THE EFFECT OF PARASITES ON WILDLIFE

Populations of animals which live in the wild are regulated by many bi otic and abiotic factors, Parasites are one of the biotic factors, Par asites may influence their hosts in different ways, They may cause the death of the host due to a direct lethal effect or an indirect effect , Direct lethal effects may occur if killing is a part of the life cyc le of the parasite or if hosts and parasites have not developed an equ ilibrium, The introduction of hosts or parasites into a new environmen t wit-h suitable hosts or parasites is an example. Death by parasitism may also be caused by a combination of the emaciating effects of para sites combined with factors such as bad weather conditions, environmen tal pollution or human handling, Parasites may also influence the beha viour of their hosts, If the hosts are intermediate hosts in the life cycle of the parasites, the alterations in behaviour may make them an easier prey for their predators, the final hosts. Parasites may also i nfluence the reproductive success of the hosts, In this respect the re lationship between the red grouse (Lagopus lagopus scoticus) and the c aecal nematode Trichostrongylus tenuis has been well worked out.