Wild ungulate foraging suppresses growth of invasive parthenium weed

Abstract

The invasive weed Parthenium hysterophorus has severely disrupted ecosystems worldwide, driven by its persistent seed bank and phytotoxic compounds that suppress surrounding vegetation and negatively impact herbivorous mammals. It is widely assumed that wild ungulates avoid parthenium weed-dominated areas due to its presumed unpalatability and toxicity, but direct evidence is limited. We experimentally tested whether ungulates in an African savanna actively forage on parthenium weed by contrasting herbivore foraging in mechanically cleared and controlled areas using exclosures in parthenium-invaded areas. We also assessed whether reduction in body condition scores was associated with foraging on parthenium weed, and whether herbivory suppresses parthenium weed regrowth. Our experimental results show that ungulates foraged on parthenium rosettes without apparent negative impacts on body condition. Notably, herbivore activity significantly reduced parthenium cover in cleared areas. These findings reveal a previously undocumented potential for leveraging wild ungulate herbivory as a biocontrol mechanism for managing parthenium weed invasions.