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I analyzed larval polytene chromosomes to determine if the hypothesized remnants of an incipient speciation event in the Simulium arcticum complex of black flies previously discovered at the Coeur d'Alene River, Idaho existed elsewhere. This population not only had Y chromosomes that defined two members of the S. arcticum complex: S. arcticum sensu stricto and S. saxosum, but also possessed combinations of sex chromosomes of the two that were in genetic equilibrium with respect to all sex chromosome types. The geographic overlap between S. saxosum to the west and S. arcticum s. s. to the east generally runs north and south of the Coeur d'Alene River. Accordingly, I made 37 additional collections in a north-south orientation during 2011–2013. Larvae from 10 of the 37 collections had sex chromosome types identical to those of the previously studied site at the Coeur d'Alene River, thus expanding the area of putative remnant populations. The St. Joe River not only had Y chromosome combinations identical to those of larvae at the Coeur d'Alene but also had a cytotype new to science based on distinct sex chromosomes (X0YIIL-79) in males. These observations: (1) increase the known geographic area of presumed remnant populations of S. arcticum s. s., of S. saxosum and their combinational types to about 3500 km2; (2) suggest that mating trials still occur; and (3) describe the structure and frequency of inversions in two new cytotypes of the S. arcticum complex.
Fires are a significant source of landscape scale disturbance in forested ecosystems, but fire effects also vary on small spatial scales due to differences in fuel loads and local environmental conditions. We tested the hypothesis that such variation influences post fire arthropod communities and faunal recovery rates on a 1 m2 scale. We measured the abundance and species richness of selected arthropod taxa pre- and post-fire in patches of leaf litter experimentally burned at different intensities. Arthropod abundance declined sharply immediately after a burn and decreased with increasing fire intensity. Consistent with other studies of this system, the effects of fire on arthropod communities were still apparent >4 w post burn. The abundance of epigeic beetles recovered more quickly than the abundance of ants or springtails in some treatments. Recovery rates also differed among treatments but did not consistently support the prediction that recovery would be faster in plots subject to low intensity burns. We conclude that small scale differences in intensity within prescribed fires have measurable effects on litter arthropod communities in Ozark forests; however, these differences appear to be overshadowed by the more general effects of fire on arthropods.
Celastrus orbiculatus Thunb. (Oriental bittersweet) is an invasive exotic liana introduced to western North Carolina in the late 1800s that has established in forests across the southern Appalachian region. The twining habit of bittersweet is recognized to have negative impacts on tree growth by constricting trunks, overtopping canopies, and increasing the probability of wind and ice damage. Our study was designed to quantify effects of invasion by C. orbiculatus on Liriodendron tulipifera (tulip poplar) growth. We cored trees on invaded sites with both twined and untwined trees to test for above and below ground competition effects of C. orbiculatus and compared growth to nearby uninvaded sites. Contrary to our expectations, we found radial growth increased after invasion. This increase is likely a release response from a disturbance that allowed C. orbiculatus to become establised. There were many historical ice storms that occured in our region during the time of C. orbiculatus invasion that may have helped it to become established in these stands. Liriodendron tulipifera are known to respond positively after ice storm thinning and this release may mask any initial negative effects of liana competition. The short duration of our study may not have been long enough to capture the transition from the effect of canopy release due to disturbance to competition with C. orbiculatus.
