Freshwater macrophyte communities in lakes of variable landscape position and development in northern Wisconsin,U.S.A.

Using multivariate analyses, we evaluated the roles of landscape position and human development in the presence, composition, and abundance of freshwater macrophyte communities among 60 study lakes located in Vilas County, Wisconsin. These lakes varied in their position in a drainage network and surrounding land use as well as size, maximum depth, chemistry, and clarity. We used non-metric multidimensional scaling ordination, cluster analyses, and classification tree analyses to assess the multivariate relationships among macrophyte communities and environmental variables including an index of human development. Macrophyte communities in lakes high in the landscape were found to be dominated by isoetids while lakes low in the drainage network were dominated by elodeids due to the difference in bicarbonate concentrations. The presence of the human-introduced crayfish, Orconectes rusticus, had a high and significant correlation with the absence of macrophytes. An increase in human development correlated with a decrease in macrophyte abundance.     

Pigment ratios and phytoplankton assessment in northern Wisconsin lakes

Nine lakes in northern Wisconsin were sampled from February through September 1996, and HPLC analysis of water column pigments was carried out on epilimnetic seston. Pigment distributions were evaluated throughout the water column during summer in Crystal Lake and Little Rock Lake. The purpose of our study was to investigate the use of phytopigments as markers of the main taxonomic groups of algae. As a first approach, multiple regression of marker pigments against chlorophyll a (chl a) was used to derive the best linear combination of the main xanthophylls (peridinin, fucoxanthin, alloxanthin, lutein, and zeaxanthin). A significant regression equation (r²= 0.98) was obtained for epilimnion data. The good fit indicates that the chl a:xanthophyll ratios were fairly constant in the epilimnion of the nine lakes over time. Chlorophyll a recalculated from the main xanthophylls in each sample showed good agreement with measured chl a in epilimnetic waters. A second approach used the CHEMTAX program to analyze the same data set. CHEMTAX provided estimates of chl a biomass for all algal classes and allowed distinction between diatoms and chrysophytes, and between chlorophytes and euglenophytes. These results showed a reasonably good agreement with biomass estimates from microscope counts, despite uncertainties associated with differences in sampling procedure. Changes of pigment ratios over time in the epilimnetic waters were also investigated, as well as differences between surface and deep samples of Little Rock Lake and Crystal Lake. We found evidence that changes in the ratio of photoprotective pigments to chl a occurred as a response to changes in light climate. Changes were also observed for certain light‐harvesting pigments. The comparison between multiple regression and CHEMTAX analyses for inferring chl a biomass from concentrations of marker pigments highlighted the need to take account of variations in pigment ratio, as well as the need to acquire additional data on the pigment composition of planktonic algae.     

The influence of Prosopis canopies on understorey vegetation: Effects of landscape position

Abstract. The influence of canopy trees and shrubs on under‐storey plants is complex and context‐dependent. Canopy plants can exert positive, negative or neutral effects on production, composition and diversity of understorey plant communities, depending on local environmental conditions and position in the landscape. We studied the influence of Prosopis velutina (mesquite) on soil moisture and nitrogen availability, and understorey vegetation along a topographic gradient in the Sonoran Desert. We found significant increases in both soil moisture and N along the gradient from desert to riparian zone. In addition, P. velutina canopies had positive effects, relative to open areas, on soil moisture in the desert, and soil N in both desert and intermediate terrace. Biomass of understorey vegetation was highest and species richness was lowest in the riparian zone. Canopies had a positive effect on biomass in both desert and terrace, and a negative effect on species richness in the terrace. The effect of the canopy depended on landscape position, with desert canopies more strongly influencing soil moisture and biomass and terrace canopies more strongly influencing soil N and species richness. Individual species distributions suggested interspecific variation in response to water‐ vs. N‐availability; they strongly influence species composition at both patch and landscape position levels.     

