Zoology - Theses
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ItemA temporal investigation of hybridisation in south-eastern Australian tree frogs( 2011)Hybridisation, the process in which individuals of two different species mate and produce hybrid offspring, has proven to be of great interest to evolutionary biology. Very few hybridising species complexes have been studied over long periods of time. Yet these long term studies can be particularly interesting for exploring the evolutionary processes maintaining species boundaries, and assessing how hybridisation patterns may change over time. In this thesis I explore hybridisation in the Litoria ewingii complex of south-eastern Australia, a classic system that has been studied for more than 40 years. This is the first study to incorporate molecular data, together with acoustic and morphological data, collected across two sampling periods spanning 40 years, to gain a detailed perspective of hybridisation dynamics in the L. ewingii complex. Microsatellite loci are particularly useful for hybridisation studies, as they can provide a direct estimate of gene flow among the hybridising species. I identified eight microsatellite loci that can be amplified in all four taxa of the L. ewingii complex: L. ewingii, L. paraewingi, L. verreauxii verreauxii and L. v. alpina. These loci were used to assess species boundaries and evolutionary processes maintaining hybridisation dynamics between L. ewingii and L. paraewingi. These markers will also provide an essential resource for future studies of gene flow and hybridisation among all species of the L. ewingii complex. Two species of the L. ewingii complex are broadly sympatric throughout their distribution in south-eastern Australia (L. ewingii and L. v. verreauxii). Although positive assortative mating has previously been shown to occur in sympatry, I found six individuals that were intermediate in morphology and acoustic structure. I provide the most conclusive evidence thus far for rare hybridisation between L. ewingii and L. v. verreauxii in regions of sympatry. This suggests that the strong divergence in premating isolation mechanisms provides an important barrier to gene flow. Hybrid zones that have been researched over long periods are particularly valuable for exploring processes involved in reproductive isolation. Litoria ewingii and L. paraewingi are such a study system, where they meet in a narrow hybrid zone in south-eastern Australia. A transect through this hybrid zone has been the focus of comprehensive studies over the last 40 years. I completed the first detailed genetic examination of the hybrid zone using the eight nuclear microsatellite loci and a mitochondrial DNA marker to characterise its structure and explore whether it was consistent with different theoretical hybrid zone models. Overall, I showed that the L. ewingii – L. paraewingi hybrid zone is best characterised as a tension zone, due to the low levels of hybridisation found within the hybrid zone and the coincidence and narrow width of the mtDNA and microsatellite clines. Thus, the balance between selection against hybridisation and dispersal of parentals into the zone is important for maintaining species boundaries between the two taxa. Furthermore, although reproductive compatibility was previously found to favour matings involving L. paraewingi females, surprisingly, a greater proportion of the identified hybrids had L. ewingii mtDNA, suggesting that further studies are required to fully understand the mechanisms maintaining species boundaries between L. ewingii and L. paraewingi. The long-term research on the L. ewingii – L. paraewingi hybrid zone provided a rare opportunity to assess changes in the hybrid zone structure. I compared contemporary mtDNA and male advertisement call data to equivalent historical data obtained from acoustic recordings and museum specimens collected in the late 1960s. Clinal analysis of the coincidence (same centre) and concordance (same width) of these traits indicated that the centre of the hybrid zone had shifted 1 km south over the last 40 years, although the width remained unchanged. The distribution of phenotypic variance also showed no significant change across the sampling period. The overall stability of the zone shows strong fit with the tension zone model, and suggests that changes in geography and population density may have contributed to the slight southward shift of the zone. This thesis highlights the importance of long-term studies of hybridisation to gain a detailed understanding of the processes maintaining species boundaries. Additionally, the utilisation of molecular methods, across both modern and historical samples, allowed a more comprehensive assessment of the factors that contribute to the maintenance and temporal evolution of the L. ewingii – L. paraewingi hybrid zone. My study contributes to a growing body of knowledge of hybridisation among members of the L. ewingii complex, and can be used to provide further understanding of factors that may influence speciation and hybridisation dynamics among this well researched amphibian species complex.
