Kalle Ruokolainen

Dissecting amazonian biodiversity.

Biogeographical and biodiversity studies in Iowland Amazonian rain forests typically refer to observed or postulated distribution barriers such as past unfavorable climates, mountains, rivers, and river floodplains that divide the uniform tierra firme (noninundated) forest. Present-day ecological heterogeneity within tierra firme has hardly been discussed in this context, although edaphic differences are known to affect species distribution patterns in both inundated areas and tierra firme. Quantification of landscape heterogeneity in Peruvian Iowland Amazonia (500,000 kilometers squared), based on field studies and satellite image analysis, shows that Peruvian Amazonia is considerably more heterogeneous than previously reported. These observations have implications for the research, management, and conservation of Amazonian biodiversity.

ANALYZING OR EXPLAINING BETA DIVERSITY? UNDERSTANDING THE TARGETS OF DIFFERENT METHODS OF ANALYSIS

It has been actively discussed recently what statistical methods are appropriate when one is interested in testing hypotheses about the origin of beta diversity, especially whether one should use the raw-data approach (e.g., canonical analysis such as RDA and CCA) or the distance approach (e.g., Mantel test and multiple regression on distance matrices). Most of the confusion seems to stem from uncertainty as to what is the response variable in the different approaches. Here our aim is to clarify this issue. We also show that, although both the raw-data approach and the distance approach can often be used to address the same ecological hypothesis, they target fundamentally different predictions of those hypotheses. As the two approaches shed light on different aspects of the ecological hypotheses, they should be viewed as complementary rather than alternative ways of analyzing data. However, in some cases only one of the approaches may be appropriate. We argue that S. P. Hubbells neutral theory can only be tested using the distance approach, because its testable predictions are stated in terms of distances, not in terms of raw data. In all cases, the decision on which method is chosen must be based on which addresses the question at hand, it cannot be based on which provides the highest proportion of explained variance in simulation studies.

LINKING FLORISTIC PATTERNS WITH SOIL HETEROGENEITY AND SATELLITE IMAGERY IN ECUADORIAN AMAZONIA

Florisitic ground surveys in tropical rain forests are laborious and time consuming, so we tested to what degree reflectance differences visible in Landsat Thematic Mapper (TM) satellite images can be used to predict differences in florisitic composition and species richness among rain forest sites. To gain ecological understanding of the rain forest ecosystem, we also tested to what extent variation in these vegetation characteristics can be explained by edaphic site conditions. The study was conducted in a relatively homogeneous area of Amazonian rain forest in Yasuni National Park, Ecuador. We established 27 transects of 5 m × 500 m within an area of ∼20 km × 25 km to study edaphic and floristic patterns mainly within the tierra firme (non-inundated) forest. In each transect, soil samples were collected for chemical and textural analyses, and the abundance of each species belonging to two understory plant groups, pteridophytes (ferns and fern allies) and the Melastomataceae, was assessed. Floristic similarity between transect pairs varied widely and ranged from almost no overlap in species composition to very high overlap. The among-transect floristic similarity patterns of the two plant groups were strongly correlated with each other no matter whether presence–absence or abundance data were used. The floristic similarity patterns were also strongly correlated with the similarity in pixel values of the infrared bands in the Landsat TM satellite image and with the similarity in most of the measured soil variables. Similarity in species richness, on the contrary, was neither correlated with similarity in pixel values nor with similarity in most of the soil variables. We conclude that reflectance patterns in satellite images can be efficiently used to predict landscape-scale floristic and edaphic patterns in tierra firme rain forest. Predicting patterns in species richness, on the other hand, is not possible in the same straightforward manner. These results have important practical implications for land use and conservation planning as well as for ecological and biodiversity research. Corresponding Editor: C. A. Wessman.

