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In this report of substantial syntopic populations, southern bog lemmings (Synaptomys cooperi) and woodland voles [Microtus (Pitymys) pinetorum] were the co-dominant rodents in a grassy oldfield in the absence of the large-bodied species of rodents common to the region. Southern bog lemmings achieved densities of 14 ha−1 on one grid and woodland voles had a peak density of 32 ha−1 on the other. Both species bred at high levels during the 18-mo study, including during the winter months.
The advantages of ant-mediated seed dispersal for myrmecochorous plants have often been framed in the context of directed dispersal and predator avoidance. Underlying and intertwining themes in these frameworks are the services of (a) moving seeds away from parent plants, (b) placing seeds in safe and ideal locations and occasionally, (c) removing elaiosomes to thwart detection by seed predators. These services are rarely simultaneously investigated from an experimental standpoint to determine which may be most important. Here, we conducted a factorial-designed field experiment to test how survival of seeds of a myrmecochrous forest herb, Asarum canadense (wild ginger), in two forest sites in southwestern Ohio, USA, was affected by the following treatments: distance from parent plant, seed burial, elaiosome removal, and their interactions. We found that when placed in artificial depots consisting of 10 seeds, only seed burial significantly aided seed survival. We supplemented this by conducting a laboratory experiment in which mice were given choices of trays containing either buried seeds with elaiosomes or without elaiosomes at densities higher than those of our field experiment and within the realm of those contained in ant nests. Mice consumed more mass of seeds with elaiosomes, suggesting that elaiosome removal may be advantageous in this context. When taken together, our results highlight the importance of seed burial and elaiosome removal for seed survival of a myrmecochorous forest herb. Though not specifically addressed in our study, the combination of these two services may positively contribute to later life history stages (e.g., seedlings) and population persistence of myrmecochorous plants and may ultimately reveal the importance of other services (e.g., short-distance seed dispersal) and their interactions.
Wild blue lupine (Lupinus perennis) in the Oak Openings Region of Northwest Ohio is an important nitrogen fixer and serves as an essential food source for the federally endangered Karner Blue butterfly (Lycaeides melissa samuelis). In order to examine potential factors that might be affecting mice predation on wild blue lupine seeds in oak savannas, we used seed trays placed in the open or on the forested edge to estimate seed predation rate. We recorded management histories, performed vegetation surveys, and used GIS to find spatial variables related to prescribed burning and edge to assess how they affect seed predation. Our major findings were that seed removal by mice for the summer averaged across sites was 22%, seed removal varied significantly across time (P < 0.05), and was more likely in areas with increased crypto-biotic crust (P < 0.0001). Seed predation rates increased under more prescribed burns over the last 10 y (P = 0.034) and 19 years (P = 0.0001). This leads us to support current management practices of a rotation of prescribed burning in open to partially closed canopy areas to create a balance between promoting lupine growth and minimal seed predation.
Intraguild predation in structurally complex habitats is thought to weaken trophic cascades and increase food web stability. However, many predators commonly found in leaf litter become restricted to simple microhabitat beneath rocks and logs during periods between rains. It is within this structurally simple microhabitat that some predators defend rich prey resources and are likely to interact strongly as the surrounding forest becomes too dry to forage broadly in space. We conducted a 4-y press experiment where we removed focal predators from unfenced field plots. To evaluate the effects of predators on one another we removed either salamanders or centipedes from beneath artificially placed cover objects and compared abundances of these and other intraguild predators to those in non-removal controls. We predicted that salamanders and centipedes would have strong negative effects on each other and on carabid beetles and spiders. We removed a total of 1288 salamanders and 1056 centipedes over 98 sampling dates. In salamander removal plots spider abundance increased by 34%, and carabid beetles decreased by 15% relative to the control. In centipede removal plots salamanders increased by 18% and carabid beetles increased by 29%, but spider abundance decreased by 15%. Interaction strengths were strongest in the drier summer months when territorial predators were confined in spatially fixed microhabitats. It is during these periods that predators may strongly regulate the abundances of guild members. In territorial species that defend areas beneath natural cover, the effect of intraguild predators may be an important mechanism that regulates distribution and abundance of forest floor predators.
