Human-induced reduction in mammalian movements impacts seed dispersal in the tropics

Seed dispersal is a key process affecting the structure, composition and
spatial dynamics of plant populations. Numerous plant species in the
tropics rely upon animals to disperse their seeds. Humans have altered
mammalian movements, which will likely affect seed dispersal distances
(SDD). Altered SDD may have a range of consequences for plant communities
including reduced seedling recruitment and plant biomass, seed trait
homogenization, altered gene flow and a reduced capacity to respond to
environmental changes. Therefore, modelling the consequences of altered
animal behaviour on ecosystem processes is important for predicting how
ecosystems will respond to human impacts. While previous research has
focused on the link between animal species extirpation and SDD, it remains
unclear how changes in mammalian movement will impact SDD. Here we
implemented a mechanistic modelling approach to examine how mammalian
movement reductions impact SDD in the tropics. We combined allometric
theory with a mechanistic seed dispersal model to estimate SDD via the
movement of 37 large frugivorous mammals (> 10 kg) in the tropics
under different levels of human footprint, a global proxy of direct and
indirect human disturbances. Our results suggest that assemblage-level SDD
reductions are estimated to be up to 80% across the tropics in response to
human disturbance. This is particularly the case in areas with high human
impact such as agricultural landscapes and suburban areas. The region with
the largest reductions in SDD was the Asia-Pacific with average reductions
of 25%, followed by Central-South America (16%) and then Africa (15%). Our
study provides insights into how human-induced changes in movement
behaviour of large mammals could translate into altered ecosystem
functioning.