Predicting exotic earthworm distribution in the northern Great Lakes region

Identifying influences of earthworm invasion and distribution in the northern Great Lakes is an important step in predicting the potential extent and impact of earthworms across the region. The occurrence of earthworm signs, indicating presence in general, and middens, indicating presence of Lumbricus terrestris exclusively, in the Huron Mountains located in the Upper Peninsula of Michigan were modeled using generalized linear models and stepwise regression to identify important environmental variables. Models were then applied to earthworm occurrence data from Seney National Wildlife Refuge, also located in the Upper Peninsula of Michigan to validate results. Occurrence of earthworm signs was associated with high soil pH, high basal area of earthworm preferred overstory species, and north facing aspects. Middens of L. terrestris were associated with high soil pH, high basal area of preferred species, and close proximity to roads. The resulting model for L. terrestris was incorporated into a geographic information system (GIS) to map the expected distribution, both current and potential, across the study area. Results indicate that L. terrestris has not yet fully saturated its potential habitat, as it is currently found close to roads and has yet to establish in most interior forests sampled. Comparing field measured data to GIS layers revealed limitations in the precision of publicly available spatial data layers that should be addressed in future attempts to predict the extent of earthworm invasion across the larger Great Lakes region. However, within the Huron Mountains, it is predicted that the distribution of L. terrestris will cover, at minimum, 41 % of the area.     

Dispersal versus climate: Expansion of Fagus and Tsuga into the Upper Great Lakes region

Pollen records for American beech (Fagus grandifolia) and eastern hemlock (Tsuga canadensis) compiled from 50 sites in Michigan and Wisconsin, USA, show that both species entered the Upper Great Lakes region about 7000 yr B.P., reaching their western and southwestern boundaries between 2000 and 1000 yr B.P. Fagus advanced northward into lower Michigan as a continuous front, except where Lake Michigan posed a geographic barrier. Colonies were established on the far side of the lake after a 1000 year lag, implying that longdistance dispersal across a 100-km wide barrier can occur. The Fagus range may not have been in equilibrium with climate for one or two thousand years before this time, when seeds were dispersed across the lake to Wisconsin. Tsuga seeds may have been dispersed 150 km or more from Ontario to reach Upper Michigan. Scattered colonies were established 6000–7000 yr B.P. on either side of Lake Michigan, which did not pose a significant barrier to this wind-dispersed species, Tsuga spread rapidly over a large region prior to 5000 yr B.P. Subsequent expansion to the west occurred more slowly, and may reflect gradual climatic changes in northern Wisconsin during the second half of the Holocene. Tsuga's range may have been limited by dispersal, rather than climate, for an unknown length of time prior to 5000 yr B.P. During this period Tsuga was expanding its range rapidly. The study shows, however, that it is difficult to devise rigorous tests to distinguish between dispersal limitations and climate as factors limiting range limits in the past.This work has been supported by the U.S. National Science Foundation.This work has been supported by the U.S. National Science Foundation.     

Climate connectivity of the bobcat in the Great Lakes region

The Great Lakes and the St. Lawrence River are imposing barriers for wildlife, and the additive effect of urban and agricultural development that dominates the lower Great Lakes region likely further reduces functional connectivity for many terrestrial species. As the climate warms, species will need to track climate across these barriers. It is important therefore to investigate land cover and bioclimatic hypotheses that may explain the northward expansion of species through the Great Lakes. We investigated the functional connectivity of a vagile generalist, the bobcat, as a representative generalist forest species common to the region. We genotyped tissue samples collected across the region at 14 microsatellite loci and compared different landscape hypotheses that might explain the observed gene flow or functional connectivity. We found that the Great Lakes and the additive influence of forest stands with either low or high canopy cover and deep lake‐effect snow have disrupted gene flow, whereas intermediate forest cover has facilitated gene flow. Functional connectivity in southern Ontario is relatively low and was limited in part by the low amount of forest cover. Pathways across the Great Lakes were through the Niagara region and through the Lower Peninsula of Michigan over the Straits of Mackinac and the St. Marys River. These pathways are important routes for bobcat range expansion north of the Great Lakes and are also likely pathways that many other mobile habitat generalists must navigate to track the changing climate. The extent to which species can navigate these routes will be important for determining the future biodiversity of areas north of the Great Lakes.     

