Population changes in Neophilaenus lineatus (L.) (Homoptera: Cercopidae) in different parts of its range

TLDR: This account will compare and contrast the changes occurring in two populations of Neophilaenus lineatus at the edge of the species' range on the Pennine hills (over a period of 9 years) with a population from lowland southern England during 6 years.

Abstract: The majority of published population studies of animals consider the circumstances pertaining to a single population in a given type of habitat. Yet authors such as Huffaker (1958), Clark et al. (1967) and Klomp (1962) have emphasized the importance of distinguishing between 'salubrious and hazardous environments' (Huffaker 1958), in interpreting a study and in particular when attempting to reconcile the seemingly polarized views of the theorists. Of course, it will not necessarily be possible in a particular case to define a habitat as salubrious or hazardous since there will be every gradation between these extremes. It should, however, be possible to study a population living in a habitat which is representative of the broad conditions under which this species is observed to live and thrive and to contrast this with a population which has been specifically chosen because it is living at the extreme edge of the species' range. In 1965 I published an account of a short-term study of a cercopid (Neophilaenus lineatus (L.)) living at high altitude in the Pennine hills of northern England (Whittaker 1965a, b). This did appear to be on the verge of extinction as judged by the fact that it became temporarily extinct at only slightly higher altitudes. This same species occurs throughout Britain in areas of uncultivated grassland. The study has since been extended with the aim of comparing these populations with one in a low-altitude grassland in southern England at Wytham Woods, Berkshire. As far as can be judged from knowledge of the distribution and biology of N. lineatus, this latter habitat is favoured by the species whilst the populations on the Pennines are living in a peripheral, hazardous environment. The grassland known as Upper Seeds at Wytham Woods also supports two other species of cercopid, and one of these, Philaenus spumarius (L.), shares a pipunculid parasite Verrallia aucta Fallen with Neophilaenus lineatus. They differ, however, in the important respect that N. lineatus feeds exclusively on monocotyledons and Philaenus spumarius on dicotyledons. This account will compare and contrast the changes occurring in two populations of Neophilaenus lineatus at the edge of the species' range on the Pennine hills (over a period of 9 years) with a population from lowland southern England during 6 years.