Local herbivores can cause significant damage to valuable plants, whether for ecological or economic reasons. However, current solutions such as killing the problem animals are increasingly unacceptable due to animal welfare concerns and social pressures. Physical barriers like fences can be expensive and impractical. Therefore, alternative options are needed.
A recent study published in Nature Ecology & Evolution by our team has discovered that herbivores primarily use their sense of smell to determine which plants they want to eat or avoid. We have found a way to use this reliance on smell to deter wallabies from vulnerable native tree seedlings. We artificially created and deployed the key smells of a shrub that wallabies avoid.
Hungry plant eaters pose a threat to conservation efforts, farmers, and foresters. They can destroy more than half of the seedlings in revegetation and post-fire recovery areas, causing billions of dollars in damage to forestry and agriculture each year. Additionally, herbivores endanger the long-term survival of many threatened plant species.
To effectively control herbivores, it is crucial to understand and utilize their natural motivations. Previous research has focused on what herbivores eat but has not explored how they find their food. Our approach introduces a new twist by using “olfactory misinformation” or “chemical camouflage” methods. These methods have proven successful in reducing invasive predators’ consumption of threatened bird eggs in New Zealand and agricultural wheat grain by house mice in Australia.
Herbivores navigate through scent landscapes, using odor to recognize and select plants and plant patches. Odor plays a key role in guiding the foraging behavior of marsupials in Australia, elephants in Africa and Asia, and deer in the United States. With this in mind, we conducted our study on swamp wallabies foraging in an eucalypt woodland in eastern Australia. Swamp wallabies have an excellent sense of smell and can locate buried eucalypt leaves among complex vegetation.
Using a recently developed approach, we identified the key scent compounds of a plant that wallabies avoid, the native shrub Boronia pinnata. We mixed these compounds to create “informative virtual neighbors” that mimic the scent of Boronia pinnata. These virtual neighbors were placed near eucalypt seedlings we aimed to protect.
In our study, we compared the effectiveness of virtual neighbors and real Boronia pinnata plants in deterring wallabies from eating eucalypt seedlings. The results were remarkable. Seedlings surrounded by virtual neighbors were 20 times less likely to be eaten compared to control groups. This level of protection was equivalent to using real plants but better because the vials used for virtual neighbors did not compete with seedlings for resources.
The success of our study suggests that this approach could be a new management tool for influencing herbivores’ behavior rather than eliminating them. We believe that the concept of virtual neighbors can be applied to any herbivore, mammal or otherwise, that relies on plant odor for foraging. With further development, smelly virtual neighbors can be deployed as a non-lethal and cost-effective solution to mitigate the problems caused by overzealous herbivores.
We would like to acknowledge all other co-authors who contributed to this work: Catherine Price, Malcolm Possell, and Cristian Gabriel Orlando from the University of Sydney, and Adrian Shrader from the University of Pretoria. We also extend our thanks to Paul Finnerty for his assistance in designing and constructing virtual neighbor holders.