Zoology - Theses
Permanent URI for this collection
Search Results
1 - 5 of 5
-
ItemThe evolution and ecology of the Gadopsis marmoratus complex( 1986)The Family Gadopsidae is the only family of fishes in South-eastern Australia which is both endemic to this region, and strictly confined to fresh water. Although several species of Gadopsis have been proposed, prior to the commencement of this study only one species, G. marmoratus Richardson, was formally recognised. This species was known to exhibit considerable geographic variation in morphology, colouration patterns, and size; and it had been suggested that the taxonomy of the genus was in need of review. This study is an attempt to: (i) determine the number of species in the, G. marmoratus complex; (ii) assess the relationships between G. marmoratus and any additional taxa in the complex; (iii) Formulate a biogeographic hypothesis to account for the geographic distributions and phylogenetic relationships of the taxa in the G. marmoratus complex; and, (iv) examine ecological characteristics of a population of Gadopsis from each side of the Great Dividing Range in Victoria. Analysis of meristic variation revealed that two sympatric taxa of Gadopsis were present in north-eastern Victoria. No evidence of hybridization between these taxa was found. The two taxa have different numbers of spines in the dorsal fin, and the specific status of the taxon with only two spines in the fin was recognised by the formal description of G. bispinosus Sanger. By adoption of an evolutionary species concept, and using univariate and multivariate statistical analyses of meristic variation, it was shown that G. marmoratus was comprised of two divergent taxa. It was proposed that these taxa be recognised as separate species, and for the purposes of this study are referred to as northern G. marmoratus and southern G. marmoratus. Multivariate statistical analyses of morphometric variation supported the proposal to recognise northern G. marmoratus and southern G. marmoratus as separate species. Electrophoretic analysis of protein variation also supported the recognition of northern G. marmoratus and southern G. marmoratus, and confirmed that hybridization was not occurring between G. bispinosus and northern G. marmoratus. The level of genetic divergence between northern G. marmoratus and southern G. marmoratus was less than that between both of these taxa and G. bispinosus. This result was interpreted to indicate a close phylogenetic relationship between northern G. marmoratus and southern G. marmoratus, and supported the relationships suggested by the phenetic analysis of meristic and morphometric variation. A biogeographic hypothesis to explain the geographic distributions and phylogenetic relationships of the three taxa was proposed. The ancestry of the Family Gadopsidae has been the subject of some dispute, and the alternative views on this subject were critically reviewed. Support was found for a basal percoid relationship for the family, and this result suggested that Gadopsis may have been of Gondwanan origin. The freshwater life-cycle of all the members of the family was interpreted as further support for a freshwater origin for Gadopsis. Several ecological characteristics of a population of G. bispinosus from the King Parrot Creek and G. marmoratus from the Yarra River system were compared. Gadopsis bispinosus in the King Parrot Creek is a small, lightly-built, short-lived species compared to G. marmoratus from the Yarra River system. The two species were found to have similar reproductive biologies. The discovery of additional species of Gadopsis has created the need for further examination of the evolution and ecology of the G. marmoratus complex, and suggestions for such further study are included at the end of this study.
-
ItemThe feeding and breeding biology of the sacred ibis Threskiornis aethiopicus in southern Victoria( 1984)This study aimed to elucidate the major selective factors affecting the biology, and particularly the breeding ecology of the Sacred Ibis (Threskiornis aethiopicus) in Australia. A comparative study of the breeding ecology of the Family Plataleidae in Australia was undertaken to define the ecological niche of the Sacred Ibis. The Australian ibis and spoonbills have very similar breeding ecology to their conspecifics and congeners elsewhere in the world. However, the breeding success of Australian birds appears to be limited by food supply whereas, in African members of the Family, for example, breeding success is limited by predation. In Australia, Sacred Ibis exhibit two broad responses to their environment: some populations showed adaptations in their breeding to an unpredictable environment; and, other populations have developed complex breeding strategies that are dependent on a highly predictable set of environmental conditions. In unpredictable environments, Sacred Ibis do not breed regularly but rather breeding is closely tied to the variable environmental conditions; the ibis move away from the breeding site when the area dries out. In unpredictable environments, clutch size is adjusted to the conditions and the ibis may employ multiple brooding. Where the environment is much more predictable, Sacred Ibis breed on a very regular cycle. In these environments, ibis are highly sedentary and clutch and brood size and multiple brooding are adjusted to maximise seasonal reproductive success, that is, Sacred Ibis raise fewer offspring per brood than the apparent maximum number possible as a trade-off against raising more broods in each breeding season. The timing and duration of the breeding attempts has had a major effect on the mating system. Sacred Ibis are essentially monogamous but one case of apparent polygyny was found. The mating system is also characterised by a high rate of promiscuous copulation and changes of mate between breeding attempts. The roles of male and female in post-fledging care of young and costs/benefits to life-time fitness are discussed. The selective factors maintaining colonial nesting are reviewed and the single most important evolutionary pressure affecting the breeding ecology of the Sacred Ibis is finding food; predation was shown to be unimportant.
