Density dependence in seabirds: Great Skuas<i>Stercorarius skua</i>start to breed at a younger age when conditions are better

Furness, Robert W.

doi:10.1080/03078698.2015.1059631

Cited by 14 publications

(17 citation statements)

References 20 publications

(26 reference statements)

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“…By contrast, at type 2 colonies with fewer hosts and smaller but rapidly growing great skua populations, Arctic skua breeding success was most strongly associated with great:Arctic skua AOT ratio. At such colonies, less competition for territories allows adolescent great skuas to breed earlier, leading to rapid population growth (Furness, ), whilst less interference competition may result in higher adult fitness and per‐capita predation of seabirds (Votier, Bearhop, Crane, Arcos, & Furness, ).…”

Section: Discussionmentioning

confidence: 99%

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

Perkins

Ratcliffe

Suddaby³

et al. 2018

Journal of Animal Ecology

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Understanding drivers of population change is critical for effective species conservation. In the northeast Atlantic Ocean, recent changes amongst seabird communities are linked to human and climate change impacts on food webs. Many species have declined severely, with food shortages, and increased predation reducing productivity. Arctic skua Stercorarius parasiticus, a kleptoparasite of other seabirds, is one such species. The aim of the study was to determine relative effects of bottom-up and top-down pressures on Arctic skuas across multiple colonies in a rapidly declining national population. Long-term monitoring data were used to quantify changes in population size and productivity of Arctic skuas, their hosts (black-legged kittiwake Rissa tridactyla, common guillemot Uria aalge, Atlantic puffin Fratercula arctica, Arctic tern Sterna paradisaea) and an apex predator (great skua Stercorarius skua) over 24 years (1992-2015) in Scotland. We used digital mapping and statistical models to determine relative effects of bottom-up (host productivity) and top-down (great skua density) pressures on Arctic skuas across 33 colonies, and assess variation between three colony types classified by host abundance. Arctic skuas declined by 81% and their hosts by 42%-92%, whereas at most colonies great skuas increased. Annual productivity declined in Arctic skuas and their hosts, and reduced Arctic skua breeding success was a driver of the species' population decline. Arctic skua productivity was positively associated with annual breeding success of hosts and negatively with great skua density. Intercolony variation suggested Arctic skua trends and productivity were most sensitive to top-down pressures at smaller colonies of host species where great skuas had increased most, whereas bottom-up pressures dominated at large colonies of host species. Scotland's Arctic skua population is declining rapidly, with bottom-up and top-down pressures simultaneously reducing breeding success to unsustainably low levels. Marine food web alterations, strongly influenced by fisheries management and climate change, are driving the decline, and this study demonstrates severe vulnerability of seabirds to rapid change in human-modified ecosystems. Potential but untested conservation solutions for Arctic skuas include marine protected areas, supplementary feeding within colonies and management of great skuas.

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Section: Discussionmentioning

confidence: 99%

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

Perkins

Ratcliffe

Suddaby³

et al. 2018

Journal of Animal Ecology

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“…], Common Guillemot, Uria aalge [Kokko et al. ], Great Skua, Catharacta skua [Furness ], Osprey, Pandion haliaetus [Bretagnolle et al. ]) as well as in mammals (gray wolf, Canis lupus [Cubaynes et al.…”

Section: Discussionmentioning

confidence: 99%

“…The South Polar Skua population in Pointe G eologie showed typical life history traits characteristic of longlived organisms, with a high and weakly variable adult survival and a low and variable fecundity (Stearns 1992, Gaillard et al 2000, Gaillard and Yoccoz 2003. As expected by life history theory, birds experienced a lower survival rate during their first two years of life after fledging, and a higher and more stable survival rate from age 3 onward, falling into the range of other Stercoraridae (Burton 1968, Wood 1971, Furness 1987, Ainley et al 1990, Pietz and Parmelee 1994, Julien et al 2013. Studies in mammals and birds have reported an increase in breeding performances with age attributed to lower experience, lower reproductive effort or higher proportion of lower-quality individuals in young ages (Gaillard et al 2000, Penteriani et al 2003, Rebke et al 2010.…”

Section: Early Life Vs Adult Life-history Traits (Prediction 1)mentioning

confidence: 96%

“…To ascertain breeding status, the territories were searched intensively. A group of nonbreeding individuals ("clubs"), a common feature of Stercorariidae (Furness 1987), of~30-50 individuals found at the same place all years in the study area was also checked, with the same survey intensity as for breeding individuals, for individual identification of banded birds. We considered observations of individuals banded as chicks in Pointe G eologie (n = 1,567) during the period 1963-2014, allowing us to know the age at recaptures with precision.…”

