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Knowledge of variation among populations is important for making decisions about conservation of rare, threatened or endangered taxa. We investigated variation within and among five populations of Dirca palustris L. an understory shrub with a sporadic distribution and life-history traits that led us to predict strong phenotypic and genetic differentiation characteristic of historically limited gene flow. Populations sampled in Florida, Alabama, Illinois, Wisconsin and North Dakota spanned the geographic distribution of the species. Phenotypic traits differed among populations, and many traits correlated with latitude and environmental characteristics of the five sites. Principal components (PC) analysis showed that the first three PCs explained only 43% of the total phenotypic variation, and neighbor-joining analysis showed phenotypic overlap among individual plants across the five populations. The most phenotypically distinct populations were in Florida (unique in the color of pubescence on bud scales) and North Dakota (unique in a number of floral and vegetative traits). We found genetic differentiation among populations based on PC and neighbor-joining analysis of ISSR data and plants reliably clustered by population of origin. Fifty-four percent of the total genetic variation was among populations, and a Mantel test of both phenotypic and genetic data showed isolation-by-distance, which is indicative of historically limited gene flow. Both allelic richness and the number of private loci for each population decreased with increasing latitude, suggesting founder effects, genetic bottlenecks or genetic drift during the postglacial re-colonization of D. palustris into higher latitudes. The populations in North Dakota and Florida, which are imperiled at the northern and southern range limits of D. palustris, have the most unique phenotypes and genotypes and should represent priorities for conservation.
We developed a suite of tetranucleotide microsatellite loci and applied them to a study of genetic variation across the geographic range of coast redwood [Sequoia sempervirens (D. Don) Endl.]. The objectives of the study were to determine if the microsatellite loci could provide useful information on genetic diversity in this hexaploid species and to investigate earlier reports of divergent lineages within coast redwood. The microsatellite loci were highly variable, yielding a total of 142 alleles. Up to six alleles were detected in each individual consistent with the ploidy of coast redwood and suggesting that parental genomes must have been at least partially homologous. This does not rule out autoployploidy in the evolution of the redwood genome. We treated the microsatellite alleles as presence-absence data and we also estimated full genotypes assuming peak intensities varied with allele dosage. Both types of analyses revealed similar trends. Variation within the 17 watersheds sampled, explained most of the genetic diversity, with less than 4% of the variation attributable to watersheds. Our data showed a weak divergence between more or less continuous populations north of 36.8°N (the Sonoma- Mendocino county border) and disjunct populations south of this latitude. This is further north than indicated from earlier studies of marker systems that would be under selection and may reflect a demographic break. In view of the importance of clonal growth, we suggest that redwood may have difficulty adapting to new climatic conditions or of migrating into displaced habitats with anticipated climate change. Furthermore, the southern lineage of populations is likely to be at greatest risk and is therefore of conservation priority.
Herbivore movement behavior is a key mediator of how host-plant populations affect herbivore populations. We examined the effects of host-plant genotype and variance among host-plant genotypes on movement rates of apterous strawberry aphids, Chaetosiphon fragaefolii (Cockerell) (Homoptera: Aphididae), on Fragaria chiloensis (L.) P. Mill. In the field we estimated aphid movement rates over several years on experimental populations of five different plant genotypes. In the greenhouse, we followed the movement of individual aphids in plant arrays of a single genotype or three different genotypes. In both cases, aphid apterae movement differed among host plant genotypes, with more movement on higher quality genotypes. Movement rate in the field was also influenced by aphid population size. In the greenhouse, aphids showed no taxis toward particular plant genotypes but left different plant genotypes at different rates. Aphids also tended to move more often among plants in three genotype arrays (with a variety of plant genotypes) than predicted by their movement in single genotype arrays. Our results suggest that dispersal among plants by strawberry aphid apterae is affected by plant characteristics associated with genotype and quality of the host plant for the herbivore.
