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

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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.
Latrodectus katipo, New Zealand, Spiders, Endangered species