Bianca Weiss

Recent evidence suggests that the ecological footprints of pre-Columbian Indigenous peoples in Amazonia persist in modern forests. Ecological impacts resulting from European colonization c. 1550 CE and the Amazonian Rubber Boom c. 1850 to 1920 CE are largely unexplored but could be important additive influences on forest structure and tree species composition. Using environmental niche models, we show the highest probabilities of pre-Columbian and colonial occupation sites, and hence human-induced ecological influences, occurred in forests along rivers. In many areas, the predicted pre-Columbian and colonial distributions overlap spatially with the potential for superimposed ecological influences. Environmental gradients are known to structure Amazonian vegetation composition, but they are also strong predictors of past human influence, both spatially and temporally. Our comparisons of model outputs with relative abundances of Amazonian tree species suggest that pre-Columbian and colonial-period ecological legacies are associated with modern forest composition.

About 30% of the Amazon Basin is covered by different wetland types that harbor a huge and unique biodiversity and provide essential ecosystem services. This study examines the floristic composition and diversity patterns of tree species in oligotrophic blackwater wetlands of two sub-basins, Abacate River in Central Amazonia and Falsino River in Eastern Amazonia, along a hydroedaphic gradient from the headwaters to the floodplains. Data collection involved nine 0.5 ha plots in each sub-basin, with monitoring of flood levels, water table depths over a year as well as soil properties. The diameter at breast height (DBH) ≥10 cm of all trees was obtained, and the species were identified. Regression models were used to relate floristic patterns to environmental gradients. Results showed distinct responses between sub-basins. Tree Alpha diversity in the Abacate River was influenced by hydroedaphic variation but not floristic composition. Conversely, floristic composition in the Falsino River was significantly explained by the hydroedaphic gradient, while alpha diversity was higher but not statistically significant. Local-scale heterogeneity drives floristic variation, leads to high species turnover, emphasizing the need for conservation strategies tailored to sub-basin-level dynamics.

Leaf and wood functional traits of trees are related to growth, reproduction, and survival, but the degree of phylogenetic conservatism in these relationships is largely unknown. In this study, we describe the variability of strategies involving leaf, wood and demographic characteristics for tree genera distributed across the Amazon Region, and quantify phylogenetic signal for the characteristics and their relationships. Leaf and wood traits are aligned with demographic variables along two main axes of variation. The first axis represents the coordination of leaf traits describing resource uptake and use, wood density, seed mass, and survival. The second axis represents the coordination between size and growth. Both axes show strong phylogenetic signal, suggesting a constrained evolution influenced by ancestral values, yet the second axis also has an additional, substantial portion of its variation that is driven by functional correlations unrelated to phylogeny, suggesting simultaneously higher evolutionary lability and coordination. Synthesis. Our results suggest that life history strategies of tropical trees are generally phylogenetically conserved, but that tree lineages may have some capability of responding to environmental changes by modulating their growth and size. Overall, we provide the largest‐scale synopsis of functional characteristics of Amazonian trees, showing substantial nuance in the evolutionary patterns of individual characteristics and their relationships. Read the free Plain Language Summary for this article on the Journal blog.

The interaction between fish and plants is vital for the dynamics of ecosystems since it influences plant distribution and regeneration patterns. In the floodable areas of the Amazon, these interactions are mainly structured by the flood pulse, which enables seed dispersal via water (hydrochory) and fish (ichthyochory), and which contributes to the formation of complex mutualistic networks. Our study evaluated the structure (modularity, nestedness, specialisation, and robustness) of the network of dispersal of seeds by frugivorous fish in a floodplain forest in Central Amazonia. We expect the binary network to have a nested pattern, while the weighted network is expected to have a non‐nested structure; that generalist frugivorous species should constitute the core of the network, while specialist frugivorous species will be peripheral; that the size of fish and seeds is related to specialisation, and that the robustness of the network weakens as generalist frugivorous fish are removed. We found 5012 intact seeds from 49 plant species in the digestive tracts of 11 species of frugivorous fish. A nested and modular pattern was found for the binary and weighted networks, albeit with a low degree of nestedness. Our network proved relatively robust when the frugivores were removed, whereby all the fish and plant species became peripheral. No relationship was found between the size of the fish and the seeds and the degree of specialisation. Considering the anthropogenic impacts that can cause modifications in seed dispersal networks, knowing the structure of mutualistic networks is fundamental in order to be able infer the vulnerability of the interactions as a result of changes in the ecosystem.

