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A central goal of comparative plant ecology is to understand how functional traits vary among species and to what extent this variation has adaptive value. Here we evaluate relationships between four functional traits (seed volume, specific leaf area, wood density, and adult stature) and two demographic attributes (diameter growth and tree mortality) for large trees of 240 tree species from five Neotropical forests. We evaluate how these key functional traits are related to survival and growth and whether similar relationships between traits and demography hold across different tropical forests. There was a tendency for a trade-off between growth and survival across rain forest tree species. Wood density, seed volume, and adult stature were significant predictors of growth and/or mortality. Both growth and mortality rates declined with an increase in wood density. This is consistent with greater construction costs and greater resistance to stem damage for denser wood. Growth and mortality rates also declined as seed volume increased. This is consistent with an adaptive syndrome in which species tolerant of low resource availability (in this case shade-tolerant species) have large seeds to establish successfully and low inherent growth and mortality rates. Growth increased and mortality decreased with an increase in adult stature, because taller species have a greater access to light and longer life spans. Specific leaf area was, surprisingly, only modestly informative for the performance of large trees and had ambiguous relationships with growth and survival. Single traits accounted for 9-55% of the interspecific variation in growth and mortality rates at individual sites. Significant correlations with demographic rates tended to be similar across forests and for phylogenetically independent contrasts as well as for cross-species analyses that treated each species as an independent observation. In combination, the morphological traits explained 41% of the variation in growth rate and 54% of the variation in mortality rate, with wood density being the best predictor of growth and mortality. Relationships between functional traits and demographic rates were statistically similar across a wide range of Neotropical forests. The consistency of these results strongly suggests that tropical rain forest species face similar trade-offs in different sites and converge on similar sets of solutions. Key words: demography; functional ecology; height; life-history theory; seed mass; shade tolerance; species coexistence; specific leaf area; trees; tropical rain forest; wood density.

In the course of an adaptive radiation, the evolution of niche parameters is of particular interest for understanding modes of speciation and the consequences for coexistence of related species within communities. We pose a general question: In the course of an evolutionary radiation, do traits related to within-community niche differences ([alpha] niche) evolve before or after differentiation of macrohabitat affinity or climatic tolerances ([beta] niche)? Here we introduce a new test to address this question, based on a modification of the method of independent contrasts. The divergence order test (DOT) is based on the average age of the nodes on a tree, weighted by the absolute magnitude of the contrast at each node for a particular trait. The comparison of these weighted averages reveals whether large divergences for one trait have occurred earlier or later in the course of diversification, relative to a second trait; significance is determined by bootstrapping from maximum-likelihood ancestral state reconstructions. The method is applied to the evolution of Ceanothus, a woody plant group in California, in which co-occurring species exhibit significant differences in a key leaf trait (specific leaf area) associated with contrasting physiological and life history strategies. Cooccurring species differ more for this trait than expected under a null model of community assembly. This [alpha] niche difference evolved early in the divergence of two major subclades within Ceanothus, whereas climatic distributions ([beta] niche traits) diversified later within each of the subclades. However, rapid evolution of climate parameters makes inferences of early divergence events highly uncertain, and differentiation of the [beta] niche might have taken place throughout the evolution of the group, without leaving a clear phylogenetic signal. Similar patterns observed in several plant and animal groups suggest that early divergence of [alpha] niche traits might be a common feature of niche evolution in many adaptive radiations. Key words: adaptive radiation; Ceanothus; Cerastes; Coast Range; community assembly; Euceanothus; habitat, niche conservatism; phylogenetic comparative methods; specific leaf area; Sierra Nevada; trait divergence; Transverse Range.

We studied the effects of C[O.sub.2] elevation on leaf and canopy photosynthesis and optimal leaf area index (LAI) for stands of the annual species Abutilon theophrasti and Ambrosia artemisiifolia. Leaf photosynthesis was modeled as a function of photosynthetic photon flux density (PPFD) and nitrogen content per unit leaf area ([N.sub.L]). There was a curvilinear relationship between the light-saturated rates of leaf photosynthesis ([P.sub.max]) and [N.sub.L]. C[O.sub.2] elevation significantly increased [P.sub.max] as a function of [N.sub.L] in both species. Dark respiration ([R.sub.d]) was linearly correlated with [N.sub.L]. C[O.sub.2] elevation slightly but significantly increased [R.sub.d] in Abutilon, while it had no significant effect on [R.sub.d] in Ambrosia. The initial slope of a light-response curve was determined from quantum yield ([Φ.sub.abs]) multiplied by leaf absorptance and then calibrated against [N.sub.L]. Daily canopy photosynthesis, calculated by integration of leaf photosynthesis with the actual distribution of leaf area, leaf N, and PPFD within a canopy, showed fairly good agreement with the canopy photosynthesis estimated from growth analysis. C[O.sub.2] elevation increased canopy photosynthesis by 3050%. based on the leaf photosynthesis model for Abutilon, we calculated daily canopy photosynthesis for a given LAI and N availability, in which N was assumed to be distributed optimally within a leaf canopy to maximize daily canopy photosynthesis. An optimal LAI to maximize daily canopy photosynthesis was obtained for each level of N availability and this optimum increased with increasing N availability. Contrary to the often predicted increase in LAI with C[O.sub.2] elevation, the optimum LAI did not increase at high C[O.sub.2] when N availability was limited. Two factors were suggested to be involved in counteracting the increase in LAI in a high-C[O.sub.2] world. One is the higher [Φ.sub.abs] of plants grown in elevated C[O.sub.2], which makes leaves in the canopy more N limited, favors higher [N.sub.L] and thus lowers optimal LAI. The other is the higher [R.sub.d] in elevated C[O.sub.2] which leads to higher light compensation points, and lowers optimal LAI. Key words: Abutilon theophrasti; Ambrosia artemisiifolia; canopy photosynthesis; C[O.sub.2] elevation; leaf area index; modeling; N distribution; optimization., INTRODUCTION Elevation in atmospheric C[O.sub.2] concentration is believed to increase dry mass productivity of [C.sub.3] plants (Bazzaz 1990). Increase in productivity of a plant canopy may result from increasing leaf [...]

