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113 results for “Population trends”
Quantifying temporal variation in dietary niche to reveal drivers of past population declines; stable isotope, harvest trends, and land use
<p><b>1.</b> Given the long and dynamic history of anthropogenic disturbances to ecosystems, it is difficult to determine the drivers of past population declines. These uncertainties dilute the efficacy of conservation efforts and might hinder species and ecosystem recovery.</p> <p><b>2.</b> Niche quantification can be a useful tool for understanding drivers of past population declines. Niche parameters reflect key resources used, providing insight into the conditions needed to achieve population stability. By reconstructing a population's niche position and space over a period of decline and comparing to historic baselines, shifts in the realized niche of a species can be assessed. Comparing shifts to historic information on resource availability and timing of declines can allow practitioners to identify probable drivers of species decline.</p> <p><span><b>3.</b> We demonstrated the utility of this technique by reconstructing parameters of isotopic dietary niche over a 130 year period and comparing isotopic niche reconstructions to land use and crop harvests during this same period via regression and Bayesian standard ellipsoid (SIBER) analyses. We use a formerly widespread but now endangered species, the eastern spotted skunk (<i>Spilogale putorius</i>), addressing the hypothesis that land use change and agricultural intensification led to a historical collapse of key dietary resources which correlates with population declines in this species. To help control for isotopic variability unrelated to population decline, we compare trends to those of a secure, but ecologically similar generalist mesocarnivore, the striped skunk (<i>Mephitis mephitis</i>), across the same spatiotemporal scale. </span></p> <p><b>4.</b> We present evidence that historic dietary changes occurred in spotted skunks in the early 1900s but not to the same degree in striped skunks. Changes in isotopic composition correspond with the temporal period of decline and are explained by concurrent changes in land use. These results support the hypothesis that loss of key dietary resources as a result of land use change and agricultural intensification played a significant role in population declines of spotted skunks in this region.</p>
Data from: Variations in age- and sex-specific survival rates help explain population trend in a discrete marine mammal population
1. Understanding the drivers underlying fluctuations in the size of animal populations is central to ecology, conservation biology and wildlife management. Reliable estimates of survival probabilities are key to population viability assessments, and patterns of variation in survival can help inferring the causal factors behind detected changes in population size. 2. We investigated whether variation in age and sex-specific survival probabilities could help explain the increasing trend in population size detected in a small, discrete population of bottlenose dolphins Tursiops truncatus off the east coast of Scotland. 3. To estimate annual survival probabilities we applied capture-recapture models to photo-identification data collected from 1989 to 2015. We used robust design models accounting for temporary emigration to estimate juvenile and adult survival, multi-state models to estimate sex-specific survival, and age-models to estimate calf survival. 4. We found strong support for an increase in juvenile/adult annual survival from 93.1% to 96.0% over the study period, most likely caused by a change in juvenile survival. Examination of sex-specific variation showed weaker support for this trend being a result of increasing female survival, which was overall higher than for males and animals of unknown sex. Calf survival was lower in the first than second year; a bias in estimating third-year survival will likely exist in similar studies. There was some support first-born calf survival being lower than for calves born subsequently. 5. Coastal marine mammal populations are subject to the impacts of environmental change, increasing anthropogenic disturbance and the effects of management measures. Survival estimates are essential to improve our understanding of population dynamics and help predict how future pressures may impact populations, but obtaining robust information on the life history of long-lived species is challenging. Our study illustrates how knowledge of survival can be increased by applying a robust analytical framework to photo-identification data.
