Tree Dispersion, Abundance, and Diversity in a Tropical Dry Forest
30 Mar 1979-Science (American Association for the Advancement of Science)-Vol. 203, Iss: 4387, pp 1299-1309
TL;DR: In this article, the distribution of tree abundance and dispersion in a tropical deciduous (dry) forest was analyzed and the generalization that tropical trees have spaced adults did not hold.
Abstract: Patterns of tree abundance and dispersion in a tropical deciduous (dry) forest are summarized. The generalization that tropical trees have spaced adults did not hold. All species were either clumped or randomly dispersed, with rare species more clumped than common species. Breeding system was unrelated to species abundance or dispersion, but clumping was related to mode of seed dispersal. Juvenile densities decreased approximately exponentially away from adults. Rare species gave evidence of poor reproductive performance compared with their performance when common in nearby forests. Patterns of relative species abundance in the dry forest are compared with patterns in other forests, and are explained by a simple stochastic model based on random-walk immigration and extinction set in motion by periodic community disturbance.
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TL;DR: Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time.
Abstract: ▪ Abstract The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: They may be (a) equalizing because they tend to minimize average fitness differences between species, or (b) stabilizing because they tend to increase negative intraspecific interactions relative to negative interspecific interactions. Stabilizing mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations in population densities and environmental factors in space and time. Equalizing mechanisms contribute to stable coexistence because they reduce large average fitness inequalities which might negate the effects of stabilizing mechanisms. Models of unstable coexitence...
5,240 citations
Cites background from "Tree Dispersion, Abundance, and Div..."
...Hubbell (73, 74) has championed and steadily refined a model of community dynamics in which coexistence is not stable: The species compete for space but are ecologically identical and therefore have equal fitnesses under all conditions....
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TL;DR: A common pattern of phylogenetic conservatism in ecological character is recognized and the challenges of using phylogenies of partial lineages are highlighted and phylogenetic approaches to three emergent properties of communities: species diversity, relative abundance distributions, and range sizes are reviewed.
Abstract: ▪ Abstract As better phylogenetic hypotheses become available for many groups of organisms, studies in community ecology can be informed by knowledge of the evolutionary relationships among coexisting species. We note three primary approaches to integrating phylogenetic information into studies of community organization: 1. examining the phylogenetic structure of community assemblages, 2. exploring the phylogenetic basis of community niche structure, and 3. adding a community context to studies of trait evolution and biogeography. We recognize a common pattern of phylogenetic conservatism in ecological character and highlight the challenges of using phylogenies of partial lineages. We also review phylogenetic approaches to three emergent properties of communities: species diversity, relative abundance distributions, and range sizes. Methodological advances in phylogenetic supertree construction, character reconstruction, null models for community assembly and character evolution, and metrics of community ...
3,615 citations
TL;DR: A general objective of this paper is to explore the degree to which dispersal process and mode are integrated and, in so doing, to catalyze their union.
Abstract: 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).
3,424 citations
TL;DR: The spatial competition hypothesis seems to explain the coexistence of the numerous plant species that compete for a single limiting resource in the grasslands of Cedar Creek Natural History Area and provides a testable, alternative explanation for other high diversity communities, such as tropical forests.
Abstract: All organisms, especially terrestrial plants and other sessile species, interact mainly with their neighbors, but neighborhoods can differ in composition because of dis- persal and mortality. There is increasingly strong evidence that the spatial structure created by these forces profoundly influences the dynamics, composition, and biodiversity of com- munities. Nonspatial models predict that no more consumer species can coexist at equilibrium than there are limiting resources. In contrast, a similar model that includes neighborhood competition and random dispersal among sites predicts stable coexistence of a potentially unlimited number of species on a single resource. Coexistence occurs because species with sufficiently high dispersal rates persist in sites not occupied by superior competitors. Co- existence requires limiting similarity and two-way or three-way interspecific trade-offs among competitive ability, colonization ability, and longevity. This spatial competition hypothesis seems to explain the coexistence of the numerous plant species that compete for a single limiting resource in the grasslands of Cedar Creek Natural History Area. It provides a testable, alternative explanation for other high diversity communities, such as tropical forests. The model can be tested (1) by determining if coexisting species have the requisite trade-offs in colonization, competition, and longevity, (2) by addition of propagules to determine if local species abundances are limited by dispersal, and (3) by comparisons of the effects on biodiversity of high rates of propagule addition for species that differ in competitive ability.
