Biological attributes of ecosystems often change nonlinearly as a function of anthropogenic and natural stress. Plant and animal communities may exhibit zones of change along a stressor gradient that are disproportionate relative to the incremental change in the stressor. The ability to predict such transitions is essential for effective management intervention because they may indicate irreversible changes in ecological processes. Despite the importance of recognizing transition zones along a stressor gradient, few, if any, investigators have examined these responses across multiple taxa, and no community threshold studies have been reported at large geographic scales. We surveyed benthic macroinvertebrate, fish, bird, diatom, and plant communities in coastal wetlands across a geospatially referenced gradient of anthropogenic stress in the Laurentian Great Lakes. We used Threshold Indicator Taxon Analysis (Baker and King 2010) to analyze each community's response to identify potential zones of disproportionate change in community structure along gradients of major watershed-scale stress: agriculture and urban/suburban development. Our results show surprising congruence in community thresholds among different taxonomic groups, particularly with respect to % developed land in the watershed. We also analyzed uncertainty associated with the community-specific thresholds to understand the ability of different assemblages to predict stress. The high and congruent sensitivity of assemblages to development demonstrates that watershed-scale stress has discernible effects on all biological communities, with increasing potential for ecosystem-scale functional changes. These findings have important implications for identifying reference-condition boundaries and for informing management and policy decisions, in particular, for selecting freshwater protected areas.

The ideal distribution hypothesis states that territorial animals identify habitats with ideal habitat suitability and alter their settlement patterns accordingly. This hypothesis assumes no cost of migrating to a more profitable patch once the current one becomes less profitable. Another underlying assumption is that individuals only use current information while deciding where to breed. To evaluate these assumptions and resultant alternative hypotheses, we studied Ovenbird ( Seiurus aurocapilla (L., 1766)) territories during 2000–2001 in six northern hardwood tracts within a landscape composed of wetlands, regenerating stands, small farms and roads. We incorporated data from our own study and from published studies across the Ovenbird geographic range, using an information-theoretic approach. Contrary to the ideal distribution hypothesis, Ovenbird territory density increased with upland openings, but density was similar across clearcut-edge-distance and forest-thinning categories. Relationships between reproduction and territory density were uncertain and therefore provided little evidence against the ideal free distribution hypothesis, but there was some evidence in favor of the alternative costly migration and ideal dominance hypotheses from the analysis of our own data and the meta-analysis, respectively. Finally, territories became denser when fecundity and pairing success were high during the previous year, and this supports the public information hypothesis. We recommend using measures of reproductive success in conjunction with territory density when assessing population status.

Selection of habitat by birds is manifest at different geographical scales. Most bird communities in forested ecosystems of the northern hemisphere are comprised of migratory species that represent more than 70% of the species and individuals within a forest patch. Historically from the 1950s to 1970s most studies were focused on the response of forest birds at the patch or forest stand scale. Since the 1980s, field studies have determined both microhabitat needs (e.g., individual trees or species) or the importance of entire landscapes in which populations occur. Advances in computation power, remote sensing, geographic information systems, and multivariate analytical techniques have greatly enhanced our understanding of bird habitat associations at these multiple geographic scales. Based on results for over 50 species, we illustrate the responses of forest birds in the Great Lakes region at three spatial scales: microhabitat, forest patch, and landscape. Management opportunities are easiest to implement at the forest patch scale, but cognizance of natural disturbance regimes, basic life history needs, and landscape context can enhance opportunities for conserving native forest bird assemblages.

Developing effective indicators of ecological condition requires calibration to determine the geographic range and ecosystem type appropriate for each indicator. Here, we demonstrate an approach for evaluating the relative influence of geography, geomorphology and human disturbance on patterns of variation in biotic indicators derived from multiple assemblages for ecosystems that span broad spatial scales. To accomplish this, we collected abundance information on six biotic assemblages (birds, fish, amphibians, aquatic macroinvertebrates, wetland vegetation, and diatoms) from over 450 locations along U.S. shorelines throughout each of the Great Lakes during 2002–2004. Sixty-six candidate taxon- and function-based indicators analyzed using hierarchical variance partitioning revealed that geographic (lake) rather than geomorphic factors (wetland type) had the greatest influence on the proportion of variance explained across all indicators, and that a significant portion of the variance was also related to response to human disturbance. Wetland vegetation, fish and bird indicators were the most, and macroinvertebrates the least, responsive to human disturbance. Proportion of rock bass, Carex lasiocarpa, and stephanodiscoid diatoms, as well as the presence of spring peepers and the number of insectivorous birds were among the indicators that responded most strongly to a human disturbance index, suggesting they have good potential as indicators of Great Lakes coastal wetland condition. Ecoprovince, wetland type, and indicator type (taxa vs function based) explained relatively little variance. Variance patterns for macroinvertebrates and birds were least concordant with those of other assemblages, while diatoms and amphibians, and fish and wetland vegetation were the most concordant assemblage pairs. Our results strongly suggest it will not be possible to develop effective indicators of Great Lakes coastal wetland condition without accounting for differences among lakes and their important interactions. This is one of the first attempts to show how ecological indicators of human disturbance vary over a broad spatial scale in wetlands.

