USGS Science⌕ Search

SEARCH · USGS Science

Results for “Predator”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources
USGS2018

Trophic implications of a phenological paradigm shift: Bald eagles and salmon in a changing climate

Climate change influences apex predators in complex ways, due to their important trophic position, capacity for resource plasticity, and sensitivity to numerous anthropogenic stressors. Bald eagles, an ecologically and culturally significant apex predator, congregate seasonally in high densities on salmon spawning rivers across the Pacific Northwest. One of the largest eagle concentrations is in the Skagit River watershed, which connects the montane wilderness of North Cascades National Park to the Puget Sound. Using multiple long‐term datasets, we evaluated local bald eagle abundance in relation to chum and coho salmon availability; salmon phenology; and the number and timing of flood events in the Skagit. We analysed changes over time as a reflection of climate change impacts, as well as differences between managed and unmanaged portions of the river. We found that peaks in chum salmon and bald eagle presence have advanced at remarkably similar rates ( c . 0.45 days/year), suggesting synchronous phenological responses within this trophic relationship. Yet the temporal relationship between chum salmon spawning and flood events, which remove salmon carcasses from the system, has not remained constant. This has resulted in a paradigm shift whereby the peak of chum spawning now occurs before the first flood event of the season rather than after. The interval between peak chum and first flood event was a significant predictor of bald eagle presence: as this interval grew over time (by nearly one day per year), bald eagle counts declined, with a steady decrease in bald eagle observations since 2002. River section was also an important factor, with fewer flood events, and more eagle observations occurring in the river section experiencing direct hydroelectric flow management. Synthesis and applications . The effects of climate change and hydroelectric management contribute to a complex human footprint in the North Cascades National Park, an otherwise largely natural ecosystem. By accounting for the differential phenological impacts of climate change on bald eagles, salmon, and flood events, Park managers and the operators of the hydroelectric system can more effectively ensure the resilience of the eagle–salmon relationship along the Skagit River.

Washington↗
USGS2020

Survival is negatively associated with glucocorticoids in a wild ungulate neonate

It is unknown how ungulate physiological responses to environmental perturbation influence overall population demographics. Moreover, neonatal physiological responses remain poorly studied despite the importance of neonatal survival to population growth. Glucocorticoid (GC) hormones potentially facilitate critical physiological and behavioral responses to environmental perturbations. However, elevated GC concentrations over time may compromise body condition and indirectly reduce survival. We evaluated baseline salivary cortisol (CORT; a primary GC in mammals) concentrations in 19 wild neonatal white-tailed deer ( Odocoileus virginianus ) in a northern (NS) and southern (SS) area in Pennsylvania. After ranking survival models consisting of variables hypothesized to influence neonate survival (i.e. weight, sex), the probability of neonate survival was best explained by CORT concentrations, where elevated CORT concentrations were associated with reduced survival probability to 12 weeks of age. Cortisol concentrations were greater in the SS where predation rates and predator densities were lower. As the first evaluation of baseline CORT concentrations in an ungulate neonate to our knowledge, this is also the first study to demonstrate CORT concentrations are negatively associated with ungulate survival at any life stage. Glucocorticoid hormones could provide a framework in which to better understand susceptibility to mortality in neonatal white-tailed deer.

Integrative Zoology↗
USGS2023

Toward absolute abundance for conservation applications: Estimating the number of contributors via microhaplotype genotyping of mixed-DNA sample