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ItemPlumage pattern function and evolution: a phylogenetic and comparative approach( 2011)Visual patterns, such as bars and spots, are common in the animal kingdom. In no other group are patterns so exquisite in their arrangement and coloration than in birds. Although bird plumage patterns appear to be visually diverse there are only four types of patterns, which can be broadly categorized into irregular and regular patterning. That these types of irregular and regular patterning are recursive is intriguing and speaks of an underlying shared mechanism on which selection can act. The prevailing assumption is that patterns predominantly function in camouflage, however evidence suggests that they also function in communication in a small number of birds. In particular it has been suggested that barred plumage patterns could be a signal of individual quality. In visual ecology, communication and camouflage seem to be in conflict with one another – visual signals are often conspicuous whereas camouflage has evolved to provide concealment. These ideas of pattern function need not be incongruous if patterns evolved a) for camouflage first and were subsequently co-opted by sexual selection for communication, and/or b) some patterns, specifically barred plumage, evolved for both camouflage and communication to overcome this functional compromise. To test these alternative ideas of pattern evolution I test whether a) patterns were co-opted for signaling in the model group waterfowl and gamebirds, and b) if the evolution of sexual dimorphism in barred plumage indicate camouflage and ⁄ or signaling functions across the class Aves. Additionally, I investigated whether development poses a constraint on pattern evolution in waterfowl and gamebirds. Tracing the most probable evolutionary pathway of plumage pattern evolution revealed that the ancestral state of plumage was uniform coloration. From uniform coloration, patterns initially evolved to be predominantly monomorphic, and subsequently evolved to be sexually dimorphic. In sexually dimorphic patterns, barred plumage frequently evolved in females and males, suggesting a role for both camouflage and communication. However, dimorphic spotted plumage only evolved in males suggesting it predominantly evolved for communication. Overall, it is likely Plumage pattern function and evolution: a phylogenetic and comparative approach ii that patterns originally evolved for camouflage and were subsequently co-opted for signaling. Focusing on the evolution of barred patterns by comparing their prevalence between the sexes I found a higher frequency of female- rather than male-biased sexual dimorphism, indicating that camouflage is its most common function. But I also found that, compared with other pigmentation patterns, barred plumage is more frequently biased towards males and its expression more frequently restricted to adulthood, suggesting that barred plumage often evolves or is maintained as a sexual communication signal. This illustrates how visual traits can accommodate the apparently incompatible functions of camouflage and communication. Lastly, I studied the recurrence of irregular and regular plumage patterns to explore why there are different kinds of patterns that are broadly recursive. By modeling pattern evolution I derived directionality and show that where species exhibit a single pattern, selection need not be constrained by development. However, instances of irregular and regular patterns in the same species are a result of selection on existing patterns. Together this demonstrates that the evolution of patterns is not difficult and that states of multiple pattern types are a result of selection.
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ItemExploring the links between nutrient cycling, macrofauna and environmental influences in estuarine sediments( 2011)Benthic environments form a key component of estuarine ecosystems; mediating the mineralization of organic matter and the recycling of nutrients whilst providing an important habitat for an array of fauna and flora. Estuarine environments tend to be more urbanised and industrialised than other coastal ecosystems, often becoming enriched with nutrients and subject to elevated loads of pollutants, such as heavy metals. The negative effects of these anthropogenic stressors have led to concerns regarding the condition and stability of estuarine environments. Excess nutrients interfere with the complex biogeochemical interactions that control the benthic nitrogen cycle, potentially leading to algal blooms and the sedimentation of high loads of organic matter which can subsequently deplete oxygen in bottom waters. Heavy metal contaminants impact the diversity and functioning of macrofauna communities and may interfere with biogeochemical microbial processes. Interactions between increased nutrients and heavy metal contaminants are complex: macrofauna influence the nitrogen cycle via bioirrigation and bioturbation activities, thus contaminant impacts on macrofauna diversity can also indirectly impact nutrient cycling. In this research project I explored the interactions between the effects of heavy metal contaminants, algal blooms, macrofauna functional activities and oxygen depletion and benthic biogeochemical processes in a multi-use temperate estuary, the Derwent, in south-eastern