Predation has usually been interpreted as being a compensatory mortality factor, removing only the doomed surplus. The literature on the wild Rabbit Oryctolagus cuniculus L. is reviewed to collate counter-evidence for a regulating influence of predation. This evidence is almost entirely circumstantial, not experimental. Predation has been reported to extend the length of time Rabbit populations remain low following a significant reduction of Rabbits by some other agent. Rabbit populations have been shown to increase very rapidly when predator density has suddenly been reduced. It has been suggested that predators affect the spread and dispersion of Rabbits both at the geographical and local levels. Predation has not, however, been shown to have an important influence at high Rabbit densities. Thus, its role can be that of a limiting factor rather than a density-dependent regulatory mortality factor.The concept of predator pressure is presented and discussed, pointing out that there is currently no standard technique used for its measurement.Further evidence on the importance of predation is presented from four recent studies in England and Wales that relate, by association, the distribution and abundance of local Rabbit populations to the local attitude towards predators. Rabbits were found to be significantly more widespread and abundant where predators were removed (not restricted to keepered game estates) or at low density, than when predators were undisturbed or at a high density. The significance of these results is discussed.The circumstantial and corroborative evidence leads strongly to the conclusion that predator pressure can act as an additive rather than compensatory mortality factor in some circumstances, and can thus be a potential regulating factor. Predation is more likely to be a limiting factor at low Rabbit density however, since a density-dependent relationship has not been demonstrated throughout the range of Rabbit densities that occur. This requires experimental demonstration to determine the threshold pressure below which predation becomes limiting. If so, reductions in Rabbit populations by short-term control operations could allow natural predation to help maintain low Rabbit densities for several years in some habitats. Conversely, the implications for Rabbit populations and thus crop damage resulting from predator control (e.g. in game management regimes) should be appreciated.

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SUMMARYThe overall pattern and consequences of myxomatosis in wild rabbit populations were studied at three farmland sites in lowland southern England and upland central Wales between 1971 and1978. When results from all years were combined, the disease showed a clear two-peaked annual cycle, with a main autumn peak between August and January, and a subsidiary spring peak during February to April.Rabbit fleas, the main vectors of myxomatosis in Britain, were present on fullgrown rabbits in sufficient numbers for transmission to occur throughout the year, but the observed seasonal pattern of the disease appeared to be influenced by seasonal mass movements of these fleas. However other factors were also important including the timing and success of the main rabbit breeding season, the proportion of rabbits which had recovered from the disease and the timing and extent of autumn rabbit mortality from other causes.Significantly more males than females, and more adults and immatures than juveniles, were observed to be infected by myxomatosis. Only 25-27 % of the total populations were seen to be infected during outbreaks. Using two independent methods of calculation, it was estimated that between 47 and 69 % of infected rabbits died from the disease (much lower than the expected 90-95 % for fully susceptible rabbits with the partly attenuated virus strains that predominated). Thus it was estimated that 12-19 % of the total rabbit populations were known to have died directly or indirectly from myxomatosis.Although the effects of myxomatosis were much less than during the 1950s and 1960s, it continued to be an important mortality factor. It may still have a regulatory effect on rabbit numbers, with autumn/winter peaks of disease reducing the numbers of rabbits present at the start of the breeding season.

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