Section: Longitudinal Data Setsmentioning

confidence: 99%

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Demographic and population responses of an apex predator to climate and its prey: a long‐term study of South Polar Skuas

Pacoureau

Delord

Jenouvrier

et al. 2019

Ecological Monographs

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Ecologists widely acknowledge that a complex interplay of endogenous (density‐dependent) and exogenous (density‐independent) factors impact demographic processes. Individuals respond differently to those forces, ultimately shaping the dynamics of wild populations. Most comprehensive studies disentangling simultaneously the effects of density dependence, climate, and prey abundance while taking into account age structure were conducted in terrestrial ecosystems. However, studies on marine populations are lacking. Here we provide insight into the mechanisms affecting four vital rates of an apex Antarctic marine predator population, the South Polar Skua Catharacta maccormicki, by combining a nearly half‐century longitudinal time series of individual life histories and abundance data, with climatic and prey abundance covariates. Using multistate capture–mark–recapture models, we estimated age classes effects on survival, breeding, successful breeding with one or two chicks and successful breeding with two chicks probabilities, and assessed the different effects of population size, climate, and prey abundance on each age‐specific demographic parameter. We found evidence for strong age effects in the four vital rates studied. Vital rates at younger ages were lower than those of older age classes for all parameters. Results clearly evidenced direct and indirect influences of local climate (summer sea ice concentration), of available prey resources (penguins), and of intrinsic factors (size of the breeding population). More covariate effects were found on reproductive rates than on survival, and younger age classes were more sensitive than the older ones. Results from a deterministic age‐structured density‐dependent matrix population model indicated greater effects of prey abundance and sea ice concentration on the total population size than on the breeding population size. Both total population size and the number of breeders were strongly affected by low values of sea ice concentration. Overall, our results highlight the greater sensitivity of reproductive traits and of younger age classes to prey abundance, climate variability, and density dependence in a marine apex predator, with important consequences on the total population size but with limited effects on the breeding population size. We discuss the mechanisms by which climate variability, prey abundance, and population size may affect differentially age‐specific vital rates, and the potential population consequences of future environmental changes.

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“…Several possible and nonexclusive hypotheses have been proposed to explain changes in breeding success across taxa. First, low food availability, poor parental condition and high density-dependence during the breeding period are usually linked to decreases in individual and population breeding success 38 , 39 . Second, behaviors that are associated with predation risk, including vigilance, alarm, avoidance, escape and defence can reduce breeding success through increased physiological stress, reduced foraging efficiency or diminished parental care 4 .…”

Section: Discussionmentioning

confidence: 99%

Predator arrival elicits differential dispersal, change in age structure and reproductive performance in a prey population

Payo‐Payo

Sanz‐Aguilar

Genovart

et al. 2018

Sci Rep

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Predators are an important ecological and evolutionary force shaping prey population dynamics. Ecologists have extensively assessed the lethal effects of invasive predators on prey populations. However, the role of non-lethal effects, such as physiological stress or behavioural responses like dispersal, has been comparatively overlooked and their potential population effects remain obscure. Over the last 23 years, we developed a mark-recapture program for the Audouin’s gull and an intensive carnivore monitoring program to assess how the appearance and invasion of the study site by carnivores affects population dynamics. We evaluate changes in turnover of discrete breeding patches within the colony, age structure and breeding performance. Once carnivores entered the colony, the number of occupied patches increased, indicating a higher patch turnover. Breeders responded by moving to areas less accessible to carnivores. More importantly, the presence of carnivores caused differential (and density-independent) breeding dispersal: experienced, better-performing breeders were more likely to leave the colony than younger breeders. This differential dispersal modified the age structure and reduced the reproductive performance of the population. Our results confirm the importance experience in the study of populations. The role of differential dispersal for animal population dynamics might be more important than previously thought, especially under scenarios of global change.

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Density dependence in seabirds: Great SkuasStercorarius skuastart to breed at a younger age when conditions are better

Cited by 14 publications

References 20 publications

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

Combined bottom‐up and top‐down pressures drive catastrophic population declines of Arctic skuas in Scotland

Demographic and population responses of an apex predator to climate and its prey: a long‐term study of South Polar Skuas

Predator arrival elicits differential dispersal, change in age structure and reproductive performance in a prey population

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