Molecular methods including metabarcoding and quantitative polymerase chain reaction have shown promise for estimating species abundance by quantifying the concentration of genetic material in field samples. However, the relationship between specimen abundance and detectable concentrations of genetic material is often variable in practice. DNA mixture analysis represents an alternative approach to quantify specimen abundance based on the presence of unique alleles in a sample. The DNA mixture approach provides novel opportunities to inform ecology and conservation by estimating the absolute abundance of target taxa through molecular methods; yet, the challenges associated with genotyping many highly variable markers in mixed-DNA samples have prevented its widespread use. To advance molecular approaches for abundance estimation, we explored the utility of microhaplotypes for DNA mixture analysis by applying a 125-marker panel to 1179 Chinook salmon ( Oncorhynchus tshawytscha ) smolts from the Sacramento-San Joaquin Delta, California, USA. We assessed the accuracy of DNA mixture analysis through a combination of mock mixtures containing DNA from up to 20 smolts and a trophic ecological application enumerating smolts in predator diets. Mock DNA mixtures of up to 10 smolts could reliably be resolved using microhaplotypes, and increasing the panel size would likely facilitate the identification of more individuals. However, while analysis of predator gastrointestinal tract contents indicated DNA mixture analysis could discern the presence of multiple prey items, poor and variable DNA quality prevented accurate genotyping and abundance estimation. Our results indicate that DNA mixture analysis can perform well with high-quality DNA, but methodological improvements in genotyping degraded DNA are necessary before this approach can be used on marginal-quality samples.

California↗
USGS2015

Assessing the robustness of quantitative fatty acid signature analysis to assumption violations

Knowledge of animal diets can provide important insights into life history and ecology, relationships among species in a community and potential response to ecosystem change or perturbation. Quantitative fatty acid signature analysis (QFASA) is a method of estimating diets from data on the composition, or signature, of fatty acids stored in adipose tissue. Given data on signatures of potential prey, a predator diet is estimated by minimizing the distance between its signature and a mixture of prey signatures. Calibration coefficients, constants derived from feeding trials, are used to account for differential metabolism of individual fatty acids. QFASA has been widely applied since its introduction and several variants of the original estimator have appeared in the literature. However, work to compare the statistical properties of QFASA estimators has been limited. One important characteristic of an estimator is its robustness to violations of model assumptions. The primary assumptions of QFASA are that prey signature data contain representatives of all prey types consumed and the calibration coefficients are known without error. We investigated the robustness of two QFASA estimators to a range of violations of these assumptions using computer simulation and recorded the resulting bias in diet estimates. We found that the Aitchison distance measure was most robust to errors in the calibration coefficients. Conversely, the Kullback–Leibler distance measure was most robust to the consumption of prey without representation in the prey signature data. In most QFASA applications, investigators will generally have some knowledge of the prey available to predators and be able to assess the completeness of prey signature data and sample additional prey as necessary. Conversely, because calibration coefficients are derived from feeding trials with captive animals and their values may be sensitive to consumer physiology and nutritional status, their applicability to free-ranging animals is difficult to establish. We therefore recommend that investigators first make any improvements to the prey signature data that seem warranted and then base estimation on the Aitchison distance measure, as it appears to minimize risk from violations of the assumption that is most difficult to verify.

Methods in Ecology and Evolution↗
USGS2018

DNA mixtures for ecology

Mixtures of DNA from multiple contributors present a novel opportunity to count individuals to inform fish and wildlife ecology. We apply a likelihood-based framework to estimate the number of contributors to a DNA mixture for ecological applications. We then assess the performance of DNA mixture estimation through a combination of simulation analyses, laboratory testing, and a field trial to estimate fish predation rates from stomach content analysis. Simulations indicated reasonably sized genetic marker panels could estimate the number of contributors to mixtures comprised of up to 10 individuals, with potential to resolve larger mixtures with additional markers. Mixture estimates demonstrated robustness to common genotyping errors associated with fish and wildlife genetics applications. Laboratory trials demonstrated that DNA combined from multiple yellow perch ( Perca flavescens ) could be successfully genotyped with a 14-loci microsatellite panel and led to successful estimation for up to 5-contributor mixtures. Stomach content analysis with DNA mixtures indicated a 5-fold increase in estimated predation rates of yellow perch by largemouth bass ( Micropterus salmoides ) relative to conventional visual assessment of diet contents which can miss partially digested prey items. DNA mixtures have potential to expand applications of count-based ecological analyses. Technical challenges in generating genotypes from DNA mixtures may initially limit their use, however, advances in next generation genotyping platforms are anticipated to surmount these obstacles. Chiefly, we envision opportunity for DNA mixtures to advance eDNA analysis beyond presence/absence based inference to enumeration of specimens.

