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Parasites and climate synchronize red grouse populations


There is circumstantial evidence that correlated climatic conditions can drive animal populations into synchronous fluctuations in abundance1,2,3,4,5. However, it is unclear whether climate directly affects the survival and fecundity of individuals, or indirectly, by influencing food and natural enemies. Here we propose that climate affects trophic interactions and could be an important mechanism for synchronizing spatially distributed populations. We show that in specific years the size of red grouse populations in northern England either increases or decreases in synchrony. In these years, widespread and correlated climatic conditions during May and July affect populations regionally and influence the density-dependent transmission of the gastrointestinal nematode Trichostrongylus tenuis, a parasite that reduces grouse fecundity6. This in turn forces grouse populations into synchrony. We conclude that specific climatic events may lead to outbreaks of infectious diseases or pests that may cause dramatic, synchronized changes in the abundance of their hosts.

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Figure 1: Locations of the 91 red grouse populations that provided annual harvesting records between 1839 and 1994.
Figure 2: Spatio-temporal patterns of synchrony between populations within each of the five regions.
Figure 3: Simplified path diagram with parameterized path coefficients of simulated interactions between climate, parasites and red grouse.


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I.M.C. thanks D. Shaw for statistical advice. We are also grateful to D. Newborn of the Game Conservancy Trust, The Earl Peel and moor owners in northern England who allowed us to aggregate the database. O. Bjørnstad, E. Post and D. Johnson provided comments on an earlier version. I.M.C. was funded by a Marie Curie fellowship.

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Correspondence to Isabella M. Cattadori.

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Cattadori, I., Haydon, D. & Hudson, P. Parasites and climate synchronize red grouse populations. Nature 433, 737–741 (2005).

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