The New Zealand Herald
Odd coupling highlights country’s biodiversity crisis
The mating of two distinctly different native species of grasshopper might simply seem a bizarre, almost vulgar quirk of New Zealand nature.
But scientists say the phenomenon they've been observing points to a much bigger and more important crisis facing our country.
It's a tragic symbol of what's become of our natural landscapes and the rich biodiversity they supported for millions of years.
With the ongoing transformation of our countryside into agricultural land has come the displacement of entire ecosystems.
Several years ago, Massey University researchers began looking at the distribution of genetic variation between the two flightless grasshopper species belonging to the Phaulacridium genus. Phaulacridium marginale is found across a wide area spanning the North Island and most of the South Island, typically in lowland grasslands.
Its much smaller cousin, P. otagense, has long been confined to small pockets in the Mackenzie Basin and Central Otago, mostly on dry slopes and riverbeds.
In a new study, Massey evolutionary biologist Professor Steve Trewick and his colleagues drew on spatial location information and climate modelling to explore how the habitat used by each of the species had been distributed and changed over time.
That work turned up even more genetic diversity in the P. otagense — but something else yet more compelling.
Trewick said there was evidence of introgression, or the sharing of genetics, by the two species as a result of hybridising.
This mixing had happened as P. marginale had reached the enclaves of P. otagense, making its habitat an even smaller stronghold in the process.
It would likely never have happened in the lush, natural, forestdominated world that was once New Zealand's landscape, but had been enabled by its transformation into pastures for agriculture.
This had paved the way for more range expansion, meaning more ecological competition and reproductive mixing.
“Large-scale landscape changes associated with agriculture have an overlooked and forgotten impact; directly through replacement of entire ecosystems, and indirectly through alteration of connectivity among locations and surviving habitat patches.” Today, New Zealand consists of 26.8 million hectares, of which agriculture covers just over half, exotic forestry makes up 8.1 per cent and native forest covers 29.6 per cent, with the rest including environments such as mountains, towns and cities. While recent estimates show sheep and beef farming land had shrunk by four million ha since 1990, dairy and forestry land increased by 1.3 million ha. “In addition to directly causing extinction and so loss of biodiversity by removal of habitat, these changes can result in novel species interactions that also contribute to diversity loss,” Trewick said. “This is important for New Zealand where our emphasis on agriculture has meant local extinction and other effects have gone unobserved. This example provides a glimpse at the extent of biological change in New Zealand since European settlement.”