Allometric Scaling of Minimal Mammal Densities

Minimum viable densities have rarely been determined directly. Theoretical analyses, based on empirical relationships between average mammal densities, suggest that minimum densities of viable populations are lower for larger mammals. This suggestion has been cast into doubt by other field studies showing populations of small insects and birds at very low densities. We collected 143 of the closest approximations of minimum viable density available, those of minimal, rare, and endangered mammal populations. We found that minimal density decreases as the −0.68 power of body mass. Minimal densities of small mammals are 1000 times those of the largest species. The correlation between minimum viable population density and body mass is negative in the majority of the mammalian taxonomic orders. Although minimum density is, on average, 10% of mean population density, viable population densities of herbivores are 13 times those of carnivores and insectivores. Populations in the wet tropics can apparently sustain themselves at densities much lower than those in temperate climates.     

Collapse and reorganization of a food web of Mwanza Gulf, Lake Victoria

Lake Victoria in East Africa is the world's second largest freshwater system. Over the past century the ecosystem has undergone drastic changes. Some 30 years after the introduction of Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) in the 1950s, the highly diverse community of native haplochromines collapsed, leaving a system dominated by only four species: the native cyprinid dagaa (Rastrineobola argentea) and shrimp (Caridina nilotica), as well as the introduced Nile perch and Nile tilapia. More recently, an unexpected resurgence of haplochromines has been reported. To understand these changes in terms of ecosystem functioning and of changes in growth of trophic groups, we created mass balances of the food web near Mwanza, Tanzania, before, during, and after the Nile perch boom (1977, 1987, and 2005), using the application ECOPATH. We connected these mass balances with a dynamic model assuming linear trends in net growth rates of the trophic groups. Our analysis suggests that the Nile perch boom initially altered the biomass distribution over trophic levels. Also, results indicate that not only fishing but also changes at the detritivores' trophic level might have played an important role in driving changes in the system. Both the mass balances and the dynamic model connecting them reveal that, after a major distortion during the Nile perch boom, the biomass distribution over the main trophic levels had largely recovered its original (1977) state by 2005. However, no such return appeared in terms of community structure. Biodiversity in the new state is dramatically lower, consisting of introduced species and a few native surviving species. We conclude that at an aggregate level Lake Victoria's ecosystem has proved to be resilient in the sense that its overall trophic structure has apparently recovered after a major perturbation. By contrast, its intricate functional structure and associated biodiversity have proved to be fragile and seem unlikely to recover.     

Evaluation of seasonal scale first flush pollutant loading and implications for urban runoff management

This study investigated how the occurrence and magnitude of first flush events in stormwater may influence the effective management of urban runoff pollution. To facilitate the understanding of the first flush phenomenon on a seasonal scale, the City of San Jose, CA carried out an investigation between May 1997 and April 2000 to characterize concentrations of pollutants in local waterbodies during eight storm events. The purpose of the investigation was twofold: (1) To determine if concentrations of specific constituents in stormwater runoff are elevated during the first substantial storm of the wet season, and (2) To identify the physical and environmental conditions surrounding such events. Concentration data for total and dissolved metals, pesticides, polyaromatic hydrocarbons, anions, total suspended solids, total organic carbon, conductivity, gasoline and diesel, and volatile and semi-volatile organics were collected at over 25 sites. Monitoring data analysis focused on identifying physical and environmental conditions yielding increased levels of pollutants during the first substantial storms of the rainy season compared to other storm events. Quantitative analysis focused on metals and anions because most observations for other constituents were below detectable levels. The results suggest that first flush phenomena did not occur consistently throughout most of the stations investigated. The results further suggest that there are specific combinations of site and storm conditions that result in a first flush effect with respect to dissolved metals. Based on the results of this and related investigations, implications for urban runoff management are discussed. For example, if dissolved metals are of principal concern, it may be worthwhile to optimize existing control strategies to minimize pollutant loading from storms that are preceded by an extended dry period.     

Book reviews

Local Politics and Participation in Britain and France

Albert Mabileau, George Moyser, Gerraint Parry, Patrick Quantin. 1989. 281 pp. Price £30.00.

ISBN: 0 521 34576 6.

