Showing papers in "American Midland Naturalist in 2004"
TL;DR: The evidence suggests that mammals, birds and herpetofauna are vulnerable to negative impacts from fire ants, and some species are more likely to experience negative population-level impacts than other species.
Abstract: The negative impacts of biological invasion are economically and ecologically significant and, while incompletely quantified, they are clearly substantial. Ants (family Formicidae) are an important, although often overlooked, component of many terrestrial ecosystems. Six species of ants are especially striking in their global ability to invade, and their impacts. This paper focuses on the impacts of the most destructive of those species, the red imported fire ant (Solenopsis invicta), and focuses on impacts on native vertebrates. Red imported fire ants often become the dominant ant species in infested areas outside of their native range due to their aggressive foraging behavior, high reproductive capability and lack of predators and/or other strong competitors. The evidence suggests that mammals, birds and herpetofauna are vulnerable to negative impacts from fire ants, and some species are more likely to experience negative population-level impacts than other species. Assessing the ecological impacts of fire ants on wild animal populations is logistically difficult, and very few studies have combined replicated experimental manipulation with adequate spatial (>10 ha) and temporal (>1 y) scale. Thus, most studies have been observational, opportunistic, small-scale or 'natural' experiments. However, significant research, including an increase in experimental and mechanistic investigations, has occurred during the past decade, and this has led to information that can lead to better management of potentially affected species.
197 citations
TL;DR: This site supports a stable freshwater mussel population through a life history strategy of low but constant recruitment and high annual adult survival, which suggests that whatever environmental variables affect survival of mussels in this site affected all three species the same.
Abstract: We used a mark-recapture method and model averaging to estimate apparent survival, recruitment and rate of population growth in a native freshwater mussel population at a site on the Cacapon River, which is a tributary to the Potomac River. Over 2200 Elliptio complanata, E. fisheriana and Lampsilis cariosa were uniquely tagged over a period of 4 y. Recapture probabilities were higher in spring and summer than in winter except for L. cariosa which had a low probability of recapture regardless of time of year. All three species had high annual adult survival rates (>90%) with lower estimated survival of small (≤55 mm) mussels (43%–69%). The variation in apparent survival over time was similar for all three species. This suggests that whatever environmental variables affect survival of mussels in this site affected all three species the same. Recruitment rates were low (1–4%) for both E. complanata and L. cariosa, with E. fisheriana having several periods of high (15–23%) recruitment. Distribution w...
74 citations
TL;DR: This paper presents five allometric equations that allow for estimation of ash-free dry biomass based on length (mm) measurements for European earthworm species (Lumbricidae) commonly seen in the United States.
Abstract: In the last decade the invasion of European earthworms into previously worm-free glaciated areas of North America has stimulated research into their impacts on native forest ecosystems in the region. As a first approximation, the impacts of invading earthworms are related to their biomass. However, direct measurements of biomass can be significantly affected by the moisture conditions under which the earthworms are collected and their relative gut contents. Ash-free dry mass is the best standardized measure of earthworm biomass, but requires the destruction of specimens. This paper presents five allometric equations that allow for estimation of ash-free dry biomass based on length (mm) measurements for European earthworm species (Lumbricidae) commonly seen in the United States.
67 citations
TL;DR: In this paper, the authors develop and test ecological niche models for the Asian longhorned beetle Anoplophora glabripennis (Motschulsky), and then project them onto North America to identify areas of potential distribution.
Abstract: The potential for ecological and economic damage caused by invasive species is only beginning to be appreciated. A recently arrived, and particularly worrisome, invader in North America is the Asian longhorned beetle Anoplophora glabripennis (Motschulsky), the larvae of which damage trees and forests. The geographic extent and likely path of its possible invasion of North American forests, however, are unknown. Herein, we develop and test ecological niche models for the species based on features of climate from the species' native distribution in eastern Asia, and then project them onto North America to identify areas of potential distribution. These models suggest that the species has the potential to invade much of eastern North America, but only limited areas in western North America, and that a focus of initiation of invasions is likely to lie in the area south of the Great Lakes. This result is particularly clear under modeled scenarios of spread and contagion.
65 citations
TL;DR: Nesting by diamondback terrapins daily from 1 May through 31 October at a beach on an island in northeastern Florida is monitored, and newly oviposited intact nests are recorded and marked for depredation, hatching or washout and nest predators are identified.
