Plant Reproductive Characteristics during Secondary Succession in Neotropical Lowland Forest Ecosystems

Abstract

During secondary succession in tropical America, reproductive characteristics of the constituent plants change as species constitution changes in the direction of 'climax' or equilibrium. Self-compatibility is more prevalent in early stages, while outcrossing is more the rule in later stages as dicliny, dioecism, and self-incompatibility beome more frequent. Observations indicate that plants of increasingly large stature and seral position are more widely spaced, and tend to have larger brightly colored flowers and larger pollinators. Associated understory plants come to have small unicolorous flowers and small pollinators as light availability decreases. Plants of early stages have primarily small, many-seeded dehiscent fruits, while plants with large, few-seeded fleshy fruits come to dominate equilibrium forests, particularly in wet forest. Canopy emergent trees, epiphytes, and lianas of mature forest are exceptional in employing wind-dispersal. Many of these changes correlate well with the thesis that pioneer plants are more highly r-selected, while plants of more mature forest tend to be K-selected. ALTHOUGH THE STUDY OF SECONDARY SUCCESSION in temperate latitudes signalled the onset of ecological endeavor (Cowles 1899, Clements 1916), only in recent years has the study of succession in the tropics made significant advances. The study of reproductive characteristics of plants in seral sequences has lagged even further behind. Our studies and those of others (Bawa 1974, Vasquez-Yanes 1974a, McKey 1975, Ruiz Zapata and Kalin Arroyo 1978) allow some preliminary conclusions and hypotheses on the nature of reproductive characteristics of plants in different seral stages. In this paper we consider the various portions of reproductive biology as a sequence of topics, i.e. floral biology, seed biology, and breeding systems. We then contrast findings from lowland wet and dry forest habitats, and finally integrate our findings and hypotheses with