How Ice Ages Spurred the Evolution of New Zealand’s Exotic and Luxurious Native Flora

Chris Lask Associate Professor of Ecology at the University of Waikato.

Analytics: Recently genetic research It has shed new light on the long-running debate over the evolutionary origins of some of New Zealand’s most exotic plants.

More than one in ten native trees and shrubs have small leaves that are spaced on tangled, wired branches, often growing in a zigzag pattern. Some of these plants were once the preserve of botanists, and have recently gained popularity as decoration plants.

Nowhere else on Earth did this form of “cut” growth originate independently in so many plant families.

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It’s an amazing case of convergent evolution response to environmental stresses. But what are the environmental pressures? The answer may help us determine how New Zealand’s ecosystems are managed.

Climate or moa?

German botanist in the nineteenth century Ludwig Diels Note that the small-leaved shrubs are typical of dry climates. He thought that the splitting form might have arisen in response to Cold and dry conditions during the ice ages.

In the seventies of the last century,browse mo“The hypothesis arose, arguing that the subdivision form is a now-obsolete defense against the browsing of large flightless birds that became extinct shortly after Polynesian settlement.

experiments It has since supported the browsing hypothesis. However, the concentration of cut plants in cold and dry areas indicates this climate He is also somehow involved.

Also, is there evidence that the small leaves of the crackers exist? less susceptible to refrigeration of large leaves. But the climate does not seem to explain extraordinary hardness From the branches of cut plants.

synthetic hypothesis

molecular dating It shows that most of the divided plant species arose during the past five million years. But fossils And the genetic evidence moa appears here for much longer. This means that moa browsing alone does not explain the evolution of division forms in many plant families.

The guide seems more consistent with the latest synthetic hypothesis The moa surf had an even greater effect when plants were exposed to a new combination of conditions: cooling around the world, the development of cold, dry climates in the recent highlands of the Southern Alps, and fertile new soil derived from glaciers. cliff.

More than one in ten native trees and shrubs have small leaves that are spaced on tangled, wired branches, often growing in a zigzag pattern.

Wikimedia Commons

More than one in ten native trees and shrubs have small leaves that are spaced on tangled, wired branches, often growing in a zigzag pattern.

Frigid, dry climates posed direct physiological challenges to plants, but they also left them more vulnerable to browsing by preventing them from growing rapidly beyond the reach of moa. Thus, climatic constraints on growth may have made anti-brown defenses more important for plant survival.

Support for this hypothesis comes from a hadith an experiencewhich found that climate affected the effect of deer browsing on competition between dividing plants and their broadleaf relatives that grow in tree gaps.

Moreover, the new fertile soil generated by erosion from glaciers would enhance the nutrient content of plant tissues, which could lead to increased browsing pressure. Studies of the African savannah show that thistles and band-like growths are typical fertile soil With abundant browsing mammals.

Do deer serve as moa substitutes?

For centuries after the moa went extinct, there were no large surfers in New Zealand, until European settlers introduced deer and other hoofed animals. Although deer are considered both game animals and a source of food, they are also considered pests due to their effect on native plants.

Nutrition Experiments Both birds and . showed hooves Herbivores are not eager to eat divided plants if substitutes with large, smooth leaves are available. Young leaves spaced apart along wired branches Reduces bite size And it makes it difficult for browsers to meet their nutritional needs.

He studied ancient scholars moa . diet By identifying pollen grains in fossilized feces (coprolites). Interpretation of the data is hampered by our inability to identify pollen at the species level in plant groups that include both dichotomous and broadleaf species. But it seems likely that the divided plants presented similar nutritional challenges to moa.

analysis Kobulites mo He points out that forest models a thousand years ago were more diverse than those we see today, after more than 150 years of browsing by deer. This indicates that the effect of moa on vegetation was less than that of deer today.

Factors that limit the effect of moa on vegetation

Unlike deer in contemporary New Zealand, the moa encountered a deadly predator across the country: the now extinct haast eagle. Although the moa can surf safely under forest canopies, it was vulnerable on watering sites and in open areas.

In contrast, although deer face strong hunting pressures in some areas, recreational hunting has little impact in remote and rugged areas such as the Kaweka Ranges, where there are uncontrolled populations of sika deer It threatens regeneration even for relatively unpalatable trees like mountain beech.

Artists' impression of a Harpagornis (Haast eagle) attacking a moa.

supplied

Artists’ impression of a Harpagornis (Haast eagle) attacking a moa.

Fast growing palatable shrubs and small trees such as KaramiAnd the Batu And the What is the They probably get the best chance of escaping moa surf when the waterfalls allow enough light to enable them to grow quickly out of their reach, at least in Warmer regions As these plants can grow more than a meter in one growing season.

Treefall gaps must have introduced two other advantages to palatable plants. Fallen tree remains impede access by large herbivores, and the canopy slots would have exposed the moa to the attack of the Haast eagle.

Moa may have been less able to exploit the vegetation on the steep slopes than today’s deer and goats. So it’s likely that moa’s effect is across the New Zealand landscape less prevalent From the current impact of hoofed browsers.

Finally, moa probably had a slower metabolism than did mammalian browsers of similar size, implying lower energy requirements and therefore lower feeding rates. Close living relatives of moa (kiwi and emu) burns less energy They are herbivorous mammals of similar body weight or large flying birds such as swans and geese.

The future of deer in New Zealand

Deer can serve as incomplete substitutes for moa, but only if they are effectively controlled throughout the country.

1080 air drops to control rats, stoats and possums usually kill deer, although death rate It varies widely. This is one way deer numbers can be kept at acceptable levels in remote and rugged areas, where the pressure of recreational hunting is minimal. aerial execution Through shooting it also showed potential.

Commercial hunting cannot be relied on for deer control, due to market volatility. When the price of venison drops, there is little incentive to hunt deer. So 1080 aerial culling or currently aerial culling seem to be the only realistic ways to reduce the impact of deer in remote and rugged areas.

This article was originally published Conversation. Read the original article.

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