Methods in Ecology and Evolution↗
USGS2022

Spatial dynamic N-mixture models with interspecific interactions

Interspecific interactions and movement are key factors that drive the coexistence of metapopulations in heterogenous landscapes. Yet, it is challenging to understand these factors because separating movement from local population processes relied on capture-based data that are difficult to collect. Recent development of spatial dynamic N-mixture models (SDNMs) made it possible to draw inference on local population growth and movement using count data of unmarked populations. However, no SDNMs have been developed to account for interspecific interactions and double counting observation errors. In this study we further developed SDNMs to account for interspecific interactions and both false negative and double counting observation errors. We conducted simulation studies to evaluate the inferential performance of these models under different ecological systems (competition, predator-prey), observation processes (binomial, Poisson), and sampling situations including the number of surveyed sites, detection, and the adoption of robust sampling design. We then illustrated the applications of these models with two case studies, one representing a competition system (mallard Anas platyrhynchos , northern pintail Anas acuta ) with binomial observations and the other representing a predator-prey system (bobcat Lynx rufus , wild turkey Meleagris gallopavo ) with Poisson observations. The results of the simulation studies showed that the models provide unbiased parameter estimates regardless of the ecological system, observation process, and sampling situation. Case studies further demonstrated the capabilities of these models in revealing important ecological processes. More specifically, the first case study revealed a negative effect of the superior competitor, Mallard, on the population growth of the inferior competitor, pintail as well as different movement patterns between these species, while the second case study reveal a top-down effect of bobcat abundance on wild turkey population growth and their differential habitat preferences. The models developed in this study could be used by themselves on count data or serve as population sub-models in integrated modeling frameworks to provide insights about metapopulation dynamics of interacting species in heterogeneous landscapes. The flexible structures of these models made them highly adaptive and relevant in population and community ecology.

Methods in Ecology and Evolution↗
USGS2025

Using periodic matrix models to simulate the effectiveness of alternative reintroduction strategies for lizards on a seasonal tropical island

Conservation translocations and reintroductions are widely used to improve conservation outcomes for declining species. Reintroductions are unlikely to be successful if the threats that led to the extirpation of the focal species, such as non-native predators, have not been ameliorated. The non-native brown treesnake ( Boiga irregularis ) was introduced to Guam in the mid-20th century and has devastated the native lizard fauna of this Pacific Island. Native lizard populations persist on small islands near Guam and could act as sources for reintroductions. Recently, trapping methods have been shown to greatly reduce the density of brown treesnakes, raising the possibility that native lizards could be reintroduced where brown treesnake abundance is controlled. Here we developed demographic models for four lizard species present on Guam to assess their validity as a trial for reintroducing species to meet native species recovery goals. These four species vary in their size, activity, and susceptibility to predation by brown treesnakes. We used periodic matrix models to simulate changes in lizard vital rates driven by the wet-dry seasonal cycle found on Guam. We found that the release of 60 individuals of each species was likely to result in successful reintroduction outcomes provided adult survival in the wild is similar to rates estimated based on life history parameters. Demographic models can be used to forecast reintroduction outcomes, including predicting the probability of success and evaluating causes of failure in the event that populations do not establish.

