| Summary: | In a series of enclosure experiments (11 over 3 years) on the waterstrider Gerris buenoi, I demonstrated that food resources were limited by both intra- and interspecific competition in the field. Over a 20 fold range of egg production rates in control enclosures, food addition and interspecific competitor exclusion consistently increased egg production. The magnitude of these effects varied up to four fold among dates. Predators consistently reduced gerrid survival; the strength of this effect also varied greatly among experiments. Following a series of tests for enclosure effects, I conclude that both resources and predators limited fitness of adult G. buenoi in the wild, and that the strength of these effects varied dramatically among dates. The effect of reproductive rate on lifetime fecundity, longevity and senescence was investigated. Reproductive rate was an increasing function of food level, and longevity was a decreasing function of reproductive rate. There was no effect of food level on lifetime fecundity. Senescence of females was indicated by a progressive decline in egg quality (developmental stability and hatching success), and increased reproductive rate advanced this decline. Therefore, senescence occurs in G. buenoi, and reproductive rate advances its onset. The mating behaviour of G. buenoi was studied with a series of laboratory experiments and field observations. Mating is multiple, females are reluctant, males persistent and mating consists of a period of copulation followed by a guarding phase. Mating in females is shown to conflict with predator avoidance and foraging, but can reduce costly harassment by males. Mating females stop foraging and retreat to refuge. Increased predation risk to mating females results largely from increased capture success by predacious notonectids.
Females control most components of mating (copulation frequency, and male guarding duration), and I demonstrate that mating decisions made by females balance the costs and benefits to her. Mating frequency was significantly less when female foraging needs were increased, and females became more willing to mate when the cost of male harassment was increased. These results demonstrate a strong degree of female control of mating decisions, and support the convenience polyandry hypothesis for superfluous mating. === Science, Faculty of === Zoology, Department of === Graduate
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