Climate, Population Viability, and the Zoogeography of Temperate Fishes

The feeding activity of warm‐ and coolwater fishes can be severely restricted during the long period of cold temperatures characteristic of winter in temperate zone lakes and rivers. The effect of such restriction is greater for smaller fish. Weight‐specific basal metabolism increases as size decreases; however, there is no corresponding increase in energy storage capacity. Thus, smaller fish tend to be less tolerant of starvation conditions because they exhaust their energy stores sooner. Such size dependence of starvation endurance has often been observed in laboratory experiments. In wild populations commonly subject to winter starvation, population viability hinges on the ability of young of year to complete a minimum amount of growth during their first year of life. From south to north, this ability is increasingly restricted as the growing season shortens and the starvation period lengthens. We show that this constraint is sufficient to explain the present locations of the northern distributional limit for yellow perch Perca flavescens in central and western North America, the northern distributional limit for Eurasian perch P. fluviatilis in Eurasia, and the northern distributional limit for smallmouth bass Micropterus dolomieui in central North America. We also forecast how shifts in North American climate may relax this constraint and permit both yellow perch and smallmouth bass to thrive well to the north of their present distributions.