Tropical forests vary substantially in the densities of trees of different sizes and thus in above-ground biomass and carbon stores. However, these tree size distributions show fundamental ...similarities suggestive of underlying general principles. The theory of metabolic ecology predicts that tree abundances will scale as the -2 power of diameter. Demographic equilibrium theory explains tree abundances in terms of the scaling of growth and mortality. We use demographic equilibrium theory to derive analytic predictions for tree size distributions corresponding to different growth and mortality functions. We test both sets of predictions using data from 14 large-scale tropical forest plots encompassing censuses of 473 ha and > 2 million trees. The data are uniformly inconsistent with the predictions of metabolic ecology. In most forests, size distributions are much closer to the predictions of demographic equilibrium, and thus, intersite variation in size distributions is explained partly by intersite variation in growth and mortality.
Arguments that ecolocial research on species-rich tropical forests is too little, too late, an irrelevancy, and a luxury we can ill afford when time is running out to save tropical forests are wrong. ...Focused basic and applied ecological research has a vital and cost-effective role to play in tropical forest conservation and management. Sustainable management of natural tropical forests is not possible without a better holistic understanding of how such forests actually work ecologically and interact with humans. Because time is short, however, we must learn "on-the-job" by conducting research as we implement management plans. We base our argument on experience with a large-scale study of the tropical forest on Barro Colorado Island (BCI), Panama. In the space of 5 years, it was possible to collect essential silvics data on stocking levels, growth, yield, survival rates, and microhabitat requirements of a large fraction of the BCI tree community of more than 300 native species. We conclude that a program of comparable studies of representative natural and managed tropical forests at key sites throughout the tropics would rapidly improve the global fund of knowledge on which to base better decisions for the conservation and management of tropical forests. International agencies and foundations should increase their support of mission-oriented, holistic research on the community ecology of tropical forests far beyond the present emphasis on basic inventories of biodiversity. On one point there is no argument: tropical forests are indeed in big trouble.
Density dependence was examined in two species of neotropical treelets, Faramea occidentalis and Desmopsis panamensis, in a 50-ha plot on Barro Colorado Island in Panama. Survival and growth ...probability of plants larger than 1 cm dbh (diameter at breast height), and recruitment into the 1-cm class, were assessed as a function of the number of conspecific neighbors in various distance and size classes. Density-dependent effects on survival and growth were strong in Faramea. Performance of 1-8 cm dbh plants declined with increasing numbers of adult neighbors within 1 m, 1-2 m, and 2-4 m, but neighbors at 4-6 had no effect. Performance also declined with increasing numbers of juvenile neighbors <4f cm dbh, but the effect was less pronounced. Saplings of Faramea grew poorly in areas of high juvenile density within 30 m, independent of the effects caused by neighbors within 4 m. In contrast to Faramea, Desmopsis showed no density dependence in survival nor in growth. For recruitment, however, the two species showed similar patterns: recruit density was lower in regions with an adult conspecific within 1 or 2 m distance, but higher in regions with high densities of adult or juvenile conspecifics between 2 and 30-60 m. Desmopsis must have suffered density-dependent effects at stages <1 cm dbh, but the effect vanished by the 1 cm dbh stage. In Faramea, strong neighborhood effects were evident in all size classes <8 cm dbh.
Diamines covalently coupled to glass substrates promoted human foreskin fibroblast adhesion in the absence of serum. These
diamine-derivatized substrates were produced by coupling ethylene diamine, ...N-methylaminoethylamine, and N,N-dimethylaminoethylamine
(NNDMAEA), to sulfonyl chloride-activated glass. Electron spectroscopy for chemical analysis demonstrated that the diamines
were coupled via their primary amine ends to produce a surface-bound secondary amine linked to a free amino moiety via a two-carbon
spacer. NNDMAEA-modified substrates containing free tertiary amines supported the highest degree of cell spreading (73 +/-
7% actively spreading cells) and the most extensive cytoskeletal organization. Both the free tertiary and surface-bound secondary
amines were shown to be required for cell spreading. Lysine- and arginine-grafted substrates supported cell spreading and
cytoskeletal organization similar to that on NNDMAEA-modified substrates. Although some stress fibers were observed within
spread cells on these substrates, focal contacts did not form. Heparinase treatment did not inhibit cell attachment or spreading
to the diamine-derivatized substrates, however chondroitinase ABC inhibited cell attachment and spreading on all substrates;
heparinase inhibited spreading on lysine- and arginine-derivatized substrates to a lesser extent. These results imply that
cell attachment to these substrates was mediated primarily by cell surface chondroitin sulfate proteoglycans. This study demonstrates
that covalently grafted NNDMAEA, lysine, and arginine can mimic the adhesion-promoting activity of the glycosaminoglycan-binding
domains of cell adhesion proteins. This study also demonstrates that the interaction with these proteoglycans depends in a
very sensitive manner on the particular structure of the immobilized amine.
