Variation in social systems of fallow deer

Abstract

The thesis investigates intraspecific variation in grouping patterns and mating systems in free-ranging populations of fallow deer Dama dama inhabiting two distinct environments. The New Forest in southern England consists of large continuous woodlands adjacent to large areas of heathland and grassland. The southern English agricultural landscape is typified by small, discontinuous woodlands interspersed with pasture and arable crops. Fallow populations occur at a range of densities in both environmental types. Despite occurring in environments markedly different in habitat composition and structure, habitat use patterns showed great similarity between sites in terms of utilization of woodland and open habitats. In all study sites, deer predominantly utilized woodlands. Differences between the two main environmental types were more pronounced in respect of population characteristics. Densities were much higher in the New Forest populations, and there was considerable variation in sex ratio within and between environmental categories. These two characteristics appeared to influence the extent of winter and spring sexual segregation exhibited by the populations. Males joined female groups when male numbers were low. In the New Forest, mixed-sex groups were the result of temporary aggregations of females and young males. In contrast, mixed-sex groups in the agricultural sites contained males of all ages. The size of social groups was strongly influenced by season, habitat openness, habitat structure and population density. A common seasonal pattern existed across all sites, with female groups largest in winter and spring, decreasing during parturition in early summer, and increasing again during the autumn rut. Male group size was smallest during the rut and varied little throughout the year. In common with most ungulates, fallow group size was largest in open habitats. Between different populations, variation in the extent of group size between woodland and open habitats may have been influenced by habitat structure and population density. High density populations inhabiting large continuous woodlands were characterised by small groups in woodland and large groups in open habitats. In contrast, in low density populations inhabiting small discontinuous woodlands group size was less variable. The flexibility in fallow grouping patterns was matched by the variation in mating systems. Males adopted a range of mating strategies which could be broadly classified according to the degree and type of territoriality during the autumn rut. In the low density agricultural populations, male territoriality was reduced and males followed groups of females throughout their range. In the higher density New Forest populations a variety of male mating strategies existed including leks, multiple stands, single territories, temporary territories, and non-territorial following. Increased territoriality and the development of multiple territory mating systems was associated with an increase in male and female density. Lekking may be initiated by locally high densites of females aggregating near favoured feeding resources. In one population in the New Forest, lekking occurred as an alternative strategy to single territory defence and non-territorial following. In this population, copulatory success was highest on the lek, but unsuccessful lek males achieved less copulations than some single territory males away from the lek.

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