Small-scale spatial dynamics in a fluctuating ungulate population


T. Coulson, Institute of Zoology, Zoological Society of London, Regent's Park, London, NW1 4RY, UK


1. The scale at which population dynamics are analysed is important, as results from analyses at different spatial scales can differ and affect interpretation.

2. In this study, detailed census data collected over a 10-year period from a population of Soay sheep (Ovis aries L.) on the Island of Hirta in the St Kilda archipelago, Scotland, is used, together with cluster analysis, to distinguish a temporally stable spatial substructure.

3. Structured demographic accounting of the variance in population change (SDA) is also used to analyse the dynamics of the whole population treated as (a) one unit; (b) one unit subdivided into three subunits; and (c) three independent units.

4. Differences in survival, recruitment and dispersal rates are demonstrated between divisions of the population, which are probably associated with variation in grazing quality.

5. If these groups were not coupled by dispersal and density-independent entrainment, the population dynamics of the three groups would diverge, however, the dynamics of the three subunits are strongly correlated.