Guam↗
USGS2024

Climate, food and humans predict communities of mammals in the United States

Aim The assembly of species into communities and ecoregions is the result of interacting factors that affect plant and animal distribution and abundance at biogeographic scales. Here, we empirically derive ecoregions for mammals to test whether human disturbance has become more important than climate and habitat resources in structuring communities. Location Conterminous United States. Time Period 2010–2021. Major Taxa Studied Twenty-five species of mammals. Methods We analysed data from 25 mammal species recorded by camera traps at 6645 locations across the conterminous United States in a joint modelling framework to estimate relative abundance of each species. We then used a clustering analysis to describe 8 broad and 16 narrow mammal communities. Results Climate was the most important predictor of mammal abundance overall, while human population density and agriculture were less important, with mixed effects across species. Seed production by forests also predicted mammal abundance, especially hard-mast tree species. The mammal community maps are similar to those of plants, with an east–west split driven by different dominant species of deer and squirrels. Communities vary along gradients of temperature in the east and precipitation in the west. Most fine-scale mammal community boundaries aligned with established plant ecoregions and were distinguished by the presence of regional specialists or shifts in relative abundance of widespread species. Maps of potential ecosystem services provided by these communities suggest high herbivory in the Rocky Mountains and eastern forests, high invertebrate predation in the subtropical south and greater predation pressure on large vertebrates in the west. Main Conclusions Our results highlight the importance of climate to modern mammals and suggest that climate change will have strong impacts on these communities. Our new empirical approach to recognizing ecoregions has potential to be applied to expanded communities of mammals or other taxa.

Conterminous United States↗
USGS2020

Nowhere to hide: The importance of instream cover for stream‐living Coastal Cutthroat Trout during seasonal low flow

Through their multiple functions, refuges may be important for stream‐living fishes, particularly during stressful events such as seasonal low flow or drought. Coastal Cutthroat Trout Oncorhynchus clarkii clarkii is an ideal study organism to understand the importance of refuge. During seasonal low flow, lower water levels limit access to refuge and emigration, survival of fish is low, and predation risk is high. Under these conditions, we studied patterns of cover use from field observations and tested predictions from multiple hypotheses about cover use in a semi‐natural experiment. Boulders were the main cover selected by trout in natural streams. Trout disproportionately used cover near deeper water, and they selected larger‐sized cover in shallower water. Trout showed plasticity to switch among behaviours, concealing under cover and emigrating as first options, followed by grouping, and then habitat shifting. Lack of feeding and growth suggested that perceived threat of predation was a more important driver of behaviour than foraging. Emigration was also linked to cover, with higher levels of emigration associated with less cover availability, revealing a potential link between refuge and demography through emigration. Except for feeding, the intensity of alternative behaviours can increase or decrease depending on refuge availability. Collectively, findings of this work indicate that cover can be considered a critical limiting resource along with other fundamental resources of food and space for stream‐living fish.

Ecology of Freshwater Fish↗
USGS2020

The role of sand lances (Ammodytes sp.) in the Northwest Atlantic Ecosystem: A synthesis of current knowledge with implications for conservation and management

The American sand lance ( Ammodytes americanus , Ammodytidae) and the Northern sand lance ( A. dubius , Ammodytidae) are small forage fishes that play an important functional role in the Northwest Atlantic Ocean (NWA). The NWA is a highly dynamic ecosystem currently facing increased risks from climate change, fishing and energy development. We need a better understanding of the biology, population dynamics and ecosystem role of Ammodytes to inform relevant management, climate adaptation and conservation efforts. To meet this need, we synthesized available data on the (a) life history, behaviour and distribution; (b) trophic ecology; (c) threats and vulnerabilities; and (d) ecosystem services role of Ammodytes in the NWA. Overall, 72 regional predators including 45 species of fishes, two squids, 16 seabirds and nine marine mammals were found to consume Ammodytes . Priority research needs identified during this effort include basic information on the patterns and drivers in abundance and distribution of Ammodytes , improved assessments of reproductive biology schedules and investigations of regional sensitivity and resilience to climate change, fishing and habitat disturbance. Food web studies are also needed to evaluate trophic linkages and to assess the consequences of inconsistent zooplankton prey and predator fields on energy flow within the NWA ecosystem. Synthesis results represent the first comprehensive assessment of Ammodytes in the NWA and are intended to inform new research and support regional ecosystem‐based management approaches.