Invasive species usurp habitat space at the expense of natives, reducing biodiversity and altering ecosystem function. The non-native invasive shrub Amur honeysuckle (Lonicera maackii) is known to have substantial effects on forest structure and biodiversity in Midwestern North America; however, its influence on nutrient cycling is relatively unexplored. We investigated throughfall volume and chemistry, and soil nutrients, under and away from L. maackii shrubs in random locations along transects in three patchily invaded second-growth forests. Significantly lower volumes of throughfall were found under L. maackii canopies than in sites located away from L. maackii. Cation concentrations in throughfall were significantly higher, and in some instances 3 × higher, under L. maackii than in “away” locations. Despite lower throughfall volumes under L. maackii compared to “away” locations, total deposition of cations in throughfall under L. maackii was also consistently higher than in adjacent areas of native forest canopy. In contrast, NH4-N concentrations in throughfall were significantly lower under L. maackii than away, suggesting N transformation and assimilation as rainwater passed through the canopy. No differences were found in soil properties between “under” and “away” locations. In summary, L. maackii significantly reduced the volume of rainwater arriving at the forest floor and altered the chemistry of that rainwater causing an increase in cation concentrations and a reduction in NH4-N. These results suggest that L. maackii invasion has the potential to cause significant alterations to nutrient cycling in forests.
Human alterations of the environment may interact with natural disturbances to alter the characteristics of biological communities in unexpected ways. I studied vegetation plots in a leveed bottomland hardwood forest at Bayou Sauvage National Wildlife Refuge near New Orleans, LA to determine how Hurricane Katrina affected the woody plant community and the distribution of the invasive Chinese tallow tree (Triadica sebifera). The storm killed approximately 68% of all trees in both overstory and understory and reduced basal area proportionately. Nearly all mortality was due to storm surge flooding, which was trapped for up to 3 wk by levees surrounding the refuge. Mortality was far greater than observed in other recent Gulf hurricanes and was three times higher than in similar forests in the nearby Pearl River basin that were struck by the highest winds from Hurricane Katrina. Flood mortality resulted in reduced community diversity and increased the dominance of the introduced T. sebifera after the storm at the expense of less flood-tolerant native species. The plant community appears likely to shift from a canopy dominated by native species to one dominated by Chinese tallow. This shift appears to be largely an unintended consequence of levee construction, which prevented storm surge from rapidly draining after the hurricane passed. The results suggest that widespread floodplain development may interact with future hurricanes to produce abrupt shifts in plant community composition and function in coastal habitats throughout the southeastern United States.
Northern red oak (Quercus rubra L.) has been described as an opportunistic, pioneer species adapted to mesic sites, though its presence and site-specific occurrence in extreme soil-water conditions is not well understood. Fifty woodlots were investigated for the presence of Q. rubra on the Maumee lake plain of southeastern Michigan. Although it was found widespread geographically, Quercus rubra was observed only in dry-mesic to mesic ecosystems where adequate moisture remains throughout the growing season on sand, sand/clay, and clay lake plain landforms. Quercus rubra was absent in sand lake plain ecosystems of nutrient-poor, deep sand (>200 cm to clay), and from high sand ridges that were not adjacent to swampy depressions. Within the sand lake plain it was observed only on relatively mesic, well- to somewhat poorly-drained ecosystems. In all landforms, Q. rubra was absent in seasonally inundated depressions. Successful overstory recruitment of Q. rubra was very rare, with the exception of a single site on the sand lake plain. Lacking major disturbances in the overstory, Q. rubra will likely be replaced by basswood (Tilia americana L.) and elm (Ulmus spp.) on the clay lake plain, sugar (Acer saccharum Marsh.), and black maple (Acer nigrum Michx. f.) on the sand/clay lake plain, and red maple (Acer rubrum L.), black cherry (Prunus serotina Ehrh.), and sugar maple on the sand lake plain. Further studies with a particular focus on water-table relations are necessary to predict future migrations of Q. rubra under a warming climate.
Pollination biology and factors affecting reproductive success of the federally endangered Echinacea laevigata (coneflower) were studied in one large and five small populations. Insect visitor exclusion from flowering heads and pollination treatments showed that seed production was 10x higher in open-pollinated treatments compared to bagged flowers that were not pollinated and 20x higher than flower heads receiving self pollen suggesting that cross-pollination was responsible for most seed production. Peak flowering occurred the 2nd–4th wk of Jun. 2004 and the large population contributed 50–68% of the flowering individuals in its plant community. During this period, Bombus (Apidae, bumblebees), Hesperiidae (skippers), and Megachile (Megachilidae, leaf-cutter bees) accounted for 73%, 12%, and 11% of the observed visits to coneflower, respectively. Species richness of coneflower flower visitors and number of flower visits was lower in each small population than in the large population. However, comparison of seed production between heads receiving supplemental pollen and open-pollination heads indicated that seed production was not pollen limited. In addition, over 93% of pollen grains stained normally in cotton blue-lactophenol in all six populations suggesting that pollen viability was high in small and large populations. However, seed production in the large population exceeded that in each of three small populations during 2005, and seedling size was larger in the large population compared to seedlings from one of the small populations. Comparison of soil cation concentrations among populations suggested that cations did not limit seed production. We suggest that genetic factors, such as inbreeding or low S allele variation, may limit seed production in the small populations.
