Population-level variation in plant secondary chemistry,and the population biology of herbivores

Summary Modern population ecology is becoming increasingly spatially-explicit. For insect hervibores, spatial variation in plant quality is a critical component of distribution and abundance. We argue that populationlevel measurements of phytochemical variation among individual plants has not kept pace with recent developments in population ecology. With examples from our own work, we demonstrate the importance of spatial variation in plant chemistry for insect herbivores, and suggest that phytochemistry should play a central role in the development of any spatially-based ecological theory.     

Environmental impact assessment: An international evaluation

Experiences with environmental impact assessment (EIA) in a number of countries are discussed in the light of both explicit and implicit goals and objectives. Adequate environmental information is not always available to decision makers because of failure to apply EIA to all relevant decisions, the continuing inadequacies of prediction and evaluation techniques, the failure to consider alternatives adequately, and the bias of some EISs. EIA frequently results in changes to proposals and may result in stricter environmental management conditions in some cases, but some people regard it as a failure because it has not stopped development. Generally, EIA leads to better integration of environmental factors into project planning. Open procedures and freedom of information encourage responsiveness to EIA procedures, which can be weakened by discretionary powers and lack of access to the courts by public interest groups. However, legal standing may have side effects that offset its advantages. EIA can encourage cooperation and coordination between agencies but does not ensure them. Similarly, it can have a limited role in coordinating interstate and international policies. In the long term, the success of EIA depends on adequate monitoring, reassessment, and enforcement over the life of the project. EIA has generally opened up new opportunities for public participation, and may help to reduce conflict. EIA procedures need to be integrated with other environmental protection and development control programs, and various means exist for reducing its cost to developers and the public.     

Forests and competing land uses in Kenya

Indigenous forests in Kenya, as in other developing countries, are under heavy pressure from competing agricultural land uses and from unsustainable cutting. The problem in Kenya is compounded by high population growth rates and an agriculturally based economy, which, even with efforts to control birth rates and industrialize, will persist into the next century. Both ecological and economic consequences of these pressures need to be considered in land-use decision making for land and forest management to be effective. This paper presents one way to combine ecological and economic considerations. The status of principal forest areas in Kenya is summarized and competing land uses compared on the basis of ecological functions and economic analysis. Replacement uses do not match the ecological functions of forest, although established stands of tree crops (forest plantations, fuel wood, tea) can have roughly comparable effects on soil and water resources. Indigenous forests have high, although difficult to estimate, economic benefits from tourism and protection of downstream agricultural productivity. Economic returns from competing land uses range widely, with tea having the highest and fuel wood plantations having returns comparable to some annual crops and dairying. Consideration of ecological and economic factors together suggests some trade-offs for improving land allocation decisions and several management opportunities for increasing benefits or reducing costs from particular land uses. The evaluation also suggests a general strategy for forest land management in Kenya.The views and interpretations expressed in this article are those of the authors and should not be attributed to the World Bank, its affiliated organizations, or any individual acting on their behalf.     

POLICY IMPACTS ON AGRICULTURAL IRRIGATION ELECTRICITY DEMAND IN THE COLUMBIA BASIN1

ABSTRACT: Accurately estimating the price elasticity of demand for irrigation electricity is important to major electricity suppliers such as the Bonneville Power Administration (BPA) of the Pacific Northwest. The BPA has a revenue maximization objective, and the elasticity of demand is central to its rate setting process. Several studies have attempted to estimate demand for irrigation electricity, but none has explicitly included federal agricultural policy and program variables. Tins paper discusses how agricultural programs may influence farmers irrigation decisions and thus their demand for irrigation electricity. It suggests that existing programs serve to make farmers more responsive to electricity rate increases than would otherwise be the case. Thus, studies that fail to include them may underestimate the responsiveness of farmers to electricity rate increases.     

Environmental assessment and the academic environmentalist

This paper is concerned with the way in which academics who are drawn into the Environmental Assessment process use their skill, knowledge and understanding. It identifies shortcomings and pitfalls and stresses the importance of integrity and monitoring.     

Movement Corridors: Conservation Bargains or Poor Investments?

Corridors for movement of organisms between refuges are confounded with corridors designed for other functions, obscuring an assessment of cost-effectiveness. The rationales for movement corridors are (1) to lower extinction rate in the sense of the equilibrium theory, (2) to lessen demographic stochasticity, (3) to stem inbreeding depression, and (4) to fulfill an inherent need for movement. There is a paucity of data showing how corridors are used and whether this use lessens extinction by solving these problems. Small, isolated populations need not be doomed to quick extinction from endogenous forces such as inbreeding depression or demographic stochasticity, if their habitats are protected from humans. In specific instances, corridors could have biological disadvantages. Corridor proposals cannot be adequately judged generically. In spite of weak theoretical and empirical bases, numerous movement corridor projects are planned. In the State of Florida, multi-million-dollar corridor proposals are unsupported by data on which species might use the corridors and to what effect. Similarly, plans for massive corridor networks to counter extinction caused by global warming are weakly supported. Alternative approaches not mutually exclusive of corridors might be more effective, but such a judgment cannot be made without a cost-benefit analysis.     