Australia, using a combination of spatial surveys and experimental approaches. Surveys found that variation in nutrient flux was best explained by dissolved oxygen (DO) conditions, total carbon (TC), benthic microalgae and macrofauna abundance. A positive relationship between DO concentration and NOx (nitrate + nitrite) and N2 fluxes and a negative relationship between DO and NH4+ and PO4- production was also indicated. Macrofauna distribution was best explained by depth, salinity, DO and bioavailable Zn and Pb as measured by diffusive gradient in thin-films metal sampling units (DGTs). Based on the results of the spatial survey, I ran manipulative laboratory experiments that tested the effects of short (< 24 hours) and long term (40 days) O2 depletion on nutrient fluxes and on the bioavailability of metals in Derwent sediments. Twenty-four hours of O2 depletion was sufficient to rapidly decrease the oxygenation and the O2 penetration depth of sediments within experimental laboratory cores. As a result NH4+ release from the sediment increased whereas NOx flux out of the sediment decreased, suggesting reduced nitrification efficiency. In addition, DGT sampling devices, which measure labile metals within sediments, detected a two-fold increase in pore-water Cd and a five-fold increase in Cu in surface sediments under reduced DO conditions. To understand the effects of extended hypoxia on nutrient cycling and metal availability and test if the effects would vary according to local environmental conditions within the estuary, I measured the flux of nutrients and metals between the sediment and water column in sealed cores incubated without O2 replenishment for 40 days using sediments collected from 3 sites with varying concentrations of contaminants, organic enrichment and macrofauna functional properties. There was an apparent relationship between how quickly the cores became hypoxic and the presence of different macrofauna functional groups. The presence of large numbers of benthic epifauna at one site, compared with infauna at another, potentially accelerated the onset of hypoxia. Further reductions in DO resulted in the mortality, decomposition and mineralisation of the macrofauna. Decomposition of epifauna was more rapid than infauna with an earlier and larger pulse of bioavailable nutrients (NH4+ and PO4+) to the water column at the epifauna dominated site. In contrast, sediments from a site containing little macrofauna and a high proportion of terrigenous organic material showed limited release of these nutrients. In the short-term hypoxia experiment labile metals accumulated in the pore-waters of surface sediments, intensifying the concentration gradient of metals across the sediment-water interface and increasing the likelihood of diffusive flux from the sediments. Therefore, I measured metal fluxes to the water column during the extended O2 depletion experiment. Manganese and Fe, which are known to significantly regulate the release of other divalent cations from sub-oxic sediments, fluxed from sediments from all sites as hypoxia developed. However, the release of As, Cd, Cu and Zn was comparatively low and unrelated to the degree of sediment contamination, although As release increased significantly under anoxic conditions. Importantly, the most significant release of Cu and Zn occurred within the first few days of hypoxia, suggesting that brief and recurring episodes of O2 depletion may present a greater risk for metal release than periods of extended hypoxia. The direct effects of reduced DO conditions on macrofauna assemblages were not measured, but I performed an experiment to assess whether the functional traits of a key and locally relevant macrofauna species, Cirriformia filigera, a metal-tolerant bioturbating polychaete worm, might alter the nutrient dynamics of highly contaminated sediments in this system. The presence of C. filigera resulted in a doubling of sediment metabolism and a tripling of denitrification, possibly as a result of C. filigera burrow construction and bioturbation. Oxygen enriched burrows infiltrate into deeper anoxic sediments resulting in a 3-D matrix of overlapping aerobic and anaerobic regions facilitating micro-organism activity and promoting nitrifier-denitrifier coupling. The large increases in NH4+ efflux measured most likely reflected the combined flushing of existing NH4+ from the sediment due to bioturbation, the diffusive and advective release of the products of OM hydrolysis in burrow walls plus excreted wastes. The key findings of this study are 1) DO declines compromise critical nutrient cycling processes within benthic sediments and the effects are modified by local biological and environmental conditions; 2) reduced DO concentrations can lead to an increase in metal availability in surface sediments resulting in small effluxes to the water column; 3) metal availability influences the distribution of macrofauna and 4) changes to the functional diversity of macrofauna communities are likely to have an effect on nutrient cycling. This work has worldwide application to urbanised coastal environments that are increasingly subject to anthropogenic stressors such as nutrient and organic enrichment, metal contamination and periods of hypoxia. In addition these results will assist environmental managers to identify sensitivities in the Derwent estuary and more reliably direct monitoring.