Abstract: In 1997 and 2000 we monitored nesting by diamondback terrapins daily from 1 May through 31 October at a beach on an island in northeastern Florida. During our visits we recorded and marked newly oviposited intact nests, monitored previously marked nests for depredation, hatching or washout and identified nest predators. We recorded nest deposition from late April through late July, but most nests were found in June (2000) or July (1997). Most nests were depredated within 48 h of oviposition. Most depredated nests were found in June or July, and those from July included both newly deposited and recently hatched nests. Depredated nests in August and September were all recently hatched. The major nest predators were raccoons, but we also noted crows, boat-tailed grackles, armadillos, ghost crabs and two species of plant roots. Hatching and emergence began in early July and continued into October. The mean emergence period for 54 nests was 68.9 d. In 1997, 21.9% of marked nests were washed out by hig...
60 citations
TL;DR: Some woodland edge effects on grassland-nesting birds should be less pronounced or absent near cropland edges of grasslands that lack wooded-edge habitat often used by nest predators and brood parasites, but might vary geographically.
Abstract: Edge effects on grassland-nesting birds should be less pronounced or absent near cropland edges of grasslands that lack wooded-edge habitat often used by nest predators and brood parasites. We compared nest predation, brood parasitism and densities of dickcissel (Spiza americana) nests in relation to distance from woodland and cropland edges of Kansas tallgrass prairie. Daily nest predation rates did not differ (P > 0.25) among distance intervals (≤50 m, 51–100 m, ≤100 m and >100 m) from either edge type or among 50-m intervals adjacent to each edge type. Brood parasitism rates by the brown-headed cowbird (Molothrus ater) were higher ≤100 m vs. >100 m from woodland edges (P = 0.04), being highest ≤50 m from woodland edges (P = 0.09). Parasitism rates were not related to distance from cropland edges, although parasitism rates ≤50 m from woodland and cropland edges were statistically similar (P = 0.16). Dickcissel nest densities were lower ≤50 m from woodland edges relative to farther distance inte...
51 citations
TL;DR: In this article, a master chronology was constructed for the oak savanna using 16 cross-dated oak sections from an oak-savanna remnant in Kenosha County, Wisconsin, where only 50% of the fire dates were associated with significantly dry years.
Abstract: In oak (Quercus) savannas in the Midwest region of the United States, fire continues to play a significant role in its persistence within the landscape; however, in southeastern Wisconsin, quantified fire history records are limited. This study documented occurrences of fire for the last 200 y using 16 cross-dated oak sections from an oak savanna remnant in Kenosha County, Wisconsin. Fire history was reconstructed by: (1) obtaining fire-scarred cross sections from cut down oaks in an area planned for an industrial park, (2) preparing sample surfaces to count rings, (3) creating skeleton plots to crossdate samples, (4) dating fire scars, (5) calculating intervals between fires and (6) determining seasonality of the fire. In addition, a master chronology was constructed for the oak savanna using the cross sections to correlate with precipitation. Throughout the entire time series, only 50% of the fire dates were associated with significantly dry years. Although the overall Weibull median interval w...
51 citations
TL;DR: The data suggest that Eastern red bats and evening bats altered their prey selection late in the summer, as assessed by insect light traps placed within foraging habitats.
Abstract: We evaluated partitioning of food resources among syntopic eastern red (Lasiurus borealis), Seminole (L. seminolus) and evening (Nycticeius humeralis) bats at the Savannah River Site, South Carolina, from June through August of 1996 and 1997. We compared diets to indices of relative prey availability, which were based on samples of the insect communities in bat foraging habitats and the amounts of time the bats foraged in each habitat. The relative proportions of insect orders consumed differed among the species. We recorded only minor differences between insect consumption and indices of prey availability, as assessed by insect light traps placed within foraging habitats. Our data suggest that Eastern red bats and evening bats altered their prey selection late in the summer.
49 citations
TL;DR: Andropogon gerardii populations are comprised of two (or more) polyploid forms over much of the range of the species, but in the current populations, however, enneaploids are big, vigorous and fertile individuals.