The Rural State?: Limits to Planning in Rural Society

Paul Cloke and Jo Little. 1990, Oxford University Press. 287 pp.

Price £30.00.

ISBN: 0 19 823287 X

Urbanisation in History: A Process of Dynamic Interactions. International Studies in Demography.

Edited by Ad van der Woude, Jan de Vries, and Akira Hayami. Clarendon Press, Oxford, 1990. 371 pp. Price £40.00.

Housing and Social Inequality

Jenny Morris and Martin Winn

Integrated Land‐Use and Transport Modelling — Decision Chains and Hierarchies

Tomas de la Barra

Beyond Green Belts — Managing Urban Growth in 21st Century

Regional Studies Association (1990). 64 pp. Price £9.95.

Learning from Rotterdam

M. J. Vroom and J. H. A. Meeus.

173 pp. Nichols, New York. Price £25.

Reviewing the Quality of Environmental Statements

N. Lee and R. Colley

EIA Centre, University of Manchester, 1990.

Occasional Paper 25, 46 pp. Price: £3.00.

Knowledge and Public Policy: the search for meaningful indicators

Judith Innes. Transaction Publishers, New Brunswick. 352 pp. Price: £16.95.

Urban Problems: An Applied Urban Analysis

Michael Pacione. Routledge, 1990.

Living with Inner City Policies: Two Essays on Inner City Life and Inner City Policies

Meryl Aldridge and John Edwards, Department of Social Policy, Royal Holloway and Bedford New College. Social Policy Papers No. 2, 1989.

Information Technology in Geography and Planning: including principles of GIS

Bracken and Webster, Routledge, London 1990. 444 pp.

Housing and Social Change in Europe and the USA

Michael Ball, Michael Harloe and Maartje Martens. Routledge, 222 pp. Price: £10.99.

Land and Property Development: Changing Context

Edited by Healey and Nabarro. 212 pp. Price: £39.50.     

Agent-based integrated assessment modelling: the example of climate change

Current approaches to deal with the socio-economic implications of climate change rely heavily on economic models that compare costs and benefits of different measures. We show that the theoretical foundations underpinning current approaches to economic modelling of climate change are inappropriate for the type of questions that are being asked. We argue therefore that another tradition of modelling, social simulation, is more appropriate in dealing with the complex environmental problems we face today.     

Getting the Scale Right: A Comparison of Analytical Methods for Vulnerability Assessment and Household-level Targeting

This paper introduces broad concepts of vulnerability, food security and famine. It argues that the concepts and theories driving development and implementation of vulnerability assessment tools are related to their utility. The review concludes that socio-geographic scale is a key issue, and challenge. It analyses three vulnerability assessment (VA) methods, using Ethiopia as a case study. Facing the challenges of vulnerability assessment and early warning requires providing accurate information at the required scale, useful for multiple decision-makers within realistic institutional capacities.     

Testing the Reliability of the Benefit Function Transfer Approach

This article presents an experiment designed to test the reliability of the benefit function transfer approach using contingent valuation methods. The experiment uses data collected from anglers surveyed across eight contiguous Texas Gulf Coast bay regions over three distinct time periods. Results indicate that the benefit function transfer approach tends to over-estimate benefits, implying that, at least for the case of recreational saltwater fishing in Texas, the benefit function transfer approach is not reliable.     

Societal Vulnerability to Climate Change and Variability

Institutions in many wealthy industrialised countries are robust and their societies appear to be relatively well insulated against the impacts of climate variability, economic problems elsewhere and so on. However, many countries are not in this position, and there is a growing group of humanity which is not benefiting from the apparent global adaptive trends. Worst case scenarios reinforce the impact of this uneven distribution of adaptive capacity, both between and within countries. Nevertheless, at the broad global scale human societies are strongly adaptive and not threatened by climate change for many decades. At the local level the picture is quite different and the survival of some populations at their present locations is in doubt. In the absence of abatement, the longer term outlook is highly uncertain. Adaptation research needs to begin with an understanding of social and economic vulnerability. It requires a different approach to the traditional IPCC impacts assessment, as human behaviour, institutional capacity and culture are more important than biophysical impacts. This is consistent with the intellectual history of the IPCC which has gradually embraced an increasing range of disciplines.