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Analysis of aggregation, a worked example: numbers of ticks on red grouse chicks

Published online by Cambridge University Press:  07 August 2001

D. A. ELSTON ,
R. MOSS ,
T. BOULINIER ,
C. ARROWSMITH  and
X. LAMBIN
D. A. ELSTON
Affiliation:
Biomathematics and Statistics Scotland, Environmental Modelling Unit, Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
R. MOSS
Affiliation:
Centre for Ecology and Hydrology, Banchory, Aberdeenshire AB31 4BW, Scotland
T. BOULINIER
Affiliation:
Laboratoire d'Ecologie, C.N.R.S–U.M.R. 7625, Université Pierre et Marie Curie, 7 Quai St Bernard, 75252 Paris, France
C. ARROWSMITH
Affiliation:
Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland Present address: 10 Strathmore Court, Thurso, KW14 7PS, Scotland.
X. LAMBIN
Affiliation:
Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland
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Abstract

The statistical aggregation of parasites among hosts is often described empirically by the negative binomial (Poisson-gamma) distribution. Alternatively, the Poisson-lognormal model can be used. This has the advantage that it can be fitted as a generalized linear mixed model, thereby quantifying the sources of aggregation in terms of both fixed and random effects. We give a worked example, assigning aggregation in the distribution of sheep ticks Ixodes ricinus on red grouse Lagopus lagopus scoticus chicks to temporal (year), spatial (altitude and location), brood and individual effects. Apparent aggregation among random individuals in random broods fell 8-fold when spatial and temporal effects had been accounted for.

Keywords

analysing aggregationgeneralized linear mixed modelIxodes ricinusLagopus lagopus scoticusPoisson-lognormal distributionvariance components
Type
Research Article
Information
Parasitology , Volume 122 , Issue 5 , May 2001 , pp. 563 - 569
Copyright
2001 Cambridge University Press

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