Mechanisms underpinning climatic impacts on natural populations: altered species interactions are more important than direct effects

Abstract

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.

Geographical variation in species' population responses to changes in temperature and precipitation

“…A literature search was conducted using ISI Web of Knowledge on 14 November 2011 for the purpose of identifying the full range of studies with potential to identify mechanisms of climate change impacts upon natural populations [16]. For this reason, the search used key words to identify studies relating demographic changes (Population*, Demograph*, Reproduct*, Decline*, Abundance, Breeding, Survival, Mortality, Fecundity, Density, Productivity) to potential climate change impacts (Climat*, Global warming, Sea-level rise, Elevated CO 2 , Elevated carbon dioxide, Global environmental change) that clearly related changes to specific environmental drivers (Temperature*, Fire*, Glaci*, Snow pack, O 2 , Oxygen, Flood*, Drought*, Ground-water levels, Precipitation, Thermal stratification, Sea-level rise, Cloud cover, Humidity, CO 2 or Carbon dioxide, UV, Ultra violet, Water current, Salinity, Nutrient, Erosi*, Wind, Rainfall, Storm, Hurricane, Cyclone, Typhoon).…”

“…Following [16], these were used to calculate an effect score (e) amenable to empirical modelling using standard approaches:…”

“…Recent evidence has highlighted that climate change will directly drive population change and extinction primarily through altered species interactions [12,16]. However, the precise climatic drivers underpinning such relationships remain unclear and may differ between leading and trailing range margins [17].…”

“…This has, to our knowledge, never been tested. In addition, we test whether population responses to climate variables differ between taxa, in order to test their generality, and by trophic level, to assess the extent to which changes in climate may have different impacts on different trophic levels, as a much predicted sign of potential ecosystem disruption in response to climate change [16,22]. This is achieved through a systematic review of the literature documenting variation in demographic responses (specifically population trends, survival and birth rates) of terrestrial and freshwater vertebrates, invertebrates and plants to climatic variation, followed by meta-analysis of the extracted data.…”

Forest conversion can help to mitigate impacts of climate change on common forest birds

“…We did not address interactions between climate change and land use, which may have important consequences (Oliver and Morecroft 2014), e.g., more frequent or more intense disturbance, such as drought and windthrow, which can result in an increase of mass insect outbreaks and therefore a change in food availability. Climate change can also directly influence plant species composition and even the climax vegetation type expected in any given region, which can affect habitat quality, food resources, interspecific competition, or predator populations (Ockendon et al 2014). Furthermore, we did not consider non-native tree species, especially Douglas fir Pseudotsuga menziesii which in some regions has become an attractive alternative as a commercial tree species (Beinhofer and Knoke 2010) and is predicted to be increasingly cultivated in future Central European forests (Curt et al 2001).…”