La theorie selon laquelle l'apport energetique necessaire a une biocenose limite la capacite de cette biocenose a contenir. Les especes permet d'expliquer 70 a 80% de la variation du nombre d'especes dans des iles extremement diverses par leur surface et leur environnement. On examine, en particulier, certaines donnees sur le nombre d'especes d'Angiospermes et d'oiseaux terrestres ou d'eau douce sur des iles du monde entier

Breeding Birds of Britain and Ireland

Species-energy theory: an extension of species-area theory

Summary

1. Changes in agriculture have been linked to widespread declines in farmland bird populations. One approach to the identification of the causes of observed population changes is to investigate historical changes in national demographic rates.



2. We analysed the British Trust for Ornithology’s nest records database to investigate whether long-term farmland population trends could have been driven by changes in several components of the annual breeding performance of 12 granivorous bird species. Clutch size, brood size, chick : egg ratio and daily nest failure rates were analysed with respect to blocks of years during which abundance (as measured by the Common Birds Census) was increasing, stable or declining. The individual components of breeding performance were combined to provide estimates of the production of fledglings per breeding attempt.



3. Most species’ population declines were not associated with poor breeding performance per attempt. Effects of environmental change on this parameter therefore cannot be a general mechanism behind the major population declines seen.



4. A fall in linnet Carduelis cannabina fledgling production per attempt, driven primarily by increased nest failure rates during the egg period, represented the strongest evidence for an important effect of breeding performance on abundance. This change could have driven the principal population decline (1975–86) for this species.



5. Conversely, at least for the declining turtle dove Streptopelia turtur, skylark Alauda arvensis, tree sparrow Passer montanus, yellowhammer Emberiza citrinella and corn bunting Miliaria calandra, breeding performance per attempt was higher while populations declined.



6. Variation in annual survival and fledgling production per breeding attempt alone could not explain changes in abundance for at least seven species. This may suggest that changes in post-fledging survival rates and/or the number of breeding attempts per year could have been important.



7. Management to improve over-winter survival may be critical in reversing the population trends of most declining species, but such management might still best be directed at the breeding season. Post-fledging survival rates and the number of breeding attempts made within a season are little-studied demographic variables that are high priorities for future research and long-term monitoring.

The importance of variation in the breeding performance of seed‐eating birds in determining their population trends on farmland

Despite increasing interest in urban ecology the factors limiting the colonisation of towns and cities by species from rural areas are poorly understood. This is largely due to the lack of a detailed conceptual framework for this urbanisation process, and of sufficient case studies. Here, we develop such a framework. This draws upon a wide range of ecological and evolutionary theory and the increasing number of studies of how the markedly divergent conditions in urban and rural areas influence the traits of urban populations and the structure of urban assemblages. We illustrate the importance of this framework by compiling a detailed case study of spatial and temporal variation in the urbanisation of the blackbird Turdus merula. Our framework identifies three separate stages in the urbanisation process: (i) arrival, (ii) adjustment, and (iii) spread. The rate of progress through each stage is influenced by environmental factors, especially human attitudes and socio-economic factors that determine the history of urban development and the quality of urban habitats, and by species' ecological and life-history traits. Some traits can positively influence progression through one stage, but delay progression through another. Rigorous assessment of the factors influencing urbanisation should thus ideally pay attention to the different stages. Urbanisation has some similarities to invasion of exotic species, but the two clearly differ. Invasion concerns geographic range expansion that is external to the species' original geographic range, whilst urbanisation typically relates to filling gaps within a species' original range. This process is exemplified by the blackbird which is now one of the commonest urban bird species throughout its Western Palearctic range. This is in stark contrast to the situation 150 years ago when the species was principally confined to forest. Blackbird urbanisation was first recorded in Germany in 1820, yet some European cities still lack urban blackbirds. This is especially so in the east, where urbanisation has spread more slowly than in the west. The timing of blackbird urbanisation exhibits a marked spatial pattern, with latitude and longitude explaining 76% of the variation. This strong spatial pattern contrasts with the weaker spatial pattern in timing of urbanisation exhibited by the woodpigeon Columba palumbus (with location explaining 39% of the variation), and with the very weak spatial pattern in timing of black-billed magpie Pica pica urbanisation (in which location explains 12% of the variation). Strong spatial patterns in timing of urbanisation are more compatible with the leap-frog urbanisation model, in which urban adapted or imprinted birds colonise other towns and cities, than with the independent urbanisation model, in which urban colonisation events occur independently of each other. Spatial patterns in isolation do not, however, confirm one particular model. Factors relating to the arrival and adjustment stages appear particularly likely to have influenced the timing of blackbird urbanisation. Spatial variation in the occurrence of urban populations and the timing of their establishment creates opportunities to assess the factors regulating urbanisation rates, and how the composition of urban assemblages develops as a result. These are major issues for urban ecology.

A conceptual framework for the colonisation of urban areas: the blackbird Turdus merula as a case study.

Changes in the abundance of 28 species of common passerines in scrub and wetland habitats were assessed from changes in annual catch sizes on Constant Effort Sites between 1983 and 1995. At sites where annual catching effort fell below the required level, annual catch sizes were inflated according to experience during years with complete coverage. Changes in abundance were assessed through application of log-linear Poisson regression models, which allow tests for temporal trends in abundance and for differences in trends in abundance between habitat types. For most species, long-term changes in adult catches were similar to changes in territory counts on Common Birds Census plots, suggesting that standardized mist-netting is a reliable method for assessing extensive changes in songbird populations. Changes in catch sizes tended to be more positive and less negative in wetter habitats than in drier habitats. Catches of most insectivorous resident species either increased or remained stable, while catches o...

Long-term changes in the abundance of passerines in Britain and Ireland as measured by constant effort mist-netting

http://academic.oup.com/auk/article-pdf/120/1/245/29688795/auk0245.pdf

Breeding Birds of Britain and Ireland

Citations

Species-energy theory: an extension of species-area theory

The importance of variation in the breeding performance of seed‐eating birds in determining their population trends on farmland

A conceptual framework for the colonisation of urban areas: the blackbird Turdus merula as a case study.

Long-term changes in the abundance of passerines in Britain and Ireland as measured by constant effort mist-netting

The UK SPA network: Its Scope and Content

Related Papers (5)

The Atlas of Breeding Birds in Britain and Ireland

Birds in Europe : their conservation status

The new atlas of breeding birds in Britain and Ireland 1988-1991

The Historical Atlas of Breeding Birds in Britain and Ireland: 1875-1900

An enquiry into the recent breeding status of some of the smaller birds of prey and crows in Britain