Manipulating individual state during migration provides evidence for carry-over effects modulated by environmental conditions

Abstract

Despite observational evidence of carry-over effects (COEs, events occurring in one season that produce residual effects on individuals the following seasons), to our knowledge no experimental studies have been carried out to explore how COEs might affect reproductive output. We simulated an environmental perturbation affecting spring-staging migrants to investigate COEs in greater snow geese (Anser caerulescens atlanticus). During three consecutive years, 2037 females captured during spring staging (approx. 3000 km south of their Arctic breeding grounds) were maintained in captivity (with or without access to food) for 0-4 days. Duration of captivity (but not food treatment) negatively affected reproductive success, probably through stress response. Reproductive success was reduced by 45 -71% in 2 years, but not in a third year with unusually favourable breeding conditions. This unprecedented manipulation indicates that COEs can have a strong effect on individual reproductive success in long-distance migrants, but that this effect can be partly compensated for by good environmental conditions on the breeding ground.

Carry-over effects, sequential density dependence and the dynamics of populations in a seasonal environment

“…In a recent study [17], greater snow geese (Anser caerulescens atlanticus) kept in captivity during the migratory period experienced a decrease in reproductive success between 45 and 71 per cent the following season and that this was likely caused by stress. We found that COEs caused by medium and high non-breeding density treatments resulted in a decrease in per capita reproductive output between 29 and 77 per cent relative to the low non-breeding density treatment.…”

“…For example, observational and experimental evidence in both resident and migratory animals suggest that events that induce individual variation in physiological condition during the non-breeding period can explain a significant amount of individual variation in the timing and success of reproduction the following breeding period [13][14][15][16][17]. Despite the fact that several studies on both resident and migratory animals provide evidence that COEs can shape individual fitness [13,15 -18], and that theoretical models suggest that they can interact with sequential density dependence to influence population dynamics [4,11,19], there is no empirical evidence that COEs influence per capita rates or have an effect at the population level.…”

Long-term monitoring at multiple trophic levels suggests heterogeneity in responses to climate change in the Canadian Arctic tundra

“…In migratory birds, population attributes can be strongly affected by environmental factors encountered away from the Arctic breeding grounds [53,65,66]. Spring migration phenology, and hence timing of breeding, may be constrained by the timing of life-cycle phases preceding migration, by different climatic variations in the wintering areas and along the migratory route, or by depleted genetic variance in migration traits [67].…”

An ontogenetic perspective on individual differences

“…Properly tackling these questions will involve a combination of observational, experimental and theoretical studies. For example, experimental work has shown it is possible to induce reversible state effects [81], but we must now strive to identify mechanistically how physiological stress is realized and subsequently dissipated [77]. These efforts should be paired with observational studies focused on bottlenecks in an organism's annual cycle [82], or following severe events that induce reversible state effects [83], to determine how such processes progress naturally.…”