Nonnative species are a major component of global change and have been linked to ecosystem disruption, reduction of native species richness, and substantial economic costs. An understanding of the patterns of occurrence of nonnative species and the environmental correlates of their abundance is necessary to formulate an informed response to the threats posed by these species. While considerable work has been conducted in Europe on the overall patterns and changes in nonnative species, few comprehensive studies are available for other areas. Because patterns of nonnative success can be region-specific, the availability of data from multiple geographic areas is important. Here we use two floristic surveys conducted in the 1930s–1950s and 1980s–2000s, respectively, as a basis for describing patterns and changes in the nonnative vascular flora of Worcester County, Massachusetts. Established, nonnative species comprised 21%–36% of all species in the county's 60 towns. Nonnative species richness was most strongly related to the percentage of land in residential use and was also positively correlated with human population density and with the extent of commercial and urban open land and significantly negatively correlated with elevation and the extent of natural land (mostly forest). Frequencies of nonnative species increased dramatically relative to those of native species between the two sampling periods. The change in the proportion of nonnative flora between the two sampling periods in different towns also showed a significant positive relationship with the change in the percentage of land in residential use. While the frequency of most nonnative species has increased, the frequency of a few species has decreased. Increasing and decreasing species differed in several attributes. Decreasing species had earlier dates of first record than increasing species and were more likely to have European, rather than Asian or North American, native ranges. Decreasers included more agricultural weeds and species of herbal or culinary importance, whereas increasers included more ornamental species. These results suggest minimizing the residential footprint is critical to limiting the spread of nonnative plants and that particular attention should be paid to the invasive potential of ornamental plants.
Creating and restoring patches of noncrop early-succession vegetation within agricultural landscapes may mitigate grassland bird population declines caused by agricultural land use and intensification. Achieving this goal requires an ability to balance avian benefits with agronomics, which may be facilitated by understanding how bird communities respond to various conservation practices. We evaluated bird richness, abundance, Shannon diversity, and Total Avian Conservation Value in 20 replicates of four Conservation Reserve Program practices in an intensive rowcrop agricultural landscape in the Mississippi Alluvial Valley from May–Jul., 2005–2007. Conservation practices included: (1) large blocks of structurally-diverse early-succession vegetation (6–8 y old trees) and three buffer types; (2) 30 m wide monotypic filter strips with tall dense switchgrass (Panicum virgatum); (3) 30 m wide diverse filter strips with a forb-native warm season grass mixture; and (4) 60 m wide early-succession riparian forest buffers (1–3 y old trees). The breeding bird community was dominated by red-winged blackbirds (Agelaius phoeniceus; 43% of total) and dickcissels (Spiza americana; 42% of total) but commonly included eastern meadowlarks (Sturnella magna), indigo buntings (Passerina cyanea), mourning doves (Zenaida macroura), and northern bobwhite (Colinus virginianus). We observed ≥1.8 × more dickcissels in large blocks and diverse filter strips than other buffers and greater Shannon diversity in large blocks than any buffers (P < 0.05). Diverse filter strips had ≥1.6 × greater overall bird density (7.2 birds/0.6 ha), on average, than all other practices. Based on these data, we conclude that buffers are attractive to farmland breeding birds and may provide important ecological benefits to supplement a conservation management system founded on large blocks of early-succession vegetation.
Relocation of federally protected freshwater mussel (Unionidae) resources as a conservation strategy has occurred for more than 30 y to ameliorate site-specific threats associated with development activities or invasive species. In this study, we evaluated survival rates of resident and relocated Potamilus capax (Green, 1832) individuals and documented short-term (1 mo) and long-term (25 mo) horizontal movements. We observed P. capax survival rates >77% for all treatment groups and horizontal movement up to 120 m annually. While significant differences in movement behavior between treatment groups occurred during the early stages of the study, movement differences between resident and relocated treatment groups became nonsignificant as the study progressed. We concluded using survival as a success measure remains valuable, but requires further evaluation. However, we assert understanding movement behavior in the focus species remains critical to strategic development of monitoring strategies.
