A refutation of Karasek's demand – discretion model of occupational stress with a range of dependent measures

Karasek's (1979) demand–discretion model of occupational stress has been highly influential but has been criticized as confounding social class variables (Payne and Fletcher, 1983), ignoring the curvilinearity of relationships (Warr, 1991), and because it has inconsistently predicted heart disease (Ganster and Fusilier, 1989). The present study examines the ability of the model to predict raised blood pressure (a risk factor in the development of CHD), anxiety, depression, job and life satisfaction, in a large heterogeneous sample of over 3000 people. It examines the predictability of the model for men and women, taking occupational classification (manual and non-manual workers) into account, to allow some control over social class confounding. It also examines nonlinear relationships in the data. The study showed that demands and discretion do separately predict psychological strain, job and life satisfaction, though they account for a very small percentage of the variance. There was no evidence of interactive effects which are central to the model. Where the model was able to predict blood pressure, relationships were consistently in the opposite direction to that hypothesized. There was also little evidence of curvilinear relationships. Interpersonal support was found to add significantly to the predictability of the dependent variables. The findings cast doubt on Karasek's model and suggest that emphasis should be shifted to those models which are more encompassing of support factors.     

Mutualism between a leguminous tree and large African monkeys as pollinators

Observations of a monkey community in a forest of the Zaire Basin show that four species intensively lick the nectar of Daniellia pynaertii (Caesalpinoideae) for 5 months of the year; nectar makes up a mean of 20% and a maximum of 50% of monthly plant feeding records (Fig. 3). Such intensive nectar-feeding by monkeys of up to 8 kg body weight probably developed in these basically frugivorous primates as an alternative strategy to cope with a shortage of fleshy fruits. This would have been possible due to the high density of the plant species, the synchrony and abundance of its flowering (Fig. 2), and the large size of the nectar drop and its nutritional value. Patterns of monkey movements among Daniellia trees show that one flowering tree may receive up to 10 species visits and 30 individual visits per day, for a total of up to 141 min. (Table 1). A monkey troop can visit 12 trees in succession over less than 3 h (Fig. 4). This suggests that monkeys are able to promote pollen transfer both among flowers of the same tree and between conspecific trees. The individual tree fruiting index is positively correlated with its flowering index and with the amount of visits by monkeys, indicating at least that monkeys do not inhibit the reproductive ability of flowers (Fig. 5). These results suggest that monkeys can be considered as a guild of effective pollinators. Long-term coevolution between the plant and its present-day pollinators seems unlikely, and we suggest that monkeys replaced other pollinators, such as Lepidoptera. This hypothesis is supported by the fact that tubular flowers adapted for pollination by Lepidoptera are found in affine species of the same genus and of affine genera, the latter being known to be pollinated by these insects. In contrast, D. pynaertii flowers typically meet the pollination syndrome currently defined for attracting large mammals: notably conspicuousness and open morphology of the flowers, nectar colour and abundance. These characteristics suggest that coadaptation between monkeys and plant or at least one-sided adaptation has operated. Correspondence to: A. Gautier-Hion     

Isolation of Atlantic cod (<Emphasis Type="Italic">Gadus morhua</Emphasis>) nursery areas

This study examines the degree of isolation among 0-group Atlantic cod in a region where a number of resident adult congregations have been found. The location of key nursery areas in Scottish coastal waters was identified from trawl surveys of settled 0-group cod around the Scottish coast. Segregation among four of these key areas; within the Clyde, Shetland Isles, Moray Firth and Buchan was investigated using otolith elemental composition. Isotope concentrations in the otoliths of cod were analysed by solution-based inductively coupled plasma mass spectrometry of the whole otolith. Discriminant analyses showed a clear separation between nursery areas based on the concentrations of three elements (manganese, barium and magnesium). The concentration of these elements was not affected by the age or size of individuals. Classification accuracy exceeded 90% for all four sites. Evidence of temporal persistence in the relative spatial differences in elemental concentrations between two sites for 2 year-classes was found. The results suggest limited exchange between sites during some period of the early life history. The significance of this limited exchange is discussed in relation to recent evidence for adult fidelity and the utility of closed areas for protecting nursery grounds.     

Compensating for the costs of polygyny in hen harriers Circus cyaneus

In polygynous species, the adults are faced with a dilemma during chick rearing. Males must decide how to distribute food between their females and food allocation patterns are often highly unequal. In turn, the females that receive less food from males have to decide how much time to invest in additional hunting. If they spend more time hunting, then they leave their young exposed to weather and predators. However, if they stay at the nest, they increase the risk of their chicks starving. One way that birds may compensate for reduced provisioning is by increasing the size of prey caught. We tested this hypothesis by comparing prey deliveries to nests of hen harriers, Circus cyaneus, with females of different breeding status. As expected, male harriers delivered less food items to the nests of polygynous females, and especially their secondary, or β females. However, both sexes were able to compensate by delivering larger items and there was no difference in the overall mass of food delivered to nests. Moreover, females spent a similar amount of time at the nest, irrespective of status, and there were no overall differences in breeding success. Our results show that polygynous female harriers can compensate for the costs of polygyny, but we suggest that their ability to do so will vary according to the abundance of both large prey and predators.     

