Population biology of Trichostrongylus tenuis in the Red Grouse Lagopus lagopus scoticus.

Abstract

The red grouse (Lagopus lagopus scoticus) is a gamebird of economic and conservation importance in the north of England and Scotland (Hudson, 1992). For the last 10 years we have been studying the interaction between red grouse and the trichostrongylid nematode Trichostrongylus tenuis, a parasite that lives in the ceca of red grouse. We have undertaken a series of experiments that examines the effects of this parasite on survival and fecundity. These experiments are complimented by analyses of long-term game bag records for red grouse and the development of mathematical models that analyze the long-term dynamics of the interaction between the grouse, the parasite, and other natural enemies of the grouse such as foxes and birds of prey. This chapter summarizes the work that has been done to date.
Red grouse have been utilized as game since the middle of the 19th century. Ecologists have been fascinated by their population biology since the 1930s, when Elton discussed the long-term cyclic patterns of abundance that grouse populations exhibit throughout the north of England and Scotland (Elton, 1942). We have assembled 400 sets of long-term bag data for grouse populations. 70% or more of these exhibit some tendency to cycle. In this chapter, we discuss the evidence that shows that the interaction between T. tenuis and red grouse is the principle mechanism causing the long-term cycles in many red grouse populations. Where this effect occurs, understanding the population biology of the parasite will be crucial to the efficient management of grouse populations.
The chapter is organized as follows. Initially, we describe individual aspects of the interaction between the parasites and their host, and some mathematical models which may be used to examine the population dynamics of the interaction between T. tenuis and red grouse. The observed dynamics of grouse and parasite populations are discussed in terms of the properties of this model. The chapter concludes with a brief description of some work on the seasonal dynamics of T. tenuis in red grouse.