Important Prey Species Research Articles

Conservation implications of the evolutionary history and genetic diversity hotspots of the snowshoe hare.

With climate warming, the ranges of many boreal species are expected to shift northward and to fragment in southern peripheral ranges. To understand the conservation implications of losing southern populations, we examined range-wide genetic diversity of the snowshoe hare (Lepus americanus), an important prey species that drives boreal ecosystem dynamics. We analysed microsatellite (8 loci) and mitochondrial DNA sequence (cytochrome b and control region) variation in almost 1000 snowshoe hares. A hierarchical structure analysis of the microsatellite data suggests initial subdivision in two groups, Boreal and southwestern. The southwestern group further splits into Greater Pacific Northwest and U.S. Rockies. The genealogical information retrieved from mtDNA is congruent with the three highly differentiated and divergent groups of snowshoe hares. These groups can correspond with evolutionarily significant units that might have evolved in separate refugia south and east of the Pleistocene ice sheets. Genetic diversity was highest at mid-latitudes of the species' range, and genetic uniqueness was greatest in southern populations, consistent with substructuring inferred from both mtDNA and microsatellite analyses at finer levels of analysis. Surprisingly, snowshoe hares in the Greater Pacific Northwest mtDNA lineage were more closely related to black-tailed jackrabbits (Lepus californicus) than to other snowshoe hares, which may result from secondary introgression or shared ancestral polymorphism. Given the genetic distinctiveness of southern populations and minimal gene flow with their northern neighbours, fragmentation and loss of southern boreal habitats could mean loss of many unique alleles and reduced evolutionary potential.

A cascade of warming impacts brings bluefin tuna to Greenland waters.

Rising ocean temperatures are causing marine fish species to shift spatial distributions and ranges, and are altering predator-prey dynamics in food webs. Most documented cases of species shifts so far involve relatively small species at lower trophic levels, and consider individual species in ecological isolation from others. Here, we show that a large highly migratory top predator fish species has entered a high latitude subpolar area beyond its usual range. Bluefin tuna, Thunnus thynnus Linnaeus 1758, were captured in waters east of Greenland (65°N) in August 2012 during exploratory fishing for Atlantic mackerel, Scomber scombrus Linnaeus 1758. The bluefin tuna were captured in a single net-haul in 9-11 °C water together with 6 tonnes of mackerel, which is a preferred prey species and itself a new immigrant to the area. Regional temperatures in August 2012 were historically high and contributed to a warming trend since 1985, when temperatures began to rise. The presence of bluefin tuna in this region is likely due to a combination of warm temperatures that are physiologically more tolerable and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.

순천 상내리 갯골에 출현하는 민물두줄망둑(Tridentiger bifasciatus)의 식성

The feeding habits of Tridentiger bifasciatus were studied using 733 individuals collected in the tidal creek at Sangnae-ri, Suncheon, Korea, using a push net, monthly, from April 2011 to March 2012. The standard length (SL) of the specimens ranged from 1.5 to 8.2 cm. The stomach content analysis indicated that T. bifasciatus consumed mainly amphipods, such as Corophium sp., while copepods, polychaetes, and shrimps were other important prey species. In addition T. bifasciatus ate small quantities of crab larvae, fish, gastropod larvae, and insects. T. bifasciatus is a generalist that feeds on various zoobenthos, including fish. T. bifasciatus underwent an ontogenetic dietary shift. Smaller individuals (1-2 cm SL) fed mainly on amphipods. The proportion of amphipods decreased as body size increased, whereas the consumption of polychaetes increased gradually. The seasonal variation in the diet composition of T. bifasciatus was significant. Insects were common prey during summer, while the amounts of other prey, including polychaetes, were similar during spring, autumn, and winter.

