Strength Of Carry-over Effects Research Articles

White-crested elaenias (Elaenia albiceps chilensis) breeding across Patagonia exhibit similar spatial and temporal movement patterns throughout the year.

For migratory birds, events happening during any period of their annual cycle can have strong carry-over effects on the subsequent periods. The strength of carry-over effects between non-breeding and breeding grounds can be shaped by the degree of migratory connectivity: whether or not individuals that breed together also migrate and/or spend the non-breeding season together. We assessed the annual cycle of the White-crested Elaenia (Elaenia albiceps chilensis), the longest-distance migrant flycatcher within South America, which breeds in Patagonia and spends the non-breeding season as far north as Amazonia. Using light-level geolocators, we tracked the annual movements of elaenias breeding on southern Patagonia and compared it with movements of elaenias breeding in northern Patagonia (1,365 km north) using Movebank Repository data. We found that elaenias breeding in southern Patagonia successively used two separate non-breeding regions while in their Brazilian non-breeding grounds, as already found for elaenias breeding in the northern Patagonia site. Elaenias breeding in both northern and southern Patagonia also showed high spread in their non-breeding grounds, high non-breeding overlap among individuals from both breeding sites, and similar migration phenology, all of which suggests weak migratory connectivity for this species. Elucidating the annual cycle of this species, with particular emphasis on females and juveniles, still requires further research across a wide expanse of South America. This information will be critical to understanding and possibly predicting this species' response to climate change and rapid land-use changes.

Personality-specific carry-over effects on breeding.

Carry-over effects describe the phenomenon whereby an animal's previous conditions influence its subsequent performance. Carry-over effects are unlikely to affect individuals uniformly, but the factors modulating their strength are poorly known. Variation in the strength of carry-over effects may reflect individual differences in pace-of-life: slow-paced, shyly behaved individuals are thought to favour an allocation to self-maintenance over current reproduction, compared to their fast-paced, boldly behaved conspecifics (the pace-of-life syndrome hypothesis). Therefore, detectable carry-over effects on breeding should be weaker in bolder individuals, as they should maintain an allocation to reproduction irrespective of previous conditions, while shy individuals should experience stronger carry-over effects. We tested this prediction in black-legged kittiwakes breeding in Svalbard. Using miniature biologging devices, we measured non-breeding activity of kittiwakes and monitored their subsequent breeding performance. We report a number of negative carry-over effects of non-breeding activity on breeding, which were generally stronger in shyer individuals: more active winters were followed by later breeding phenology and poorer breeding performance in shy birds, but these effects were weaker or undetected in bolder individuals. Our study quantifies individual variability in the strength of carry-over effects on breeding and provides a mechanism explaining widespread differences in individual reproductive success.

Variation in the effects of larval history on juvenile performance of a temperate reef fish

For organisms with complex life cycles, the transition between life stages can act as a significant demographic and selective bottleneck. Variation in developmental and growth rates among individuals present in one stage (e.g. larvae), due to initial differences in parental input and/or environmental conditions experienced, can propagate to future stages (e.g. juveniles), and such ‘carry-over effects’ can shape fitness and phenotypic distributions within a population. However, variation in the strength of carry-over effects between life stages and the intensity of selective mortality acting on intrinsic variation, and how these might be mediated by environmental variability in natural systems, is poorly known. Here, we evaluate variation in the strength to which larval growth histories can mediate juvenile performance (growth and survival), for a reef fish (Forsterygion lapillum) common to rocky reefs of New Zealand. We used otoliths to reconstruct demographic histories of recently settled fish that were sampled across cohorts, sites and microhabitats. We quantified sources of variation in the strength of carry-over effects and selective mortality that operate on larval growth histories. We found overall that individuals that grew fast as larvae tended to experience proportional growth advantages as juveniles. However, the strength of growth advantages being maintained into the juvenile period varied among cohorts, sites and microhabitats. Specifically, a stronger growth advantage was found on some microhabitats (e.g. mixed stands of macroalgae) relative to others (e.g. monocultures of Carpophyllum maschalocarpum) for some cohorts and sites only. For other cohorts and sites, the degree of coupling between larval and juvenile growth rates was either indistinguishable between microhabitats or else not evident. Similarly, the intensity of growth-based selective mortality varied among cohorts, sites and microhabitats: for the cohort and site where carry-over effects differed between microhabitats, we also observed difference in the intensity to which fish with rapid larval growth rates were favoured. Overall, our results highlight how this spatial and temporal patchiness in extrinsic factors can interact with intrinsic variation of recruiting individuals to have a major influence on the resulting distribution of juveniles and their phenotypic traits.