Plant invasion: Another threat to the São Paulo Marsh Antwren (Formicivora paludicola), a species on the verge of extinction

Abstract

During the past 100 years in densely populated south-eastern Brazil, wetlands have been severely transformed due to urbanization, agriculture and mining. The recently discovered São Paulo Marsh Antwren (Formicivora paludicola) is endemic to these wetlands, and is listed as "Critically Endangered" by the IUCN. The species is only found in an area of 1.42 km2, it has a sparse and fragmented distribution, low dispersal capacity, and has probably lost around 300 km2 of habitat in the past 100 years. Furthermore, very little is known about F. paludicola natural history, and so it is difficult to construct a robust conservation plan. Using Kernel home range estimations and the Adjusted-SD/Torus Shift test (a novel tool for animal-habitat association studies), we showed that the species avoids patches of the alien invasive ginger lily (Hedychium coronarium). Given the high density of their population (3.6 mature individuals/ha), F. paludicola could thrive in relatively small areas of suitable wetlands protected from human occupation and water contamination, however special attention should be paid to biological invasions, which may represent a serious threat to the remaining populations. Protecting a few small wetlands used by F. paludicola would be an important step towards general conservation and restoration of Atlantic Forest wetlands and its endemic endangered species.

Fig 1. Occurrence of Formicivora paludicola.

Circles and triangles indicate marshes where São Paulo Marsh Antwren (Formicivora paludicola) is found at Upper Tietê Basin and Upper Paraíba do Sul Basin (south-eastern Brasil). Triangles indicate the three sites where we examined animal-habitat association. Modified from [27].

Fig 2. Home-range of Formicivora paludicola.

Kernel home-range estimates for (a) Mogi, (c) São José and (e) Salesópolis marshes, respectively and (b, d, f) 95% Minimum Convex Polygons obtained for the same sites. Numbers indicate individual birds (Table 1). World Imagery—Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo, and the GIS User Community. Map image is the intellectual property of Esri and is used herein under license. Copyright © 2017 Esri and its licensors. All rights reserved.

Fig 3. Density functions of habitat association in São José.

Estimated density functions of Adjusted-SD test along a habitat gradient showing association between F. paludicola and four habitat variables in two subsets of São José. p(x) is the probability that a selected point is within habitat “x”, then, these graphs represent how abundant a habitat feature is in the study plot. p(E|x) is the conditional probability of F. paludicola being observed at any selected point that has habitat feature “x”. The single peak in the p(E|x) indicates a strong association (positive or negative) between the presence of the bird with the habitat variable.