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Soil biota such as arbuscular mycorrhizal fungi (AMF) have been shown to increase invasive plant species success in a wide variety of systems by providing both direct and indirect benefits to the invader. For example, Centaurea stoebe invasion in the western US is at least partially due to AMF networks allowing Centaurea to parasitize some native plant species. Centaurea also invades sand dune systems of the northern Great Lakes region, which often have reduced or altered soil communities compared to other grasslands. In these habitats, AMF may play a different role in invasion success of this species. We conducted a greenhouse experiment to compare effects of soil biota and AMF on competitive interactions between Centaurea and two varieties of Ammophila breviligulata, a dominant native grass of Great Lakes sand dunes. We found that Centaurea growth was slowed by the presence of Ammophila competitors, while AMF had no direct or indirect effect on growth. Both Ammophila varieties were uninhibited by the presence of Centaurea. The commercially available Cape variety of Ammophila had more than twice the inhibitory effect of a native Michigan variety on Centaurea growth. It does not appear that Centaurea takes advantage of AMF networks in this dune system. Indeed, since Centaurea growth is actually reduced in direct competition with Ammophila, we suspect that invasion of dunes by this species is a result of disturbance. For land managers, planting Ammophila in open areas as part of a restoration plan may slow spread of Centaurea in this system.
Knowledge of seed ecology is important for the restoration of ecosystems degraded by anthropogenic activities. Current efforts to preserve and reintroduce populations of plant species endemic to Florida are hindered by a lack of information on demographic responses to human alteration. Comparisons of seed removal, germination, and establishment in both intact and degraded habitats will aid in management decisions for species in need of protection. Our objectives were to assess the impact of post-dispersal seed predation on plant populations in degraded and intact habitats, and to investigate the effects of habitat and microsite on seed germination and establishment. For five rare Florida scrub species with different seed sizes (Liatris ohlingerae, Eryngium cuneifolium, Polygonella basiramia, Hypericum cumulicola, Paronychia chartacea subsp. chartacea), we conducted a seed removal experiment with seeds exposed to insects and vertebrates, and to insects only, with a no-access control. We also planted seeds in replicated degraded and intact scrub sites (Spring Field Trial: in bare sand, Winter Field Trial: in bare sand, litter only, and under shrubs with litter), and determined background germination rates in a growth chamber. The contrasting pattern in seed removal among treatments suggested that habitat and seed size affect the likelihood of removal in Florida scrub. Species with large seeds such as L. ohlingerae were removed in higher frequency in degraded scrub, likely by vertebrates. Species with small seeds such as H. cumulicola and P. chartacea were removed by invertebrates and in higher frequency in intact scrub. E. cuneifolium had significantly more seedlings in degraded scrub and P. chartacea had significantly more germination in the intact scrub in the Spring Field Trial. E. cuneifolium, H. cumulicola and P. chartacea had higher germination in bare sand than in litter only or under shrubs. Our data indicate that scrub herbs are differentially vulnerable at particular life history stages and that this vulnerability can be context dependent. Restoration success will require a careful assessment of potential seed predators and abiotic conditions favoring germination and survival of study species in degraded habitat; efforts to increase heterogeneity in areas slated for restoration will likely promote the establishment of multiple targeted species.
Despite the widespread interest in plant community restoration, few studies have assessed white-tailed deer (Odocoileus virginianus Zimm.) herbivory on herbaceous species and even fewer studies have focused on deer herbivory in restored plant communities. During 2007–2009, we investigated the effect of deer density and associated deer browse on two restored forest and three restored savanna plant communities in Lake County, Illinois. We used 300 small (1.4 m diameter × 1.6 m height) exclosed plots and 1-m2 unexclosed plots to compare the effects of deer herbivory on forbs. We quantified and compared percent non-herbaceous ground cover, species diversity, species evenness, and floristic quality between exclosed plots and unexclosed plots, as well as among preserves within each plant community type. Species diversity and floristic quality of forbs may be maximized at a deer density between 6–22 deer km2 in restored forest communities in northeastern Illinois. Floristic quality was higher in exclosed plots compared to unexclosed plots at all savanna sites. In both plant communities, species evenness may have increased with higher deer density due to an increase in non-preferred plants and non-native species invading locations where preferred native forbs were chronically consumed. Our results highlight the importance of assessing the species diversity, evenness, and floristic quality of target plant communities to determine the impact of deer herbivory at varying deer densities.