Abstract Microsite, patch, and landscape conditions may interact to influence nest predation. In northern Minnesota, silvicultural and agricultural practices may be involved in recent increases in nest predators and regional declines in several ground-nesting songbirds. To examine this problem, we evaluated 17 hierarchical models of predation on Ovenbird (Seiurus aurocapilla) nests that included microsite variables, distances to edges, and amount of core forest within a 2-km radius surrounding six study plots. During 2000 and 2001, 157 Ovenbird nests were monitored to estimate nest predation rates. A model that included the main effects of litter depth and core forest area and an interaction term between the two best described variation in predation on Ovenbird nests (AICc weight = 0.83). The nest predation rate from this model was 0.51 ± 0.01 (mean ± SE), assuming mean values of litter depth and amount of core forest. Shallow litter was associated with higher nest predation in three plots surrounded by less core habitat (40–60 ha), whereas there was no relationship in three plots surrounded by more core area (100–150 ha). Management that promotes deep leaf litter and the maintenance of large, intact forest tracts will likely benefit Ovenbirds and other forest songbirds. Factores que Influencian la Depredación de Nidos de Seiurus aurocapilla en los Bosques del Norte: Interacciones a través de las Escalas Espaciales

Submergent aquatic vegetation (SAV) is a powerful indicator of environmental conditions in both marine and fresh water ecosystems. Quickbird imagery was used to map SAV at three sites across the Great Lakes. Unsupervised classifications were performed at each site using summer Quickbird sensor data. At one site, a multi-temporal classification approach was added, combining visible red difference (May-August) with August red and green visible band data. Multi-temporal SAV classification was superior to single-date results at this site. Muck bottom was not seriously confused with SAV, which was unexpected. Multi-temporal classification results showed less confusion between deep water and SAV, although spectral variability due to sub-surface sandbar structure was a source of error in both single- and multi-date classifications. Nevertheless, some of the confounding effects of water column on SAV classification appear to have been mitigated using this multi-temporal approach. Future efforts would be well served by incorporating detailed, continuous, bathymetry data in the classification process. Quickbird sensor data are very useful for classifying SAV under US Great Lakes conditions. However, regional classification efforts using these data may be impractical at this time, as high cost, rigid tasking parameters and unpredictable water conditions limit availability of suitable imagery.

Aim We examined relationships between breeding bird distribution of 10 forest songbirds in the Great Lakes Basin, large-scale climate and the distribution of land cover types as estimated by advanced very high resolution radiometer (AVHRR) and multi-spectral scanner (MSS) land cover classifications. Our objective was to examine the ability of regional climate, AVHRR (1 km resolution) land cover and MSS (200 m resolution) land cover to predict the distribution of breeding forest birds at the scale of the Great Lakes Basin and at the resolution of Breeding Bird Atlas data (5-10 km(2)). Specifically we addressed the following questions. (1) How well do AVHRR or MSS classifications capture the variation in distribution of bird species? (2) Is one land cover classification more useful than the other for predicting distribution? (3) How do models based on climate compare with models based on land cover? (4) Can the combination of both climate and land cover improve the predictive ability of these models.Location Modelling was conducted over the area of the Great Lakes Basin including parts of Ontario, Canada and parts of Illinois, Indiana, Michigan, New York, Ohio, Pennsylvania Wisconsin, and Minnesota, USA.Methods We conducted single variable logistic regression with the forest classes of AVHRR and MSS land cover using evidence of breeding as the response variable. We conducted multiple logistic regression with stepwise selection to select models from five sets of explanatory variables (AVHRR, MSS, climate, AVHRR + climate, MSS + climate).Results Generally, species were related to both AVHRR and MSS land cover types in the direction expected based on the known local habitat use of the species. Neither land cover classification appeared to produce consistently more intuitive results. Good models were generated using each of the explanatory data sets examined here. And at least one but usually all five variable sets produced acceptable or excellent models for each species.Main conclusions Both climate and large scale land cover were effective predictors of the distribution of the 10 forest bird species examined here. Models generated from these data had good classification accuracy of independent validation data. Good models were produced from all explanatory data sets or combinations suggesting that the distribution of climate, AVHRR land cover, and MSS land cover all captured similar variance in the distribution of the birds. It is difficult to separate the effects of climate and vegetation on the species' distributions at this scale.

