invasive mammal impacts on forest tree weta wendy ruscoe wildlife ecology & epidemiology team...
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Invasive mammal impacts on forest tree weta
Wendy Ruscoe
Wildlife Ecology & Epidemiology Team
Landcare Research, Lincoln
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’
Threats
1. Predation by invasive mammals(rodents, cats, mustelids, hedgehogs)
2. Habitat loss.
3. Herbivory (invasive herbivores) removing/changing habitat structure.
Rats – the primary culprit!?• Some species confined to rat-free islands.• Effects of rat eradications
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.
Study: Impacts of Rats on Weta
• Part of a larger experiment
• Removed rats (and other pests) and monitored tree weta.
• Monitored rats
1080 Aerial Control
1080 Aerial + Diphacinone
(2yrs)
Stoat Trapping
No Treatment
x 2
Experimental Setup–manipulating rat populations.
900 ha900 ha
900 ha 900 ha
1080 Aerial Control
1080 Aerial + Diphacinone (2yrs)
Stoat Trapping
No Treatment
Effect on rat populations – 3 years Post Treatment:
x 2
• 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.
?
Treatment effect on rat populations – 3 years Post Treatment:
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???
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.