Impacts of environmental heterogeneity on natural selection in a wild bird population*

Abstract

Natural selection has been studied for several decades, resulting in the computation of thousands of selection estimates. Although the importance of environmental conditions on selection has often been suggested, published estimates rarely take into account the effects of environmental heterogeneity on selection patterns. Here, we estimated linear and nonlinear viability selection gradients on morphological traits of 12‐day old nestlings in a wild population of tree swallows (Tachycineta bicolor) across a large‐scale heterogeneous study system in southern Québec, Canada. We assessed the environmental drivers of nestling survival and evaluated their effects on strength and direction of selection gradients. Separate analyses of environmental variables showed that high temperatures and heavy rainfall caused stronger positive linear selection on morphological traits. Weaker linear selection was also measured in more extensively cultivated areas. Both strength and shape of nonlinear quadratic and correlational components of selection were modified by environmental variables. Considering all environmental variables revealed that precipitation since hatching affected patterns of linear selection on traits, while temperatures since hatching shaped nonlinear selection patterns. Our study underlines the importance of quantifying linear and nonlinear natural selection under various environmental conditions and how the evolutionary response of traits may be affected by ongoing human‐induced environmental changes.

Negative effects of agricultural intensification on the food provisioning rate of a declining aerial insectivore

“…Furthermore, if parents cannot compensate for lowered gain rates, then broods may incur the cost through reduced growth rates or elevated mortality (Naef-Daenzer et al 1999, Tremblay et al 2004). In fact, evidence suggest food provisioning Tree swallows as well as their broods already incur these types of costs, as agro-intensive landscapes result in parents spending less time in the nest (Lamoureux 2010, Stanton et al 2016), expressing reduced body condition (Pigeon et al 2013, Stanton et al 2017), and both reduced fledging success and nestling growth rates (Houle et al 2020, Garrett et al 2021). Some of these natal effects are of concern as they may be carried over into later life stages (Harrison et al 2011).…”

“…In fact, evidence suggest food provisioning Tree Swallows as well as their broods already incur these types of costs. For example, parents breeding in more agro-intensive landscapes spend less time in the nest (Lamoureux 2010, Stanton et al 2016, express reduced body condition (Pigeon et al 2013, Stanton et al 2017, and both reduced fledging success and nestling growth (Houle et al 2020, Garrett et al 2021a). Some of these natal effects are of concern as they may be carried over into later life stages (Harrison et al 2011).…”

Combined influence of food availability and agricultural intensification on a declining aerial insectivore

“…We therefore assess the influence of prey availability on the fledging success, the duration of the nestling period and the morphological traits of fledglings (hitherto referred collectively as fitness proxies). Evidence suggests food availability and agricultural landscapes can be influential to both nestling growth and condition, and yet has only recently received more attention as a possible driver of aerial insectivore declines (Smith and Bruun 1998, Granbom and Smith 2006, Pigeon et al 2013, Almasi et al 2015, Kusack et al 2020, Houle et al 2020). Therefore we assess the possibility that links between agricultural intensification and declining populations of aerial insectivores are not only through a reduction in the number of fledglings, but also through reduced offspring condition, as this may carry over and affect future recruitment and productivity (Stutchbury et al 2011, Naef-Daenzer and Grüebler 2016, Saino et al 2018, Evans et al 2020, Jones and Ward 2020).…”

Interacting effects of cold snaps, rain, and agriculture on the fledging success of a declining aerial insectivore

“…Model covariate summaries can be found in Table 1 and were averaged across a 12-day window post-hatching. This period is when Tree Swallow nestlings become homeothermic, reach peak body mass, and experience the greatest nestling mortality, thus representing the period where resource availability is presumably most crucial (McCarty and Winkler 1999, Houle et al 2020). Cold temperatures and precipitation may act both directly on nestlings through thermoregulation and indirectly through a reduction in resource availability.…”