Biotropica 

About: Biotropica is an academic journal published by Wiley-Blackwell. The journal publishes majorly in the area(s): Species richness & Population. It has an ISSN identifier of 0006-3606. Over the lifetime, 3950 publications have been published receiving 179641 citations.

Patterns of Floristic Differentiation among Atlantic Forests in Southeastern Brazil and the Influence of Climate1

Abstract: The tree flora of southeastern Brazilian Atlantic forests was investigated according to two main aspects: (a) the variations in floristic composition of both rain and semi-deciduous forests were analyzed in terms of geographic and climatic variables by performing multivariate analyses on 125 existing floristic checklists; and (b) the links of both rain and semi-deciduous forests to Amazonian forests and Cerrados (woody savanna) were assessed. All analyses were performed at the species, genus, and family levels. The information obtained for the 125 forest areas was organized into an environmental database containing geographic and climatic records, and a floristic database containing binary presence records for 2532 species, 520 genera, and 106 families. Canonical correspondence analyses (CCA) were utilized to assess the relationship between geographic and climatic variables, and tree flora composition. Venn diagrams and cluster analyses were used to assess the floristic links to Amazonian forests...

Gap Partitioning among Tropical Rainforest Trees

Abstract: Published observations on adaptations for seed disperal and seedling establishment are consistent with the hypothesis that rainforest trees partition forest clearings as establishment sites for offspring. Gaps vary importantly in two ways. The size of the opening affects the microclimate of the gap and therefore the conditions for seedling establishment. For any individual tree, the frequency of occurrence of gaps of a particular size range affects the probability that its propagules will reach a gap of suitable size for germination and establishment. In most rainforests large gaps (involving the death of several trees) are probably more rare than small gaps (involving single trees or branches). Interspecific competition for establishment sites has resulted in adaptive compromises in the regeneration strategies of each species. Traits that increase the probability of establishing seedlings in gaps of a particular size range appear to lower establishment in gaps outside this size range. I suggest that the coexistence of many rainforest tree species is at least partially due to their partitioning of canopy gaps by size. Therefore the size-class frequercy distribution of gaps peculiar to a given rainforest is expected to influence the types and diversity of species present. Examination of vegetation data from New and Old World rainforests reveals many patterns consistent with this hypothesis. This framework provides a mechanism for predictive and experimental studies of competitive interactions among rainforest trees. MECHANISMS PROPOSED to account for patterns of species richness within animal communities have relied heavily on resource partitioning (cf. Schoener 1974). Similar hypotheses have been less successful in accounting for plant species diversity. Different plants have similar modes of resource acquisition and share the same few essential resources (light, moistLre, minerals). It is not clear how such uniform resources could be partitioned by physiologically similar species in complex communities (e.g. Richards 1969). Although rainforest species exhibit patterns associated with variation in topography or soil (e.g. Ashton 1964a, Grieg-Smith et al. 1967, Poore 1968, Williams et al. 1969, Austin et a/. 1972, Ashton 1977), species with non-random distributions often show no association with edaphic variation (Schulz 1960, Poore 1968), and overlap along edaphic gradients is high between similar species. It remains difficult to account for high diversity in relatively uniform topographic and edaphic environments. In face of high plant species diversity unexplained by resource partitioning, theorists have invoked stochastic or historical processes to account for modern patterns (e.g. Federov 1966, Van Steenis 1969, Prance 1973, Stebbins 1974, and see Ashton 1969 for a discussion). These hypotheses assume that competitive interaction among plant species is of little importance in the determination of relative abundances of species. Here I suggest that a mechanism for resource partitioning among rainforest trees exists in their differential regeneration in treefall gaps of different sizes and spatial distributions. At a superficial level some of these differences are a well-established part of natural history lore (e.g. Richards 1964, Van Steenis 1958, Budowski 1965) and form the basis of sustained-yield forestry systems (e.g. Taylor 1962, Whitmore 1975). Several papers have emphasized that gaps are an important source of environmental heterogeneity in rainforest (Schulz 1960, Whitmore 1975, 1978, Hartshorn 1978). Nevertheless, it is evident from the literature that gap regeneration strategies have not been considered an important component of competitive interactions among trees. Few studies of rainforest vegetation include attention to the nature and distribution of natural gaps or to differential seedling establishment in them. This paper summarizes data on regeneration patterns of trees within the framework of hypotheses that (1) tree species partition gaps of different spatial distributions and sizes and that (2) partitioning occurs because regeneration strategies keyed to gaps of particular size ranges involve adaptive compromises that restrict the competitive success of the species in gaps of differing sizes. High mortality rates of seeds and seedlings (e.g. Liew and Wong 1973) suggest that selection pressures are likely to be particularly strong on factors affecting dispersal of seeds and establishment of seedlings. Gaps as establishment sites for seedlings are critical resources, and gap partitioning provides an important mechanism through which empirically to examine interspecific competitive interactions among tree species. Rainforest spatial structure and species diversity are reviewed in this light. Experimental tests of the relationships between TROPICAL SUCCESSION 47-55 1980 47 This content downloaded from 157.55.39.159 on Sun, 18 Sep 2016 06:29:01 UTC All use subject to http://about.jstor.org/terms traits described and regeneration success in gaps of different sizes are largely lacking. Support for these hypotheses is therefore based on empirical studies of forest structure and field observations accumulating over the last 50 years of ecological studies of rainforests. This framework is presented in the hope of stimulating the generation of testable hypotheses on competitive interactions among rainforest trees and experimental research on fruit, seed, and seed-

