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Defining the trophic position of stream organisms is a first step in understanding the ecology of lotic systems. Whereas trophic positions of stream fishes have been traditionally assigned based on dietary analysis, stable isotope ratios may provide additional information on the validity of this approach and may be used to verify energy acquisition assumed from dietary studies. In this study, we assessed the concordance of literature-based trophic classifications and isotopic δ15N signatures for small-bodied fishes from four streams in Kansas, Oklahoma and New Mexico. ANOVA results revealed no significant difference (F2,27 = 1.71, P = 0.201) in trophic position based on δ15N values among three broad trophic classifications derived from literature sources (algivores/detritivores, omnivores and invertivores). Both the prevalence of omnivory in stream fishes and potential biases associated with isotope fractionation at different trophic levels poses potential problems when classifying lotic fish into trophic positions.
At least one formerly large population of American brook lamprey (Lampetra appendix) has been extirpated in Minnesota, but little is known about the species in the state. We examined densities and age structures of American brook lamprey larvae in several streams in southeastern Minnesota. Mean densities of lamprey larvae in the best habitats available in 13 streams varied from 0.33–5.78 larvae/m2. Seven of nine streams examined had missing age classes of larvae, with five streams missing two or more classes. Habitat use and length–weight relationships of larvae were similar to those reported previously for this and other species of lamprey. Many L. appendix populations in Minnesota are healthy, but others are susceptible to extirpation because of low densities and multiple missing age classes. The current status of many of these populations, and their susceptibility to further disturbance, need to be more thoroughly examined to better assess the need for legal protection for the species in Minnesota.
Little is known about the spatial and temporal dynamics of abundance and habitat use of the goldstripe darter (Etheostoma parvipinne). We assessed population dynamics, species associates and habitat use of this rarely studied darter in 14 first-order streams within pine plantations in north-central Mississippi. The pattern of goldstripe darter abundance among sampling periods differed among streams. Three streams with the greatest abundance of goldstripe darters exhibited significant differences in abundance among sampling periods, while the remaining 10 streams did not differ in abundance among sampling periods. Goldstripe darters exhibited the greatest associations with creek chub (Semotilus atromaculatus), brown madtom (Noturus phaeus) and least brook lamprey (Lampetra aepyptera). Goldstripe darter abundance was positively correlated with canopy cover, water temperature and sand. Our results suggest that management plans designed to maintain and develop forested riparian zones adjacent to first-order streams would assist with the conservation of goldstripe darters.
Gene products of 17 putative loci were analyzed to determine the genetic diversity for 85 individuals of Etheostoma moorei Raney & Suttkus, a darter species endemic to Arkansas, that has been subjected to severe habitat and numerical decline. Number of alleles per locus (1.3), heterozygosity (0.048) and polymorphism (25.9%) values were high relative to those of other darter species. Geographic samples did not exhibit isolation-by-distance, which may be associated with repeated extirpation and recolonization events. Of concern is the high number of polyallelic loci in Hardy-Weinberg disequilibrium (26%), indicative of populations undergoing genetic change. Several causative explanations were investigated with founder effect and inbreeding being the most plausible hypotheses. As these populations continue to decline in numbers, loss of genetic diversity appears imminent.
We tested philopatry by common musk turtles Sternotherus odoratus in a Virginia lake for 9 wk during summer 2003. Using unbaited crab pots, 10 trapping sites were established in the littoral zone around the lake perimeter and pots were sampled daily, yielding 560 turtle captures. Musk turtles trapped at the two sites separated by the greatest distance (1.1 km) were marked and released at the opposite site; turtles captured at the eight sites in-between were marked and released at the capture site. Of 287 captures of turtles released at their capture site, 57 were recaptured and 43 of these were at the original capture site. Of 140 captures of turtles displaced 1.1 km, 76 were recaptured and 15 of these were turtles that returned to their site of original capture. Turtles moved significantly more once they had been displaced, and males moved more frequently, but not over longer distances than females. These data indicate that S. odoratus is capable of homing and that site fidelity is exhibited by both male and female turtles. In a lake where the ratio of male:female turtles is approximately 1:1, the occurrence of philopatry is consistent with turtles having discrete home ranges.
