Documenting lemming population change in the Arctic: Can we detect trends?

Lemmings are a key component of tundra food webs and changes in their dynamics can affect the whole ecosystem. We present a comprehensive overview of lemming monitoring and research activities, and assess recent trends in lemming abundance across the circumpolar Arctic. Since 2000, lemmings have been monitored at 49 sites of which 38 are still active. The sites were not evenly distributed with notably Russia and high Arctic Canada underrepresented. Abundance was monitored at all sites, but methods and levels of precision varied greatly. Other important attributes such as health, genetic diversity and potential drivers of population change, were often not monitored. There was no evidence that lemming populations were decreasing in general, although a negative trend was detected for low arctic populations sympatric with voles. To keep the pace of arctic change, we recommend maintaining long-term programmes while harmonizing methods, improving spatial coverage and integrating an ecosystem perspective.     

Landscape Equivalency Analysis: Methodology for Estimating Spatially Explicit Biodiversity Credits

We propose a biodiversity credit system for trading endangered species habitat designed to minimize and reverse the negative effects of habitat loss and fragmentation, the leading cause of species endangerment in the United States. Given the increasing demand for land, approaches that explicitly balance economic goals against conservation goals are required. The Endangered Species Act balances these conflicts based on the cost to replace habitat. Conservation banking is a means to manage this balance, and we argue for its use to mitigate the effects of habitat fragmentation. Mitigating the effects of land development on biodiversity requires decisions that recognize regional ecological effects resulting from local economic decisions. We propose Landscape Equivalency Analysis (LEA), a landscape-scale approach similar to HEA, as an accounting system to calculate conservation banking credits so that habitat trades do not exacerbate regional ecological effects of local decisions. Credits purchased by public agencies or NGOs for purposes other than mitigating a take create a net investment in natural capital leading to habitat defragmentation. Credits calculated by LEA use metapopulation genetic theory to estimate sustainability criteria against which all trades are judged. The approach is rooted in well-accepted ecological, evolutionary, and economic theory, which helps compensate for the degree of uncertainty regarding the effects of habitat loss and fragmentation on endangered species. LEA requires application of greater scientific rigor than typically applied to endangered species management on private lands but provides an objective, conceptually sound basis for achieving the often conflicting goals of economic efficiency and long-term ecological sustainability.     

Synergistic interactions between chemical alarm cues and the presence of conspecific and heterospecific fish shoals

Chemical and visual sources of information are used by aquatic prey during risk assessment. Here, we test the behavioral response of littoral prey fish to combinations of chemical alarm cues (skin extract) and the visual presence of a fish shoal. We scented minnow traps with either alarm cues or water (control) placed inside the trap, a jar that contained either a fish shoal or nothing (control), and recorded the number and species of fish captured. We predicted that chemical alarm cues would reduce the number of fish captured and that a fish shoal would increase the number of fish captured. The predicted effect of chemical and visual cues combined depended on the nature of the interaction. We found that the lowest catch rate was for the combination of alarm cue + no shoal, but the highest catch rate occurred for the combination of alarm cue + shoal. Fish shoal + water had the second highest catch rate and no shoal + water had the second lowest catch rate. We conclude that chemical alarm cues induce area avoidance in the absence of a shoal, but a strong behavioral proclivity to increase shoal cohesion in the presence of a shoal. The presence of a shoal in the traps induced alarmed fish to shoal with them and thus, enter the traps. This occurred even though traps were the source of the alarm cue.Communicated by A. Mathis     

Cation leaching in a sandy forest soil treated with acidified rain

Contribution from Fourth World Wilderness Congress-Acid Rain Symposium, Denver (Estes Park), Colorado, September 11–18, 1987.     

