Predators, alternative prey and climate influence annual breeding success of a long‐lived sea duck

Abstract

Summary1. Perturbations to ecosystems have the potential to directly and indirectly affect species interactions, with subsequent impacts on population dynamics and the vital rates that regulate them.2. The few long-term studies of common eider breeding ecology indicate that reproductive success is low in most years, interrupted by occasional boom years. However, no study has explicitly examined the drivers of long-term variation in reproductive success. 3. Here, we use encounter history data collected across 41 years to examine the effects of arctic foxes (a terrestrial nest predator), local abundance and spatial distribution of lesser snow geese (an alternative prey source), and spring climate on common eider nest success. 4. Eider nest success declined over the course of the study, but was also highly variable across years. Our results supported the hypothesis that the long-term decline in eider nest success was caused by apparent competition with lesser snow geese, mediated by shared predators. This effect persisted even following a large-scale exodus of nesting geese from the eider colony. Nest success was also lowest in years of low arctic fox index, presumably driven by prey switching in years of low small mammal availability. However, increased snow goose abundance appeared to buffer this effect through prey swamping. The effect of spring climate depended on the stage of the breeding season; cold and wet and warm and dry conditions in early spring were correlated with decreased nest success, whereas warm and wet conditions in late spring increased eider nest success. 5. These results underscore the significance of both trophic interactions and climate in regulating highly variable vital rates, which likely have important consequences for population dynamics and the conservation of long-lived iteroparous species.

Relationships between Long-Term Demography and Weather in a Sub-Arctic Population of Common Eider

“…Like other sea-ducks, the life-history strategy of common eider is essentially that of a long-lived species, with stable, high adult survival but low annual breeding output, although with a potential for high production during favorable years [29], [46], [70], [71,]. Adult survival generally is 0.87 or higher and constant over time for many populations [28], [72]) although not all of them [73].…”

“…Previous studies have indicated that weather conditions in the months prior to nesting can influence breeding numbers, first nest initiation dates, nest site selection, clutch sizes and nest success [26], [27], [28], [29]. Weather conditions can also influence eider body condition and phenology because: 1) this species uses endogenous reserves for incubation [30], [31]; 2) is a short-distance migrant, both breeding and wintering at high latitudes [26], [27], [32] and so is exposed to high latitude weather conditions year round; and 3) environmental variation (such as weather) can induce physiological changes which can manifest as differing breeding trade-offs, such as nest site selection, nest desertion, yolk hormone levels and immune function [31], [32], [33].…”

“…These correlations with regional-scale NAO indices are likely to result from local-scale effects of weather conditions on duckling productivity and/or recruitment but the details of these relationships are unknown. Lastly, effects of weather may vary within breeding seasons; unfavorable (cold/wet or warm/dry) conditions early in spring may negatively affect nest success whereas favorable conditions in late spring (warm/wet) can positively affect nest success [29].…”

Full Issue

“…No other models were within 2.0 AIC c of the top model (Table 3), and there was little support for SOI AugÀNov , SOI Aug tÀ1 ÀNov tÀ1 , or MnFec tÀ1 (Table 3, Appendix C Table 10). Individually, SOI AugÀNov , SOI Aug tÀ1 ÀNov tÀ1 , and MnFec tÀ1 explained only 8.5%, 12.9%, and 0.1% of the variance, respectively, in breeding probability, based on analysis of deviance (using the method of Iles et al 2013). …”

“…Indeed, when reinforced by large-scale environmental conditions, density dependence appears to generate and sustain cyclic dynamics in some systems (Yan et al 2013). However, mechanisms responsible for multiannual population cycles are likely system-dependent and involve complex interactions among multiple endogenous and exogenous factors (Berryman 2002, Ims et al 2007, Krebs 2011, Iles et al 2013). Our study differed from typical investigations of cyclic population dynamics in that we investigated possible causes of biennial reproductive cycles in a predator that does not exhibit cyclic changes in abundance (our study population experienced a gradual but steady decline over the study period; Gutiérrez 2013, Tempel et al 2014).…”