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.

No abstract

Aim To explore the potential impacts of climatic change on species with different migratory strategies using Sylvia warblers breeding in Europe as a 'model' species group.Location Europe and Africa.Methods Climate response surfaces and generalized additive models (GAMs) were used to model relationships between species recorded breeding and nonbreeding ranges and recent climate. Species potential future breeding and nonbreeding ranges were simulated for three scenarios of late 21st-century climate. The simulated potential future and present ranges were compared in terms of their relative extent and overlap, as well as their location. The impact of any shifts in potential range location on migration distance were quantified.Results Potential breeding ranges consistently showed a shift northwards, whereas potential non-breeding ranges showed no consistent directional shift, even when trans-Saharan migrants were considered separately from resident/ short-distance or partial migrants. Future potential range extent relative to simulated recent range extent varied considerably among species, although on average range extent increased. Overlap between future and recent simulated range was generally low, averaging < 36% for both breeding and non-breeding ranges. Overlap was consistently less for range-restricted than for widespread species. Migration distance increased generally, by about twice as much in the case of trans-Saharan migrant species than for short-distance migrants. In many cases potential future non-breeding areas were simulated in regions far from the species present non-breeding area, suggesting that new migration strategies and routes may need to be developed in response to climatic change.Main conclusions Migratory species can be expected to suffer greater negative impacts from climatic change than species that are resident or undertake only short-distance or partial migrations. Trans-Saharan migrants face the greatest potential increases in migration distances, whereas range-restricted species are expected to experience major population reductions because of the limited, or in some cases lack of, overlap between their present and potential future ranges.

No abstract

Despite increasing concerns about the vulnerability of species' populations to climate change, there has been little overall synthesis of how individual population responses to variation in climate differ between taxa, with trophic level or geographically. To address this, we extracted data from 132 long-term (greater than or equal to 20 years) studies of population responses to temperature and precipitation covering 236 animal and plant species across terrestrial and freshwater habitats. Our results identify likely geographical differences in the effects of climate change on populations and communities in line with macroecological theory. Temperature tended to have a greater overall impact on populations than precipitation, although the effects of increased precipitation varied strongly with latitude, being most positive at low latitudes. Population responses to increased temperature were generally positive, but did not vary significantly with latitude. Studies reporting significant climatic trends through time tended to show more negative effects of temperature and more positive effects of precipitation upon populations than other studies, indicating climate change has already impacted many populations. Most studies of climate change impacts on biodiversity have focused on temperature and are from middle to high northern latitudes. Our results suggest their findings may be less applicable to low latitudes.