Evidence for the displacement of an endemic New Zealand spider,Latrodectus katipoPowell by the South African speciesSteatoda capensisHann (Araneae: Theridiidae)

Abstract

The competitive interactions betweenLatrodectus katipo and Steatoda capensis were studied under the hypothesis that L. katipo is being displaced from its natural habitat by competition from S. capensis. Use of trophic andspatialresources were studied. High overlap for both resources was found. Data on reproductive potential revealed that S. capenisis has a significantly higher reproductive output. Laboratory predation experiments indicated L. katipo adults are not inferior to S. capensis. Evidence suggesting displacement following L. katipo population crashes was obtained. Differences in reproductive potential and seasonal reproduction are proposed as the mechanism underlying the displacement.

Descriptions of fourSteatodaspecies (Araneae, Theridiidae) found in New Zealand

“…Females continue to produce egg sacs year round, but produce most in December-March. The mean number of eggs per sac over all sacs for S. capensis studied in Motueka, Nelson, was 183.6 (SD 53.9; n = 37) with a range of 92-309 (Hann 1990b). The egg sacs are 8-10 mm in diameter, white and slightly fluffy in appearance, and are usually attended by the female until hatching.…”

“…Steatoda capensis studied in Motueka, Nelson, fed mainly on a common sandhopper, Talorchestia quoyana (Amphipoda), and a variety of coleoptera including Cecyropa lucunda, Mimopeus elongatus, Ceratognathus irroratus, Thelyphassa diaphana, and Conoderus exsul (Hann 1990b). As S. capensis is found in many different types of habitat, it probably accepts a diverse range of prey.…”

“…Steatoda capensis has been implicated in the displacement of the endemic true katipo, L. katipo, from coastal regions of the Wellington province (Hann 1990b Steatoda lepida new comb. Hann, 1990.…”

Regional patterns in the invasion success of Cheiracanthium spiders (Miturgidae) in vineyard ecosystems

“…Once established, invasive spiders may be viewed as either beneficial arthropods in agroecosystems, or as disruptive predators in native ecosystems. Documented displacements of native by invasive spider species are rare, although Hann (1990) reported an invasive web-building spider competed with and ultimately displaced an endemic web-building species in New Zealand.…”

“…The negative impacts of invasive ant species, for example, have been enormous (Holway et al 2002). As generalist arthropod predators, spiders have the potential to affect native arthropod species; nevertheless, spiders have been largely overlooked as invasive species (but see Nyffeler et al 1986;Hann 1990;Burger et al 2001;Gruner 2005). Once established, invasive spiders may be viewed as either beneficial arthropods in agroecosystems, or as disruptive predators in native ecosystems.…”