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Bighorn sheep (Ovis canadensis) were re- introduced to the Black Hills of South Dakota and Wyoming beginning in 1965. Various pneumonia outbreaks caused populations to decline periodically, resulting in little to no lamb recruitment. An isolated population of bighorn sheep resides on Elk Mountain along the South Dakota-Wyoming border in the southern Black Hills. We estimated population size, survival, and recruitment rates of bighorn sheep on Elk Mountain by radio-collaring adult and neonatal sheep from 2012 to 2014. Overall annual ewe survival was 88.1% (se = 0.05), ram survival was 85.1% (se = 0.10), and 26 wk lamb survival was 44.7% (se = 0.09). Recruitment through 26 wk averaged 35% (SD = 0.02) across years. Population estimates for the 3 y were 80 (se = 0.58), 100 (se = 2.42), and 115 (se = 6.89) individuals, respectively. The Elk Mountain bighorn sheep herd experienced lamb survival and recruitment during 2012-2014; coupled with minor predation losses and a lack of deadly pneumonia, this herd is expected to continue to grow in size.
Wolves (Canis lupus) are opportunistic predators and will capitalize on available abundant food sources. However, wolf diet has primarily been examined at monthly, seasonal, or annual scales, which can obscure short-term responses to available food. We examined weekly wolf diet from late June to early October by collecting scats from a single wolf pack in northeastern Minnesota. During our 15 wk study, nonungulate food types constituted 58% of diet biomass. Deer (Odocoileus virginianus) fawns were a major food item until mid-July after which berries (primarily Vaccinium and Rubus spp.) composed 56–83% of weekly diet biomass until mid-August. After mid-August, snowshoe hares (Lepus americanus) and adult deer were the primary prey. Weekly diet diversity approximately doubled from June to October as wolves began using several food types in similar proportions as the summer transitioned into fall. Recreational hunting of black bears (Ursus americanus) contributed to weekly wolf diet in the fall as wolves consumed foods from bear bait piles and from gut piles/carcasses of successfully harvested or fatally wounded bears. To our knowledge, we are the first to examine wolf diet via scat analysis at weekly intervals, which enabled us to provide a detailed description of diet plasticity of this wolf pack, as well as the rapidity with which wolves can respond to new available food sources.
Texas is estimated to harbor more than 2 million feral hogs, Sus scrofa. The increasing abundance of feral hogs throughout the United States is a testament to their ability to adapt to nearly any environment. We GPS-collared and tracked 16 feral hogs in the spring of 2015 and 2016 in the Texas Panhandle, United States. We determined home range and core area size using kernel density (KDE) and minimum convex polygon (MCP) estimators and selection of habitats by feral hogs in two field sites. Mean (±se) KDE home range and core area sizes were 9.73 ± 1.74 km2 and 1.31 ± 0.23 km2, respectively. Mean (±se) MCP home range and core area sizes were 15.13 ± 3.49 km2 and 3.14 ± 0.69 km2, respectively. Home range sizes were slightly larger but comparable to other home range sizes in Texas, and with home range and core area sizes larger for males than female. Feral hogs did not exhibit second-and-third order habitat selection at random (P < 0.005) in both field sites. Hogs selected for woodland and floodplain habitats over human developed areas. Feral hogs spent more time in agricultural habitats during crepuscular and nighttime periods and more time in natural habitats throughout the day. These results suggest management techniques in northern Texas need to be executed for the removal or deterrence of feral hogs in areas of cultivated crops, ideally before the planting period through the harvesting season.
The influence of forest fragmentation and associated habitat edges differentially affects forest-dependent organisms, particularly when certain species are able to use resources from surrounding matrix habitats. The white-footed mouse is a forest habitat generalist and is known to disperse among adjoining farmland habitats, including agricultural matrix, in fragmented agro-ecosystems. However, little is known about spatial variation in population density within adjoining farmland habitats or how this relationship varies seasonally. In addition quantifying the extent to which white-footed mice use agricultural matrix as habitat is important for inferring potential ecosystem services (predation of weed seed and waste grain) rendered within row-crop fields. We used spatially explicit capture-recapture models to estimate density of white-footed mice along a gradient of patch (forest fragment) interior to matrix (crop field) interior that spanned fragmented habitat edges. Spatial variation in population density within adjoining habitats was related to the distance from habitat edge, and the magnitude of this relationship (edge effect) varied among seasons and crop cycles within the agricultural matrix. Within-field densities were greater during periods of summer crop growth relative to spring crop emergence or following fall crop harvest. Populations of white-footed mice in forest fragments appear to seasonally spill over from patch habitat into surrounding agricultural matrix. Acquisition of resources from surrounding agricultural matrix may contribute to the inverse density-area relationship observed for white-footed mice within forested habitat in fragmented landscapes. Furthermore, seasonal foraging within matrix habitat likely provides weed seed predation ecosystem services in row-crop fields.
