During the COVID-19 pandemic, studies confirmed that some people’s levels of depression, anxiety, and stress rose due to a lack of access to nature. On the other hand, individuals who had backyards, could hear birds chirping, or simply owned house plants displayed marginally lower levels of depression and anxiety. These are the effects of perceived biodiversity, a phenomenon found to have a higher effect on mental well-being than the actual, measured biodiversity of an ecosystem. Whether increased by the deep purple color of flowers in a garden or the variety of leaf shapes within a park, perceived biodiversity is the amount of species and ecosystems that a person believes are present in an environment. This perception is due to a combination of sensory input and a neuroscientific phenomenon dubbed “top-down processing”: the synthesis of past memories and experiences to come to conclusions about a current experience. Fascinated by this intersection of ecological conservation and cognitive science, ecological scientists Kevin Rozario and Taylor Shaw developed an experiment to test perceived biodiversity in the context of species richness.
Their team conducted two sorting studies with the goal of identifying drivers of perceived biodiversity and understanding how accurately people can measure biodiversity intuitively. In the first study, participants sorted fifty-seven habitat photographs and ranked them based on the perceived level of biodiversity. The same was done for the second study, for which audio recordings of birds chirping were sorted. Researchers had previously ranked the images and audios based on their actual biodiversity. Forty-eight participants took part in the image and audio trials, none with prior academic experience in ecology. To prevent any unconscious biases, participants completed both a closed and open sort for each study. In the open sort, participants sorted files into categories based on any grouping criteria they wanted. Within the closed sort, participants chose whether to place the samples in categories of low, medium, or high biodiversity.
The researchers then recorded indicators of diversity and the participants’ sorting orders to determine which cues best appealed to a person’s top-down processing. The research team found that the most frequent visual cue was vegetation abundance, followed by lighting. Even when participants sorted images for biodiversity based on their own independently created categories, their perception of biodiversity was in relative accordance with contemporary analytical approaches. “When light comes through the canopy and reaches the forest ground, a whole different community of species evolves from that light, indicative of more plant density,” Rozario said. This means that the visual and auditory cues humans instinctively rely on are indeed strong, empirically supported metrics of an ecosystem’s biodiversity.
The study’s identification of the cues driving ecological interpretation could lead to cost-efficient methods of landscaping and planning green spaces based on what people perceive as biodiversity. “My recommendation for forest managers is to first create forests or urban parks with high levels of biodiversity while considering visual cues for diversity,” Rozario said. “The more layers we introduce into a forest, the more niches to support different tree species and animal species we will have, likely increasing people’s wellbeing. It’s a win-win.” An ecosystem consisting of a noticeable variety of tree types, as well as a diverse range of birds and vocalizations, would not only promote actual biodiversity, but perceived, which could provide a tangible impact on the mental health of individuals exposed to these areas.