Dietary samples from nestling Tree Swallows (Tachycineta bicolor) in northwestern Minnesota were compared to invertebrate availability as measured by aerial tow nets. The majority of the biomass in the nestlings' diet was adult insects with larval stages of aquatic origin, while absolute numbers of insects of both aquatic and terrestrial origin were similar. Orders of invertebrates in the diet and available were similar in number but not in biomass. Diet showed little variation by time of day, date of sampling or the age of the nestling. The mean number of odonates in the nestling Tree Swallows' diet increased exponentially as the percentage of open water and open water + cattail marsh increased within a 400-m foraging radius.

We studied how forest-bird nest success varied by landscape context from 1996 to 1998 in an agricultural region of southeastern Minnesota, southwestern Wisconsin, and northeastern Iowa. Nest success was 48% for all nests, 82% for cavity-nesting species, and 42% for cup-nesting species. Mayfield-adjusted nest success for five common species ranged from 23% for the American Redstart (Setophaga ruticilla) to 43% for the Eastern Wood-Pewee (Contopus virens). Nest success was lowest for open-cup nesters, species that reject Brown-headed Cowbird (Molothrus ater) eggs, species that nest near forest edges, and Neo-tropical migrants. The proportion of forest core area in a 5-km radius around the plot had a weakly negative relationship with daily survival rate of nests for all species pooled and for medium or high canopy nesters, species associated with interior and edge habitats, open-cup nesters, and nests located between 75 and 199 m from an edge. The proportion of forest core area was positively related to daily survival rate only for ground and low nesters. Our findings are in contrast to a number of studies from the eastern United States reporting strong positive associations between forest area and nesting success. Supported models of habitat associations changed with the spatial scale of analysis and included variables not often considered in studies of forest birds, including the proportion of water, shrubs, and grasslands in the landscape. Forest area may not be a strong indicator of nest success in landscapes where all the available forests are fragmented.

▪ Abstract Ecological indicators have widespread appeal to scientists, environmental managers, and the general public. Indicators have long been used to detect changes in nature, but the scientific maturation in indicator development primarily has occurred in the past 40 years. Currently, indicators are mainly used to assess the condition of the environment, as early-warning signals of ecological problems, and as barometers for trends in ecological resources. Use of ecological indicators requires clearly stated objectives; the recognition of spatial and tempor al scales; assessments of statistical variability, precision, and accuracy; linkages with specific stressors; and coupling with economic and social indicators. Legislatively mandated use of ecological indicators occurs in many countries worldwide and is included in international accords. As scientific advancements and innovation in the development and use of ecological indicators continue through applications of molecular biology, computer technology such as geographic information systems, data management such as bioinformatics, and remote sensing, our ability to apply ecological indicators to detect signals of environmental change will be substantially enhanced.

Regression models were developed to predict relative bird abundance in a naturally heterogeneous landscape using patch and landscape spatial scales. Breeding birds were surveyed with point counts on 140 study sites in 1997 and 1998. Aerial photographs were digitized to obtain habitat patch information, such as area, shape, and edge contrast. Classified remote-sensing data were gathered to provide information on landscape composition and configuration within a 1-km2 area around the study sites. Stepwise multiple linear regression was used to develop 40 species-specific models within specific habitat types using patch and landscape characteristics. In 38 out of the 40 models, area of the habitat patch was first selected as the most important predictor of relative bird abundance. Variables related to the landscape were retained in 6 of the 40 models. In this naturally heterogeneous region, the landscape surrounding the patch contributed little to explaining relative bird abundance. The models were evaluated by examining how well they predicted relative bird abundance in a test set not included in the original analyses. The results of the test data were reasonable: >79% of the test observations were within the prediction intervals established by the training data.

