Spatial associations between invasive tree lupin and populations of two katipo spiders at Kaitorete Spit, New Zealand.
Spatial associations between the invasive tree lupin (Lupinus arboreus), the New Zealand endemic widow spider Latrodectus katipo (katipo), and the introduced South African spider Steatoda capensis (false katipo) were examined within the nationally significant Kaitorete Spit dune system in Canterbury, New Zealand. These dunes are considered to be a stronghold for L. katipo, but with the decline in preferred vegetation for capture-web attachment as a result of tree lupin invasion, a decline in the spider's population was expected. On other New Zealand dune systems a decline in L. katipo abundance has corresponded with an increase in the abundance of the introduced S. capensis. Spider population data collected over a 6-year period and vegetation data collected in 2008 and 2009 were used to examine the spatial associations at Kaitorete Spit. The abundance of S. capensis was not significantly related to the abundance of L. katipo. The ratio of S. capensis to L. katipo declined annually over the 6 years. The 2008 and 2009 vegetation surveys found that S. capensis was not located in areas where tree lupin was present. Latrodectus katipo was found in areas with up to 40% tree lupin cover. The abundance of L. katipo recorded in areas dominated by tree lupin was not significantly different from the abundances recorded in association with native plant cover. The presence of L. arboreus at Kaitorete Spit is not considered to be a direct threat to the population of L. katipo; Kaitorete Spit is still a stronghold.