No description available.

No description available.

Limited understanding of the ecology of ground-dwelling invertebrates in Tasmania has hampered our ability to assess the adequacy of forest management. This thesis documents the distributions of ground-dwelling beetle assemblages in managed, wet eucalypt forests of southern Tasmania, and explores the response of beetles to ecological gradients caused by riparian influences near small streams (since retained riparian corridors are a major conservation tool), and edge effects from recently clearfelled logging coupes. Extensive pitfall trapping using replicated transects at four sites was employed to compare the beetle fauna between five habitats: young logging regeneration, the interior of upslope mature forest, the riparian-upslope transition in mature forest interior, and across coupe edges (both into upslope mature forest and into streamside reserves). Data screening ensured that the primary transect design, which employed traps positioned at unequal distances within transects, was unlikely to produce patterning in beetle distributions attributable to spatial autocorrelation or pitfall trap depletion. Beetles responded to riparian influences, showing subtle shifts in assemblage composition, and generally reduced abundance or species richness nearer to streams. However, site differences outweighed riparian effects. Beetles assemblage composition differed substantially between young logging regeneration and mature forest: several species were identified as indicators of each habitat. Beetles responded more strongly to edge effects than to riparian influences. Depth of edge influence extended ~ 22 m into unlogged non-riparian forest, but further into streamside reserve edges (up to ~ 65 m). Four beetle species, Choleva TFIC sp 01 (Leiodidae), Decilaus nigronotatus, D. lateralis and D. striatus (all Curculionidae), were indicators of mature forest interior. A second survey compared beetles between logging regeneration, upslope mature forest interior, mature forest interior riparian areas, and streamside reserves that had been logged on both sides, in five stands of each of the four habitats. Streamside reserves (average width 40 +/-6 m (+/- 95% CI) from reserve edge to stream) supported different beetle assemblages to unlogged areas, and were probably entirely edge-effected. These results suggest that current corridor provisions, which rely heavily on riparian reserves, may be inadequate to conserve beetles dependent on mature forest interior. Reserve corridors may need to be wider, and should more often be positioned upslope away from riparian areas. Alternatively, a mix of different types of reservation strategies (e.g. conserving some contiguous blocks of mature forest in lieu of widened corridors) needs to be developed to increase the probability that edge-sensitive and mature forest specialist taxa will be conserved.