Abstract: Andropogon gerardii populations are comprised of two (or more) polyploid forms over much of the range of the species. To understand the impact of intraspecific polyploidy, polyploid cytotypes were compared over 4 y in native grasslands in Boulder, Colorado. Boulder A. gerardii populations averaged 59.6% hexaploids (60 chromosomes), 35.3% enneaploids (90 chromosomes) and 5.1% intermediate (aneuploid) chromosome numbers using flow cytometry to infer chromosome numbers. Neither mean clone area nor mean annual change in clone area differed significantly between ploidy levels. Hexaploid clones produced significantly more viable seeds than enneaploids. Enneaploids are not replacing themselves, whether that is measured absolutely or relative to hexaploids. Enneaploid reproductive effort was greater than hexaploid reproductive effort in some years and they produce substantial numbers of good seeds, but those seeds rarely have enneaploid cytotypes. The populations should eventually become entirely hexaploid. In the current populations, however, enneaploids are big, vigorous and fertile individuals.
49 citations
TL;DR: In this article, the authors examined how water level fluctuations and sediment characteristics affected interactions among unionids and zebra mussels in a Lake Erie coastal marsh and found a diverse unionid community (15 species) with many juvenile unionids.
Abstract: Infestation by introduced zebra mussels has extirpated native unionids in many Great Lake habitats. Shallow areas in coastal wetlands are intermittently dewatered by seiches and seasonal water level changes, and we examined how water level fluctuations and sediment characteristics affected interactions among unionids and zebra mussels in a Lake Erie coastal marsh. In 2001 we sampled unionid distributions and measured zebra mussel colonization on PVC plates at 1 cm, 18 cm and >35 cm water depths. We found a diverse unionid community (15 species) with many juvenile unionids. Unionid densities (0.01 unionids/m2) were comparable to other coastal wetlands, but are lower than reported in offshore areas before zebra mussels were introduced. Zebra mussels colonized plates at >3000 individuals/m2 in some locations. Although >60% of unionids had byssal threads on their shells, >75% of unionids had no attached zebra mussels. Therefore, zebra mussels are colonizing unionids, but are not surviving. Unionid nu...
48 citations
TL;DR: Badgers probably have little impact on marmot demography except for localized, short-term increases in mortality, but may significantly affect the fitness of individual marmots.
Abstract: Badger (Taxidea taxus) activity was recorded in colonies of yellow-bellied marmots (Marmota flaviventris) during behavioral observations and trapping. Badgers were observed seven times in a marmot colony and extensive digging at marmot burrows was recorded five times in 40 y. When four badgers occupied a burrow at the edge of a marmot colony, the behavior of marmots and badgers was observed for 7 d and the marmots for an additional 6 d after the badgers departed. Badgers hunted at a significantly higher rate in the afternoon than in the morning. The adult female usually hunted alone, failed to capture any adult marmots, but did kill young marmots. When badgers were present, marmots had more frequent alarm calls, lower rates of foraging and higher rates of vigilance than when badgers were absent. I estimated that badgers killed 67 of 1423 individual marmots. The risk of being killed by a badger was highest for young, intermediate for yearlings and lowest for adults. Badgers probably have little impact on marmot demography except for localized, short-term increases in mortality, but may significantly affect the fitness of individual marmots.
TL;DR: In this article, the authors evaluate soil quality and the relationships between selected soil properties across a climosequence in a transition zone between tallgrass prairie in humid-temperate (Ozark Highlands) and humid-subtropical (Grand Prairie) climate regimes in Arkansas.
Abstract: Climate, specifically moisture and temperature, influences plant growth and nutrient cycling; thus, climate also influences prairie development. Relatively little research has been conducted in the ecological transition zone between the Great Plains and the more humid forests. Since moisture and temperature affect many ecosystem processes, the wetter climate of the southern forest region should influence soil biogeochemical cycling quite differently from that in grassland soils. The objective of this study was to evaluate soil quality and the relationships between selected soil properties across a climosequence in a transition zone between tallgrass prairie in humid-temperate (Ozark Highlands) and humid-subtropical (Grand Prairie) climate regimes in Arkansas. Soil physical, chemical and biological properties of the upper 10 cm differed significantly between physiographic regions. Linear relationships between total soil nitrogen (N) and carbon (C), extractable phosphorus and manganese, electrical conductivity and soil organic matter concentration differed significantly between physiographic regions. Total soil N and C decreased with increasing soil bulk density in both physiographic regions. The relationship between total C and bulk density differed by physiographic region, while the relationship between total N and bulk density did not. Soil organic matter concentration, C:N ratio, and many extractable nutrients, were higher and relationships between selected soil properties differed under native tallgrass prairie in a relatively warm and wet climate than that in a relatively cooler and drier climate. The results of this study suggest that prairie preservation, restoration and management practices should differ depending on climate regimes.
