Mice, rats, and other rodents threaten food production and act as reservoirs for disease throughout the world. In Asia alone, the rice loss every year caused by rodents could feed about 200 million people. Damage to crops in Africa and South America is equally dramatic. Rodent control often comes too late, is inefficient, or is considered too expensive. Using the multimammate mouse (Mastomys natalensis) in Tanzania and the house mouse (Mus domesticus) in southeastern Australia as primary case studies, we demonstrate how ecology and economics can be combined to identify management strategies to make rodent control work more efficiently than it does today. Three more rodent–pest systems – including two from Asia, the rice‐field rat (Rattus argentiventer) and Brandt's vole (Microtus brandti), and one from South America, the leaf‐eared mouse (Phyllotis darwini) – are presented within the same bio‐economic perspective. For all these species, the ability to relate outbreaks to interannual climatic variability creates the potential to assess the economic benefits of forecasting rodent outbreaks.
R odents are among the most important global pests (Prakash 1988; Singleton et al. 1999a), and are often featured in fiction, as in Albert Camus' The Plague. The black rat (Rattus rattus) played a key role in the plague during the Middle Ages (Scott and Duncan 2001). Farmers in many parts of the world, particularly those in developing countries, tend to view economic losses due to rats and mice as unavoidable (Posamentier 1997; Singleton et al. 1999a). In fact, the impact of rodents has been greatly underestimated and largely ignored in the general scientific literature, with a small number of exceptions (Elton 1942; Singleton et al. 1999a). Competing with rodents for food Worldwide, there are about 1700 species of rodents, but only 5-10% are major pest species in agricultural and urban environments, and even fewer cause problems over larger geographic areas. Some of these consume substantial amounts of agricultural produce (Table 1), and in many developing countries, farmers consider rodents the main impediment to higher yields (Makundi et al. 1999). Every year, rats in Asia consume food crops that could feed 200 million people for an entire year (Singleton 2003). In Indonesia, rodents are the most important pre-harvest pests in economic terms, causing on average at least 15% annual losses of rice (Geddes 1992). In Africa, the numbers are similar. Damage due to rodents in Tanzania causes an estimated annual yield loss of 5-15% of maize (corn), corresponding to about $45 million, and food which could feed about 2 million people (Leirs 2003; Table 1). In parts of South America, native rodents cause crop damage varying between 5-90% of total production (Rodriquez 1993). Obviously, we need better pest control strategies than we have today. The design of rodent control strategies has both an ecological dimension, relating to the interaction of the pest population and its resources and enemies (Singleton et al. 1999a), and an economic dimension, relating to crop damage, which affects yield, and the use of pesticides, which in turn affects production costs (Carlson and 367
An age structured model of a fishery is studied where two fishing fleets, or fishing agents, are targeting two different mature age classes of the fish stock. The agents are using different fishing gear with different fishing selectivity. The model includes young and old mature fish that can be harvested, in addition to an age class of immature fish. The paper describes the optimal harvesting policy under different assumptions on the objectives of the social planner and on fishing selectivity. First, biomass yield is maximized under perfect fishing selectivity, second, equilibrium profit (rent) is maximized under perfect fishing selectivity, and third, equilibrium profit is maximized under imperfect fishing selectivity. The paper provides results that differ significantly from the standard lumped parameter (also surplus production, or biomass) model.
The paper analyses the conflict between wildlife conservation and its accompanying land-use in an East African context. In the model there are two agents. First, there is an agency managing the wildlife and the habitat of the wildlife, which is referred to as parkland. On the other hand, there is the group of agro-pastoralists living in the vicinity of the wildlife habitat, whose land-use is referred to as rangelands. The parkland is used for tourism production and hunting, while the rangelands are used for agro-pastoral production. Both agents will find it beneficial to expand their land-use, so there is a land-use conflict. This is analysed in two steps. First, social optimality is studied; then we study the utilization of the wildlife and its accompanying land-use when there is no unified resource policy and the park agency follows its self-interest. The effects on the two different management schemes of changing economic conditions, such as the recommendations of the CITES convention and a programme subsidizing agro-pastoral production, are discussed.
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