Zoology - Theses
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ItemPatterns in the distribution and abundance of reef fishes in South Eastern Australia( 2011)This research investigated patterns in the distribution and abundance of nearshore fishes of south-eastern Australia. I used two methods to survey fishes, underwater visual census (UVC) and baited remote underwater video (BRUV). A comparison between these methods revealed that BRUV recorded higher relative abundance of mobile predators, while UVC observed higher relative abundance of herbivores, territorial species, and small site-attached species. These results suggest that studies surveying diversity would do best to employ multiple methods. In cases where funds are limited, UVC may provide a more complete estimate of diversity than BRUV as UVC recorded higher diversity, species richness and more individuals. Combining measures of abundance with habitat data, I investigated fish-habitat associations, specifically exploring how altering spatial grain influenced the strength of correlations between fish and habitat. Species of different sizes responded to habitat measured over different scales, with large-bodied species only displaying strong correlations with habitat when it was measured over large scales. These results suggest that research quantifying fish-habitat associations needs to take spatial grain into account. In addition, many species may respond to changes in habitat at scales larger than are typically investigated. Understanding not only how species interact with their environment but also the scale at which these associations occur is essential for management and conservation. I investigated biogeographic patterns in the distribution of fishes in Victoria using abundance measured by BRUV and UVC. The BRUV data displayed a cline in change across the state in which dissimilarities between locations were linearly related to distance. In contrast, data collected using UVC indicated the presence of a large faunal break in the vicinity of Ninety Mile Beach, and a second break between Cape Conran and Cape Howe, suggesting that contemporary habitat discontinuity, flow and/or temperature may be important factors structuring communities in this region. At a still larger scale, I explored relationships at upper and lower bounds between body size, geographic range size and abundance using data collected from Australia and New Zealand. At maxima, the relationship between body size and abundance was negative but steeper than expected, possibly driven by diver-averse behaviour of large species. At minima, body size and geographic range size were positively related, implying that body size determines the minimum area that a species must occupy. In contrast, at the upper bound this relationship was negative for non-perciform fishes, a K-selected group whose geographic range size could be constrained by their limited dispersal capacity. Distribution-abundance relationships deviated from predictions, with a negative relationship at the upper bound for Perciformes, which could be driven by the high dispersal potential of widespread species that results in diffuse low-density populations. From these results, I concluded, first, that fishes appear to differ from terrestrial taxa, which may be attributed in part to large-bodied fishes’ limited capacity for dispersal. Second, the approach of applying regressions to maxima and minima uncovered relationships that would have been obscured had they been investigated at the mean, highlighting the importance of exploring limits in macroecological relationships.
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ItemThe distribution and ecology of ants in vineyards( 2009)Ants are highly abundant and ubiquitous in many terrestrial ecosystems. They perform many important ecological functions and have been widely employed as bioindicators for various terrestrial monitoring programmes. In agroecosystems, their role is controversial because ants can act as predators against herbivorous pest but also associate with and protect honeydew-producing hemipteran pests. The ecology, function and interactions of ants with other arthropods in vineyards are poorly known and this thesis therefore examines their distribution and ecology in south-eastern Australian vineyards. An extensive survey of 50 vineyards distributed in five regions in South Australia and Victoria recorded 147 native ant species and one invasive species, Linepithema humile (Mayr). Species richness, compositional similarities and assemblage structure varied within and across regions. High species turnover and variation in assemblage structure were found across regions and implications of these patterns are discussed. The invasive L. humile was only detected in some vineyards in one region. The potential impact of management practices and off-farm vegetation on augmenting ant diversity and conserving biodiversity are considered. The impact of non-target agrochemical applications on ants was investigated in 19 vineyards that received varying levels of agrochemical input. Ant assemblage structure and assemblages were not found to be impacted by pesticides. In contrast, ant assemblage structure was influenced by the presence of shelterbelts near the sampling area. Reasons for the resilience of ants to pesticides are given and assessment at the colony level instead of worker abundance is suggested. An ant-exclusion experiment was designed to test the impact of native ants on both canopy and ground arthropods concurrently. The potential influence of ants on predation and parasitism on eggs of light brown apple moth (LBAM), a grape pest, was also examined. Adult grapevine scale insects and earwigs under bark were also counted after a season of ant-exclusion. While ant exclusion was successful, there was no detectable difference in the abundance of most arthropod orders and feeding groups between ant-excluded and control vines, although ground spiders were more abundant under ant-excluded vines, despite increased ground ant foraging pressure. LBAM egg parasitism and predation were low and probably affected by weather and other arthropods. Ant exclusion did not reduce survival of scale insects, although the distribution and abundance of scale insects were negatively associated with earwigs. Reasons for the lack of negative effects of ants are discussed. The spatial patterns of ants were investigated with intensive pitfall trappings in two vineyards to examine if non-random patterns occur and whether these might be the result of competitive species interactions as well as non-crop vegetation adjacent to the vineyards. Null model analyses suggested competitive species interactions within ant assemblages that might have been driven by dominant species even though both positive and negative associations between dominants were also found. Consistent spatial aggregations indicated significant spatial overlap in distributions of some species. Such overlap suggests that potential co-existence might be attributed to temporal partitioning or differences in foraging strategies. The presence of vegetation had a marked influence on ant assemblage structure and competitive interactions, and might also facilitate co-existence by increasing resource heterogeneity. The implications of these findings for sampling strategies and ecological processes within vineyards are discussed. This thesis has provided new information about ants in vineyards. The high ant diversity could be important in maintaining ecosystem services. Among the 33 ant genera recorded, Iridomyrmex, Paratrechina and Rhytidoponera have the greatest potential in contributing to canopy pest suppression although their associations with honeydew-producing hemipterans need to be considered. Stable isotope analysis or/and molecular gut content analysis should reveal their trophic position in vineyards. Evaluation of crop yield that is directly attributed to soil conditioning by ants in agroecosystems should be explored. The importance of landscape composition, complexity and connectivity is highlighted and role of agroecosystems in conserving biodiversity is emphasised. Future research should be directed towards understanding how landscape composition and complexity may enhance ant diversity and alter dynamics and interactions that may be functionally important (biological control, soil conditioning, etc) in a landscape context.