A test of the mismatch hypothesis: How is timing of reproduction related to food abundance in an aerial insectivore?

Abstract

In seasonal environments, vertebrates are generally thought to time their reproduction so offspring are raised during the peak of food abundance. The mismatch hypothesis predicts that reproductive success is maximized when animals synchronize their reproduction with the food supply. Understanding the mechanisms influencing the timing of reproduction has taken on new urgency as climate change is altering environmental conditions during reproduction, and there is concern that species will not be able to synchronize their reproduction with changing food supplies. Using data from five sites over 24 years (37 site-years), we tested the assumptions of the mismatch hypothesis in the Tree Swallow (Tachycineta bicolor), a widespread aerial insectivore, whose timing of egg-laying has shifted earlier by nine days since the 1950s. Contrary to the mismatch hypothesis, the start of egg-laying was strongly related to food abundance (flying insect biomass) during the laying period and not to timing of the seasonal peak in food supply. In fact, food abundance generally continued to increase throughout the breeding season, and there was no evidence of selection based on the mistiming of laying with the seasonal peak of food abundance. In contrast, there was selection for laying earlier, because birds that lay earlier generally have larger clutches and fledge more young. Overall, initial reproductive decisions in this insectivore appear to be based on the food supply during egg formation and not the nestling period. Thus, the mismatch hypothesis may not apply in environments with relatively constant or abundant food throughout the breeding season. Although climate change is often associated with earlier reproduction, our results caution that it is not necessarily driven by selection for synchronized reproduction.

Seasonal patterns in reproductive success of temperate‐breeding birds: Experimental tests of the date and quality hypotheses

“…However, insect abundances sometimes remain steady or even increase during the breeding season (e.g., Dunn, Winkler, Whittingham, Hannon, & Robertson, 2011; McCarty & Winkler, 1999a; Nooker, Dunn, & Whittingham, 2005); thus, declining prey abundance is unlikely to be a universal driver of seasonally declining reproductive success. Insect biomass is an imperfect proxy for the food available to tree swallows because they are selective foragers so not all insects sampled represent equally suitable prey (McCarty & Winkler, 1999a).…”

Asynchrony of Seasons: Genetic Differentiation Associated with Geographic Variation in Climatic Seasonality and Reproductive Phenology

“…This assumption rests on evidence that precipitation regimes correlate with other climatic/environmental variables and are tightly related to food availability. Therefore, because organisms seek to reproduce during peaks of high resource availability (Wingfield et al 1992;Durant et al 2007;Dunn et al 2011), even if precipitation is not the main cue used by birds to activate their phenology, other cues used to predict environmental fluctuations in food abundance are likely coupled with precipitation regimes. We acknowledge, however, that although substantial evidence supports the match between reproductive phenology and food abundance (Dittami and Gwinner 1985;Gwinner 2003), food may not be the ultimate force triggering reproduction; in some cases, predation rates or intraspecific competition might play a more prominent role (Wingfield et al 1992;Ahumada 2001;Friesen et al 2007).…”

“…Because breeding is an energetically demanding process with obvious ties to lifetime fitness, reproduction should correlate with appropriate environmental conditions for offspring survival, such as an abundant supply of resources (Durant et al 2007;Burger and Both 2011;Dunn et al 2011). The precise fit between reproductive periods and favorable environmental conditions is achieved by individuals via cues reflecting changes in the environment (Hahn and MacDougall-Shackleton 2008), such that populations exhibit breeding seasons that track periods of high energy availability.…”

Anticipation and tracking of pulsed resources drive population dynamics in eastern chipmunks

“…This response suggests that females normally pursue energetically conservative reproductive strategies, such that the prospects for juvenile survival are a more important determinant of variation in reproductive output than proximate energetic constraints affecting the capacity of females to successfully reproduce (Boutin et al 2006). Alternatively, given the potential for nutrient (e.g., nitrogen), rather than energetic limits to reproduction and the high nutrient content of immature plant parts (e.g., seeds, buds) and immature insects, White (2007) and Dunn et al (2011) suggest that increases in reproductive effort prior to resource pulses may simply reflect responses to high nutrient availability rather than anticipation of high energy availability. Yet, several lines of evidence make us believe that chipmunks express adaptive reproductive plasticity by using anticipatory reproductive effort during mast years and restrained reproduction during years of mast failure.…”