TL;DR: In this paper, the authors compared characteristics of nest trees used by Virginia northern flying squirrels with randomly selected trees during summer and fall of 2000 and 2001, and found that the squirrels used an average of 3.6 nest trees/month, switching trees frequently.
Abstract: Little is known about nest tree use of the endangered Virginia northern flying squirrel (Glaucomys sabrinus fuscus). Because nesting sites could be a limiting factor, it is important to understand the denning ecology to further manage and protect this subspecies. We compared characteristics of nest trees used by Virginia northern flying squirrels with randomly selected trees during summer and fall of 2000 and 2001. We tracked 13 Virginia northern flying squirrels to 59 nest trees. The squirrels used an average of 3.6 nest trees/month, switching trees frequently. Sixty-nine percent of the nests were in cavities and 31% were leaf nests. Yellow birch (Betula alleghaniensis) and Fraser magnolia (Magnolia fraseri) were selected for nest trees more than expected based on availability. A large portion of nest trees were in larger and taller trees than trees in the surrounding area. There also was a significant number of trees located next to or near skidder and hiking trails. Although a large number of nest trees were similar across sites, there was variation in the characteristics of nest trees used, suggesting that Virginia northern flying squirrels may not be as specialized in nest tree selection as indicated by previous studies.
TL;DR: The authors examined the effects of fire regime and bison activity on the plant communities of active bison wallows and the surrounding grazing lawns at Konza Prairie Biological Station in northeastern Kansas, USA.
Abstract: We examined the effects of fire regime and bison activity on the plant communities of active bison wallows and the surrounding grazing lawns at Konza Prairie Biological Station in northeastern Kansas, USA. In both mid-June and late July the grazed sites had higher species richness and more vegetation cover than the wallow edges regardless of fire regime. The percent cover of most dominant perennial species was significantly higher on grazing lawns than in wallows. Annual species and exotic species had significantly higher cover in wallows than in grazing lawns and in annually burned sites compared to those burned at a 4-y interval. Overall, treatment effects on community structure and individual species abundance were stronger in the June. However, in July there was significantly more bare ground wallows around sites burned at a 4-y interval, suggesting increased wallowing activity at these sites. This finding suggests a strong effect of fire regime on seasonal bison activity, which further indicates the importance of multiple interacting disturbances for generating local- and landscape-level vegetation patterns in tall grass prairie.
TL;DR: The authors compared 11 ecological variables thought to be important for assessing the habitat of the endangered Virginia northern flying squirrel (Glaucomys sabrinus fuscus) at 11 occupied and 9 unoccupied sites within northern hardwood-montane conifer forests in the central Appalachians of West Virginia.
Abstract: We compared 11 ecological variables thought to be important for assessing the habitat of the endangered Virginia northern flying squirrel (Glaucomys sabrinus fuscus) at 11 occupied and 9 unoccupied sites within northern hardwood-montane conifer forests in the central Appalachians of West Virginia. Forest stands at sites occupied by G. s. fuscus had significantly higher relative importance values of montane conifers such as red spruce (Picea rubens) and little or no presence of northern red oak (Quercus rubra) than did sites that were believed unoccupied. Probabilities derived from logistic regression analyses indicated that sites were considered occupied when relative importance values of montane conifers in forest stands exceeded approximately 35%. Conversely, we detected no differences in elevation, absolute forest basal area, overstory tree species richness, total shrub density, percent coarse woody debris cover, percent herbaceous cover, percent emergent rock cover and percent soil organic matter (humus) between occupied and unoccupied sites. We observed low levels hypogeal fungi across all sites and fungi presence did not differ between occupied and unoccupied sites. Patchily distributed fungi combined with the much reduced and altered forest habitat in the region provide additional insights into the rarity of G. s. fuscus in the central Appalachians.
