Aim Northerly shifts, related to recent climate warming, have been observed in the distributions of taxa in many ecosystems and ecological roles. However, significant variation occurs among species in the magnitude of these shifts. Few studies have investigated the effects of climate warming on the distributions of freshwater species.Location A total of 1527 lakes across Ontario, Canada.Methods We used contemporary and historical survey data to examine the relationships between species occurrences and climate and to measure the magnitude and direction of northern range-boundary shifts in 13 warm and coolwater freshwater fishes. We also tested whether range-boundary shifts differed between baitfishes and sportfishes. We then related differences in species range-boundary shifts to species traits including those related to dispersal, reproduction and ecological niche breadth.Results Many fishes are now more likely to occur in lakes where climate was historically limiting. Sportfish northern range boundaries shifted northward significantly over nearly 30 years at a rate of approximately 12.9-17.5 km per decade depending on the measure used; in contrast, baitfish northern range boundaries often shifted southward. Also, species traits explained much of the variation in species range boundaries.Main conclusions The northern range boundaries of warm and coolwater sportfishes in Ontario lakes appear to be shifting northward as expected based on observed climate warming. These species are shifting at rates comparable with taxa in marine and terrestrial ecosystems around the globe. In contrast to expectations, the northern range boundaries of small-bodied baitfishes appear to often contract southward. Differences in range shifts by sportfishes and baitfishes may be related to dispersal, particularly by anglers and/or their ecological roles. Understanding the range-boundary shifts underway in Ontario lake communities will help predict future shifts by freshwater fishes.

Native communities are thought to mediate the establishment and performance of invasive species through competitive and consumptive interactions, a concept referred to as ''biotic resistance.'' We investigated the generality of this concept across ecosystems. Despite the conspicuousness of freshwater invasions, investigations of biotic resistance have focused mostly on terrestrial and, more recently, marine coastal communities. We collected in-situ studies that tested the impacts of native freshwater communities on invading primary producers and consumers. Meta-analysis demonstrated that evidence of competitive biotic resistance in freshwater habitats was not as strong as that in marine and terrestrial ecosystems. In freshwater ecosystems consumptive resistance was significantly stronger than competitive resistance and consumptive resistance appeared to be as strong in freshwater as in marine and terrestrial systems. The limited number of studies considering freshwater biotic resistance hindered our ability to understand the importance of factors including latitude, experimental duration, and method. However, the strength of biotic resistance varied among freshwater habitats; specifically, biotic resistance was strongest in lentic environments. Our analysis identifies mechanisms underlying biotic resistance in freshwater ecosystems that warrant further investigation given the potential ongoing and future impacts of invasive species in these systems.

We examined how the marine cottid fish Clinocottus acuticeps used vegetated microhabitats within an estuarine system in the Pacific Northwest, USA. C. acuticeps was more abundant and grew faster in microhabitats in algal beds compared with open microhabitats. Furthermore, the condition index (CI) increased in vegetated microhabitats and decreased in open habitats which, combined with the variability in growth measured in both habitats, suggests that fish may regulate their growth more narrowly when food resources and protective cover provided by the algal bed function as complementary resources. Reduced growth in open microhabitats may be a physiological response to increased predation risk. Additionally, giving-up densities (GUDs) were similar in both habitats, in both field and laboratory experiments, where fish foraged in the presence of predators and under different levels of protection by algae. These results, combined with the implications of the growth experiments, suggest that C. acuticeps utilizes a risk-reckless strategy in the face of a tradeoff between food and safety by maximizing food intake despite predation risk. Nevertheless, we maintain that the increased growth and lower predation risk associated with algae microhabitats imply that, ultimately, fitness may be higher in individuals that primarily use vegetated habitats.KEY WORDS: Habitat selection · Prey · Refuge · Clinocottus acuticeps · Giving-up density (GUD) · Risk-reckless Resale or republication not permitted without written consent of the publisher

Biodiversity conservation often is aimed at areas of high species richness and endemism. Our understanding of freshwater fish diversity in the Neotropics is biased by lack of exploration within mountainous regions that historically have been difficult to access. These regions are particularly likely to contain high species endemism. The upper Mazaruni River drainage is hydrogeographically and climatically distinct from the rest of the Essequibo Basin. Recent ichthyological expeditions to the upper Mazaruni discovered up to 32 species previously unknown to science and a fish assemblage with perhaps the highest level of endemism in the Neotropics. This unique ichthyofauna is threatened by gold mining that has severely degraded aquatic habitats and therefore requires immediate protection.

There is a poor understanding of the importance of biotic interactions in determining species distributions with climate change. Theory from invasion biology suggests that the success of species introductions outside of their historical ranges may be either positively (biotic acceptance) or negatively (biotic resistance) related to native biodiversity. Using data on fish community composition from two survey periods separated by approximately 28 years during which climate was warming, we examined the factors influencing the establishment of three predatory centrarchids: Smallmouth Bass (Micropterus dolomieu), Largemouth Bass (M. salmoides), and Rock Bass (Ambloplites rupestris) in lakes at their expanding northern range boundaries in Ontario. Variance partitioning demonstrated that, at a regional scale, abiotic factors play a stronger role in determining the establishment of these species than biotic factors. Pairing lakes within watersheds where each species had established with lakes sharing similar abiotic conditions where the species had not established revealed both positive and negative relationships between the establishment of centrarchids and the historical presence of other predatory species. The establishment of these species near their northern range boundaries is primarily determined by abiotic factors at a regional scale; however, biotic factors become important at the lake-to-lake scale. Studies of exotic species invasions have previously highlighted how spatial scale mediates the importance of abiotic vs. biotic factors on species establishment. Our study demonstrates how concepts from invasion biology can inform our understanding of the factors controlling species distributions with changing climate.