Data from: Numbers and population trends of large herbivores in Mole National Park, Ghana
<p>Mole National Park (MNP) is Ghana's oldest and largest wildlife preserve. Eight large herbivores were counted in four different seasons in 2013/2014 on transects covering 4.7% of the park to estimate their population sizes and trends after changes in park management; all species were more abundant than previously reported. Averaging counts across seasons, and including all age classes, gave an estimated population of 1595 elephants, which is likely to be a substantial proportion of the west African elephant population. Kob were the most abundant herbivore, with an estimated population of 9092, followed by bushbuck (6758), warthog (6247) and hartebeest (6039). Roan, buffalo and waterbuck population estimates were 4382, 4272 and 4140 respectively. The impact of widespread burning on herbivore populations is currently unknown, but probably helps maintain both numbers and diversity. While all herbivore populations were higher than previously estimated, it was hard to determine the extent of recent increases due to methodological limitations of earlier aerial surveys. However, the distribution of large herbivores seems to be little changed, suggesting that both numbers and distribution are still limited by poaching and seasonal water availability.</p>
Data from: Tracking ice phenology by migratory waterbirds: settling phenology and breeding success of species with divergent population trends
<p>Dependence on climate-driven environmental cues in the initiation of life cycle stages is a critical attribute when assessing vulnerability of species to climate change impacts. This study focused on spring ice phenology as a cue to the settling of migratory waterbirds, asking whether there is an asynchrony between ice phenology and setting phenology that could affect breeding success of six species with divergent population trends. In the 37 study lakes in southeastern Finland, the ice-out date not only varied considerably between years, but became progressively earlier during the study period, 1991–2018. Settling phenology of all species tracked inter-annual variation in ice phenology. However, the degree of asynchrony between ice phenology and settling phenology varied between species, allowing discrimination between early and late settlers. Considerable inter-annual variation also occurred within species, but in only one species did the degree of asynchrony correlate with the ice-out date: for the horned grebe Podiceps auritus an earlier ice-out date meant greater asynchrony between settling phenology and ice phenology. The degree of asynchrony between settling phenology and ice phenology did not affect breeding success in any species. However, ice phenology per se affected breeding success of horned grebes: earlier ice-out was associated with lower annual breeding success. Breeding numbers of horned grebe showed a long-term decline. Results suggest that short-distance migratory birds are able to respond to climate change-driven phenological changes in their breeding environments, and that this ability may not depend on the relative timing of breeding.</p>
Data from: Bucking the trend: genetic analysis reveals high diversity, large population size and low differentiation in a deep ocean cetacean
Understanding the genetic structure of a population is essential to its conservation and management. We report the level of genetic diversity and determine the population structure of a cryptic deep ocean cetacean, the Gray's beaked whale (Mesoplodon grayi). We analysed 530 bp of mitochondrial control region and 12 microsatellite loci from 94 individuals stranded around New Zealand and Australia. The samples cover a large area of the species distribution (~6000 km) and were collected over a 22-year period. We show high genetic diversity (h=0.933–0.987, π=0.763–0.996% and Rs=4.22–4.37, He=0.624–0.675), and, in contrast to other cetaceans, we found a complete lack of genetic structure in both maternally and biparentally inherited markers. The oceanic habitats around New Zealand are diverse with extremely deep waters, seamounts and submarine canyons that are suitable for Gray's beaked whales and their prey. We propose that the abundance of this rich habitat has promoted genetic homogeneity in this species. Furthermore, it has been suggested that the lack of beaked whale sightings is the result of their low abundance, but this is in contrast to our estimates of female effective population size based on mitochondrial data. In conclusion, the high diversity and lack of genetic structure can be explained by a historically large population size, in combination with no known exploitation, few apparent behavioural barriers and abundant habitat.