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ItemImpacts of habitat fragmentation on dispersal of native mammals( 2011)Habitat fragmentation is widely regarded as a major threat to biodiversity worldwide. In addition to the reduction of the total area of habitat available for wildlife, clearing of native vegetation creates disconnected patches of habitat immersed in a matrix, which does not provide resources for most species of wildlife. The remaining habitat patches often accommodate small populations of native animals, which suffer increased susceptibility to extinction. Movement of individuals between habitat patches, however, can interconnect such populations so that they effectively behave as larger and more stable metapopulations. Hence the traversability of any matrix for wildlife is an important attribute of fragmented landscapes and impacts on their ability to support viable populations. Further, the capability of different species to cross various matrix types varies. ‘Landscape connectivity’ describes the functional isolation of remnant areas of habitat and considers not only the distance between them but also the species-specific ability to successfully move through the matrix. In this thesis I examine the dispersal behaviour and population genetic structure of two species of marsupials in a fragmented landscape. I describe the movements of bobucks (Trichosurus cunninghami) and agile antechinus (Antechinus agilis) in the Strathbogie Ranges in north-eastern Victoria. Being forest-dependent, both species occur solely in remnants of native forest. Both also have a life-history pattern that is characterised by the dispersal of subadult males. However, they differ greatly in body size. I used GPS (for bobucks) and VHF (for antechinus) tracking to monitor individuals within their home ranges in the pre- and post-dispersal stages of their life cycle as well as during dispersal. I also used genetic parentage assignment tests to identify movements of antechinus. While the literature reports that the vast majority of subadult males of both species disperse, in my study a high proportion remained philopatric. Exploratory movements, beyond the boundaries of their home ranges, were recorded for adult and subadult bobucks; however, subadult males that later dispersed rarely exhibited this behaviour. In the months before the dispersal season, subadult bobucks that would subsequently remain philopatric appeared to occupy larger home ranges than dispersers. One possible explanation for this observation is that resource availability drives dispersal in this species and only those individuals that cannot secure access to sufficient resources in their natal home ranges disperse. In order to examine the response of dispersers to different landscape elements I monitored individuals during dispersal. Some bobucks and antechinus dispersed long distances. The very detailed dispersal pathways of bobucks, that I recorded using GPS tracking, revealed a clear pattern with all individuals dispersing along wooded landscape elements when these were available. Individuals were able to cross considerable distances across pasture using paddock trees and linear forest remnants as stepping stones and dispersal corridors. While some antechinus are likely to have crossed small gaps in linear forest remnant habitat, they appeared to be more restricted to forest during dispersal than bobucks. Genetic parentage analysis revealed that some male antechinus moved very considerable distances during the mating season, a behaviour that could significantly increase gene flow in this species. I applied genotypic analyses to infer gene flow in this system and used a landscape genetic approach to determine the connectivity of habitat in the Strathbogie Ranges for both bobucks and antechinus. I also investigated the influence of wooded landscape elements on gene flow in these two species. These analyses indicated that the distribution of forest remnants and individual trees play no role in determining gene flow in bobucks or antechinus within the Strathbogie Ranges. Surprisingly higher spatial genetic structure, which could indicate restricted dispersal, was detected in the larger, more mobile bobucks compared to antechinus. This seems to contradict my findings based on direct observations of dispersers in both species, namely the importance of paddock trees and linear forest remnants as dispersal conduits for bobucks and stronger restriction to forest of dispersing antechinus in comparison to bobucks. In fact, however, this discrepancy emphasises the difference between measurements of dispersal via direct observations versus genotypic inferences of gene flow. While observations of individual dispersers can provide detailed information on the behaviour of animals when they are traversing fragmented landscapes, data on their survival and breeding success post-dispersal is virtually impossible to obtain for many species. In contrast, molecular genetic analyses yield information on the reproductive outcome of dispersal across several generations, but usually cannot inform about dispersal pathways. The two approaches that I used are complementary, and combining them can help to avoid inaccurate conclusions about landscape connectivity for metapopulations, that are based on either technique alone. In my study, the landscape genetic model applied may have underestimated the true value of paddock trees as conduits for bobuck dispersal. Also the small number of antechinus that I was able to monitor during dispersal probably led to an underestimation of this species’ ability to leave its preferred forest habitat and traverse the matrix. Overall, the availability of linear forest remnants, scattered paddock trees and small patches of forest in the Strathbogie Ranges appeared to create high functional connectivity for populations of both species. My research emphasises the importance of maintaining and/or restoring structurally complex landscape elements, so that these can act as dispersal conduits for different species with differing mobility. This approach is an important tool to mitigate the effects of habitat fragmentation on native wildlife.
