Invasive Species in New Zealand Worsen Biodiversity Crisis

brown rats, stoats skew new zealand ecosystem to dangerous levels of inequality

By Jonny Lupsha, Wondrium Staff Writer

Non-native predator species in New Zealand are a major problem. Unfortunately, they’re also an expensive problem in terms of both money and resources. Invasive species diminish an ecology’s crucial biodiversity.

Disproportionate population numbers across species happens when invasive, non-native species are introduced into an ecosystem and take over as dominant. Photo by Somogyi Laszlo / Shutterstock

Mammalian predators only arrived in New Zealand a few centuries ago. Their ranks are killing off native species that evolved without them. In 2016, the New Zealand government promised to rid the island country of most of its non-native predators by 2050. This ambitious goal has had great successes in reducing the numbers of stoats, brown rats, and possums, but hope is fading as costs rise. Money and resources are poured into the effort at a rate that may make it unsustainable.

Eliminating invasive predators is a top priority for New Zealand because the unwelcome visitors are seriously harming the nation’s biodiversity, which is vital for keeping an ecology thriving. In his video series, Earth at the Crossroads: Understanding the Ecology of a Changing Planet, Dr. Eric G. Strauss, Presidential Professor in Ecology at Loyola Marymount University in Los Angeles, explains what biodiversity is and how non-native species threaten it.

A Little Community Spirit

When it comes to animal life, community stability is vital.

“Stability describes the number and distribution of species within an ecosystem,” Dr. Strauss said. “Biodiversity is the result of all the colonization and local extinctions that take place. Colonization adds species to systems; extinction removes them.”

According to Dr. Strauss, philosopher J. Baird Callicott gave the best definition of biodiversity. Callicot said that biodiversity is the variety of life at every hierarchical level and spatial scale of biological organization. Dr. Strauss said that this includes genes within populations, populations within species, species within communities, communities within landscapes, landscapes within biomes, and biomes within the biosphere.

An ecosystem with a more even distribution of several species is considered to be healthier than one with a dominant species. This can be explained with an analogy using an ordinary comb.

“If you take a comb and turn it on its back, the tines, or the teeth, of the comb are even,” Dr. Strauss said. “If you lay a piece of paper across that, those tines would all touch the paper. In a theoretical, ecological sense from a standpoint of biodiversity, the fact that each tine supports the paper is a healthy system.”

One tine can be removed without the paper losing its support, but if all tines are of different lengths, the tine loses support. In this analogy, losing a single tine could cause the system to fall apart.

The Invaders

One of the factors that can contribute to an unevenness of comb tines—in other words, disproportionate population numbers across the species—is the introduction of invasive species into an ecosystem.

“Invasive species are also an important consideration when we think about maintaining biodiversity,” Dr. Strauss said. “Unfortunately, approximately 50,000 exotic species have made their way into the United States, and about 5,000 of those species are plants. In general, invasive species tend to degrade local ecosystems.”

In the culinary arts, there’s an old phrase: If it grows together, it goes together. In other words, species of animals and plants native to the same geographic area often work well together in a sustainable ecosystem. Most often, the non-native species don’t allow for a balanced ecosystem to thrive.

Among other problems, invasive species provide new predatory dangers to an ecosystem, as New Zealand has seen. Animals that haven’t evolved to protect themselves from the invaders can be killed off in disproportionate numbers—a shortening of the tines.

Edited by Angela Shoemaker, Wondrium Daily