Growth of shredders on leaf litter biofilms: the effect of light intensity

1. The effect of light intensity on the decomposition of poplar (Populus nigra) leaves and growth of the shredders, Asellus aquaticus and Gammarus pulex, was studied in a laboratory experiment. The response was studied along a gradient of six light intensities of 0, 5, 23, 54, 97 and 156 μmol m^?2 s^?1. It was hypothesised that an increase in light intensity would increase growth of shredders, because of an increase of algae (i.e. food quality) in the leaf‐biofilm. 2. Light intensity affected both leaf‐biofilm quality and consumer behaviour and affected several aspects of the decomposition‐consumer interaction. In the absence of invertebrates, leaf mass loss was lower in the dark, while light intensity had no significant effect on mass loss of poplar leaf in the presence of invertebrates. Light intensity affected algal biomass, density and composition, and had a significant positive effect on the growth of both shredders. 3. Our results suggest that algae can be an important component of the nutritional value of the leaf‐biofilm for benthic invertebrates, directly as an additional food source and indirectly through a link with bacteria and/or fungi. 4. The River Continuum Concept mainly emphasises allochthonous inputs to headwater streams and autochthonous production further downstream. Our results suggest that light, by its effect on the biofilms on leaf surfaces, might be a more important factor in headwaters than is usually assumed.     

安氏薮羚的性二型对采食行为的影响(英文)

安氏薮羚(Tragelaphus angasii)是具有性别体二型的动物,其体型大小的差异可能对采食行为和生境选择有显著影响.利用连续行为取样法检测了雌雄个体在生境和植物利用上的差异,记录采食植物种类和采食高度并进行了性别间比较.在每个采食周期末,采用点中心方形样方法(PCQ)对植被进行一次调查,利用判别函数分析鉴别雌雄个体之间在种类和高度上是否存在差异.雌羚在三类生境中花费的采食时间相似,但雄羚表现出对砂地林的偏好.另外,在同一生境内雄羚利用更多的木本种类且采食较高的部位,而雌羚喜欢采食低层草本植物.安氏薮羚雌雄个体在生境内具有食性(采食种类)和空间(生境斑块)上的分离.我们认为这是由性二型引起的性别间营养与能量需求差异和不同繁殖策略造成的,最终使得精食者动物在具有复杂结构空间异质性的生境内表现为空间性别分离     

Evaluating Methods for Counting Cryptic Carnivores

ABSTRACT Numerous techniques have been proposed to estimate carnivore abundance and density, but few have been validated against populations of known size. We used a density estimate established by intensive monitoring of a population of radiotagged leopards (Panthera pardus) with a detection probability of 1.0 to evaluate efficacy of track counts and camera-trap surveys as population estimators. We calculated densities from track counts using 2 methods and compared performance of 10 methods for calculating the effectively sampled area for camera-trapping data. Compared to our reference density (7.33 ± 0.44 leopards/100 km²), camera-trapping generally produced more accurate but less precise estimates than did track counts. The most accurate result (6.97 ± 1.88 leopards/100 km²) came from camera-trap data with a sampled area buffered by a boundary strip representing the mean maximum distance moved by leopards outside the survey area (MMDMOSA) established by telemetry. However, contrary to recent suggestions, the traditional method of using half the mean maximum distance moved from photographic recaptures did not result in gross overestimates of population density (6.56 ± 1.92 leopards/100 km²) but rather displayed the next best performance after MMDMOSA. The only track-count method comparable to reference density employed a capture-recapture framework applied to data when individuals were identified from their tracks (6.45 ± 1.43 leopards/100 km²) but the underlying assumptions of this technique limit more widespread application. Our results demonstrate that if applied correctly, camera-trap surveys represent the best balance of rigor and cost-effectiveness for estimating abundance and density of cryptic carnivore species that can be identified individually.     

Making sense out of Ca2+ signals: their role in regulating stomatal movements

Plant cells maintain high Ca²⁺ concentration gradients between the cytosol and the extracellular matrix, as well as intracellular compartments. During evolution, the regulatory mechanisms, maintaining low cytosolic free Ca²⁺ concentrations, most likely provided the backbone for the development of Ca²⁺‐dependent signalling pathways. In this review, the current understanding of molecular mechanisms involved in Ca²⁺ homeostasis of plants cells is evaluated. The question is addressed to which extent the mechanisms, controlling the cytosolic Ca²⁺ concentration, are linked to Ca²⁺‐based signalling. A large number of environmental stimuli can evoke Ca²⁺ signals, but the Ca²⁺‐induced responses are likely to differ depending on the stimulus applied. Two mechanisms are put forward to explain signal specificity of Ca²⁺‐dependent responses. A signal may evoke a specific Ca²⁺ signature that is recognized by downstream signalling components. Alternatively, Ca²⁺ signals are accompanied by Ca²⁺‐independent signalling events that determine the specificity of the response. The existence of such parallel‐acting pathways explains why guard cell responses to abscisic acid (ABA) can occur in the absence, as well as in the presence, of Ca²⁺ signals. Future research may shed new light on the relation between parallel acting Ca²⁺‐dependent and ‐independent events, and may provide insights in their evolutionary origin.     

