Eduardo Martins Venticinque

An estimate of the number of tropical tree species

Significance People are fascinated by the amazing diversity of tropical forests and will be surprised to learn that robust estimates of the number of tropical tree species are lacking. We show that there are at least 40,000, but possibly more than 53,000, tree species in the tropics, in contrast to only 124 across temperate Europe. Almost all tropical tree species are restricted to their respective continents, and the Indo-Pacific region appears to be as species-rich as tropical America, with each of these two regions being almost five times as rich in tree species as African tropical forests. Our study shows that most tree species are extremely rare, meaning that they may be under serious risk of extinction at current deforestation rates. The high species richness of tropical forests has long been recognized, yet there remains substantial uncertainty regarding the actual number of tropical tree species. Using a pantropical tree inventory database from closed canopy forests, consisting of 657,630 trees belonging to 11,371 species, we use a fitted value of Fisher’s alpha and an approximate pantropical stem total to estimate the minimum number of tropical forest tree species to fall between ∼40,000 and ∼53,000, i.e., at the high end of previous estimates. Contrary to common assumption, the Indo-Pacific region was found to be as species-rich as the Neotropics, with both regions having a minimum of ∼19,000–25,000 tree species. Continental Africa is relatively depauperate with a minimum of ∼4,500–6,000 tree species. Very few species are shared among the African, American, and the Indo-Pacific regions. We provide a methodological framework for estimating species richness in trees that may help refine species richness estimates of tree-dependent taxa.

Effects of Dam‐Induced Landscape Fragmentation on Amazonian Ant–Plant Mutualistic Networks

Mutualistic networks are critical to biological diversity maintenance; however, their structures and functionality may be threatened by a swiftly changing world. In the Amazon, the increasing number of dams poses a large threat to biological diversity because they greatly alter and fragment the surrounding landscape. Tight coevolutionary interactions typical of tropical forests, such as the ant-myrmecophyte mutualism, where the myrmecophyte plants provide domatia nesting space to their symbiotic ants, may be jeopardized by the landscape changes caused by dams. We analyzed 31 ant-myrmecophyte mutualistic networks in undisturbed and disturbed sites surrounding Balbina, the largest Central Amazonian dam. We tested how ant-myrmecophyte networks differ among dam-induced islands, lake edges, and undisturbed forests in terms of species richness, composition, structure, and robustness (number of species remaining in the network after partner extinctions). We also tested how landscape configuration in terms of area, isolation, shape, and neighborhood alters the structure of the ant-myrmecophyte networks on islands. Ant-myrmecophytic networks were highly compartmentalized in undisturbed forests, and the compartments had few strongly connected mutualistic partners. In contrast, networks at lake edges and on islands were not compartmentalized and were negatively affected by island area and isolation in terms of species richness, density, and composition. Habitat loss and fragmentation led to coextinction cascades that contributed to the elimination of entire ant-plant compartments. Furthermore, many myrmecophytic plants in disturbed sites lost their mutualistic ant partners or were colonized by opportunistic, nonspecialized ants. Robustness of ant-myrmecophyte networks on islands was lower than robustness near lake edges and in undisturbed forest and was particularly susceptible to the extinction of plants. Beyond the immediate habitat loss caused by the building of large dams in Amazonia, persistent edge effects and habitat fragmentation associated with dams had large negative effects on animal-plant mutualistic networks.

Effects of forest fragmentation on four Ctenus spider populations (Araneae: Ctenidae) in central Amazonia, Brazil

The effects of habitat fragmentation on four Ctenus spider populations in central Amazonia were investigated. Fourteen Ctenidae species were collected in nine forest fragments (⩽10 ha) and nine continuous forest sites (>1000 ha). Four species, belonging to the genus Ctenus (C. amphora, C. crulsi, C. manauara and C. villasboasi), were found in sufficient numbers to determine by covariance analyses, how isolation and litter depth affect their population densities. Litter depth did not affect spider densities, however, controlled experiments involving litter manipulation are more appropriate to test these relations. C. amphora and C. villasboasi presented much smaller populations in fragments, while C. manauara and C. crulsi apparently were not affected by forest fragmentation. On the other hand, the abundance of these species in the edges of fragments and continuous forest were similar, suggesting a decrease in the populations of C. amphora and C. villasboasi between 5 and 150 m from the edges. Thus, isolation and forest reduction increase the chances of local extinction and threaten the diversity of ctenid spiders. Resumo Os efeitos da fragmentação de hábitats sobre quatro populações de Ctenus foram investigados na Amazônia central. Quatorze espécies de Ctenidae foram coletadas em nove fragmentos florestais (⩽10 ha) e nove áreas de mata contínua (>1000 ha). Quatro espécies do gênero Ctenus (C. amphora, C. crulsi, C. manauara e C. villasboasi) foram coletadas em número suficiente para a determinação, por meio de análises de covariância, dos efeitos do isolamento e da profundidade da liteira sobre a abundância de suas populações. C. amphora e C. villasboasi apresentaram populações muito menores nos fragmentos, por outro lado, C. manauara e C. crulsi aparentemente não foram afetadas pela fragmentação da floresta. A profundidade da liteira não afetou a densidade de aranhas, no entanto, experimentos controlados com manipulação de liteira são métodos mais adequados para testar esta relação. As bordas de fragmentos e mata continua foram similares quanto a abundância das espécies mais comuns de Ctenus, porém, a proximidade em relação a borda (de 5 a 150 m) pode ter reduzido a abundância de C. amphora e C. villasboasi. Assim, o isolamento e a redução da floreta aumentam as chances de extinções locais e ameaçam a diversidade de ctenídeos.

