Any events that challenge the survival of living organisms may be classified as stressors. These stressors could include, for example, lack of food, increased population pressure, predatory pressure, climatic events or in the case of humans, loss of a loved one, lack of financial security or uncertainty in the future. Although most physiological systems are affected by stress, those systems that regulate reproductive physiology and behaviour are the most sensitive. All multicellular organisms show a stress related effect on reproduction, although the more complex organisms, such as mammals,...