Recent phylogenetic analyses have led to a re-evaluation of metazoan relationships, resulting in the grouping a number of invertebrates known as the spiralians. They include molluscs, and share highly conserved cleavage patterns, cell lineages and embryogenesis, but exhibit a wide diversity of adult body plans. This makes them an excellent group for studying the mechanisms by which changes to developmental programs give rise to evolution of new body plans. Spiralian cleavage results in an embryo that is divided into quadrants of tiered blastomeres designated A, B, C and D, which form the left, ventral, right and dorsal regions of the embryo respectively (Verdonk and van den Biggelaar, 1983). The establishment of the dorsoventral axis and the organization of the embryo are closely linked in molluscs and involve the specification of the dorsal, D-quadrant. In equally cleaving gastropods, one macromere at the 32-cell stage is induced by the overlying micromeres to become the D-quadrant macromere, 3D (van den Biggelaar and Guerrier 1979, Arnolds et al., 1983; Boring, 1989). The 3D macromere is required for the formation of the mesendoderm, a dorsoventral cleavage pattern and the specification and organization of the ectoderm (van den Biggelaar and Guerrier 1979, Boring 1989, Damen and Dictus 1994, 1996) This thesis investigates the molecular mechanisms of gastrulation in the gastropod mollusc Haliotis asinina. In particular it focuses on the role that the 3D macromere plays in regulating the development of the molluscan embryo. The induction of the 3D-macromere was inhibited by independent treatments: first by interrupting the MAPK signalling cascade using the inhibitor U0126; and second by preventing micromere-macromere interactions with the chemical monensin. Genetic markers for morphogenetic domains were used to assess the hypothesised roles of 3D in generating the mesendodermal lineage, inducing the surrounding ectodermal micromeres, establishing the dorsoventral axis, and regulating morphogenetic movement. Microarray analysis of treated embryos was conducted to determine the role that 3D induction plays in regulating gene expression during early development. Both U0126 and monensin treatments of H. asinina embryos yielded abnormal trochophores, similar to those of other gastropods whose normal development has been perturbed by inhibiting 3D specification (Arnolds et al., 1983; Boring, 1989; Damen and Dictus, 1996a; Kühtreiber et al., 1988; Lambert and Nagy, 2003; Martindale, 1986; Martindale et al., 1985; Raven, 1976; van den Biggelaar and Guerrier, 1979). Analysing these treatments revealed that MAPK is a crucial component of the 3D induction pathway in H. asinina, as found for Ilyanassa and Tectura (Lambert and Nagy, 2003; Lambert and Nagy, 2001), with its inhibition resulting in a loss of mesendodermal patterning. The induction of the 3D-macromere results in the establishment of a molluscan organiser, which is responsible for widespread gene activation during early development and is required for proper morphogenetic movements associated with gastrulation. There appears to be similarities in the inductive processes in gastrulation between vertebrates and gastropods. In particular the patterning of the midline and flanking neuroectoderm, which is induced to form neuronal tissue by underlying mesoderm. Inhibition of 3D induction prevented neurogenesis, supporting the hypothesis of a 3D-dependant inducer of the neuroectoderm, possibly the mesodermal bands (van den Biggelaar and Dictus, 2004). The establishment of the dorsoventral axis and patterning of the gastrulating gastropod appears more complex that previously suggested. It appears that the patterning of the gastropod is compartmentalised. The 3D macromere is required for the induction of quadrant identity and patterning of the pretrochal ectoderm, and preventing 3D induction results in a radialisation of gene expression patterns. In the posttrochal ectoderm preventing 3D induction does not prevent dorsoventral patterning in at least the vegetal ectoderm. This suggests that there is either 3D independent induction or regulatory processes involved in the axial patterning of the mollusc.

No description available.

No description available.

Biological disturbance was found to be one of the most important mechanisms control1ing community organisation in the temperate sub-tidal region. The different types of biological disturbance structuring three encrusting communities were investigated on the east coast of Northland, New Zealand. The operation of each type was determined and the rate of disturbance measured. Experimental exclusion treatments were set up to demonstrate the effects of the major disturbance agents on community structure. The urchin Evechinus chloroticus was the most abundant agent of biological disturbance and affected the widest spectrum of encrusting organisms. The abundant balistid fish Navodon scaber was another major agent of biological disturbance in this region. Disturbance of algal populations also resulted from a guild of abundant herbivorous gastropods. Two episodes of fungal/bacterial infection degraded numbers of the large sponges Ancorina alata and Polymastia fusca. The operation of the different disturbance agents was found to be generally unpredictable in both time and space. There was no escape from biological disturbance for encrusting organisms in either small or large size. Re-occupation processes on patches of free primary space were investigated both experimentally and by using settlement plates (artificial free space patches). Recruitment was found to be irregular in space and time, especially for long-lived sessile organisms. Settlement processes as well as growth and mortality of newly settled organisms were investigated with a view to understanding community development. Only one verifiable example of substrate preparation or biological succession was found to operate in the communities studied. It is postulated that community organisation is flexible and not rigidly directed along a single successional pathway. Multiple developmental pathways and multiple stable configurations are possible in the same locality, resulting from the operation of different disturbance regimes.

