Temperature as an Ecological Resource

Ectothermic vertebrates respond to the temperature of theirhabitat in a manner that is remarkably similar to their responseto more traditional ecological resources such as food. We reviewthe response to temperature primarily from literature on fishesin terms of ecological concepts related to niche theory andcompetition. The width of the fundamental thermal niche is about4°C when measured by a mean plus and minus one standarddeviation of the distribution of temperature occupied in a laboratorygradient. Fish of temperate freshwater appear to fall into threethermal guilds along the temperature resource axis —cold,cool, and warm water fishes. Realized thermal niches are similarin central tendency to fundamental niches, but niche width appearsto be more narrow for the realized niche in limited sample data.The success of interference competition for space with preferredtemperature is tied to social dominance in a manner analogousto food competition. Thermal niche shifts in the face of interspecificcompetition for preferred temperature appear supported by onelaboratory study. Exploitation competition in respect to temperatureseems nebulous. If animals successfully compete for their thermalniche, growth and perhaps other measures of fitness are maximized.Cost/benefit models for thermal resources and food resourceslead to similar predictions about resource use. We suggest thatviewing temperature and other niche axes in the way ecologistshave viewed food resources would be useful.