Common carp Cyprinus carpio is a ubiquitous invasive species that commonly imposes negative effects on aquatic ecosystems. However, research evaluating the effects of carp on native fishes is limited. Carp are highly fecund and larvae and juveniles can be abundant. If age-0 carp use similar prey resources as native fishes, they may compete if food becomes limited. We used traditional diet analysis for samples during Jul. and Aug. 2008 in Brant Lake. Stable isotopes were used for samples collected during Aug. and Sep. 2009 in Brant Lake and Lake Sinai to examine prey resource use by age-0 carp and four native fishes: bluegill Lepomis macrochirus, black crappie Pomoxis nigromaculatus, yellow perch Perca flavescens, and orangespotted sunfish Lepomis humilis. Age-0 carp were generally as or more abundant than native fishes. In Jul. Daphnia dominated the diets of all fishes sampled, resulting in high (>60%) dietary overlap ranging from 87–98%. In Aug. Daphnia density in Brant Lake declined and dominant diet prey types shifted for carp (to Trichoptera and Daphnia), yellow perch (to Amphipoda), and the three Centrarchids (to Cyclops and Diaptomus). This diet shift resulted in lower diet overlap between Centrarchids and either carp (<40%) or yellow perch (3–16%) but high diet overlap within Centrarchids (67–97%). Stable isotope analysis further indicated greater resource overlap when most fishes relied on zooplankton and lesser overlap as fishes shifted to benthic prey. Our results suggest that resource competition between age-0 carp and native fishes is most likely to occur during early summer if Daphnia availability becomes limited but becomes less likely as dominant prey in diets increasingly diverge among fish species over time.
Reproductive biology and early life history data are critical for the conservation and management of rare fishes. During 2008–2012 a captive propagation study was conducted on the Diamond Darter, Crystallaria cincotta, a rare species with a single extant population in the lower Elk River, West Virginia. Water temperatures during spawning ranged from 11.1–23.3 C. Females and males spawned with quick vibrations, burying eggs in fine sand in relatively swift clean depositional areas. Egg size was 1.8–1.9 mm, and embryos developed within 7 to 11 d. Diamond Darters were 6.7–7.2 mm total length (TL) at hatch. Larvae ranged from 9.0–11.0 mm TL following a 5–10 d period of yolk sac absorption. Larvae had relatively large mouth gapes and teeth and were provided brine shrimp Artemia sp., Ceriodaphnia dubia neonates, marine Brachionus rotifers, and powdered foods (50–400 µm) but did not appear to feed in captivity, except for one observation of larval cannibalization. Larvae survived for a maximum of 10 d. To increase larval survival and reduce the possibility of cannibalism, other alternative food sources are needed during captive propagation.
Brook trout (Salvelinus fontinalis) from Lake Superior and its tributaries exhibit a variety of life histories and different growth characteristics; however, life history-specific effects on population dynamics are not well understood. The goal of this study was to characterize the movement patterns of brook trout in two streams with access to Lake Superior and compare age and growth metrics between fish that moved into Lake Superior (coasters) and resident brook trout that remained within the streams (residents). There were no significant differences in length, condition factor, or relative weight between coasters and residents from a given stream. Less than 5% of PIT tagged fish were detected emigrating from the study streams, although there was a peak in migration during the fall. The length distribution of fish differed among years for both streams. The data demonstrate that migratory brook trout are likely present, though rare, in the study streams and multiple life histories are present in sympatry. The lack of differences in growth metrics among the different life history groups has implications for the management and restoration of migratory brook trout populations and demonstrates that identification of migratory brook trout within Lake Superior tributaries may not be straightforward.
Native stream fish zoogeography has changed substantially across North America during the last century because habitat degradation, stream fragmentation and introductions of nonnative species have led to numerous extinctions, extirpations, and altered distributions. Insufficient information regarding imperiled species often results in reactive, rather than proactive, management, and knowledge of species status and ecology is critical in identifying conservation priorities. We used fish collection records and a habitat assessment to update the status of five fishes of conservation interest in South Dakota (Northern Redbelly Dace Chrosomus eos, Finescale Dace Chrosomus neogaeus, Northern Pearl Dace Margariscus nachtriebi, Blacknose Shiner Notropis heterolepis, and Plains Topminnow Fundulus sciadicus). We compiled records from previous collections within the White, Little White, and Keya Paha River Basins in South Dakota as well as adjoining and neighboring drainage basins in Nebraska. We also sampled fish and habitat at 42 stream reaches within the White, Little White, and Keya Paha river basins during 2010–2012, focusing on tributary streams. We detected all target species except for Finescale Dace. All species preferred tributary streams over larger rivers (third order or greater). All target species except Blacknose Shiner exhibited patchy distribution and abundance patterns, normally occurring at low relative abundance where present but occasionally detected at moderate to high relative abundance. Each target species was limited to landscapes with perennial, springfed streams that are not present in neighboring drainages. This study updates the distribution of conservation listed species, identifies landscape level habitat filters, and offers guidance for conservation and research efforts.