This study compared the diversity, richness, abundance, and biomass of fish collected in three environments in the Central Amazon: (1) the reservoir of the Balbina hydroelectric dam; (2) the Uatumã River downstream of the dam; and (3) the Abacate River. Through the analysis of food resources, we determined the fish trophic guilds for each environment. We hypothesized that the undisturbed environment of the Abacate River would present the highest values of diversity, richness, abundance, and biomass, followed by the Uatumã River and the reservoir, and that there would be significant differences among the trophic guilds among the three environments. The highest taxonomic richness was observed for the Uatumã River, followed by the Abacate River and the reservoir. There was no statistical difference in the species richness of the trophic guilds among the three sampled sites, but the three areas differed in abundance. The highest value of guild biomass was observed for the Uatumã River, followed by the reservoir and the Abacate River. Characteristics of the Uatumã and Abacate River systems, such as size, greater complexity and heterogeneity of habitats, and flood regime, may be the cause of the greater species richness in these rivers, compared to the reservoir.

In tropical and highly diverse systems, Seed Dispersal Effectiveness (SDE) is a very useful approach to investigating the role of seed dispersers in one of the most important and complex phases of plants by analysing the quantitative (QC) and qualitative (QL) components of the seed dispersal process. Although fishes are recognized as an important guild of frugivores in flooded environments, we still know very little about the dispersal effectiveness performed by this group. Our study evaluated two quantitative subcomponents of effectiveness, where we used: (a) the volume of intact and crushed seeds found in the stomach and intestine of fish (QC₁), and (b) the total number of tested and viable seeds (QC₂). From these subcomponents, a two‐dimensional landscape of effectiveness was generated and a fish species was ranked according to the quantitative component of the SDE. Eight species of fish consumed 1054 seeds belonging to 16 plant species. Sphinctanthus striiflorus, Corynostylis pubescens, Connarus sp. and Piper sp., were the most abundant plant species in fish's diets, totalling 95% (N = 983) of the seeds consumed. We used a tetrazolium viability test protocol and about 678 (85%) of the 797 seeds tested were viable and 119 (14.7%) were unviable; the viability test was inconclusive for less than 1% of the seeds. Our findings showed that, as seen in other effectiveness studies with terrestrial vertebrate dispersers, fish species also have different degrees of effectiveness. Additionally, we pointed out that the fish species more specialized in the consumption of fruits and seeds were quantitatively more effective dispersers, while species with lower SDE corresponded to generalists that just occasionally consume seeds. We suggest that high‐diversity fish assemblages allow for greater complementarity in the seed dispersal interaction, which can potentially favour the recruitment of plant species via ichthyochory.

The large flood pulse of the Amazon basin is a principal driver of environmental heterogeneity with important implications for ecosystem function and the assembly of natural communities. Understanding species ecological response to the flood pulse is thus a key question with implications for theories of species coexistence, resource management, and conservation. Yet these remain largely undescribed for most species, and in particular for trees. The large flood pulse and high tree diversity of the Negro River floodplain makes it an ideal system to begin filling this knowledge gap. We merged historical hydrologic data with 41 forest inventories under variable flooding conditions distributed across the Negro River basin, comprising a total area of 34 ha, to (i) assess the importance of flood duration as a driver of compositional variation, (ii) model the response curve shapes of 111 of the most frequent tree species in function of flood duration, and (iii) derive their niche properties (optima and tolerance). We found that flood duration is a strong driver of compositional turnover, although the majority site-to-site variation in forest composition still remains unexplained. About 73% of species responded to the flood duration gradient, exhibiting a diversity of shapes, but most frequently skewed. About 29% of species were clearly favored by flood durations >120 days year^–1, and 44% of species favored by shorter floods. The median niche breadth was 85 flood days year^–1, corresponding to approximately 30% of the flood duration gradient. A significant subset of species (27%) did not respond to flooding, but rather exhibited wide tolerance to the flood gradient. The response models provided here offer valuable information regarding tree species differential capacity to grow, survive, and regenerate along an ecologically important gradient and are spatially valid for the Amazon Negro basin. These attributes make them an appealing tool with wide applicability for field and experimental studies in the region, as well as for vegetation monitoring and simulation models of floodplain forest change in the face of hydrologic alteration.