Grey seal diet analysis in Ireland highlights the importance of using multiple diagnostic features

Seals and humans are top predators in many marine ecosystems, often targeting the same food resource. With global declines in fish stocks, competition between these top predators is of increasing interest to scientists and resource managers. To understand and quantify this competition, robust data on the diet of seals are necessary. We present new information on the diet of grey seals Halichoerus grypus from a colony on Great Blasket Island, southwest Ireland, with particular reference to commercially important prey species such as salmonids. Inter-annual vari- ation in diet was investigated based on the recovery and identification of sagittal fish otoliths, bones and cephalopod beaks from faecal samples collected in 2009 and 2010. A total of 939 prey items were recovered, representing a minimum of 41 prey species. Thirty species were identified from otoliths while a further 11 species, including salmonids, were identified from additional diagnostic structures. The diet of grey seals was largely dominated by Gadiformes (21% corrected biomass), particularly Trisopterus spp., which contributed 7% in terms of corrected biomass and 52% by frequency of occurrence, while salmonids comprised over 36% of diet by corrected biomass. Inter-annual variation in sandeel (Ammodytidae) and blue whiting Micromesistius poutassou abundance was apparent, while the former was an important contributor to the diet in terms of corrected biomass (11%). The results support the principle that an 'all structures' approach to pinniped diet estimation can significantly increase the rate of detection for most fish groups, and result in improved estimation of seal diet.

Gastrointestinal parasites of bottlenose dolphins Tursiops truncatus from the extreme southwestern Atlantic, with notes on diet composition

We surveyed the gastrointestinal tracts of 6 bottlenose dolphins Tursiops truncatus from Patagonia to check for helminth parasites and characterize dolphin diet. All dolphins harbored parasites (6477 helminths). We recorded 7 species, including nematodes Anisakis simplex s.l., Pseudoterranova decipiens, acanthocephalans Corynosoma cetaceum, C. australe, and digeneans Braunina cordiformis, Pholeter gastrophilus and Synthesium tursionis. Among the gastric helminths, the most prevalent species were C. cetaceum and A. simplex while C. australe and S. tursionis inhabited the intestine at low prevalence. This is the first report of C. australe and P. decipiens in bottlenose dolphins. Regarding diet, 5 stomachs contained food remains (consisting of 103 prey items). The most important prey species were Geotria australis and Stromateus brasiliensis, but their role in parasite transmission is unclear. At the community level, the gastrointestinal parasite community of T. truncatus was depauperate and strongly overlapped the community described for pelagic dolphins inhabiting Patagonia, suggesting a strong local influence in shaping helminth communities. Nevertheless, these observations are at odds with the notion that oceanic cetaceans have comparatively poorer helminth fauna than neritic species such as bottlenose dolphins, due to the lower likelihood of parasite exchange.

New Prey Fishes in Diet of Black Sea Bottlenose Dolphins, Tursiops truncatus (Mammalia, Cetacea)

Abstract We report 7 new prey fishes in diet of the Black Sea bottlenose dolphins Tursiops truncatus (Montagu, 1821) and the first records of 9 prey items from their stomach contents: herring (Alosa sp.), sand smelt (Atherina sp.), horse mackerel (Trachurus mediterraneus), picarel (Spicara flexuosa), Mediterranean sand eel (Gymnammodytes cicerellus), Atlantic stargazer (Uranoscopus scaber), garfish (Belone belone), gobies (Gobiidae indet.) and blennies (Blenniidae indet.). Th e Atlantic stargazer was recorded as a prey species for the common bottlenose dolphin for the first time. Th e horse mackerel and the picarel, formerly recorded in the diet of Mediterranean bottlenose dolphins, now were frequently found in the examined Black Sea dolphins. Th e list of prey fishes for Black Sea bottlenose dolphins now includes 23 items, with many small pelagic and demersal fishes, and it is similar to that of Mediterranean dolphins. Whiting (Merlangius merlangus) is still an important prey species, as 50-70 years ago, whereas turbot (Psetta maeotica), not recorded by us, could lose its importance due to population decline. As before, red mullet (Mullus barbatus) is recorded in winter feeding. Feeding on mullets (Mugilidae) is not a universal trait, and it is possibly restricted to local geographical areas.

