Seed dispersal of a native tree is promoted by the invasion of ornithocorous shrubs and modulated by their density

VERGARA-TABARES, DAVID LAUTARO; BLENDINGER PG; TELLO A; PELUC SI; TECCO PA

Corbet

Simposio; 7th Frugivores and Seed Dispersers Symposium; 2020

Fleshy-fruited invasive plants establish mutualistic interactions with native seed dispersers and may indirectly affect the mutualisms between native partners. They may disrupt native plant dispersion through competition by seed dispersers or promote increased seed dispersal via the attraction of fruit-eating birds. In addition, the magnitude and/or the direction of the effect on native plants may be modulated by invaders density. The marked seasonality of fruit availability that characterize temperate communities may be reduced by invasive plants fructifying asynchronously with natives. This happens in mountains of central Argentina, where ornithocorous invasive shrubs (Pyracantha spp.) fruit in winter ?the scarcity period? and fruit-eating bird abundance increase in invaded sites. During autumn, the fructification of the dominant native tree Lithraea molleoides overlaps the beginning of the invaders fruiting period. This allows to test opposite predictions regarding the effect of invasive fruit offer on native seed dispersal. We compared L. molleoides fruit consumption by fruit-eating birds during the non-overlapped period and the overlapped period across three densities of Pyracantha spp shrubs (high invasion, low invasion and non-invasion). We counted fruit consumption by 2-hours periods on 14-15 L. molleoides at six sites. Using GLMM, we found that fruit consumption was significantly related to period (F1,167 = 10.60; P= 0.001) and invasion density (F2,167 = 10.33; P= 0.005). Fruit consumption of the native tree increased in invaded sites during the overlapping period. This response was greater in highly invaded sites. The new resource provided by Pyracantha does seemingly not disrupt plant dispersion of the dominant native tree. It rather promotes fruit removal by seed dispersers and this effect may be exacerbated with higher densities of these invasive shrubs. We highlight that fruit tracking by birds may be the mechanism responsible for the increment of seed dispersal in sites shared with ornithocorous invasive shrubs.