Distribution of Pteridophyta and Melastomataceae along an edaphic gradient in an Amazonian rain forest

Abstract. Pteridophyta and Melastomataceae were studied in an area of non-flooded (tierra firme) rain forest in Peruvian Amazonia, close to the village of Mishana (River Nanay, in the vicinity of Iquitos City). The general objective of the study was to establish a method for rapidly documenting changes in the floristic composition among and within rain forests in geologically different areas. More specifically, the changes in the plant communities were documented along an edaphic and topographic gradient from clay soil on level ground to quartzitic sand on a hill top. Two 5-m-wide, parallel transects were established 50 m apart. A total of 40 species of pteridophytes were found; 18 of these were confined to clayey soil and 11 to sandy soil. The total number of Melastomataceae on the transects was 22, and 14 of these were confined to clayey soil while only two were confined to sandy soil. Further differences in the abundance of many species correlated with drainage conditions and the accumulation of organic matter on the soil surface. Cluster analyses were made using both edaphic and floristic criteria, and in all cases the transects could be divided into distinct sections. Both transects gave rather similar results, and therefore it was concluded that the chosen transect width was sufficient to document the prevalent floristic patterns.

USE OF MELASTOMATACEAE AND PTERIDOPHYTES FOR REVEALING PHYTOGEOGRAPHICAL PATTERNS IN AMAZONIAN RAIN FORESTS

Similarities and differences among eight upland rain forest sites in Peruvian Amazonia were measured separately by using Melastomataceae, pteridophyte and tree species compositions and edaphic characteristics of the sites. All three plant groups showed a similar pattern among the sites, and this pattern could be explained by edaphic differences but not by geographical distances among the sites. The explicability of site-specific edaphic characteristics on the basis of geological history is discussed. The results suggest that both pteridophytes and Melastomataceae can be used as indicators of floristically different rain forest types that are edaphically defined. Distribution patterns of these plant groups can be studied much more rapidly than the patterns of trees and therefore both Melastomataceae and pteridophytes may be used in large scale phytogeographical studies that are urgently needed in the face of rapidly advancing deforestation.

Geological control of floristic composition in Amazonian forests

Aim Conservation and land-use planning require accurate maps of patterns in species composition and an understanding of the factors that control them. Substantial doubt exists, however, about the existence and determinants of large-area floristic divisions in Amazonia. Here we ask whether Amazonian forests are partitioned into broad-scale floristic units on the basis of geological formations and their edaphic properties. Location Western and central Amazonia. Methods We used Landsat imagery and Shuttle Radar Topography Mission (SRTM) digital elevation data to identify a possible floristic and geological discontinuity of over 300 km in northern Peru. We then used plant inventories and soil sampling to document changes in species composition and soil properties across this boundary. Data were obtained from 138 sites distributed along more than 450 km of road and river. On the basis of our findings, we used broad-scale Landsat and SRTM mosaics to identify similar patterns across western and central Amazonia. Results The discontinuity identified in Landsat and SRTM data corresponded to a 15-fold change in soil cation concentrations and an almost total change in plant species composition. This discontinuity appears to be caused by the widespread removal of cation-poor surface sediments by river incision to expose cation-rich sediments beneath. Examination of broad-scale Landsat and SRTM mosaics indicated that equivalent processes have generated a north–south discontinuity of over 1500 km in western Brazil. Due to similarities with our study area, we suggest that this discontinuity represents a chemical and ecological limit between western and central Amazonia. Main conclusions Our findings suggest that Amazonian forests are partitioned into large-area units on the basis of geological formations and their edaphic properties. The evolution of these units through geological time may provide a general mechanism for biotic diversification in Amazonia. These compositional units, moreover, may correspond to broad-scale functional units. The existence of large-area compositional and functional units would suggest that protected-area, carbon sequestration, and other land-use strategies in Amazonia be implemented on a region-by-region basis. The methods described here can be used to map these patterns, and thus enable effective conservation and management of Amazonian forests.