Presettlement Florida had a variety of open habitats, including grasslands and savannas. This study examined the historic distribution of the Florida grasslands using U.S. General Land Office land surveys made during the 19th century. All survey maps with areas labeled “prairie” or “savanna” were compiled into a composite map. A total of 791,140 ha of prairies and 15,820 ha of savanna were shown on the maps. The most extensive prairies were located in central Florida stretching from the west coast of Lake Okeechobee into Hillsboro and Manatee counties. Patches of prairie and savanna extended north into Clay County. South of Lake Okeechobee, prairies were found in the Big Cypress Swamp, along the western edge of the Everglades and along the eastern coast. Surveyor's notes and historical documents were then used to find additional references to grasslands. These references indicate that there were extensive prairies and savannas in the northern part of the peninsula and in the panhandle. Areas with prairie and savanna were compared to soil descriptions found in county soil surveys by the U.S. Department of Agriculture. Soils typical of forested areas (spodosols and alfisols) were more common in Florida prairies and savannas than mollisol soils that are characteristic of grasslands. The soil data, in addition with the proximity of prairies to pine forests, supports the hypothesis that these ecosystems are determined more by topography, fire frequency and flooding patterns than by soil type.
Bison (Bos bison) were a keystone species in the tallgrass prairie region of the Great Plains of North America. Cattle (Bos taurus) have been described as a functional equivalent to bison and have replaced bison in most of the grassland that remains intact. However, non-grazing behaviors influence grassland dynamics and are dissimilar between bison and cattle. Wallowing behavior (a non-grazing behavior by bison, but not cattle) creates disturbances (wallows) that were a common feature (may have numbered more than 100 million) of tallgrass prairie prior to extirpation of bison and conversion of most land to row-crop agriculture. We hypothesized that wallows are a unique disturbance that significantly influence both the structure and function of tallgrass prairie. We examined the response of plants to wallowing disturbances on Konza Prairie Biological Station, Kansas, where a herd of approximately 200 bison had year-round access to 1000 ha of native tallgrass prairie. We determined the influence of this disturbance type on aboveground net primary production (ANPP), plant species richness and diversity, and plant life form richness and diversity. The ANPP at the edge of wallowing disturbances was double the production in wallows and in adjacent prairie, which were not different from year to year. Plant species richness and diversity were significantly lower in wallows than at the edge of wallows and in adjacent prairie during all years of the study. However, composition of species were dissimilar among locations (e.g., 16% of all plant species samples were found only in the wallows); and, therefore, wallows increased the local and likely regional diversity of plant species. Likewise, wallowing disturbances increased local richness and diversity of plant life forms. It appears that these once common wallowing disturbances increase the diversity of tallgrass prairie beyond that of prairie that is grazed only (i.e., prairie with cattle).
Fescue Prairie is one of the most threatened ecosystems in Canada, and burning is essential for conserving remnants of this grassland. Burning is a key process in the natural disturbance regime, but its effect on the soil seed bank in Fescue Prairie is poorly understood. We tested the hypotheses that (1) preburn history influences the density and composition of seedlings emerging from the soil seed bank, and (2) burning in different seasons reduces densities and changes the composition of seedlings emerging from soil seed banks compared with non-burned controls in Fescue Prairie. Seedling emergence from seed banks was studied for 5 y in non-burned controls and following burning before, during or after the growing season on sites with different preburn histories (sites burned two times or sites burned >90 y before this study). Preburn history had no effect (P ≥ 0.14) on the density of native graminoids, native forbs, non-native species, total species richness (R) and diversity (H′) of species emerging. Burning during or after the growing season reduced H′ of emergent seedlings by 13% compared with burning before the growing season (P = 0.02). Total seedling densities, densities of graminoids and forbs, R and H′ all varied significantly (P ≤ 0.01) among years. Non-metric multidimensional scaling indicated species composition for seedlings emerging from seed banks correlated with preburn history, years after applying seasonal burning treatments, and soil water content in plant communities but not with season of burning. After burning remnant Fescue Prairies, inter-annual variation in the densities, R and H′ of seedlings emerging from seed banks usually overshadows preburn history and seasonal burning effects on emergent seedlings; however, species composition changes with preburn history, soil water content and years after burning.