Stomach contents of bycaught minke whales (Balaenoptera acutorostrata) in Korean waters

We investigated the stomach contents of 54 minke whales (Balaenoptera acutorostrata) from bycatch in Korean waters from 2000 to 2008 to examine their diet and feeding habits. Body length of the whales ranged from 3.9 to 8.5 m with a mean of 5.45 m (SD =1.07 m). A total of 10 prey species (3 crustacean, 5 fish and 2 cephalopod) were identified from the whale stomachs. We used the Combined Rank Index (CRI) to estimate the relative importance of prey species. Euphausia pacifica was the most important prey species in this sample, occurring in 70.4% (n=38) of the stomachs. Pacific anchovy (Engraulis japonicus) was the second most important prey species, occurring in 11.1% (n=6) of the stomachs. Most minke whale stomachs contained a single prey species (74.5%). Euphausiids were found in the majority of the stomachs of all whale length-classes and they also were the dominant prey species in most seasons except for autumn. This information can be useful for the understanding of the trophic role of minke whales in this area.

Effectiveness of habitat management in the recovery of low-density populations of wild rabbit

Understanding the relationship between spatial patterns of landscape attributes and population presence and abundance is essential for understanding population processes as well as supporting management and conservation strategies. This study evaluates the influence of three factors: environment, habitat management, and season on the presence and abundance of the wild rabbit (Oryctolagus cuniculus), an important prey species for Mediterranean endangered predator species. To address this issue, we estimated wild rabbit presence and abundance by latrine counting in transects located in 45 plots within a 250 × 250 m grid from June 2007 until June 2009 in a 1,200 ha hunting area in southern Portugal. We then analyzed how wild rabbit presence and abundance correlate with the aforementioned factors. Our results showed that the main variable influencing wild rabbit presence and abundance was the distance to the artificial warrens. North and northeast slope directions were negatively related to wild rabbit presence. Conversely, rabbit presence was positively correlated with short distances to ecotone, artificial warrens, and spring. Regarding rabbit abundance, in addition to artificial warrens, soft soils, bushes, and season also had a positive effect. We found that environmental variables, management practices, and season each affect wild rabbit presence and abundance differently at a home range scale in low-density population. Thus, our major recommendations are reducing the distance to artificial warrens and ecotone, ideally to less than 100 m, and promoting habitat quality improvement on slopes with plenty of sun exposure.

Identifying subtidal burying habitat of Pacific sand lance (Ammodytes hexapterus) in the Strait of Georgia, British Columbia, Canada

Pacific sand lance (Ammodytes hexapterus), an important prey species for many vertebrate predators in the northeast Pacific, lacks a swim bladder and relies on coarse sand substrates to bury in overnight and during the winter. Surprisingly little information is available describing the spatial distribution and extent of its burying habitat along the British Columbia coast. Thus, a habitat suitability model was developed for Pacific sand lance in the Strait of Georgia that considered information on shallow depths (<80m), high bottom current speeds (25–63cms−1) and coarse sand (0.25–2.0mm grain diameter). Overall, the model identified 6% of the study domain as suitable burying habitat, with the southern Strait containing the largest burying areas. By-catch data from mid-water trawl and purse seine sets was also used to map the location of pelagic schools of foraging sand lance. The persistent location of large Pacific sand lance by-catches over many years identified key foraging areas adjacent to several burying habitats. The median distance of 88 sand lance schools to coarse sand patches was 2km; 75% of the schools were found within 4.9km of coarse sand. The mapping of suitable burying and foraging areas in the Strait of Georgia will assist managers in guarding against anthropogenic activities that might impact the relatively uncommon and patchy habitats of a key coastal food-web species.