The role of ecological knowledge in explaining biogeography and biodiversity in Amazonia

Biogeographical studies in Amazonia have commonly taken a historical, rather than an ecological approach. General patterns have been sought in the distribution maps of different species, and these have been explained in terms of past or present distribution barriers, especially past climates and large rivers. Implicitly, and often also explicitly, it is assumed that Amazonia is ecologically so uniform that present-day ecological conditions are rather insignificant in determining species distribution patterns and speciation. However, this assumption is more based on the lack of relevant data than on actual observations of environmental uniformity or ecological unspecialization of the species. Recent studies have indeed documented ecological heterogeneity and floristic differences among sites that were previously thought similar. In the absence of direct knowledge of the past, more complete ecological and environmental understanding of the present-day Amazonia are needed for evaluating the relative roles of historical and ecological factors in Amazonian biogeography and biodiversity.

The most widespread Amazonian palms tend to be tall and habitat generalists

Abstract We studied correlations between geographical range sizes and plant structural and ecological characteristics of 45 palm taxa occurring in western Amazonian lowland rainforests. The studied plant features were stem height, fruit size, cespitose growth form, response to variation in soil cation content and occurrence in seven different not soil-related habitat types. The most widespread palms tended to be tall, be utilised by people and have relatively wide tolerances to differences in soil fertility and habitat quality. Cespitose growth form and fruit size were not related to the variation in range size. Tallness may be associated with better seed dispersers which contributes to wider ranges. The positive link between range size and edaphic and habitat generality demonstrates the importance of relatively deterministic environmental factors in controlling the distributions of plants. Other studies linking plant attributes with range size have produced rather disagreeing results and this study is not able to clarify the overall picture. It may be that the discrepancies arise at least partly from ecological differences among the studied floras. If the result that tall plants are more widespread than small plants in rain forest floras is a general one, it would have important implications for the prospects of generalising the results of plant ecological studies performed with only one or a restricted set of growth forms to the rest of the flora.

Comparing composition and diversity of parasitoid wasps and plants in an Amazonian rain-forest mosaic

Local species richness and between-site similarity in species composition of parasitoid wasps (Hymenoptera: Ichneumonidae; Pimplinae and Rhyssinae) were correlated with those of four plant groups (pteridophytes, Melastomataceae, Burseraceae and Arecaceae) in a western Amazonian lowland rain forest mosaic. The mosaic structure of the forest was related to variation in soils within the non-inundated terrain. Significant matrix correlation between patterns in parasitoid wasp species composition and plant species composition was found. Most of the overall correlation was due to idiobiont parasitoids of weakly concealed hosts, which attack host larvae and pupae in exposed situations, with two of the four ecologically defined parasitoid groups showing no correlation at all. A positive correlation between the number of plant species and the number of Pimplinae and Rhyssinae species at a site was found when the latter was corrected for collecting effort. Consequently, the degree of floristic difference between sites may be indicative of the difference in species composition of ichneumonids, and the species richness of plants may serve as a predictor of the species richness of parasitoid wasps. Although these results were obtained in a mosaic including structurally and floristically clearly different types of rain forest, the correlation coefficients were relatively low, and the present results lend only weak support to the idea of using plant distributions as indicators of animal distributions.

Two biases in estimating range sizes of Amazonian plant species

The Amazonian rain forests form one of the largest areas of continuous forest in the world, and they harbour a substantial part of the world’s biodiversity (World Conservation Monitoring Centre 1992). The extravagant species richness of Amazonia makes collecting information on species distribution patterns there a formidable challenge. Relatively few studies have been able to provide data that cover both a large enough number of species and wide enough geographical areas to allow relevant biogeographical and ecological generalizations (such studies concerning plants include Balslev 1988, de Oliveira & Daly 1999, Pitman et al. 1999, Prance 1973, ter Steege et al. 2000, Terborgh & Andresen 1998, Tuomisto & Poulsen 1996). The scarcity of field observations is undoubtedly one of the reasons why very different ideas exist about the mechanisms that control plant distributions and patterns of species richness in Amazonia (Balslev 1988, Condit 1996, Gentry 1988, Nelson et al. 1990, Pitman et al. 1999, Prance 1973, 1982; ter Steege et al. 2000, Tuomisto et al. 1995). Quantitative tree inventories, regional plant check-lists and taxonomic revisions are the main sources of information for documenting Amazonian plant distribution patterns, and luckily new information is continuously accumulating