Due to fire suppression and land use changes, Missouri glade habitats have undergone long-term declines in area and function leading to consequent declines in many bird species that rely on these habitats. We examined breeding bird species composition and vegetation community composition on three glade sites undergoing restoration with prescribed fire and compared them to three unburned glade sites and three unburned forest sites. Although we documented subtle changes in vegetation characteristics in response to prescribed fire, important structural characteristics, such as canopy cover (>55% at all study sites) and grass cover (<10% at all study sites) remain outside ranges used to characterize glades. Despite this, bird community structure shifted towards grass-shrubland (glade) birds (e.g., prairie warbler (Dendroica discolor), blue-winged warbler (Vermivora pinus), yellow-breasted chat (Icteria virens)) in glades that had been managed with prescribed fire. Using canonical correspondence analyses and stepwise forward logistic regression, we found that grass-shrubland (glade) birds were associated with habitat characteristics such as high stem density of small (0–6.3 cm diameter at breast height) trees, greater herbaceous cover, greater rock cover and a more open canopy. However, we did not detect any bird species historically associated with glades, such as Bachman's sparrow (Aimophila aestivalis) or field sparrow (Spizella pusilla) on any study sites but did frequently detect red-eyed vireos (Vireo olivaceous) on all sites. Short term application of prescribed fire has not yet produced functionally restored glades. Long term applications of prescribed fire, used in conjunction with mechanical and/or chemical removal of woody overstory, are necessary to achieve restoration at these sites.
Biological invasions are associated with declining biodiversity in many ecosystems, but it is often unclear if invasions are directly responsible for such changes, or if invasions are a symptom of environmental degradation. In addition, the mechanism underlying the effects of many invasive species is unknown. To determine if invaders are driving changes in invaded communities, and to identify causal mechanisms, studies that manipulate the presence of invaders are needed. We experimentally introduced the invasive grass Microstegium vimineum into replicated field plots that had been planted with the native woodland herb Senna hebecarpa. After 3 y, we quantified Senna establishment, growth and reproduction. We then conducted a greenhouse experiment to determine if changes in Senna success were due to alteration of soil microbial communities or nutrient depletion in invaded plots. Microstegium-invaded plots had 74% fewer Senna plants and Senna growing in invaded plots were 21% shorter and weighed 64% less than in control plots. The proportion of Senna plants that reproduced was 67% lower and plants produced 78% fewer seeds on average in invaded than in control plots. In contrast to the field results, there were no differences in the growth of Senna when grown in Microstegium-invaded or control soil in the greenhouse, and the invasion treatment did not alter the effects of soil sterilization or fertilization. Further, we found no evidence that Microstegium success is determined by feedbacks with the soil community. Our results demonstrate that Microstegium has negative effects on a native species, but we found no evidence that the suppressive effects of Microstegium invasions are mediated by plant-soil interactions in invaded areas.
Throughout Midwestern forests, invasion by the exotic plant garlic mustard [Alliaria petiolata M. Bieb. (Cavara & Grande)] has become increasingly problematic. A multi-criteria risk model was developed to predict invasion in the Upper Peninsula of Michigan where garlic mustard is present but not yet widely distributed. The model uses geographic information system (GIS) data to predict the risk of invasion at three phases: introduction, establishment and spread. Known occurrence data for garlic mustard were used to validate the model predictions, with 89% of points correctly identified at moderate to high risk for invasion. The risk model predicted 13% of the Upper Peninsula to be at high risk and 33% at moderate risk for establishment of garlic mustard. Field sampling of randomly generated points across the Upper Peninsula provided only two additional observations of garlic mustard presence. The low encounter rate during field sampling may indicate that garlic mustard has not yet reached its full invasion potential in the Upper Peninsula. This presents an opportunity to use the model predictions and associated risk maps for monitoring and management in a relatively uninvaded region.
