Browsing by Author "Costall, Jessica Anne"

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    The ecology and conservation of Latrodectus katipo, New Zealand's endangered widow spider : a thesis presented in partial fulfillment of the requirements for the degree of Masters of Science in Ecology at Massey University
    (Massey University, 2006) Costall, Jessica Anne
    New Zealand has two endemic widow spider species; Latrodectus katipo Powell, 1871 and L. atritus Urquhart 1890. This study focused on the population dynamics and habitat usage of L. katipo, which has undergone serious decline in its abundance and range over the last thirty years. Previous population studies have not included male or juvenile katipo because of their smaller size. A survey of katipo populations was conducted along the Manawatu coastline. There was considerable variation in population density and structure between sites. The highest katipo population density of 21.8 per hectare was recorded at Koitiata. Koitiata, Himatangi, Foxton and Tangimoana populations had a large proportion of juveniles. At Wanganui South and Castlecliff beaches no juveniles could be found, suggesting that reproductive output is very low and that these sites may require conservation attention. Accurate monitoring is critical to the management of any endangered species, however katipo are not monitored regularly in most areas as current population monitoring methods (transect or quadrat searches) are time and labour-intensive, and require highly-trained observers. I investigated the use of artificial cover objects (ACOs) which have a number of advantages over current monitoring methods; in particular they can be quickly and easily checked by observers. Katipo populations at three sites at Himatangi Beach were monitored between January and July, 2005. More traditional habitat searches were completed concurrently to provide population density estimates. The occupancy rate of the ACOs was strongly correlated with population density, and ACOs are therefore proposed as a reliable alternative monitoring method for katipo. The habitat searches showed that katipo have a longer breeding season at Himatangi than reported in South Island based studies, with males and newly hatched juveniles being found in the field up until about June, as opposed to just during summer months. The katipo population density was relatively constant between January and July, 2005, compared to that of Steatoda capensis, an introduced South African spider. Choice experiments were conducted to investigate whether katipo have preference for certain plant species or driftwood as web sites. Native sand-binding shrubs such as Coprosma acerosa are favoured by katipo over other plant species for web construction, and the exotic grass Ammophila arenaria is avoided by katipo even when growing at low densities. L. katipo spiderlings were raised in the laboratory to observe their development. Katipo eggsacs typically produce about 80 spiderlings, however eggsacs I studied contained between 40 and 146 spiderlings. There is substantial variation in the growth rates and abdominal markings of katipo spiderlings during development. Manawatu katipo are unique in that they often retain large areas of white abdominal markings at maturity.
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    The effects of restoration on the structure and function of litter invertebrate communities in New Zealand native forest remnants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Costall, Jessica Anne
    Much of New Zealand‘s remaining lowland forest exists as small, often degraded and heavily disturbed remnants on private farmland. Disturbances, such as livestock grazing and browsing by mammalian pests, are known to have a detrimental effect on native vegetation of these remnants. However, it is unclear what impact these disturbances have on the structure and function of forest floor invertebrate communities. Existing studies of forest fragmentation have predominantly focused on the effects of remnant area and shape, rather than remnant condition. This study examines how litter invertebrate habitat, community structure, and leaf litter decomposition, vary between grazed and ungrazed (fenced) remnants of differing size, and nearby forest reserves. Secondly, I examine how invertebrate community structure and function recover with time since livestock exclusion, with and without additional mammalian pest control. I found that grazed remnants provide dramatically altered habitat for litter invertebrates, compared to fenced remnants and large forest reserves. Grazed remnants are typified by having higher soil compaction, minimal understorey vegetation, and reduced litter cover. Consequently, grazed remnants have depauperate, yet highly variable invertebrate communities, compared to fenced remnants and forest reserves. Even very small forest remnants can support litter invertebrate communities very similar to that of larger forest reserves, provided they are protected from livestock grazing. Furthermore, invertebrate communities show strong recovery over time since livestock exclusion, particularly when livestock exclusion is combined with mammalian pest control measures. I found that litter decomposition rates did not differ between management treatments in my first observational study. However, in the second observational study, leaf decomposition rates at the edge of remnants increased with time since livestock exclusion, suggesting that restoration actions can lead to changes in ecological functioning. Small native forest remnants have high ecological value and substantial restoration gains can be made through the relatively simple action of fencing to exclude livestock.