ecosystem importance: New Zealand's story (Introduction)

by David Turell , Sunday, September 04, 2022, 16:16 (809 days ago) @ David Turell

A top predator always appears:

https://knowablemagazine.org/article/living-world/2022/how-giant-eagle-dominated-ancien...

"New Zealand has long been known as a place for the birds — quite literally. Before people arrived 700 years ago, the archipelago hosted an idiosyncratic ecosystem, nearly free of mammals. More than 200 bird species filled a food web all their own. Rather than cows or antelopes, there was a family of flightless birds known as moa. And in place of apex predators like tigers, New Zealand had Haast’s eagle.

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"Scientists now believe that this superlative bird was one in a wave of feathered invaders that conquered New Zealand over a relatively short period. And this was not the only wave of invasions. Haast’s eagle — despite being gone for centuries — has revealed that we live in a much more connected world than we once thought, says biologist Michael Knapp of the University of Otago, who has studied the eagle. If such seemingly isolated islands have repeatedly attracted so many incoming species, he says, then “natural invasions” must be a major force in ecosystems across the world.

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"New Zealand retained unusual species — including, famously, the flightless kiwi. Combined with these extant oddballs, the moa fossils helped to establish the idea that New Zealand was a lost world, a place where ancient creatures, sheltered by distance from the rest of the world, managed to survive mass extinction events. Later geologists confirmed that these rocky islands had once been a part of a supercontinent they called Gondwana, but split away about 80 million years ago. In 1990, a television series described New Zealand’s islands as “Moa’s Ark,” popularizing the catchy name of the long-held model of how its bird-filled ecosystem came to be.

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"Knapp notes that other raptors, perhaps owls or falcons, could have fed on the islands’ smallest birds. But there were plenty of moa running around, ranging in size from turkeys to ostriches — too big to be picked off by most raptors. “That’s huge amounts of meat that isn’t taken,” Knapp says. Such a scenario would have quickly selected for the largest eagles, who would have had the easiest time consuming such prey.

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"Knapp uses Haast’s eagle and Eyles’s harrier as case studies in a paper published in the 2021 Annual Review of Ecology, Evolution, and Systematics; these are illustrative examples of “natural invasions,” he thinks. Australian species cross the Tasman Sea quite often, but they typically struggle to compete against the islands’ existing species. But when cooler temperatures killed some forests, these new arrivals found a familiar ecological niche — one that no New Zealand species had yet evolved to fill.

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"The one thing that’s never mysterious about Haast’s eagle is what species wiped it out. Perhaps the eagles were hunted. Certainly, the moa were, which would be enough to doom the predator. “If you're evolving to fit a specific and very rare niche, then you have a hard time when that niche is gone,” Knapp says. One way or another, human beings take the blame.

"So while you could take the recent wave of Australian immigrants as a reminder that ecosystems adapt — that life goes on as new species fill the gap — this story is also cautionary. Evolutionary history is full of strange twists and turns, but also dead ends."

Comment: every ecosystem in the world is the same. A top predator niche will always be filled. It solves the problem of food supply for all. All the while, dhw worries about all those evolutionary branches that did not lead to humans. Simple concept: they all led to the necessary ecosystems of today, supporting a hungry human population approaching eight million!!! Great evolutionary design!