Alexandra’s dry hills could be the last stronghold of an increasingly rare native grasshopper.
Little Valley Rd has a population of the endemic Otago lowland grasshopper, Phaulacridium otagoense
It may not seem that significant. However, a hybrid swarm is expected to take over the Otago and common New Zealand species.
Massey University evolutionary biologist Prof Mary Morgan-Richards has been carrying out a grasshopper study where it was discovered that the two distinct species, the Otago lowland grasshopper Phaulacridium otagoense) and the more common New Zealand lowland grasshopper Phaulacridium marginale) were mating and mixing at random.
Agriculture had intensified over the past 50 years and the study suggests that the hybridisation is the result of changes to the grasshoppers’ habitat through the introduction of mammals that eat the natural vegetation, and the colonisation of many non-native plant species.
Little Valley Rd was the exception, where Prof Morgan-Richard’s team had found some grasshoppers that looked like the Otago and common New Zealand species, but very few of the “intermediate” (hybrid) grasshoppers.
“This was unusual in our study, as the other locations where both species occurred had many grasshoppers that were intermediate, and very few that looked like the two named species.
“We do not know why Little Valley Rd is different but it is more like the situation described in the 1970s and 1980s, when the two species lived side-by-side without forming lots of hybrids.”
She suggested the Little Valley area had many Otago lowland grasshoppers and the common New Zealand species had just arrived, as its distribution expanded.
In a recently published article in the Journal of Evolutionary Biology, Prof Morgan-Richards describes how things had changed since these species were studied in the 1970s.
About 50 years ago, the two species were separate and distinct and were found living next to one another in distinct habitats.
“It looks likely that the two grasshopper species will ultimately be replaced by one hybrid lineage while we watch.”
This could have an impact on native skinks, such as grand and Otago skinks, and native geckos such as the schist gecko and Cromwell Kawarau gecko, which feed on the Otago species, she said.
These grasshoppers are herbivores. They eat grass but prefer herbs, and they, in turn, are eaten by a range of predators such as hedgehogs, pipits, lizards and spiders.
In the past, there would have been more insect-eating birds feeding during the day. These days, mammals will eat grasshoppers. Even feral cats eat insects.
Researchers believed rapid environmental change in the climate or the landscape had played a role in the rise of hybrid grasshoppers.
“Obviously, there’s been a lot of soil erosion from the rabbits, there’s been an increase of weeds, but also intensification of agriculture, changing with irrigation,” Prof Morgan-Richards said.
Her study describes the Otago lowland grasshopper as smaller and preferring drier soils. It is found on degraded tussock grassland characterised by areas of bare, stony ground, with patches of the endemic Raoulia.
The common New Zealand lowland grasshopper is found in places with more ground cover that are less eroded by overgrazing, but the insect also has wider range of habitats where it does well.
The common lowland species seems to be common in many disturbed sites and can cope with wetter soil.
“Irrigation is expected to result in less habitat available for the Otago endemic. As agriculture/horticulture expands we can expect reduction in the distribution of the Otago species, and probably expansion of the hybrid form.”