Species distribution models (SDMs) are widely used in ecology and conservation. Presence-only SDMs such as MaxEnt frequently use natural history collections (NHCs) as occurrence data, given their huge numbers and accessibility. NHCs are often spatially biased which may generate inaccuracies in SDMs. Here, we test how the distribution of NHCs and MaxEnt predictions relates to a spatial abundance model, based on a large plot dataset for Amazonian tree species, using inverse distance weighting (IDW). We also propose a new pipeline to deal with inconsistencies in NHCs and to limit the area of occupancy of the species. We found a significant but weak positive relationship between the distribution of NHCs and IDW for 66% of the species. The relationship between SDMs and IDW was also significant but weakly positive for 95% of the species, and sensitivity for both analyses was high. Furthermore, the pipeline removed half of the NHCs records. Presence-only SDM applications should consider this limitation, especially for large biodiversity assessments projects, when they are automatically generated without subsequent checking. Our pipeline provides a conservative estimate of a species’ area of occupancy, within an area slightly larger than its extent of occurrence, compatible to e.g. IUCN red list assessments.

No abstract

Tropical forests are known for their high diversity. Yet, forest patches do occur in the tropics where a single tree species is dominant. Such “monodominant” forests are known from all of the main tropical regions. For Amazonia, we sampled the occurrence of monodominance in a massive, basin-wide database of forest-inventory plots from the Amazon Tree Diversity Network (ATDN). Utilizing a simple defining metric of at least half of the trees ≥ 10 cm diameter belonging to one species, we found only a few occurrences of monodominance in Amazonia, and the phenomenon was not significantly linked to previously hypothesized life history traits such wood density, seed mass, ectomycorrhizal associations, or Rhizobium nodulation. In our analysis, coppicing (the formation of sprouts at the base of the tree or on roots) was the only trait significantly linked to monodominance. While at specific locales coppicing or ectomycorrhizal associations may confer a considerable advantage to a tree species and lead to its monodominance, very few species have these traits. Mining of the ATDN dataset suggests that monodominance is quite rare in Amazonia, and may be linked primarily to edaphic factors.

Amazonian forests are extraordinarily diverse, but the estimated species richness is very much debated. Here, we apply an ensemble of parametric estimators and a novel technique that includes conspecific spatial aggregation to an extended database of forest plots with up-to-date taxonomy. We show that the species abundance distribution of Amazonia is best approximated by a logseries with aggregated individuals, where aggregation increases with rarity. By averaging several methods to estimate total richness, we confirm that over 15,000 tree species are expected to occur in Amazonia. We also show that using ten times the number of plots would result in an increase to just ~50% of those 15,000 estimated species. To get a more complete sample of all tree species, rigorous field campaigns may be needed but the number of trees in Amazonia will remain an estimate for years to come.

Species richness estimation is one of the most widely used analyses carried out by ecologists, and nonparametric estimators are probably the most used techniques to carry out such estimations. We tested the assumptions and results of nonparametric estimators and those of a logseries approach to species richness estimation for simulated tropical forests and five data sets from the field. We conclude that nonparametric estimators are not suitable to estimate species richness in tropical forests, where sampling intensity is usually low and richness is high, because the assumptions of the methods do not meet the sampling strategy used in most studies. The logseries, while also requiring substantial sampling, is much more effective in estimating species richness than commonly used nonparametric estimators, and its assumptions better match the way field data is being collected.

