Zoology - Theses
Permanent URI for this collection
Search Results
1 - 4 of 4
-
ItemNo Preview AvailableStudies in population genetics(University of Melbourne, 1959)Population genetics and. population dynamics have formed two distinct avenues of approach to a field of study which has become increasingly important over the last thirty years. Each has proved highly susceptible to mathematical analysis and to quantitative, rather than merely descriptive, treatment. It is, however, surprising to find that relatively little has been done to unite these two aspects of population biology, while in each theoretical work has tended to outstrip the small foundation provided by the observations so far recorded in the literature. Thus Birch (1957.P.217) was led to say... "I am quite sceptical of the predictive value of such mathematical models as have to date been proposed for natural populations". More serious still is the fact that the attempt to fit slender experimental data to such models has often blinded the experimenter to the possibility that factors of importance other than those considered in his model may contribute to the observed properties of the population. In particular, there has been little attention given to the genetic control of the form and rate of population growth; the work of Buzzati-Traverso (1955) was the first major experimental analysis to produce useful results along these lines. Much of the work on Drosophila populations has been done on small breeding groups which have been assumed to have reached an equilibrium density, although it seems likely that laboratory populations of Drosophila develop in the same way as those of Lucilia (Nicholson, 1954 and earlier papers), in which the population number fluctuates quite widely about a mean, not absolute, "equilibrium" level. Further, the number of individuals in the populations has not usually been determined with accuracy, so that it has seldom been possible to study small changes in population size. Preoccupation with "competition" experiments involving oligogenic markers has led even experienced workers to ignore the importance of modifying influences, particularly polygenic systems, associated with the genetic background. In this connection Buzzati-Traverso (loc.cit.) stated: "The fact is that the change in frequency of a single gene (or chromosome) during a number of generations means that the individuals carrying its allele will produce more or fewer adult offspring in the next generation than the individuals not carrying it. The factor which is decisive for changing frequency is a "productivity differential" involving of necessity the whole genotype and not one gene alone, for the latter will have different survival values in different genetic milies. Some extreme mutants, like those mostly used in laboratory experiments, may affect specifically the productivity of its carriers to such an extent as to make the effects of the rest of the genotype and of interactions of the mutant with it insignificant. But under natural conditions the commonest ease is very likely that of 'small* mutants where the natural selection mechanism probably involves many genes at one time" Even in the case of 'extreme' mutants erroneous or unsupported conclusions have been published (see later discussion of the relative adaptive values of the alleles at the white locus of Drosophila given by Merrell & Underhill, 1956); while in other instances over-emphasis of one particular factor has often prevented a balanced statement of the factors operating in laboratory population experiments. The discovery of selective mating in Drosophila, for example, resulted in the application of mating test results to population cage results without regard to other factors which might be causing the observed gene frequency changes. The work of Nicoletti & Solima (1956) and Morpurgo & Nicoletti (1956), amongst others, has passed largely unnoticed, although these authors adduced considerable evidence to support their view that selective mating is in fact not a controlling factor in laboratory cage competitions even where it can be demonstrated to occur in mating tests of the genotypes involved. In the same way, a sharp distinction has not always been made between the overall adaptive value of a genotype in a particular environment. The differential migration rates reported by liar land & Jackson (1958) under the title �Advantage of the white eye mutant of Drosophila melanogaster over the wild type in an artificial environment" provides an instance of such confusion. The only real measure of "advantage" or "superiority" is the relative contribution of a genotype to the gene pool of the succeeding generation, but these authors mention no breeding experiments at all. It is, however, clear that they have identified one of the factors which might be of importance in determining the frequency of white relative to that of its wild type allele in populations maintained in a particular environment. The main object of the present work has been to investigate further the relation of the genetic structure of a population to its rate and type of growth. Some attention has been given to problems of the sex-ratio and to change in gene frequency; in each case the underlying mechanisms have been studied. Emphasis throughout has been placed on the determination of the relative importance of the possible component factors under conditions of intense competition such as those found in population cage experiments.