ABSTRACT: Forest buffers adjacent to water bodies are widely prescribed in forest management to protect ecological functions of riparian systems. To date, buffers have been applied on the landscape uniformly without quantifying their effectiveness or the effects they have on landscape characteristics. Our objective was to quantify landscape characteristics (amount of edge and interior forest) when buffers were applied to water bodies in a 100 by 100 km area of northern Minnesota. We used a Landsat classified image in a geographic information system platform to apply two buffer widths −28.5 m and 57 m — to water bodies, including nonforested wetlands, intermittent or perennial streams, and lakes. A total of 107,141 ha (18.3 percent) of the forest area was adjacent to and within 28.5 m of these water bodies, while 201,457 ha of forest was within 57 m, representing 34.4 percent of the total forest area. Imposing a 28.5 m buffer on water bodies increased the amount of edge and interior forest in the study area. When water bodies were buffered with a 57 m forest strip, we found a slight increase in forest edge from the current condition, and this buffer width resulted in the largest amount of interior forest. Interior forest increased with the 57 m buffer due to the density of water bodies in this region; adjacent water bodies coalesced when buffers were applied and formed isolated forest islands that contained forest interior habitat. Instead of wholesale application of set width riparian buffers, we suggest that ecological conditions of riparian areas be evaluated on a site level and that areas that currently provide important riparian conditions be maintained on the landscape with appropriate management practices.

We constructed alternative spatial models at two scales to predict Brownheaded Cowbird (Molothrus ater) parasitism rates from land cover maps. The local-scale models tested competing hypotheses about the relationship between cowbird parasitism and distance of host nests from a forest edge (forest-nonforest boundary). The landscape models tested competing hypotheses about how landscape features (e.g., forests, agricultural fields) interact to determine rates of cowbird parasitism. The models incorporate spatial neighborhoods with a radius of 2.5 km in their formulation, reflecting the scale of the majority of cowbird commuting activity. Field data on parasitism by cowbirds (parasitism rate and number of cowbird eggs per nest) were collected at 28 sites in the Driftless Area Ecoregion of Wisconsin, Minnesota, and Iowa and were compared to the predictions of the alternative models. At the local scale, there was a significant positive relationship between cowbird parasitism and mean distance of nest sites from the forest edge. At the landscape scale, the best fitting models were the forest-dependent and forest-fragmentation-dependent models, in which more heavily forested and less fragmented landscapes, had higher parasitism rates. However, much of the explanatory power of these models results from the inclusion of the local-scale relationship in these models. We found lower rates of cowbird parasitism than did most Midwestern studies, and we identified landscape patterns of cowbird parasitism that are opposite to those reported in several other studies of Midwestern songbirds. We caution that cowbird parasitism patterns can be unpredictable, depending upon ecoregional location and the spatial extent, and that our models should be tested in other ecoregions before they are applied there. Our study confirms that cowbird biology has a strong spatial component, and that improved spatial models applied at multiple spatial scales will be required to predict the effects of landscape and forest management on cowbird parasitism of forest birds.

The prairie sharp‐tailed grouse Tympanuchus phasianellus campestris occurs throughout the north central region of North America. It is of management concern because it has decreased in the southeast portion of its range over the past three decades, including marked declines in Minnesota and the Great Lakes region, USA. Although there is general knowledge about the habitat requirements for this species, no quantitative lek site or landscape information has been documented. We quantified landscape composition around active and inactive sharp‐tailed grouse lek sites and random points in brush landscapes in northeast Minnesota at multiple scales (200–3,000 m radii circles). Our objective was to compare landscape composition among these sites. We also developed a model to predict the probability of grouse lek site occurrence in the study area. Landscape composition around active and inactive lek sites differed from each other primarily at the 500 m and 1,000 m radii scales. Inactive sites had higher proportions of upland forest and brush cover types and active sites had a higher percentage of native grass than inactive sites. No differences were found in landscape composition between site types at the 200 m radius scale and only one landscape variable (number of cover types) was different at the 3,000 m radius scale. We found non‐random distributions of this grouse species at four different scales. Random brush land sites differed from both active and inactive sites having higher percentages of forest and brush cover. In contrast, lek sites had more bare ground, emergent aquatic vegetation, bog brush and roads than the random points. A regression model for the grouse at the 3,000 m scale was used to predict the probability of grouse occurrence in the landscape. The model resulted in a spatial map with about 8% of the area having a probability of grouse occurrence of >80%. This information can be used to locate new lek sites and to guide management activities for this species.

