Modeling the demography and population dynamics of a subtropical seabird, and the influence of environmental factors (original) (raw)
Related papers
Marine Ecology Progress Series, 2009
An emerging consequence of global climate change is its potential effect on the timing of seasonal biological events. Analysis of long-term datasets reveals a high degree of plasticity in the nature of phenological responses both within and among species, and understanding these differences is central to understanding the mechanisms and implications of climate-related change. We investigated factors influencing timing of breeding (median laying date) in a colonial nesting seabird, the common guillemot Uria aalge, over 23 breeding seasons between 1973 and 2008. There was a trend for earlier laying over this period, and earlier laying was associated with higher average breeding success. Multiple regression models (with de-trended explanatory variables to control for linear trends over time) indicate that the timing of breeding is positively correlated with a wide-scale climatic driver, the winter North Atlantic Oscillation (WNAO), and negatively correlated with population size: guillemots lay later in years with high WNAO indices and earlier in years with larger populations. Responses to environmental conditions are probably related to indirect effects on timing or abundance of food availability, direct effects of weather or both. The mechanism(s) leading to a possible relationship between laying date and population size are less clear. They may be related to Allee-type effects associated with social stimulation, improved foraging efficiency or a densitydependent increase in breeding site quality. Given the correlative nature of these results, we are cautious about the role of non-climatic (intrinsic) factors, but we cannot exclude that they play a role alongside climatic (extrinsic) factors in influencing reproductive phenology.
Annual survival of North American Razorbills (Alca torda) varies with ocean climate indices
Canadian Journal of Zoology, 2008
According to life-history theory, survival in long-lived animals is not expected to vary greatly with environmental conditions. However, recent studies of a number of seabirds have shown that ocean climate indices such as the Pacific Decadal Oscillation index and sea surface temperature are correlated with adult survival. Here we evaluated whether annual adult survival of Razorbills (Alca torda L., 1758) at two breeding colonies covaried with oceanographic conditions in the North Atlantic during 1995-2006. We also examined pre-breeder survival (from fledging to age 2). The relationship between local adult survival and the North Atlantic Oscillation and two oceanographic variables (Labrador Current temperature profile and Bay of Fundy sea surface temperature) were evaluated using the program MARK. Capture-mark-recapture data fit the assumptions of the program MARK reasonably well with ĉ values ranging from 1.390 to 2.404. Pre-breeder survival rates were high for Machias Seal Island (K = 0.778 ± 0.041) and low for the Gannet Islands (K = 0.482 ± 0.033), likely the result of hunting pressure. On Machias Seal Island, constant adult survival (K = 0.967 ± 0.028) was the best model; however, time-dependent models that included a climate covariate performed nearly as well. On the Gannet Islands, adult survival (K = 0.890 ± 0.053) was negatively correlated with Labrador Current temperature. Overall, our results show significant differences in survival rates across sites over the same time period and highlight the importance of multisite studies and smaller scale climate indices for local populations. In addition, our study contributes to the growing body of evidence that survival in long-lived animals may vary with environmental conditions more than previously expected.
PLOS ONE
In response to climate warming, a southward shift in productive frontal systems serving as the main foraging sites for many top predator species is likely to occur in Subantarctic areas. Central place foragers, such as seabirds and pinnipeds, are thus likely to cope with an increase in the distance between foraging locations and their land-based breeding colonies. Understanding how central place foragers should modify their foraging behavior in response to changes in prey accessibility appears crucial. A spatially explicit individual-based simulation model (Marine Central Place Forager Simulator (MarCPFS)), including bioenergetic components, was built to evaluate effects of possible changes in prey resources accessibility on individual performances and breeding success. The study was calibrated on a particular example: the Antarctic fur seal (Arctocephalus gazella), which alternates between oceanic areas in which females feed and the land-based colony in which they suckle their young over a 120 days rearing period. Our model shows the importance of the distance covered to feed and prey aggregation which appeared to be key factors to which animals are highly sensitive. Memorization and learning abilities also appear to be essential breeding success traits. Females were found to be most successful for intermediate levels of prey aggregation and short distance to the resource, resulting in optimal female body length. Increased distance to resources due to climate warming should hinder pups' growth and survival while female body length should increase.