The risk allocation hypothesis predicts that animals should be most averse to risk during brief and infrequent high risk situations. For animals in shallow aquatic habitats, encounters with terrestrial predators may represent such a situation. Terrestrial flight responses, acute movements from water onto land following a disturbance, may be a viable escape strategy during encounters with terrestrial predators foraging in shallow aquatic habitats. Sonoran mud turtles (Kinosternon sonoriense) occur in intermittent aquatic habitats in the Peloncillo Mountains, New Mexico. When Sonoran mud turtles were captured by hand in shallow pools or shallow stock tanks they frequently underwent terrestrial flight responses. In five of six trials in shallow stock tanks, and three of seven trials in shallow pools, turtles left the water within 20 min of being released, often climbing out of sight up relatively steep slopes. This behavior was not observed in four trials in which turtles were captured with hoop nets in deep stock tanks. Turtles that underwent terrestrial flight responses were significantly larger than non-responders. Terrestrial flight responses appear to be a risk aversion strategy in Sonoran mud turtles occupying shallow aquatic habitats. This unusual behavior may be widespread among animals that inhabit shallow aquatic habitats.
While many aspects of the reproductive ecology of Eastern Box Turtles are well known, numerous gaps remain regarding inter-populational variation in clutch size, egg viability and clutch frequency, all vital components of population models. We collected data on nesting ecology of a dense Long Island population of Eastern Box Turtles for three years. Average clutch size was only 4.1 eggs/clutch, which is surprisingly low compared to a nearby population. Conversely, egg viability at this site was site was surprisingly high (95%). It also appears that Eastern Box Turtles lay only one clutch/year, in the later half of June, in southeastern New York.
Eastern box turtles (Terrapene carolina carolina) are widespread in U.S. eastern deciduous forests, yet many populations are experiencing dramatic declines. Herein, we present an assessment of annual survival for adult eastern box turtles that were radio-tracked over a period of 2 y. Using a known fates Kaplan-Meier estimator, the baseline annual survival estimate for adult eastern box turtles in Indiana's south-central region is 96.2%. Annual survival rates varied slightly between the hibernal period (95.6%) and the active period (96.7%). These initial data provide wildlife managers with a baseline from which a recovery period can be calculated. In areas where road mortality and human interface are high, this estimate should be adjusted to ensure the time for recovery is adequate. Further research is recommended over generations and age-classes to better inform management of this protected species.
Urban-adapter species facultatively exploit human-subsidized resources in the urban and suburban matrix. We used the woodchuck (Marmota monax) to study how aspects of autecology in an urban-adapter can vary across a gradient of urbanization. We captured and monitored woodchucks by radiotelemetry in southern Illinois from summer 2007 to spring 2009. We captured 47 woodchucks (19 adults, 19 yearlings, 8 young-of-the-year) during the active seasons, and implanted radiotransmitters in 17 adults and 3 yearlings (13 F, 7 M). Overall annual survival was estimated to be 0.76 ± 0.12, with three confirmed mortalities during the study period. Survival and home-range size did not vary by % urban landcover in a buffer surrounding an individual's home range. Habitat-selection analyses indicated that rural edge was the highest-ranked habitat at the home-range scale, whereas urban cover (specifically, developed areas with human structures) was most highly ranked at the within-home-range scale. Body condition was negatively related to % urban landcover. Overall, our findings indicated no clear relationship between woodchuck ecology and urbanization level within our study area. However, our data on body condition and adipose composition, although preliminary, suggested a possible mechanism for variation in overwinter survival across the urban-rural gradient.
