A population decline in Weddell seals: real or sampling artefact?

1992 ◽  
Vol 19 (1) ◽  
pp. 59 ◽  
Author(s):  
K Green ◽  
V Wong ◽  
HR Burton
Keyword(s):  
Food Availability ◽  
Population Decline ◽  
Breeding Population ◽  
Population Trends ◽  
Weddell Seals ◽  
Population Sizes

Aerial counts of Weddell seals during the moult did not provide a useful index of population trends. Seals may spent longer foraging in the water in some years than in others (possibly because of changes in food availability), with the result that differing proportions of the population are counted in different years. It is concluded that little can be inferred about interannual differences in population sizes without reference to the size of the breeding population.

scholarly journals Long-term population trends of the Red-legged CormorantPhalacrocorax gaimardion the Argentine coast

2014 ◽  
Vol 25 (2) ◽  
pp. 234-241 ◽  
Author(s):  
ANA MILLONES ◽  
PATRICIA GANDINI ◽  
ESTEBAN FRERE
Keyword(s):  
Population Change ◽  
Breeding Population ◽  
Temporal Variations ◽  
Population Trends ◽  
World Population ◽  
Ocean Productivity ◽  
Marine Primary Productivity ◽  
Long Term Trend ◽  
Positive Effect

SummaryThe world population of Red-legged CormorantPhalacrocorax gaimardiis reasonably small and has showed rapid declines. In Argentina, this species breeds in 13 localities and is considered as ‘Endangered’ by the national government. In this study, we provide information about population trends of the Red-legged Cormorant on the Argentine coast, between 1990 and 2009. We also discuss whether these trends could be related to sea surface temperature and marine primary productivity, both of which are considered oceanographic factors that can affect breeding seabirds. The long-term trend in the breeding population showed a slight decrease of 1.2% per year. Seven colonies showed an average population change < 1. Periods of stability and increase were identified over the study period, but they were insufficient to compensate for the decreases. The largest colony of Red-legged Cormorants (La Mina, with more than 55% of the entire breeding population) seems to determine the overall population trend. We did not find a direct relationship between the overall number of Red-legged Cormorants and the two oceanographic factors analysed. However, our analysis detected a positive effect of ocean productivity close to the coast on the largest colony at the beginning of the breeding season, suggesting that coastal ocean productivity could be an important factor affecting temporal variations in the Argentinian population.

scholarly journals Direct evidence of poison-driven widespread population decline in a wild vertebrate

2020 ◽  
Vol 117 (28) ◽  
pp. 16418-16423 ◽  
Author(s):  
Patricia Mateo-Tomás ◽  
Pedro P. Olea ◽  
Eva Mínguez ◽  
Rafael Mateo ◽  
Javier Viñuela
Keyword(s):  
Large Scale ◽  
Population Decline ◽  
Population Level ◽  
Breeding Population ◽  
Time Frame ◽  
Regulatory Control ◽  
Individual Level ◽  
Lead Ammunition ◽  
Organochlorine Insecticides ◽  
Local Extinctions

Toxicants such as organochlorine insecticides, lead ammunition, and veterinary drugs have caused severe wildlife poisoning, pushing the populations of several apex species to the edge of extinction. These prime cases epitomize the serious threat that wildlife poisoning poses to biodiversity. Much of the evidence on population effects of wildlife poisoning rests on assessments conducted at an individual level, from which population-level effects are inferred. Contrastingly, we demonstrate a straightforward relationship between poison-induced individual mortality and population changes in the threatened red kite (Milvus milvus). By linking field data of 1,075 poisoned red kites to changes in occupancy and abundance across 274 sites (10 × 10-km squares) over a 20-y time frame, we show a clear relationship between red kite poisoning and the decline of its breeding population in Spain, including local extinctions. Our results further support the species listing as endangered, after a breeding population decline of 31% to 43% in two decades of this once-abundant raptor. Given that poisoning threatens the global populations of more than 2,600 animal species worldwide, a greater understanding of its population-level effects may aid biodiversity conservation through increased regulatory control of chemical substances. Our results illustrate the great potential of long-term and large-scale on-ground monitoring to assist in this task.

