Linking animal migration and ecosystem processes: data-driven simulation of seed dispersal by migratory herbivores

Animal migration is a key process underlying active subsidies and plant dispersal over long distances, which affects the connectivity and functioning of ecosystems. However, we still lack a predictive framework to quantify how migratory animals affect ecosystem processes.

Here, we quantitatively integrate animal behavior and ecosystem functioning by developing a modeling framework that is able to make predictions to inform ecosystem management and conservation. Our framework models individual-level migration trajectories across the spatial distributions of populations as well as the resulting dispersal and fate of seeds carried by the migratory animals. As a case study, we applied our framework to model the spread of guava seeds, Psidium guajava, by a population of migratory Galapagos tortoises, Chelonoidis porteri. Galapagos tortoises are large herbivores and prodigious seed dispersers, while Guava is one of the most problematic invasive species in the Galapagos archipelago. Our model predicted the spread of guava seeds alongside tortoises’ downslope migration range, and identified areas most likely to see guava germination and establishment. In particular, we predict that tortoises are dispersing a significant amount of guava seeds into the Galapagos National Park, which has important consequences for the native flora. Our framework allows for a wide range of applications to investigate how migratory animals affect ecosystem processes, such as nutrient transport across ecosystems. Our framework is also a valuable tool for predicting how animal-mediated seed dispersal can be affected by environmental change. These different applications can have important conservation implications for the management of ecosystems that include migratory animals.