Mass-action models of predator-prey interactions assume that predators encounter prey according to their relative densities as scaled by functional responses, although models seldom specify critical natural history and behavioral mechanisms that ensure that encounters actually occur. As a case study of this assumption, we assess the hypothesis that daily and seasonal activity and microhabitat use by wandering wolf spiders (Lycosidae: Schizocosa) searching for four common grasshopper species (Orthoptera: Acrididae) are coincident under natural conditions. There was great overlap in seasonal phenology and use of microhabitats between spiders and grasshoppers. Grasshoppers that were suitably sized (10–20 mm in length) as prey for spiders were relatively abundant from late spring through summer in this grassland. Three of the four common grasshopper species used microhabitat in a similar way, but differed from a fourth common species, Phoetaliotes nebrascensis. However, when they were active, spiders were about equally distributed between open microhabitats on the ground and up in the vegetation so that all grasshopper species were at risk. In response to temperature, spiders were active for only a portion of the day during which grasshoppers were also active so that the actual daily “window-of-opportunity” for capture each day was much smaller than expected. Spiders were more likely to be active during the early morning and evening, while grasshoppers were active during all daylight hours, most likely because of differences in thermal preferences. Schizocosa and their grasshopper prey are largely coincident in time and space except for overlap in daily activity which, presumably, reflects differences in thermal preferences. Consequently, overlap in daily time budgets that ensure actual encounter was reduced about 50%. The significance of this difference to the inclusion of simple mass-action dynamics in predator-prey models requires further consideration, but may be important.
Despite the common geographic occurrence of inland (athalassic) saline habitats, their biota has not been extensively studied. Diatoms have been estimated to contribute as much as 25% to the earth's primary production (Werner, 1977). However, in hypersaline systems the proportion of in situ carbon fixation by diatoms is likely to be higher. We used substrate samples taken from the Salt Plains National Wildlife Refuge, an athalassic hypersaline ecosystem, to investigate the relationship between diatom genus diversity, composition and salinity. These samples range in salinity from 14 to 306 ppt and contain 21 genera. Six genera (Cymbella, Mastogloia, Psammodictyon, Amphora, Navicula and Nitzschia) comprise 97% of the diatoms counted in all samples. Diatom genus diversity shows an inverse relationship with salinity, while genus richness shows no clear relationship with salinity. Hence, loss in diversity is the result of dominance by fewer taxa at higher salinities. The relative abundance of the genus Navicula is positively correlated with salinity, with it dominating the highest salinity sites. We used a canonical correspondence analysis (CCA) to explore the relationship between salinity and relative abundance of diatom genera. The primary variables influencing diatom genus composition at the Salt Plains were found to be the variability of salinity within a site and the overall magnitude of salinity.
The copepod community occurring in the uppermost part of karst was investigated by collecting animals from 13 ceiling drips in Organ Cave, West Virginia, over a 30 d period. A total of 444 copepods belonging to six genera and ten species were found. There was considerable heterogeneity, both spatially and temporally. Among physical parameters (oxygen, drip rate, conductivity, temperature, pH, ceiling thickness and redox), overall abundance was strongly influenced by drip rate. Community composition, analyzed by Canonical Correspondence Analysis, was correlated with drip rate, oxygen and ceiling thickness. Community similarity, as measured by Jaccard index, declined with geographic distance, but after a distance of several hundred meters, the average similarity and range of values increased, as “new” communities appeared. The overall pattern appears to be a relatively fine-scale patchwork of communities at a scale of hundred or so meters. The hotbed of copepod diversity in caves is the epikarst, not the streams.
Translocated Rocky Mountain wapiti (Cervus elaphus nelsoni) released in the southern Cascade Range of Washington State in the early twentieth century hybridized with resident Roosevelt wapiti (C. e. roosevelti). Archaeological remains of wapiti from this area dating between 1400 A.D. and 1835 A.D. are significantly larger than both subspecies, but bones of descendant hybrid wapiti killed by the 18 May 1980 volcanic eruption of Mount St. Helens are intermediate in size between the two subspecies. Deer (Odocoileus sp.) remains from the same archaeological sites as the wapiti remains are no different in size than bones of modern deer, indicating size change in wapiti was not environmentally driven. Anthropogenically facilitated hybridization supplemented and likely saved the local population from extirpation but resulted in smaller individual animals.
