The reproductive strategy of clonal plants has intrigued scientists and naturalists for decades. Many of these plants invest much energy each year to produce large amounts of fruits with seeds, and yet their seedlings are rarely found in the field. A clear example of this is the bilberry Vaccinium myrtillus, a key food for many animals in temperate and boreal regions of Eurasia that has been suggested to need “windows of opportunity” to germinate. These windows, characterized by high humidity and nutrient content, are by definition unpredictable in time and/or space and would always occur at very low frequencies. However, studies about clonal plants’ recruitment strategies are usually based on experiments carried out under controlled conditions (e.g. laboratory) and have rarely considered frugivores’ effects.
In this study, we analyzed whether defecation by carnivores facilitates the occurrence of these windows. To do this, we marked brown bear, mesocarnivore (red foxes and martens) and passerine faeces containing bilberry seeds in the Tatra Mountains (Poland) and followed the fate of the embedded seeds for up to two years. We found germination strongly associated with the locations where frugivores had defecated: bilberry seedlings were detected in 100%, 88% and 50% of brown bear, mesocarnivore and passerine faeces, respectively. These numbers were significantly higher than those found in control areas located in the vicinity of the faeces. In bear scats, investigated in more detail, 16% of the seedlings survived at least one year. The largest numbers of seedlings were associated to bear scats (154.4 ± 237.3 seedlings/m2), especially to those defecated upon the soil disturbances these animals create next to their resting sites (360 ± 277 seedlings/m2).
Bears’ resting sites usually have small excavations that facilitate the mobilization of nutrients and expose the soil surface, generating optimal conditions for the germination of bilberry seeds and other related species. Our results demonstrate that seed dispersal by animals facilitates repeated seedling recruitment of clonal plants in natural conditions, suggesting that frugivory must be considered when analyzing the reproductive strategies of these species.
Link to the paper: https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.3861
Link to the BearConnect project website: http://www.bearconnect.org