Northwest Atlantic↗
USGS2017

Puffins reveal contrasting relationships between forage fish and ocean climate in the North Pacific

Long-term studies of predator food habits (i.e., ‘predator-based sampling’) are useful for identifying patterns of spatial and temporal variability of forage nekton in marine ecosystems. We investigated temporal changes in forage fish availability and relationships to ocean climate by analyzing diet composition of three puffin species (horned puffin Fratercula corniculata , tufted puffin Fratercula cirrhata , and rhinoceros auklet Cerorhinca monocerata ) from five sites in the North Pacific from 1978–2012. Dominant forage species included squids and hexagrammids in the western Aleutians, gadids and Pacific sand lance ( Ammodytes personatus ) in the eastern Aleutians and western Gulf of Alaska (GoA), and sand lance and capelin ( Mallotus villosus ) in the northern and eastern GoA. Interannual fluctuations in forage availability dominated variability in the western Aleutians, whereas lower-frequency shifts in forage fish availability dominated elsewhere. We produced regional multivariate indicators of sand lance, capelin, and age-0 gadid availability by combining data across species and sites using Principal Component Analysis, and related these indices to environmental factors including sea level pressure (SPL), winds, and sea surface temperature (SST). There was coherence in the availability of sand lance and capelin across the study area. Sand lance availability increased linearly with environmental conditions leading to warmer ocean temperatures, whereas capelin availability increased in a non-linear manner when environmental changes led to lower ocean temperatures. Long-term studies of puffin diet composition appear to be a promising tool for understanding the availability of these difficult-to-survey forage nekton in remote regions of the North Pacific.

Fisheries Oceanography↗
USGS2025

Flying fish habitat and co-occurrence with seabirds in the northern Gulf of Mexico

Flying fish (family Exocoetidae ) play an important role in marine food webs, linking sub-surface and aerial predators. The association of seabirds with sub-surface predators in subtropical and tropical regions through facilitated foraging events is a well-known phenomenon and is sometimes used to identify fishing grounds for flying fish, flying fish roe, and tunas. In the northern Gulf of Mexico (nGoM), few studies have assessed flying fish distribution, and none have directly evaluated flying fish–seabird co-occurrence. Using vessel-based observations of surfacing flying fish flights, we characterized the distribution of flying fish and their co-occurrence patterns with seabirds in the nGoM. We modeled the distribution and relative density of flying fish flights using Generalized Additive Models. We then assessed co-occurrence patterns of flying fish with all seabird species seen in the area, encompassing the footprint of flying fish detections. Flying fish were detected across the U.S. Exclusive Economic Zone, with flight densities greater on the mid-continental shelf and into pelagic waters south of Louisiana, and greater flight densities were associated with regionally low chlorophyll- a and warm water. Flying fish flights were greatest in spring months through early fall months. Sooty terns ( Onychoprion fuscatus ), considered near-obligate commensals with tuna, contributed a much higher percent of the cumulative density of the seabirds co-occurring with versus without flying fish. Flying fish could be an ecological attractant for high abundances of visually conspicuous sooty terns, the presence of which may lead to the formation of ephemeral facilitated foraging events consisting of mixed-species seabird flocks.

Fisheries Oceanography↗
USGS2016

Nest survival is influenced by parental behaviour and heterospecifics in a mixed-species colony

Studies of avian nest success often focus on examining influences of variation in environmental and seasonal factors. However, in-depth evaluations can also incorporate variation in individual incubation behaviour to further advance our understanding of avian reproductive ecology. We examined these relationships in colonially nesting Black-crowned Night-Herons Nycticorax nycticorax using intensive video-monitoring methods to quantify incubation behaviours. We modelled nest survival as a function of both extrinsic factors and incubation behaviours over a 3-year period (2010–12) on Alcatraz Island, USA. Model-averaged parameter estimates indicated that nest survival increased as a function of greater incubation constancy (% of time spent incubating eggs within a 24-h period), and average daily precipitation throughout the nesting stage. Common Ravens Corvus corax are the only known nest predator of Night-Herons on Alcatraz Island, as on many other coastal Pacific islands. We also investigated the effects of heterospecific nesting of California Gulls Larus californicus and Western Gulls Larus occidentalis in a mixed-species colony with Night-Herons, based on nesting proximity data collected over a 2-year period (2011–12). This second analysis indicated that, in addition to incubation behaviours, nesting heterospecifics are an important factor for explaining variation in Night-Heron nest survival. However, contrary to our original expectation, we found that Night-Herons experienced increased nest survival with increasing distance from gull colony boundaries. These results may apply to other areas with multiple colonial nesting species and similar predator communities and climatic patterns.