In forest gaps, the geometry of canopy openings above a plant determines the spatial distribution of diffuse and direct radiation, which may be received from different sectors of the sky. We examined crown orientation and light interception by seedlings of four species of pioneer trees, Cecropia obtusifolia, Heliocarpus appendiculatus, Piper auritum, and Trema micrantha, transplanted into natural forest gaps at the Los Tuxtlas Tropical Biology Station, Veracruz, Mexico. The four species differed in the number and mean size of leaves, but total leaf area was not significantly different among equal age plants. The mean azimuth and zenith angle of diffuse and direct radiation were determined from hemispherical photographs taken above each plant. Mean diffuse radiation vectors were distributed around the zenith, with a significant clustering in an easterly direction, while mean direct radiation vectors were distributed along the solar track in the southern portion of the sky. The mean orientation of the crown of each seedling was determined from detailed, three-dimensional reconstruction of leaf display using a canopy architecture model. A directional correlation test indicated that seedling crowns were oriented toward diffuse radiation received from the gap, and not toward direct radiation. The mean orientation of the crown, at the whole plant level, was primarily determined by nonrandom orientation of individual leaves. The mechanisms of this differential response to diffuse vs. direct radiation are not known. For diffuse radiation, the total light capture capacity integrated over all sky directions increased with seedling leaf area, while efficiency of capture per unit area decreased. Based on simulations, the light interception efficiency of each plant in its own microsite was 5-25% greater than would be achieved in the sites of conspecifics or in symmetric canopy openings centered on the zenith. These analyses provide a quantitative estimate of the value of nonrandom leaf and crown orientation for whole-plant light interception in natural environments. Key words: canopy architecture; leaf orientation; light interception; phototropism; pioneer trees., INTRODUCTION Forest gaps are noted for high spatial and temporal heterogeneity in environmental conditions (Bazzaz and Wayne 1993). The diurnal radiation environment in a gap is typically characterized by a [...]

1. Populations of an annual plant, Abutilon theophrasti, were grown at four densities (100, 500, 1500 and 4000 m to the -2) and two CO2 concentrations (350 and 700 microns 11 to the -1) to examine the influence of CO2 environment on density-dependent patterns of demography and reproduction. Variables measured included survivorship, proportion of plants flowering and fruiting, number of fruiting individuals, number of seeds per individual, total seed production per population, mean seed mass, and germination of seeds produced in each environment. 2. All variables, except the number of fruiting individuals, declined with increasing density, and at the highest density no individuals set seed. The number of fruiting individuals was highest at a density of 500 m to the -2. In the elevated CO2 environment, survivorship was significantly reduced but the proportion of plants flowering and fruiting and the number of fruiting individuals in each population all increased. Total population seed production was higher in the elevated CO2 environment at all densities, although the differences were not significant. Significant effects of CO2 concentration were observed only for population-level variables, but not for mean individual fecundity or seed size. Seed germination declined with increasing maternal density, and no germination was recorded for seeds produced at 1500m to the -2. 3. Simple models of population dynamics, utilizing difference equations, were constructed to examine potential population-level consequences of these density and CO2 effects. In the absence of a persistent seed pool, the simulated populations exhibited damped or stable oscillations under low germination values, but displayed non-cyclic ('chaotic') oscillations or went extinct for higher germination due to the complete failure of seed-set at high density. Because of its higher fecundity, the elevated-CO2 population generally exhibited greater oscillations, and the critical germination value at which the simulated populations went extinct was much lower for the elevated-CO2 than for the ambient-CO2 population.

We studied leaf area production in two annual plant species, Abutilon theophrasti and Amaranthus retroflexus, under three day/night temperature regimes (18 [degrees]/14 [ degrees], 28 [degrees]/22 [degrees], and 38 [degrees]/31 [degrees] C) and two concentrations of carbon dioxide (400 and 700 [mu]L/L). The production of whole-plant leaf area during the first 30 d of growth was analyzed in terms of the leaf initiation rate, leaf expansion, individual leaf area, and, in Amaranthus, production of branch leaves. Temperature and [CO.sub.2] influenced leaf area production through effects on the rate of development, determined by the production of nodes on the main stem (the plastochron index), and through shifts in the relationship between whole-plant leaf area and the number of main stem nodes. In Abutilon, leaf initiation rate was highest at 38 [degrees], but area of individual leaves was greatest at 28 [degrees]. Total leaf area was greatly reduced at 18 [degrees] due to slow leaf initiation rates. Elevated [CO.sub.2] concentration increased leaf initiation rate at 28 [degrees], resulting in an increase in whole-plant leaf area. In Amaranthus, leaf initiation rate increased with temperature, and was increased by elevated [CO.sub.2] at 28 [degrees]. Individual leaf area was greatest at 28 [degrees], and was increased by elevated [CO.sub.2] at 28 [degrees] but decreased at 38 [degrees]. Branch leaf area displayed a similar response to [CO.sub.2], but was greater at 38 [degrees]. Overall, whole-plant leaf area was slightly increased at 38 degrees] relative to 28 [degrees], and elevated [CO.sub.2] levels resulted in increased leaf area at 28 [degrees] but decreased leaf area at 38 [degrees]. The effects on leaf area closely parallel rates of biomass accumulation in the same experiment, suggesting that responses of developmental processes to elevated [CO.sub.2] and interacting factors may play an important role in mediating effects on plant growth.