TL;DR: In this paper, the authors analyzed fish assemblage data from 21 sites over three periods (1967, 1995 and 2001) from an adventitious stream drainage (Piasa Creek: Jersey, Madison and Macoupin CO., IL).
Abstract: Recent studies of stream fish assemblages have begun to incorporate landscape properties in explaining the dynamics seen at individual sites in riverine systems. In this approach, stream and river landscapes (riverscapes) are viewed over greater spatial and temporal scales to understand the dynamics seen at individuals sites. Adventitious streams are feeder tributaries of mainstreams at least three orders greater in magnitude. Interface sites between adventitious streams and their mainstreams are often more diverse and variable than either the feeder stream or mainstream alone. We analyzed fish assemblage data from 21 sites over three periods (1967, 1995 and 2001) from an adventitious stream drainage (Piasa Creek: Jersey, Madison and Macoupin CO., IL) to test the hypothesis that assemblage variability and diversity would be greater at downstream interface sites than those further upstream. There was a correlation between distance from the mouth of the stream and assemblage variability over time, ...
TL;DR: Within the state, patterns of species distribution are complex and are affected by environmental differences among the watersheds, the presence of suitable dispersal routes and widespread introductions.
Abstract: Fishes present in 19 watersheds in New York are inventoried. One hundred seventy-six taxa (171 species) reside in these watersheds. Eighteen taxa are extra-limital exotic fishes, that is, they are not native to any New York watershed. The remaining 158 taxa are native in at least one New York watershed, although transfer of species among watersheds within the state is, and has been, widespread. Sixteen species are diadromous or estuarine and eight of these species support land-locked populations, so 150 taxa are strictly freshwater and native. Watersheds differed markedly in richness and composition. Over 100 taxa are reported from five watersheds and seven have fewer than 75 taxa. Twelve species are now extirpated from all New York watersheds and 28 other species have disappeared from at least one of their historic watersheds. Fifty-seven native species are infrequently caught, are considered rare and are candidates for special consideration. Within the state, patterns of species distribution ar...
TL;DR: The preference gypsy moths exhibited towards oak species indirectly resulted in a higher growth rate for understory tree species, possibly due to increased light availability and the decreased competitive capacity of the defoliated oaks.
Abstract: We calculated relative growth rates of all species over 10 cm circumference at breast height from 1997–1999, 1999–2001 and 2001–2003 in a 70 by 100 m plot in an oak forest in southeastern Michigan. Red maple and black cherry represented most of the understory species while white and black oaks dominated the canopy. During the summer of 1999, outbreak levels of gypsy moths preferentially defoliated oaks on the plot, often resulting in 100% defoliation. The relative growth rates (RGR) of red maple and black cherry were significantly higher during the time period where gypsy moths were at outbreak levels. Oaks had lower RGR during the gypsy moth attack than in the subsequent time period. Consequently, the preference gypsy moths exhibited towards oak species indirectly resulted in a higher growth rate for understory tree species, possibly due to increased light availability and the decreased competitive capacity of the defoliated oaks. This indirect effect could accelerate the succession at which oak...
TL;DR: Limiting invasion of eastern red cedar in forests may require early detection and selective removal of pioneer seedlings in cross timbers and other habitats that attract a high diversity or density of frugivores.
Abstract: Increased abundance and distribution of eastern redcedar (Juniperus virginianus), a native species in the Great Plains, has been associated with changes in ecosystem functioning and landscape cover. Knowledge of the main consumers and dispersal agents of eastern red cedar cones is essential to understanding the invasive spread of the species. We examined animal removal of cedar cones in three habitats (tallgrass prairie, eastern red cedar and woodland-prairie margins) in the Cross Timbers ecoregion using three exclosure treatments during autumn and winter. Exclosure treatments excluded study trees from ungulates, from terrestrial rodents and ungulates or from neither (control). Loss of cones from branches varied by a habitat-time interaction, but was not affected by exclosure type. Loss of cones from containers located under experimental trees varied by a habitat-treatment-time interaction. In December and January, cone consumption from containers in no-exclosure treatments was highest in margins...
TL;DR: Evidence that female eastern pipistrelles are faithful to small roost areas both within and between years, and that juvenile females exhibit female natal philopatry is provided.