Over the past few decades white-tailed deer (Odocoileus virginianus) densities have increased to levels well above their historic range of variability in many parts of the U.S. Under this condition deer can act as a keystone herbivore in forest ecosystems potentially changing the structure, composition, and productivity of many forest types. White-tailed deer herbivory in habitat types other than forests, such as wetlands, is poorly understood. Our objectives were to quantify white-tailed deer herbivory and evaluate if herbivory impacted plant community composition, structure, and productivity within a landscape dominated by a diversity of wetland vegetation types at Shiawassee National Wildlife Refuge during 2011 and 2012. We constructed replicated exclosures in three different wetland vegetation types (two perennial marshes, four moist soil units, and three lakeplain prairies) and compared them with areas open to foraging within core and edge areas of each respective wetland type. We quantified horizontal cover, vertical cover, plant species richness, total above ground biomass, and reproductive biomass in exclosures and open areas during both years. At current low densities (<4 deer/km2 in 2013), white-tailed deer did not impact wetland vegetation characteristics. Mean horizontal cover class was 80–100% in all wetlands. Mean vertical cover was greatest in lakeplain prairies (100%) and lowest in perennial marshes (25%). Species richness was greatest in moist soil units (5.9) and lowest in perennial marshes (1.6). Total above ground biomass production was greatest in perennial marshes (399.3 kg/ha) and lowest in moist soil units (183.3 kg/ha), while reproductive biomass production was greatest in moist soil units (49.2kg/ha) and lowest in lakeplain prairies (29.4 kg/ha). Multivariate analysis with nonmetric multidimensional scaling (NMS) ordination and multi-response permutation procedure (MRPP) analysis yielded no differences in community composition between exclosures and open areas or core and edge areas. Our results will help biologists and ecologists understand herbivory pressures in wetland vegetation types and may assist managers in minimizing community effects of browsing to meet wetland and waterbird conservation goals.
While arthropod herbivory on invasive plant species is generally low, herbivory by generalist mammals is often high. We tested whether exclusion of white-tailed deer, Odocoileus virginianus, increased the cover and growth of Lonicera maackii, an invasive shrub, in forested natural areas in Ohio, U.S.A. We found leaf frequency of L. maackii in two height ranges, 0.5–1 m and 1–1.5 m, was significantly greater where deer had been excluded for 4 y. Furthermore, the basal area growth of these shrubs over 5 y tended to be higher, and the final basal area of small shrubs was significantly higher, in exclosures. These findings, along with direct evidence of deer browse from the literature, indicate deer browse on this invasive shrub is sufficient to affect its architecture and growth, and potentially mitigate its negative effect on native plants.
Carnivorous plants experience the same constraints as most predators, in that they must attract, capture, and consume prey. Natural populations of the yellow pitcher plant Sarracenia flava show most plants are composed of one to two ramets, with relatively few active leaves. An experiment was conducted to determine the effect of number of leaves on insect capture by creating spatially distinct S. flava groups of different sizes. Groups with more leaves attracted more prey, but prey capture per leaf was not correlated with group size. The per-leaf capture rate of different insect types, mostly wasps and bees, was also not correlated with group size. For this predator there was no advantage or disadvantage of foraging in groups.
Partridge pea (Chamaecrista fasciculata) is a common annual legume that has many important uses for humans and wildlife. During the growing season, partridge pea produces numerous flowers that are visited by many bee and wasp species. However, which bees/wasps act as the principle pollinators of partridge pea has not been explored thoroughly. We used mesh cages with different hole sizes (2.5, 0.64, 0.32, and 0.16 cm2) to screen out different sized pollinators and collected data on pod length, seed number, and percentage of pods formed per flower number (pod set). We also collected partridge pea flower insect visitors and estimated pollen loads on their bodies to determine the amount of pollen available for pollination services. Overall, partridge peas in cages with larger holes produced longer pods and more seeds compared to those in cages with smaller holes. However, no significant difference in pod set was observed among plants grown in the various size cages. Thirteen flower visitors were observed to visit open partridge pea flowers. The most common insect visitors were Bombus spp., Agapostemon splendens, and Apis mellifera. Apis mellifera contained significantly less pollen on its body compared to that on all other common bees. Likely pollinators of partridge pea in Florida are larger bees such as Xylocopa and Bombus and possibly Agapostemon splendens, a smaller halictid bee.
