Temperature, food and the availability of mates may all limit rates of egg production is freshwater diaptomids. We have used the reproductive phases of Diaptomus paliidus to develop an index of food limitation ( f ) and an index of mate limitation ( M ), each of which responds independently of temperature. The response of the food limitation index to high and low temperatures and high and low food concentrations was examined in a two-way factorial experiment in the laboratory. The index was highly responsive to a change in food concentration, stable during a change in temperature alone at the high food level and responsive to the synergistic interaction of food and temperature effects when both factors were limiting. Laboratory data indicate that the f index should not be biased by mate limitation unless male densities are 6.7 × 10 −l0 males 1 −1 or less. The mate limitation index was highly responsive to mate availability, and ranged from a low of 9–19 in the presence of abundant males to 100 in tbe absence of males. Applications of the f and M indices to a natural population of D. paliidus over 6 weeks indicated that both food and mate availability were limiting the reproductive rates of the copepods during the sampling period.
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Williamson et al. (1987) studied this question.