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Results for “Journal of Ecology”

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At least 631 records · Page 35Linked to original sources
USGS1987

Relationship of deer and moose populations to previous winters' snow

(1) Linear regression was used to relate snow accumulation during single and consecutive winters with white-tailed deer ( Odocoileus virginianus ) fawn:doe ratios, moose ( Alces alces ) twinning rates and calf:cow ratios, and annual changes in deer and moose populations. Significant relationships were found between snow accumulation during individual winters and these dependent variables during the following year. However, the strongest relationships were between the dependent variables and the sums of the snow accumulations over the previous three winters. The percentage of the variability explained was 36 to 51. (2) Significant relationships were also found between winter vulnerability of moose calves and the sum of the snow accumulations in the current, and up to seven previous, winters, with about 49% of the variability explained. (3) No relationship was found between wolf numbers and the above dependent variables. (4) These relationships imply that winter influences on maternal nutrition can accumulate for several years and that this cumulative effect strongly determines fecundity and/or calf and fawn survivability. Although wolf ( Canis lupus L.) predation is the main direct mortality agent on fawns and calves, wolf density itself appears to be secondary to winter weather in influencing the deer and moose populations.

Journal of Animal Ecology↗
USGS1994

Functional response of wolves preying on barren-ground caribou in a multiple-prey ecosystem

1. We investigated the functional response of wolves (Canis lupus) to varying abundance of ungulate prey to test the hypothesis that switching from alternate prey to preferred prey results in regulation of a caribou (Rangifer tarandus) population at low densities. 2. We determined prey selection, kill rates, and prey abundance for four wolf packs during three 30-day periods in March 1989, March 1990, November 1990, and created a simple discrete model to evaluate the potential for the expected numerical and observed functional responses of wolves to regulate caribou populations. 3. We observed a quickly decelerating type II functional response that, in the absence of numerical response, implicates an anti-regulatory effect of wolf predation on barren-ground caribou dynamics. 4. There was little potential for regulation caused by the multiplicative effect of increasing functional and numerical responses because of presence of alternative prey. This resulted in high wolf:caribou ratios at low prey densities which precluded the effects of an increasing functional response. 5. Inversely density-dependent predation by other predators, such as bears, reduces the potential for predators to regulate caribou populations at low densities, and small reductions in predation by one predator may have disproportionately large effects on the total predation rate.

Journal of Animal Ecology↗
USGS1994

Using stable isotopes to determine seabird trophic relationships

1. The stable isotopes of nitrogen (δ 15 N ) and carbon (δ 13 C) were analysed in 22 species of marine birds from coastal waters of the northeast Pacific Ocean. Analyses confirm that stable nitrogen isotopes can predict seabird trophic positions. 2. Based on δ 15 N analyses, seabird trophic-level inferences generally agree with those of conventional dietary studies, but suggest that lower trophic-level organisms are more important to several seabirds than was recognized previously. 3. Stable-carbon isotope analysis may be a good indicator of inshore vs. offshore feeding preference. 4. In general, stable-isotope analysis to determine trophic level offers many advantages over conventional dietary approaches since trophic inferences are based on time-integrated estimates of assimilated and not just ingested foods, and isotopic abundance represents a continuous variable that is amenable to statistical analysis.

Alaska, British Columbia↗
USGS1995

The cumulative effect of consecutive winters' snow depth on moose and deer populations: a defence

1. L. D. Mech et al. presented evidence that moose Alces alces and deer Odocoileus virginianus population parameters re influenced by a cumulative effect of three winters' snow depth. They postulated that snow depth affects adult ungulates cumulatively from winter to winter and results in measurable offspring effects after the third winter. 2. F. Messier challenged those findings and claimed that the population parameters studied were instead affected by ungulate density and wolf indexes. 3. This paper refutes Messier's claims by demonstrating that his results were an artifact of two methodological errors. The first was that, in his main analyses, Messier used only the first previous winter's snow depth rather than the sum of the previous three winters' snow depth, which was the primary point of Mech et al. Secondly, Messier smoothed the ungulate population data, which removed 22-51% of the variability from the raw data. 4. When we repeated Messier's analyses on the raw data and using the sum of the previous three winter's snow depth, his findings did not hold up.

