Mapping ignorance: 300 years of collecting flowering plants in Africa

Aim: Spatial and temporal biases in species-occurrence data can compromise broad-scale biogeographical research and conservation planning. Although spatial biases have been frequently scrutinized, temporal biases and the overall quality of species-occurrence data have received far less attention. This study aims to answer three questions: (1) How reliable are species-occurrence data for flowering plants in Africa? (2) Where and when did botanical sampling occur in the past 300 years? (3) How complete are plant inventories for Africa?. Location: Africa. Methods: By filtering a publicly available dataset containing 3.5 million records of flowering plants, we obtained 934,676 herbarium specimens with complete information regarding species name, date and location of collection. Based on these specimens, we estimated inventory completeness for sampling units (SUs) of 25 km × 25 km. We then tested whether the spatial distribution of well-sampled SUs was correlated with temporal parameters of botanical sampling. Finally, we determined whether inventory completeness in individual countries was related to old or recently collected specimens. Results: Thirty-one per cent of SUs contained at least one specimen, whereas only 2.4% of SUs contained a sufficient number of specimens to reliably estimate inventory completeness. We found that the location of poorly sampled areas remained almost unchanged for half a century. Moreover, there was pronounced temporal bias towards old specimens in South Africa, the country that holds half of the available data for the continent. There, high inventory completeness stems from specimens collected several decades ago. Main conclusions: Despite the increasing availability of species occurrence data for Africa, broad-scale biogeographical research is still compromised by the uncertain quality and spatial and temporal biases of such data. To avoid erroneous inferences, the quality and biases in species-occurrence data should be critically evaluated and quantified prior to use. To this end, we propose a quantification method based on inventory completeness using easily accessible species-occurrence data.J.H. was funded by a Spanish DGCyT Ramón y Cajal grant and by a CNPq Special Visiting Researcher grant (no. 401471/2014-4).Peer Reviewe

Environmental correlates of seed weight of tropical semi-arid woody species

[Aims]: The survival and distribution of plant species in the extreme environmental conditions of semi-arid regions is strongly dependent on traits associated with drought resistance. Seed weight may be particularly important, since larger seeds are predicted to promote survival in harsh environments, especially those of low soil moisture. Here, we test this hypothesis using data on the seed weight of 277 woody plant species in the semi-arid Caatinga biome of northeast Brazil.[Methods]: We used Structural Equation Models (SEM) to test for associations between seed weight and biophysical conditions, including temperature, precipitation, climatic seasonality, soil-vegetation interaction and soil compaction.[Results]: Species occurrence data were geographically biased due to large areas of the biome that remain under-collected. The strongest statistical association was between seed weight and soil compaction, with mean temperature of the driest quarter and aridity directly influencing soil compaction (and indirectly influencing seed weight).[Conclusions]: We conclude that the larger seeds of woody species in the Caatinga are primarily an adaptation to compacted soil, uneven distribution of rainfall and high temperatures, intrinsic conditions of the Caatinga biome.This study was funded by the Brazilian Coordination for the Improvement of Higher Education Personnel (CAPES) - Finance Code 001. Ana Malhado and Richard Ladle are supported by Brazilian National Council for Scientific and Technological Development (CNPq) grants (#310953/2014-6, #310349/2015-0, #309980/2018-6). JS was funded by the CNPq pos-doctoral fellowship (#434391/2016-6). FAM was funded by a CAPES post-doctoral fellowship (#120147/2016-01)

Drip-tips are associated with intensity of precipitation in the Amazonrain forest

Drip-tips are a common feature of the leaves of rain forest trees, but their functional significance remains contested. The most widely accepted hypothesis is that drip-tips assist drainage of the lamina thereby aiding drying of the leaf surface and reducing the rate of colonization and abundance of epiphyllic organisms. The drying action of drip-tips may also enhance transpiration and reduce the need for investment in support structures. Furthermore, drip-tips may help prevent splash erosion around the base of the tree. Data from 130 forest Amazonian plots are used to investigate the abundance and distribution of drip-tips and, through regression methods that incorporate spatial autocorrelation, seek to identify associations between the frequency of drip-tips and a range of climatic variables. The average frequency of species and trees with drip-tips across all plots was 32 and 33 percent, respectively. Trees and species with drip-tips were significantly more prevalent in the Central-East Amazon than the other regions. Drip-tips were also associated with tree species that have smaller maximum heights and with trees with smaller trunk diameters. The proportion of species and individuals with drip-tips was more strongly correlated with precipitation of the wettest trimester than with total annual precipitation or length of the dry season. Our results extend and provide support for both existing hypotheses for the functional benefit of possessing a drip-tip. Moreover, the currently unrecognized macrogeographic association between the frequency of drip-tips in trees of the tropical forest understory and areas of heavy precipitation suggests a new function for this trait

Quantifying spatial ignorance in the effort to collect terrestrial fauna in Namibia, Africa

Effective conservation efforts and predictions of future impacts on biodiversity depend heavily on publicly available information about species distributions. However, data on species distributions is often patchy, especially in many countries of the Global South where resources for biological surveys have been historically limited. In this study, we use biodiversity ignorance scores to quantify and visualize gaps and biases in biodiversity data for Namibia, with a focus on five terrestrial taxa at a spatial scale of 10 x 10 km. We model the relationship between ignorance scores and socio-geographical variables using generalized additive models for location, scale and shape (GAMLSS). Our findings demonstrate that despite a high volume of occurrence records available on the Global Biodiversity Information Facility (GBIF), publicly available knowledge of Namibia's terrestrial biodiversity remains very limited, with large areas contributing few or no records for key taxa. The exception is birds that have benefitted from a massive influx of data from the citizen science platform eBird. Our study also highlights the importance of citizen science initiatives for biodiversity knowledge and reinforces the usefulness of ignorance scores as a simple intuitive indicator of the relative availability and distribution of species occurrence records. However, further research, biological surveys, and renewed efforts to make existing data held by museums and other institutions widely available are still necessary to enhance biodiversity data coverage in countries with patchy data

Are compound leaves an adaptation to seasonal drought or to rapid growth? Evidence from the Amazon rain forest

Aim: To assess the hypotheses that compound leaves of trees in the Amazon forest are an adaptation to drought and/or rapid growth.\ud \ud Location: Amazon rain forest, South America.\ud \ud Methods: Genera from 137 permanent forest plots spread across Amazonia were classified into those with compound leaves and those with simple leaves. Metrics of compound leaf prevalence were then calculated for each plot and regression models that accounted for spatial autocorrelation were used to identify associations between climate variables and compound leaf structure. We also tested for associations between compound leaf structure and a variety of ecological variables related to life history and growth strategies, including wood density, annual increase in diameter and maximum height.\ud \ud Results: One plant family, Fabaceae, accounts for 53% of compound-leaved individuals in the dataset, and has a geographical distribution strongly centred on north-east Amazonia. On exclusion of Fabaceae from the analysis we found no significant support for the seasonal drought hypothesis. However, we found evidence supporting the rapid growth hypothesis, with possession of compound leaves being associated with faster diameter growth rates and lower wood densities.\ud \ud Main conclusion: This study provides evidence that possession of compound leaves constitutes one of a suite of traits and life-history strategies that promote rapid growth in rain forest trees. Our findings highlight the importance of carefully considering the geographical distribution of dominant taxa and spatial clustering of data points when inferring ecological causation from environment–trait associations