Unpacking multi-trophic herbivore-grass-endophyte interactions: feedbacks across different scales in vegetation responses to Soay sheep herbivory

Grazing can induce changes in both plant productivity and nutritional quality, which may subsequently influence herbivore carrying capacity. While research on Soay sheep (Ovis aries L.) dynamics on Hirta Island in the St. Kilda archipelago has elucidated the complexity of population drivers, including parasites, the role of herbivore-generated feedbacks as an intrinsic regulating factor remains unclear. The sheep lack large predators and every 3–9 years undergo population crashes (overcompensatory mortality). We investigated the effects of grazing on (1) sward productivity and (2) quality (toxicity) of the primary forage species, red fescue (Festuca rubra L.), which is highly infected by an alkaloid-synthesizing fungal endophyte. Grazing had a negative impact on both forage quantity and quality. At higher sheep densities, impacts on sward growth were magnified, resulting in a nonlinear relationship with plant productivity. Simultaneously, endophyte hyphal load (and by inference, toxicity) peaked close to the time of a crash. A greenhouse experiment showed that alkaloid concentration in F. rubra increased in response to artificial defoliation. We conclude that at high sheep densities, grazing-mediated reductions in productivity, together with sustained alkaloid production, are likely to influence sheep dynamics. Future research should consider the interactive effects of forage toxicity, quantity, and nutritional content.     

A framework for adapting survey design through time for wildlife population assessment

Sampling strategies for monitoring the status and trends in wildlife populations are often determined before the first survey is undertaken. However, there may be little information about the distribution of the population and so the sample design may be inefficient. Through time, as data are collected, more information about the distribution of animals in the survey region is obtained but it can be difficult to incorporate this information in the survey design. This paper introduces a framework for monitoring motile wildlife populations within which the design of future surveys can be adapted using data from past surveys whilst ensuring consistency in design-based estimates of status and trends through time. In each survey, part of the sample is selected from the previous survey sample using simple random sampling. The rest is selected with inclusion probability proportional to predicted abundance. Abundance is predicted using a model constructed from previous survey data and covariates for the whole survey region. Unbiased design-based estimators of status and trends and their variances are derived from two-phase sampling theory. Simulations over the short and long-term indicate that in general more precise estimates of status and trends are obtained using this mixed strategy than a strategy in which all of the sample is retained or all selected with probability proportional to predicted abundance. Furthermore the mixed strategy is robust to poor predictions of abundance. Estimates of status are more precise than those obtained from a rotating panel design.     

Investigating the Uncertainties in the Simple Mass Balance Equation for Acidity Critical Loads for Terrestrial Ecosystems in the United Kingdom

The Simple Mass Balance (SMB)equation has been developed and used as one ofthe principal methods for calculating criticalloads of acidity for forest ecosystems. Criticalloads have formed the basis for informing policyrelated to the control and abatement of emissionsof acidifying pollutants. The SMB equationrelies on a variety of assumptions and dataderived from a variety of sources. Each of thesecomponent constituents has a potential source oferror depending on the method(s) used for theirderivation and the value(s) assigned. The resultis the possibility of generating a range ofcritical load values for a single ecosystem. This paper summarises the SMB equation, examinesthe uncertainties in deriving input values andreviews other works on the key assumptions.     

Climate change impacts on rainfed cropping production systems in the tropics and the case of smallholder farms in North-west Cambodia

The consequences of climate change on smallholder farms are locally specific and difficult to quantify because of variations in farming systems, complexity of agricultural and non-agricultural livelihood activities and climate-related vulnerability. One way to better understand the issues is to learn from the experiences of farmers themselves. Thus, this study aimed to better understand rainfed upland cropping systems in NW Cambodia and to identify practical, social and economic constraints to adoption of known climate adaptation options applicable to local agro-ecosystems. The study also sought to document the climate change perceptions and adaptation options employed by farmers to mitigate the climate risks. A household survey was conducted in the districts of Sala Krau and Samlout in North-west Cambodia in 2013 where 390 representatives of households were randomly selected for interviews, group discussions and field observations. The majority of respondents perceived that changes had occurred in the rainfall pattern such as a later start to the monsoon season, decreasing annual rainfall, increasing frequencies of drought and dry spells, and warmer temperatures. Farmers reported reductions in crop yields of 16–27 % over the five-year period of 2008–2012. However, these reductions were not evident in provincial data for the same period. Farmers claimed climate impacts resulted in significant yield reductions, but they appear not to have an effective strategy to adapt to the changes in climate. Further regional research is required to refine climate change adaptation strategies for rainfed upland cropping systems in Cambodia.     

The consequences of poaching and anthropogenic change for forest elephants

Poaching has devastated forest elephant populations (Loxodonta cyclotis), and their habitat is dramatically changing. The long‐term effects of poaching and other anthropogenic threats have been well studied in savannah elephants (Loxodonta africana), but the impacts of these changes for Central Africa's forest elephants have not been discussed. We examined potential repercussions of these threats and the related consequences for forest elephants in Central Africa by summarizing the lessons learned from savannah elephants and small forest elephant populations in West Africa. Forest elephant social organization is less known than the social organization of savannah elephants, but the close evolutionary history of these species suggests that they will respond to anthropogenic threats in broadly similar ways. The loss of older, experienced individuals in an elephant population disrupts ecological, social, and population parameters. Severe reduction of elephant abundance within Central Africa's forests can alter plant communities and ecosystem functions. Poaching, habitat alterations, and human population increase are probably compressing forest elephants into protected areas and increasing human–elephant conflict, which negatively affects their conservation. We encourage conservationists to look beyond documenting forest elephant population decline and address the causes of these declines when developing conversation strategies. We suggest assessing the effectiveness of the existing protected‐area networks for landscape connectivity in light of current industrial and infrastructure development. Longitudinal assessments of the effects of landscape changes on forest elephant sociality and behavior are also needed. Finally, lessons learned from West African elephant population loss and habitat fragmentation should be used to inform strategies for land‐use planning and managing human–elephant interactions.