowledge of their ecology and dynamics was applied to site management.