Distribution and community-level effects of the Chinese mystery snail (Bellamya chinensis) in northern Wisconsin lakes

Managing invasive species requires information about their distributions and potential effects, but community-level impacts of invasive animals remain poorly understood. The Chinese mystery snail (Bellamya chinensis) is a large invasive gastropod that achieves high densities in waters across North America, yet little is known about its ecological significance in invaded systems. We surveyed 44 lakes to describe the patterns and determinants of B. chinensis distributions in northern Wisconsin, USA, and to assess the likelihood of effects on native snail communities in the invaded systems. B. chinensis was widespread among surveyed lakes (21 of 42 lakes with snails) and its occurrence was correlated with indicators of lake productivity and anthropogenic dispersal vectors (boat landings, distance to population centers, shoreline housing density). Some native snail species tended not to occur at sites where B. chinensis was abundant; among these was Lymnaea stagnalis, which suffered reduced survival in the presence of B. chinensis in a recently published mesocosm study. However, there was no difference in overall snail assemblage structure at either the site or lake level as a function of B. chinensis presence or abundance. Lake occurrences of many snail species have apparently been lost over time, but a comparison to a 1930s survey showed that there was no increased likelihood of species loss in lakes invaded by B. chinensis (or by the invasive crayfish Orconectes rusticus). Although B. chinensis is widespread and sometimes abundant in northern Wisconsin lakes, it does not appear to have strong systematic impacts on native snail assemblages.     

No biotic homogenisation across decades but consistent effects of landscape position and pH on macrophyte communities in boreal lakes

It has been predicted that spatial beta diversity shows a decreasing trend in the Anthropocene due to increasing human impact, causing biotic homogenisation. We aimed to discover if vascular aquatic macrophyte communities show different spatial patterns in beta diversity in relation to land use and environmental characteristics in different decades from 1940s to 2010s. We aimed to discover if spatial structures differ between species-, phylogeny- and functional-based beta diversity. We used presence–absence data of aquatic macrophytes from five decades from small boreal lakes. We utilized generalised dissimilarity modelling to analyse spatial patterns in beta diversity in relation to environmental gradients. We found that lake elevation and pH were the most important variables in each decade, while land use was not particularly important in shaping beta diversity patterns. We did not find signs of a decreasing trend in spatial beta diversity in our study area during the past 70 yr. We did not find signs of either biotic homogenisation or biotic differentiation (taxonomic, phylogenetic or functional). Vascular aquatic macrophyte communities showed only slightly different beta diversity patterns in relation to human impact across decades. The patterns of different facets of beta diversity diverged only slightly from each other. Lake position in the landscape, reflecting both natural connectivity and lake characteristics, explained the patterns found in beta diversity, probably because our study area has faced only modest changes in land use from 1940s to 2010s when compared globally. Our study highlights the fact that biotic homogenisation is not an unambiguous process acting similarly at all spatial and temporal scales or in different environments and different organism groups.     

Importance of landscape position and legacy: the evolution of the lakes in Taylor Valley, Antarctica

1. The major factor influencing the chemical composition and evolution of the major lakes in Taylor Valley, Antarctica, is their location within the landscape. Present-day microclimatic variation and its manifestation over the past 6000 years have led to the differences observed in these lakes today.
2. Geographical and topographical variables within the Taylor Valley magnify subtle changes in the hydrological balances of these lakes. Even short-term variation of the surface temperatures and albedo greatly impact the run-off into the lakes, leading to positive or negative water balances.
3. The legacy of past climatic changes has had a profound effect on the ecology of the lakes today.     

Ecology and management of northern pike in Wisconsin

Northern pike (pike) Esox lucius Linnaeus are broadly distributed across Wisconsin and provide an important sport fishery for anglers. Historical management has included use of angling regulations, stocking, and protection of critical habitat areas. Pike management is often a lower priority in comparison to more intensively managed species such as muskellunge Esox masquinongy Mitchell and walleye Sander vitreous. Pike provide angling opportunities year around, with higher catch rates and live release during open water, and higher harvest rates during winter. While length of pike caught during the two seasons is generally similar, there is some evidence that larger fish are caught during winter months. Results from minimum length limit changes implemented in 1995 have been equivocal and warrant further monitoring using standardized protocol to better determine effects on populations. If natural recruitment is not limited, pike populations can reach high densities and stunting can result. Loss of nearshore habitat has continued at an increased rate as more lake homes are built and shorelines graded, and altered with riprap, sand blankets, or sea walls. If natural recruitment is lacking, fry or fingerling stocking sustains or rehabilitates populations. Most pike stocking occurs in the southeastern portion of the state where habitat loss has been extensive. Stocking in other areas is largely to re-establish populations following a chemical reclamation or from winterkill. Future management needs to establish sampling protocols to ensure comparable data on both a temporal and a spatial scale. Long-term monitoring with these methods is essential to help determine effects of various factors (e.g., regulations, habitat loss) on populations. Guest editors: J. M. Farrell, C. Skov, M. Mingelbier, T. Margenau & J. E. Cooper International Pike Symposium: Merging Knowledge of Ecology, Biology, and Management for a Circumpolar Species     