Journal of Animal Ecology↗
USGS1997

Interactive effects of prey and weather on golden eagle reproduction

1. The reproduction of the golden eagle Aquila chrysaetos was studied in southwestern Idaho for 23 years, and the relationship between eagle reproduction and jackrabbit Lepus californicus abundance, weather factors, and their interactions, was modelled using general linear models. Backward elimination procedures were used to arrive at parsimonious models. 2. The number of golden eagle pairs occupying nesting territories each year showed a significant decline through time that was unrelated to either annual rabbit abundance or winter severity. However, eagle hatching dates were significantly related to both winter severity and jackrabbit abundance. Eagles hatched earlier when jackrabbits were abundant, and they hatched later after severe winters. 3. Jackrabbit abundance influenced the proportion of pairs that laid eggs, the proportion of pairs that were successful, mean brood size at fledging, and the number of young fledged per pair. Weather interacted with prey to influence eagle reproductive rates. 4. Both jackrabbit abundance and winter severity were important in predicting the percentage of eagle pairs that laid eggs. Percentage laying was related positively to jackrabbit abundance and inversely related to winter severity. 5. The variables most useful in predicting percentage of laying pairs successful were rabbit abundance and the number of extremely hot days during brood-rearing. The number of hot days and rabbit abundance were also significant in a model predicting eagle brood size at fledging. Both success and brood size were positively related to jackrabbit abundance and inversely related to the frequency of hot days in spring. 6. Eagle reproduction was limited by rabbit abundance during approximately twothirds of the years studied. Weather influenced how severely eagle reproduction declined in those years. 7. This study demonstrates that prey and weather can interact to limit a large raptor population's productivity. Smaller raptors could be affected more strongly, especially in colder or wetter climates.

Journal of Animal Ecology↗
USGS2009

Larval habitat for the avian malaria vector culex quinquefasciatus (Diptera: Culicidae) in altered mid-elevation mesic-dry forests in Hawai'i

Effective management of avian malaria (Plasmodium relictum) in Hawai'i's endemic honeycreepers (Drepanidinae) requires the identification and subsequent reduction or treatment of larval habitat for the mosquito vector, Culex quinquefasciatus (Diptera: Culicidae). We conducted ground surveys, treehole surveys, and helicopter aerial surveys from 20012003 to identify all potential larval mosquito habitat within two 100+ ha mesic-dry forest study sites in Hawai'i Volcanoes National Park, Hawai'i; 'Ainahou Ranch and Mauna Loa Strip Road. At 'Ainahou Ranch, anthropogenic sites (43%) were more likely to contain mosquitoes than naturally occurring (8%) sites. Larvae of Cx. quinquefasciatus were predominately found in anthropogenic sites while Aedes albopictus larvae occurred less frequently in both anthropogenic sites and naturally-occurring sites. Additionally, moderate-size (???20-22,000 liters) anthropogenic potential larval habitat had >50% probability of mosquito presence compared to larger- and smaller-volume habitat (<50%). Less than 20% of trees surveyed at ' Ainahou Ranch had treeholes and few mosquito larvae were detected. Aerial surveys at 'Ainahou Ranch detected 56% (95% CI: 42-68%) of the potential larval habitat identified in ground surveys. At Mauna Loa Strip Road, Cx. quinquefasciatus larvae were only found in the rock holes of small intermittent stream drainages that made up 20% (5 of 25) of the total potential larval habitat. The volume of the potential larval habitat did not influence the probability of mosquito occurrence at Mauna Loa Strip Road. Our results suggest that Cx. quinquefasciatus abundance, and subsequently avian malaria, may be controlled by larval habitat reduction in the mesic-dry landscapes of Hawai'i where anthropogenic sources predominate.

Journal of Vector Ecology↗
USGS2006

Assessing peridomestic entomological factors as predictors for Lyme disease

The roles of entomologic risk factors, including density of nymphal blacklegged ticks ( Ixodes scapularis ), prevalence of nymphal infection with the etiologic agent ( Borrelia burgdorferi) , and density of infected nymphs, in determining the risk of human Lyme disease were assessed at residences in the endemic community of South Kingstown, RI. Nymphs were sampled between May and July from the wooded edge around 51 and 47 residential properties in 2002 and 2003, respectively. Nymphs were collected from all residences sampled. Tick densities, infection rates, and densities of infected nymphs were all significantly higher around homes reporting Lyme disease histories in 2003, while only infection rates were significantly higher in 2002. However, densities of infected nymphs did not significantly predict the probability of Lyme disease at a residence (by logistic regression) in either year. There were no significant differences in entomologic risk factors between homes with state-confirmed Lyme disease histories and homes with self-reported cases (not reported to the state health department). Therefore, although entomologic risk factors tended to be higher at residences with cases of Lyme disease, entomological indices, in the absence of human behavior measures, were not useful predictors of Lyme disease at the scale of individual residences in a tick-endemic community.

