Effects of Intra-populational Factors on Immunocompetence of Animals
种群内部因素对动物免疫功能的影响

The relationship between immunocompetence and population dynamics has been received much attention by animal ecologists recent years. The effects of intra\|populational factors on the immunocom\| petence were reviewed and some immunoregulation hypotheses were introduced. Population density and sociality are important factors to affect immune functions. Single living and low population density can suppress the immunocompetence for highly sociality species. However, the rapid changes in environmental conditions and population densities also can cause the modifications in immune functions. Social hierarchy can influence the immunocompetence, too. Within a population, dominant individuals usually have higher immune responses than the others. However, the subdominants and submissive individuals show different behaviors and different immune responses. The intensity, duration and frequency of the social conflict are close related to the immune functions. Sex and hormones are also important factors responsible for immunocompetence. Generally female individuals have higher immune responses than males and this was thought that mainly because of the functions of sexual hormones. Estrogen can enhance the humoral immunity but suppress the cell\|mediated immunity. Androgen can suppress both sides of acquired immunity. Some immunosuppression hypotheses (such as resource allocation hypothesis, immunocompetence handicap hypothesis, and immunoredistri\| bution hypothesis) are proposed based on the functions of sexual hormones. Reproductive effort can suppress the immunocompetence, therefore, animals usually have lower immune responses during reproductive period. The effect of mating system on immunocompetence is complex. Those male and females that face greater selection pressure for reproductive success may have higher immune responses. Animal's immune functions can influence the population dynamics. Within a population, individual's immunocompetence can be affected by both genetic and environmental factors, and the changes in capacity of immune responses can be related to the population fluctuation. To choose the immunological indices and their effects on the experimental results are evaluated. Some suggestions for the future research in this field are proposed.