Thesis (M.S.)--Oregon State University, 1962. / Typescript. Includes bibliographical references (leaves 68-69). Also available on the World Wide Web.

This study considers the natural history and ecology of water-strider species occurring on the Fraser Plateau of south-central British Columbia. The overall aim was to assess the effects of spatial heterogeneity on factors controlling the distribution and relative abundance of gerrid species. The relationships among temperature, population dynamics and habitat use were investigated. From a regional perspective, spatial heterogeneity allows species population dynamics to converge in time while keeping them separate in space. , Laboratory rearing studies were used to calculate physiological time-scales for developmental processes. Patterns of mating behaviour, fecundity and fertility are described for Serris comatus and G. pinqreensis in the laboratory and G- incoqnitus in the field. Egg laying and juvenile growth are shown to be strongly temperature dependent in all species studied. Temperature thresholds for development differ, both among species, and often among stages of a particular species. Low thresholds recorded for G. pinqreensis can lead to significant growth advantages for this species during early spring. Instar differences seem to be adapted to seasonal temperature regimes experienced by gerrids. Gerris species and instars showed distinct optimum temperatures for survival. These optima vary with developmental thresholds. It is suggested that species may be best adapted for growth under different temperature regimes. A method was developed for estimating absolute densities in the field from relative abundance measures using linear regression techniques. Gerrid size and presence or absence of vegetation markedly affect capture rates. No effect of species or type of emergent cover was demonstrated. Availability for capture varies with leg-length in G. buenoi and G. pinqreensis. This relationship is used to estimate availability constants for other water-strider species. Field surveys between 1975 and 1977 established that G. buenoi, G. comatus and G. pinqreensis were the most abundant water-strider species in- the study area. Each of these was strongly associated with a single type of vegetation in the field; G. buenoi with grass/sedge habitats, G. comatus with floating vegetation and G. pinqreensis with bulrush habitat. Limnoporus dissortis and L. notabilis were commonly encountered on small, temporary ponds, G. incognitus was first taken during 1976 in the study area and small populations are confined to brushy, well-shaded habitats. G. buenoi, G. comatus and G. pinqreensis are all potentially bivoltine in the study area; Limnoporus spp. are univoltine. Generation timing varies tremendously among lakes and periods of maximum abundance for each species are not separated in time. Strong between-lake habitat associations in the field result proximately from habitat fidelity at the time of spring colonization. The tendency of gerrids to overwinter near the mother pond and trial and error habitat selection during spring dispersal enforce habitat fidelity during colonization. Species distributions within lakes are affected by habitat availability. Habitat preference experiments demonstrate that G. pinqreensis and G. comatus have active preferences for emergent cover and open habitats respectively. G. buenoi is a habitat generalist but its distribution can be affected by a tendency to avoid other species. Smaller stages of each species are found close to shore and often in areas of dense emergent vegetation. Enclosure experiments demonstrated that G. pinqreensis can exclude G. buenoi and G. comatus from bulrush habitats, which are most favorable for the growth and development of all species. Fifth instar G. buenoi and G. comatus showed greatest weight specific differences in foraging efficiency among late instars may help produce the habitat associations observed for these two species. Fifth instar G. pinqreensis showed poor survival when enclosed in freshwater habitats, suggesting the hypothesis that its distribution is restricted by the presence of surface-feeding predators other than water-striders. It is suggested that competition for space, predation, density-independent mortality and colonization dynamics all interact on the template of spatial heterogeneity to produce regional patterns of distribution and abundance. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

Sexual size dimorphism (SSD), or the difference in body size between males and females, is common in almost all taxa of animals and is usually assumed to be adaptive. Darwin's two main mechanisms for the evolution of SSD, sexual selection for larger males and fecundity selection for larger females, have often been demonstrated. However, males and females frequently share both genes and environment and more recent papers have noted that males and females must experience differences in lifetime selection on body size for SSD to be maintained. Over two generations I examined lifetime selection acting on adult body size (total length) in a common insect where females are larger than males, the waterstrider Aquarius remigis. Both fecundity selection for larger females and sexual selection for larger males are occurring in this species and both selective forces appear to target specific components of body size rather than total length; sexual selection targeting male genital length and fecundity selection targeting female abdomen length. While body size did not appear to influence adult prereproductive survival, longevity during the reproductive season was negatively related to body size for both sexes. When the opposing selection of reproductive success and reproductive longevity are combined, both males and females have an intermediate optimum body size. A remarkable result of this stabilizing selection was that the optimum size of males was smaller than that of females. I also examined the repeatability of reproductive success in both sexes and the trade-off between egg size and egg number. Finally, estimates of the quantitative genetic basis of the traits examined indicate that both male and female body size, and components of body size, are heritable and can respond to the selection detected. Components of body size in A. remigis are variable in both the degree and direction of sexual dimorphism and the genetic analysis indicates partial isolation of dimorphic and

No description available.

Experiments based on the method of mark-recapture can be used for estimation of the abundance of natural populations, for monitoring dispersion of groups or individual specimens within a population using group or individual marking. Semiaquatic bugs (Heteroptera: Gerromorpha) were marked and recaptured many times in the field during research, individual marking was much less used since marking of small insects is difficult. The aim of this work is to develop a method of individual marking of semiaquatic bugs so that it would meet conditions such as durability, legibility and non affecting health of the marked specimen. Semiaquatic bugs of Aquarius paludum, Gerris lacustris, Limnoporus rufoscutellatus (Gerridae) and Velia caprai (Veliidae) species were selected as experimental organisms. Partial aims of this thesis were to try using this method to describe the abundance of the monitored population and to monitor dispersion of the selected species, both at lotic (V. caprai) and lentic habitats (water striders, family Gerridae). A new method of individual marking of semiaquatic bugs was developed on the basis of modifications of the commonly used methods. After a series of tests and in-field research, this method proved to be suitable as it met the essential conditions for marking insects. The abundance of the monitored population was estimated and dispersion of the selected species (V. caprai) in running water was described by using this method. The partial aims of this thesis were met, too. It was confirmed that individuals of the V. caprai species move between the monitored areas along the water course. This inclination to move is greater than tendency to remain in the place of release. The gained data also show conclusively higher rate of movement of V. caprai specimens in the upstream direction, compared to the downstream. The tendency of V. caprai to travel larger distance upstream than downstream, is significant too. No statistically relevant difference in either direction of the water course (up or down) in the surpassed altitude difference was confirmed. The differences in the monitored phenomena between the sexes and generations were compared as well. The differences, however, were not significant. A movement of the adults of the water cricket Velia caprai thus can be characterized as an upstream migration, common in insects of lotic habtitats. A part of the study taking place in still waters showed, that G. lacustris specimens move on the surface of the pond, but not to a larger degree than they remain in place. On the other hand, A. paludum specimens were proved to move away from the place of release rather than remaining in that place. These also overcome greater distance than G. lacustris specimens.

<p>Diss. (sammanfattning) Umeå : Umeå universitet, 1992, härtill 8 uppsatser</p> / digitalisering@umu