Besprechungen

The Science of Nature -     

Concentrations of mercury in otters (Lutra lutra L.) in Scotland in relation to rainfall

The incidence and severity of visible foliar ozone injury on black cherry (Prunus serotina) seedlings and saplings and tall milkweed (Asclepias exaltata) plants in Great Smoky Mountains National Park (GRSM) were determined by surveys along selected trails conducted during late summer 1992. The incidence (% injured plants) of ozone injury on black cherry was 47% and the percent injured leaves/injured plant and average leaf area injured were 43 and 6%, respectively. Maximum severity (avg. leaf area of the most severely injured leaf) was 12%. Black cherry seedlings and saplings exhibiting ozone injury were taller than non-injured plants. When insect feeding was present, it occurred 96% of the time on plants with ozone injury. Significantly more injury (p=0.007) on black cherry (% injured leaves/injured black cherry) occurred in the NW section of GRSM compared with the other Park sections. Regression analyses showed no relationships in ozone injury with respect to aspect, slope or elevation. Tall milkweed was evaluated twice during August for ozone injury. The incidence (% injured plants) of ozone injury was 74 and 79% for the first and second survey, respectively. The percentage of injured leaves per plant from the first to second survey was 63 to 79%, respectively. Tall milkweeds showing ozone injury were taller than the non-injured plants. The percentage of insect-damaged plants was 50% among plants without ozone injury and 60% among ozone-injured plants. Non-injured tall milkweed had fewer flowers and/or pods than the injured plants. Mean leaf area injured increased over time, and mean maximum leaf area injured increased from 8 to 11% during the same period. Regression analyses showed no differences in ozone injury regarding aspect, slope or elevation. Our findings indicate that ozone injury is widespread throughout the Park on sensitive vegetation.     

Concentrations of some organochlorines in otters (Lutra lutra L.) in Scotland: Implications for populations

The concentrations of polychlorinated biphenyls (PCBs) and residues of organochlorine pesticides (HEOD and DDE) were measured in livers of otters (Lutra lutra) from different areas in Scotland. Whilst HEOD and DDE occurred at very low concentrations only, PCBs were present in high levels in some areas, the highest in Shetland (geom mean 2.05 ppm wet wt), related probably to high levels in sediments in the north-east Atlantic. PCBs were a mixture of congeners in which higher-chlorinated ones predominated, especially 138, 153, 170 and 180, a pattern comparable to that observed in otters from continental Europe. Individual values of total PCB reached levels of over 14 ppm wet weight, even in otters in good condition in thriving populations. Otter population densities were known in some of the study areas; in Shetland numbers increased over the study period, and the density was relatively high also elsewhere in Scotland. There was a strong negative correlation between PCB and body condition, but no correlation between PCB concentration and age of otters (mean age=4.1 years), which suggests that PCBs do not accumulate substantially in otters in the long term. The observations cast doubt on the significance of published 'critical levels' of PCBs to otter populations, based on data obtained from captive mink.     

Foraging and spatial organisation of the European badger,Meles meles L.

Behavioral Ecology and Sociobiology -     

Estimating the functional form for the density dependence from life history data

Two contrasting approaches to the analysis of population dynamics are currently popular: demographic approaches where the associations between demographic rates and statistics summarizing the population dynamics are identified; and time series approaches where the associations between population dynamics, population density, and environmental covariates are investigated. In this paper, we develop an approach to combine these methods and apply it to detailed data from Soay sheep (Ovis aries). We examine how density dependence and climate contribute to fluctuations in population size via age- and sex-specific demographic rates, and how fluctuations in demographic structure influence population dynamics. Density dependence contributes most, followed by climatic variation, age structure fluctuations and interactions between density and climate. We then simplify the density-dependent, stochastic, age-structured demographic model and derive a new phenomenological time series which captures the dynamics better than previously selected functions. The simple method we develop has potential to provide substantial insight into the relative contributions of population and individual-level processes to the dynamics of populations in stochastic environments.