Connecting fruit production to seedling establishment in two co-occurring Miconia species: Consequences of seed dispersal by birds in upper Amazonia

Abstract

This study investigated links between seed production by two species of Miconia (Melastomataceae), whose seeds are dispersed by birds, and later stages of recruitment in lowland forests of eastern Ecuador. Seed dispersal and survival in later stages are crucial for understanding and predicting patterns of plant population dynamics as well as for understanding patterns of diversity in tropical forests. A major goal was to determine if the spatial template of seed deposition established by birds predicted probability of recruitment. We used observational and experimental approaches to compare patterns of recruitment in Miconia fosteri and M. serrulata. We calculated probabilities of transition between successive stages of recruitment for each species in three habitats. The number of plants with fruit, number of fruits removed, and, to a lesser extent, patterns of seed deposition varied between species and among habitats, whereas seed survival, germination, and establishment showed little variation among habitats. The location of seed deposition directly influenced the cumulative probabilities of survival. Among-habitat differences in the probabilities of recruitment set by seed deposition were not modified by later stages, although probability of recruitment was 2.5 times higher for M. serrulata than for M. fosteri after 1 year. The more critical stages for recruitment were seed removal and deposition. Our results from multiple life-cycle stages suggest that habitat associations among plants that reach reproductive maturity become established at early life stages and were mostly a consequence of seed dispersal by birds. These results differ from those obtained in temperate zones and suggest fundamental differences in the importance of recruitment processes. Dispersers, such as manakins, play significant roles in recruitment and population dynamics of M. fosteri, M. serrulata and numerous other understory plants of Neotropical forests. Their role in plant recruitment could be much greater than previously considered in megadiverse tropical forests. Thus, loss of dispersers could have long-term and far-reaching implications for maintenance of diversity.