Conflict between biotic and climatic selective pressures acting on an extended phenotype in a subarctic, but not temperate, environment

Abstract

Climatic selective pressures are thought to dominate biotic selective pressures at higher latitudes. However, few studies have experimentally tested how these selective pressures differentially act on traits across latitudes because traits can rarely be manipulated independently of the organism in nature. We overcame this challenge by using an extended phenotypeactive bird nests-and conducted reciprocal transplant experiments between a subarctic and temperate site, separated by 148 of latitude. At the subarctic site, biotic selective pressures (nest predation) favoured smaller, non-local temperate nests, whereas climatic selective pressures (temperature) favoured larger local nests, particularly at colder temperatures. By contrast, at the temperate site, climatic and biotic selective pressures acted similarly on temperate and subarctic nests. Our results illustrate a functional trade-off in the subarctic between nest morphologies favoured by biotic versus climatic selective pressures, with climate favouring local nest morphologies. At our temperate site, however, allocative trade-offs in the time and effort devoted to nest construction favour smaller, local nests. Our findings illustrate a conflict between biotic and climatic selective pressures at the northern extremes of a species geographical range, and suggest that tradeoffs between trait function and trait elaboration act differentially across latitude to create broad geographic variation in traits.

Incubation in a Temperate Passerine: Do Environmental Conditions Affect Incubation Period Duration and Hatching Success?

“…We followed many previous studies by measuring incubation period as the number of days between clutch completion and hatching (Nilsson and Smith, 1988;Wiebe and Martin, 2000;Martin, 2002;Martin et al, 2007;Rohwer et al, 2015;Bueno-Enciso et al, 2017). Our procedure for determining incubation period was as follows.…”

Geographic variation in incubation behavior of a widely distributed passerine bird

“…Given that climate, predation, and food availability affect incubation behavior across species [12,14], variation in these same factors across the breeding range of a single species should influence incubation behaviors between populations. However, data on geographic variation in incubation behaviors within species is scarce (incubation behaviors [20,21,29]; nestling care [30–33]), despite wide variation in climate and predation risks across breeding sites [34,35]. Not only should climate and predation pressure differ across the breeding range [34,35], but so too should life-history strategies [36–38], all of which may influence incubation behaviors.…”

“…However, data on geographic variation in incubation behaviors within species is scarce (incubation behaviors [20,21,29]; nestling care [30–33]), despite wide variation in climate and predation risks across breeding sites [34,35]. Not only should climate and predation pressure differ across the breeding range [34,35], but so too should life-history strategies [36–38], all of which may influence incubation behaviors. Life-history theory predicts that populations breeding at high latitude sites should invest more in current reproduction at the costs of future reproductive opportunities, especially if the likelihood of subsequent breeding attempts is small [37].…”

“…Yellow warblers also show striking geographic variation in nest morphologies with subarctic-breeding females constructing thicker, better-insulated nests compared to temperate-breeding females [44,45]. Previous experiments that transplanted nests between subarctic and temperate sites, however, found no differences in incubation behavior as a result of different nest morphologies, at least at the subarctic site [35]. This suggests that that the effect of nest morphology on incubation behavior is small and only expressed under more severe temperature or predation regimes, or that incubation behavior varies little with changing nest microclimates.…”

Lower elevation animal species do not tend to be better competitors than their higher elevation relatives

“…While some studies have revealed patterns consistent with this prediction (Gross & Price, 2000;Hargreaves, Samis, & Eckert, 2014;Rohwer, Bonier, & Martin, 2015;Sunday, Bates, & Dulvy, 2012), others have shown opposing patterns (Cahill et al, 2014;Freeman, Lee-Yaw, Sunday, & Hargreaves, 2018). Therefore, whether competition (or other biotic interactions) generally limits species' warm range edges in nature remains an open question.…”