Identification of the selective forces on plant dispersal engenders theoretical argument, empirical study, and speculation. We separate evidence, testable hypotheses, and conjecture surrounding two major questions in dispersal ecology. The first asks what ecological, and ultimately evolutionary, advantages exist in seed dispersal. Astonishingly little is known about the advantages to a parent plant that are actually conferred by investment in dispersal structures. Does dispersal enable seeds and ultimately seedlings to escape mortality near the parent? Is continual recolonization of unstable habitats the primary advantage? Must seeds find rare microhabitats suitable for reestablishment? Such issues are addressed through joint consideration of dispersal and establishment-those stages both mediated by parental provisioning and subject to the highest mortality in the life of a plant. The second broad question asks what general and explicit environmental forces influence the timing and mode of dispersal. Do climates or seasons favor one dispersal mode over another? Do differences in number, size, morphology, or nutritional quality of fruits influence frugivore choice, and consequently differential dispersal of species or individuals within species? Studies of dispersal process and mode should be intimately connected. A general objective of this paper is to explore the degree to which they are integrated and, in so doing, to catalyze their union. We emphasize topics most in need of critical attention: the evolutionary ecology of dispersal process and mode. Excellent recent reviews consider such related topics as dispersal mechanism (131, 184), seed dormancy (1, 30), phytogeography (11, 115, 146), masting and predator satiation (105, 156), and succession (68, 69, 189).

https://www.jstor.org/stable/info/2097067

Ecology of Seed Dispersal

A new hypothesis, based on differences in the rates at which populations of competing species approach competitive equilibrium (reduction or exclusion of some species), is proposed to explain patte...

A General Hypothesis of Species Diversity

Life zone ecology.

J+=j

Early studies of nutrient cycling in moist tropical forests described productive forests rich in nutrients (98, 114, 176) in which rates of primary production and the amounts of nutrients cycled clearly exceeded those in temperate zone forests. Reviews of global-scale patterns in biomass, production, and nutrient cycling reported these results as representative of tropical forests (130, 175). At the same time, tropical forest soils were described as acid, infertile clays that harden irreversibly to "laterite" when cleared (106), or as bleached quartz sands low in mineral nutrients (88). This apparent paradox was crystallized by Whittaker (174) in the statement "The tropical rain forest thus has a relatively rich nutrient economy perched on a nutrient-poor substrate" (p. 271). Reviews of more recent research on overall patterns of mineral cycling in the tropics (78, 124), and of important components such as biomass (20, 21), litterfall nutrients (123, 164), and decomposition (5), clearly show that patterns of nutrient cycling in tropical forests are diverse. It makes no more sense to describe a 'typical' tropical forest than a 'typical' temperate forest (33, 151). Variations in mineral cycling nonetheless follow coherent, explicable patterns in tropical forests. Our purposes in undertaking this review are: (a) to illustrate the patterns of nutrient cycling in moist tropical forests; (b) to identify the mechanisms which regulate those patterns; and (c) to show how those patterns affect the productivity, physiology, and population biology of tropical forests and their large-scale linkages with aquatic ecosystems and the atmosphere. We emphasize the cycling of nitrogen, phosphorus, potassium, calcium, and magnesium; these are the best-studied soil-derived nutrients, and they are the nutrients most likely to limit primary production and other ecosystem functions.

P. W. Richards

Papers

The tropical rain forest

The Tropical Rain Forest

The Tropical Rain Forest

The Tropical Rain Forest

The Tropical Rain Forest.