Litter-dwelling arthropods play crucial roles in litter decomposition and nutrient cycling, and changes in their diversity or abundance can affect these processes. Previous studies have outlined individual effects of invasive plants and overabundant ungulates on litter-dwelling arthropod communities but have paid little attention to whether invasive plants and ungulates interact to affect these arthropod communities. We examined how invasive Amur honeysuckle (Lonicera maackii) and grazing by white-tailed deer (Odocoileus virginianus) affected diversity, abundance, and taxonomic composition of litter-dwelling arthropod communities in a deciduous forest in southwestern Ohio. We also examined whether deer or honeysuckle affected substrate composition and depth of litter. We found no significant effect of honeysuckle, deer, or their interaction on arthropod diversity, but exclusion of deer increased total arthropod abundance and abundance of Araneae, and thereby affected taxonomic composition of the litter community. These effects were likely related to greater plant cover and less soil compaction in areas from which deer were excluded. Honeysuckle negatively affected Araneae abundance and positively affected Acari abundance, possibly revealing an indirect effect of Araneae on Acari. A honeysuckle × deer interaction on abundance of Acari was important only during the first year of our study. There were no differences in arthropod abundance between honeysuckle-absent and honeysuckle-removed plots, indicating rapid restoration of the litter community after honeysuckle removal. Neither honeysuckle nor deer affected composition or depth of litter. Our findings suggest that current management techniques that control the effects of honeysuckle and deer on native plant communities by separate measures may be sufficient to reduce impacts on litter-dwelling arthropods.
Despite immense diversity, insect conservation is typically species specific. Effective insect conservation will require efforts that capture insect species and communities at all levels of biological organization. Surrogate conservation targets, such as habitat based conservation planning tools were designed to capture poorly understood taxa such as invertebrates. We evaluated a botanically-based community filter across disturbance gradients in NW Indiana to determine if moth communities (Lepidoptera) responded similarly to vascular plant assemblages. Our 13 sample sites included high-quality ecosystem remnants (sand prairies and oak barrens) and their local degradation endpoints (exotic old fields and fire-suppressed oak woodlands). Monthly, we quantitatively sampled moths using ultraviolet light traps and inventoried vascular plant species at each sample site. Analysis of moth and plant community relationships using Bray-Curtis coefficients of dissimilarity produced statistically congruent relationships between moth and plant assemblages at the sample sites indicating that these two taxonomic groups respond to ecological gradients and disturbance similarly. Other measures of botanical community integrity used to select conservation areas such as floristic quality assessment index and diversity indices do not translate directly to measures of moth species richness or diversity. We suggest that in this system, vascular plant assemblages are a reasonable conservation surrogate for moth communities.