Heavy metal contamination of sediments in the Upper Connecting Channels of the Great Lakes

In 1985, sampling at 250 stations throughout the St. Marys, St. Clair, and Detroit rivers and Lake St. Clair — the connecting channels of the upper Great Lakes — revealed widespread metal contamination of the sediments. Concentrations of cadmium, chromium, copper, lead, mercury, nickel, and zinc each exceeded U.S. Environmental Protection Agency sediment pollution guidelines at one or more stations throughout the study area. Sediments were polluted more frequently by copper, nickel, zinc, and lead than by cadmium, chromium, or mercury. Sediments with the highest concentrations of metals were found (in descending order) in the Detroit River, the St. Marys River, the St. Clair River, and Lake St. Clair. Although metal contamination of sediments was most common and sediment concentrations of metals were generally highest near industrial areas, substantial contamination of sediments by metals was present in sediment deposition areas up to 60 km from any known source of pollution.Contribution 735 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

Patterns of invasion in the Laurentian Great Lakes in relation to changes in vector activity

The Laurentian Great Lakes basin has been invaded by at least 182 non-indigenous species. A new invader is discovered every 28 weeks, which is the highest rate recorded for a freshwater ecosystem. Over the past century, invasions have occurred in phases linked to changes in the dominant vectors. The number of ship-vectored invaders recorded per decade is correlated with the intensity of vessel traffic within the basin. Ballast water release from ocean vessels is the putative vector for 65% of all invasions recorded since the opening of the St. Lawrence Seaway in 1959. As a preventive measure, ocean vessels have been required since 1993 to exchange their freshwater or estuarine ballast with highly saline ocean water prior to entering the Great Lakes. However, this procedure has not prevented ship-vectored species introductions. Most ships visiting the Great Lakes declare 'no ballast on board' (NOBOB) and are exempt from the regulation, even though they carry residual water that is discharged into the Great Lakes during their activities of off-loading inbound cargo and loading outbound cargo. Recently introduced species consist predominantly of benthic invertebrates with broad salinity tolerance. Such species are most likely to survive in a ballast tank following ballast water exchange, as well as transport in the residual water and tank sediments of NOBOB ships. Thus, the Great Lakes remain at risk of being invaded by dozens of euryhaline invertebrates that have spread into Eurasian ports from whence originates the bulk of foreign ships visiting the basin.     

Description of a new species of myxozoan from Notropis hudsonius in the Great Lakes region of Canada

Myxobolus burti n. sp. is described from striated muscle of Notropis hudsonius (Cyprinidae) collected from localities in Lake Superior, Lake Michigan, Lake Huron, Lake St. Claire, Lake Erie, Lake Ontario, and the St. Lawrence River. Myxobolus burti is intracellular, forming thin-walled, cigar-shaped plasmodia within striated muscle cells of the body. It exhibits disporoblastic, oval spores, approximately 10 μm long, 8 μm wide, and 6 μm thick, with a length-to-width ratio of 1.3 ∶ 1. They resemble most closely those of Myxobolus bellus Kudo, 1934, and Myxobolus mutabilis Kudo, 1934, but have polar capsules unequal in length (5.3 vs. 4.7 μm) and oblique filament coils. The new parasite was not encountered in routine examination of other small-bodied fishes at collection locations and thus looks to be specific to N. hudsonius. A comparative plate of similar species encountered during surveys of these fishes in the northeast is presented to contrast the uniqueness of the new species.     

