Quantifying Animal Welfare Impacts of Biological Invasions

Evans & Mendl introduced a new framework to quantify and categorize the animal welfare impacts caused by invasive species, according to their paper published in the journal *Ecological Applications* on June 12, 2026. The study, titled “Quantifying and categorising the animal welfare impacts caused by biological invasions,” presents a systematic approach to assess how non-native species affect native wildlife, marking the first known tool of its kind. The framework combines ecological data with welfare metrics, enabling researchers to evaluate both direct harm—such as predation or habitat disruption—and indirect effects, like stress from competition for resources.

The methodology, developed by Evans, a conservation biologist at the University of Cambridge, and Mendl, an animal welfare scientist at the Royal Veterinary College, integrates field observations, population models, and behavioral indicators. For example, the tool could measure the stress levels of native birds exposed to invasive predators by analyzing vocalizations, foraging patterns, and nesting success rates. “This allows us to move beyond qualitative assessments and assign measurable weights to different types of suffering,” Evans explained in a press release. The paper cites case studies from Australia, where cane toads have devastated local fauna, and the Galápagos Islands, where introduced rats threaten endemic species.

The framework’s publication follows growing concern over the ecological and ethical implications of invasive species. According to the International Union for Conservation of Nature (IUCN), over 1,000 invasive species are currently classified as threats to biodiversity, with many causing severe welfare issues for native animals. However, existing tools for assessing these impacts have often focused on population-level data rather than individual animal experiences. “This gap has left policymakers without clear guidance on balancing conservation goals with animal welfare,” Mendl said. The new system aims to address that by providing a standardized metric for evaluating trade-offs, such as whether eradicating an invasive species might cause more harm to some animals than others.

Researchers have highlighted the potential applications of the framework in both academic and policy settings. Dr. Lisa Tran, a wildlife ecologist at the University of Melbourne, noted that the tool could help refine strategies for managing invasive species in sensitive ecosystems. “For instance, if a feral cat population is harming a vulnerable bird species, the framework could quantify the cats’ impact on the birds’ survival and well-being, informing decisions about control measures,” she said. The paper also suggests the tool could be used to evaluate the ethical implications of introducing non-native species for ecological restoration, such as using goats to control invasive plants in certain regions.

The study’s authors acknowledge limitations, including the need for extensive data collection and the challenge of applying the framework across diverse ecosystems. Evans emphasized that the tool is not a replacement for existing conservation practices but a complement. “It’s a way to add a layer of ethical consideration to ecological decision-making,” he said. The paper calls for collaboration between ecologists, animal welfare experts, and policymakers to refine and implement the framework. A companion dataset, containing baseline metrics for 50 invasive species, is available through the journal’s website.

Environmental organizations have responded cautiously to the development. The Humane Society International praised the effort to “bridge the gap between ecological science and animal welfare,” but cautioned against over-reliance on quantitative metrics. “While this tool is a step forward, it’s important to remember that animal suffering cannot always be reduced to numbers,” said spokesperson James Carter. Meanwhile, the Wildlife Conservation Society noted that the framework could enhance transparency in invasive species management, particularly in regions with high biodiversity.

The paper’s release coincides with increased global attention on invasive species, driven by climate change and human activity. A 2025 UN report warned that the rate of biological invasions has doubled since the 1970s, exacerbating threats to ecosystems worldwide. As governments and conservation groups seek more nuanced approaches to managing these challenges, Evans & Mendl’s framework offers a novel perspective. “This isn’t just about saving species—it’s about understanding the full scope of their suffering,” Mendl said. The study’s authors plan to present their findings at the International Conference on Invasive Species in September 2026, where they hope to spark broader dialogue on integrating welfare considerations into ecological research.