The influence of mixing on rotifer assemblages of Michigan lakes

Seasonal changes in the rotifer assemblages of 42 lakes in northern lower Michigan was closely related to lake mixing characteristics, basin morphometry, and the presence of an oxygenated coldwater refuge. Three major classes of lakes (dimictic, discontinuous polymitic, and continuous polymictic) were evident by their capacity to maintain coldwater species as seasons progressed from winter through fall. The disappearance of coldwater assemblages from dimictic lakes coincided with oxygen depletion in the hypolimnion or with erosion of the hypolimnion through mixing. Coldwater species disappeared from large discontinuous polymictic lakes when deep epilimnetic mixing occured in late summer and fall. Species assemblages of nearly all stratified lakes converged with those of continuous polymictic lakes when the hypolimnetic refuge deteriorated in summer and fall. Local weather conditions, however, between years had a pronounced effect on the persistence of cold water species through the seasons by affecting the temperature and oxygen conditions of the hypolimnion. Large lakes of the region contain many of the coldwater species of the Laurentian Great Lakes but some taxa are conspicuosly absent. Cold stenothermal rotifers persist in the lakes of the region despite adverse environmental conditions. Their life histories and ability to form resting stages permit them to escape periods of oxygen depletion and thermal stress. In contrast, the crustacean glacial marine fauna (i.e. Mysis relicta, Limnocalanus macrurus, and Scenecella calanoides) was absent from all of the study lakes even though many of the present-day basins were once connected to the Laurentian Great Lakes. These species long life cycles, lack of diapausing stages, and limited dispersal may make them vulnerable to local extinction with the deterioration and loss of the coldwater refuge.     

The influence of foot position on body dynamics

During locomotion, the human body exhibits inherent dynamic properties such as mass (M), stiffness (K) and damping (B). During the gait cycle, foot contact with the ground progresses from the heel to the toe. Contact forces between the foot and ground are defined as ground reaction forces (GRF). It is unclear how body dynamics are affected by foot landing position. If the shape of GRF is indicative of body dynamics, our understanding of gait patterns in normal and pathologic conditions may improve. The aims of this study were to determine:(1) whether foot landing position affects the inherent dynamics of the human body and (2) the extent to which the GRF curve reflects the response of inherent body dynamics to sudden loading.Eight non-disabled control volunteers performed a series of small jumps and landed on one leg with a fully extended knee in three foot landing positions: heel, mid-foot, and toe. They then walked at self-paced velocity over force plates. For each foot landing position, values of K, B and the dimensionless damping coefficient, ξ, were calculated from the period of vertical body oscillations, T, and compared with an ANOVA test. In addition, the time between the two peaks of the vertical GRF, T_GRF, was compared with T. We found that that K and B decreased and ξ did not change (p<0.01) between heel to toe-landing positions. T_GRF was not different than T for the toe-landing position, which suggests that the dynamic body response has major impact on the shape of GRF.     

The influence of foot position on standing balance

To test the hypothesis that variations in foot position would significantly affect standing balance, we studied ten normal subjects on a Kistler force platform which measured the travel and center of pressure displacement. With the feet together there was substantially more mediolateral (ML) travel than with the axes of the feet 15, 30 or 45 cm apart and the mean ML position of the center of pressure was displaced toward the right; there was no consistent effect on anteroposterior (AP) travel or position. As the right foot was placed 10 and 30 cm forward or back, the least amount of ML and AP travel occurred with the feet even or at 10 cm either direction; the mean AP and ML position moved toward the foot which was placed more posteriorly. Of the five foot angles ranging from toes-out 45 degrees to toes-in 45 degrees, the extent of ML and AP travel was lowest in the toes-out 25 degrees position and greatest in the toes-in 45 degrees position; the mean AP and ML position was farthest forward and to the right with toes-in 45 degrees. These findings have implications for the prosthetic replacement of the lower limbs, sports, ergonomics and postural sway studies.     