Production of Hexagenia limbata nymphs in contaminated sediments in the Upper Great Lakes Connecting Channels

In April through October 1986, we sampled sediments and populations of nymphs of the burrowing mayfly, Hexagenia limbata (Serville), at 11 locations throughout the connecting channels of the upper Great Lakes, to determine if sediment contaminants adversely affected nymph production. Production over this period was high (980 to 9231 mg dry wt m^-2) at the five locations where measured sediment levels of oil, cyanide, and six metals were below the threshold criteria of the U.S. Environmental Protection Agency and the Ontario Ministry of Environment for contaminated or polluted sediments, and also where the criterion for visible oil given in the Water Quality Agreement between the U.S.A. and Canada for connecting waters of the Great Lakes was not exceeded. At the other six locations where sediments were polluted, production was markedly lower (359 to 872 mg dry wt m^-2). This finding is significant because it indicates that existing sediment quality criteria can be applied to protect H. limbata from oil, cyanide, and metals in the Great Lakes and connecting channels where the species fulfills a major role in secondary production and trophic transfer of energy.Contribution 733, of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

Non-indigenous species in the Great Lakes: were colonization and damage to ecosystem health predictable?

The Great Lakes ecosystem is home to at least 139 non-indigenous species of fauna and flora which have become established following invasions or intentional introductions. About ten percent of the exotic species have caused economic or ecological damage to the system. A sample of this group is reviewed to determine if ecological concepts are useful in helping to predict colonization and impacts to ecosystem health. Successful colonization by most of the species reviewed was predictable from habitat requirements and behaviour. Ecosystem disturbance was a factor in the success of some of the colonists but was not an overriding ecological requirement. Perturbations to ecosystem health are more difficult to predict and in most cases were not readily apparent from knowledge about the ecology of invaders or native communities. The main damage to ecosystem health by the species reviewed resulted from competition, predation and habitat modification. Difficulties in predicting both invasions and damage from successful colonists point to the need to prevent non-indigenous species from reaching the Great Lakes basin.     

Hybridization of Cyprinus carpio and Carassius auratus,the first two exotic species in the lower Laurentian Great Lakes

Synopsis A preliminary comparison of Cyprinus carpio × Carassius auratus hybrids with the parent species is made by means of hybrid indices for 29 morphometric and 19 meristic characters. Of these 48 characters 29 were intermediate, seven were identical with one of the parents and 12 were extreme. Marked osteological differences in the crania of the parent species were noted as possible diagnostic characters for the identification of hybrids.Note     

Large-scale terrestrial gastropod community composition patterns in the Great Lakes region of North America

Abstract: Previous ordination studies of land snail community composition have been limited to four or fewer habitat types from sites separated by no more than 300 km. To investigate the nature of large-scale patterns, North American land snail assemblages at 421 sites, representing 26 habitat types and covering a 1400 × 800 km area, were ordinated using global, nonmetric multi-dimensional scaling (NMDS). These data were then subjected to model-based cluster analysis and kmeans clustering to identify the main compositional groups and most important environmental covariables. Six primary compositional groups were identified. Three of these largely represent upland forest and rock outcrop sites, while the remaining largely represent either lowland forest, lowland grassland or upland grassland habitats. The geographical location and moisture level of sites also influences community composition. A strong compositional difference exists between sites having duff vs. turf soil surface layers. Only 8% of sites were improperly classified when soil surface architecture was used as the sole predictor variable. Fully 43% of taxa exhibited significant preferences towards one of these surface types, while only 15% of relatively common (10 + occurrence) taxa showed no preferences. Twelve groups of closely related taxa within the same genus had members that favoured different surface types, indicating that differential selection pressures have existed over evolutionary time scales. While turf faunas appeared unaffected by anthropogenic disturbance, duff faunas were strongly impacted, suggesting that their conservation will require protection of soil surface architecture.     

Genetic and morphological characterisation of the Ankole Longhorn cattle in the African Great Lakes region

The study investigated the population structure, diversity and differentiation of almost all of the ecotypes representing the African Ankole Longhorn cattle breed on the basis of morphometric (shape and size), genotypic and spatial distance data. Twentyone morphometric measurements were used to describe the morphology of 439 individuals from 11 sub-populations located in five countries around the Great Lakes region of central and eastern Africa. Additionally, 472 individuals were genotyped using 15 DNA microsatellites. Femoral length, horn length, horn circumference, rump height, body length and fore-limb circumference showed the largest differences between regions. An overall F_ST index indicated that 2.7% of the total genetic variation was present among sub-populations. The least differentiation was observed between the two sub-populations of Mbarara south and Luwero in Uganda, while the highest level of differentiation was observed between the Mugamba in Burundi and Malagarasi in Tanzania. An estimated membership of four for the inferred clusters from a model-based Bayesian approach was obtained. Both analyses on distance-based and model-based methods consistently isolated the Mugamba sub-population in Burundi from the others.     