Ibis↗
USGS2018

Nesting ecology of a naturalized population of Mallards Anas platyrhynchos in New Zealand

Investigating the reproductive ecology of naturalized species provides insights into the role of the source population's characteristics vs. post‐release adaptation that influence the success of introduction programmes. Introduced and naturalized Mallards Anas platyrhynchos are widely established in New Zealand (NZ), but little is known regarding their reproductive ecology. We evaluated the nesting ecology of female Mallards at two study sites in NZ (Southland and Waikato) in 2014–15. We radiotagged 241 pre‐breeding females with abdominal‐implant transmitters and measured breeding incidence, nesting chronology and re‐nesting propensity. We monitored 271 nests to evaluate nest survival, clutch and egg size, egg hatchability and partial clutch depredation. Breeding incidence averaged (mean ± se) 0.91 ± 0.03, clutch size averaged 9.9 ± 0.1 eggs, 94 ± 2% of eggs hatched in successful nests, partial depredation affected 6 ± 1% of eggs in clutches that were not fully destroyed by predators, and re‐nesting propensity following failure of nests or broods was 0.50 ± 0.003. Nesting season (first nest initiated to last nest hatched) lasted 4.5 months and mean initiation date of first detected nest attempts was 28 August ± 3.3 days. Smaller females were less likely to nest, but older, larger or better condition females nested earlier, re‐nested more often and laid larger clutches than did younger, smaller or poorer condition females. Younger females in Southland had higher nest survival; cumulative nest survival ranged from 0.25 ± 0.007 for adult females in Waikato to 0.50 ± 0.007 for yearling females in Southland. Compared with Mallards in their native range, the nesting season in NZ was longer, clutches and eggs were larger, and nest survival was generally greater. Different predators and climate, introgression with native heterospecifics and/or the sedentary nature of Mallards in NZ may have contributed to these differences.

Ibis↗
USGS2019

Characterization of the exoskeleton of the Antarctic king crab Paralomis birsteini

Ocean acidification is projected to inhibit the biogenic production of calcium-carbonate skeletons in marine organisms. Antarctic waters represent a natural environment in which to examine the long-term effects of carbonate undersaturation on calcification in marine predators. King crabs (Decapoda: Anomura: Lithodidae), which currently inhabit the undersaturated environment of the continental slope off Antarctica, are potential invasives on the Antarctic shelf as oceanic temperatures rise. Here, we describe the chemical, physical, and mechanical properties of the exoskeleton of the deep-water Antarctic lithodid Paralomis birsteini and compare our measurements with two decapod species from shallow water at lower latitudes: Cancer borealis (Brachyura: Cancridae) and Callinectes sapidus (Brachyura: Portunidae). Paralomis birsteini deposit proportionally more calcium carbonate in their predatory chelae than their protective carapaces, compared with the other two crab species. When exoskeleton thickness and microhardness were compared between the chelae and carapace, the magnitude of the difference between these body regions was significantly greater in P. birsteini than in the other species tested. Hence, there appeared to be a greater disparity in P. birsteini in overall investment in calcium-carbonate structures among regions of the exoskeleton. The imperatives of prey consumption and predator avoidance may be influencing the deposition of calcium to different parts of the exoskeleton in lithodids living in an environment undersaturated with respect to calcium carbonate.

Invertebrate Biology↗
USGS2012

Priority effects among young‐of‐the‐year fish: reduced growth of bluegill sunfish (Lepomis macrochirus) caused by yellow perch (Perca flavescens)?