2,515 citations
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References
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TL;DR: The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community as mentioned in this paper.
Abstract: The commonly observed high diversity of trees in tropical rain forests and corals on tropical reefs is a nonequilibrium state which, if not disturbed further, will progress toward a low-diversity equilibrium community. This may not happen if gradual changes in climate favor different species. If equilibrium is reached, a lesser degree of diversity may be sustained by niche diversification or by a compensatory mortality that favors inferior competitors. However, tropical forests and reefs are subject to severe disturbances often enough that equilibrium may never be attained.
7,795 citations
TL;DR: Any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents.
Abstract: A high number of tree species, low density of adults of each species, and long distances between conspecific adults are characteristic of many low-land tropical forest habitats. I propose that these three traits, in large part, are the result of the action of predators on seeds and seedlings. A model is presented that allows detailed examination of the effect of different predators, dispersal agents, seed-crop sizes, etc. on these three traits. In short, any event that increases the efficiency of the predators at eating seeds and seedlings of a given tree species may lead to a reduction in population density of the adults of that species and/or to increased distance between new adults and their parents. Either event will lead to more space in the habitat for other species of trees, and therefore higher total number of tree species, provided seed sources are available over evolutionary time. As one moves from the wet lowland tropics to the dry tropics or temperate zones, the seed and seedling predators in ...
4,267 citations
Book•
22 Nov 1973
TL;DR: This book discusses ecosystem dynamics under Changing Climates, which includes community dynamics at the community level, and factors that limit Distributions, which limit the amount of variation in population size.
Abstract: This CD-ROM helps students learn to think like field ecologists, whether estimating the number of mice on an imaginary island or restoring prairie land in Iowa, through 26 interactive field experiments and tutorials. The CD-ROM also includes test questions, quiz questions, weblinks, and a glossary. Included with every student copy of the text.
4,098 citations
TL;DR: In this article, the authors studied the vulnerability of several species to trapping on the islands and found that the islands appeared to lag behind the mainland in the development of their populations and the populations of small mammals fluctuate quite widely and the several populations appear to be somewhat independent of each other.
Abstract: but since logging operations and the burning and reburning that followed this logging, aspen and white birch have taken over the role as dominants. Thirty-two islands and 5 mainland areas were chosen for the study. Three species of hibernators, Eutamias minimum, Tamias striatus and Zapus hudsonias were taken on the mainland with only the Zapus being found on the islands. All six of the non-hibernating species taken were found on the islands. These include Microtus pennsylvanicus, Synaptomys cooper, Clethrionomys gapperi, Peromyscus rncaniculatus, Blarina brevicauda and Sorex cinereus. The degree of occupancy changed from 4 out of 21 islands in 1950 to 21 of 24 islands in 1952. Along with this increase in the proportion of islands occupied there was an increase in the number of species found on most of the islands although the average number of species found on each occupied island did not change appreciably. This increase in islands occupied was correlated with an increase in the density of the mainland populations. The water seemed to be an efficient barrier to travel during the summer but the ice of winter became a highway for dispersal of the various nonhibernating species in the winter. Considerable difference was found in the vulnerability of the several species to trapping. The Perornyscus were readily caught. The Clethrionomys were not as easy to capture as the former but were still readily taken. The Microtus, however, posed a different problem. They were difficult to capture and on two islands of about 2.2 and 4 acres respectively we were not able to elim-inate them after 16 days of trapping on a 15-foot grid. The populations of small mammals fluctuate quite widely and the several populations appear to be somewhat independent of each other. The islands appeared to lag behind the mainland in the development of their populations.
3,497 citations