Unsustainable bushmeat hunting is a major threat to mammal species, particularly in West/Central Africa. We developed a multispecies dynamic simulation model of hunter behaviour, parameterized using data from the Ashanti region, Ghana. The model distinguishes between two hunting techniques, snaring and gun hunting. We analyse the impact of key economic parameters on off-takes. Economic incentives determine the effort devoted to hunting, the choice of hunting technique, and the species that are consumed domestically or traded in markets. These factors, together with the growth rates and catchabilities of hunted species, determine the ecological impact of hunting. The results suggest that increased bushmeat prices are likely to lead to a switch from snaring, which is cheaper but less efficient, to gun hunting, with a consequent impact on vulnerable species. Increases in agricultural prices have an ambiguous effect on hunter behaviour, depending on the balance between incentives to invest in agriculture and increased consumption as incomes improve. Penalties are more effective if they target bushmeat sales, rather than the act of hunting. This model represents a step forward because it explicitly considers bushmeat as a component of the household economy. This has important implications as regards the development of policies to conserve species hunted for bushmeat.

SUMMARYData on prices and quantities of wildlife on sale in markets are increasingly being used as indicators of the sustainability of bushmeat hunting, being relatively easy to collect. However, it is not clear how much can actually be inferred from trends in such data. This study analyses changes in price, quantity, method of capture and kill location of bushmeat species entering the Atwemonom bushmeat market in the city of Kumasi (Ghana) over the period 1987−2002, using data collected by an official of the Ghana Wildlife Department. The analysis was confined to the seven most commonly traded species and to the open season only, in order to maximize the reliability of the data. Over the period, there was an increase in real bushmeat prices, in the proportion of animals killed by means other than guns and the trade made up by grasscutters (Thryonomys swinderianus). A higher proportion of animals originated from distant areas, rather than from villages close to Kumasi. These trends are compatible both with depletion of the bushmeat resource and with an economically rational response by hunters to increasing prices. The analysis highlights both the utility and the limitations of detailed long-term market data as a tool for assessing the sustainability of wildlife hunting. Data on the origin of animals sold in the market and the gear type are necessary but not sufficient for understanding the drivers of changes in price and quantity of species on sale in markets; without complementary detailed local data on hunter behaviour, market data are of little value.

Methane (CH 4 ) is a strong greenhouse gas known to have perturbed global climate in the past, especially when released in large quantities over short time periods from continental or marine sources. It is therefore crucial to understand and, if possible, quantify the individual and combined response of these variable methane sources to natural climate variability. However, past changes in the stability of greenhouse gas reservoirs remain uncertain and poorly constrained by geological evidence. Here, we present a record from the Congo fan of a highly specific bacteriohopanepolyol (BHP) biomarker for aerobic methane oxidation (AMO), 35-aminobacteriohopane-30,31,32,33,34-pentol (aminopentol), that identifies discrete periods of increased AMO as far back as 1.2 Ma. Fluctuations in the concentration of aminopentol, and other 35-aminoBHPs, follow a pattern that correlates with late Quaternary glacial-interglacial climate cycles, with highest concentrations during warm periods. We discuss possible sources of aminopentol, and the methane consumed by the precursor methanotrophs, within the context of the Congo River setting, including supply of methane oxidation markers from terrestrial watersheds and/or marine sources (gas hydrate and/or deep subsurface gas reservoir). Compound-specific carbon isotope values of À30& to À40& for BHPs in ODP 1075 and strong similarities between the BHP signature of the core and surface sediments from the Congo estuary and floodplain wetlands from the interior of the Congo River Basin, support a methanotrophic and likely terrigenous origin of the 35-aminoBHPs found in the fan sediments. This new evidence supports a causal connection between marine sediment BHP records of tropical deep sea fans and wetland settings in the feeding river catchments, and thus tropical continental hydrology. Further research is needed to better constrain the different sources and pathways of methane emission. However, this study identifies the large potential of aminoBHPs, in particular aminopentol, to trace and, once better calibrated and understood, quantify past methane sources and fluxes from terrestrial and potentially also marine sources.

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There is considerable debate in the literature over whether or not to legalise the trade in rhino horns. Here a system dynamics model is developed that considers five components: rhino abundance, rhino demand, a price model, an income model and a supply model. The results indicate that income elasticities are much greater than previously observed, while demand is relatively insensitive to price. At the same time, legalising the trade without income modification policies did not prevent extinction. The theory of s-curve growth may provide some indications of future growth patterns of Asian economies. Results suggest that, even though the demand curve for rhino horn may be downward sloping as conventional theory predicts, non-conventional demand management strategies may be more effective than price orientated demand curve strategies such as trade legalisation in curbing supply.

Can markets assist by providing support for ecological restoration, and if so, under what conditions? The first step in addressing this question is to develop a consistent methodology for economic evaluation of ecological restoration projects. A risk analysis process was followed in which a system dynamics model was constructed for eight diverse case study sites where ecological restoration is currently being pursued. Restoration costs vary across each of these sites, as do the benefits associated with restored ecosystem functioning. The system dynamics model simulates the ecological, hydrological and economic benefits of ecological restoration and informs a portfolio mapping exercise where payoffs are matched against the likelihood of success of a project, as well as a number of other factors (such as project costs and risk measures). This is the first known application that couples ecological restoration with system dynamics and portfolio mapping. The results suggest an approach that is able to move beyond traditional indicators of project success, since the effect of discounting is virtually eliminated. We conclude that systems dynamic modelling with portfolio mapping can guide decisions on when markets for restoration activities may be feasible.

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The article describes the results of two surveys conducted in six villages in the Ashanti region of Ghana. The first was undertaken in August 2002 and the second during July 2004. A total of 468 hunters and non-hunters were surveyed using targeted and systematic interviewing techniques. The results indicate that hunting is an important contributor to total income in the villages, particularly for poorer households. We find some evidence that hunting increases during lean periods, especially for hunters in the household survey. Distance to Kumasi is a significant determinant of the number of animals sold on the market, and also influences the type of gear used for hunting. Compliance with wildlife laws, notably species restrictions and the closed season is low, particularly amongst professional hunters. JEL Q12, Q21, Q57