The U.S. General Land Office surveys, conducted between the late 1700s to early 1900s, provide records of trees prior to widespread European and American colonial settlement. However, potential and documented surveyor bias raises questions about the reliability of historical tree density estimates and other metrics based on density estimated from these records. In this study, we present two complementary approaches to adjust density estimates for possible surveyor bias. We addressed the problem of surveyor bias of density estimates by simulating the effects of (1) rank of selected trees (compared to assuming the nearest trees were selected) and (2) specific surveyor bias in selection of (a) quadrant location, (b) quadrant configuration, (c) azimuth, and (d) combined species and diameter. We then developed regression equations to calculate adjustment quotients for these biases, making the adjustment quotients transferable to any similar datasets. For the rank-based approach, an unvarying rank of 2 (selection of the second nearest tree instead of always the nearest tree) decreased density estimates to about 25 to 45% of the actual density, depending on number of trees per survey point, resulting in corrected density estimates that are 2.2 to 4 times greater than uncorrected density estimates. However, constant selection of the second nearest tree did not occur; varying ranks decreased density estimates to around 55 to 65% of the density, resulting in corrected density estimates about 1.5 to 1.8 times greater than uncorrected values. For the bias-based approach, depending on the specific General Land Office dataset, bias for tree species and diameter alone may decrease density estimates by about 35%. Quadrant configuration and azimuth preference may decrease density estimates by about 15% each. The quadrant location bias has negligible effects on the density estimates. The overall density estimates may be about 35 to 55% of the actual density and correction of the density estimate will approximately double the value. These methods can provide a range of estimates, from low values of uncorrected density to high values of corrected density, about the amount that varying surveyor bias may have decreased density estimates for any areas where bias is detected (i.e., non-random frequencies) in point-centered quarter surveys. Adjustments will increase reliability of historical forest density estimates and their applications for restoration.
Woody plant encroachment and proliferation in grasslands is occurring worldwide and has significant but variable effects on ecosystem processes, including primary production, litter decomposition, and N cycling. In mesic systems, recent reports suggest aboveground net primary production (ANPP) is stimulated by grass-to-woodland conversion; however, significant losses of soil C may accompany this land cover change in these environments. This study aimed to quantify how changes in plant production inputs (both above- and belowground), litter decomposition, and N cycling may feed back to reduce soil C pools in a mesic tallgrass prairie in central Texas, USA, that has undergone grass-to-woodland conversion over the past 60–70 y. Belowground net primary production (BNPP) in woodland was half that of adjacent grassland, and contrary to recent reports, no significant differences in ANPP between the two vegetation types were observed. Decomposition rates of aboveground woody and grass material were surprisingly similar. However, higher N concentrations in woodland leaves and stems meant woodland received more than 3× the amount of N via litterfall than adjacent grassland, and woody litter mineralized N when decomposing, while grassland litter tended to retain it. Losses of soil C accompanying grass-to-woodland conversion at this site (woodland soil C was ∼20% less than that of adjacent grassland) may be the result of both reduced BNPP inputs to the soil C pool and increased rates of N cycling stimulating soil organic matter decomposition. Given that the processes controlling whether grasslands accrue or lose C and N when they are replaced by woody species vary across time and depend on the species involved and the biotic and edaphic conditions and management history of the site, more complex models that incorporate these parameters may be required to understand and predict when gains and losses of C will accompany vegetation change.
Nitrogen dynamics in wetlands are often assumed to vary with water tables and the resulting patterns of soil moisture, and other soil properties. To test this hypothesis, we have examined N mineralization patterns in two replicate sequences of three forested wetland types located on a shallow water table gradient in the New Jersey Pinelands during a 12 mo sampling period. Each sequence of the three forested wetlands consists of pine wetlands and pine-hardwood swamps with sandy mineral soils and cedar swamps with peat soils along the shallow water table gradient. Although water tables differed between the two mineral-soil wetlands, there were no differences in soil properties between them, including patterns of extractable N or net N mineralization rate. However, peat soils from the cedar swamps had net N mineralization rate 5–10 times higher than the mineral soils from the other two types of wetlands over the sampling period. Although soil moisture was correlated with water table position within wetlands, net N mineralization rate did not vary with water tables, nor did it vary with soil moisture variations within sites. Overall, net N mineralization rate reflects soil type (histosols vs. mineral hydric soil) and organic matter quality (C∶N) ratio.