Rhode Island↗
USGS2022

One Health in action: Flea control and interpretative education at Badlands National Park

One Health involves interdisciplinary collaboration to improve, protect, and preserve the health of humans, wildlife, and ecosystems, and advocates for unified approaches to One Health challenges (Buttke et al. 2015). Here, we focus on a One Health challenge of nearly global distribution: Yersinia pestis , the flea-borne bacterial agent of plague. The bacterium poses a significant risk to humans and wildlife, causing social strife in some regions and transforming ecosystems (Eads and Biggins 2015). The conservation implications are profound in the western United States, where Y. pestis was first introduced in 1900. Considerable effort is devoted to plague mitigation, sometimes for human or wildlife health purposes separately. We present a synergy between plague mitigation for human and wildlife health.

South Dakota↗
USGS1992

Morphology of ruffe (Gymnocephalus cernuus) protolarvae from the St. Louis River, Lake Superior

We describe hatching and the morphological and meristic characteristics of 2.5-5.6 mm long ruffe protolarvae (Gymnocephalus cernuus). Eggs and sperm from St. Louis River ruffe were mixed, producing fertilized eggs that were 0.9-1.2 mm in diameter. Newly hatched protolarvae were 2.5-3.2 mm long. They had 14-15 preanal and 23-24 postanal myomeres, a continuous finfold of even width, unpigmented eyes, and a large anterior oil globule in the yolk sac, and the head deflected over the yolk sac. Pectoral fin buds appeared on the dorsal side of the yolk sac 5 hours after hatching. Two-day-old protolarvae had fully pigmented eyes, and the head was free from the yolk sac. Three-day-old protolarvae were 3.9-4.3 mm long and possessed opercula, gills, pectoral fins, and a functional jaw. Feeding and swimming began about one week after hatching when the yolk sac was almost completely absorbed. Protolarvae grew rapidly at 20-22 degrees C and were 4.9-5.6 mm long after 13 days. Newly hatched ruffe protolarvae are distinguished from other Lake Superior percids by having the fewest preanal myomeres (14-15), the head deflected over the yolk sac, continuous finfold of even width, and a total length of less than 4.0 mm.

Journal of Freshwater Ecology↗
USGS1985

Distribution and food habits of young-of-the-year fishes in a backwater lake of the upper Mississippi River

The distribution patterns and food habits of young-of-the-year (YOY) fishes in a lentic area adjacent to the main channel of Pool 7 of the upper Mississippi River were studied. Habitats sampled grouped distinctly based on percent composition and abundance of YOY fishes with those having submergent vegetation dominated by a number of important sport species. In late spring, the grouping of stations depended on the presence or absence of newly transformed northern pike (Esox lucius). In early summer, stations did not differ as distinctly in composition, but in total abundance of young. Those stations with submergent vegetation had total catches which were more than double those elsewhere. By late summer, submergent and mixed vegetation stations formed a distinct assemblage influenced by the preponderance of three species of sunfishes. (DBO).

Journal of Freshwater Ecology↗
USGS1992

Heavy metals in the threeridge mussel Amblema plicata plicata (Say, 1817) in the upper Mississippi River

Concentrations of mercury and zinc in the threeridge mussel Amblema plicata plicata, sampled in 1987 from Pools 3 and 10 in the upper Mississippi River, were comparable to concentrations in mussels from moderately contaminated systems, while copper concentrations were similar to concentrations in mussels from more polluted waters. Cadmium concentrations in mussels were significantly less at a lightly contaminated site (Pool 10, range 0.53 to 0.92 mu g/g dry weight) than at a site where metal abundances were strongly influenced by industrial and domestic inputs (Pool 3, range 0.80 to 1.25 mu g/g dry weight). Yet, cadmium concentrations in Pool 3 were an order of magnitude less than values reported for mussels from more metal-polluted systems. In contrast, concentrations of copper, mercury, and zinc did not differ between sites. Cadmium and zinc concentrations generally increased with size of the mussel, copper concentrations decreased with size, and mercury concentrations were unrelated to size.a

