Seed dispersal networks in an urban novel ecosystem

Abstract

The conflict resulting from the expansion of human activities into natural habitats affects the structure and functioning of ecosystems. Similarly, the anthropogenic redistribution of many species all over the world affects the composition of biological communities, possibly altering their capacity to sustain key ecological functions, such as seed dispersal. Urban parks are extreme examples of such novel ecosystems resulting from the anthropogenic redistribution of species in a new ecological framework. Here, we describe the avian seed dispersal network in an urban recreational woodland in central Portugal (c.79 ha). Four quantitative seed dispersal networks were assembled by identifying intact seeds in the droppings of mist-netted birds throughout the year. Overall, 1,244 seeds were identified, representing 33 links between 15 plant species and 11 bird species. Most birds dispersed alien seeds, but these represented a small proportion of the overall network (20 % of the seeds and 13 % of the droppings). Blackcap (Sylvia atricapilla) was the main disperser of native and alien seeds in all seasons, particularly those of the invasive Phytolacca americana. Fleshy fruits were more abundant in summer, but were more consumed in winter, presumably when other foods were difficult to find. Our study suggests that even in a highly managed urban park, seed dispersal networks can be temporally complex and variable and that a network approach can be an important monitoring tool to detect the status of crucial ecosystem functions in rapidly changing habitats such as urban parks.