Seed Dispersal

Abstract

The sedentary life of adult plants accentuates the critical importance of the short phase during which individual plants move: the dispersal of seeds, a common, widespread and fascinating phenomenon. Ultimately, selective pressures favouring dispersal include inbreeding avoidance, reduction of competition with kin and nonkin and the tracking of establishment opportunities in time and space. Proximately, dispersal mechanisms include nonrandom release from the mother plant, and transport by multiple dispersal vectors not necessarily those inferred from the seed morphology. The resulting patterns, often described by dispersal kernels, typically show a decline in seed deposition with distance from the source and a tail of long-distance dispersal events. Yet, environmental heterogeneity may cause more complex dispersal patterns. Dispersal has important consequences for the fate of individuals, populations, communities and ecosystems, enabling metapopulations and metacommunities to persist and playing a critical role in shaping the evolutionary and plastic response of plants to changing environments. Key concepts Dispersal is a widespread phenomenon among plants, selected to avoid inbreeding, to reduce competition with kin and nonkin and to cope with spatiotemporally variable environments. Causes for dispersal evolution act in concert, interact and may affect differently the evolution of short- and long-distance dispersal. Seeds typically depart from the source plant in a nonrandom fashion, suggesting selection to coordinate seed release with favourable conditions for dispersal and/or establishment. Seeds of a given plant species are typically dispersed by multiple vectors, including ‘nonstandard’ vectors differing from those inferred from the seed morphology. Dispersal kernels describe how seed deposition varies – in one, two or three spatial dimensions – in relation to the distance from the seed source. One-dimensional dispersal kernels generally show a decline in seed number (or density) with distance, and a ‘fat’ tail implying more long-distance dispersal events than expected from a negative exponential distribution. Complex dispersal kernels arise because seed deposition often varies not only with distance but also with direction and environmental heterogeneity. Dispersal plays a key role in allowing plants to adapt to climate changes, to spread within and outside their native range and to maintain metapopulations and metacommunities. New methods to model the underlying mechanisms, to analyze gene flow and genetic structure and to quantify dispersal patterns increase our understanding and predictability of seed dispersal in general, and long-distance dispersal in particular