scholarly journals Information on population trends and biological constraints from bat counts in roost cavities: a 22-year case study of a pipistrelle bats (Pipistrellus pipistrellus Schreber) hibernaculum

2015 ◽  
Vol 42 (1) ◽  
pp. 35 ◽  
Author(s):  
Christian Kerbiriou ◽  
Jean François Julien ◽  
Sophie Monsarrat ◽  
Philippe Lustrat ◽  
Alexandre Haquart ◽  
...  
Keyword(s):  
Population Dynamics ◽  
Population Size ◽  
Spatial Scales ◽  
Population Decline ◽  
Current Trend ◽  
Biodiversity Loss ◽  
Population Trends ◽  
Railway Tunnel ◽  
Biodiversity Indicators ◽  
Pipistrellus Pipistrellus

Context According to the current trend of biodiversity loss, information on population trends at large temporal and spatial scales is necessary. However, well documented animal population dynamics are generally based on intensive protocols requiring animal manipulation, which can be impossible to conduct in species for which conservation is a concern. Aims For many bat species, an alternative approach entails performing an appropriate analysis of counts in roost cavities. Because of managers’ perception of chaotic variations through time, relatively few count monitoring surveys are regularly analysed. Here, we present the analysis of a twenty-two-year survey of a large hibernaculum of pipistrelle bats (Pipistrellus pipistrellus) located in a railway tunnel in Paris, France. Methods We propose that using combinations of population-dynamics modelling using demographic parameters from the literature and statistical analyses helps with identifying the biological and methodological effects underlying the dynamics observed in census analyses. Key results We determined that some of the observed year-to-year variations of population size cannot be explained only by the intrinsic dynamics of the population. In particular, in 1993–94, the population size increased by >40%, which should have implied a massive immigration. This change coincided with the end of the operation of the railway line. After consideration of a drastic trend of population decline (7% year–1), we were able to detect this event and several environmental effects. Specifically, the winter conditions and the temperature in July affected the colony size, presumably because of aggregative behaviour and reproduction success, respectively. Conclusions Emigration–immigration processes might have preponderant effects on population dynamics. In addition, our analysis demonstrated that (1) the study population suffered a large decline, (2) a combination of human disturbance and meteorological variation explains these dynamics and (3) emigration–immigration processes have preponderant effects on the population dynamics. Implications To conduct a meaningful analysis of non-standard time series and provide a source of data for implementing biodiversity indicators, it is necessary to include (1) the local knowledge of the people involved in the field surveys in these analyses (the existence of disturbances and site protections) and (2) meteorological information for the appropriate seasons of the year.

Incubating snowy plovers (Charadrius nivosus) exhibit site-specific patterns of disturbance from human activities

2016 ◽  
Vol 43 (4) ◽  
pp. 288 ◽  
Author(s):  
Cara A. Faillace ◽  
Bradley W. Smith
Keyword(s):  
Human Activities ◽  
Population Decline ◽  
Breeding Population ◽  
Perceived Threat ◽  
Model Framework ◽  
Site Specific ◽  
Beach Width ◽  
Single Person ◽  
Snowy Plovers ◽  
Range Of Variation