The theory of metabolic ecology predicts specific relationships among tree stem diameter, biomass, height, growth and mortality. As demographic rates are important to estimates of carbon fluxes in ...forests, this theory might offer important insights into the global carbon budget, and deserves careful assessment. We assembled data from 10 old‐growth tropical forests encompassing censuses of 367 ha and > 1.7 million trees to test the theory's predictions. We also developed a set of alternative predictions that retained some assumptions of metabolic ecology while also considering how availability of a key limiting resource, light, changes with tree size. Our results show that there are no universal scaling relationships of growth or mortality with size among trees in tropical forests. Observed patterns were consistent with our alternative model in the one site where we had the data necessary to evaluate it, and were inconsistent with the predictions of metabolic ecology in all forests.
Spatial scaling in model plant communities Zillio, Tommaso; Volkov, Igor; Banavar, Jayanth R ...
Physical review letters,
08/2005, Letnik:
95, Številka:
9
Journal Article
Recenzirano
Odprti dostop
We present an analytically tractable variant of the voter model that provides a quantitatively accurate description of Beta diversity (two-point correlation function) in two tropical forests. The ...model exhibits novel scaling behavior that leads to links between ecological measures such as relative species abundance and the species-area relationship.
An extended theoretical framework for the continuous population approach to forest inventories is derived. Here, we treat a simultaneous selection of sample points with any prescribed sampling ...intensity over a continuous population. Different ways to use available auxiliary information, for example, from remote sensing, by selection of approximately balanced or spatially balanced samples are considered. A large data set of spatially continuous individual tree‐level data is used to demonstrate the potential of these theoretical approaches. This study shows new ways to integrate remote sensing information in designs for forest inventory applications, which can significantly reduce the variance of the Horvitz–Thompson estimator for target variables related to the auxiliary information.
We point out a general problem in fitting continuous time spatially explicit models to a temporal sequence of spatial data observed at discrete times. To illustrate the problem, we examined the ...continuous time Markov model for forest gap dynamics. A forest is assumed to be apportioned into discrete cells (or sites) arranged in a regular square lattice. Each site is characterized as either a gap or a non-gap site according to the vegetation height of trees. The model incorporates the influence of neighboring sites on transition rate: transition rate from a non-gap to a gap site increases linearly with the number of neighbors that are currently in the gap state, and vice versa. We fitted the model to the spatiotemporal data of canopy height observed at the permanent plot in Barro Colorado Island (BCI). When we used the approximate maximum likelihood method to estimate the parameters of the model, the estimated transition rates included a large bias—in particular, the strength of interaction between nearby sites was underestimated. This bias originated from the assumption that each transition between two observation times is independent. The interaction between sites at local scale creates a long chain of transitions within a single census interval, which violates the independence of each transition. We show that a computer-intensive method, called Monte Carlo bias correction (MCBC), is very effective in removing the bias included in the estimate. The global and local gap densities measuring spatial aggregation of gap sites were computed from simulated and real gap dynamics to assess the model. When the approximate likelihood estimates were applied to the model, the predicted local gap density was clearly lower than the observed one. The use of MCBC estimates, suggesting a strong interaction between sites, improved this discrepancy.
In this document, the Ecological Society of America proposes the Sustainable Biosphere Initiative (SBI), an initiative that focuses on the necessary role of ecological science in the wise management ...of Earth's resources and the maintenance of Earth's life support systems. This document is intended as a call-to-arms for all ecologists, but it also will serve as a means to communicate with individuals in other disciplines with whom ecologists must join forces to address our common predicament.
Neutral theory in ecology is based on the symmetry assumption that ecologically similar species in a community can be treated as demographically equivalent on a per capita basis—equivalent in birth ...and death rates, in rates of dispersal, and even in the probability of speciating. Although only a first approximation, the symmetry assumption allows the development of a quantitative neutral theory of relative species abundance and dynamic null hypotheses for the assembly of communities in ecological time and for phylogeny and phylogeography in evolutionary time. Although Steve Gould was not a neutralist, he made use of ideas of symmetry and of null models in his science, both of which are fundamental to neutral theory in ecology. Here I give a brief overview of the current status of neural theory in ecology and phylogeny and, where relevant, connect these newer ideas to Gould's work. In particular, I focus on modes of speciation under neutrality, particularly peripheral isolate speciation, and their implications for relative species abundance and species life spans. Gould was one of the pioneers in the study of neutral models of phylogeny, but the modern theory suggests that at least some of the conclusions from these early neutral models were premature. Modern neutral theory is a remarkably rich source of new ideas to test in ecology and paleobiology, the potential of which has only begun to be realized.
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