Zoology - Theses
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ItemA comparative study of the flora and fauna of exotic pine plantations and adjacent, indigenous eucalypt forests in Gippsland, Victoria( 1978-01)The introduction and establishment of a new and markedly different environment within a long established natural system provides an excellent opportunity to study the principles of adaptation and colonisation by native species. In Australia, an example is furnished by the conversion of large areas of native eucalypt forests to mono-cultured plantations of Monterey Pine (Pinus radiata). The principal aim of this study was to assess which species of native mammals, birds and higher plants are able to utilise or occupy such plantations. Successional aspects of community structure, and colonisation in pine forest systems, were investigated by considering stands of different ages. A variety of adjacent native eucalypt forests provided controls and indicated the range of potential colonisers. Various habitats in both forest types were studied with regard to potential nest sites and availability of food, in order to determine those habitats most favourable for mammals and birds. The effect, on wildlife, of clearing eucalypt forests, but leaving forest remnants along gullies, was also assessed.
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ItemLife-history strategies of five species of intertidal limpet( 1977)The life-long strategies of five species of intertidal limpet, Cellana tramoserica, Notoacmea petterdi, Patella peroni, Patelloida alticostata, and Siphonaria diemenensis, which occur on the same shore but in different tidal zones, are considered in relation to their different environments. Attention is focused upon reproductive effort, which is defined as the percentage of assimilated energy devoted to reproduction, and which is measured for each species by using annual energy budgets. Environmental and demographic factors, which previous workers have suggested may have important influences on the level of reproductive effort, are investigated. In particular, interspecific differences in reproductive effort are compared with differences in the availability of food resources, differences in the magnitude of density-independent causes of mortality, differences in adult mortality rates and differences in extrinsic adult mortality rates (i.e. the adult mortality rates that would occur in the absence of expenditure of energy in reproduction.) The results of the present study indicate that reproductive effort is correlated with the availability of food resources, but that the primary determinant of the optimum level of reproductive effort is the rate of extrinsic adult mortality.
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ItemIndividual variation in reproductive success in the sacred ibis( 1988)Factors affecting the reproductive success of individually colour-banded sacred ibis, Threskiornis aethiopicus stricitpennis (Gould), at Healesville Sanctuary, Victoria, were studied from November, 1983, to March, 1987. Although the majority of clutches were of three eggs, the modal fledging success was two young, due to starvation of the third chick. The likely adaptive value of brood reduction is discussed. Characteristics of individuals (e.g. weight, body condition, culmen length, estimated age and dominance status) had no discernible effect on the number of chicks raised to fledging from one attempt (fledging success). The structure of the dominance hierarchy among male sacred ibis at Healesville is described. Dominance relationships among females were not consistent and, therefore, analysis of dominance status was restricted to males. Weight was the major trait contributing to a male's dominance status. High-status males achieved a higher seasonal reproductive success than did low-status males in two seasons when resources were apparently at low levels. Reproductive success over five consecutive years was largely dependent on survival, but, no significant relationships between individual traits and survival were found. Male sacred ibis achieving high seasonal reproductive success tended to survive better than did less successful males. Thus, variation in success measured over a short term (one season) underestimated the variation between males in success measured over a long term (five years). Variation in success of females also increased with the longer sampling period, but not at as fast a rate as variation in male success. Variation in success is therefore significantly greater in males than females, even though the sacred ibis is a monogamous species. Variability in reproductive success and number of attempts among individuals is facilitated by the changes of mate frequently observed in individuals breeding more than once in a season. Female sacred ibis were found to invest more in any one attempt than were male ibis. Consequently, individual females averaged fewer nesting attempts per season than did males and, with the sex-ratio of unity, females were a limiting resource for males. The resulting opportunity for selection on males is apparently fulfilled to some degree, with high-status, heavy and old males being particularly successful in competition for mates.