Chemical defence in chewing and sucking insect herbivores: Plant-derived cardenolides in the monarch butterfly and oleander aphid

Summary Cardenolide sequestration by a hemimetabolous aphid and a holometabolous butterfly from the neotropical milkweed,Asclepias curassavica L., is compared. The oleander aphid,Aphis nerii B. de F., sequestered a similarly narrow range of cardenolide concentrations to the monarch butterfly,Danaus plexippus (L.), from the wide range of concentrations available in leaves of A.curassavica. However, A.nerii sequestered significantly less cardenolide (269 µg/0.1 g) thanD. plexippus (528 µg/0.1 g). The honeydew excreted by A.nerii was comprised of 46% cardenolide. The complete polarity range of 25 cardenolides detected by thin layer chromatography in A.curassavica was represented in the 17 whole aphid cardenolides and the 20 aphid honeydew cardenolides detected. D.plexippus sequestered a narrower polarity range of 11 cardenolides, having eliminated low polarity cardenolide genins and glycosides. It is suggested that these chemical differences may be related to interactions among the broad feeding tactics of sucking or chewing milkweed leaves, life history constraints of holometabolyversus hemimetaboly, the distribution of milkweed food resources in space and time, and the dynamics of natural enemies.     

Cloud water and throughfall deposition of mercury and trace elements in a high elevation spruce-fir forest at Mt. Mansfield,Vermont

As part of the Lake Champlain Basin watershed study of mercury (Hg) and pollutant deposition, cloud water and cloud throughfall collections were conducted at the south summit (1204 m) of Mt. Mansfield, Vermont between August 1 and October 31, 1998, for multi-element chemical analysis. A passive Teflon string collector was deployed during non-precipitating events to sample cloud/fog water at timberline, while three sets of paired funnels collected cloud throughfall under the red spruce-balsam fir canopy. Samples were analyzed for concentrations of Hg, major ions, and 10 trace elements. Ultra-clean sampling and analysis techniques were utilized throughout the study. Six events were sampled for cloud water alone and four events were sampled for both cloud water and cloud throughfall. Cloud throughfall chemistry showed substantial modification from incident cloud water. Much higher concentrations of Hg (2.3 x), base cations (Ca2+, K-, Mg2+; 3-18 x) and certain trace elements (Ni, Cu, Mn, Rb, Sr; 2-34 x) were observed in throughfall than in cloud water. These results confirm that cloud water can leach a wide variety of elements from tree foliage and wash off dry deposited elements. Cloud water deposited an average of 0.42 +/- 0.12 mm of water per hour. Estimated cloud water deposition of Hg was 7.4 microg m(-2) for the period August 1-October 31, approximately twice that deposited by rain during this period at a nearby low elevation Hg monitoring site. Our results indicate that cloud water and Hg deposition at Mt. Mansfield are likely to have considerable ecological effects.     

Measuring Suspended‐Sediment Concentration and Turbidity in the Middle Mississippi and Lower Missouri Rivers Using Landsat Data

The Middle Mississippi River (MMR) and lower Missouri River (MOR) provide critical navigation waterways, ecological habitat, and flood conveyance. They are also directly linked to processes affecting geomorphic and ecological conditions in the lower MR and Delta. For this study, a method was developed to measure suspended‐sediment concentration (SSC) and turbidity along the MMR and the lower MOR using Landsat imagery. Data from nine United States Geological Survey water‐quality monitoring stations were used to create a model‐development dataset and a model‐validation dataset. Concurrent gaging data were identified for available Landsat images to generate the datasets. Surface‐reflectance filters were developed to eliminate images with cirrus cloud coverage or vessel traffic. Using the filtered model‐development dataset, unique reflectance‐SSC and reflectance‐turbidity models were developed for three Landsat sensors: Landsat 8 Operational Land Imager, Landsat 7 Enhanced Thematic Mapper Plus, and Landsat 4–5 Thematic Mapper. Coefficient of determination values for the models ranged from 0.72 to 0.88 for the model‐development dataset. The model‐validation dataset was used to evaluate the performance of the models and had coefficient of determination values ranging from 0.62 to 0.79.