Among different bat species, echolocation call structure varies predictably according to habitat use. Much of this interspecific variation in echolocation calls reflects the physical constraints of sound propagation and echo formation in open versus spatially complex habitats. Bats must use calls that are suitable for detecting obstacles and prey in a particular setting; thus, bats that use similar habitats and catch similar prey produce similar calls. The same can be true for variation in echolocation calls within a single species that uses a variety of habitats. I recorded the echolocation calls and habitat use of a habitat generalist bat, Myotis lucifugus in order to determine whether the echolocation calls of M. lucifugus vary predictably across habitats, and if call variation is the result of individual flexibility in habitat use and echolocation behavior. I found that M. lucifugus used calls with higher frequencies, shorter durations and steeper frequency modulation in cluttered habitats than in open habitats. This type of call is consistent with a short-range target-detection strategy whereas the lower frequencies, longer call durations and shallower frequency modulation of bats in open habitats are consistent with longer-range target detection strategies. Furthermore, radiotelemetry indicated that individuals routinely foraged in different habitats. Taken together, these results suggest that call variation across habitats is the result of individual plasticity in echolocation behavior.
Knowledge of the habitat and spatial characteristics of natal dens used by female river otters (Lontra canadensis) is limited to a few observations. Documentation of these characteristics in human-altered landscapes may improve management opportunities for this species. We monitored 8 adult (>2 y old) radio-marked female otters during the natal denning season (March–May) in southeastern Minnesota during 2003–2004 and quantified 10 micro- and 2 macro-habitat characteristics of dens. Females began denning in March, with a mean initiation date of 31 March, and used natal dens for a mean of 49 d (se = 3). Two females used man-made brush piles as dens, four used small limestone caves, one used a cavity in the roots of a big-toothed aspen (Populus grandidentata) and one used a beaver (Castor canadensis) bank-den. Dens were located a mean of 316 m (se = 79) from the nearest body of water and averaged 61 m (se = 15) of elevation higher than the nearest body of water. Seven of eight females placed dens outside of their normal activity areas, and all females appeared to select den sites that were protected from flood events. Our results suggest that to promote successful reproduction of river otter populations, managers should protect potential denning sites in upland habitats adjacent to bodies of water.
The Louisiana black bear (Ursus americanus luteolus) is listed federally as a threatened subspecies and current information about food habits is necessary for developing a sound conservation strategy. We collected and analyzed 251 scats from bears in the Tensas River Basin (TRB) population in northeast Louisiana. We compared diets of the two subpopulations (Tensas and Deltic) of the TRB and we observed differences during summer and fall. We suggest that the greater diversity of mast consumed by bears on Deltic may provide demographic stability to this small isolated subpopulation. Across the TRB, corn (Zea mays) made up the greatest percentage volume of scats and dominated summer and fall diet, whereas beetles (Coleoptera) were the food item found most frequently in scats. Other important food items included: blackberries and dewberries (Rubus spp.), acorns (Quercus spp.), palmetto fruit (Sabal minor), grasses/sedges (Poaceae or Cyperaceae), herbaceous vegetation and other species of soft mast.
Knowing the distribution of species at the landscape level can give insight into the proximate mechanisms determining the species' range on a regional scale. We used a survey of road-killed animals to investigate landscape features associated with the presence of Virginia opossums (Didelphis virginiana) in central Massachusetts. Volunteers noted road-killed opossums on their daily commutes through the Connecticut River Valley and surrounding towns in 2000 and 2002. We used a GIS to characterize both the locations of roadkills and random points according to elevation, land use, distance to open water, traffic speed and number of observers on the road and then used logistic regression to determine the association of roadkill sites with these variables. Dead opossums were found most often at low-elevation sites with less forest cover and more human development. Although the opossum usually is considered a habitat generalist found primarily in association with woodlands, opossums in central Massachusetts are not associated with woodlands and, instead, are most often found in and near urbanized areas.
