The New Zealand Herald

Odd coupling highlights country’s biodiversi­ty crisis


Jamie Morton

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.”

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