The golden-mantled ground squirrel (Callospermophilus lateralis) is considered an asocial species, characterized by agonistic interactions, nonsharing of territories and early dispersal. The species is poorly studied, so we used radiotelemetry to determine home range size, home range overlap and dispersal. Home ranges of 12 adult females averaged 3.75 ha (range = 1.14–13.52) using the 95% fixed kernel method. Home ranges overlapped substantially but core areas did not, indicating territoriality may be expressed over only a portion of the home range, and an index of dynamic interaction was neutral, indicating neither attraction nor avoidance between females. Most (80%) of 20 juveniles dispersed during their first summer, but some delayed dispersal until at least their yearling summer. Our results provide support for the classification of golden-mantled ground squirrels as asocial but suggest that the expression of territoriality and early dispersal may be variable.
The food habits of river otters (Lontra canadensis) on three rivers in the Red River of the North drainage of eastern North Dakota were evaluated using an analysis of 569 scats collected between 4 Oct. 2006 and 26 Nov. 2007. Fish and crayfish were the primary prey items, occurring in 83.0% and 51.1% of scats, respectively. Other prey included insects (26.7%), birds (7.9%), amphibians (6.7%), mammals (6.0%) and freshwater mussels (0.2%). Fish of Cyprinidae (carp and minnows) were the most prominent fish in the diet, occurring in 64.7% of scats. Other relatively common fish in the diet included Ictaluridae (catfish, 17.4% frequency of occurrence), Catostomidae (suckers, 13.0%), and Centrarchidae (sunfish, 11.2%). The diet of river otters changed seasonally, including a decline in the frequency of fish in the summer diet, and a corresponding increase in the occurrence of crayfish. Consumed fish ranged from 3.5 to 71.0 cm total length, with a mean of 20.7 cm (se ± 0.5, n = 658). Fish 10.1–20.0 cm were the most frequently consumed size class (36.5% relative frequency), with the majority of other consumed fish being ≤10.0 cm (24.6%), 20.1–30.0 cm (14.1%), 30.1–40.0 cm (14.0%), or 40.1–50.0 cm (8.2%). The size of consumed fish changed seasonally, with spring having the largest mean prey size.
We examined bat collision mortality, activity and species composition at an 89-turbine wind resource area in farmland of north-central Iowa from mid-Apr. to mid-Dec., 2003 and mid-Mar. to mid-Dec., 2004. We found 30 bats beneath turbines on cleared ground and gravel access areas in 2003 and 45 bats in 2004. After adjusting for search probability, search efficiency and scavenging rate, we estimated total bat mortality at 396 ± 72 (95% ci) in 2003 and 636 ± 112 (95% ci) in 2004. Although carcasses were mostly migratory tree bats, we found a considerable proportion of little brown bats (Myotis lucifugus). We recorded 1465 bat echolocation call files at turbine sites ( = 34.88 call files/detector-night) and 1536 bat call files at adjacent non-turbine sites ( = 36.57 call files/detector-night). Bat activity did not differ significantly between turbine and non-turbine sites. A large proportion of recorded call files were made by Myotis sp. but this may be because we detected activity at ground level only. There was no relationship between types of turbine lights and either collision mortality or echolocation activity. The highest levels of bat echolocation activity and collision mortality were recorded during Jul. and Aug. during the autumn dispersal and migration period. The fatality rates for bats in general and little brown bats in particular were higher at the Top of Iowa Wind Resource Area than at other, comparable studies in the region. Future efforts to study behavior of bats in flight around turbines as well as cumulative impact studies should not ignore non-tree dwelling bats, generally regarded as minimally affected.
We report on an eastern coyote or coywolf (Canis latrans × lycaon) pack in a heavily urbanized area at the northern edge of Boston, Massachusetts, living at a high pack density. We radio-collared four members of this social unit, a breeding pair and two of their juvenile offspring and tracked them from May 2004–Apr. 2005. The pack had a small cumulative territory area (overall = 2.05 km2), yet lived at a normal group size (fall = 6–7, winter = 4) for coyotes/coywolves in eastern North America. Fall density for this pack was 2.92–3.41/km2 and winter density was 1.95/km2, representing the highest recorded density for coyotes in this region.