Effect of landscape factors on fish distribution in arctic Alaskan lakes

1. The distribution of species is affected by many factors operating at a variety of temporal and spatial scales in a heterogeneous landscape. In lakes, fish communities are dynamic, influenced by landscape‐level factors that control colonisation and extinction. 2. We used classification and regression tree (CART) analyses to quantify the importance of landscape‐level factors in determining the distribution of fish species in 168 arctic Alaskan lakes. Factors including lake size, depth, outflow gradient, distance to other lakes, lake order, altitude, river drainage and age of glacial surface were analysed. These factors could affect either access of fish to a lake (colonisation variables), or their survival in a lake that already had been colonised (extinction variables). 3. The presence of a species was predicted accurately in 78.4% ± 10.5% (mean ± SD) of cases, and absence in 75.0% ± 6.1% of cases. The relative importance of extinction versus colonisation variables varied with species. Extinction variables were most important for lake trout (Salvelinus namaycush) and slimy sculpin (Cottus cognatus), a mixture of extinction and colonisation variables was important for arctic char (Salvelinus alpinus), and colonisation variables were most important for arctic grayling (Thymallus arcticus) and round whitefish (Prosopium cylindraceum). 4. Ecological differences among species account for much of the difference in relative importance of colonisation versus extinction variables. In addition, stream piracy events have occurred over geologic time scales, which have resulted in lakes that are currently inaccessible but support relict fish populations. 5. Climate warming, currently occurring in the arctic, is likely to alter further the stream network, which could have dramatic effects on fish distributions by affecting access to isolated lakes or isolating lakes that are currently accessible.     

The influence of turbidity on net phytoplankton photosynthesis in some Irish lakes

SUMMARY. An important influence on gross photosynthetic rates per unit area is the success with which phytoplankton competes for the available light with non-algal suspended material and dissolved organic compounds. Using a range of Irish lakes, with euphotic zones varying between 0.7 and 20 m and with chlorophyll-α values between 1 and 860 mg m⁻³, the effect on gross rates of photosynthesis is analysed for changes in the balance between the factors contributing to light attenuation. Net values per unit area are also likely to be modified in well-mixed systems as the ratio of light to dark regions in the water column are altered with changes in light penetration. Depth gradients in dark respiration are reported for L. Neagh which vary according to previous light history and nutrient stress. Possible cases of restraint on phytoplankton growth are discussed for optically deep situations.     

Large-scale forest composition influences northern goshawk nesting in Wisconsin

The northern goshawk (Accipiter gentilis atricapillus) is a woodland raptor that uses a variety of forest types for nesting across its breeding range, but strongly depends on older forests with large trees and open understories. Goshawks may select nesting locations by maximizing the convergence of nesting and foraging habitats. Insights into goshawk responses to heterogeneous landscapes can be gained by examining the location of active nest sites through time and at multiple spatial scales. We examined the landscape-scale forest conditions that influenced the probability of active goshawk nests in the United States Forest Service, Chequamegon-Nicolet National Forest (CNNF) in northern Wisconsin. We used goshawk nest survey and monitoring data from 1997 to 2006 to determine the probability of an active nest site over time in relation to forest composition and road density at 3 scales (200-m, 500-m, and 1,000-m radii). Goshawk nests were located primarily in upland hardwood (64%), conifer (23%), and older aspen–birch (≥26 yrs old; 11%) habitat cover types. We used Bayesian temporal autoregressive models of nest locations across multiple spatial scales to analyze these data. The probability of active goshawk nest occurrence increased with increasing conifer cover (1,000 m) and decreased with increasing cover of older aspen–birch and density of primary roads (500 m). In addition, lesser proportions of older aspen–birch at intermediate scales around goshawk nests had a stronger effect on the probability of a nest being active than conifer and primary roads. Thus, the ratio of conifer cover (within 1,000 m) to older aspen–birch cover (within 500 m) in landscapes surrounding nest sites was the key driver in predicting the probability of an active nest site. This finding can be used by forest managers to help sustain the active status of a goshawk nesting area through time (i.e., annually), and foster goshawk nesting activity in areas where active nesting is not currently occurring. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

