One of the prolific invasive species recorded on the camera traps during the study, rabbits are a favourite prey of top invasive predators like feral cats and ferrets. Photo / Supplied
One of the prolific invasive species recorded on the camera traps during the study, rabbits are a favourite prey of top invasive predators like feral cats and ferrets. Photo / Supplied
A study in Hawke's Bay has revealed compromise rather than conflict between invasive predators when it comes to preying on our natives.
Research published by Patrick Garvey, Al Glen and Roger Pech in the journal Ecological Applications shows feral cats, ferrets and stoats coexist, despite competing aggressively for the sameresources.
Cats were the dominant predator in the arrangement, hunting day and night with a preference for rodents in forests to rabbits in pastures.
Stoats preferred daylight and would avoid cat turf, while ferrets hunted underground at night.
Dr Garvey said understanding the interactions between species was a way to determine how to effectively deploy pest-removal strategies.
"The New Zealand government recently adopted an ambitious goal to eradicate stoats, ship rats and possums (Trichosurus vulpecula) from the entire country by 2050.
"But our study revealed the complex dynamics in invasive communities, where the removal of one community member may benefit another."
"Where complex interactions between native and introduced biota occur at landscape scales, upsetting the established equilibrium can have unforeseen impacts."
These complex interactions sometimes meant removing larger predators like cats could lead to a rise in smaller predator numbers and removing introduced prey like rats and rabbits could lead to predators eating more native fauna.
The interaction between predators has created a delicate balance where the eradication of one predator may lead to worse infestations of other kinds of invasive species. Photo / Supplied
The researchers tested this effect by getting professional trappers to remove the ferrets and cats to observe the effect on stoats, the smaller predator.
Dr Garvey said stoats went from being undetected to the most common invasive predator at the site within six months.
"Our research shows selectively removing a portion of the invasive community from a network of interacting species requires an understanding of changing spatial and temporal relationships to prevent undesirable outcomes."
An example of this is how cats can suppress stoats and indirectly relieve pressure on some native species such as cavity-nesting birds like the rifleman or saddleback, but it wouldn't compensate for the direct negative impacts that cats inflict on native species.
"Interspecific competition needs to be considered in any management plan, because controlling all New Zealand's invasive mammals without unexpected and potentially adverse impacts remains a serious challenge."
The study took place over three seasons at two farmland sites in Hawke's Bay 15 kilometres apart with no recent history of predator control.
Hawke's Bay operations manager for DoC Tryphena Cracknell said DoC control operations tend to focus on the broader range of pest species through a variety of methods rather than single species eradication.
"It wouldn't make sense to eradicate one pest species if another pest species is likely to have the same/or similar impact on native species."
She said DoC carries out predator control within the Boundary Stream Scenic Reserve to protect many native species, including translocated species.
"The predator control work being carried out by DoC in Boundary Stream Scenic Reserve is classified as 'sustained control' rather than 'eradication'."
She said the only 'eradication' operation being undertaken as part of Predator Free Hawke's Bay is possum eradication at Mahia peninsula led by Hawke's Bay Regional Council.
She said predator control was targeted at a wide range of pest species including rats, cats, mustelids and possums.