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ItemFertility control of common brushtail possums, Trichosurus vulpecula, in free-ranging populations( 2011)The common brushtail possum, Trichosurus vulpecula, is a serious ecological and agricultural pest in New Zealand, where it was introduced, and is very abundant in many Australian cities. Management of overabundant native species is contentious, with wildlife managers increasingly using fertility control as a humane option. My study developed three DNA vaccines based on coat protein 4 (CP4) and vesicle associated protein 1 (VAP1), previously shown to reduce fertility by ca 40% for a mean period of 1.4 years and 1.5 years respectively. CP4 and VAP1 cDNA were amplified by PCR, separately cloned into pcDNA3.1 plasmid vector, transformed into Escherichia coli, confirmed by sequencing, purified from endotoxins, and verified by in vitro expression in mammalian cells before use. The DNA vaccines were pcDNA3.1-CP4, pcDNA3.1-VAP1, a combined vaccine of the two (pcDNA3.1-CP4 + pcDNA3.1-VAP1), and a control vaccine (pcDNA3.1 blank plasmid). The effect of vaccines on animal behaviour was tested both on captive and free-ranging possums. Compared to controls, immunization with CP4 or the combined vaccine resulted in significant behavioural changes related to social rank and number of dens used in captivity and home range areas, long-range movements and den types used in the wild. The combined vaccine, the most effective vaccine, caused the highest degree of changes, while VAP1, the weakest contraceptive produced the lowest degree of changes. The social rank increased significantly in pcDNA3.1-CP4 and combined vaccine-immunized possums compared to controls. However, the dominance behaviour was positively correlated with weight gain. The absence of weight gain in wild females in my study after treatment means that dominance patterns in free-ranging possums are unlikely to change as a result of this factor after vaccination. Similarly, while immunized females used a higher number of dens compared to controls in captivity, the number of dens used by free-ranging females did not change between groups following treatment. Both pcDNA3.1-CP4 and combined vaccine-immunized females undertook significantly higher proportion of long-range movements and had a larger home range area compared to controls. These movements were associated with the absence of dependent young. No evidence of dispersal or mortalities was found.
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ItemColour pattern evolution in Australian dragon lizards (Agamidae)( 2011)Many animals communicate using elaborate visual signals such as conspicuous colours and patterns, which are influenced by numerous selective forces. However, the relative influences of natural and sexual selection on types of colour and pattern exhibited and the number and complexity of diverse colour pattern elements remain unclear for most taxa. In this study, I applied phylogenetic comparative approaches to examine the evolution of colour patterns in 69 Australian agamid lizard species, a morphologically and ecologically diverse group that relies primarily on visual communication. I examined colour patterns on nine body regions, which include dorsal, lateral, and ventral areas. I tested for associations with indices reflecting different selective pressures from both visual predators and conspecifics. Indices of natural selection included habitat openness, life style, substrate types, and ecological generalism, and my indices of sexual selection were the degree of sexual dichromatism and body and head size dimorphism (SSD). I found that both carotenoid/pteridine-based yellow-red colours and melanin-based black colour are likely to be used as sexual signals in male agamid lizards, as indicated by their association with two indices of sexual selection, the degree of sexual dichromatism and sexual size dimorphism. The use of both yellow-red and black sexual signals suggests that the costs associated with different colour production mechanisms do not limit the expression of sexual signals. Furthermore, the prevalence of different types of colour on different body regions potentially reflects different signalling strategies in this group. I then examined the evolution of colour pattern complexity in Australian agamid lizards. I developed a novel approach to quantify colour pattern complexity based on the Shannon-Wiener species diversity index. Sex differences in colour pattern complexity and the degree of complexity in males were associated with SSD and sexual dichromatism, respectively. These results suggest that the evolution of colour pattern complexity is driven primarily by sexual selection. Greater colour pattern complexity of males than females suggests that sexual selection has led to signal innovation in males, involving the use of additional and/or novel signal types, rather than elaboration of existing signals, which does not influence complexity. By contrast, I found no strong associations between any ecological factors and colour patterns or with the degree of colour pattern complexity, which suggests that the influence of natural selection on colour pattern evolution in this group is difficult to identify within a broad phylogenetic comparative study.
