Explanation of the research work carried
As a first step, we conducted the first global assessment of the relative importance of human-habitat associations in shaping the native distributions of species introduced worldwide, in relation to other key important drivers, that is climate and land-use. For this, we applied deviance partitioning analysis and species distribution models (SDM) to 776 introduced alien bird species from five continents. While an independent effect of climate, and a joint effect of climate and nonurban land uses, appear as major factors governing alien species distribution in their native ranges, significant independent contributions of anthropogenic variables were found for most species. The effect of anthropogenic variables was mostly positive, or concave with highest responses at intermediate values. Notably, human-habitat associations in the native distributions of alien birds were significantly higher than expected, relative to a pool of available species from the same bird families (N = 3,565). Thus, introduced alien birds are a non-random sample with respect to their association with human-altered habitats.
As a second step, we conducted a global assessment of niche conservatism in climatic and human disturbance spaces for bird species showing different responses to humans in their native ranges, and evaluate the effect of considering human variables on the performance of invasion predictions. For this, we compare the native and alien distributions of 158 bird species with established alien populations and enough available data. Invasion predictions built on climatic species distribution models (SDM) that either ignore, or incorporate, human-related variables. Alien bird species tended to invade areas with similar climatic and human disturbance conditions to their native range, but exceptions occur and relate to species responses to human-modified habitats in native ranges. Incorporating information about human-related variables in SDM results in a more accurate prediction of invasion risk, irrespective of species responses to human influence in native ranges.
Finally, we tested whether SDMs accounting for within-taxon niche variation in climate and human-habitat associations in the native range provide better fits and projected distributions for alien bird species than species-level SDMs. We focused on 15 alien bird species, selected because of the availability of robust phylogeographic information. We explored niche variation in climatic and human disturbance spaces occupied by different lineages in the native range and fit SDMs for species and their intra-taxon phylogeographic lineages. We compared the extent of projected distributions and their accuracy with respect to observed occurrence data in alien ranges. Niche analyses revealed significant intraspecific niche structuration within all species considered. Phylogenetic groups within species occupied partially overlapping but distinct portions of the climate and human spaces available in the native range. Notably, models accounting for intra-taxon variation projected larger habitat suitability at a global scale than models conducted at the species level. However, when compared to species occurrences in alien ranges, accounting for within-taxon niche structure did not significantly improve model predictions.
Dissemination
For each of the three work packages of the proposal a main article has been written - one already published in Journal of Applied Ecology. Two additional, more transversal papers have been also published and 3 papers more are currently under review. Main results of the proposal have been also disseminated by attending and participating at internal seminars (1 as invited speaker), as well as one national (British Ornithological Union 2018 Annual Conference, University of Nottingham, UK) and two international conferences (10th International Conference on Biological Invasions. European Group on Biological Invasions (NEOBIOTA), 2018, Dublin, Ireland; 9th Biennial Conference. International Biogeography Society 2019, Málaga, Spain). I was also invited as keynote speaker to the Symposium ‘Invasive birds in Europe: trends, drivers and impacts’ at the European Ornithological Congress, held shortly-after the end of this project, in August 2019 in Romania. To further disseminate my research to a wider audience I have also participated in a public engagement meeting ‘Biological invasions: meeting point between research and management' organized by the CREAF, SCB and ICHN in 2017 in Barcelona, Spain; disseminate results through multimedia press releases, my website, social networks and intranet.
