Large herbivores are not always harmful in new territories 

A comprehensive analysis led by Erick Lundgren challenges conventional views on the ecological impact of large herbivores, shedding light on the real drivers behind changes in plant abundance and diversity. 

The research, which is based on over 200 studies across six continents, brings forth a compelling argument that the physical characteristics and dietary habits of large herbivores play a more significant role in shaping ecosystems than the binary classification of being native or non-native species.

Introduced species 

The traditional perspective within conservation and ecological studies has often been that non-native animals exert more detrimental effects on their new environments compared to their native counterparts. 

“Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory,” wrote the researchers. “Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects on plants compared with native megafauna.”

Misguided policies 

This belief has been the cornerstone of various conservation policies aimed at the eradication or control of introduced species – many of which are on the brink of extinction in their indigenous habitats. 

Such policies have been influenced by concerns that invasive animals have greater negative impacts on plant life and ecosystem stability.

The meta-analysis by Lundgren and colleagues, however, paints a different picture. After carefully reviewing data from 221 studies, the experts found no significant evidence to support the notion that the origin of these megafauna – whether they are native or introduced – dictates their impact on plant diversity and abundance. 

Ecological dynamics 

Furthermore, the research delves into other potential factors like the invasiveness of the species, their feral status, evolutionary history with local flora, and their phylogenetic and functional uniqueness – only to find that these too fall short of explaining variations in plant ecosystems.

The key factors that emerged from this extensive study are the physical and functional traits of the megafauna, specifically their body size and dietary preferences. These elements are identified as having a more pronounced effect on the ecological dynamics between large herbivores and plant life. 

Shifting the focus

The results of the study suggest that a shift in focus is needed from where large herbivores come from to how their intrinsic biological traits influence their interactions with the environment.

The researchers advocate for a more nuanced approach to studying the impact of introduced megafauna, emphasizing the importance of functional ecology – a branch of science that studies the roles and functions of species in their habitat – over the simplistic native versus non-native dichotomy. 

The experts argue for a separation of the normative aspects of whether large herbivores “belong” in their environments from the objective analysis of their ecological functions.

Study implications 

This research not only challenges prevailing narratives within conservation science but also prompts a re-evaluation of management and conservation strategies concerning large herbivores worldwide. 

“We argue that the effects of introduced megafauna should be studied as any other wildlife would be studied, through the lens of functional ecology, with the normative dimensions of their ‘belonging’ considered separately and with transparency,” wrote the study authors. 

The study is published in the journal Science. 

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