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>

Founding Events and the Maintenance of Genetic Diversity in Reintroduced Populations

<p>As habitat loss, introduced predators, and disease epidemics threaten species worldwide, translocation provides one of the most powerful tools for species conservation. However, reintroduced populations of threatened species are often founded by a small number of individuals (typically 30 in New Zealand) and generally have low success rates. The loss of genetic diversity combined with inbreeding depression in a small reintroduced population could reduce the probability of establishment and persistence. Effective management of genetic diversity is therefore central to the success of reintroduced populations in both the short- and long-term. Using population modelling and empirical data from source and reintroduced populations of skinks and tuatara, I examined factors that influence inbreeding dynamics and the long-term maintenance of genetic diversity in translocated populations. The translocation of gravid females aided in increasing the effective population size after reintroduction. Models showed that supplementation of reintroduced populations reduced the loss of heterozygosity over 10 generations in species with low reproductive output, but not for species with higher output. Harvesting from a reintroduced population for a second-order translocation accelerated the loss of heterozygosity in species with low intrinsic rates of population growth. Male reproductive skew also accelerated the loss of genetic diversity over 10 generations, but the effect was only significant when the population size was small. Further, when populations at opposite ends of a species' historic range are disproportionately vulnerable to extinction and background inbreeding is high, genetic differentiation among populations may be an artefact of an historic genetic gradient coupled with rapid genetic drift. In these situations, marked genetic differences should not preclude hybridising populations to mitigate the risks of inbreeding after reintroduction. These results improve translocation planning for many species by offering guidelines for maximising genetic diversity in founder groups and managing populations to improve the long-term maintenance of diversity. For example, founder groups should be larger than 30 for reintroductions of species with low reproductive output, high mortality rates after release, highly polygynous mating systems, and high levels of background inbreeding. This study also provides a basis for the development of more complex models of losses of genetic diversity after translocation and how genetic drift may affect the long-term persistence of these valuable populations.</p>

Founding Events and the Maintenance of Genetic Diversity in Reintroduced Populations

<p>As habitat loss, introduced predators, and disease epidemics threaten species worldwide, translocation provides one of the most powerful tools for species conservation. However, reintroduced populations of threatened species are often founded by a small number of individuals (typically 30 in New Zealand) and generally have low success rates. The loss of genetic diversity combined with inbreeding depression in a small reintroduced population could reduce the probability of establishment and persistence. Effective management of genetic diversity is therefore central to the success of reintroduced populations in both the short- and long-term. Using population modelling and empirical data from source and reintroduced populations of skinks and tuatara, I examined factors that influence inbreeding dynamics and the long-term maintenance of genetic diversity in translocated populations. The translocation of gravid females aided in increasing the effective population size after reintroduction. Models showed that supplementation of reintroduced populations reduced the loss of heterozygosity over 10 generations in species with low reproductive output, but not for species with higher output. Harvesting from a reintroduced population for a second-order translocation accelerated the loss of heterozygosity in species with low intrinsic rates of population growth. Male reproductive skew also accelerated the loss of genetic diversity over 10 generations, but the effect was only significant when the population size was small. Further, when populations at opposite ends of a species' historic range are disproportionately vulnerable to extinction and background inbreeding is high, genetic differentiation among populations may be an artefact of an historic genetic gradient coupled with rapid genetic drift. In these situations, marked genetic differences should not preclude hybridising populations to mitigate the risks of inbreeding after reintroduction. These results improve translocation planning for many species by offering guidelines for maximising genetic diversity in founder groups and managing populations to improve the long-term maintenance of diversity. For example, founder groups should be larger than 30 for reintroductions of species with low reproductive output, high mortality rates after release, highly polygynous mating systems, and high levels of background inbreeding. This study also provides a basis for the development of more complex models of losses of genetic diversity after translocation and how genetic drift may affect the long-term persistence of these valuable populations.</p>