Paleolimnologic Evidence for Recent Eutrophication in the Valley of the Great Lakes (Mongolia)

Climate warming and major land-use changes have profoundly affected the Mongolian landscape in the past several decades. Previous studies have recognized the impacts of a warmer, more arid climate and Mongolia’s 1991 transition from a command to a market economy on terrestrial ecosystems, including impaired sustainability of subsistence herding and threats to wild animals. In this study, we examined the combined effects of changing climate and herding practices on lake eutrophication in Western Mongolia. We sampled 65 lakes for modern nutrients and found the majority of lakes were eutrophic to hyper-eutrophic. Sediment cores were taken from five of the lakes to compare current lake status to paleolimnologial measures of lake eutrophication over the past 100–2000 years, including changes in diatom assemblages, diatom-inferred total phosphorus, biogenic silica, organic matter, and sediment accumulation rates. Variance partitioning analysis showed that recent shifts in diatom assemblages were related to changes in both climate and herding practices. The results presented here demonstrate a need for further study and long-term monitoring of water quality in Mongolia to understand the complicated interactions of climate and land use on aquatic resources and to preserve water quality in this remote and ecologically important region.     

Distribution of Hexagenia nymphs and visible oil in sediments of the Upper Great Lakes Connecting Channels

As part of the study of the Upper Great Lakes Connecting Channels sponsored by the U.S. Environmental Protection Agency, the U.S. Fish and Wildlife Service examined the occurrence of Hexagenia nymphs and visible oil in sediments at 250 stations throughout the St. Marys River and the St. Clair-Detroit River system from May 14 to June 11, 1985. The mean density of Hexagenia nymphs per square meter averaged 194 for the total study area, 224 in the St. Marys River, 117 in the St. Clair River, 279 in Lake St. Clair, and 94 in the Detroit River. The maximum density of nymphs ranged from 1,081 to 1,164 m^-2 in the three rivers and was 3,099 m^-2 in Lake St. Clair. A comparison of nymph density at 46 stations where oil was observed in sediments physically suitable for nymphs showed that densities were lower in oiled sediments (61 m^-2) than in sediments without oil (224 m^-2). Densities of nymphs were relatively high at only four stations where oil was observed in sediments. In general, oiled sediments and low densities of nymphs occurred together downstream from industrial and municipal discharges.Contribution number 736 of the National Fisheries Research Center-Great Lakes, U.S. Fish and Wildlife Service, 1451 Green Road, Ann Arbor, MI 48105.     

Mercury risks versus nutritional benefits of tribal commercial fish harvests in the Upper Laurentian Great Lakes

The Inter-Tribal Fisheries and Assessment Program (ITFAP) of the Chippewa Ottawa Resource Authority (CORA) in Sault Ste. Marie, Michigan, has been monitoring contaminant concentrations in the fillet portions of lake trout (Salvelinus namaycush) and lake whitefish (Coregonus clupeaformis) from the waters of lakes Superior, Huron, and Michigan since 1991. The primary purpose of this article is to present a risk quantification of methylmercury (MeHg) that is adjusted for nutritional benefit, originally presented by Ginsberg and Toal (2009 Ginsberg GL and Toal BF. 2009. Quantitative approach for incorporating methylmercury risks and omega-3 fatty acid benefits in developing species-specific fish consumption advice. Environ Health Perspect 117:267–75[Crossref], [PubMed], [Web of Science ®] , [Google Scholar], 2015) on trends in contaminant concentrations in fillet portions of these commercial fish that we recently reported in Dellinger et al. (2014 Dellinger JA, Moths MD, Dellinger M, et al. 2014. Contaminant trends in freshwater fish from the Great Lakes: A 20 year analysis. Hum Ecol Risk Assess 20:461–78[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]). Both species of fish caught by tribal fishermen showed clear benefits to cardiovascular health and infant neurodevelopment if consumed at a rate of six ounces per week. However, other popularly consumed fish such as cod, tuna, and tilapia are estimated to have only marginal benefit or net negative effects on cardiovascular health and infant neurodevelopment. This dynamic assessment of benefits and risks further demonstrates the importance of traditionally caught fish in tribal health.     