-
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.
-
ItemEcological studies of barnacles in temperate mangrove forests( 1997)I have examined the horizontal distribution and abundance of Elminius covertus across three zones, landward, middle and seaward, of mangrove forests at Rhyll, Phillip Island, Victoria during 1995-1997. In the seaward zone of the forest, the vertical abundance of E. covertus between 0-15 cm from the bottom was also investigated. To determine what processes affect these horizontal and vertical patterns, presettlement, settlement and recruitment of E. covertus have been examined. The horizontal distribution of adults reflected the horizontal pattern of recruitment and settlement. The horizontal pattern of settlement was determined by larval supply and larval behaviour. Post-settlement factors had little influence on this pattern. Consequently, the horizontal pattern of adults were ultimately explained by patterns of larval supply and larval behaviour. The distribution of adults on pneumatophores reflected the vertical pattern of recruitment, but contrasted with the vertical pattern of settlement. Variability in the vertical distribution of settlers reflects larval settling behaviour not larval availability and the vertical pattern of recruits and adults is determined by post-settlement mortality. The patterns of settlement of E. covertus on seedlings of Avicennia marina in the seaward zone of the forest were also documented, with the greatest density of barnacles found on the stem, followed by the lower-leaf and upper-leaf surfaces. No further studies were undertaken to test what processes determine this pattern. The presence of E. covertus produced no negative effects on the survival and growth of seedlings of A. marina. Seedling survival appears to depend on other factors, such as, intermittent smothering by drift algae, seagrasses, and sediment as well as unfavourable climatic conditions, especially low temperatures and strong winds and currents.
-
ItemThe ecology of Australonereis ehlersi (Augener, 1913) and Ceratonereis erythraeensis Fauvel, 1919 (Polychaeta, nereidae) living offshore from the Werribee sewage-treatment farm, Port Phillip Bay, Victoria, Australia( 1981)Summary: 1. The ecology of the nereid polychaetes Ceratonereis erythraeensis and Australonereis ehlersi was studied along intertidal and shallow subtidal sandflats offshore from the Werribee Sewage-treatment Farm, Port Phillip Bay, Victoria. 2. Populations were sampled monthly from February, 1976 to April, 1977 at 24 stations along 2 km of shoreline. 3. The mouth of the Little River and the 145 W drain were centred within the study area; secondarily-treated effluent is released from this drain, and flows over the intertidal area. The effluent is high in nutrients and low in suspended solids. 4. Both nereids were abundant at Werribee, but displayed divergent distributions. Ceratonereis was distributed intertidally with very dense aggregations at the 145 W drain (mean densities up to 14,000 individuals/m2) and at Station 2, about 400 m southwest of the Little River. Australonereis rarely was collected at the drain; this nereid was more abundant in intertidal and subtidal areas away from the drain. Mean densities reached up to 3,000 individuals/m2 during periods of recruitment. 5. Factor analysis showed Ceratonereis to be closely associated with muddy-sands of the upper-intertidal area, while Australonereis was associated with well-sorted, fine-sand habitats of the lower intertidal and shallow subtidal regions. 6. Examination of gut material revealed that both species mainly were selective deposit feeders. Ceratonereis ingested a wide range of grain sizes (medium sand to silt and clay) compared with Australonereis (mainly silt and clay). Ceratonereis also consumed dead or living animals, if available, therefore displaying a relatively broad diet. Australonereis strictly consumed fine sediments, and may be a suspension feeding nereid; this behaviour would be compatible with its tubicolous existence in fine-sand habitats. 7. Food for both species is micro-organisms (such as bacteria, protozoans, diatoms, and dinoflagellates) associated with mineral grains, detritus, and organic mineral aggregates. Production by this microbiota is 600 to 700 times greater than similar sand habitats in the Bay. Food, therefore, probably represents an unlimited resource for the particle-consuming nereids. 8. Both nereids live about 1-1.5 years, display rapid growth, reproduce from spring to autumn, and probably die after spawning. Ceratonereis brooded embryos in specially constructed tubes; 13-15setiger-stage juveniles emerged after about 4-6 weeks of incubation. A description of the development of the embryo is given. In contrast, Australonereis produced a free-swimming larva; duration in the plankton and development is unknown. 9. Ceratonereis was a major prey item of red-necked stints Calidris ruficollis, sharp-tailed sandpipers C. acuminata, and curlew sandpipers C. ferruginea. These waders consumed medium- to large-sized Ceratonereis, and most likely are responsible for controlling densities of this nereid in intertidal areas at Werribee. 10. Factors which regulate the distribution of both nereid are discussed. Ceratonereis is considered a "pollution-tolerant” species whose subtidal distribution probably is controlled by invertebrate and fish predators. Australonereis is less tolerant of stressful conditions, and densities at the drain may be limited by physical factors and biological competition for space.