This study assessed the influence of annual snowpack on long term changes in the predatory regime of four high elevation ponds in the mountains of northwest Wyoming. Over 36 y of observation, in two ponds the primary predator alternated between phantom midge Chaoborus americanus larvae and Diaptomus shoshone predatory copepods, whereas the predatory regime did not change in the other two shallower ponds. Switching of predators correlated with extreme amounts of winter snow, either high or low, which determined the depth at which drying or complete freezing of the pond occurred. Chaoborus americanus colonized ponds after the wettest years and disappeared after the driest years. The results provide an unusual long term perspective of the effects of weather on predator dominance.
Cladoceran community dynamics in limnetic systems often are correlated with temperature patterns. We sought to relate cladoceran temporal patterns and community composition to spatial and temporal temperature patterns in a cooling water reservoir (Newton Lake, Jasper County, Illinois). Effluent released into Newton Lake creates a temperature gradient where portions of the reservoir experience summer maxima in excess of 35 C, while other portions resemble a typical temperate system. We measured temperature and collected zooplankton at four locations arranged at increasing distances from the power plant cooling water outfalls. Cladoceran community density was higher near the warm effluent during winter, although no statistically significant differences amongst sites were observed during summer. Bray-Curtis dissimilarity values and nonmetric multi-dimensional scaling suggest cladoceran communities in the reservoir respond to this altered temperature with respect to abundance and seasonality of species. Daphnia lumholtzi, an exotic cladoceran, also is present in Newton Lake and sometimes is the dominant cladoceran taxon. High abundance of D. lumholtzi seems to be unrelated to warm effluents as it occurs at all sampling locations. Although morphological features of D. lumholtzi are thought to deter depredation, temporal and spatial distance likely occurs between this species and gape-limited vertebrate planktivores, thereby reducing potential negative impacts of this species in Newton Lake.
North American freshwater mussels of the Order Unionoida are critically imperiled, primarily due to stream habitat modifications and fragmentation by reservoirs. Whereas many species respond negatively to impoundments, some species benefit by increases in lentic habitat. During winter drawdown of Tuttle Creek Reservoir, KS in 2006–2007, we collected freshwater mussel shells to characterize spatial variation in assemblage structure within the reservoir and compare reservoir assemblages to stream assemblages within the surrounding drainage basin. Of the 22 unionid species that occurred in the basin, six were found in Tuttle Creek Reservoir. Species richness in the reservoir did not differ from that found in both small and large streams. Species composition in streams varied along a gradient from small to large (1st-7th) order streams, and mussel assemblages in the reservoir were most similar to that of large order streams. This study identified the subset of stream-dwelling unionid species that are habitat generalists and capable of persisting in reservoirs.
Male sailfin mollies, Poecilia latipinna, exhibit alternative mating strategies that are correlated with body size. Larger males court females and often prevent smaller males from accessing females, while smaller males often forcefully inseminate females. This pattern is well documented in the laboratory but has not been studied thoroughly in the field, where patterns of mating behavior are known to vary among natural populations. In an observational study of a P. latipinna population, we measured the proportion of time males from three size classes (small, intermediate, and large) spent exhibiting five mating behaviors: courting, thrusting, nibbling, chasing other males away, and being chased. We predicted that large males would spend more time courting females and chasing away other males, while small males would spend more time thrusting, nibbling, and being chased by other males. We also predicted that intermediate males would behave intermediately. Our findings partially supported those of previous laboratory studies: small males spent more time attempting to forcefully inseminate females but large males did not spend more time courting. Courtship displays were rare in our observations. Large males did spend more time chasing away other males however. Intermediate males behaved intermediately in some cases but also exhibited mating behavior typically characteristic of large males.
