Conservation biology of the goldstripe gecko (Hoplodactylus chrysosireticus) and interactions with Duvaucel's gecko (Hoplodactylus duvaucelii) on Mana Island, Cook Strait, New Zealand : a thesis presented in partial fulfilment for the degree of Master of Science in Ecology at Massey University
The conservation biology of goldstripe geckos (Hoplodactylus chrysosireticus) on Mana Island was considered in two ways. First, by studying the ecology, behaviour and population dynamics of H. chrysosireticus on Mana Island and in Taranaki and second, by assessing their behaviour in the presence of newly introduced Duvaucel's geckos (Hoplodactylus duvaucelii) on Mana Island. The activity patterns of H. chrysosireticus were observed at night and during the day on Mana Island between November 1996 and October 1997. H. chrysosireticus were found to exhibit higher levels of diurnal behaviour than previously thought, with over two-thirds of all animals caught during daylight hours (170 out of 257 individuals; mean catch rate = 2.59 per person hour), a behaviour uncharacteristic of the genus. A female-biased sex ratio (0.53:1 male: female) was found among adult H. chrysosireticus on Mana Island but a male bias (1:0.5 male: female) was observed in the Taranaki population. This could be due either to a female-specific behaviour making them more catchable and hence taken more frequently by predators on the mainland, or to the effect of stochastic processes working on a small population. Growth curve estimations showed H. chrysosireticus is slow growing and long-lived, reaching breeding age at around five years. Population size estimates for the main sub-population on Mana Island generated an estimate of 90 (95%C.I 70-136) animals, less than half (200-300) that arising from a survey of the same area in 1993 (200-300) using different survey and calculation methods. Juvenile mortality was high (63% estimate) in the first year and overall population growth slow. The geckos showed high site fidelity with over 90% moving less than 5m from their original point of capture. Population growth on Mana Island is slow despite the absence of mammalian predators, raising serious questions about the security of the remaining mainland populations. Two sets of simultaneous cage and enclosure experiments, designed to observe interactions between H. chrysosireticus and H. duvaucelii were conducted on Mana Island between December 1997 and February 1998. H. chrysosireticus were observed to increase their activity during the day in flax (F2,13 P=0.0040) and climb more in manuka (F2,5 P=0.0450) when in the presence of H. duvaucelii. H. duvaucelii also appear to have preyed upon young H. chrysosireticus when in close contact. The implications of introducing H. duvaucelii to Mana Island and future conservation measures for H. chrysosireticus are discussed.