Shifts in species' distribution and abundance in response to climate change have been well documented, but the underpinning processes are still poorly understood. We present the results of a systematic literature review and meta-analysis investigating the frequency and importance of different mechanisms by which climate has impacted natural populations. Most studies were from temperate latitudes of North America and Europe; almost half investigated bird populations. We found significantly greater support for indirect, biotic mechanisms than direct, abiotic mechanisms as mediators of the impact of climate on populations. In addition, biotic effects tended to have greater support than abiotic factors in studies of species from higher trophic levels. For primary consumers, the impact of climate was equally mediated by biotic and abiotic mechanisms, whereas for higher level consumers the mechanisms were most frequently biotic, such as predation or food availability. Biotic mechanisms were more frequently supported in studies that reported a directional trend in climate than in studies with no such climatic change, although sample sizes for this comparison were small. We call for more mechanistic studies of climate change impacts on populations, particularly in tropical systems.

Summary1. Agri-environment schemes (AES) are used extensively across Europe to address biodiversity declines in farmland. In England, Environmental Stewardship (ES) was introduced in 2005 to address the shortcomings of previous schemes, but as for schemes in other countries, assessments to date have revealed little evidence for national-scale biodiversity benefits. 2. Here, we assess the efficacy of ES in driving changes in national farmland bird populations over the period 2002-2010, using BTO ⁄ JNCC ⁄ RSPB Breeding Bird Survey data. We tested for associations between ES management options, grouped into categories reflecting intended biological effects (e.g. stubble), and species' population growth rates, wherever benefits of management might be expected to occur. 3. We found strong evidence for positive effects of management that provides winter food resources (i.e. ES stubble and wild bird seed [WBS] crops) on population growth rates across multiple granivorous species, at three landscape scales. The results for management aiming to provide breeding season benefits (i.e. grassland, field margin and boundary [hedge, ditch] management) showed mixed patterns of positive and negative associations. 4. The results for stubble and WBS provide the first evidence for landscape-scale responses of biodiversity to AES management. The negative relationships identified may also show the importance of management context driving unforeseen predation or competition effects. 5. Synthesis and Applications. This study demonstrates that agri-environment scheme management has the potential to have national-scale effects on avian population growth rates, although our results suggest that some components of the scheme have had little effect on bird populations. Therefore, whilst this study provides the first proof-of-concept for broad-and-shallow scheme impacts on biodiversity, our results underline the importance of targeting towards populationlimiting factors, here winter food resources. A combination of low uptake of key in-field options that provide winter seed and a failure to cover the late-winter period effectively explains the lack of national population responses. Such issues need to be addressed before schemes like Environmental Stewardship will achieve their goals. This study shows the value of feedback from monitoring for informing scheme design, through identifying problems and testing solutions.

Climate data created from historic climate observations are integral to most assessments of potential climate change impacts, and frequently comprise the baseline period used to infer species‐climate relationships. They are often also central to downscaling coarse resolution climate simulations from General Circulation Models (GCMs) to project future climate scenarios at ecologically relevant spatial scales. Uncertainty in these baseline data can be large, particularly where weather observations are sparse and climate dynamics are complex (e.g. over mountainous or coastal regions). Yet, importantly, this uncertainty is almost universally overlooked when assessing potential responses of species to climate change. Here, we assessed the importance of historic baseline climate uncertainty for projections of species' responses to future climate change. We built species distribution models (SDMs) for 895 African bird species of conservation concern, using six different climate baselines. We projected these models to two future periods (2040–2069, 2070–2099), using downscaled climate projections, and calculated species turnover and changes in species‐specific climate suitability. We found that the choice of baseline climate data constituted an important source of uncertainty in projections of both species turnover and species‐specific climate suitability, often comparable with, or more important than, uncertainty arising from the choice of GCM. Importantly, the relative contribution of these factors to projection uncertainty varied spatially. Moreover, when projecting SDMs to sites of biodiversity importance (Important Bird and Biodiversity Areas), these uncertainties altered site‐level impacts, which could affect conservation prioritization. Our results highlight that projections of species' responses to climate change are sensitive to uncertainty in the baseline climatology. We recommend that this should be considered routinely in such analyses.

Aim The conservation value of sites is often based on species richness (SR). However, metrics of phylogenetic diversity (PD) reflect a community's evolutionary potential and reveal the potential for additional conservation value above that based purely on SR. Although PD is typically correlated with SR, localized differences in this relationship have been found in different taxa. Here, we explore geographical variation in global avian PD. We identify where PD is higher or lower than expected (from SR) and explore correlates of those differences, to find communities with high irreplaceability, in terms of the uniqueness of evolutionary histories. Location Global terrestrial.Methods Using comprehensive avian phylogenies and global distributional data for all extant birds, we calculated SR and Faith's PD, a widely applied measure of community PD, across the terrestrial world. We modelled the relationship between avian PD for terrestrial birds and its potential environmental correlates. Analyses were conducted at a global scale and also for individual biogeographical realms. Potential explanatory variables of PD included SR, long-term climate stability, climatic diversity (using altitudinal range as a proxy), habitat diversity and proximity to neighbouring realms.Results We identified areas of high and low relative PD (rPD; PD relative to that expected given SR). Areas of high rPD were associated with deserts and islands, while areas of low rPD were associated with historical glaciation. Our results suggest that rPD is correlated with different environmental variables in different parts of the world.Main conclusions There is geographical variation in avian rPD, much of which can be explained by putative drivers. However, the importance of these drivers shows pronounced regional variation. Moreover, the variation in avian rPD differs substantially from patterns found for mammals and amphibians. We suggest that PD adds additional insights about the irreplaceability of communities to conventional metrics of biodiversity based on SR, and could be usefully included in assessments of site valuation and prioritization.

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A technique for the quantitative measurement of fluid velocities in the range 0–5 cm/sec is described. The technique uses a pH indicator, is applicable in aqueous solutions and permits visualization and measurement of three-dimensional flow fields.

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