-
ItemHistory, habitat and management: considerations in the selection of potential reintroduction and translocation sites for the brush-tailed rock-wallaby, Petrogale penicillata, in East Gippsland Victoria( 2002)Currently, there are estimated to be no more than 25 Brush-tailed Rock-wallabies, Petrogale penicillata, of Victorian origin remaining, with half of these in captivity as part of a breeding program. The decline of Brush-tailed Rock-wallabies has been attributed to several factors including hunting, predation, competition and stochastic events such as wildfire and disease. In Victoria, rock-wallabies have continued to decline in number, even after the cessation of hunting and implementation of an intensive predator control program. Without the intervention of captive-breeding and reintroduction or translocation programs, this critically endangered species will soon become extinct in Victoria. Reintroduction and translocation are becoming increasingly popular in the recovery of endangered species, however, many past attempts have had unknown or poor success rates. Conditions influencing the success of reintroduction and translocation programs are not well understood and for the most part, past efforts have been conducted in an ad hoc manner with little monitoring and documentation. One of the factors considered important in success is identification and selection of sites with high habitat quality, as unfavourable habitat is likely to result in the loss of animals through dispersal, predation or lack of other essential requirements. In addition to Wakefield (1961) and Short's (1980) observations of Brush-tailed Rock-wallabies occupying restricted habitat, presumably in response to the introduction of the Red Fox, Vulpes vulpes, this study found that there has been further restrictions in habitat use in East Gippsland, Victoria since the 1960s. Extant Brush-tailed Rock-wallabies sites were found to be larger than unoccupied sites, face predominantly north to north-east, have a general slope greater than 45° and a greater number of ledges per 100m of transect. It was also found that rock-wallabies preferred larger refuges with more than one entrance, low exposure to weather and another refuge or ledge within 10m. Preferred ledges were also large, faced predominantly north to east and within 10m of another refuge or ledge. The advantages these characteristics offer in the selection of future reintroduction and translocation sites are discussed. However, habitat suitability is not the only factor important to the selection of reintroduction or translocation sites. The selection of release sites will need to consider the ability to effectively undertake monitoring and management activities, and balance these requirements with the ecological requirements. This study also investigated past and current management (e.g., burning and predator control) of the study area and found that there has been a substantial change in land use that may have contributed to the persistence of Brush-tailed Rock-wallabies at the current sites in East Gippsland. This knowledge offers clues to future management. Other factors influencing site management are also discussed, and release sites with secure land tenure, which are easily accessible throughout the year and have a good network of vehicle tracks are considered favourable for reintroduction and translocation. In addition, release sites should not be in areas that conflict with visitor activities and should have strong community support.
-
ItemSystematics of the family Octopodidae (Mollusca:Cephalopoda) of South-Eastern Australia( 1988)The systematic of the inshore, benthic octopus of south-eastern Australia are examined. An historical survey of octopods from the region is followed by accounts of nominal species now recorded from waters of south-eastern Australia. Three genera and nine species are described and illustrated: Octopus australis, O. maorum, O. pallidus, O. superciliosus, Hapalochlaena maculosa, Grimpella thaumastocheir, plus three species of Octopus new to science. For each species, a study of external morphology and internal anatomy, type details, and distributional information, are included. Two species previously described from south-eastern Australia are reduced to synonymy: Octopus flindersi and O. duplex. Three species previously recorded from the region are excluded from the fauna: O.filamentosus, O. membranaceus and O. microphthalmus. A key to identification of valid species of octopus from south-eastern Australia is provided. The octopod fauna of the region comprises a high proportion of endemic species. Information on biogeography, and on affinities of some taxa with the fauna of New Zealand, is outlined.
-
ItemThe Australian freshwater malacostraca and their epizoic fauna( 1964)Because of their disjunctive distribution, the Parastacidae (Crustacea, Decapoda) and the Phreatoicoidea (Crustacea, Isopoda) have long been of considerable zoogeographic interest. The Phreatoicoidea are known from South Africa, India, Australia and New Zealand; the Parastacidae from Madagascar, New Guinea, Australia, New Zealand and South America. Of potentially great value, then, is a study of the epizoic fauna found closely associated with these fresh-water crustacea, and in some cases, sharing the disjunctive distribution. When new species of the peritrichous ciliate Lagenophrys were discovered on the cuticle of those crustacea, the opportunity was taken to initiate an investigation into zoogeographical implication of the distribution of a host-epizooid complex. The hosts were of established interest. Lagenophrys was of presumed interest because of low vagility during its dispersal phase, and because of the apparently high specificity of northern hemisphere members of the genus. In this thesis attention has been concentrated on the peritrichous epizooids. Although ideally a study should ultimately analyse the whole complex, the difficulties involved in such disparate taxonomies allowed of brief notes only on the other groups. Observations of the genus Temnocephala are included in the systematic section below but the other groups will be merely mentioned. Half the thesis is devoted to problems directly concerning the Parastacidae. For maximum value from the data on the epizoic fauna, precise determinations of host species were essential. In the course of investigation, it became clear that a review of Parastacidae systematics would be a prerequisite. (It will be seen that the Parastacidae form the most important group of hosts for the peritrichs investigated.) This situation arose partly from the lack of facilities at present obtaining in Australia for identification of the Parastacidae, and partly from ambiguities in the currently accepted systematics. These problems are posted in the section on Parastacidae, and their influence on problems of specificity is discussed in the final section.