Abstract: Bats in forests have strict roosting habitat requirements. The current paradigm in bat conservation has been to identify the specific characteristics of individual roost trees that are selected by bats. Although this strategy is both practical and useful, it is also important to recognize landscape level interactions between bats and their roost habitats. Few studies have documented fidelity patterns of individual bats to specific roost habitat areas both within and between years. If bats are faithful to roost areas, conservation and management practices must incorporate the identification of the minimum size of areas required by bats during the summer season. We provide evidence that female eastern pipistrelles are faithful to small roost areas both within and between years, and that juvenile females exhibit female natal philopatry.
TL;DR: Results suggest that C. varia's impact might be continued through altered soil nitrogen, and the strong response of P. pratensis could hinder restoration efforts by competing with native species.
Abstract: I investigated the effect of Coronilla varia invasion and subsequent reduction on the plant community and soil nitrogen availability in a degraded Illinois sand prairie. The presence of C. varia significantly increased soil nitrogen availability and significantly decreased native species richness and cover, but neither helped nor hindered a common non-native grass, Poa pratensis. One year after the drastic reduction of C. varia, soil nitrogen remained somewhat elevated and native species richness and cover low, but P. pratensis cover increased nearly six-fold. These results suggest that C. varia's impact might be continued through altered soil nitrogen. More important, however, was the strong response of P. pratensis, which could hinder restoration efforts by competing with native species.
TL;DR: The four main environmental gradients influencing overall assemblage structure for both age groups were river elevation, water velocity, conductivity and depth of gear deployment, and partial canonical correspondence analyses (pCCA) demonstrated significant effects of physical habitats.
Abstract: We investigated variation of fish assemblages in response to environmental factors using Long Term Resource Monitoring Program data. Data were collected from 1993 to 2000 from five physical habitats in the unimpounded upper Mississippi River. We captured 89 species composing 18 families. Of these, 26% were fluvial specialists, 25% were fluvial dependent and 49% were generalists. The numerically dominant component of the adult fish assemblage (species accounting for >10% of total catch) accounted for 50% of the assemblage and was comprised of only three species: gizzard shad (Dorosoma cepedianum; 25%), common carp (Cyprinus carpio; 15%) and channel catfish (Ictalurus punctatus; 10%). The dominant component of the YOY fish assemblage was comprised of only two species, which accounted for 76% of the total catch: freshwater drum (Aplodinotus grunniens; 39%) and gizzard shad (37%). We used a cross-validation multivariate approach to explore how adult and young-of-the-year (YOY) assemblages varied with respect to physical habitat and environmental gradients. Furthermore, we were interested how the fish assemblages changed over time. Partial canonical correspondence analyses (pCCA) demonstrated significant effects of physical habitats. Such effects differed between young-of-the-year and adult fishes. The four main environmental gradients influencing overall assemblage structure for both age groups were river elevation, water velocity, conductivity and depth of gear deployment. Morisita's index revealed similar adult assemblage structure over time. However, the YOY assemblage present in 1995 was dissimilar from assemblages present during the other years. We speculate this is a lag effect from the backwater spawning episodes (floodpulse) that occurred with the 500-y flood in 1993. Shannon-Weiner diversity and Camargo's evenness indices were low, but stable across years for the adult assemblage, but varied across years for the YOY assemblage.
TL;DR: The ability of C. orbiculatus to survive under deep shade despite its slow growth implies that intact forests are vulnerable to invasion and that established understory populations should be controlled before harvesting or thinning the forest.
Abstract: The invasive vine Celastrus orbiculatus Thunb. (Oriental bittersweet) dominates gap and edge environments, but may also colonize undisturbed forest. We compared survival and growth of C. orbiculatus seedlings in field plots under 2%, 28% and 100% sun. From transplanting through the first autumn, survival and growth did not differ among treatments. In the second growing season, survival at 2% sun was 76%, compared to 96% in 28% sun. Growth and biomass were greater in the 100% and 28% sun treatments than 2% sun. The ratio of leaf to total biomass (LBR) decreased with shade, but leaf mass per leaf area (LMA) decreased proportionally more, so that the leaf area per unit biomass (LAR) increased in the shade. Photosynthesis, stomatal conductance and the ratio of photosynthesis to conductance (A/g) decreased in the shade. The ability of C. orbiculatus to survive under deep shade despite its slow growth implies that intact forests are vulnerable to invasion and that established understory populations sho...
