ABSTRACT
This chapter introduces the theories and explains the thinking behind them, focuses on birds and mammals and refers to fish only occasionally. In temperate and high latitudes, where most research is conducted, almost all animals and plants reproduce seasonally, and only a few species, many of which are domesticated or live in close association with man, breed throughout the year. The central role played by energetics in determining the reproductive strategy of both individuals and populations was recognized by ecologists, and they have developed a good deal of theory to support their contentions. The chapter deals with the control of reproductive cycles by “physical” rather than the “social” external environmental factors. Animals are said to be refractory if they are insensitive to stimulation by exogenous conditions that at other times have effects on the reproductive system. Some of the clearest examples of refractoriness are seen in birds.
