Annual and seasonal changes in the distribution of waders and shelduck in the Severn Estuary A contribution to the Severn barrage prefeasibility study

SIGLELD:8253.977(STP--44). / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Multivariate analyses of factors affecting the distribution and abundance of shorebirds in the Severn Estuary A contribution to the Severn barrage prefeasibility study

SIGLELD:8253.977(STP--45). / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Life-history strategies in parasitoid wasps: a comparative analysis of 'ovigeny'

1. Ecologists concerned with life-history strategies of parasitoid wasps have recently focused on interspecific variation in the fraction of the maximum potential lifetime egg complement that is mature when the female emerges into the environment. Species that have all of this complement mature upon emergence are termed 'pro-ovigenic', while those that do not are termed 'synovigenic'. We document and quantify the diversity of egg maturation patterns among 638 species of parasitoid wasps from 28 families. 2. We test a series of hypotheses concerning variation in 'ovigeny' and likely life- history correlates by devising a quantitative index - the proportion of the maximum potential lifetime complement that is mature upon female emergence. 3. Synovigeny, which we define as emerging with at least some immature eggs, was found to be by far the predominant egg maturation pattern (98.12% of species). Even allowing for some taxonomic bias in our sample of species, pro-ovigeny is rare among parasitoid wasps. 4. There is strong evidence for a predicted continuum in ovigeny index among parasitoid wasps, from pro-ovigenic (ovigeny index = 1) to extremely synovigenic species (ovigeny index = 0). 5. As predicted, synovigenic species are longer-lived than pro- ovigenic ones, and ovigeny index and life span are negatively correlated across parasitoid taxa, suggesting a life span cost of concentrating reproductive effort early in adult life. 6. There is equivocal evidence that host feeding (i.e, consumption of host haemolymph and/or tissues by adult wasps) is confined to synovigenic parasitoid wasps. It is also not certain from our analyses whether host feeding is associated with a relatively low ovigeny index. 7. As predicted, egg resorption capability is concentrated among producers of yolk-rich eggs. Also, the hypothesis that it is associated with a tendency towards a low ovigeny index is supported. Parasitoid species that produce yolk-rich eggs also exhibit a lower ovigeny index than species that produce yolk-deficient eggs. 8. Ovigeny index appears to be linked to parasitoid development mode (koinobiosis-idiobiosis). 9. We conclude that 'ovigeny' is a concept applicable to insects generally. [KEYWORDS: feeding strategies; pro-ovigeny; synovigeny; timing of reproduction Leptopilina-boulardi hymenoptera; host-feeding strategies; egg limitation; reproductive-biology; clutch size; independent contrasts; functional-response; asobara-tabida; drosophila-melanogaster; evolutionary argument

From Abbott Thayer to the present day: what have we learned about the function of countershading?

Of the many visual characteristics of animals, countershading (darker pigmentation on those surfaces exposed to the most lighting) is one of the most common, and paradoxically one of the least well understood. Countershading has been hypothesized to reduce the detectability of prey to visually hunting predators, and while the function of a countershaded colour pattern was proposed over 100 years ago, the field has progressed slowly; convincing evidence for the protective effects of countershading has only recently emerged. Several mechanisms have been invoked for the concealing function of countershading and are discussed in this review, but the actual mechanisms by which countershading functions to reduce attacks by predators lack firm empirical testing. While there is some subjective evidence that countershaded animals match the background on which they rest, no quantitative measure of background matching has been published for countershaded animals; I now present the first such results. Most studies also fail to consider plausible alternative explanations for the colour pattern, such as protection from UV or abrasion, and thermoregulation. This paper examines the evidence to support each of these possible explanations for countershading and discusses the need for future empirical work

How blue are British tits? Sex, age and environmental effects

Capsule The blue colour of the coverts and crowns of Blue Tits Cyanistes caeruleus and Great Tits Parus major is influenced by sex, age and environmental factors. Aims To quantify the blueness of two species of tits breeding in different habitats in Britain. Methods By manipulating daylength in the laboratory, adult Blue Tits were induced to moult at fast and slow speeds. When they had finished, the blue colour of their wing coverts and crowns was measured (in the range visible to human observers), and compared with the colour of birds caught in the field. Results As well as highly significant sex and age differences in colour, Blue Tits were 26% bluer in 1998 than 2000, and male Great Tits were 15% less blue in small woods than in large woods in our study population in East Anglia, England. Both species became more saturated with blue up to the age of three years. British Cy. c. obscurus were darker blue than Cy. c. caeruleus of Continental Europe . Conclusions There are significant environmental influences on the blueness of British tits in addition to the well-known age and sex effects

To graze or not to graze? Sheep, voles, forestry and nature conservation in the British uplands

The British uplands are internationally important for their unique plant and bird communities. They have considerable economic, nature conservation, landscape, aesthetic and tourism-related value and as a result are under a variety of different pressures, most notably from sheep farming, shooting interests, commercial forestry and conservation interests. In order to optimize biodiversity in the uplands, the challenge is to find how to balance the different land-use pressures. One key upland species that is potentially affected by livestock grazing, and is of considerable interest to both foresters and nature conservationists, is the field vole Microtus agrestis. Relaxation of livestock grazing can result in an increase in vole numbers. This in turn could have both positive and negative implications for biodiversity as (i) field voles are a major source of prey for other species and (ii) they are a cause of damage to newly planted trees and potentially damaging in areas of native woodland regeneration. A replicated, randomized block experiment, consisting of six replicates of four livestock grazing treatments, was established in 2003 (with baseline data collected in 2002). This enabled us to examine the effects of livestock grazing on field vole abundance. We have demonstrated experimentally for the first time that livestock grazing pressure affects the abundance of field voles (as measured by a vole sign index) in the uplands. In the first year of the experiment, immediate treatment effects were detectable, with a lower abundance of voles in the conventionally grazed treatment compared with those in the ungrazed treatment, and with intermediate vole abundances in the lightly grazed treatments. The significant treatment effects became more apparent in 2004, with a higher abundance of voles in the extensively grazed mixed treatment (i.e. sheep and cattle) than in the extensively grazed treatment that contained only sheep. Synthesis and applications. In order to maximize biodiversity in the uplands, our results suggest that low intensity livestock grazing, used in a novel ways, could be a useful management tool to reduce vole abundance (and hence subsequent tree damage) compared with excluding livestock from young plantations completely. Furthermore, vole abundance would be higher at low grazing intensity compared with conventional stocking rates, thus still providing food for raptors and other vole-eating vertebrates. Indeed, low-intensity sheep and mixed livestock grazing might improve prey availability as a direct consequence of increased heterogeneity in vegetation structure. Our results suggest that it may be possible to maintain the open character of moorland habitats, and benefit key upland species generally, by reducing sheep grazing pressure and introducing low-intensity mixed livestock grazing throughout the uplands