Demographic and environmental causes of the decline of rural Song Thrushes Turdus philomelos in lowland Britain

We review current knowledge of demographic mechanisms and environmental factors implicated in the population decline of Song Thrushes Turdus philomelos in rural Britain since the mid-1970s, and present new analyses of regional variation in population changes. Increased mortality during the first year of life (from fledging to recruitment) is highlighted as a potential demographic mechanism having driven the population decline, while Song Thrushes in a rapidly declining farmland population were making too few nesting attempts to sustain local numbers. Breeding Song Thrushes are strongly associated with non-cropped habitats such as woodland edge, field boundaries, gardens and scrub; they make substantial use of grassland, but avoid cereals when foraging. Earthworms constitute a key component of Song Thrush diet and the availability of this prey is strongly influenced by moisture levels in surface soils. Several lines of evidence suggest that dry surface soils during summer are deleterious to the productivity and survival of Song Thrushes, and regional variation in the rates of population change in Britain during 1970–86 was negatively correlated with the extent of under-field drainage on farmland (the main function of which is to promote the drying of surface soils). Increasing dryness of agricultural soils and the loss of grassland from eastern arable counties have probably both contributed to the declines of rural Song Thrushes in Britain. Loss of hedgerows and scrub, and the degradation of woodland may also have contributed to population declines but the role of predators remains unclear. Recovery of rural Song Thrush populations requires challenging new policy initiatives that should aim to restore nesting cover (scrub and woodland understorey), grazed grassland in arable-dominated areas and damper soils in summer.     

Perizin, an acaricide to combat the mite Varroa jacobsoni: its distribution in and influence on the honeybee Apis mellifera

Abstract. The distribution of coumaphos (the active component of perizin), fed to individual honeybees, in the honey stomach, haemolymph, midgut and rectum was studied over time. Concurrently, we investigated changes occurring in the haemolymph volume due to the ingestion of perizin, and we examined the influence of a Nosema apis infection on the survival of bees that had been fed perizin. The maximum amount of coumaphos in the haemolymph was found 4h after ingestion, but it was only 2–3% of the total amount recovered. After 15 min 55% of the total amount of the coumaphos recovered was in the honey stomach and available for distribution within the colony by trophallaxis, while 45% had already passed the proventriculus. Ultimately the coumaphos accumulated in the rectum. The volume of the haemolymph significantly increased in bees which were fed perizin compared with bees which were fed syrup and with non-fed bees. The lethal dose of coumaphos to 3-day-old bees was three times higher than the lethal dose for 18- and 1-day-old bees. The number of Nosema apis spores in the alimentary canal was not correlated with the survival of the bees that were fed perizin. It is concluded that coumaphos can act as a systemic agent and can be distributed to other individuals in a colony through trophallaxis, but these effects are limited to a maximum period of 12h after ingestion.     

Conservation management of Lapwing Vanellus vanellus on lowland arable farmland in the UK

Lapwing Vanellus vanellus is known to be declining throughout much of its UK breeding range. The ecological requirements of the species are well known and a variety of mechanisms exist which can be implemented to help recovery. Arable options within agri-environment schemes can be used to provide breeding habitat throughout the species' UK range, and targeted recovery projects have been shown to have the potential to deliver increases in breeding pairs at the local level. The farming community need to be made aware of the requirements of Lapwing if agriculture and conservation needs are to be integrated.     

Absence of effects of predator control on nesting success of Northern Lapwings Vanellus vanellus: implications for conservation

The control of generalist predator populations is increasingly adopted as a management tool to combat declines in ground‐nesting bird populations. However, compensatory predation by uncontrolled species frequently occurs, so determining the relative impacts of different predatory species, and hence the relative benefits of their control, can be difficult. Islands, with their reduced faunas, provide natural experimental units for investigating specific predator–prey interactions in detail. We studied Northern Lapwing Vanellus vanellus breeding success on an island where feral Ferrets Mustela furo and Hooded Crows Corvus cornix were subjected to trial control regimes over 2 years. In both years, Lapwing hatching success was >80%, with neither Ferret nor Crow control selected as important predictors. Fledging rates in both years were 0.7 young per pair, despite highly effective predator removal, although Crow control potentially resulted in compensatory predation by Common Ravens C. corax. Neither mustelid nor corvid control produced significant immediate benefits for Lapwings. This suggests that mesopredator release of mustelids in mainland situations is unlikely to be a consistent threat to Lapwing, and provides further evidence that declines in this species are unlikely to be tackled successfully through predator management alone.     

Optimal patch use by foraging workers of Lasius fuliginosus, L. niger and Myrmica ruginodis

1. The predictions of the marginal value theorem, that foragers should spend more time in both better quality patches and more distant patches, were tested with three European ant species, Lasius fuliginosus , L. niger and Myrmica ruginodis.
2. As the quality of patches of sucrose solution increased, the feeding time of foraging workers of L. niger also increased.
3. At constant patch quality, feeding times of L. niger and M. ruginodis increased with increasing distance of the patch from the nest entrance.
4. Foraging workers of L. fuliginosus showed a similar response to patch distance in the field, but feeding times were also significantly influenced by air temperature, decreasing as temperature increased.
5. These results show qualitative agreement with the predictions of the marginal value theorem.