Effects of multiple herbivores were isolated in a rare, old-growth, maritime forest that has been affected by high white-tailed deer (Odocoileus virginianus) populations for several decades. Three decades of change in the plant community was described using permanent plots and nearly two decades of recovery using deer exclosures. Additional short-term exclosure experiments were used to separate the effect of rabbit and vole herbivory and the influence of canopy type on understory vegetation. We assessed whether natural enclosures formed by high densities of greenbrier (Smilax rotundifolia and S. glauca) provide spatial refugia for plant species from deer. Significant differences in fenced plots indicate that deer, rabbits and voles individually affect the understory vegetation, though rabbits and voles are secondary to deer that are the major herbivore in the American holly (Ilex opaca) forest. Plant cover decreased within permanent plots from 1967 to 1986; during the same time period deer densities increased drastically island-wide. Since plots were fenced in 1986 no additional significant changes were detected, but this is likely due to an inadequate sample size. The cover of all species depended on the interaction of fencing and canopy type with significantly higher plant cover in fenced plots beneath mixed or exclusively deciduous canopy. The proportion of woody stems surpassing 0.5 m tall was significantly higher when stems were fenced. Browsing impacts were apparent on approximately a quarter of the vegetation in June 2003. Plant cover, richness and diversity were higher within natural greenbrier enclosures. Overall the exclosure studies indicate the potential natural recovery that could occur within the forest if deer herbivory were limited. Few species have been extirpated, although several are confined to the greenbrier enclosures. Under the current level of herbivory, the maritime holly forest composition will be altered, changing the characteristic canopy of a critically imperiled plant community.
Over 150,000 ha of standing forest was altered as a result of a large-scale blowdown in the Boundary Waters Canoe Area Wilderness, Minnesota in 1999. We collected data in summers 2000 and 2001 to assess the effects of windthrow perturbation on small mammal communities in northern coniferous forests. Small mammal diversity, as well as density of the two most common species, red-backed voles (Clethrionomys gapperi) and woodland jumping mice (Napaeozapus insignis), were determined in three different treatments with varying proportions of blowdown (<33%, 33–66% and >66% blowdown). Diversity of small mammals increased from 2000 to 2001 and was highest in forest stands with <33% blowdown. The density of the two most abundant species of small mammals also differed among blowdown categories. Red-backed voles predominated at all sites, but exhibited peak densities (>25 individuals/ha) at sites most affected by blowdown. In contrast, density of woodland jumping mice exhibited an inverse relationship with red-backed voles, attaining peak densities (8 individuals/ha) in stands with <33% blowdown. Age ratios (juveniles: adults) were not influenced by year for either woodland jumping mice or red-backed vole populations, but differed for vole populations among blowdown categories. Juvenile red-backed voles predominated at sites with 33–66% (2.2: 1) and <33% blowdown (1.2: 1). Red-backed voles selected for blowdown and appeared to displace other small mammal species from this habitat. Because red-backed voles feed on coniferous seedlings, are primary dispersers of mycorrhizae and are prey for many predators, their selection of blowdown habitat could significantly influence community assemblages and forest succession following blowdowns.
Swine (Sus scrofa Linnaeus) are an invasive species with a negative impact on native terrestrial plant and animal diversity. Further, in its native range, excessive population size has been perceived as a potential problem. The effects of swine on aquatic organisms remain poorly documented. We investigated the effect of an unmanaged population of feral and free ranging swine upon aquatic habitat, invertebrates and microbes in a coastal plain stream in Louisiana. Sampling was conducted twice yearly, spring and fall, from August 2002 through April 2004, at five sites within the Mill Creek watershed. We measured stream characteristics, carbon and nitrogen, biochemical oxygen demand, fecal coliform counts and heterotrophic plate counts. We collected invertebrates from woody debris, microbes from the water column and identified both to the lowest practical taxon. Invertebrate, microbial, habitat and swine relationships were assessed with detrended and canonical correspondence analysis. Swine activity did not appear to alter stream habitats. However, swine changed the microbial taxonomic composition in the stream increasing pathogens. Swine also appeared to have a positive relationship with gastropods (snails) and a negative relationship with collecting and scraping (predominantly insect) taxa in the streams. We suggest the decline of scraper taxa may be related to the changes in microbial composition. Shifts in the invertebrate community can impact other organisms in the ecosystem, and the full extent of swine impacts on other aquatic organisms may also be negative.