1. When available, Daphnia spp. are often preferred by age-0 yellow perch and bluegill sunfish because of energetic profitability. We hypothesised that predation by age-0 yellow perch could lead to a midsummer decline (MSD) of Daphnia spp. and that priority effects may favour yellow perch because they hatch before bluegill, allowing them to capitalise on Daphnia spp. prior to bluegill emergence. 2. Data were collected from 2004 to 2010 in Pelican Lake, Nebraska, U.S.A. The lake experienced a prolonged MSD in all but 1 year (2005), generally occurring within the first 2 weeks of June except in 2008 and 2010 when it occurred at the end of June. MSD timing is not solely related to seasonal patterns of age-0 yellow perch consumption. Nevertheless, when Daphnia spp. biomass was low during 2004 and 2006–2010 (<4 mg wet weight L −1 ), predation by age-0 yellow perch seems to have suppressed Daphnia spp. biomass (i.e. <1.0 mg wet weight L −1 ). The exception was 2005 when age-0 yellow perch were absent. 3. Growth of age-0 bluegill was significantly faster in 2005, when Daphnia spp. were available in greater densities (>4 mg wet weight L −1 ) compared with the other years (<0.2 mg wet weight L −1 ). 4. We conclude that age-0 yellow perch are capable of reducing Daphnia biomass prior to the arrival of age-0 bluegill, ultimately slowing bluegill growth. Thus, priority effects favour age-0 yellow perch when competing with age-0 bluegill for Daphnia . However, these effects may be minimised if there is a shorter time between hatching of the two species, higher Daphnia spp. densities or lower age-0 yellow perch densities.

Nebraska↗
USGS2009

Body size and predatory performance in wolves: Is bigger better?

Large body size hinders locomotor performance in ways that may lead to trade-offs in predator foraging ability that limit the net predatory benefit of larger size. For example, size-related improvements in handling prey may come at the expense of pursuing prey and thus negate any enhancement in overall predatory performance due to increasing size. 2. This hypothesis was tested with longitudinal data from repeated observations of 94 individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park, USA. Wolf size was estimated from an individually based sex-specific growth model derived from body mass measurements of 304 wolves. 3. Larger size granted individual wolves a net predatory advantage despite substantial variation in its effect on the performance of different predatory tasks; larger size improved performance of a strength-related task (grappling and subduing elk) but failed to improve performance of a locomotor-related task (selecting an elk from a group) for wolves > 39 kg. 4. Sexual dimorphism in wolf size also explained why males outperformed females in each of the three tasks considered (attacking, selecting, and killing). 5. These findings support the generalization that bigger predators are overall better hunters, but they also indicate that increasing size ultimately limits elements of predatory behaviour that require superior locomotor performance. We argue that this could potentially narrow the dietary niche of larger carnivores as well as limit the evolution of larger size if prey are substantially more difficult to pursue than to handle. ?? 2009 British Ecological Society.

Journal of Animal Ecology↗
USGS2009

Using drift nets to capture early life stages and monitor spawning of the yangtze river chinese sturgeon (Acipenser sinensis)

A sampling system for capturing sturgeon eggs using a D-shaped bottom anchored drift net was used to capture early life stages (ELS) of Chinese sturgeon, Acipenser sinensis, and monitor annual spawning success at Yichang on the Yangtze River, 1996-2004, before and just after the Three Gorges Dam began operation. Captured were 96 875 ELS (early life stages: eggs, yolk-sac larvae = eleuthero embryos, and larvae); most were eggs and only 2477 were yolk-sac larvae. Most ELS were captured in the main river channel and inside the bend at the Yichang spawning reach. Yolk-sac larvae were captured for a maximum of 3 days after hatching began, indicating quick dispersal downstream. The back-calculated day of egg fertilization over the eight years indicated a maximum spawning window of 23 days (20 October-10 November). Spawning in all years was restricted temporally, occurred mostly at night and during one or two spawning periods, each lasting several days. The brief temporal spawning window may reduce egg predation by opportunistic predators by flooding the river bottom with millions of eggs. During 1996-2002, the percentage of fertilized eggs in an annual 20-egg sample was between 63.5 to 94.1%; however, in 2003 the percentage fertilized was only 23.8%. This sudden decline may be related to the altered environmental conditions at Yichang caused by operation of the Three Gorges Dam. Further studies are needed to monitor spawning and changes in egg fertilization in this threatened population. ?? 2009 Blackwell Verlag GmbH.

Conference Paper↗