Data from: Possible causes of divergent population trends in sympatric African herbivores
Sympatric herbivores experience similar environmental conditions but can vary in their population trends. Identifying factors causing these differences could assist conservation efforts aimed at maintaining fully functional ecosystems. From 1996 – 2013, tsessebe and wildebeest populations in the Okavango Delta, Botswana, declined by 73% and 90%, respectively, whereas zebra populations remained stable. These sympatric, medium sized herbivores are exposed to similar natural and anthropogenic pressures, but apparently differ in their responses to those pressures. To identify factors that could cause these differences, we fitted GPS-enabled collars to six zebra, eight tsessebe and seven wildebeest in the Moremi Game Reserve, Botswana. We calculated utilisation distributions (UDs) from GPS data, and used 95% isopleths to compare seasonal home range size between species. We calculated utilisation intensity (UI) from the UDs and generated spatial layers representing resources and disturbances, and then used model averaging to identify factors affecting UI for each species. We calculated second and third order habitat selection ratios to determine whether species were habitat specialists or generalists. Zebra occupied larger home ranges than tsessebe and wildebeest, showed weaker responses to spatial variables and displayed no third order habitat selection; zebra social systems are also more fluid, allowing for information exchange between stable harems. Herbivore species that are sedentary, occupy small home ranges, are habitat specialists and exist in relatively isolated groups are likely to be less resistant and resilient to the rapid pace of environmental change forecast by climate change scenarios. Resources contained within existing protected areas are unlikely to maintain populations of such species at sufficiently high levels, potentially leading to functional extinction. Special precautions may be needed to ensure that such species can persist in the wild, such as buffer zones around existing protected areas, which would allow greater potential for adaptive movement should current environmental conditions change.
Data from: Species' traits explain differences in Red list status and long-term population trends in longhorn beetles
Some species are more likely to go extinct than others and this is partially due to species' traits. Therefore, it is important to establish links between traits and extinction risks. Different aspects of a species' biology also relates to different sources of threat, such as fragmented populations or low population growth rate. In a comparative study of Swedish longhorn beetles (Coleoptera: Cerambycidae), we related species' traits to two aspects of extinction risk – population decline and small/fragmented populations – measured by long-term population trends and IUCN Red list classifications. Trait relationships were analysed with generalized linear models and multi-model inference. We found that extinction risk generally increased with longer generation times, corresponding to slower life histories. Adult activity period was also related to both metrics of extinction risk, but in different ways. We also found that extinction risk increased with larval host plant specialization, but only for Red list classification. Large body size was related to increased Red list classification in species overwintering as adults, and overwintering stage also structured the effects of several other traits. Our results show that both intrinsic demographic traits and ecological traits affect extinction risks, and also suggest that risks are shaped by multiple mechanisms. Therefore, researchers should carefully choose their metric of extinction risk for comparative studies, as the Red list classification may best capture current risk, whereas population trends can be used more proactively but may reflect historical relationships between traits and extinction risk.
Data from: Wind farms affect the occurrence, abundance and population trends of small passerine birds: the case of the Dupont's lark
1.The assessment of the effects of wind farms on bird populations is commonly based on collision fatality records. This could undervalue the effect of wind farms on small-sized birds. We evaluate the effect of wind turbines on occurrence, abundance and population trends of a threatened small passerine species, the Dupont's lark Chersophilus duponti. To our knowledge, this is one of the first studies addressing the effect of wind farms on population trends using time series data from multiple wind farms. 2.We estimated population trends by fitting a switching linear trend model with the software TRIM (Trend & Indices for Monitoring data). We used multiannual data surveys of five populations in the presence of wind farms and nine in their absence (2008–2016 period). Furthermore, we fitted a logistic and a negative binomial regression model to test the effect of wind farm proximity on species occurrence and abundance in 2016, respectively. We incorporated local connectivity and habitat availability estimates in both models as predictors. 3.Results showed a negative trend overall, but that was significantly more regressive in the presence of wind farms: 21.0% versus 5.8% average annual decline in the absence of wind farms. 4.Dupont's lark occurrence and abundance in 2016 were negatively affected by measures of population isolation and positively affected by the distance to wind farms. 5.These results highlight the negative effect of isolation and wind farm proximity on Dupont's lark population parameters. Taking into account the metapopulation structure exhibited by the species in the study area, this work established a 4.5 km threshold distance from wind farms, beyond which Dupont's lark populations should be unaffected. 6.Synthesis and applications. This work highlights the negative impact of wind farms on small-sized birds and provides a 4.5 km threshold distance that should be taken into account in the design of future wind energy projects. Moreover, we suggest an analytical approach based on population trends, species abundance and occurrence variation in relation to wind farms, useful for the assessment of wind farm impacts on small-sized birds.