TL;DR: In this paper, the authors collected ground-dwelling spiders (Araneae) from thin ( 50 m) riparian forests and hedgerows located next to soybean or corn fields in south-west Ohio.
Abstract: Generalist predators, such as spiders, play an important role as natural enemies in agroecosystems and, given the annual disturbance of most field crops, these predators typically re-colonize fields from adjacent habitats such as hedgerows or riparian forests. To test whether the biota of these source habitats differed, we collected ground-dwelling spiders (Araneae) from thin ( 50 m) riparian forests and hedgerows (<15 m wide) located next to soybean or corn fields in south-west Ohio. Pitfall traps collected spiders at the stream edge, the interior of forests or hedgerows and the agricultural edge. Rarefaction analysis and non-metric multidimensional scaling (NMDS) ordination tested how spider diversity and community structure, respectively, differed between hedgerows and riparian forests and by trap location. Wide riparian forests harbored a higher diversity of spiders than thin riparian forests and hedgerows contained the lowest spider diversity. The latter result...
TL;DR: Veery (Catharus fuscescens) nest sites were compared to unused sites in a Middle-Atlantic Piedmont forest to determine if nest placement was random or biased with respect to forest structure and alien vegetation, and data suggest that alien shrubs have replaced native shrub species and exerted a largely additive effect on foliage density providing the proximate cues for nest placement.
Abstract: Veery (Catharus fuscescens) nest sites were compared to unused sites in a Middle-Atlantic Piedmont forest to determine if nest placement was random or biased with respect to forest structure and alien vegetation. Thus far, available data shows alien plants have a detrimental or neutral effect on the ecology of forest birds; however, empirical data regarding the proximate influence of invasive alien shrubs on avian nest placement in North American forests is lacking. Nest sites were distributed non-randomly in relation to vegetation density and were characterized by dense foliage below 1.5 m with sparse overstory at 2.5 to 3 m. Sites occurred within moist forest in floodplains and on south- and east-facing slopes. All nest sites contained alien shrubs, and alien vegetation supported 84% of nests. Shrub diversity did not differ between nest sites and unused sites yet more alien shrub species were found at nest sites. The density of native shrub-layer foliage did not differ between the two treatments; however, the density of alien shrub foliage was greater at nest sites. In this forest there was no relationship between the density of alien vegetation and the density of native vegetation. These data suggest that alien shrubs have replaced native shrub species and exerted a largely additive effect on foliage density providing the proximate cues for nest placement. The high success rate (70%) of nests within sites used in analyses suggests that the alien shrubs providing these cues are not substantially elevating nest failure rates. Thus, some temperate-breeding Neotropical forest-interior birds may react positively to a change in forest structure resulting from the invasion of alien shrubs. Ecological release resulting from the increase in available nest sites created by alien shrubs may explain the recent regional spread of the Veery. Region-specific studies are needed to determine the forest breeding birds that are affected, either positively or negatively, by the altered spatial heterogeneity created by alien shrubs.
TL;DR: In this paper, the authors examined plant recruitment in a Lake Erie coastal marsh on bare mudflats exposed during 2 y of below average water levels and found that 18 species were found on mudflat and 19 species were reared from the seedbanks.
Abstract: Coastal wetlands of the Laurentian Great Lakes provide many valuable ecological functions and, currently, there are extensive efforts to preserve and manage remaining habitats. We examined plant recruitment in a Lake Erie coastal marsh on bare mudflats exposed during 2 y of below average water levels. In 2000 mudflat vegetation was sampled in shallow, medium and deep water transects and compared to germinable seeds found in sediments from 0–15 cm below the surface. Effects of sediment disturbance and herbivory on plant recruitment were tested in 1 m2 quadrats in 2000 and vegetation was sampled in 2001 to assess how well the disturbance/herbivory experiment predicted plant communities that became established on the mudflats. In 2000, 18 species were found on mudflats and 19 species were reared from the seedbanks. Seed densities (∼3000 seedlings/m2) were comparable to other freshwater wetlands and did not differ by sediment depth. Taxa richness was highest in sediments 0–5 cm below the surface. Mos...
