Most studies on biological invasions focus on the later stages of the invasion process, i.e. after species have already become naturalized. It is frequently overlooked, however, that patterns in origin, phylogeny, and traits of naturalized alien species might largely reflect which species have been introduced in the first place. Here, we quantify and account for such introduction biases by analyzing 5,317 plant species introduced for cultivation in Southern Africa. We show that this cultivated alien flora represents a non-random subset of the global flora, and that this bias at the introduction stage largely drives patterns in origin, growth form and phylogenetic composition of the naturalized flora. For example, while species from Australasia are, compared to the global flora, disproportionally overrepresented in the naturalized cultivated flora of Southern Africa, this pattern is solely driven by their higher likelihood of having been introduced for cultivation. We also show that among cultivated aliens, naturalization success was correlated with intermediate seed mass and height, as well as high specific leaf area. Our quantification of introduction biases demonstrates that they are huge, and that accounting for it is essential to avoid over- or under-estimation of the characteristics of successfully naturalized alien plants.
Digital point-occurrence records from the Global Biodiversity Information Facility (GBIF) and other repositories enable a wide range of research in macroecology and biogeography. However, data errors may hamper immediate use. Manual data cleaning is time-consuming and often unfeasible, given that the databases may contain thousands or millions of records. Automated data cleaning pipelines are therefore of high importance. This study examined the extent to which cleaned data from six pipelines using data cleaning tools (e.g., the GBIF web application, different R packages) affect downstream species distribution models. In addition, we assessed how the pipeline data differ from expert data. From 13,889 North American Ephedra observations in GBIF, the pipelines removed 31.7% to 62.7% false-positives, invalid coordinates, and duplicates, leading to data sets that included between 9,484 (GBIF application) and 5,196 records (manual-guided filtering). The expert data consisted of 703 thoroughly handpicked records, comparable to data from field studies. Although differences in the record numbers were relatively large, stacked species distribution models (sSDM) from the pipelines and the expert data were strongly related (mean Pearson’s r across the pipelines: 0.9986, versus the expert data: 0.9173). The ever-stronger correlations resulted from occurrence information that became increasingly condensed in the course of the workflow (from individual occurrences to collectivized occurrences in grid cells to predicted probabilities in the sSDMs). In sum, our results suggest that the R package-based pipelines reliably identified invalid coordinates. In contrast, the GBIF-filtered data still contained both spatial and taxonomic errors. However, major drawbacks emerge from the fact that no pipeline fully discovered misidentified specimens without the assistance of expert taxonomic knowledge. We conclude that application-filtered GBIF data will still need additional review to achieve higher spatial data quality. Achieving high-quality taxonomic data will require extra effort, probably by thoroughly analyzing the data for misidentified taxa, supported by experts.
Predation can take unexpected turns. For instance, various invertebrate species - most commonly spiders - may prey on tetrapods. Here, we report observations of spiders (Sparassidae, Olios sp.) preying on amphibians (Hyperoliidae, Heterixalus andrakata) in north-eastern Madagascar. To do so, the spiders built highly-specialized traps by weaving two leaves together. Four cases by different individuals of the same species show that spiders hide at the rear end of the trap. One case reports the feeding on a small frog caught inside the trap. Previous reports on amphibian predation by spiders describe opportunistic and indiscriminate predation behaviour by generalist ground-dwelling or aquatic spiders. The only more targeted cases concern large orb-weaver spiders building large webs that may serve as an effective trap for small vertebrates, but those only make up a small percentage of prey compared to insects. In contrast, the novel traps type reported here seems to be solely targeted at catching amphibians seeking shelter during the daytime. We thus report systematic trapping of amphibian by spiders, a newly recorded behaviour.