The abundance of Latrodectus katipo Powell 1871 is affected by season and vegetation type

Abstract

Our study aims to elucidate the factors affecting the population abundance of Latrodectus katipo Powell, 1871, a declining species endemic to New Zealand. The abundance of L. katipo was compared adjacent to two different plant species: the endemic sedge, pingao (Ficinia spiralis A. Rich.), and the exotic grass, marram (Ammophila arenaria (L.) Link). In addition to the effects of marram versus pingao, seasonal effects on L. katipo abundance were examined. Using artificial cover objects (ACOs), presence/absence data were collected for L. katipo. Sixty ACOs were divided between Golden Bay, Kaitorete Spit and New Brighton. Thirty-three ACOs were placed next to marram plants and 27 ACOs were placed next to pingao plants. Kaitorete Spit was the principal study site examined due to the larger L. katipo population there. ACOs were checked for L. katipo presence every 15 days for two months per season, and for all four seasons at Kaitorete Spit and once per season for three seasons at New Brighton and Golden Bay. No L. katipo were found at Golden Bay or New Brighton. A GLMM indicated a significantly higher probability of finding L. katipo under ACOs placed next to pingao as opposed to marram. L. katipo presence was also highest in summer. We conclude that conserving L. katipo will involve reducing the amount of marram in New Zealand’s sand dunes, and that studies monitoring L. katipo population dynamics should do so in summer when L. katipo are most abundant.