The plains of midwestern North America have undergone significant anthropogenic alterations following European settlement with consequent effects to lotic fish assemblage structure. We examined trends in fish assemblage structure and function in Nebraska's lotic systems using site-specific, presence-absence data from historical (1939–1940) and contemporary surveys (2003–2005; n = 183). Shifts in fish assemblage structure were characterized by declines of specialist species (e.g., western silvery minnow Hybognathus argyritis) and increases in nonnative, sport, and generalist species (e.g., common carp Cyprinus carpio). Our research illustrates differences between historical and contemporary surveys for both taxonomic and functional metrics. Changes in fish assemblage structure were correlated with a contemporary measure of anthropogenic alteration (Human Threat Index; HTI) and were most pronounced for large-scale threats (i.e., watershed HTI, overall HTI). The HTI is a composite index of cumulative anthropogenic alterations experienced by a stream system and was used to investigate broad-scale implications of anthropogenic activity on fish assemblage structure. Fish assemblages among sites were more similar in contemporary surveys than in historical surveys, such changes might indicate a homogenization of the fish assemblages. Losses of native species and increases in introduced species have occurred in Nebraska's lotic systems across a broad temporal span and shifts are likely related to high levels of human perturbation.
Logjams, or accumulations of wood in streams, can increase aquatic macroinvertebrate production through organic material retention and habitat diversification. Past studies showed a positive correlation between web-building spiders near streams and aquatic insect emergence. We hypothesized there would be an increase in terrestrial web-building spider density near logjams. To test this, we counted webs within 6 m of the stream bank along a 40 m reach in a northern Minnesota stream centered on a spanning logjam. We then estimated the availability of web-building substrate during late May and late Aug. of 2011. Webs in May heavily concentrated around the logjam, whereas webs in Aug. appeared dispersed throughout the reach. The web-building substrate did not show a significant correlation with web density in May, but it had a significant effect in Aug. These results cautiously suggest logjams have a positive effect on spider web density, but that effect varies through time. Further studies may explicitly link logjam-mediated prey to spider web distributions.
We investigated the potential for resource partitioning between the Coastal giant salamander (Dicamptodon tenebrosus) and the Cascade torrent salamander (Rhyacotriton cascadae) by examining their diet and microhabitats in forest streams. Larval D. tenebrosus and R. cascadae fed primarily upon aquatic insect larvae. We found similar foods in larval and adult R. cascadae and combined these results. Dicamptodon larvae consumed ephemeropteran, plecopteran, and trichopteran larvae in about equal amounts whereas R. cascadae ate more trichopteran and less ephemeropteran larvae than D. tenebrosus. Diet of all R. cascadae overlapped more with smaller than larger sized D. tenebrosus larvae. Comparisons of diets with available foods indicated R. cascadae is more selective or more gape-limited in its feeding habits than D. tenebrosus larvae. The two salamanders differed in use of microhabitats in creeks, which may contribute to their diet differences.
Despite the functional importance of isolated wetlands as supporters and sources of diverse assemblages of amphibians and reptiles, they lack federal protection and local protection is often insufficient to halt their destruction. A key step in guiding informed policy towards isolated wetlands is to understand their economic value. This study combines a year of intensive amphibian surveys within a wetland with the assignment of values to each of the captured species based upon their reported commercial values. The 392,605 amphibians comprising 17 species captured at this wetland in 1 y were valued at $3,605,848 (U.S. dollars). Juvenile amphibians produced in the wetland in a single year accounted for the 95% of the reported value ($3,413,821). This value far exceeds the value of other natural habitats evaluated with similar methods and exceeds by two orders of magnitude the value of this land had it been converted to agriculture. Although this study does not advocate amphibian harvest as an economic use for wetlands, it does highlight the value, diversity, and abundance of amphibians inhabiting these small, isolated, and often unprotected wetlands and provides a foundation for future research, management, mitigation, and policy.