Effects of climate change and variability on population dynamics in a long-lived shorebird
Ecology, 2010
Climate change affects both the mean and variability of climatic variables, but their relative impact on the dynamics of populations is still largely unexplored. Based on a long-term study of the demography of a declining Eurasian Oystercatcher (Haematopus ostralegus) population, we quantify the effect of changes in mean and variance of winter temperature on different vital rates across the life cycle. Subsequently, we quantify, using stochastic stage-structured models, how changes in the mean and variance of this environmental variable affect important characteristics of the future population dynamics, such as the time to extinction. Local mean winter temperature is predicted to strongly increase, and we show that this is likely to increase the population's persistence time via its positive effects on adult survival that outweigh the negative effects that higher temperatures have on fecundity. Interannual variation in winter temperature is predicted to decrease, which is also likely to increase persistence time via its positive effects on adult survival that outweigh the negative effects that lower temperature variability has on fecundity. Overall, a 0.18C change in mean temperature is predicted to alter median time to extinction by 1.5 times as many years as would a 0.18C change in the standard deviation in temperature, suggesting that the dynamics of oystercatchers are more sensitive to changes in the mean than in the interannual variability of this climatic variable. Moreover, as climate models predict larger changes in the mean than in the standard deviation of local winter temperature, the effects of future climatic variability on this population's time to extinction are expected to be overwhelmed by the effects of changes in climatic means. We discuss the mechanisms by which climatic variability can either increase or decrease population viability and how this might depend both on species' life histories and on the vital rates affected. This study illustrates that, for making reliable inferences about population consequences in species in which life history changes with age or stage, it is crucial to investigate the impact of climate change on vital rates across the entire life cycle. Disturbingly, such data are unavailable for most species of conservation concern.
Linking climate variability, productivity and stress to demography in a long-lived seabird
Marine Ecology Progress Series, 2012
We examined the reproductive ecology of black-legged kittiwakes Rissa tridactyla in several breeding colonies in the North Pacific to test if inter-annual changes in the Pacific Decadal Oscillation (PDO), Winter Ice Cover (ICI), or local sea-surface temperature (SST) predict changes in productivity (fledglings per nest) or nutritional stress (corticosterone). We explored the implications of the observed variation in productivity and stress for projected population dynamics based on a previously demonstrated corticosterone−survival relationship. Although productivity was highly variable (0 to 0.9 fledglings nest −1), the relationships between productivity and environmental indices were weak, with local SST providing slightly more explanatory power than PDO or ICI, suggesting that local factors rather than large-scale climate variability may determine variation in productivity. The relationships between stress and environmental indices were stronger than the relationship between productivity and environment. The measured response of stress to environment showed opposite signs between the southern and northern colonies, and typically implied annual mortality rates varying from 11 to 17%. The observed relationships between climate and stress indicate that anticipated warming might bring at least short-term demographic benefits for kittiwakes in the Bering shelf region, while having negative impacts on birds breeding in the Gulf of Alaska and western Aleutians. We predict decline (without immigration) for colonies with the lowest productivity and conclude that climate variability is likely to affect survival of North Pacific kittiwakes on a region-specific basis. Longevity of these birds may not always be sufficient to buffer their populations from low reproductive performance.
Population Change in a Marine Bird Colony is Driven By Changes in Recruitment
The population dynamics of long-lived birds are thought to be very sensitive to changes in adult survival. However, where natal philopatry is low, recruitment from the larger metapopulation may have the strongest effect on population growth rate even in long-lived species. Here, we illustrate such a situation where changes in a seabird colony size appeared to be the consequence of changes in recruitment. We studied the population dynamics of a declining colony of Ancient Murrelets (Synthliboramphus antiquus) at East Limestone Island, British Columbia. During 1990-2010, Ancient Murrelet chicks were trapped at East Limestone Island while departing to sea, using a standard trapping method carried on throughout the departure period. Adult murrelets were trapped while departing from the colony during 1990-2003. Numbers of chicks trapped declined during 1990-1995, probably because of raccoon predation, increased slightly from 1995-2000 and subsequently declined again. Reproductive success was 30% lower during 2000-2003 than in earlier years, mainly because of an increase in desertions. The proportion of nonbreeders among adult birds trapped at night also declined over the study period. Mortality of adult birds, thought to be mainly prebreeders, from predators more than doubled over the same period. Apparent adult survival of breeders remained constant during 1991-2002 once the first year after banding was excluded, but the apparent survival rates in the first year after banding fell and the survival