We completed an integrated, 6–year study on the potential ecological effects of two mosquito control agents, methoprene (applied as Altosid TM sand granules) and Bacillus thuringiensis var. israelensis (Bti, applied as Vectobac‐G TM granules), on zooplankton, insects, and breeding birds in wetlands of central Minnesota, USA, from 1988 to 1993. The study was a before‐and‐after design with pretreatment (1988‐1990) and posttreatment (1991–1993) of 27 wetlands. Study sites were randomly selected and placed within one of three groups of sites, nine control, nine Bti ‐treated, and nine methoprene‐treated. Selected populations of zooplankton, insects, and breeding birds were sampled within each of these wetlands. Insect densities were reduced by 57 to 83% and biomass was reduced by 50 to 83% in the second (1992) and third (1993) years of treatment. No negative effects on zooplankton or breeding birds could be attributed to treatment or changes to insect communities. Many factors may explain the lack of effects on breeding birds including, reductions in insects occurred after the nesting season was over, nest loss rates due to predation were very high (70%) and may have been a greater limiting factor to birds than mosquito control, and the density of breeding birds may be below carrying capacities, especially because not all wetlands in the landscape were treated and sufficient food may have been available. It is unclear what the long‐term consequences of insect reductions mean to wetland health. The lack of close coupling between zooplankton, insects, and breeding birds probably reflects the ecological complexity of these wetlands such as the presence of other limiting factors on population distribution and abundance. Although the study period was relatively long (3 years of treatment) compared with most ecological studies of pesticides, it may not have been long enough to fully predict the effects of decades of continued mosquito control.

Because logging has replaced fire as the most extensive and frequent disturbance regime in northeastern Minnesota, monitoring bird populations and their habitats has become increasingly important. We surveyed early-successional forests created by fire or logging for birds and their habitat during the 1994 and 1995 breeding seasons. We found that overall bird species richness and number of individuals (territorial males/ ha) were higher (P < 0.05) in burned forests than in logged forests. The American crow (Corvus brachyrhynchos), house wren (Troglodytes aedon), common yellowthroat (Geothlypis trichas), clay-colored sparrov (Spizella pallida), song sparrow (Melospiza melodia), Lincoln's sparrow (M. lincolnii), and brown-headed cowbird (Molothrus ater) were more abundant in burned areas. The Nashville warbler (Vermivora ruficapilla), chestnut-sided warbler (Dendroica pensylvanica), black-throated green warbler (D virens), and mourning warbler (Oporornis agilis) were present in greater numbers in the logged areas. We related these differences in bird presence and abundance to vegetation differences in the burned and logged habitat types. Burned areas had higher densities of dead trees, wider size ranges of dead trees, and greater heterogeneity in the shrub layer. Logged areas had higher densities of live trees, more live tree species, and wider size ranges of live trees. Red maple (Acer rubrum) was the live tree species found in greatest abundance in logged areas. If management goals include simulating natural disturbances like fire and maintaining bird populations, more dead trees should be left within logged habitats and the variability among logged areas should be increased.

In this paper, recent studies of birds and small mammals inhabiting Populus (hybrid poplar and cottonwood) plantations are summarized. Plantations provide habitat at least as favorable for native birds and mammals (as evidenced by overall density, species richness, and species composition) as agricultural croplands. However, by the same measures, plantation habitat is poorer quality than natural or semi-natural forest. Bird and small mammal species composition on plantations is a mixture of openland (crop and grassland) and forest species that is unique compared to other nearby habitats, and does not resemble that of either grasslands or forests. Plantations may not function as forest at either habitat or landscape scales. For highly mobile animals such as birds, landscape composition plays a central role in determining occupancy of plantations. For less mobile organisms, within-plantation habitat quality is more critical. Sources of non-uniformity in plantation vegetation are important determinants of occupancy. Although unplanned variation in vegetation structure occurs on some plantations, assuring the presence of heterogeneity may require specific planning. There is no evidence of altered population interactions (nest predation or parasitism, small-mammal population performance, or interchange among local populations) as a result of plantation establishment.

Quantitative structure–activity relationship (QSAR) models are routinely used in predicting toxicologic and ecotoxicologic effects of untested chemicals. One critical factor in QSAR‐based risk assessment is the proper assignment of a chemical to a mode of action and associated QSAR. In this paper, we used molecular similarity, neural networks, and discriminant analysis methods to predict acute toxic modes of action for a set of 283 chemicals. The majority of these molecules had been previously determined through toxicodynamic studies in fish to be narcotics (two classes), electrophiles/proelectrophiles, uncouplers of oxidative phosphorylation, acetylcholinesterase inhibitors, and neurotoxicants. Nonempirical parameters, such as topological indices and atom pairs, were used as structural descriptors for the development of similarity‐based, statistical, and neural network models. Rates of correct classification ranged from 65 to 95% for these 283 chemicals.