Disentangling the effects of multiple environmental drivers on population changes within communities

Abstract

The effects of different environmental drivers on the changes in species' population abundances can be difficult to disentangle as they often act simultaneously. Researchers have built statistical models that include environmental variables (such as annual temperature) or species attributes (such as a species' temperature preference), which are assumed to detect the impacts of specific drivers (such as climate change). However, these approaches are often applied separately or, if combined, not explicitly compared. We show the complementary insights gained by applying both these approaches to a community dataset on Danish terrestrial birds. We use our analysis to compare the relative importance of climate change and agricultural land-use change for the abundance changes within the community between 1983 and 2013. Population models were fitted to the community data of species' annual abundances with predictors comprising: species attributes (species' temperature and habitat preferences), environmental variables (climatic and agricultural land-use change variables) or both. Relationships between species' abundances and environmental variables were used to identify the drivers associated with average abundance changes of species in the community. Relationships between species' abundances and their attributes were used to understand the drivers causing interspecific variation in abundance changes. Warmer winters were positively associated with community-level abundances, and warm-adapted species had more positive abundance changes than cold-adapted ones. Agricultural land-use area was negatively associated with community-level abundances, and birds using a high proportion of meadow and habitat specialists had more negative abundance changes than birds using other habitats and habitat generalists. Effect sizes of environmental variables were larger for agricultural land-use change while those of species attributes were larger for climate change. The environmental data approach suggested that agricultural land-use change has decreased the average abundances of species in the community, affecting total community size while the species attribute-based approach suggested that climate change has caused variation in abundance among species, affecting community composition. Environmental variables and species attributes that are hypothesized to link to specific drivers can be used together to provide complementary information on the impacts of different drivers on communities.

Spatial gradients in country‐level population trends of European birds

“…By that means, we can infer how species' populations respond to respective environmental factors (Webb, Hoeting, Ames, Pyne, & Poff, ). For instance, population decline of forest species may indicate deterioration of forest habitat and population increase of resident species may reflect weakening effect of harsh winter weather on their population limitation due to warming climate (Bowler, Heldbjerg, Fox, O'Hara, & Böhning‐Gaese, ).…”

The power to detect regional declines in common bird populations using continental monitoring data

“…This is particularly worrying as it reveals the broad‐scale loss of capacity in many landscapes to support abundance (Bowler et al. ) and likely presages the breakdown of important ecosystem processes and services (Gaston , Winfree et al. , Baker et al.…”

“…Alongside threats to rare and range-restricted species, long-term population monitoring has identified large declines in the abundance of many common species (Inger et al 2015). This is particularly worrying as it reveals the broad-scale loss of capacity in many landscapes to support abundance (Bowler et al 2018) and likely presages the breakdown of important ecosystem processes and services (Gaston 2011, Winfree et al 2015, Baker et al 2019. Information on these biodiversity trends is vital for evaluating the state of biodiversity and for directing conservation resources in an attempt to slow declines (Tittensor et al 2014, Navarro et al 2017.…”

Habitat selection by the European hare in arable landscapes: The importance of small‐scale habitat structure for conservation

“…Since the beginning of the 20th century, agriculture intensified steadily in Europe, leading to increased yields due to larger field sizes, the use of agro-chemicals, and the improved efficiency of machinery (Marshall & Moonen, 2002;O'Brien & De La Escosura, 1992;Smith, Jennings, Robinson, & Harris, 2004). This intensification ultimately led to a decreased habitat heterogeneity (Benton, Vickery, & Wilson, 2003), causing a steep decline in biodiversity (Reidsma, Tekelenburg, Berg, & Alkemade, 2006), for example, abundance and species richness of plant species (Storkey, Meyer, Still, & Leuschner, 2011) and farmland birds (Bowler, Heldbjerg, Fox, O'Hara, & Böhning-Gaese, 2018;Donald, Green, & Heath, 2001;Heldbjerg, Sunde, & Fox, 2017).…”