Developing indices of relative abundance for monitoring cave and ground wētā (Orthoptera) in southern beech forest, New Zealand

Abstract

We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark-recapture estimates from 25 m 2 enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate highresolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates. ARTICLE HISTORY

Low structural complexity of nonnative grassland habitat exposes prey to higher predation

“…New Zealand's native wētā are also known to be less active at low temperatures (Carpenter et al. ), making them less vulnerable at these times. Greater locust survival at low temperature may also reflect hedgehogs’ lower hunting activity (Jones and Sanders ).…”

“…Our results support the hypothesized negative relationship between overnight temperature and locust survival, presumably reflecting locusts' lower activity (Mellanby 1939) or their emission of fewer odor cues at low temperature, which would make them less detectable by hedgehogs. New Zealand's native w et a are also known to be less active at low temperatures (Carpenter et al 2016), making them less vulnerable at these times. Greater locust survival at low temperature may also reflect hedgehogs' lower hunting activity .…”

The impact of mammalian insectivores Rattus rattus (Rat), Mus musculus (Mouse) & Erinaceus europeus (Hedgehog) on the size and abundance of mainland Coleoptera and Orthoptera

“…In addition, the importance of interactions between New Zealand's invertebrates and mammalian predators is yet to be quantified apart from for a few well-studied invertebrate species such as giant wētā in the genera Deinacrida and Motuwētā and some large weevil species (Kuschel & Worthy, 1996;Miskelly et al, 2018;Watts & Thornburrow, 2009;Winks et al, 1998). A lack of knowledge of invertebrate life histories and the high level of taxonomic expertise required to correctly identify invertebrate species has hampered efforts in this area (Carpenter et al, 2016). It is likely that among New Zealand's invertebrate fauna some species will have been adversely affected whilst some may have benefitted however, the identity of all but a small proportion of these species remains unknown Watts et al, 2019).…”

“…This may account for the lack of a significant size response in male tree wētā as the presence of rats is unlikely to change the competitive dynamics of male to male tree wētā competition. These antagonistic encounters occurs more frequently between males which will then face off in a bout of combat, but males have also been observed removing female wētā from tree cavities (Carpenter et al, 2016;Fitness et al, 2015;Moller, 1985).…”

“…This differs from the result of pitfall trapped cave wētā which were predicted do decline both in terms of catch and size. Whilst there is a significant body of knowledge relating to the ecology and behaviour of tree wētā, far less is known about cave wētā (Carpenter et al, 2016;Fitness et al, 2015). Cave wētā can refer to over 50 different species and behaviour differences between species are poorly understood.…”