Ecology of the Cooper's Hawk in North Florida

AbstractWe studied adult Cooper's hawks Accipiter cooperii on two study areas in north Florida from 1995 to 2001, an area dominated by large plantations managed for northern bobwhite Colinus virginianus and an area of mixed farmland and woods with no direct bobwhite management. We monitored 76 Cooper's hawk nesting attempts at 31 discrete nest areas, and radio-tagged 19 breeding males and 30 breeding females that we radio-tracked for up to 5 y. Nesting density (565 to 1,494 ha per occupied nest area) was comparable but productivity (1.8 and 2.8 young fledged per occupied and successful nest area, respectively) was lower than for the species elsewhere. Prey may have been more limiting than in other areas studied because chipmunks Tamias striatus, an important prey elsewhere, were absent. Annual Cooper's hawk survival averaged 84% for males and 81% for females, except in 1998 when survival was substantially lower. Average annual home-range size for male Cooper's hawks was 15.3 km2 inclusive of one nesting area. Female annual ranges averaged 30.3 km2, and included from three to nine nesting areas. Daily space use was similar between the sexes, but females had separate breeding and nonbreeding ranges whereas males were sedentary. Females used the same nonbreeding areas among years, but switched nesting areas 68% of the time compared with only 17% for males. Birds comprised 88% of the breeding and 98% of the nonbreeding season diet of Cooper's hawks by frequency. Important prey species all year were mourning doves Zenaida macroura, blue jays Cyanocitta cristata, and northern bobwhite; during summer, cattle egrets Bubulcus ibis, northern mockingbirds Mimus polyglottos and northern cardinals Cardinalis cardinalis were also important; and during autumn and winter, killdeer Charadrius vociferus, yellow-billed cuckoos Coccyzus americanus, and chickens were important. Female Cooper's hawks took larger prey than males; females were responsible for most cattle egret and chicken kills; whereas, males took most blue jays, killdeer, northern mockingbirds, and northern cardinals. Of avian prey brought to nests, 64% were nestling birds. Most adult male Cooper's hawks were adept at raiding bird nest boxes. Male Cooper's hawks captured 85% of the prey fed to nestlings. Female Cooper's hawks relied on males for food from early March until young were ≥12 d old, and 6 of 10 breeding females monitored intensively were never observed foraging for their broods. Most prey brought to nestling Cooper's hawks was captured within 2 km of nests, and foraging effort was consistent throughout the day. During the nonbreeding season, most prey captures occurred before 0900 hours or at dusk. Northern bobwhite made up 2% of male and 6% of female Cooper's hawk prey annually by frequency; this extrapolated to 18 bobwhite/year/adult Cooper's hawk on both study areas, 59% of which were captured between November and February. Outside the breeding season, male Cooper's hawks foraged evenly over their home range whereas females tended to focus on prey concentrations. Because female Cooper's hawks were so adept at finding and exploiting prey hotspots, perhaps the best strategy for reducing predation on bobwhite is habitat management that produces an even distribution of bobwhite across the landscape.

Linking environmental flows with the distribution of black bream Acanthopagrus butcheri eggs, larvae and prey in a drought affected estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 483:273-287 (2013) - DOI: https://doi.org/10.3354/meps10280 Linking environmental flows with the distribution of black bream Acanthopagrus butcheri eggs, larvae and prey in a drought affected estuary Joel Williams1,*, Greg P. Jenkins1,2, Jeremy S. Hindell3, Stephen E. Swearer1 1Department of Zoology, University of Melbourne, Parkville, Victoria 3010, Australia 2Fisheries Research Branch, Department of Primary Industries, Queenscliff, Victoria 3225, Australia 3Arthur Rylah Institute, Department of Sustainability and Environment, Heidelberg, Victoria 3084, Australia *Email: jwi@unimelb.edu.au ABSTRACT: Estuaries are under threat from changes in freshwater flows resulting from anthropogenic impacts and climate change, with unknown consequences for estuarine biota. In the past decade, significant rain deficits in south-eastern Australia have coincided with a decrease in commercial catches of black bream Acanthopagrus butcheri, an important commercial and recreational fish species that spawn in estuaries. We investigated the temporal and spatial distribution of black bream eggs and larvae, and copepods—preferred larval prey—in relation to the hydrology of the Mitchell River, a drought-stricken tributary of Australia’s largest estuarine lagoon system. We collected eggs, larvae, zooplankton and water quality data at multiple depths from 8 sampling sites over 7 fieldtrips from August to December 2008. The hydrology of the Mitchell River during this study was highly complex and influenced by freshwater flow. Spatial coupling between black bream larvae, copepods and the halocline was observed in the upper estuary. Nauplii of the copepod Gladioferens pectinatus, an important prey species for larval fish, dominated the zooplankton assemblage (>80%) and larval gut contents. This study demonstrates that freshwater flows and the generation of salinity stratification have a large influence on the size of suitable habitat for larval bream. Drought, water abstraction and climate change could potentially reduce flows to the point where salinity stratification in the estuary is diminished, resulting in declines in replenishment to populations of black bream and possibly other estuarine-dependent fish. KEY WORDS: Ichthyoplankton · Larvae · Prey · Copepod · Stratification · Zooplankton · Halocline Full text in pdf format PreviousNextCite this article as: Williams J, Jenkins GP, Hindell JS, Swearer SE (2013) Linking environmental flows with the distribution of black bream Acanthopagrus butcheri eggs, larvae and prey in a drought affected estuary. Mar Ecol Prog Ser 483:273-287. https://doi.org/10.3354/meps10280 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 483. Online publication date: May 30, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Zooplankton stable isotopes as integrators of bottom-up variability in coastal margins: A case study from the Strait of Georgia and adjacent coastal regions