Aim: To 1) assess the environmental suitability for rainforest tree species of the families Moraceae and Urticaceae across Amazonia during the Mid-Late Holocene and 2) determine the extent to which their distributions increased in response to long-term climate change over this period. Location: Amazonia.Taxon: Tree species of Moraceae and Urticaceae.Methods: We used MaxEnt (maximum entropy modelling) and inverse distance weighting (IDW) interpolation to produce environmental suitability and relative abundance models at 0.5 degree resolution for Moraceae and Urticaceae tree species, based on natural history collections and a large plot dataset. To test the responses of the Amazon rainforest to longterm climate change, we quantified the increase in environmental suitability and modelled species richness for both families since the Mid Holocene (past 6,000 years). To test the correlation between the relative abundance of these species in the modern vegetation versus modern pollen assemblages, we analysed the surface pollen spectra from 46 previously published paleoecological sites. Results:We found that the mean environmental suitability, for the Amazon basin as a whole, for species of Moraceae and Urticaceae showed a slight increase (6.5%) over the past 6,000 years, although southern ecotonal Amazonia and the Guiana Shield showed much higher increases (up to 68%). The accompanied modelled mean species richness increased by as much as 120% throughout Amazonia. The mean relative abundance of Moraceae and Urticaceae correlated significantly with the modern pollen assemblages for these families (R 2 = 52%). Main conclusions:Increasing precipitation between the Mid and Late Holocene expanded the range of suitable environmental conditions for Amazonian humid rainforest tree species in the Moraceae and Urticaceae families, thus leading to rainforest expansion in ecotonal areas of Amazonia, consistent with previously published fossil pollen data.

Aim To investigate the geographic patterns and ecological correlates in the geographic distribution of the most common tree dispersal modes in Amazonia (endozoochory, synzoochory, anemochory and hydrochory). We examined if the proportional abundance of these dispersal modes could be explained by the availability of dispersal agents (disperser‐availability hypothesis) and/or the availability of resources for constructing zoochorous fruits (resource‐availability hypothesis). Time period Tree‐inventory plots established between 1934 and 2019. Major taxa studied Trees with a diameter at breast height (DBH) ≥ 9.55 cm. Location Amazonia, here defined as the lowland rain forests of the Amazon River basin and the Guiana Shield. Methods We assigned dispersal modes to a total of 5433 species and morphospecies within 1877 tree‐inventory plots across terra‐firme, seasonally flooded, and permanently flooded forests. We investigated geographic patterns in the proportional abundance of dispersal modes. We performed an abundance‐weighted mean pairwise distance (MPD) test and fit generalized linear models (GLMs) to explain the geographic distribution of dispersal modes. Results Anemochory was significantly, positively associated with mean annual wind speed, and hydrochory was significantly higher in flooded forests. Dispersal modes did not consistently show significant associations with the availability of resources for constructing zoochorous fruits. A lower dissimilarity in dispersal modes, resulting from a higher dominance of endozoochory, occurred in terra‐firme forests (excluding podzols) compared to flooded forests. Main conclusions The disperser‐availability hypothesis was well supported for abiotic dispersal modes (anemochory and hydrochory). The availability of resources for constructing zoochorous fruits seems an unlikely explanation for the distribution of dispersal modes in Amazonia. The association between frugivores and the proportional abundance of zoochory requires further research, as tree recruitment not only depends on dispersal vectors but also on conditions that favour or limit seedling recruitment across forest types.

Na Floresta Nacional Saracá-Taquera, estado do Pará, a lavra da bauxita é feita a céu aberto. As operações de lavra envolvem desde a supressão da floresta ombrófila densa até a restauração das áreas através de reflorestamentos heterogêneos, onde são empregadas por volta de 80 espécies. Objetivou-se, neste trabalho, apresentar um índice de fitossociologia horizontal (IFH), obtido pelas mesmas variáveis que fornecem o índice de valor de importância (IVI), através do ranqueamento das espécies amostradas nos inventários da floresta ombrófila densa em categorias ecológicas de prioridade alta, intermediária e baixa. Nos inventários fitossociológicos do platô Saracá, foram registrados 23.166 indivíduos, totalizando 796 espécies e 58 famílias. A adequação da análise fatorial foi determinada pelos testes de Bartlett, que avaliaram a significância geral da matriz de correlação, indicando que as correlações são significantes no nível de 1% de probabilidade, e de Kaiser-Meyer-Olkin (KMO), que indicou que as variáveis estão correlacionadas e que o modelo fatorial apresentou um nível bom de adequação aos dados. Os testes estatísticos validaram a amostra de dados para emprego da técnica de análise multivariada e, portanto, para a construção do índice de fitossociologia horizontal com variável dummy – IFH, que selecionou 65 espécies-chave para plantio em trabalhos de restauração florestal, contra apenas seis indicadas pelo índice IVI.