Context Many shorebirds are threatened by human-caused disturbance. For snowy plovers, disturbance within nesting habitats has been implicated as a major contributing factor in their population decline through deleterious effects on breeding success. Very little is known about site specificity of disturbance from human activities for this species. Aims We examined the disturbance of incubating snowy plovers to determine if nesting shorebirds within one breeding population exhibited site-specific patterns of disturbance from human activities. Methods We recorded flush (i.e. flight or escape from a perceived threat) distances and time spent off the nest following approach by a single person on Sanibel and Cayo Costa Islands, two islands in south-west Florida that differ in daily human visitation, and by a person walking a dog on Sanibel. We used a Bayesian model framework to determine effects of location and approach type on flush distance and time spent off of the nest. Key results Birds nesting on Sanibel flushed at shorter distances from a solitary person without a dog than did birds nesting on Cayo Costa, but spent similar amounts of time off of nests following a flush. On Sanibel, nesting birds also flushed at significantly greater distances and spent significantly more time off of nests when flushed by a person walking a dog rather than by a person alone. Conclusions Within a population, nesting snowy plovers exhibit site- and stimulus-dependent patterns of disturbance. The intraspecific variation falls within the range of variation recorded among species of birds studied elsewhere. Although we cannot determine causation, we suggest habituation to human activities from a combination of high beach usage, smaller nesting exclusion zones, and narrower beach width on Sanibel compared to Cayo Costa as a likely explanation for this difference. Implications Set-back distances for symbolic fencing have been generalised across species and nesting locations. Our results suggest that disturbance of nesting shorebirds can be site-dependent even within one breeding population of a species. Set-back distances around shorebird nests must account for location and types of activities encountered, implying the need for more conservative implementation of set-back distances.

Juvenile survival and recruitment in a population of Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica

1987 ◽  
Vol 65 (12) ◽  
pp. 2993-2997 ◽  
Author(s):  
J. Ward Testa
Keyword(s):  
Census Data ◽  
Survival Rates ◽  
Breeding Population ◽  
Weddell Seal ◽  
Adult Survival ◽  
Juvenile Survival ◽  
Apparent Survival ◽  
Mcmurdo Sound ◽  
Juvenile Dispersal ◽  
Weddell Seals

Survival and recruitment of Weddell seal pups were studied in eastern McMurdo Sound, Antarctica. Pups were marked and their apparent survival estimated by mark–recapture methods. The resulting estimates were used together with published estimates of adult survival, yearly sighting probabilities, and direct counts of pup production to simulate the dynamics of the population and evaluate the assumption that it is closed to immigration. Estimates derived from census data in 1982 and 1983 were over five times larger than those simulated. This discrepancy was due to the extremely low juvenile survival rates calculated from marked seals. Since few animals born in Erebus Bay return to breed, the large adult breeding population must be the result of substantial immigration, indicating an important role for juvenile dispersal in the population dynamics of Weddell seals.

scholarly journals Recent status and population decline of the Great Bustard Otis tarda in Iran

2015 ◽  
Vol 25 (3) ◽  
pp. 377-384 ◽  
Author(s):  
AHMAD BARATI ◽  
RAHIM ABDULKARIMI ◽  
JUAN CARLOS ALONSO
Keyword(s):  
Literature Review ◽  
Current Distribution ◽  
Population Decline ◽  
Population Trends ◽  
Great Bustard ◽  
Otis Tarda ◽  
Conservation Measures ◽  
Marked Decline

SummaryThe current distribution and recent population trends of the Great Bustard (Otis tarda) in Iran were investigated based on a literature review and unpublished data (1995–2008) followed by three years of census (2009–2011) in areas where the species is still breeding. Results suggest that Great Bustards have disappeared from a large part of their former distribution in the country, including East Azarbayjan, Hamedan and Kurdistan provinces. The surviving groups are concentrated in West Azarbayjan where numbers are rapidly declining. The present population is estimated at about 43–48 birds in 2011, confirming a marked decline compared to the 200–300 birds estimated in the early 1990s. About 80–90% of the extant birds are concentrated in the plains of Boukan. Strict conservation measures are urgently needed to prevent the extinction of this species in Iran.

scholarly journals The distribution of heterozygosity in temperate and tropical species of Drosophila

1981 ◽  
Vol 38 (2) ◽  
pp. 137-156 ◽  
Author(s):  
B. D. H. Latter
Keyword(s):  
Breeding Population ◽  
Tropical Species ◽  
Average Intensity ◽  
Consistent Difference ◽  
Neutral Model ◽  
Relative Contribution ◽  
Group I ◽  
Significant Difference ◽  
Population Sizes ◽  
The Mean

