Ecology and Development in an Island Population of Wellington Tree Weta (Hemideina crassidens).

<p>Sexual selection and the mating system of the Wellington tree weta has been extensively studied during the last 15 years. In the past 10 years, nutritional ecology and factors affecting the distribution of species in the genus Hemideina have also been examined in great detail. This recent work and the extensive studies of New Zealand tree weta species that preceded it provide much context and comparison for this thesis, which examines the ecology of a population of tree weta living on Matiu/Somes Island. Less is known about factors affecting the development of the exaggerated male weaponry that is characteristic of much of the genus Hemideina. This thesis firstly presents a mark-recapture study conducted over 42 months on Matiu/Somes Island to obtain ecological information about the population. Secondly, this thesis presents an experiment on the effects of protein supplement on growth and weaponry in male Wellington tree weta derived from the Matiu/Somes Island population. The results of the field study indicate that male tree weta live longer than females on Matiu/Somes Island and weapon size is positively related to adult longevity of males. Seasonal patterns shown in the population on Matiu/Somes Island and inferences about aspects of their life cycle are discussed. Female tree weta on Matiu/Somes Island formed harems throughout each year and there was a positive relationship between males weapon size and the number of females in a harem. Results do not indicate seasonal differences in harem-forming behaviours of females. The results of the captive rearing study include a shorter development time and larger weaponry as adults in males raised on a protein supplemented diet, compared to individuals raised on an entirely herbivorous diet. Details of differences in the course of development are also discussed for the two diet treatment groups.</p>

Ecology and Development in an Island Population of Wellington Tree Weta (Hemideina crassidens).

<p>Sexual selection and the mating system of the Wellington tree weta has been extensively studied during the last 15 years. In the past 10 years, nutritional ecology and factors affecting the distribution of species in the genus Hemideina have also been examined in great detail. This recent work and the extensive studies of New Zealand tree weta species that preceded it provide much context and comparison for this thesis, which examines the ecology of a population of tree weta living on Matiu/Somes Island. Less is known about factors affecting the development of the exaggerated male weaponry that is characteristic of much of the genus Hemideina. This thesis firstly presents a mark-recapture study conducted over 42 months on Matiu/Somes Island to obtain ecological information about the population. Secondly, this thesis presents an experiment on the effects of protein supplement on growth and weaponry in male Wellington tree weta derived from the Matiu/Somes Island population. The results of the field study indicate that male tree weta live longer than females on Matiu/Somes Island and weapon size is positively related to adult longevity of males. Seasonal patterns shown in the population on Matiu/Somes Island and inferences about aspects of their life cycle are discussed. Female tree weta on Matiu/Somes Island formed harems throughout each year and there was a positive relationship between males weapon size and the number of females in a harem. Results do not indicate seasonal differences in harem-forming behaviours of females. The results of the captive rearing study include a shorter development time and larger weaponry as adults in males raised on a protein supplemented diet, compared to individuals raised on an entirely herbivorous diet. Details of differences in the course of development are also discussed for the two diet treatment groups.</p>

The impacts of an introduced mammalian predator (Mus musculus) on tree weta (Hemideina trewicki) and skinks (Oligosoma polychroma, Oligosoma infrapunctatum and Oligosoma lineoocellatum) in Cape Sanctuary, Hawkes Bay

<p>The introduction of exotic species, particularly predators, into new ecosystems is one of the biggest causes of loss of biodiversity across the globe. Understanding the impacts that introduced species have on native species is crucial in conservation management, particularly for those species that are conservation-reliant. I examined the impact that an introduced mammalian predator (Mus muscularus) had on native prey populations of common (Oligosoma polychroma), speckled (Oligosoma infrapunctatum) and spotted (Oligosoma lineoocellatum) skinks and Hawkes Bay tree weta (Hemideina trewicki). I conducted a mark-recapture study using pitfall traps to examine the impact of mice on skink populations. I conducted a mark-recapture study through manual counts to examine the impact of mice on tree weta. I also examined occupancy of weta refuges while in the presence of mice. There were no captures of spotted skinks, and very low captures of common skinks. There was no significant change in capture numbers for speckled skink, however observed numbers did decline from November 2013 to November 2014. There was a significant decline in capture rates for tree weta over the course of my study. It was difficult to establish mice as the sole cause of any observed changes, however it is likely that they are a limiting factor for skink and weta populations, and have the potential to be a major factor in the observed decline in the tree weta population. My results highlight the importance of monitoring native populations, particularly those that are small and are in the presence of introduced predators. By monitoring native populations conservation management can make better informed decisions to work towards populations not being ‘conservation-reliant’.</p>

The impacts of an introduced mammalian predator (Mus musculus) on tree weta (Hemideina trewicki) and skinks (Oligosoma polychroma, Oligosoma infrapunctatum and Oligosoma lineoocellatum) in Cape Sanctuary, Hawkes Bay

<p>The introduction of exotic species, particularly predators, into new ecosystems is one of the biggest causes of loss of biodiversity across the globe. Understanding the impacts that introduced species have on native species is crucial in conservation management, particularly for those species that are conservation-reliant. I examined the impact that an introduced mammalian predator (Mus muscularus) had on native prey populations of common (Oligosoma polychroma), speckled (Oligosoma infrapunctatum) and spotted (Oligosoma lineoocellatum) skinks and Hawkes Bay tree weta (Hemideina trewicki). I conducted a mark-recapture study using pitfall traps to examine the impact of mice on skink populations. I conducted a mark-recapture study through manual counts to examine the impact of mice on tree weta. I also examined occupancy of weta refuges while in the presence of mice. There were no captures of spotted skinks, and very low captures of common skinks. There was no significant change in capture numbers for speckled skink, however observed numbers did decline from November 2013 to November 2014. There was a significant decline in capture rates for tree weta over the course of my study. It was difficult to establish mice as the sole cause of any observed changes, however it is likely that they are a limiting factor for skink and weta populations, and have the potential to be a major factor in the observed decline in the tree weta population. My results highlight the importance of monitoring native populations, particularly those that are small and are in the presence of introduced predators. By monitoring native populations conservation management can make better informed decisions to work towards populations not being ‘conservation-reliant’.</p>