Unexpected high diversity of galling insects in the Amazonian upper canopy: the savanna out there.

A relatively large number of studies reassert the strong relationship between galling insect diversity and extreme hydric and thermal status in some habitats, and an overall pattern of a greater number of galling species in the understory of scleromorphic vegetation. We compared galling insect diversity in the forest canopy and its relationship with tree richness among upland terra firme, várzea, and igapó floodplains in Amazonia, Brazil. The soils of these forest types have highly different hydric and nutritional status. Overall, we examined the upper layer of 1,091 tree crowns. Galling species richness and abundance were higher in terra firme forests compared to várzea and igapó forests. GLM-ANCOVA models revealed that the number of tree species sampled in each forest type was determinant in the gall-forming insect diversity. The ratio between galling insect richness and number of tree species sampled (GIR/TSS ratio) was higher in the terra firme forest and in seasonally flooded igapó, while the várzea presented the lowest GIR/TSS ratio. In this study, we recorded unprecedented values of galling species diversity and abundance per sampling point. The GIR/TSS ratio from várzea was approximately 2.5 times higher than the highest value of this ratio ever reported in the literature. Based on this fact, we ascertained that várzea and igapó floodplain forests (with lower GIA and GIR), together with the speciose terra firme galling community emerge as the gall diversity apex landscape among all biogeographic regions already investigated. Contrary to expectation, our results also support the “harsh environment hypothesis”, and unveil the Amazonian upper canopy as similar to Mediterranean vegetation habitats, hygrothermically stressed environments with leaf temperature at lethal limits and high levels of leaf sclerophylly.

Empty forest or empty rivers? A century of commercial hunting in Amazonia

Trend analysis of the massive international hide trade in Amazonia reveals differential resilience to hunting for aquatic and terrestrial wildlife. The Amazon basin is the largest and most species-rich tropical forest and river system in the world, playing a pivotal role in global climate regulation and harboring hundreds of traditional and indigenous cultures. It is a matter of intense debate whether the ecosystem is threatened by hunting practices, whereby an “empty forest” loses critical ecological functions. Strikingly, no previous study has examined Amazonian ecosystem resilience through the perspective of the massive 20th century international trade in furs and skins. We present the first historical account of the scale and impacts of this trade and show that whereas aquatic species suffered basin-wide population collapse, terrestrial species did not. We link this differential resilience to the persistence of adequate spatial refuges for terrestrial species, enabling populations to be sustained through source-sink dynamics, contrasting with unremitting hunting pressure on more accessible aquatic habitats. Our findings attest the high vulnerability of aquatic fauna to unregulated hunting, particularly during years of severe drought. We propose that the relative resilience of terrestrial species suggests a marked opportunity for managing, rather than criminalizing, contemporary traditional subsistence hunting in Amazonia, through both the engagement of local people in community-based comanagement programs and science-led conservation governance.

Goliath catfish spawning in the far western Amazon confirmed by the distribution of mature adults, drifting larvae and migrating juveniles

We mapped the inferred long-distance migrations of four species of Amazonian goliath catfishes (Brachyplatystoma rousseauxii, B. platynemum, B. juruense and B. vaillantii) based on the presence of individuals with mature gonads and conducted statistical analysis of the expected long-distance downstream migrations of their larvae and juveniles. By linking the distribution of larval, juvenile and mature adult size classes across the Amazon, the results showed: (i) that the main spawning regions of these goliath catfish species are in the western Amazon; (ii) at least three species—B. rousseauxii, B. platynemum, and B. juruense—spawn partially or mainly as far upstream as the Andes; (iii) the main spawning area of B. rousseauxii is in or near the Andes; and (iv) the life history migration distances of B. rousseauxii are the longest strictly freshwater fish migrations in the world. These results provide an empirical baseline for tagging experiments, life histories extrapolated from otolith microchemistry interpretations and other methods to establish goliath catfish migratory routes, their seasonal timing and possible return (homing) to western headwater tributaries where they were born.