The decline of savanna habitat in the upper Midwest has resulted in a decline of savanna and grassland birds. Many savanna restoration efforts involve the re- introduction of fire, a method which kills fire-sensitive trees, often leaving them standing as snags. The purpose of this study was to assess how the number of snags (standing dead trees) is associated with the breeding bird community and to document how the number of snags at a site varied over a 23 y period of restoration by fire. The effect of snags on bird communities was studied by establishing bird census plots along a wide range of snag abundances. To determine for what purposes birds utilized snags, observers documented all visits during an hour-long period for pairs of a dead and live tree. Change in the abundance of snags over time was documented over 23 y in a 16 ha grid. We found both bird species richness and abundance were positively associated with the number of snags and that birds used dead trees for mating and reproductive purposes more than live trees. We found the introduction of fire for restoration purposes initially resulted in an increase in the number of snags, but repeated fires eventually caused the number of snags to decline substantially. If a primary goal of savanna restoration is to enhance breeding bird community, our results show how burn regimes can be managed to maximize the number of dead tree snags for as long as possible.
Interactions among predators can have important consequences for lower trophic levels. Here, we use individual tag data on juvenile salmonids to quantify how their geographic, taxonomic, and life-history representation in the diets of great blue herons (Ardea herodias) changed after a pair of bald eagles (Haliaeetus leucocephalus) usurped the colony's nesting site, forcing the colony to relocate. Heron diet composition changed significantly despite the short relocation distance (4.1 km). This was driven by a shift in space use, as herons to a greater extent began consuming fish from a river basin farther away from the bald eagle nest. As a consequence the species composition in heron diets changed significantly, with the largest increase in coho (Oncorhynchus kisutch) and largest decrease in Chinook salmon (O. tshawytscha). The representation of Chinook life-history types in the diets also shifted. Fall Chinook was the numerically dominant life-history type in the diets but decreased relative to spring and summer Chinook following relocation, accounting for differences in availability. Expressed by rearing type (natural or hatchery-produced), the prevalence of natural-origin Chinook in the diets increased whereas hatchery-origin Chinook decreased. For steelhead rearing type there were no significant changes. Finally, herons increased their use of a nearby tributary watershed following the relocation. Notwithstanding the potential confounding factors inherent to natural experiments, our results demonstrated marked shifts in space use among herons in response to the relocation and continued presence of bald eagles, which in turn shifted their predation pressure to other salmonid species.
Hobbseus yalobushensis, the Yalobusha rivulet crayfish, is a species of conservation concern because it is known from only six localities in parts of three central Mississippi counties. No studies have focused on the species since its description in 1989. Our objectives were to: (1) identify additional H. yalobushensis localities within a landscape managed intensively for loblolly pine (Pinus taeda) production, (2) relate stream size, water quality variables, and flow permanence to species presence or density, (3) characterize the aquatic community in relation to H. yalobushensis, (4) better define elements of the species' life history, and (5) compile unpublished H. yalobushensis localities from post-1989 collection records. During February and March 2011–2013, we made 56 samples in 24 reaches of 16 streams in Calhoun County, Mississippi. We documented captured crayfishes, fishes, and amphibians and measured habitat and water quality variables. Catch-per-unit-effort (CPUE, number per 100 s electrofished) of H. yalobushensis was significantly higher in intermittent than perennial stream reaches. Predatory fishes were the best indicator of H. yalobushensis absence, and the CPUE of all fishes had the strongest negative correlations with H. yalobushensis CPUE. Hobbseus yalobushensis CPUE was also negatively correlated with that of three other crayfishes. At least three age classes were evident based on length-frequency charts. Hobbseus yalobushensis has persisted in a landscape of intensively managed loblolly pine where streamside management zones were maintained according to Mississippi forestry best management practices. Future research needs include: evaluating the species' persistence under other land management practices (e.g., row crop agriculture); examining whether predatory fishes and other crayfishes influence the species' distribution; extending sampling to additional intermittent streams to clarify the species' range and distribution; and monitoring long-term population trends.
Garlic mustard [Alliaria petiolate (M. Bieb.) Cava & Grande] is a problematic European invader of temperate Eastern North American forests. We studied its germination response at reduced oxygen (O2) concentrations. Seeds of garlic mustard were exposed to different O2 concentrations (20.9, 15, 10, 5, and 2.5 %) in two laboratory experiments. Germination rate increased, and it took fewer days to attain 50 % germination (t50) at 15 % O2 than at 20.9 % O2. Germination declined at 5 % O2, and seedlings became stunted at 2.5 % O2. The ability of garlic mustard to thrive under low O2 concentrations may allow it to invade a wide variety of suboptimal habitats, such as shady understories where leaf litter cover the forest floors and on compressed and compact soils. Its ability to grow at low O2 levels may contribute to its invasiveness.