Hydrophyllum brownei is a rare endemic species restricted to the Ouachita Mountains of Arkansas. One objective of this study was to model H. brownei population density by investigating the influence of sun exposure, soil characteristics and crowding. The most parsimonious model including shade alone best predicted population density, in which increasing shade was correlated with greater population densities. Reproductive capacity of different parts of the root was tested and individuals of the species were found to produce vegetative shoots from all portions of the root. This indicates that individuals are prolific vegetative reproducers, especially in circumstances of intense physical soil disturbance that break apart root systems. Leaf number was strongly correlated with number of root swellings and was determined to be a good predictor of individual plant stage. It was found that populations were structured either “normally,” with about equal numbers of individuals in all stage classes, or “dynamically,” skewed to a greater number of early stage individuals. Levels of shade relate to population density and site disturbances likely influence the density and stage structure of populations due to the life history trait of extensive vegetative reproduction from the roots. Further questions about genetic diversity and the ability to colonize new sites should be investigated to gain a better understanding of limits to H. brownei's distribution.
Seasonal breeding schedules for wild mammals, such as North American river otters (Lontra canadensis), often vary across their range. Previous studies in temperate regions found that river otters typically breed in March and April. Here we report on breeding condition and copulation of otters in June from Yellowstone Lake in Yellowstone National Park. Our findings suggest Yellowstone Lake otters have a relatively long breeding season, extending into June, or their breeding schedule is delayed so that energetically-demanding lactation coincides with spawning runs of Yellowstone cutthroat trout (Oncorhynchus clarki bouvieri).
Purple prairie-clover (Dalea purpurea Ventenat) is a common perennial forb that flowers during mid-summer throughout the Great Plains and adjacent biomes. Seed of D. purpurea is used for prairie restoration. This study characterizes the reproductive biology of D. purpurea. Manual pollination field trials showed that D. purpurea has a mixed pollination system. It is primarily xenogamous (45% of flowers manually pollinated with outcross pollen yielded plump seeds), but partially self-compatible (19% of selfed flowers yielded seeds). Flowers neither visited by bees nor manually pollinated rarely yielded mature seed (0–6% of flowers). A review of extensive bee community surveys from sites with prairie wildflower communities revealed that D. purpurea attracts a rich and diverse native bee fauna. Managed agricultural pollinators (Apis mellifera, Megachile rotundata) also work its flowers for pollen and nectar, yielding >20,000 seeds per plant. These observations bode well both for pollinating D. purpurea in small commercial seed fields as well as for its value for sustaining native pollinator faunas in prairie restorations.
Round goby Neogobius melanostomus is expanding its range within Illinois. Prior to 2004, the round goby existed primarily in the Lake Michigan waters of Illinois and was slowly moving inland via the Illinois Waterway. Two fish community monitoring programs, administered by the Illinois Natural History Survey's Illinois River Biological Station, have detected this fish species as it further expanded its range in the Waterway. Although little is known how this non-native benthic fish could threaten ecosystems in Illinois, the rate of invasion appears to be quickening.
The abundance and distribution of animal species appears to be limited by availability of suitable habitat, and often a critical component to these suitable habitats is the presence of one or more particular plant species, and/or plant species diversity. Abundance of the Long-nosed Leopard Lizard (Gambelia wislizenii) is inversely related to percent cover by all shrubs combined, in addition to percent cover by sagebrush, throughout the Alvord Desert in southeast Oregon. In many locales throughout the Great Basin desert sagebrush (Artemisia tridentata) is the dominant shrub, and its abundance is inversely related to shrub species diversity. However, in the Alvord basin, where there are abundant dry lake beds and salt-flats, G. wislizenii lizard abundance is relatively high, percent cover by shrubs varies and shrub species diversity can be high. In these areas Greasewood (Sarcobatus vermiculatus) is the dominant shrub, while sagebrush is non-abundant. Gambelia wislizenii population density patterns are discussed in light of putative uses of these shrub communities by Gambelia and other lizards, as well as recreational vehicles.
We examined food habits of the federally threatened leopard darter in six rivers in southeastern Oklahoma and southwestern Arkansas using guts collected from 1994 to 1997. The families Baetidae and Chironomidae were the most common food items selected by leopard darters. In general, leopard darters are selecting food items that are relatively common in the environment; thus, food availability may not be a factor limiting abundance.