TL;DR: The results are compatible with the growth-differentiation balance (GDB) hypothesis, but indicate some of the difficulties that will be encountered in testing the GDB hypothesis rigorously.
Abstract: A series of experiments was conducted to examine the effects of competition on allometry and defense using tomato plants (Lycopersicon esculentum). No mortality occurred over the 4-wk test period, even with a plant density of 30 plants per 10-cm2. However, allometric patterns for log canopy diameter vs. log height indicated that competition occurred as early as 8 d after transplant and for pots with as few as two young plants (density of about 2 plants per 10-cm2). There was a change towards less root mass for greater height as competition increased. Leaf concentration of the allelochemicals chlorogenic acid, rutin and tomatine increased with decreasing competition, with the sum of these exhibiting a sigmoid-like pattern for allelochemical concentration. But competition did not affect leaf proteinase inhibitor activity, or petiole glandular trichomes or total trichomes. While the results are compatible with the growth-differentiation balance (GDB) hypothesis, they also indicate some of the difficulties that will be encountered in testing the GDB hypothesis rigorously.
TL;DR: The utility of fecal corticosteroid measures in assessing the adrenal status of wild populations of rodents is clearly indicated, with data consistent with the plasma corticosterone level profile exhibited by wild-caught individuals of both species maintained in captivity.
Abstract: Fecal corticosteroid levels were monitored in free-living populations of deer mice (Peromyscus maniculatus) and southern red-backed voles (Clethrionomys gapperi) in North-Central Idaho. Sex, reproductive condition and age had no significant effect on fecal corticosteroid level in either species, but fecal corticosteroid levels were significantly higher in deer mice than red-backed voles regardless of sex or age. These data are consistent with the plasma corticosterone level profile exhibited by wild-caught individuals of both species maintained in captivity. In addition, for deer mice estimated population size was significantly correlated with fecal corticosteroid levels. Overall, these data clearly indicate the utility of fecal corticosteroid measures in assessing the adrenal status of wild populations of rodents.
TL;DR: Mounds formed by pocket gophers in a longleaf pine—wiregrass savanna had larger daily soil temperature fluctuations than surrounding matrix locations and lower total carbon, total nitrogen, available ammonium, available phosphate and slightly lower soil moisture than matrix locations.
Abstract: Mounds formed by pocket gophers (Geomys pinetis) in a longleaf pine—wiregrass savanna had larger daily soil temperature fluctuations than surrounding matrix locations. Microsite temperature differences persisted for more than a year, but were largest during summer months. Mound soil also had lower total carbon, total nitrogen, available ammonium, available phosphate and slightly lower soil moisture than matrix locations. These differences occurred in the context of an ecosystem where frequent fire consumes organic matter and removes herbaceous cover. The distinct microclimate and nutrient characteristics of gopher mounds did not significantly influence wiregrass germination, wiregrass seedling survival or longleaf pine seedling survival. Wiregrass germination and seedling survival in the first growing season was low and did not differ between mound and matrix locations. Longleaf pine seedling survival in the first growing season was 64–77% in the absence of fire, but no more than 15% in blocks th...
TL;DR: It is demonstrated that higher elevations with lower soil moisture have higher germination and seedling survival, and specific elevations around the lake that are most vulnerable to Chinese tallow invasion are predicted.
Abstract: Chinese tallow (Sapium sebiferum) is an invasive tree in the southeastern United States that has been a management concern in Florida. We used observational and experimental approaches to explore factors influencing Chinese tallow invasion around the perimeter of Lake Jackson, Leon County, Florida. Twenty-one transect sites were randomly chosen, 12 with, and 9 without Chinese tallow. We used abundances of co-occurring species and abiotic environmental data to study factors associated with Chinese tallow abundance among and within transects. Canonical correspondence analysis indicated that soil moisture availability and other soil characteristics correlated with Chinese tallow invasion, but that Chinese tallow was not associated with other species distributions. A seeding experiment demonstrated that higher elevations with lower soil moisture have higher germination and seedling survival. This experiment predicts specific elevations around the lake that are most vulnerable to Chinese tallow invasion. Presence or absence of Chinese tallow among transects was not a significant predictor of germination success, suggesting that not all sites suitable for invasion have been invaded. In addition, controlled burning decreased germination probability and may therefore be useful for invasion control.