Modelling the relative efficacy of culling and sterilisation for controlling populations

Abstract

Simple logistic models are used to investigate and compare the effects of continuous control by culling or sterilisation on population density. The models consider populations regulated by density-dependent mortality or density-dependent recruitment, with monogamous or polygamous mating systems, and with one or both sexes sterilised. For the first time, an analytical solution is presented for the effect of sterilisation on density-dependent population growth. The models suggest that the mating system has a considerable effect on the relative efficacy of sterilisation, and that previous models for sterilisation may have overestimated the impact of sterilisation by assuming idealised monogamous mating. In general, and except for populations with monogamous mating or 'harem' systems and both sexes sterilised, culling gives a more rapid reduction in density than does sterilisation. However, the long-term degree of suppression obtained with the same levels of control applied is likely to be similar. Populations with density-dependent mortality will be reduced by sterilisation more quickly than those regulated by density-dependent recruitment, and the effect on the steady-state density of a given proportion that is sterile is greater in the first case than in the second. However, the effect of a given continuous sterilisation rate (e.g. baiting effort) on density is the same in both cases. We compare our model results with those of others and question previous conclusions about the circumstances under which sterilisation is most effective.

Feral Pigeons: Problems, Dynamics and Control Methods

“…Several models indicate that for monogamous species with high mortality rates and high productivity, such as feral pigeons, culling is likely less effective than the reduction of reproductive potential for controlling population (Barlow et al, 1997;Dolbeer, 1998). Actually, even though culling has been widely applied to feral pigeon populations in several cities in the past (see e.g.…”

The Trojan female technique: a novel, effective and humane approach for pest population control

“…Model refinement beyond this first proof of principle is thus desirable to explore further the nuances of how the TFT approach performs under different population and environmental scenarios. Further, the likely effects of both mating system and recruitment compensation on control efficacy at reduced population size, as noted for other fertility control approaches [59,65,66], need to be explored beyond our simple treatment in figure 3. Nonetheless, the conceptual demonstration presented here shows that the TFT has significant theoretical potential-a potential that is readily adaptable to any pest species, because mitochondria are common to all higher organisms [67].…”

The potential for biological control of stoats (Mustela erminea)

“…While annual mortality rates of first-year stoats are similar between podocarp and beech forests in non-mast years, mortality of adults between their second and fourth years tends to be lower in podocarp forests (King et al 1996a;Powell & King 1997). Bomford (1990) and Barlow et al (1997) concluded from general models that sterilising males only is unlikely to significantly reduce population size. This may be true of stoats because there will always be some non-sterilised males able to impregnate enough females (who remain on heat until fertilised) to offset the effects of any male-only fertility control programme on the total production of young.…”