Patterns in reproductive dynamics of burrowing ghost shrimp Trypaea australiensis from small to intermediate scales

Many studies have examined latitudinal differences in reproduction of marine invertebrates, but few have measured variation at small to intermediate scales (kilometres to hundreds of kilometres), which may confound comparisons across broader geographic regions. Here, we examined variation in the reproductive biology of a little-studied species of burrowing ghost shrimp (Trypaea australiensis) at spatial scales ranging from km (between sites within estuaries) to 100s of km (among estuaries), over a 2-year period in south-eastern Australia. Sex ratios of populations were consistently biased towards females through time and space. Although reproduction started in summer months across all spatial scales, there was a pattern of earlier spawning from southern to northern estuaries. Integration of results from previous studies of T. australiensis supported a similar pattern of earlier breeding from high to low latitudes. Fecundity of shrimp increased linearly with female size, but the relationship varied inconsistently across the different spatial scales. Similarly, sizes at maturity varied from small to intermediate scales and observed patterns were not consistent with general predictions e.g. shrimp were smaller and ovigerous at smaller sizes at sites in the southern-most estuary, compared to estuaries further north. We found no differences in the sizes of embryos across the different spatial scales, but confirm that T. australiensis employs a strategy of high fecundity and small embryo size compared to other thalassinidean shrimp. Our results suggest that factors at smaller scales (e.g. food availability) may be important in affecting reproductive dynamics of T. australiensis, but further research is needed in testing hypotheses about patterns observed here. A lack of similar studies on other marine organisms remains an impediment to understanding life-history strategies and the sustainable management and conservation of populations.     

Swidden agriculture in a protected area: the Matsigenka native communities of Manu National Park, Peru

In this study, we investigate whether traditional swidden agriculture on nutrient-poor tropical soils can sustainably support a growing indigenous population within Manu National Park, Peru. Based on interviews with 50 Matsigenka farmers, as well as GPS mapping and field visits, we established the location and size of all 124 swidden gardens cultivated in 2000 and 2001. Using a GIS-based soil map of Manu Park, we identify the total extent of potential arable land (1) throughout the park zones currently available for Matsigenka habitation, and (2) within the vicinity of the two study communities. Taking into account current per capita garden size, cultivation and fallow practices, we calculate the maximum human carrying capacity of swidden agriculture for (1) all available park zones and (2) the immediate vicinity of the two current communities. Even given the second, highly limited scenario, the sustainable human carrying capacity is estimated to be 2,138 individuals, which is far higher than the current population of about 420 people. Thus, arable land does not appear to be a limiting factor for the growth of the indigenous population in Manu Park at the current time. Other possible limiting factors for population growth are identified and discussed. We conclude that a conservation policy of population stabilization around the current settlements is viable in that it will not result in reduced resource availability over the next few decades, and that the challenge is to identify and mitigate the forces causing population fissioning and spread. Readers should send their comments on this paper to BhaskarNath@aol.com within 3 months of publication of this issue.     

Identification of polychlorinated planar chemicals in fishes from major watersheds near the Great Lakes

Fish from 18 major watersheds near the Great Lakes were collected in 1979, 1980, or 1981, and analyzed by gas chromatography-mass spectrometry for polychlorinated planar organic chemical residues. Isomers of 36 different chemicals were identified by mass spectral data but not quantitated. The list includes isomers of chlorinated dibenzo-p-dioxins and dibenzofurans.     

Loss of PM2.5 nitrate from filter samples in central California

Evaporative loss of particulate matter (with aerodynamic diameter < 2.5 microm, [PM2.5]) ammonium nitrate from quartz-fiber filters during aerosol sampling was evaluated from December 3, 1999, through February 3, 2001, at two urban (Fresno and Bakersfield) and three nonurban (Bethel Island, Sierra Nevada Foothills, and Angiola) sites in central California. Compared with total particulate nitrate, evaporative nitrate losses ranged from < 10% during cold months to > 80% during warm months. In agreement with theory, evaporative loss from quartz-fiber filters in nitric acid denuded samplers is controlled by the ambient nitric acid-to-particulate nitrate ratio, which is determined mainly by ambient temperature. Accurate estimation of nitrate volatilization requires a detailed thermodynamic model and comprehensive chemical measurements. For the 14-month average of PM2.5 acquired on Teflon-membrane filters, measured PM2.5 mass was 8-16% lower than actual PM2.5 mass owing to nitrate volatilization. For 24-hr samples, measured PM2.5 was as much as 32-44% lower than actual PM2.5 at three California Central Valley locations.