Numbers of wild anadromous Atlantic salmon (Salmo salar) have declined demonstrably throughout their native range. The current status of runs on rivers historically supporting salmon indicate widespread declines and extirpations in Europe and North America primarily in southern portions of the range. Many of these declines or extirpations can be attributed to the construction of mainstem dams, pollution (including acid rain), and total dewatering of streams. Purported effects on declines during the 1960s through the 1990s include overfishing, and more recently, changing ocean conditions, and intensive aquaculture. Most factors affecting salmon numbers do not act singly, but rather in concert, which masks the relative contribution of each factor. Salmon researchers and managers should not look for a single culprit in declining numbers of salmon, but rather, seek solutions through rigorous data gathering and testing of multiple effects integrated across space and time.

The systematics of the subfamilies Salmoninae and Coregoninae of recently glaciated regions are reviewed. Interrelation between systematics and fisheries biology are stressed, pointing out the abundance of intraspecific genetic diversity of some salmonid fishes manifested in ecological and behavioral specializations, but not necessarily by morphological divergence. Innate, reproductive homing behavior of salmonid fishes may allow closely related populations to exist in sympatry and maintain reproductive isolation. Examples are cited to support the contention that many sympatric "sibling species" have evolved from a common ancestor in postglacial times. Closely related, sympatric populations are a major taxonomic problem, but this phenomenon which allows a species to consist of genetically discrete units with reproductive isolation between the stocks is of great significance for fisheries management. Postglacial salmonid communities are typically fragile and highly susceptible to disruption or destruction by introductions, eutrophication, and exploitation. Every effort should be made to protect the genetic diversity of a species.

Weather and climate affect many ecological processes, making spatially continuous yet fine-resolution weather data desirable for ecological research and predictions. Numerous downscaled weather data sets exist, but little attempt has been made to evaluate them systematically. Here we address this shortcoming by focusing on four major questions: (1) How accurate are downscaled, gridded climate data sets in terms of temperature and precipitation estimates? (2) Are there significant regional differences in accuracy among data sets? (3) How accurate are their mean values compared with extremes? (4) Does their accuracy depend on spatial resolution? We compared eight widely used downscaled data sets that provide gridded daily weather data for recent decades across the United States. We found considerable differences among data sets and between downscaled and weather station data. Temperature is represented more accurately than precipitation, and climate averages are more accurate than weather extremes. The data set exhibiting the best agreement with station data varies among ecoregions. Surprisingly, the accuracy of the data sets does not depend on spatial resolution. Although some inherent differences among data sets and weather station data are to be expected, our findings highlight how much different interpolation methods affect downscaled weather data, even for local comparisons with nearby weather stations located inside a grid cell. More broadly, our results highlight the need for careful consideration among different available data sets in terms of which variables they describe best, where they perform best, and their resolution, when selecting a downscaled weather data set for a given ecological application.

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Ambush predators provide more persistent cues of predation risk compared to coursing predators and are predicted to exert stronger effects on behaviour of their prey. We studied anti-predator responses of ungulates by means of camera traps to an olfactory cue (fresh scat) of an ambush predator, the Eurasian lynx (Lynx lynx). Roe deer (Capreolus capreolus) and red deer (Cervus elaphus) both important prey species for lynx were not more vigilant when exposed to lynx scent, but reduced their visitation duration. Our results contrast with previously reported responses of red deer to scent from a coursing predator, the wolf (Canis lupus), where only vigilance and foraging behaviour but not visitation duration changed in response to wolf scat. This indicates that ungulates are able to recognize the risk of predation from predators with differing hunting modes based on olfactory cues and adjust their anti-predatory behaviour.