The influence of body position on maximal performance in cycling

Six healthy male subjects performed a 3-min supramaximal test in four different cycling positions: two with different trunk angles and two with different saddle-tube angles. Maximal power output and maximal oxygen uptake (VO2max) were measured. Maximal power output was significantly higher in a standard sitting (SS, 381 W, SD 49) upright position compared to all other positions: standard racing (SR, 364 W, SD 49), recumbent backwards (RB, 355 W, SD 44) and recumbent forwards (RF, 341 W, SD 54). Although VO2max was also highest in SS (4.31 l.min-1, SD 0.5) upright position, the differences in VO2max were not significant (SR, 4.2 l.min-1, SD 0.53; RB, 4.17 l.min-1, SD 0.58; RF, 4.11 l.min-1, SD 0.66). It is concluded that (supra)maximal tests on a cycle ergometer should be performed in a sitting upright position and not in a racing position. In some cases when cycling on the road, higher speeds can be attained when sitting upright. This is especially true when cycling uphill when high power must be generated to overcome gravity but the road speed, and hence the power required to overcome air resistance, is relatively low.     

Projected shifts in fish species dominance in Wisconsin lakes under climate change

Temperate lakes may contain both coolwater fish species such as walleye (Sander vitreus) and warmwater fish species such as largemouth bass (Micropterus salmoides). Recent declining walleye and increasing largemouth bass populations have raised questions regarding the future trajectories and management actions for these species. We developed a thermodynamic model of water temperatures driven by downscaled climate data and lake‐specific characteristics to estimate daily water temperature profiles for 2148 lakes in Wisconsin, US, under contemporary (1989–2014) and future (2040–2064 and 2065–2089) conditions. We correlated contemporary walleye recruitment and largemouth bass relative abundance to modeled water temperature, lake morphometry, and lake productivity, and projected lake‐specific changes in each species under future climate conditions. Walleye recruitment success was negatively related and largemouth bass abundance was positively related to water temperature degree days. Both species exhibited a threshold response at the same degree day value, albeit in opposite directions. Degree days were predicted to increase in the future, although the magnitude of increase varied among lakes, time periods, and global circulation models (GCMs). Under future conditions, we predicted a loss of walleye recruitment in 33–75% of lakes where recruitment is currently supported and a 27–60% increase in the number of lakes suitable for high largemouth bass abundance. The percentage of lakes capable of supporting abundant largemouth bass but failed walleye recruitment was predicted to increase from 58% in contemporary conditions to 86% by mid‐century and to 91% of lakes by late century, based on median projections across GCMs. Conversely, the percentage of lakes with successful walleye recruitment and low largemouth bass abundance was predicted to decline from 9% of lakes in contemporary conditions to only 1% of lakes in both future periods. Importantly, we identify up to 85 resilient lakes predicted to continue to support natural walleye recruitment. Management resources could target preserving these resilient walleye populations.     

The influence of plants on atmospheric methane in an agriculture-dominated landscape

The primary objective of this study was to clarify the influence of crop plants on atmospheric methane (CH₄) in an agriculture-dominated landscape in the Upper Midwest of the United States. Measurements were carried out at two contrasting scales. At the plant scale, CH₄ fluxes from soybean and corn plants were measured with a laser-based plant chamber system. At the landscape scale, the land surface flux was estimated with a modified Bowen ratio technique using measurements made on a tall tower. The chamber data revealed a diurnal pattern for the plant CH₄ flux: it was positive (an emission rate of 0.4?±?0.1 nmol m^?2 s^?1, average of soybean and corn, in reference to the unit ground area) during the day, and negative (an uptake rate of ?0.8?±?0.8 nmol m^?2 s^?1) during the night. At the landscape scale, the flux was estimated to be 14.8 nmol m^?2 s^?1 at night and highly uncertain during the day, but the available references and the flux estimates from the equilibrium methods suggested that the CH₄ flux during the entire observation period was similar to the estimated nighttime flux. Thus, soybean and corn plants have a negligible role in the landscape-scale CH₄ budget.     

Ecto- and endoparasites of the black bear in northern Wisconsin

Parasites collected from free-ranging black bears, Ursus americanus, in northern Wisconsin included Dermacentor variabilis, D. albipictus, Ixodes scapularis, Demodex sp., Trichodectes pinguis euarctidos, Baylisascaris transfuga and Dirofilaria ursi. Mange, possibly caused by the Demodex sp., also was observed. Dental caries were common and periodontal disease was observed in one animal.