Journal of Freshwater Ecology↗
USGS1986

Analysis of utilization of desert habitats with dynamic simulation

The effects of climate and herbivores on cool desert shrubs in north-western Utah were investigated with a dynamic simulation model. Cool desert shrublands are extensively managed as grazing lands, and are defoliated annually by domestic livestock. A primary production model was used to simulate harvest yields and shrub responses under a variety of climatic regimes and defoliation patterns. The model consists of six plant components, and it is based on equations of growth analysis. Plant responses were simulated under various combinations of 20 annual weather patterns and 14 defoliation strategies. Results of the simulations exhibit some unexpected linearities in model behavior, and emphasize the importance of both the pattern of climate and the level of plant vigor in determining optimal harvest strategies. Model behaviors are interpreted in terms of shrub morphology, physiology and ecology.

Journal of Environmental Management↗
USGS2001

Integrated pest management and allocation of control efforts for vector-borne diseases

Applications of various control methods were evaluated to determine how to integrate methods so as to minimize the number of human cases of vector-borne diseases. These diseases can be controlled by lowering the number of vector-human contacts (e.g., by pesticide applications or use of repellents), or by lowering the proportion of vectors infected with pathogens (e.g., by lowering or vaccinating reservoir host populations). Control methods should be combined in such a way as to most efficiently lower the probability of human encounter with an infected vector. Simulations using a simple probabilistic model of pathogen transmission suggest that the most efficient way to integrate different control methods is to combine methods that have the same effect (e.g., combine treatments that lower the vector population; or combine treatments that lower pathogen prevalence in vectors). Combining techniques that have different effects (e.g., a technique that lowers vector populations with a technique that lowers pathogen prevalence in vectors) will be less efficient than combining two techniques that both lower vector populations or combining two techniques that both lower pathogen prevalence, costs being the same. Costs of alternative control methods generally differ, so the efficiency of various combinations at lowering human contact with infected vectors should be estimated at available funding levels. Data should be collected from initial trials to improve the effects of subsequent interventions on the number of human cases.

Journal of Vector Ecology↗
USGS2006

Variation in probability of first reproduction of Weddell seals

Summary 1. For many species, when to begin reproduction is an important life-history decision that varies by individual and can have substantial implications for lifetime reproductive success and fitness. 2. We estimated age-specific probabilities of first-time breeding and modelled variation in these rates to determine age at first reproduction and understand why it varies in a population of Weddell seals in Erebus Bay, Antarctica. We used multistate mark?recapture modelling methods and encounter histories of 4965 known-age female seals to test predictions about age-related variation in probability of first reproduction and the effects of annual variation, cohort and population density. 3. Mean age at first reproduction in this southerly located study population (7.62 years of age, SD =1.71) was greater than age at first reproduction for a Weddell seal population at a more northerly and typical latitude for breeding Weddell seals (mean =4?5 years of age). This difference suggests that age at first reproduction may be influenced by whether a population inhabits the core or periphery of its range. 4. Age at first reproduction varied from 4 to 14 years, but there was no age by which all seals recruited to the breeding population, suggesting that individual heterogeneity exists among females in this population. 5. In the best model, the probability of breeding for the first time varied by age and year, and the amount of annual variation varied with age (average variance ratio for age-specific rates =4.3%). 6. Our results affirmed the predictions of life-history theory that age at first reproduction in long-lived mammals will be sensitive to environmental variation. In terms of life history evolution, this variability suggests that Weddell seals display flexibility in age at first reproduction in order to maximize reproductive output under varying environmental conditions. Future analyses will attempt to test predictions regarding relationships between environmental covariates and annual variation in age at first reproduction and evaluate the relationship between age at first reproduction and lifetime reproductive success.

Journal of Animal Ecology↗
USGS2008

Importance of sampling design and analysis in animal population studies: a comment on Sergio et al