The death of eastern hemlock (Tsuga canadensis) trees in response to infestation by the introduced hemlock woolly adelgid (Adelges tsugae) may affect ecosystem processes and structure of streams. Prior to hemlock mortality, we documented the conditions of eight small streams and their associated riparian forests within the Appalachian Mountains of North Carolina, U.S.A. Hemlock was the dominant tree species on all riparian sites and was always associated with rhododendron (Rhododendron maximum). Significant trends of increasing canopy openness, increasing light to the streams and increasing annual temperature range were observed. Contributions of hemlock to litterfall, in-stream wood, and benthic organic matter were important at the beginning of the study, suggesting that the loss of hemlock may significantly modify the trophic dynamics and physical structure of southern Appalachian streams. Increased growth of rhododendron in response to hemlock mortality may compensate for the trophic influences of hemlock loss. However, because of rhododendron's negative effect on growth of seedlings of other tree species, the greatest ecosystem impact of hemlock wooly adelgid may be more extensive rhododendron thickets within the riparian corridors of southern Appalachian streams.
We characterized coldwater stream fish community response to habitat degradation and channelization for agriculture. Coldwater streams are not common in the lower midwestern United States, and these streams differ from warmwater streams with respect to their diversity and community response to degradation. Six sites were sampled on the coldwater Mac-o-chee Creek in Ohio. Three reaches were classified as geomorphically constrained (by a roadway) and three as recovering (unconstrained and not channelized or cleaned for more than 100 y). Within each reach 31 mesohabitat units were sampled and were delineated as riffles, runs, or pools. Our goals were: (1) to examine how habitat and geomorphic impairment influences the abundance and community structure of coldwater fishes; and (2) to test whether the constraints on recovery from channelization were more influential in structuring communities than mesohabitat types. Our hypothesis was that we would find lower species diversity overall in the recovering sites because they would be more indicative of a coldwater fauna. In contrast, we hypothesized that the sites that are not able to recover (geomorphically constrained) would be more indicative of a warmwater fauna, and thus more diverse. We found lower species abundances, diversity, and species richness in recovering stream reaches than impaired reaches. Mesohabitat types present are influenced by channelization and recovery but are also largely a product of geomorphologic setting of the study streams. The effects of habitat degradation on the biota and the resulting trophic structure are important for designing restoration targets for coldwater systems, which may be naturally less diverse than warmwater counterparts. For example, biometric scores like Index of Biotic Integrity (IBI) are often used as restoration targets, but this would be inappropriate unless a coldwater-specific IBI were used.
Slimy sculpin Cottus cognatus are being reintroduced into coldwater streams in the upper Midwestern United States, where they were extirpated by stream degradation during the early- to mid-1900s. Habitat use and selection by slimy sculpin were examined in nine coldwater tributaries of the Upper Mississippi River in southeastern Minnesota to determine which stream habitats are important for successful reintroduction. Most (>70%) individuals (n = 1932) used coarse substrates and vegetation, shallow water (<30 cm), slow current velocities (<20 cm/sec), and moderately embedded (15–60%) substrates. Compared to habitat availability, adults selected boulder substrate and vegetation, whereas young-of-year (YOY) selected gravel, rubble, and vegetation. YOY sculpin selected shallow water (<30 cm), whereas adults exhibited broader selection (1–60 cm). Both age groups selected the slower bottom velocities (especially <20 cm/sec). Habitat use and selection by adult fish were consistent among 3 y of surveys. Habitat suitability index values for sculpin were similar among native sculpin streams and streams where sculpin have been or may be reintroduced within the same geographic region. Slimy sculpin displayed habitat selection similar to that of other sculpin species, except for selecting much slower current velocities. Suitable physical habitats are present in coldwater streams in southeastern Minnesota to support further reintroduction of slimy sculpin. Failed reintroductions of sculpin likely are not related to lack of suitable physical habitats.
