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Introduced species have the potential to cause serious ecological disruption, particularly on oceanic islands. When introduced species invade natural areas, endemic species may be threatened, especially when the invasive species represent guilds or functional groups that were previously lacking. Hawai‘i has no native slugs, but over a dozen species are now established. Slugs are important seedling predators in their native habitats, and in introduced habitats they can cause major shifts in the abundance some plant species. In order to better investigate slug impacts on native plants in Hawai‘i, I carried out research which 1. identified differences in the acceptability of five native plant species to five alien slug species 2. assessed the effect of slug herbivory on the growth and survival of three native and two alien plant species, and 3. measured changes in seedling regeneration due to slug herbivory. Results from feeding assays indicated a significant difference in palatability among plant species, but no statistical difference in overall feeding preference among slug species. Urera kaalae (Urticaceae) was found to be significantly more palatable than the other four plant species and, thus, is predicted to be more vulnerable to slug herbivory in the field. I tracked the fate of planted seedlings and natural germinants from the seed bank in both slug-excluded and slug-accessible plots in diverse mesic forest in the Wai‘anae Mountains on the island of O‘ahu. Among seedlings that survived to the end of the experiment, there was no significant difference between slug herbivory treatments in growth index measurements. There was little germination from the seed bank, with no statistical difference in total number of seedlings between treatments. However, two of the three native species, Schidea obovata (Caryophyllaceae) and Cyanea superba (Campanulaceae) had significant reductions in survival of 49% and 53%, respectively, in the slug-exposed treatment. Survival of two invasive species, Clidemia hirta (Meslastomataceae) and Psidium cattleianum (Myrtaceae) was not significantly affected by slugs. This study demonstrates that slugs may pose a serious threat to native plant species by reducing their survival and thereby facilitate the success of certain invasive species. / viii, 87 leaves / Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 78-87). / Also available via World Wide Web

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Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Dec. 23, 2009). Includes bibliographical references.

Slugs are major pests of oilseed rape and wheat. Current chemical control measures often do not give adequate protection to plants, and pose an environmental hazard. Laboratory experiments investigated the potential of seed treatments to control slug damage in oilseed rape. Four compounds: metaldehyde, methiocarb, cinnamamide and 3,5-dimethoxycinnamic acid (DMCA) were tested for phytotoxicity and ability to reduce damage. Metaldehyde and methiocarb seed treatments protected seedlings as well as or better than baited pellets. A broad-spectrum insecticide imidacloprid was tested as a seed treatment to control slug damage to oilseed rape and winter wheat in laboratory experiments. Imidacloprid did not reduce slug damage to oilseed rape at any dose or to wheat at low doses. Higher doses of imidacloprid on winter wheat significantly reduced slug damage. In a field experiment with winter wheat, imidacloprid seed treatments reduced slug damage to a lower level than bait pellets but had inconsistent and short lived activity. The most promising seed treatments, metaldehyde and methiocarb, were tested in semi-field trials and found to have a reduction in efficacy in comparison to laboratory trials. To determine why field efficacy was reduced, seedlings were grown under a range of environmental conditions. The metaldehyde content of seedlings was measured using a novel method of GC-FID analysis. Data suggested that reduced field efficacy results from microbial breakdown and/or loss of active ingredient caused by percolating soil water. Once seedlings had emerged, neither volatalization nor simulated rainwater reduced the metaldehyde content of seedlings. New seed treatment formulations were developed and tested in 3 mini-plot trials on oilseed rape and wheat. In 2 of the mini-plot trials the industry-produced metaldehyde seed treatment protected seeds and seedlings, as well as bait pellets. In the third mini-plot trial, very heavy rainfall at sowing resulted in only bait pellets successfully reducing slug damage.

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This study investigated the physiological ecology, larval biology and population genetics of the nudibranch molluscs Adalaria proxima (A & H) and Onchidoris muricata (Müller). These two species are annual, simultaneous hermaphrodites and are ecologically very similar with the exception that A. proxima reproduces by means of pelagic lecithotrophic larvae whereas Omuricata has long-term planktotrophic larvae. The aim of the study was therefore to determine the selective pressures which resulted in the evolution of different larval types in these two species, and to ascertain the ecological and population genetic consequences thereof. Simple energy budgets comprising the major components (consumption, growth, respiration and reproduction) were constructed for laboratory populations of each species. In both A. proxima and O. muricata, feeding rate displayed an asymptotic increase with body size. Mean feeding rates of A. proxima were greater than those of comparable O. muricata individuals, and overall assimilation efficiency was higher in A. proxima than in O. muricata. This difference was reflected in the somatic growth rates which were correspondingly greater in A. proxima than in O. muricata. Net growth efficiencies were broadly comparable between the two species, however, growth of A. proxima was approximately linear over' time whilst that of O. muricata displayed a curvilinear, almost exponential, pattern. This is interpreted as demonstrating that some form of constraint (possibly feeding rate) operated on the growth rates of A. proxima but not on those of O. muricata. Respiration rates were found to be relatively constant within given animals, but significant differences were found between individuals. The allometry of respiration rate was not constant; Omuricata demonstrated a more rapid increase in respiration rate with increasing body size than did A. proxima. Individual variations in respiration rate did not reflect variations in the energy partitioned to either growth or reproduction. Reproductive patterns in the two species were dissimilar. A. proxima laid fewer spawn masses containing fewer, larger ova than those laid by O. muricata individuals. In addition, the spawning period of A. proxima was shorter than that of O. muricata (60 days and 105 days respectively). Both species exhibited a similar (proportional) degree of somatic catabolism over these periods. The consequently more rapid "degrowth" of A. proxima is interpreted as the necessary utilization of an energy resource (i. e. the soma) caused by an inability to meet the energy demands of reproduction through feeding alone. This was not the case in Oanuricata individuals which exhibited a much smaller maximum body size and were able to feed at a sufficiently rapid rate to maintain reproduction. In the latter case, the longer reproductive period served to maximise the total reproductive output. Several different measures of "Reproductive Effort" (RE) were calculated. These generally indicated that the RE of Omuricata was considerably greater than that of A. proxima. Although such differences have been used in the literature to classify the respective costs of different larval types or "reproductive strategies", the variability of the RE's obtained from the different measures used here has led to the suggestion that the general lack of association between RE and reproductive strategy which has been reported elsewhere may (partially) be attributable to the different measures of RE employed in different studies. Studies of the embryonic and larval period showed that the egg-to-juvenile period of O. muricata was approximately 50% longer than that of A. proxima. This difference was primarily attributable to the extended pelagic development of O. muricata larvae. Estimates of the degree of dispersal, and hence gene-flow, between populations of these species were tested by investigating the biochemical genetics of such populations. No data were available for O. muricata, but A. proxima populations proved to be more genetically heterogeneous than had been expected. It is therefore concluded that actual pelagic dispersal may be considerably abbreviated over that expected on the basis of larval culture data alone. A model is developed to explain the possible consequences of different egg-to-juvenile periods (which accrue from different larval types) on both the ecology of the benthic adult, and on overall energy partitioning to reproduction. However, although (probable) proximate causes and effects of the different reproductive traits exhibited by A. proxima and Oanuricata are shown, it has not been possible to determine the exact selective pressures which caused A. proxima to diverge from the ancestral "O. muricata" stock through the evolution of a pelagic lecithotrophic larva.

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No description available.