1. The use of predators as indicators and umbrellas in conservation has been criticized. In the Trentino region, Sergio et al. (2006; hereafter SEA) counted almost twice as many bird species in quadrats located in raptor territories than in controls. However, SEA detected astonishingly few species. We used contemporary Swiss Breeding Bird Survey data from an adjacent region and a novel statistical model that corrects for overlooked species to estimate the expected number of bird species per quadrat in that region. 2. There are two anomalies in SEA which render their results ambiguous. First, SEA detected on average only 6.8 species, whereas a value of 32 might be expected. Hence, they probably overlooked almost 80% of all species. Secondly, the precision of their mean species counts was greater in two-thirds of cases than in the unlikely case that all quadrats harboured exactly the same number of equally detectable species. This suggests that they detected consistently only a biased, unrepresentative subset of species. 3. Conceptually, expected species counts are the product of true species number and species detectability p. Plenty of factors may affect p, including date, hour, observer, previous knowledge of a site and mobbing behaviour of passerines in the presence of predators. Such differences in p between raptor and control quadrats could have easily created the observed effects. Without a method that corrects for such biases, or without quantitative evidence that species detectability was indeed similar between raptor and control quadrats, the meaning of SEA's counts is hard to evaluate. Therefore, the evidence presented by SEA in favour of raptors as indicator species for enhanced levels of biodiversity remains inconclusive. 4. Synthesis and application. Ecologists should pay greater attention to sampling design and analysis in animal population estimation. Species richness estimation means sampling a community. Samples should be representative for the community studied and the sampling fraction among communities compared should be the same on average, otherwise formal estimation approaches must be applied to avoid misleading inference.

Journal of Applied Ecology↗
USGS2009

A cautionary note on substituting spatial subunits for repeated temporal sampling in studies of site occupancy

1. Assessing the probability that a given site is occupied by a species of interest is important to resource managers, as well as metapopulation or landscape ecologists. Managers require accurate estimates of the state of the system, in order to make informed decisions. Models that yield estimates of occupancy, while accounting for imperfect detection, have proven useful by removing a potentially important source of bias. To account for detection probability, multiple independent searches per site for the species are required, under the assumption that the species is available for detection during each search of an occupied site. 2. We demonstrate that when multiple samples per site are defined by searching different locations within a site, absence of the species from a subset of these spatial subunits induces estimation bias when locations are exhaustively assessed or sampled without replacement. 3. We further demonstrate that this bias can be removed by choosing sampling locations with replacement, or if the species is highly mobile over a short period of time. 4. Resampling an existing data set does not mitigate bias due to exhaustive assessment of locations or sampling without replacement. 5. Synthesis and applications. Selecting sampling locations for presence/absence surveys with replacement is practical in most cases. Such an adjustment to field methods will prevent one source of bias, and therefore produce more robust statistical inferences about species occupancy. This will in turn permit managers to make resource decisions based on better knowledge of the state of the system.

Journal of Applied Ecology↗
USGS2010

Potential spread of highly pathogenic avian influenza H5N1 by wildfowl: dispersal ranges and rates determined from large-scale satellite telemetry

1. Migratory birds are major candidates for long-distance dispersal of zoonotic pathogens. In recent years, wildfowl have been suspected of contributing to the rapid geographic spread of the highly pathogenic avian influenza (HPAI) H5N1 virus. Experimental infection studies reveal that some wild ducks, geese and swans shed this virus asymptomatically and hence have the potential to spread it as they move. 2. We evaluate the dispersive potential of HPAI H5N1 viruses by wildfowl through an analysis of the movement range and movement rate of birds monitored by satellite telemetry in relation to the apparent asymptomatic infection duration (AID) measured in experimental studies. We analysed the first large-scale data set of wildfowl movements, including 228 birds from 19 species monitored by satellite telemetry in 2006&ndash;2009, over HPAI H5N1 affected regions of Asia, Europe and Africa. 3. Our results indicate that individual migratory wildfowl have the potential to disperse HPAI H5N1 over extensive distances, being able to perform movements of up to 2900 km within timeframes compatible with the duration of asymptomatic infection. 4. However, the likelihood of such virus dispersal over long distances by individual wildfowl is low: we estimate that for an individual migratory bird there are, on average, only 5&ndash;15 days per year when infection could result in the dispersal of HPAI H5N1 virus over 500 km. 5. Staging at stopover sites during migration is typically longer than the period of infection and viral shedding, preventing birds from dispersing a virus over several consecutive but interrupted long-distance movements. Intercontinental virus dispersion would therefore probably require relay transmission between a series of successively infected migratory birds. 6. Synthesis and applications . Our results provide a detailed quantitative assessment of the dispersive potential of HPAI H5N1 virus by selected migratory birds. Such dispersive potential rests on the assumption that free-living wildfowl will respond analogously to captive, experimentally-infected birds, and that asymptomatic infection will not alter their movement abilities. Our approach of combining experimental exposure data and telemetry information provides an analytical framework for quantifying the risk of spread of avian-borne diseases.

Journal of Applied Ecology↗