Research investigating how invasive predator control impacts insects

30 April 2020

A University of Waikato researcher says New Zealand’s successful predator control measures which are helping our native birds thrive, may be having an unexpected impact on our native insect populations.

Dr Andrew Barnes and PhD student Nigel Binks have been studying how invasive predator control measures are impacting insect populations at sites around the Waikato. They plan to extend their studies later this year, into large areas of Beech forest in the South Island currently controlled by 1080.

Dr Barnes said their initial research at Waikato sites showed predator control was having a strong, significant and positive impact on New Zealand’s native bird species but the flow on effect of that seemed to be an impact on invertebrate or insect communities which spend a lot of their lives below ground.

“The impact might be more pervasive than we originally thought. It’s something we just don’t know enough about and what we’re trying to learn about now,” he said.

Dr Barnes said they used food webs to carry out their research, which measure the transfer of energy between predators and their prey in an ecosystem.

“In the past, studies have focused on how invasive predator control impacts species such as the Kiwi. A food web approach allows us to look at how predator control impacts all species in the ecosystem and to look at it on a much larger scale,” he said.

He said using a food web approach was the next generation of invasive predator research in New Zealand as scientists worked to understand how these predators affected whole ecosystems, rather than just specific species.

For example, if predator control meant there were more Kiwi in an area, how did that impact on insect populations in the area, or the flora and fauna in a conservation site, he said.

“Quantifying the energy flow that happens when predators eat prey or herbivores eat plants lets us calculate how much energy is used. We can then scale it up to work out how much predation and herbivory there is in an ecosystem and how much potential for damage there is,” he said.

Locations such as the Sanctuary Mountain Maungatautari Ecological Reserve, Walter Scott Reserve near Pirongia, and Kaimai Forest had been the focus of their studies in the Waikato.

Dr Barnes said Maungatautari with its predator proof fence had the strongest predator controls, while Walter Scott Reserve had strong trapping controls and the sites in the Kaimai Forest Park had the least predator controls.

“The cool thing from the initial research is we’ve found a lot of these community led projects are having a strong, significant and positive impact on our native bird communities,” Dr Barnes said.

“What we’ve also discovered is it seems to be having some impact on our insect communities too, but we need to do more work to understand how much,” he said.

The research was expected to continue later this year and extend into South Island sites which would allow them to test their research and food web approach on a much larger scale, he said.

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