of birds banded as chicks to age three halved over the same period. A matrix model of population dynamics suggested that even during the early part of the study immigration from other breeding areas must have been substantial, supporting earlier observations that natal philopatry in this species is low. The general colony decline after 2000 probably was related to diminished recruitment, as evidenced by the lower proportion of nonbreeders in the trapped sample. Hence the trend is determined by the recruitment decisions of externally reared birds, rather than demographic factors operating on the local breeding population, an unusual situation for a colonial marine bird. Because of the contraction in the colony it may now be subject to a level of predation pressure from which recovery will be impossible without some form of intervention. RÉSUMÉ. On pense que la dynamique des populations d'oiseaux ayant une longévité accrue est sensible aux changements dans la survie des adultes. Toutefois, lorsque le degré de philopatrie est faible, le recrutement au sein de la métapopulation a peut-être davantage d'effet sur le taux de croissance de la population, même chez les espèces à longévité accrue. Dans le présent article, nous illustrons un cas où les changements d'effectifs d'une colonie d'oiseaux marins semblent être la conséquence des fluctuations du taux de recrutement, au moyen de l'étude de la dynamique de population d'une colonie de Guillemots à cou blanc (Synthliboramphus antiquus) en déclin à l'île Limestone Est en Colombie-Britannique. De 1990 à 2010, de jeunes guillemots ont été capturés sur l'île Limestone Est au moment de quitter la colonie, à l'aide d'une méthode de capture standard utilisée tout au long de la période des départs. Les guillemots adultes ont pour leur part été capturés au moment de leur départ de la colonie, de 1990 à 2003. Le nombre
Ultimate and proximate factors affecting the breeding performance of a marine top-predator
Oikos, 2002
. Ultimate and proximate factors affecting the breeding performance of a marine Variability in ecosystems affects the life history of organisms. In marine ecosystems where interannual variability is high, relationships between fluctuations in oceanographic parameters and top-predator breeding performance are increasingly documented but it is less clear why such relationships exist. In this study, we examined the connections between marine environment fluctuations and breeding performance of a long-lived top-predator, the black-browed albatross Diomedea melanophris at Kerguelen, through study of resource acquisition and allocation processes. Our results show that this population used the same foraging zones and spent similar time foraging year after year, but adult body condition varied between years. Foraging trips are regulated mainly by changes in body condition. During years of low resource availability, birds return to their nest with lower body condition and adults in low body condition were more frequent and therefore were more likely to stop breeding. Poor breeding success was related to the presence of colder waters in the foraging zones of breeding albatrosses as measured by the positive correlation between sea surface temperatures and breeding success measured over 18 years. Lower breeding success was mainly due to failure by inexperienced birds. The results of this study demonstrate how oceanographic conditions affect breeding performance through allocation processes. We compared these results to those at South Georgia where the breeding success is lower and more variable. This population relies mainly on krill, a resource that shows a very variable year-to-year availability compared to fish prey consumed by Kerguelen birds. This study shows that, in the same species, differences in resource variability and availability affect the demographic strategies probably through differences in allocation strategies.
Journal of Animal Ecology, 2013
1. Large-scale seasonal climatic indices, such as the North Atlantic Oscillation (NAO) index or the Southern Oscillation Index (SOI), account for major variations in weather and climate around the world and may influence population dynamics in many organisms. However, assessing the extent of climate impacts on species and their life-history traits requires reliable quantitative statistical approaches. 2. We used a new analytical tool in mark-recapture, the multi-event modelling, to simultaneously assess the influence of climatic variation on multiple demographic parameters (i.e. adult survival, transient probability, reproductive skipping and nest dispersal) at two Mediterranean colonies of the Cory's shearwater Calonectris diomedea, a trans-equatorial migratory long-lived seabird. We also analysed the impact of climate in the breeding success at the two colonies. 3. We found a clear temporal variation of survival for Cory's shearwaters, strongly associated to the large-scale SOI especially in one of the colonies (up to 66% of variance explained). Atlantic hurricane season is modulated by the SOI and coincides with shearwater migration to their wintering areas, directly affecting survival probabilities. However, the SOI was a better predictor of survival probabilities than the frequency of hurricanes; thus, we cannot discard an indirect additive effect of SOI via food availability. Accordingly, the proportion of transients was also correlated with SOI values, indicating higher costs of first reproduction (resulting in either mortality or permanent dispersal) when bad environmental conditions occurred during winter before reproduction. 4. Breeding success was also affected by climatic factors, the NAO explaining c. 41% of variance, probably as a result of its effect in the timing of peak abundance of squid and small pelagics, the main prey for shearwaters. No climatic effect was found either on reproductive skipping or on nest dispersal.