Aliens will provide: response of trophic guilds and disperser birds to a new temporal resource offered by ornithocorous exotic shrubs

Frugivorous birds detect and respond positively to spatio-temporal changes in fruit availability. The fluctuation of these resources, common in temperate environments, can be modified by the naturalization of ornithocorous plants. In the mountain forest of central Argentina the exotic shrubs of the genus Pyracantha provide a new temporary resource, because they fructify in autumn-winter (asynchronously with respect to native plants). We evaluated, using point counts during five periods of the year, how the fluctuation of resources between invaded and non-invaded sites affects the abundance of bird trophic guilds and seed dispersers. A GLMM showed that the interaction between the presence of Pyracantha and time period significantly affected the abundance of frugivores (χ24,768 = 75.99, P <0.001), which were more abundant in autumn-winter in sites with Pyracantha and similar in spring-summer between situations. Granivores and insectivores were not related to the presence of Pyracantha. As for the most common dispersers (Turdus chiguanco, T. rufiventris and T. amarochalinus), the interaction between period-presence of Pyracantha significantly affected their abundance, showing a similar pattern to the frugivorous guild. The results indicate that the abundance of frugivorous birds (and the abundance of the main dispersers) is temporally and spatially associated with fruit availability provided by the exotic. The patterns suggest that the availability of fruits is an important ecological factor affecting the abundance of frugivorous birds and, the main Pyracantha´s dispersers have a strong association with fruits, which may contribute to the effectiveness of Pyracantha dispersal.