Biological disturbance was found to be one of the most important mechanisms control1ing community organisation in the temperate sub-tidal region. The different types of biological disturbance structuring three encrusting communities were investigated on the east coast of Northland, New Zealand. The operation of each type was determined and the rate of disturbance measured. Experimental exclusion treatments were set up to demonstrate the effects of the major disturbance agents on community structure. The urchin Evechinus chloroticus was the most abundant agent of biological disturbance and affected the widest spectrum of encrusting organisms. The abundant balistid fish Navodon scaber was another major agent of biological disturbance in this region. Disturbance of algal populations also resulted from a guild of abundant herbivorous gastropods. Two episodes of fungal/bacterial infection degraded numbers of the large sponges Ancorina alata and Polymastia fusca. The operation of the different disturbance agents was found to be generally unpredictable in both time and space. There was no escape from biological disturbance for encrusting organisms in either small or large size. Re-occupation processes on patches of free primary space were investigated both experimentally and by using settlement plates (artificial free space patches). Recruitment was found to be irregular in space and time, especially for long-lived sessile organisms. Settlement processes as well as growth and mortality of newly settled organisms were investigated with a view to understanding community development. Only one verifiable example of substrate preparation or biological succession was found to operate in the communities studied. It is postulated that community organisation is flexible and not rigidly directed along a single successional pathway. Multiple developmental pathways and multiple stable configurations are possible in the same locality, resulting from the operation of different disturbance regimes.

Biological disturbance was found to be one of the most important mechanisms control1ing community organisation in the temperate sub-tidal region. The different types of biological disturbance structuring three encrusting communities were investigated on the east coast of Northland, New Zealand. The operation of each type was determined and the rate of disturbance measured. Experimental exclusion treatments were set up to demonstrate the effects of the major disturbance agents on community structure. The urchin Evechinus chloroticus was the most abundant agent of biological disturbance and affected the widest spectrum of encrusting organisms. The abundant balistid fish Navodon scaber was another major agent of biological disturbance in this region. Disturbance of algal populations also resulted from a guild of abundant herbivorous gastropods. Two episodes of fungal/bacterial infection degraded numbers of the large sponges Ancorina alata and Polymastia fusca. The operation of the different disturbance agents was found to be generally unpredictable in both time and space. There was no escape from biological disturbance for encrusting organisms in either small or large size. Re-occupation processes on patches of free primary space were investigated both experimentally and by using settlement plates (artificial free space patches). Recruitment was found to be irregular in space and time, especially for long-lived sessile organisms. Settlement processes as well as growth and mortality of newly settled organisms were investigated with a view to understanding community development. Only one verifiable example of substrate preparation or biological succession was found to operate in the communities studied. It is postulated that community organisation is flexible and not rigidly directed along a single successional pathway. Multiple developmental pathways and multiple stable configurations are possible in the same locality, resulting from the operation of different disturbance regimes.

Biological disturbance was found to be one of the most important mechanisms control1ing community organisation in the temperate sub-tidal region. The different types of biological disturbance structuring three encrusting communities were investigated on the east coast of Northland, New Zealand. The operation of each type was determined and the rate of disturbance measured. Experimental exclusion treatments were set up to demonstrate the effects of the major disturbance agents on community structure. The urchin Evechinus chloroticus was the most abundant agent of biological disturbance and affected the widest spectrum of encrusting organisms. The abundant balistid fish Navodon scaber was another major agent of biological disturbance in this region. Disturbance of algal populations also resulted from a guild of abundant herbivorous gastropods. Two episodes of fungal/bacterial infection degraded numbers of the large sponges Ancorina alata and Polymastia fusca. The operation of the different disturbance agents was found to be generally unpredictable in both time and space. There was no escape from biological disturbance for encrusting organisms in either small or large size. Re-occupation processes on patches of free primary space were investigated both experimentally and by using settlement plates (artificial free space patches). Recruitment was found to be irregular in space and time, especially for long-lived sessile organisms. Settlement processes as well as growth and mortality of newly settled organisms were investigated with a view to understanding community development. Only one verifiable example of substrate preparation or biological succession was found to operate in the communities studied. It is postulated that community organisation is flexible and not rigidly directed along a single successional pathway. Multiple developmental pathways and multiple stable configurations are possible in the same locality, resulting from the operation of different disturbance regimes.