List of species of spiders (Arachnida, Araneae) from the Pico da Neblina, state of Amazonas, Brazil

We present a list of species of spiders collected at the Pico da Neblina, the highest mountain in Brazil (Amazonas, Brazil). We sampled at six altitudes (100, 400, 860, 1,550, 2,000 and 2,400 m a.s.l.), through manual active search, during the night and with a beating tray, during the day. We obtained a total of 3,143 adult individuals, which were assigned to 529 species, from 39 families. The most species rich families were Theridiidae (108 species), Araneidae (98 species) and Salticidae (60 species). Most species were rarely collected, as 389 (73% of total richness) species were represented by up to five individuals, and 197 (37% of total richness) of them by just one individual. We briefly compare our results with those from other spider surveys in the Amazon basin.

Are Leaves a Good Option in Caatinga's Menu? First Record of Folivory in Artibeus planirostris (Phyllostomidae) in the Semiarid Forest, Brazil

Folivory can be defined as the consumption of foliage, including leaves, stems and leaf content. This trophic strategy has been documented in two families of bats, Pteropodidae (Old World fruit bats) and Phyllostomidae (New World leaf-nosed bats). Existing folivory hypotheses for bats suggest this behavior provides a dietary supplement of protein and other essential minerals due to a deficiency of these in a frugivorous diet. The Caatinga is a seasonally deciduous tropical dry forest where most of the vegetation is leafless and dormant during the extended dry season. Here we present the first evidence of folivory in bats from the Brazilian Caatinga, with evidence for the phyllostomid Artibeus planirostris ingesting the leaves of at least 16 species of plants. We include a bibliographic review of bat folivory in the tropics. Additionally, we propose a new hypothesis on folivory in bats for this semiarid environment.

Climatic Variables Do Not Directly Predict Spider Richness and Abundance in Semiarid Caatinga Vegetation, Brazil

ABSTRACT Spiders are abundant in tropical ecosystems and exert predatory pressure on a wide variety of invertebrate populations and also serve as prey for many others organisms, being part of complex interrelationships influenced directly and indirectly by a myriad of factors. We examined the influence of biotic (i.e., prey availability) and abiotic (i.e., temperature, precipitation, relative humidity, real evapotranspiration) factors on species richness and abundance during a two-year period in the semiarid Caatinga vegetation in northeastern Brazil. Data were analyzed through partial autocorrelation functions, cross correlations, and a path analysis. A total of 2522 spiders were collected with beating tray, pitfall traps, and malaise traps, comprising 91 species and 34 families. Spider abundance peaked in the rainy season. Our results suggest that total invertebrate abundance has a direct influence on spider richness and abundance, whereas the effects of precipitation were mainly indirectly related to most spider assemblage parameters. The increase in vegetation cover with the rainy season in the Caatinga provides more breeding and foraging sites for spiders and stimulates their activities. Additionally, rainfall in arid and semiarid ecosystems stimulated the activity and reproduction of many herbivore and detritivore invertebrates dependent on plant biomass and necromass consumption, leading to an increase in spider prey availability.

Kinship and Social Behavior of Lowland Tapirs (Tapirus terrestris) in a Central Amazon Landscape

We tested the hypothesis that tapirs tolerate individuals from adjacent and overlapping home ranges if they are related. We obtained genetic data from fecal samples collected in the Balbina reservoir landscape, central Amazon. Samples were genotyped at 14 microsatellite loci, of which five produced high quality informative genotypes. Based on an analysis of 32 individuals, we inferred a single panmictic population with high levels of heterozygosity. Kinship analysis identified 10 pairs of full siblings or parent-offspring, 10 pairs of half siblings and 25 unrelated pairs. In 10 cases, the related individuals were situated on opposite margins of the reservoir, suggesting that tapirs are capable of crossing the main river, even after damming. The polygamous model was the most likely mating system for Tapirus terrestris. Morans I index of allele sharing between pairs of individuals geographically close (<3 km) was similar to that observed between individual pairs at larger distances (>3 km). Confirming this result, the related individuals were not geographically closer than unrelated ones (W = 188.5; p = 0.339). Thus, we found no evidence of a preference for being close to relatives and observed a tendency for dispersal. The small importance of relatedness in determining spatial distribution of individuals is unusual in mammals, but not unheard of. Finally, non-invasive sampling allowed efficient access to the genetic data, despite the warm and humid climate of the Amazon, which accelerates DNA degradation.