The Breeding Biology and Habitat Relationships of the Yellowhead

<p>This study aimed to find an explanation for the decline of yellowheads and formulate recommendations for management and further research on the species. There were three main lines of investigation: basic population ecology and behaviour; the effect of introduced predators on breeding; and the habitat relationships of the species. A detailed study of a yellowhead population in the Eglinton Valley in Fiordland National Park was undertaken. Birds were caught and banded and their behaviour, breeding and survival monitored for 4 years. The relationship between yellowhead distribution and vegetation, topography, and fertility were investigated in part of Mt Aspiring National Park during one summer. Yellowheads suffered high rates of predation from stoats during "plagues" that occurred after heavy beech seeding. Three aspects of yellowhead biology made them vulnerable to mammalian predation: (1) they nested in holes and predators killed not only eggs and nestlings, but also incubating adults; (2) only the females incubated, thus losses to predators had a greater effect on the population than if equal numbers of males and females were killed; and (3) yellowheads nested later than most other forest passerines and were still nesting when stoat numbers reached their summer peak. Though the yellowhead's hole nesting habit made them vulnerable to mammals it restricted nest parasitism and predation by long-tailed cuckoos and hole nesting is likely to have evolved in response to cuckoos. Yellowheads were found to be tall forest specialists; they occurred more frequently in tall forests than short ones, and preferentially used the largest trees. Their choice of nest sites had no effect on their preference for any forest types. The forests they favoured grew mainly on fertile valley floors at low altitudes. Yellowhead populations in "good habitats" raised two broods a year and these populations are probably sufficiently productive to withstand stoat plagues occurring once every 5 years, the average frequency of this event. Populations in "poor habitats" raise only one brood and their productivity is probably insufficient to match losses to stoats. Such populations are probably slowly declining, and are very vulnerable to extinction. A habitat suitability index was devised and forests in the north of the South Island from which yellowheads have disappeared, were compared with those in the south where yellowheads persist. Northern forests were as good for yellowheads as southern ones. Thus, the combination of habitat preference and predation cannot account for the recent disappearance of yellowheads from the northern half of the South Island. The decline in yellowheads was attributed to both predation by introduced mammals and competition with introduced vespulid wasps. Predation may have eliminated yellowheads from podocarp-dominated forests where predator numbers are constantly high, but they survive in some beech forests where predator numbers rise only once every five years. However, even within beech forests only the most productive populations are sufficiently productive to survive predation and these populations are probably susceptible to competition with wasps which eat large numbers of invertebrates. Yellowheads are likely to be more vulnerable to wasp competition than other forest insectivores because: (1) predation has reduced their productivity more than other birds because they nest in holes; (2) they are specialised in low altitude, tall forest that the wasps also favour; (3) their breeding is later than most other forest birds and their period of juvenile dependence much longer. Yellowheads are still feeding fledgling yellowheads at the time when wasps numbers reach their peak in the autumn, whereas the offspring of other forest birds are independent by this stage.</p>

The Breeding Biology and Habitat Relationships of the Yellowhead

<p>This study aimed to find an explanation for the decline of yellowheads and formulate recommendations for management and further research on the species. There were three main lines of investigation: basic population ecology and behaviour; the effect of introduced predators on breeding; and the habitat relationships of the species. A detailed study of a yellowhead population in the Eglinton Valley in Fiordland National Park was undertaken. Birds were caught and banded and their behaviour, breeding and survival monitored for 4 years. The relationship between yellowhead distribution and vegetation, topography, and fertility were investigated in part of Mt Aspiring National Park during one summer. Yellowheads suffered high rates of predation from stoats during "plagues" that occurred after heavy beech seeding. Three aspects of yellowhead biology made them vulnerable to mammalian predation: (1) they nested in holes and predators killed not only eggs and nestlings, but also incubating adults; (2) only the females incubated, thus losses to predators had a greater effect on the population than if equal numbers of males and females were killed; and (3) yellowheads nested later than most other forest passerines and were still nesting when stoat numbers reached their summer peak. Though the yellowhead's hole nesting habit made them vulnerable to mammals it restricted nest parasitism and predation by long-tailed cuckoos and hole nesting is likely to have evolved in response to cuckoos. Yellowheads were found to be tall forest specialists; they occurred more frequently in tall forests than short ones, and preferentially used the largest trees. Their choice of nest sites had no effect on their preference for any forest types. The forests they favoured grew mainly on fertile valley floors at low altitudes. Yellowhead populations in "good habitats" raised two broods a year and these populations are probably sufficiently productive to withstand stoat plagues occurring once every 5 years, the average frequency of this event. Populations in "poor habitats" raise only one brood and their productivity is probably insufficient to match losses to stoats. Such populations are probably slowly declining, and are very vulnerable to extinction. A habitat suitability index was devised and forests in the north of the South Island from which yellowheads have disappeared, were compared with those in the south where yellowheads persist. Northern forests were as good for yellowheads as southern ones. Thus, the combination of habitat preference and predation cannot account for the recent disappearance of yellowheads from the northern half of the South Island. The decline in yellowheads was attributed to both predation by introduced mammals and competition with introduced vespulid wasps. Predation may have eliminated yellowheads from podocarp-dominated forests where predator numbers are constantly high, but they survive in some beech forests where predator numbers rise only once every five years. However, even within beech forests only the most productive populations are sufficiently productive to survive predation and these populations are probably susceptible to competition with wasps which eat large numbers of invertebrates. Yellowheads are likely to be more vulnerable to wasp competition than other forest insectivores because: (1) predation has reduced their productivity more than other birds because they nest in holes; (2) they are specialised in low altitude, tall forest that the wasps also favour; (3) their breeding is later than most other forest birds and their period of juvenile dependence much longer. Yellowheads are still feeding fledgling yellowheads at the time when wasps numbers reach their peak in the autumn, whereas the offspring of other forest birds are independent by this stage.</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>