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ItemDecapod crustacean diversity along Australia's western continental margin( 2011)A challenge for biodiversity conservation on continental margins is the lack of information on species distributions. Australia has an expansive continental margin that is largely unexplored. To protect and manage biodiversity in Australia’s deep marine environments, biological and abiotic surrogates have been used to classify biodiversity. The aim of this thesis is to describe patterns of decapod diversity on an extensive continental margin and investigate the ability of physical and biological surrogates to represent underlying diversity patterns. The description of biological patterns at large spatial scales requires reliable taxonomic identifications, and consequently a substantial part of the thesis is taxonomic in nature. Surveys of Australia’s western continental margin (~100 to 1000 m depths) were undertaken in 2005 and 2007 by CSIRO Marine and Atmospheric Research in conjunction with museum taxonomists. Species identified from the north-west margin (survey SS05/2007) are reported here and the results of both surveys are summarised. In total, 890 provisional species of decapod crustaceans were discovered during the two surveys, of which 30% are new to science. Many of the species collected and identified (327 or 37%) are known to occur elsewhere, from the tropical Indian Ocean to the West Pacific, and 142 species were recorded in Australia for the first time. A small component of the new fauna discovered during the surveys is described here. These include two new species of the hippolytid shrimp genus Lebbeus and six new species of squat lobster of the family Chirostylidae. Although 45 species of Lebbeus exist worldwide, only one had previously been described from Australia. Squat lobsters including those of the family Chirostylidae are rapidly advancing our understanding of deep-sea environments across broad spatial scales and therefore the taxonomy and distribution of these animals is a research priority. In addition to the six new species described, seven new records of Indo-West Pacific species are reported for Australia. This study increases the number of chirostylid species in Australia from 40 to 53. Keys to Australian species of the genera Gastroptychus, Uroptychodes and Uroptychus are provided. The distributional records of decapods along the margin were used to determine the relative importance of environmental and spatial predictor variables on both species richness (alpha diversity) and species turnover. The best predictors of species turnover were temperature, oxygen and salinity, factors that reflect the oceanographic features that dominate distinct depth bathomes along the slope. On both the shelf and the upper slope, I differentiated an assemblage north of 22°S from another south of 23°S in the vicinity of North-west Cape. This location correlates with changes in oxygen concentration along the margin and marks the head of the Leeuwin Current system. The number of species within samples was highly variable, but a small significant increase in diversity towards the tropics was evident. On the shelf edge (~100 m) temperature was correlated with latitude, oxygen and salinity, and thus the independent effects of each variable could not be separated. On the shallow upper slope (~400 m) temperature was disassociated from latitude, and latitude proved to be the best predictor of sample species richness. The predictive power of latitude over other variables indicates that proximity to the highly diverse Indo-West Pacific is important. Management of both terrestrial and marine environments often uses vertebrates as a surrogate for the diversity of the overall fauna, as their distributions are better documented than those of most invertebrates. In the case of Australia’s deep-water marine planning, the distributions of fishes were used to classify bioregions. To ensure this classification represents underlying biodiversity, the spatial patterns of fishes with three invertebrate taxa were compared along a latitudinal gradient. Changes in community structure along the margin were broadly congruent for fishes and all invertebrate taxa. In contrast, broad-scale species richness patterns differed between major taxa, leading to the conclusion that one taxonomic group cannot be taken to represent others in terms of species richness or taxonomic distinctness. The results of this thesis lend support to Australia’s marine planning framework in which bioregions are defined according to the distributions of fishes and major oceanographic features. As in other large-scale studies which seek to examine the drivers of diversity in the deep sea, attributing causal relationships is difficult as many covariates are correlated. However, it was possible to distinguish some variables which have greater explanatory power than others. Future research will invariably consider the distributions of fauna over much larger scales as biological and environmental datasets are assembled at global scales, and this may help to explain the physical and historical constraints of deep-sea distributions.