SUMMARYElectrophoretic surveys for nine species of Drosophila have been summarized in terms of the relative contribution to heterozygosity of each of ten gene frequency classes, the mean frequency of heterozygotes within subpopulations, and the degree of genetic divergence between subpopulations. It has been shown that the neutral model proposed by Kimura, and modified by Ohta to include the accumulation of slightly disadvantageous mutations, is capable of explaining all features of the data. The consistent difference between group I and group II enzymes can be explained by a difference in the average intensity of selection against mutational variants in the two groups. A highly significant difference between the temperate and tropical species in the distribution of heterozygosity appears to be due to the smaller effective breeding population sizes in the case of the temperate species.

Energy requirements and food consumption of Eudyptes penguins at the Prince Edward Islands

1989 ◽  
Vol 1 (1) ◽  
pp. 15-21 ◽  
Author(s):  
Christopher R. Brown
Keyword(s):  
Food Consumption ◽  
Breeding Population ◽  
Energy Requirements ◽  
Bioenergetic Model ◽  
Energy Expenditures ◽  
Prince Edward Islands ◽  
Eudyptes Chrysolophus ◽  
Population Sizes ◽  
Available Information ◽  
Moulting Cycle

Macaroni penguins (Eudyptes chrysolophus) and rockhopper penguins (E. chrysocome) account for a substantial proportion of the avian biomass at the subantarctic Prince Edward Islands (47°S, 38°E) in summer, when both species are breeding at the islands. Information on breeding population sizes, breeding and moulting activities, and diets were combined with measurements of the penguins' energy expenditures to construct a bioenergetic model of their energy requirements and food consumption at the islands. Total energy requirements of adults and chicks amounted to 460 × 109 kJ and 162 × 109 kJ for macaroni and rockhopper penguins, respectively. Food consumption was estimated to amount to a total of 166 000 tonnes during the seven-month breeding and moulting cycle, of which macaroni penguins consumed 75%. Most, if not all, of this food is taken within a 200-km radius of the islands. Available information suggests that potential primary production in the immediate vicinity of the islands is sufficient to support the macaroni and rockhopper penguin populations. However, the importance in the diets of the penguins of several prey species more typical of Antarctic and subtropical regions suggests that the penguins rely to a large extent on the importation of prey populations from other areas.

scholarly journals Coalescent models at small effective population sizes and population declines are positively misleading

2019 ◽  
Author(s):  
M. Elise Lauterbur
Keyword(s):  
Genetic Diversity ◽  
Sample Size ◽  
Population Size ◽  
Effective Population Size ◽  
Genetic Relationships ◽  
Population Decline ◽  
Population Declines ◽  
Effective Population ◽  
Analytical Approximations ◽  
Population Sizes

AbstractPopulation genetics employs two major models for conceptualizing genetic relationships among individuals – outcome-driven (coalescent) and process-driven (forward). These models are complementary, but the basic Kingman coalescent and its extensions make fundamental assumptions to allow analytical approximations: a constant effective population size much larger than the sample size. These make the probability of multiple coalescent events per generation negligible. Although these assumptions are often violated in species of conservation concern, conservation genetics often uses coalescent models of effective population sizes and trajectories in endangered species. Despite this, the effect of very small effective population sizes, and their interaction with bottlenecks and sample sizes, on such analyses of genetic diversity remains unexplored. Here, I use simulations to analyze the influence of small effective population size, population decline, and their relationship with sample size, on coalescent-based estimates of genetic diversity. Compared to forward process-based estimates, coalescent models significantly overestimate genetic diversity in oversampled populations with very small effective sizes. When sampled soon after a decline, coalescent models overestimate genetic diversity in small populations regardless of sample size. Such overestimates artificially inflate estimates of both bottleneck and population split times. For conservation applications with small effective population sizes, forward simulations that do not make population size assumptions are computationally tractable and should be considered instead of coalescent-based models. These findings underscore the importance of the theoretical basis of analytical techniques as applied to conservation questions.

Sign in / Sign up

Export Citation Format

Share Document