The gain of non-native species and the concurrent loss of native species can trigger a cascade of indirect effects on the community. Moreover, indirect effects may be exacerbated when the affected species are involved in keystone interactions. Yet, field-based empirical studies that demonstrate the cascading effects of the loss of keystone mutualism interactions are exceedingly rare. In this study, we take advantage of an ongoing natural experiment triggered by the invasion of non-native ungulates to examine the cascading effects on communities, soil function and ecosystem services of the loss of the keystone interaction among a hummingbird-mistletoe-marsupial caused by the consumption of the main host of the mistletoe, the common shrub Aristotelia chilensis in the temperate forest of Patagonia-Argentina.
Results/Conclusions
We found that the loss of the keystone interaction in a hummingbird-mistletoe-marsupial resulted in diverse indirect effects. In our study, Mammalian herbivory modifies foliage arthropods communities by affecting the abundance and distribution of plants that they live on; browsed A. chilensis plants in invaded sites supported fewer species and individuals of foliage arthropods than unbrowsed plants in the intact sites. Additionally, we found that the arthropod community composition on unbrowsed A. chilensis in intact sites differed significantly from the community on browsed A. chilensis in invaded sites. On the other hand, we did not find a difference in soil function. Soil respiration was similar beneath the canopy of browsed and unbrowsed A. chilensis. Additionally, we found that in invaded sites the pollination and dispersal networks were less robust (fewer number of species) and less connected (fewer interactions between species) than in intact sites. Our results demonstrate that the gains and losses of species are both consequences and drivers of global change that can lead to under-appreciated cascading co-extinctions. Taken together, our findings demonstrate the importance of viewing biodiversity not only as the sum of different components but also as the direct and indirect interactions among them.