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ItemThe ecology of hydroids (Hydrozoa: Cnidaria) in Port Phillip Bay, Australia, and their impacts as fouling species in longline mussel culture( 2011)Hydroids (Cnidaria:Hydrozoa) are a frequently abundant component of marine sessile communities associated with natural and artificial habitats. Many hydroids have the potential for economic impacts through extensive fouling of piles, pontoons, vessel hulls and aquaculture facilities. Detrimental effects of hydroid biofouling on mussel aquaculture have been documented overseas, yet little is understood about the relationship between hydroids and juvenile/adult mussels, or of the role of hydroids in biofouling assemblages. In Port Phillip Bay, hydroids displayed seasonal and spatial patterns of distribution, growth, reproduction and larval recruitment. In commercial mussel farms, hydroid morphology was generally found to facilitate recruitment of the blue mussel, Mytilus galloprovincialis, and there was a significant correlation between the presence of the branched hydroid Obelia dichotoma on mussel ropes and mussel recruitment. However, although attractive to mussel larvae, the stolonal hydroid Ectopleura crocea may be negatively affecting mussel production. Significant detrimental effects of fouling on mussel condition were found, particularly on juvenile mussels. This may be a result of filtration interference, as fouling by E. crocea on mussel shells was site specific, mostly occurring on the body, edge and dorsal shell regions. Analysis of the plankton and the trophic ecology of E. crocea determined that competition for food between M. galloprovincialis and E. crocea may also be affecting mussel growth. E. crocea colonies captured an assortment of prey items but the most common items were various crustaceans, diatoms and bivalves. Laboratory feeding studies confirmed that plantigrade larvae (those settling out from the plankton) were consumed more readily than other bivalve life stages. The consistency in prey numbers of many taxa in the diet of E. crocea at each site, regardless of the temporal variation in prey availability, implies some selectivity in hydroid feeding. This thesis used a range of mensurative and experimental approaches to investigate the ecology of hydroids in Port Phillip Bay, Australia, and determine their impacts as fouling species in the commercial longline culture of blue mussels, Mytilus galloprovincialis. To my knowledge, this research represents the first documented assessment of the range of impacts of hydroids such as O. dichotoma and E. crocea in longline mussel culture.
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ItemPopulation assessments of ungulate prey and Komodo dragons across protected areas in eastern Indonesia( 2011)Prey species can influence the population dynamics of their predators. Therefore, to conserve and manage endangered or threatened species, it is crucial to understand predator-prey relationships and to monitor the abundance of predators and their prey. The Komodo dragon (Varanus komodoensis) is an apex predator endemic to Indonesia. It is considered a vulnerable species due to demographic decline and a limited distribution. However to date, little monitoring has been conducted to estimate the spatial and temporal variation in the abundances of the Komodo dragon and its ungulate prey species. This study evaluated the usefulness of faecal counts and distance sampling for monitoring the abundance of the three major prey species of Komodo dragons. This study also investigated site occupancy of Komodo dragons, and examined the influence of site-specific covariates (prey abundance, habitat type and level of protection) on site occupancy across 11 sites on five islands in and around Komodo National Park, eastern Indonesia. Faecal densities of three ungulate prey species: Timor deer (Cervus timorensis), feral pig (Sus scrofa) and water buffalo (Bubalus bubalis), were positively correlated with their population densities estimated from distance sampling. The abundance of Timor deer was negatively influenced by the abundance of water buffalo, possibly through competition for space and food. Whilst for feral pig and water buffalo all models give weak support (wi ≤ 0.37) to explain the variation in their abundances. Several competing models were evaluated to estimate their effects on the site occupancy of Komodo dragons. The two most parsimonious models indicated that ungulate prey, representing a deer density model (∆= 0.00; w= 0.68) and an additive model incorporating deer and buffalo density ((∆= 1.61; w= 0.30) were both positively correlated with site occupancy estimates for Komodo dragons and presumably the abundance of Komodo dragons. The site occupancy of Komodo dragons and the abundance of their prey on small islands and Wae Wuul Nature Reserve on Flores Island were lower than on the larger islands within