Frugivory and seed dispersal by animals are essential processes for the normal functioning of most ecosystems. Different animals differ in their effectiveness as seed dispersers because 1) they disperse different amounts of seeds, 2) they treat the seeds differently in the mouth and gut, and 3) they defecate upon substrates that have different suitability for seed germination. Different dispersers may also complement each other by defecating seeds in different habitats and periods of time. However, this topic has only received little attention.
We investigated the complementarity of seed dispersal services provided by birds and mammals dispersing bilberry (Vaccinium myrtillus) seeds in an alpine ecosystem, the Tatra Mountains (Poland). We collected bird droppings and mammal scats containing bilberry seeds in coniferous forests and alpine meadows. Birds were identified by DNA barcoding techniques in the laboratory while mammals were assigned in the field based on the size, shape and smell of the scats. We found that at least 13 birds and 3 mammals dispersed bilberry seeds in the Tatra Mountains. Two bird species -song thrushes Turdus philomelos and fieldfares T. pilaris-, brown bears Ursus arctos and red foxes Vulpes vulpes were the most effective seed dispersers. Birds and mammals differed in the quantity and quality of seed dispersal: mammals, especially bears, dispersed the majority of the seeds but those defecated by birds had a higher probability to germinate because their droppings contained less seeds and were defecated in more suitable microhabitats. Interestingly, birds and mammals also differed in terms of habitat and timing of seed dispersal: birds dispersed most seeds in the middle of the fruiting season and within the forest, while seed dispersal by mammals peaked in the upper meadows and at the end of the season.
Our results, recently published in the Journal of Ecology, demonstrate that avian and mammalian seed dispersers complement each other in alpine ecosystems. This spatiotemporal complementarity, which facilitates the arrival of seeds to different sites and during the entire fruiting season, maximizes the chances of bilberry seed germination and may be key for the persistence of bilberry populations, especially in the current context of climate change.
For further reading, go to the paper: https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13799
, , , , , , & (2021). Functional complementarity of seed dispersal services provided by birds and mammals in an alpine ecosystem. Journal of Ecology, 00, 1– 16. https://doi.org/10.1111/1365-2745.13799