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Invasive mammal impacts on forest tree weta

Invasive mammal impacts on forest tree weta. Wendy Ruscoe Wildlife Ecology & Epidemiology Team Landcare Research, Lincoln. Weta. >70 species. Tusked weta. Cave weta. Tree weta. Ground weta. Giant weta. Weta in the environment. Consumers of invertebrates, fruit. Seed dispersal

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Invasive mammal impacts on forest tree weta

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  1. Invasive mammal impacts on forest tree weta Wendy Ruscoe Wildlife Ecology & Epidemiology Team Landcare Research, Lincoln

  2. Weta >70 species Tusked weta Cave weta Tree weta Ground weta Giant weta

  3. Weta in the environment • Consumers of invertebrates, fruit. • Seed dispersal • Food: tuatara, kiwi, weka, saddleback and laughing owl are native predators • 16 species considered ‘threatened’

  4. Threats • Predation by invasive mammals (rodents, cats, mustelids, hedgehogs) • Habitat loss. • Herbivory (invasive herbivores) removing/changing habitat structure. Rats – the primary culprit!? • Some species confined to rat-free islands. • Effects of rat eradications

  5. Rat diet • Predominantly seeds, fruit, and invertebrates (up to 50% of diet). • Tree weta and stick insects predominate. Sweetapple & Nugent 2007, P. Sweetapple pers. comm.

  6. Study: Impacts of Rats on Weta • Part of a larger experiment • Removed rats (and other pests) and monitored tree weta. • Monitored rats

  7. Experimental Setup–manipulating rat populations. No Treatment Stoat Trapping x 2 900 ha 900 ha 900 ha 900 ha 1080 Aerial + Diphacinone (2yrs) 1080 Aerial Control

  8. Effect on rat populations – 3 years Post Treatment: Stoat Trapping No Treatment x 2 1080 Aerial + Diphacinone (2yrs) 1080 Aerial Control

  9. Treatment effect on rat populations – 3 years Post Treatment: • Stoat Trapping and No Treatment: ‘average’ rat numbers in both areas. • 1080 operation: 1 year of really Low rats and then 1-2 years of High rat numbers. • 1080+continuous diphacinone poisoning: Low rat numbers for 3 years. ?

  10. Changes in tree weta occupancyNon treatment sites – average rat numbers Treatments

  11. Changes in tree weta occupancy1080 + diphacinone – Low rat numbers Treatments

  12. Changes in tree weta occupancy1080 only – Low then high rat numbers Treatments

  13. Effects of Rat Control (1080 + ongoing control) • Higher numbers of tree weta maintained • Effects of a 1080 operation on weta: • Higher numbers of tree weta in the mid-term <3 years. ‘Window of relieve from predation’ • **** No negative impact within 3 years *** • But after that???

  14. Biodiversity ‘outcome’ monitoring • Provide a low-tech alternative to bird monitoring to show benefits of pest control. • Tree weta respond reasonably quickly to pest control operations that impact rats. • They are easy to monitor and can engage the general public.

  15. Thanks • Funding provided by Foundation for Research, Science & Technology • Department of Conservation • Field staff.

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