Case Study: Red Grouse and Parasites

Edexcel A-level BiologyThe Nature of EcosystemsLesson 22 of 39

Red grouse living on heather moorland in northern England and Scotland show population cycles, with numbers crashing every 4 to 8 years or so. A long-running study by Peter Hudson and colleagues tested whether a parasitic nematode worm, Trichostrongylus tenuis, which lives in the gut of the grouse, causes these crashes.

Heavily infected birds are in poorer condition, lay fewer eggs, rear fewer chicks and are easier for predators to catch. The worm larvae are picked up by eating heather shoots, so infection spreads more when grouse are at high density. Parasitism therefore has its biggest effect when the population is large.

More in The Nature of Ecosystems

• Finding a Mate
• Territory
• Parasitism and Disease
• Case Study: Snowshoe Hare and Lynx
• Density Dependent Factors
• Density Independent Factors
• Competition
• Intraspecific Competition

All 39 lessons in The Nature of Ecosystems · All Edexcel A-level Biology topics