Komodo National Park. This study concluded that faecal counts are more useful than distance sampling for population monitoring of the ungulate prey of komodo dragons, and recommends annual monitoring of ungulates in and around Komodo National Park to be undertaken using faecal counts. This study also recommends that continuous monitoring of Komodo dragon site occupancy and estimation of trends in prey densities should be implemented for detecting spatial and temporal changes across time. The implementation of long term population monitoring would ensure that robust data is available for managers to address population trends. I also propose conservation efforts essential to ensure the persistence of Komodo dragon populations: (i) increasing the level of protection to reduce the risk of deer hunting, (ii) translocating Timor deer to low abundance areas to recover their populations, (iii) excluding domesticated buffalo from Wae Wuul Nature Reserve, and (iv) investing in sustained annual monitoring program for the Komodo dragon and its ungulate prey populations, to be implemented across Komodo dragon distributions, and especially in small islands and the Wae Wuul Nature Reserve.
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ItemEffects of variable recruitment on the structure and development of marine sessile communities( 2011)The species composition, density and frequency of dispersive propagules (e.g. seeds, spores and larvae) that recruit into any given habitat are highly variable in most biological systems. Such variation in recruitment has been shown to have important consequences on populations, but little is known about recruitment effects on communities of organisms occupying the same habitat. In particular, few direct experimental studies exist that examine how recruitment influences the composition and assembly of whole communities. For this thesis, I used a range of experiments where I manipulated the species composition, density and frequency of recruitment for a variety of taxa and followed the subsequent development of hard-substrate communities of sessile animals living in temperate marine waters over 6 months periods occurring in 2009, 2010 and 2011. The effects of recruitment on communities were complex. Different patterns of recruitment of individual species influenced community structure but these effects varied greatly depending on the identity of species recruits, the time of community development and across three different sites. Variable recruitment of arborescent bryozoans and didemnid ascidians had little effect on community structure. Recruitment of the colonial ascidian Botryllus schlosseri had short lived effects on community structure, while barnacles had more persistent effects at one site. At another site, recruitment of B. schlosseri and the bryozoans Watersipora subtorquata had strong persistent effects on community structure, dominating space where they recruited and influencing the abundances of a variety of different taxa. When species recruited together at the same time rather than as single species they also had effects on community dynamics. These effects were not simply an additive of the effects of single species, suggesting that mixtures of recruits can have synergistic effects on communities. However, different recruitment effects did not persist into later community stages. The frequency at which recruits entered communities also had variable effects on community structure. When Botryllus schlosseri and didemnid ascidians entered communities in a single large event or steady recruitment of the same number of individuals it did not have a strong influence on community structure. In a separate experiment botryllid ascidians caused changes in the structure of communities when they recruited steadily compared to when they recruited in a single recruitment pulse. When two different groups of taxa, a bryozoan (Conopeum seurati) and barnacles recruited in the presence of an established dominant solitary ascidian, Pyura stolonifera, they caused differences in community structure. Established P. stolonifera did not alter the effects of recruitment of these taxa at the community level, but did alter the effects of recruitment on some individual taxa that subsequently arrived in communities. The combined effects of bryozoan and barnacle recruitment and established P. stolonifera on subsequently arriving taxa were complex and non-uniform. The results of this thesis demonstrate that species composition and frequency of recruitment can have an important influence on the formation and structure of marine sessile communities but that these effects can vary greatly between species, sites and times. These findings are likely to have implications for our understanding of a range of communities that rely on recruitment of dispersive propagules and may respond to varying recruitment patterns in ways similar to those found in this thesis.