Guest blog by Filipa Coutinho Soares, PhD student, and Ricardo Faustino de Lima, Researcher, at Centre for Ecology, Evolution and Environmental Changes and Faculdade de Ciências da Universidade de Lisboa

Research led by scientists from the Faculty of Sciences of the University of Lisbon, and involving RSPB among others, analysed the distribution of birds on São Tomé. We found that non-native bird species on São Tomé Island are associated to anthropogenic land-uses, while the habitat associations of native species suggest the survival of many endemics is dependent upon native forest.

The forests of Sao Tome support a unique fauna and flora with many endemic species (c) Ricardo Lima

Habitat loss and non-native species are two key drivers of biodiversity decline. The importance of understanding the ecological interactions between the two is recognized, and it has been shown that anthropogenic land-use change can facilitate the establishment and expansion of non-native species.

A recent study led by MSc student Filipa Soares, and published in Animal Conservation, provides further evidence for positive interactions between land-use intensification and the expansion of non-native species, using São Tomé as a model. This small oceanic island, located in the Gulf of Guinea (Central Africa), is known for its remarkable endemic-rich avifauna. Its forests are among the most important for the conservation of forest birds worldwide.

However, as in many other islands, human occupation led to the introduction, intentional or not, of many species from different taxonomic groups. Among the non-native birds, we can find several small species that are native to non-forested ecosystems in continental Africa (e.g., black-winged bishop, laughing dove, bronze mannikin, common waxbill, blue-breasted cordon-bleu).

Detailed information on the distribution of bird species has been collected across the island by members of the research team for over a decade. This information was analysed by an international team, led by researchers from the Centre for Ecology, Evolution and Environmental Changes (University of Lisbon), and supported by RSPB and SPEA (BirdLife International in Portugal) and locally by several Santomeans. The results provide important clues to understand the interactions between land-use change and biological invasions.

Land-use intensification favours non-native birds

Our results revealed that land use was the most important factor determining the distribution birds in São Tomé. Non-native species were more likely to occur on anthropogenic non-forested ecosystems in the drier flat lowlands of the island (Fig. 1a and b). Native species, many of which are endemic and globally threatened, preferred remote rainforest at higher altitudes (Fig. 1c and d).

Fig 1. Maps showing the distribution of (a) land use, (b) non-native species richness, (c) proportion of native species and (d) threatened species richness.

There was a clear opposite pattern in the distribution of non-native species richness and native species proportion. It is evident that non-native species thrive particularly well in land-use types most influenced by man (Fig. 1b). As a result, the assemblages of these land uses are composed of up to one half on non-native species, whereas those of better-preserved habitats remain totally dominated by native species (Fig. 1c). Moreover, there is a strong association between the distribution of threatened species and that of native forest (Fig. 1d). From Soares et al 2020

Habitat associations are associated with diet

This study showed an association between habitat preference and diet. A large proportion of the non-native species rely on seeds, which are more readily available outside forested environments. Conversely, very few native birds are strict granivores, often relying instead on invertebrates and fruits and berries. This difference in diet between non-native and native species should reduce the chance of competition over food between the two groups of birds.

Palm oil plantations such as this one are often favoured by non native species (c) Ricardo Lima

What does this mean for conservation?

This study has clear implications for the conservation of birds, and potentially other groups of species, on Sao Tome. It shows that non-native birds are somewhat dependent on anthropogenic environmental changes, in this case forest loss and degradation, to expand their distribution. It also shows that the long-term persistence of native birds relies on the native forests, highlighting the urgent need to protect these ecosystems, where human impact is still low. Such evidence provides further support and guidance to ongoing conservation initiatives. In particular the results will be used to further inform an EU funded project on the island (ECOFAC 6 project), being led by BirdLife Africa. This project aims to improve infrastructure and management of the two natural parks on the island group, helping conserve the native species that rely on these parks, and improving the livehoods of the people who live around the parks.

Acknowledgements

This research would not have been possible without the collaboration of local authorities and the support of multiple funders (FCT – “Fundação para a Ciência e para a Tecnologia”, Rufford Small Grant for Nature Conservation, BirdLife’s Preventing Extinctions Program, Royal Society for the Protection of Birds, Disney Worldwide Conservation Fund, U.S. Fish and Wildlife Service Critically Endangered Animals Conservation Fund, Mohammed bin Zayed Species Conservation Fund, Waterbird Society Kushlan Research Grant).

Full reference: Soares, F.C., Panisi, M., Sampaio, H., Soares, E., Santana, A., Buchanan, G.M., Leal, A.I., Palmeirim, J.M., de Lima, R.F. (2020) Land-use intensification promotes non-native species in a tropical island bird assemblage. Animal Conservation. https://doi.org/10.1111/acv.12568

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