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

<p>The impact of introduced mammalian predators on indigenous vertebrates is relatively well documented, however the general responses of indigenous invertebrate communities is less well known. Many indigenous invertebrates, particularly the large flightless species such as those in the genus Deinacrida (Orthoptera) and Anagotus (Curculionidae) have been extirpated from much of their range due largely to the impacts of introduced predators. Despite these well-known examples very little is known about the general impact of introduced predators on invertebrate communities. Beginning in 2012 pitfall traps and artificial wētā motels were established across seven study sites in the Aorangi and Remutaka ranges east of Wellington alternately baited with squid and monitored two to three times annually. Mammal tracking took place in the form of tracking tunnels giving three mammal indexes for rats (Rattus rattus), mice (Mus musculus) and hedgehogs (Erinaceus europeus). Cavity dwelling wētā in wētā motels were measured and counted in situ whilst pitfall trapped Coleoptera and Orthoptera were transported to the lab for measuring and identification. Linear mixed effects model, type 3 ANOVAS and generalised linear mixed models were used to examine whether mammal index had any impact on the size and the catch or occupancy of invertebrates. Increased rat and mouse tracking was associated with reduced coleoptera catch whilst increased hedgehog tracking was correlated with increases in Coleoptera catch. Pitfall trapped wētā (Hemiandrus spp) showed strong negative responses to increased rat tracking, neutral responses to mice and positive responses to hedgehogs. Tree wētā (Hemideina crassidens) occupancy rates declined in response to increased mouse abundance whilst the mean size of tree wētā residing in wētā motels showed an increase in response to rats and mice. These results show the complexity of understanding mammal invertebrate interactions which cannot be expected to be the same in all environments or across all taxa. Environmental factors typically impact far more strongly on invertebrate populations than they do on vertebrates and can obscure the impacts of top down predation in such studies. The results reported in this study only became apparent after 5+ years of sampling, demonstrating the importance of long-term temporal analysis of invertebrate communities in response to mammals before trends start to emerge. More research is required into the basic ecology and population dynamics of invertebrate communities before more general trends can be discerned.</p>

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

<p>The impact of introduced mammalian predators on indigenous vertebrates is relatively well documented, however the general responses of indigenous invertebrate communities is less well known. Many indigenous invertebrates, particularly the large flightless species such as those in the genus Deinacrida (Orthoptera) and Anagotus (Curculionidae) have been extirpated from much of their range due largely to the impacts of introduced predators. Despite these well-known examples very little is known about the general impact of introduced predators on invertebrate communities. Beginning in 2012 pitfall traps and artificial wētā motels were established across seven study sites in the Aorangi and Remutaka ranges east of Wellington alternately baited with squid and monitored two to three times annually. Mammal tracking took place in the form of tracking tunnels giving three mammal indexes for rats (Rattus rattus), mice (Mus musculus) and hedgehogs (Erinaceus europeus). Cavity dwelling wētā in wētā motels were measured and counted in situ whilst pitfall trapped Coleoptera and Orthoptera were transported to the lab for measuring and identification. Linear mixed effects model, type 3 ANOVAS and generalised linear mixed models were used to examine whether mammal index had any impact on the size and the catch or occupancy of invertebrates. Increased rat and mouse tracking was associated with reduced coleoptera catch whilst increased hedgehog tracking was correlated with increases in Coleoptera catch. Pitfall trapped wētā (Hemiandrus spp) showed strong negative responses to increased rat tracking, neutral responses to mice and positive responses to hedgehogs. Tree wētā (Hemideina crassidens) occupancy rates declined in response to increased mouse abundance whilst the mean size of tree wētā residing in wētā motels showed an increase in response to rats and mice. These results show the complexity of understanding mammal invertebrate interactions which cannot be expected to be the same in all environments or across all taxa. Environmental factors typically impact far more strongly on invertebrate populations than they do on vertebrates and can obscure the impacts of top down predation in such studies. The results reported in this study only became apparent after 5+ years of sampling, demonstrating the importance of long-term temporal analysis of invertebrate communities in response to mammals before trends start to emerge. More research is required into the basic ecology and population dynamics of invertebrate communities before more general trends can be discerned.</p>

Viability and fertility of hybrid New Zealand tree wētā Hemideina spp. (Orthoptera: Anostostomatidae)

Natural hybridization between species provides an opportunity to study the mechanisms that maintain independent lineages and may help us understand the process of speciation. The New Zealand tree wētā speciesHemideinathoracicaproduces F1hybrids where it lives in sympatry with two closely related species:HemideinacrassidensandHemideinatrewicki. This study looked at the viability and fertility of F1hybrid wētā betweenH.thoracicaandH.crassidensthat were collected from the wild and kept in captivity. The hybrids appeared to have normal viability from the late juvenile stage, with all male wētā maturing at a late instar. Male F1hybrids displayed normal mating behavior and one male produced offspring in captivity. In contrast to Haldane’s rule, female F1hybrids appeared to be infertile; they refused to mate and did not produce eggs. No evidence ofWolbachiainfection was identified in any of the three North IslandHemideinaspecies.