Understanding how environmental “bottom-up” conditions affect the production or survival of higher trophic levels is an integral component of ecosystem management. However, linking environmental conditions to higher trophic levels is difficult because of differences in turnover time. Carbon (δ13C) and nitrogen (δ15N) isotopes in animal tissues can elucidate these links because they can potentially integrate variability in nutrient concentrations, primary production, and food web structure on a time-scale that reflects the tissue turnover time of consumers. Here we assess environmental and trophic correlates of zooplankton stable isotopes in the Strait of Georgia and three adjacent coastal regions. Zooplankton stable isotopes show strong seasonal variability, and are typically highest in the summer. Regional δ15N signatures appear to be synchronized with the timing of production maxima in each region, and broadly reflect variability in nitrate and chlorophyll. In contrast zooplankton δ13C have relatively weak regional signatures. The environmental variables that best explain zooplankton stable isotopes vary between regions, and between seasons. On the west coast of Vancouver Island, zooplankton δ15N is significantly correlated with sea surface temperature throughout the year. In the Strait correlations between zooplankton stable isotopes and environmental variables are season-specific. In the spring, δ15N and δ13C are correlated with chlorophyll, zooplankton biomass and nitrate, but in the summer zooplankton δ15N is only weakly correlated with the biomass of carnivorous zooplankton. In both regions, between-year variability in zooplankton stable isotopes appears to reflect between-year variability in oceanographic conditions. A time-series of stable isotopes collected from a copepod (Neocalanus plumchrus) from the Strait of Georgia suggests that chlorophyll, nitrate and zooplankton biomass varied dramatically between 2001 and 2006, and sheds light on environmental conditions that accompanied that collapse of this important prey species. We discuss the implications of our findings for an ecosystem management approach to conservation.

Losing ground: past history and future fate of Arctic small mammals in a changing climate

According to the IPCC, the global average temperature is likely to increase by 1.4-5.8°C over the period from 1990 to 2100. In Polar regions, the magnitude of such climatic changes is even larger than in temperate and tropical biomes. This amplified response is particularly worrisome given that the so-far moderate warming is already impacting Arctic ecosystems. Predicting species responses to rapid warming in the near future can be informed by investigating past responses, as, like the rest of the planet, the Arctic experienced recurrent cycles of temperature increase and decrease (glacial-interglacial changes) in the past. In this study, we compare the response of two important prey species of the Arctic ecosystem, the collared lemming and the narrow-skulled vole, to Late Quaternary climate change. Using ancient DNA and Ecological Niche Modeling (ENM), we show that the two species, which occupy similar, but not identical ecological niches, show markedly different responses to climatic and environmental changes within broadly similar habitats. We empirically demonstrate, utilizing coalescent model-testing approaches, that collared lemming populations decreased substantially after the Last Glacial Maximum; a result consistent with distributional loss over the same period based on ENM results. Given this strong association, we projected the current niche onto future climate conditions based on IPCC 4.0 scenarios, and forecast accelerating loss of habitat along southern range boundaries with likely associated demographic consequences. Narrow-skulled vole distribution and demography, by contrast, was only moderately impacted by past climatic changes, but predicted future changes may begin to affect their current western range boundaries. Our work, founded on multiple lines of evidence suggests a future of rapidly geographically shifting Arctic small mammal prey communities, some of whom are on the edge of existence, and whose fate may have ramifications for the whole Arctic food web and ecosystem.