The Storage and Production of Organic Matter in Tropical Forests and Their Role in the Global Carbon Cycle

Abstract: To investigate the storage relationships between and production of organic matter in tropical forests and climate, data on forest biomass, soil organic matter, litter storage, primary production, and litterfall were surveyed from the literature and organized using the Holdridge Life Zone system of classification. Ordinary least squares regressions were applied to all the data sets using the ratio of temperature to precipitation (T/P) as an index to climate and the independent variable. Total forest biomass (40-538 t/ha) gave a significant inverted U-shaped relationship with T/P, with peak values in the tropical moist forest life zone and lower ones in wetter and drier forest life zones. Soil carbon content (24-599 t C/ ha) decreased exponentially and significantly with increasing T/P (i.e., from wet to dry forest life zones). No significant relationship was found between litter storage and T/P. Gross primary production (19-120 t/ha yr) decreased curvilinearly and significantly with increasing T/P. Neither net primary production (11-21 t/ha yr) nor wood production (1-11 t/ha yr) were related to T/P. The ratio of leaf litter production to net primary production (0.25-0.65) was inversely related to T/P, suggesting different strategies of allocation of the net primary production in different life zones. The relationship between total litterfall (1.0-15.3 t/ha yr, excluding large wood) and T/P was significant and its shape similar to that obtained for biomass versus T/P; litterfall was highest in tropical moist forest life zones and lower in wetter or drier ones. The linear relationship between biomass and litterfall suggested that the turnover time of biomass in mature tropical forests is similar for all life zones, and is of the order of 34 yr. To determine the role of tropical forests in the global carbon cycle, literature estimates of areas of tropical forests were placed into six life zone groupings. The total tropical and subtropical basal and altitudinal forest area of 1838 million ha was comprised of 42 percent dry forest, 33 percent moist forest, and 25 percent wet and rain forest life zone groups. Organic-matter storage data were also combined into the six life zone groups and the means for each group calculated. The product of forest areas in the six groups and the mean organic matter per unit area in the groups yielded a total storage of 787 billion t organic matter, with vegetation accounting for 58, soils 41, and litter 1 percent. About half of the total storage was located in the tropical basal wet, moist, and dry forest life zone groups. Litterfall data were treated in the same way as organic-matter storage, resulting in a total litter production in tropical forests of 12.3 billion t organic matter/yr. Most litter was produced in the tropical basal moist forest group (30%) and least in the tropical basal dry forest group (10%). Turnover time of litter in tropical forests was less than 1 yr. Lowest turnover times were in very wet (1 yr) and in dry (0.9-1.9 yr) life zone groups. Tropical forests play an important role in the global carbon cycle because they store 46 percent of the world's living terrestrial carbon pool and 11 percent of the world's soil carbon pool.

Basin‐Wide Effects of Game Harvest on Vertebrate Population Densities in Amazonian Forests: Implications for Animal‐Mediated Seed Dispersal

Abstract: Vertebrate responses to hunting are widely variable for target and nontarget species depending on the history of hunting and productivity of any given site and the life history traits of game species. We provide a comprehensive meta-analysis of changes in population density or other abundance estimates for 30 mid-sized to large mammal, bird and reptile species in 101 hunted and nonhunted, but otherwise undisturbed, Neotropical forest sites. The data set was analyzed using both an unnested approach, based on population density estimates, and a nested approach in which pairwise comparisons of abundance metrics were restricted to geographic groups of sites sharing similar habitat and soil conditions. This resulted in 25 geographic clusters of sites within which 1811 population abundance estimates were compared across different levels of hunting pressure. Average nested changes in abundance across increasingly greater levels of hunting pressure ranged from moderately positive to highly negative. Populations of all species combined declined across greater differences in hunting pressure by up to 74.8 percent from their numeric abundance in less intensively hunted sites, but harvest-sensitive species faired far worse. Of the 30 species examined, 22 declined significantly at high levels of hunting. Body size significantly affected the direction and magnitude of abundance changes, with large-bodied species declining faster in overhunted sites. Frugivorous species showed more marked declines in abundance in heavily hunted sites than seed predators and browsers, regardless of the effects of body size. The implications of hunting for seed dispersal are discussed in terms of community dynamics in semi-defaunated tropical forests.