Walleye from the upper Cumberland River drainage were examined by means of mitochondrial DNA restriction fragment length polymorphism (RFLP) analysis, microsatellite analysis of nuclear DNA, and sequencing of the mitochondrial DNA control region. The objectives of this study were to identify native Eastern Highland and introduced Great Lakes walleye and determine if introgression occurs between the two stocks. Additional collections were made from rivers of the Eastern Highlands to establish evolutionary relationships. Native and introduced walleye appear reproductively partitioned in the upper Cumberland River drainage, with natives persisting in the tributary Rockcastle River and introduced Great Lakes walleye reproducing in the Big South Fork of the Cumberland River. Additional partitioning between native and introduced stocks may occur in the Kanawha River, in the Ohio River drainage. Native walleye from the Cumberland River share a common ancestor with others from Eastern Highland rivers but are distantly related to populations from the southern Mobile River basin and the northern Great Lakes.
The giant earthworm, Rhinodrilus priollii Righi 1967, is among the largest terrestrial invertebrates known worldwide, reaching lengths >2 m. To investigate the evolutionary history of the species and aspects of their reproductive biology, we collected R. priollii specimens from several field sites in central Amazonia. Phylogenetic analyses of 16 individuals using a fragment of cytochrome c oxidase subunit 1 (CO1) identified seven haplotypes that diverged between 2–8%. Population structures indicate episodes of gene flow between populations and their divergence within the past 1–2 million years. Histological examination of clitella from sexually mature specimens identified cocoon secretory cells throughout the dorsal and dorsoventral epidermis. Unlike previously described secretory cells, those in R. priollii contained granules with a proteinaceous core covered by external glycosylation. Further, collagenous matrices formed the bulk of swollen clitella while albumin-secreting cells were noticeably absent, collectively suggesting a mechanism of cocoon production somewhat different from that described in other clitellate megadriles.
Free-ranging, juvenile thirteen-lined ground squirrels (Ictidomys tridecemlineatus) in southwestern Michigan were fitted in late summer or fall with external skin-temperature loggers. Data were obtained the following spring for five males and three females. During the heterothermal period, all squirrels exhibited 11–22 prolonged ( = 9.4 d) torpor bouts punctuated by typically brief ( = 14.3 h) arousal bouts, with mean monthly torpor bouts becoming longer and deeper until Feb. and reversing thereafter. Torpor-bout duration increased as minimum skin and soil temperatures decreased. On average, males initiated the first torpor bout later in fall, terminated the last torpor bout significantly earlier in spring and thus spent less time in the heterothermal period than did females. Three males displayed relatively short torpor bouts and long arousal bouts as they approached the end of hibernation. Squirrels gained weight variably in fall and spring, and one female lost 39% of body mass during hibernation.
Multiple specimens of the rusty crayfish (Orconectes rusticus) collected from the Susquehanna River in Pennsylvania exhibited Rheotanytarsus sp. (Diptera: Chironomidae) living on their carapaces and chelipeds. Although chironomid larvae have been reported as living on many aquatic organisms, this is the first record of chironomids living phoretically on crayfish.
We report on three presumed wolf pups captured in Michigan's northern Lower Peninsula, potentially representing the first documented case of wolf reproduction in the Lower Peninsula since wolves were extirpated there a century ago. The pups, two females and one male, were assumed to be wolves based on physical characteristics. Genetic profiles assigned all three pups as coyotes but revealed evidence of maternal introgression from a Great Lakes wolf in their pedigree. These findings suggest that Great Lakes wolves are capable of interbreeding with coyotes when conspecifics are rare.
In Georgia, there are three distinct populations of black bears (Ursus americanus, including two subspecies americanus and floridanus). The Middle Georgia population has been shown to exhibit high genetic similarities within the population and we wanted to determine if the Ocmulgee River was a barrier to bear movements. One out of 9 collared females and 7 of 17 collared males crossed the Ocmulgee River. River flow (bear = 70.7 cubic m/sec, random = 92.7 cubic m/sec) and river depth (bear = 2.6 m, random = 2.8 m) were significantly lower when bears crossed the river than random samples. The river did appear to be a barrier to females but not males. Females may be less likely than males to cross the river because of behavioral differences (e.g., cub rearing) and smaller home ranges.