Predation by grey wolf on wild ungulates and livestock in centralIran

AbstractThe grey wolfCanis lupushas the largest geographical range of large mammalian carnivores in westAsia. However, it is one of the least studied species, particularly inIran. Feeding ecology is a critical aspect of predator ecology and has important implications when formulating species and ecosystem management strategies. Also, predation on livestock is a crucial cause of wolf–human conflicts throughout the wolf's global range. Accordingly, we investigated the diet of the grey wolf inGhamishlou, an area with high population densities of wild and domestic ungulates in centralIran, betweenJuly 2007 andApril 2009. Scat analysis indicated that livestock was the single most important prey species for wolves with 47.1% of total biomass consumed, whereas Persian gazelle comprised 27.0% and wild sheep 15.9%. Wild kills were significantly skewed towards males relative to their proportion in the population, and were mainly preyed on during post‐rutting months. Based on interview surveys, less than 1% of mean herd size was lost to wolf depredation; however, almost six times more died from non‐depredation causes during each winter. We concluded that the high occurrence of livestock in the wolves' diet is mainly because of scavenging rather than depredation; however, owing to high pressure of wolves on local herds during non‐winter seasons in other areas with depleted prey populations, local people dislike wolves and try to eradicate them. Finally, management implications are discussed and solutions are recommended.

Seabird-fish interactions: the fall and rise of a common guillemot Uria aalge population

A major challenge in population ecology is the prediction of population responses to environmental variance. Food availability has long been hypothesized to play a major role in regulating seabird populations. In general, seabirds feed on small pelagic fish and/or young age classes of larger predatory fish. Here we used a logistic population model to predict the temporal variation in the population size of common guillemots Uria aalge in a colony in NE Norway (Hornoya) between 1987 and 2011 in relation to the variation in abundance (acoustic and trawl surveys) of important fish prey species in the Barents Sea. The fish species considered, all of which have been described in the diet of common guillemot chicks and adults on Hornoya, were capelin Mallotus villosus (all age classes), 1-group herring Clupea harengus and 0-group cod Gadus morhua. The guillemot population collapsed by more than 80% during the winter 1986/1987, when the abundance indices of all fish prey species were very low, but has since steadily in - creased. The annual variation in population growth rate after the population collapse could best be explained by the variation in abundance of 0-group cod (unlagged), and the 0-group cod and capelin 6 and 4 yr earlier, respectively (equalling the age of maturation of guillemots). We also present a numerical ocean model to identify mechanisms affecting spatio-temporal prey availabil- ity of 0-group cod around the colony during the breeding season. These results undermine earlier focus on the capelin stock as the main cause of the population crash in common guillemots.

Environmental variability and fledging body mass of Common Guillemot Uria aalge chicks

To gain a better understanding of population processes and in the light of the critically endangered status of the Common Guillemot Uria aalge in Norway, we investigate which environmental factors might affect the fitness of guillemot chicks as they depart from the nest site over a 16-year period on a colony in NE Norway. Although prey composition did not seem to influence the fledging body mass of the chicks, there were significant relationships between the yearly variations in chick body mass and abundance of two important prey species (1-group herring Clupea harengus that is an important chick food item and 0-group cod Gadus morhua that is an important adult food item), population size and the sea surface temperature around the colony. The positive influence of young herring and cod on Common Guillemot chick mass occurred during a period of warming in the Barents Sea such that future recruitment into the population will depend partly on the long-term changes in ocean climate in the region.