Slimy sculpin Cottus cognatus are being reintroduced into coldwater streams in southeastern Minnesota to restore native biotic diversity and provide forage for large trout, but success has been variable. We examined slimy sculpin diets and prey consumption in a series of field and laboratory experiments to assess the potential role of invertebrate prey in affecting reintroduction success. Sculpin consumed 35 different types of prey in the field, but frequency of occurrence was highest and preferences (Ivlev's selectivity index) strongest for Diptera larvae and Amphipoda. Benthic samples indicated that preferred prey items were abundant in most streams. In 24-h feeding experiments, sculpin typically consumed 5 to 15 prey/day, and exhibited selective feeding for Amphipoda (Gammarus), Isopoda (Asellus), and Ephemeroptera (Baetis) while rejecting Trichoptera (Brachycentrus) and Gastropoda (Physella). Sculpin are euryphagous and flexible to varying prey availability in different streams, demonstrating both mixed diets and multiple prey preferences that allow fish to maximize their consumption when confronted with differing prey assemblages. Our data indicate that preferred prey taxa are not limiting and that lack of suitable prey is not a factor in the limited success of sculpin reintroductions in some streams.
Riffle-pool formation creates a pattern of alternating habitat types in streams, potentially dividing populations of organisms restricted to either riffles or pools. Such subdivision could lead to small-scale variation in ecological patterns, such as foraging behavior, driven by riffle- and pool-scale variation in habitat or prey availability. I examined prey use by the benthic insectivore orangethroat darter (Etheostoma spectabile) in a midwestern (USA) riffle-pool stream. Etheostoma spectabile primarily occupies riffles, where it forages on benthic macroinvertebrates. I tested for effects of body size and variation among riffles on size and number of prey consumed, then examined selectivity for and against common prey items for the study reach as a whole, and for individual riffles. I also compared variation in diet breadth among riffles to patterns predicted by foraging theory. Number of total prey items and of three common prey items consumed varied significantly among riffles. Overall number of prey items consumed did not vary with darter body size, and number consumed varied with body size for only 1 prey taxon. Prey selection varied greatly among riffles, and for four of seven prey items was a function of habitat differences. Contrary to theory, diet breadth within riffles was not dependent on abundance of energetically favorable prey, largely due to a lack of selection for these prey items. These results indicate that variation among riffles can have a strong effect on prey use by E. spectabile, and that attempts to characterize foraging behavior over longer stream reaches may omit an important level of variation. For species restricted to small patches within larger habitats, ecological processes may be driven by local patch characteristics more than by larger scale phenomenon, or intrinsic factors such as body size.
Many North American minnows (Cyprinidae) exhibit nest association, a spawning mode in which one species (associate) uses nests constructed by another species (host). Although this relationship may be obligate for some species, many nest associates can use alternative reproductive modes, indicating that the strength of the relationship between associate and host may vary. Quantifying the strength of the nest association relationship represents a necessary first step for understanding the importance of this interaction to stream fish communities. To address this question, we conducted a literature review of ecological and ethological reproductive traits for 11 nest associates of Nocomis occurring in the New River basin, Virginia. We used phylogenetic eigenvector regression (PVR) to remove the effects of phylogenetic relatedness among species and used nonmetric multidimensional scaling (NMS) to ordinate a phylogenetically independent trait similarity matrix of the 11 species. Based on the ordination results, we delineated a group of strong and weak nest associates. Strong nest associates showed significant geographic range overlap with Nocomis, while weak ones did not. No difference in spawning temperature range overlap occurred between the two groups. We then tested for effects of nest association strength on species' rarity and found that most (6 of 7) strong nest associates held rare classifications based on one or more of geographic extent, habitat breadth, or local abundance. Conversely, all weak nest associates reflected common classifications. These results indicate that nest association strength is related to rarity; this potentially crucial aspect of conservation has been previously overlooked. Clearly, conservation of rare and imperiled nest associates should be pursued through protection of their host and, consequently, the mutualism they have evolved to exploit.
In teleost fishes, 11-ketotestosterone (11KT) is a critical androgen regulating primary and secondary sex characteristics. In the sexually dimorphic Lythrurus fasciolaris (Cyprinidae), dominant nuptial males display heavy tuberculation on the head and nape, dark dorsolateral vertical bars, and dramatic red coloration in the fins, venter, and operculum area. This study aimed to quantify 11KT circulating levels in males and females, and determine any correlation with key male reproductive status indicators such as nuptial coloration, size, and gonadosomatic index (GSI). Thirty-one wild-caught L. fasciolaris were divided into three groups according to reproductive status: dominant males (D), non-dominant males (ND), and females (F). Physical measurements, digital imaging, and blood samples were used to quantify body size, GSI, nuptial coloration, and 11KT circulating levels. Dominant males had higher 11KT levels and nuptial coloration traits compared to ND males and females (red area, hue, saturation), and a higher GSI than ND males. Non-dominant males had more 11KT and coloration than females. Increased 11KT levels corresponded to increased coloration, size and GSI.