We analyzed how dissolved organic carbon (DOC) concentration in lakes of the North American temperate forest (Upper Great Lakes region) is related to nine catchment characteristics (lake area, lake perimeter, drainage area, ratio of drainage area to lake area, proportion of watershed occupied by wetlands, proportion of lake perimeter in wetlands, shoreline development, elevation, and watershed slope) and compared selected relationships to those from other regions across the globe. For the temperate lakes, the proportion of the lake perimeter and the proportion of the watershed occupied by wetlands were the best predictors of DOC in both univariate (r 2 ϭ 0.34 and 0.30, respectively) and multivariate regression models. Forested wetlands, in particular those with coniferous vegetation, explained the largest proportion of lake DOC variability. Wetlands with scrub-shrubs and emergent vegetation explained very little or no variability. Secondary to wetlands, lake DOC decreased with lake area and watershed slope. When we combined the temperate lake data set with that of 10 other geographical regions of the world (ranging from subtropical to tundra), the only two variables significant in predicting DOC were proportion of wetlands in the watershed (r 2 ϭ 0.36) and lake elevation (r 2 ϭ 0.34). We conclude that regional or small-scale DOC models likely have limited applicability in predicting DOC in other geographical areas of the world.

Most studies of the impacts of invasive species are done at small spatial and short temporal scales, greatly limiting generalizations to natural ecosystems. In contrast, we examined the long-term, whole-lake impacts of predation by the introduced rusty crayfish ( Orconectes rusticus ) on snail communities in 10 lakes in northern Wisconsin, USA. In 1987 and 2002, crayfish and snails were surveyed in lakes that initially differed in O. rusticus abundance; during the 15 years between surveys, crayfish abundance changed substantially in four lakes. In the two lakes where O. rusticus populations increased from low to high densities, large reductions occurred in snail abundance. As predicted, snails declined much more in habitats preferred by O. rusticus (sand and cobble) than in habitats that are avoided by the crayfish (muck). In the two lakes where O. rusticus abundance decreased dramatically after 1987, no significant increase occurred in snail densities, illustrating the difference in response time of snail populations to release from predation relative to increasing predation. Contrary to prediction, no consistent difference in snail species composition existed between high and low crayfish density lakes.

Invasive nonindigenous species are defined by their impacts: they substantially change native communities or ecosystems. Accordingly, invasive species might transform their habitats in ways that eventually become unfavorable to them, causing population declines or even extirpations. Here we use over 40 yr of systematically collected data on the abundance of the invasive rusty crayfish Faxonius rusticus from 17 lakes in northern Wisconsin, USA to explore whether population declines of this invader are related to the prevalence of rocky habitat, which shelters crayfish from predators and is unchanged by crayfish. We predicted that lakes with rock‐dominated substrates would be resistant to F. rusticus population declines, whereas lakes lacking rock‐dominated substrates would experience F. rusticus declines due to crayfish destruction of shelter‐providing macrophytes. We found that in nearly one‐half (47%) of the study lakes, F. rusticus experienced population declines over the study time period, and these lakes had significantly lower proportions of rock substrate than lakes that did not experience population declines. We recommend that more studies should investigate the potential for invasive species‐mediated community or ecosystem feedbacks to eventually contribute to their own population declines.

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