Territorial ants depress plant growth through cascading non-trophic effects in an alpine meadow

Understanding non-trophic interactions is critical to mechanistically linking community structure and ecosystem functioning. Despite the widespread occurrence of territoriality across animal taxa and ecosystems, the cascading ecological consequences of non-trophic interactions between territorial animals and intruders have been poorly studied. We experimentally investigated the non-trophic interaction between territorial ants and members of a dung decomposer community (i.e. predatory arthropods, maggots and coprophagous beetles) in an alpine meadow. We further examined how this non-trophic interaction cascaded to influence ecosystem properties including dung removal rate, soil nutrient status and aboveground plant biomass surrounding dung pats. Results indicated that territorial interference of ants on key decomposers cascaded to affect plant growth. Specifically, ants significantly decreased the abundance of coprophagous beetles at the time of their peak-abundance and hence decreased dung removal rates and soil nitrogen concentrations, ultimately decreasing aboveground plant biomass. The strength of this non-trophic cascading effect was comparable to those reported in studies addressing trophic cascades triggered by predator-prey interactions. Our findings suggest that the non-trophic interactions and associated cascading effects stemming from territorial behavior should be incorporated into ecological network modeling and research addressing biodiversity-ecosystem functioning relationships.