Assessing the intrinsic resilience of a particularly fast-growing teleost prey species (red cod, Pseudophycis bachus)

Understanding the life-history parameters that influence productivity is important in assessing the intrinsic resilience of a species to exploitation. The life-history characteristics of red cod, Pseudophycis bachus, were investigated to assess the intrinsic resilience of this important prey species to increased predation pressure by a range of high trophic-level predators. Red cod has a particularly short longevity; in Australian shelf waters it is uncommon to encounter individuals older than 2+ years. There are few shelf-water species that exhibit the rapid rate of growth that was observed where females and males attained ~300-mm total length in the first year. A particularly rapid growth rate, and a reproductive strategy characterised by early maturity and high fecundity, suggests that the species is relatively resilient. However, red cod is short lived, which exposes populations to large shifts in biomass. Harvesting of this species by predators, particularly during years of poor recruitment, may be significant in shaping the dynamics of red cod populations.

Cooccurrence and food niche overlap of two common predators (red fox Vulpes vulpes and common buzzard Buteo buteo) in an agricultural landscape

The mechanism of coexistence and interspecific relationships between 2 predatory species has been an important topic in ecology for many years. To date, researchers have focused mostly on very similar species, such as 2 mammals or 2 birds of prey, occupying the same habitat. However, the situation where a predatory mammal may live sympatrically with a common bird of prey is probably more common. A good example is the coexistence of the red fox and the common buzzard. The relationship between these species with respect to spatial distribution, the abundance of a potentially important prey species (common vole), diet, trophic niche breadth, and niche overlap was studied in western Poland during 2006-2009. The distances between fox dens and buzzard nests were significantly shorter than would be expected by chance. The abundance of common vole was higher in sites where both predators were present than in the control sites, where neither predator was recorded. The trophic niche overlap between both predators was moderate (62.1%). However, the trophic niche breadth of the common buzzard was narrower (2.733) than that of the red fox (3.875), which implies that the fox is a more generalist predator.

Modeling the Influence of Forest Structure on Microsite Habitat Use by Snowshoe Hares

Snowshoe hare (Lepus americanus) is an important prey species for many Carnivora and has strong influences on community structure and function in northern forests. An understanding of within-stand (microsite) forest structural characteristics that promote high use by hares is important to provide forest management guidelines. We measured forest structural characteristics at the microsite-scale in north-central Maine and used an information-theoretic modeling approach to infer which characteristics were most strongly associated with use by hares during winter. We measured overwinter hare pellet density to model relationships among microsite-scale vegetation structure and hare use. Overwinter pellet density was positively associated with live stem cover (3 × coniferous saplings + deciduous saplings) and negatively associated with overstory canopy closure; the two variables explained 71% of the variation in microsite use by hares. The highest pellet densities were in grids with canopy closure &lt;72% and stem cover units &gt;22,000 stems/ha. Silvicultural practices that create dense areas of conifer and deciduous saplings should receive high within-stand use by hares in winter. These conditions can be achieved by promoting the release of advanced regeneration and reducing overstory cover to encourage establishment of shade-intolerant species; clearcutting is one such silvicultural prescription to achieve these conditions.

Trophic spectrum of the sailfishIstiophorus platypteruscaught off Acapulco in the southern Mexican Pacific

The sailfishIstiophorus platypterusis one of the most common billfish species in the Mexican Pacific. Information about its feeding habits in the coastal region of Acapulco, Guerrero is extremely limited. In the present study we quantified the diet of sailfish, based on captures made from March 2008 to December 2009 by the sport fishing fleet of Acapulco. We analysed a total of 561 stomachs, of which 254 contained food (45%). The size interval of examined specimens was between 101 and 212 cm postorbital length and between 15 and 47 kg total weight. In general, teleosts were the most important prey, followed by cephalopods. According to index of relative importance, the most important species in the diet were the fishAuxis thazard(63.04%) andFistularia commersonii(6.62%), followed by the cephalopodOctopusspp. (4.58%). There were no significant differences in the diet by sex (males and females), sexual maturity (immature and mature), or by season (warm and cold seasons). In all cases the most important prey species wasA. thazard. We conclude that the sailfishI. platypterusoff Acapulco behaves as a specialist predator because, despite the consumption of a high number of prey items, it feeds preferentially on a reduced number of prey species that form schools, and are available and abundant in the ocean.