Rapid urbanization declined mammals and mammal-mediated seed dispersal in a megacity, central China

Abstract

Rapid urbanization has caused a series of environmental problems, but its influences on animal-related ecological functions (e.g., seed dispersal) have not been fully studied. Mammals are ideal models for studying the functional consequences of urbanization because they are sensitive to environmental changes. It is well known that large- and medium-sized mammals are vulnerable in fragmentation ecosystem. However, little is known about the functional responses of small mammals (e.g., rodents) to the rapid urbanization. Using infrared cameras and tagged seeds, here, we quantified mammals and mammal-mediated seed dispersal (i.e., Quercus variabilis) in 11 forest patches along city-suburb-exurban gradient in a rapidly urbanizing megacity, central China. We wanted to determine the effects of defaunation on seed dispersal in the isolated urban forests. The results showed that abundance of seed dispersers was higher in the natural exurban forests than in the city forests, while abundance of seed predators did not vary significantly along the city-suburb-exurban gradient. The percentage of seed dispersal was positively associated with the abundance seed dispersers, while the percentage of seed predation increased with the abundance of seed predators. Seed dispersers loss (e.g., small rodents) disrupted the mammal-mediated seed dispersal, possibly contributing to the degradation of urbanized forests. These results suggest that defaunation effects are obvious in the rapidly urbanizing cities, in that abundance of seed dispersers, and mammal-mediated seed dispersal are undergoing decline in the urbanized forests. In order to maintain seed dispersal and natural regeneration of urban forests, diversity of small mammals (e.g., rodents) and their ecological services should be considered in ecological-based urban planning and management.