STOC population trend - Galaxy training material
<p>Galaxy training material example file</p> <p>https://galaxyproject.github.io/training-material/</p> <p> </p>
Data from: Non-breeding range size predicts the magnitude of population trends in trans-Saharan migratory passerine birds
Understanding why populations of some migratory species show a directional change over time, i.e. increase or decrease, while others do not, remains a challenge for ecological research. One possible explanation is that species with smaller non-breeding ranges may have more pronounced directional population trends, and their populations are thus more sensitive to the variation in environmental conditions in their non-breeding quarters. According to the serial residency hypothesis, this sensitivity should lead to higher magnitudes (i.e. absolute values) of population trends for species with smaller non-breeding ranges, with the direction of trend being either positive or negative depending on the nature of the environmental change. We tested this hypothesis using population trends over 2001–2012 for 36 sub-Saharan migratory passerine birds breeding in Europe. Namely, we related the magnitude of the species' population trends to the size of their sub-Saharan non-breeding grounds, whilst controlling for factors including number of migration routes, non-breeding habitat niche and wetness, breeding habitat type and life-history strategy. The magnitude of species' population trends grew with decreasing absolute size of sub-Saharan non-breeding ranges, and this result remained significant when non-breeding range size was expressed relative to the size of the breeding range. After repeating the analysis with the trend direction, the relationship with the non-breeding range size disappeared, indicating that both population decreases and increases are frequent amongst species with small non-breeding range sizes. Therefore, species with small non-breeding ranges are at a higher risk of population decline due to adverse factors such as habitat loss or climatic extremes, but their populations are also more likely to increase when suitable conditions appear. As non-breeding ranges may originate from stochasticity of non-breeding site selection in naive birds ('serial-residency' hypothesis), it is crucial to maintain a network of stable and resilient habitats over large areas of birds' non-breeding quarters.
Fig. 5 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 5. Number of adult Cicindela dorsalis dorsalis at Janes and Cedar Islands, Maryland, 1998–2014, based on one count per year during peak season.
Fig. 2. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Area 5 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 2. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Area 5 (Calvert County, Maryland), Geographic Recovery Area 6 (Tangier Sound, Maryland), and Geographic Recovery Area 7 (Eastern Shore of Chesapeake Bay, Virginia) as of July 2014.
Fig. 1. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Areas 5–9 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 1. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Areas 5–9, Maryland and Virginia as of July 2014.
Fig. 7 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 7. Shoreline change at Flag Ponds, Maryland, 1993–2013. Arrow shows shoreline area of prime larval habitat in the late 1980s into the early 1990s and its change to non-habitat.
Fig. 4 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 4. Number of adult Cicindela doralis dorsalis at five Calvert County, Maryland sites from 1986 to 2014, based on one count per year during peak season. PM = Parker Marsh; SC = Scientists Cliffs; WS = Western Shores; FP = Flag Ponds; CP = Cove Point.
Fig. 3. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Area 8 in Population Trends of the Northeastern Beach Tiger Beetle,Cicindela dorsalis dorsalisSay (Coleoptera: Carabidae: Cicindelinae) in Virginia and Maryland, 1980s Through 2014
Fig. 3. Occupied and extirpated sites for Cicindela dorsalis dorsalis within Geographic Recovery Area 8 (Western Shore of Chesapeake Bay, north of Rappahannock River, Virginia) and Geographic Recovery Area 9 (Western Shore of Chesapeake Bay, south of Rappahannock River) as of July 2014.
FIGURE 1 in Population Trends Of The Red Palm Mite, Raoiella Indica Hirst (Acari: Tenuipalpidae) And Associated Entomopathogenic Fungi In Trinidad, Antigua, St Kitts And Nevis And Dominica
FIGURE 1: Average population of Red Palm Mite in the different islands evaluated.
Data from: Possible causes of divergent population trends in sympatric African herbivores
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Data from: Linking forest management to moose population trends: the role of the nutritional landscape
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Data from: Differences in spatial synchrony and interspecific concordance inform guild-level population trends for aerial insectivorous birds
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