Living at the edge of the front; reduced predation risk to invasive round goby in a Great Lakes tributary

The objective of this research was to determine if the highly invasive round goby (Neogobius melanostomus) experiences lower predation risk during early stages of invasion. We compared round goby predation rates between a recently invaded area (occupied for ≈1 year) and a longer established area (≈7 years) of the Trent River, Ontario, Canada. Tethering trials were conducted in three habitat types, and comparable habitats in the two areas were similar in water temperature, velocity and depth. Predation rates of tethered round gobies were on average 27% lower in the recently invaded area. Reduced predation in the recently invaded area may be due to the short duration of round goby occupancy and/or differences in predator communities between the two study areas. Data before the round goby invasion suggest that predator communities were similar between the two range areas, but differences in predator abundance cannot be ruled out as a potential mechanism. Other possible mechanisms include a numerical or learned response by predators over time to a novel prey item. Reduced predation rate during the initial stages of invasion may contribute to the fitness of individuals that migrate into areas not previously occupied, and thus facilitate successful range expansion.     

Vulnerability of xylem vessels to cavitation in sugar maple. Scaling from individual vessels to whole branches

The relation between xylem vessel age and vulnerability to cavitation of sugar maple (Acer saccharum Marsh.) was quantified by measuring the pressure required to force air across bordered pit membranes separating individual xylem vessels. We found that the bordered pit membranes of vessels located in current year xylem could withstand greater applied gas pressures (3.8 MPa) compared with bordered pit membranes in vessels located in older annular rings (2.0 MPa). A longitudinal transect along 6-year-old branches indicated that the pressure required to push gas across bordered pit membranes of current year xylem did not vary with distance from the growing tip. To understand the contribution of age-related changes in vulnerability to the overall resistance to cavitation, we combined data on the pressure thresholds of individual xylem vessels with measurements of the relative flow rate through each annual ring. The annual ring of the current year contributed only 16% of the total flow measured on 10-cm-long segments cut from 6-year-old branches, but it contributed more than 70% of the total flow when measured through 6-year-old branches to the point of leaf attachment. The vulnerability curve calculated using relative flow rates measured on branch segments were similar to vulnerability curves measured on 6-year-old branches (pressure that reduces hydraulic conductance by 50% = 1.6-2.4 MPa), whereas the vulnerability curve calculated using relative flow rates measured on 6-year-old branches were similar to ones measured on the extension growth of the current year (pressure that reduces hydraulic conductance by 50% = 3.8 MPa). These data suggest that, in sugar maple, the xylem of the current year can withstand larger xylem tensions than older wood and dominates water delivery to leaves.     

Post-glacial recolonization of the Great Lakes region by the common gartersnake (Thamnophis sirtalis) inferred from mtDNA sequences

Pleistocene events played an important role in the differentiation of North American vertebrate populations. Michigan, in particular, and the Great Lakes region, in general, were greatly influenced by the last glaciation. While several hypotheses regarding the recolonization of this region have been advanced, none have been strongly supported. We generated 148 complete ND2 mitochondrial DNA (mtDNA) sequences from common gartersnake (Thamnophis sirtalis) populations throughout the Great Lakes region to evaluate phylogeographic patterns and population structure and to determine whether the distribution of haplotypic variants is related to the post-Pleistocene retreat of the Wisconsinan glacier. The common gartersnake was utilized, as it is believed to have been one of the primary vertebrate invaders of the Great Lakes region following the most recent period of glacial retreat and because it has been a model species for a variety of evolutionary, ecological, behavioral, and physiological studies. Several genetically distinct evolutionary lineages were supported by both genealogical and molecular population genetic analyses, although to different degrees. The geographic distribution of the majority of these lineages is interpreted as reflecting post-glacial recolonization dynamics during the late Pleistocene. These findings generally support previous hypotheses of range expansion in this region.