Killing animals that "don't belong" in an ecosystem is a harmful strategy

A new study is challenging the conventional approach to conservation that often leads to killing the non-native animals in a particular area in order to protect plant species.

This practice, which costs millions of dollars and results in the death of millions of healthy wild animals, is based on the assumption that introduced large herbivores, or megafauna, harm ecosystems by damaging sensitive plants, reducing native plant diversity, and supporting invasive plant species.

However, this new research from Aarhus University, Denmark, and the University of Oxford, UK, suggests that the distinction between native and non-native large herbivores may not be as clear-cut as previously thought.

Challenging practices of killing non-native animals

The researchers conducted a comprehensive analysis comparing the effects of native and introduced large mammal species on plant abundance and diversity across 221 studies worldwide.

Their findings revealed that both groups have similar impacts on native plant communities.

Dr. Jeppe Kristensen from the University of Oxford’s Environmental Change Institute shared his thoughts.

“We do not find evidence to support the claim that native large herbivores have different impacts on ecosystems, specifically plant communities in this case, than their non-native counterparts,” said Dr. Kristensen.

“Therefore, we should study the ecological roles these animals – native or not – play in ecosystems rather than judge them based on their belonging.”

Trait-based effects on ecosystems

Interestingly, the study found that the ecological effects of invasive animals are more closely related to their traits than their nativeness.

For example, small-bodied selective feeders like deer tend to reduce plant diversity, whereas larger, non-selective feeders such as buffalo are more likely to enhance it.

This is attributed to the inability of large animals to selectively feed, which prevents the dominance of certain plant species and promotes biodiversity.

Moreover, the study notes the unique impact of individual animal body mass over the collective weight of animals in an area, underscoring the distinct roles large animals play in shaping ecosystems.

Dr Kristensen explained, “While one elephant can push over a mid-sized tree, 50 red deer cannot. You can’t total the body mass to understand the effect of animal presence on the landscape, you have to consider the effect of each animal species present.”

Paradox of culling: Rethinking conservation

This research also addresses the broader implications of eradicating non-native animals, many of which are endangered in their native habitats.

The paradox of spending millions to remove these animals from areas where they are considered invasive, while their populations decline elsewhere, raises questions about current conservation priorities.

Professor Jens-Christian Svenning from Aarhus University suggests, “This interpretation suggests that functional niches vacated by extinctions and extirpations in recent prehistory, often due to humans, are better refilled with animals with similar functional traits as the ones that were lost even if these new species are non-native or feral.”

The study emphasizes the need to reassess how we perceive native and non-native species and their roles in ecosystems.

Rather than focusing solely on the concept of belonging, conservation strategies should prioritize re-establishing essential ecosystem functions, potentially through the adaptive introduction of non-native species.

Lead author Dr Erick Lundgren (Aarhus University) concluded, ‘”Our findings suggest it is time to start using the same standards to understand the effects of native and introduced organisms alike and to consider seriously the implications of eradication and culling programs that are based on cultural notions of “belonging.” Instead, introduced animals should be studied in the same way as any native wildlife, through the lens of functional ecology.”

Include non-native animals instead of killing them

In summary, this transformative study urges the conservation community to reconsider long-held beliefs about the role of native and non-native species within ecosystems.

By demonstrating that the impact of large herbivores on plant diversity and abundance is more a matter of individual traits than origin, it challenges the costly and often counterproductive practice of killing non-native animal species solely based on their non-native status.

Instead, the findings advocate for an adaptive conservation approach that prioritizes ecological function and embraces the potential of non-native species to fill crucial roles left vacant by extinct species.

This paradigm shift could not only enhance biodiversity conservation efforts but also encourage a more nuanced and inclusive understanding of species’ contributions to ecosystem health and resilience.

The full study was published in the journal Science.

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