Understanding factors driving successful invasions is one of the cornerstones of invasion biology. Bird invasions have been frequently used as study models, and the foundation of current knowledge largely relies on species purposefully introduced during the 19th and early 20th centuries in countries colonized by Europeans. However, the profile of exotic bird species has changed radically in the last decades, as birds are now mostly introduced into the invasion process through unplanned releases from the worldwide pet and avicultural trade. Here we assessed the role of the three main drivers of invasion success (i.e., event-, species-, and location-level factors) on the establishment and spatial spread of exotic birds using an unprecedented dataset recorded throughout the last 100 y in the Iberian Peninsula. Our multimodel inference phylogenetic approach showed that the barriers that need to be overcome by a species to successfully establish or spread are not the same. Whereas establishment is largely related to event-level factors, apparently stochastic features of the introduction (time since first introduction and propagule pressure) and to the origin of introduced species (wild-caught species show higher invasiveness than captive-bred ones), the spread across the invaded region seems to be determined by the extent to which climatic conditions in the new region resemble those of the species' native range. Overall, these results contrast with what we learned from successful deliberate introductions and highlight that different management interventions should apply at different invasion stages, the most efficient strategies being related to event-level factors.

Aim Invasion processes are probably better understood for birds than for any other taxon, thanks to detailed information available on deliberate introductions performed by Europeans when they colonized other continents. Little is known, however, about current avian introductions in developed countries, including Europe. Using an unprecedented dataset on exotic birds, we assessed the sources and magnitude of recent avian introductions and characterized the transitions between main invasion stages (transport, introduction and establishment) and their temporal evolution. Location Spain and Portugal. Methods We compiled records of species introduced between 1912 and 2012, including information on transport and introduction pathways. We assessed non‐randomness in the phylogenetic relationships and the biogeographic origin of species crossing each invasion stage and evaluated temporal changes in introduction patterns. Results At least 1026 exotic species have been transported to Spain and Portugal (ca. 10% of the world's birds) during the last 100 years. Of these, 377 (37%) have been recorded as introduced into the wild, of which up to 32 (9%) species have established breeding populations. Exotic species entered the invasion pathway mostly through the accidental escape of internationally traded birds, and temporal changes in introduction rates mirrored changes in the number of imported birds. The subsets of taxa successfully passing through the different invasion stages were non‐random with respect to their biogeographic origin and were phylogenetically clustered in several distantly related clades. Main conclusions Our findings show that the magnitude of transport, introduction and establishment of exotic birds is much greater than usually described at a regional level, and support the hypothesis that most species fail to transit the different steps of the invasion process (the so‐called tens rule). The temporal changes in introduction rates are broadly consistent with the recent global rise of accidental introductions associated with the wildlife trade.

Agricultural intensification over the last 60 decades has been linked to decreases in biodiversity and in the breeding populations of several avian species in farmlands. However, agricultural intensification has not affected all species in the same way and transformed landscapes can still provide suitable habitats for species tolerant to some degree of anthropogenic change. Understanding habitat selection in man-made landscapes is a pre-requisite to effective management and conservation of the species that use them. However, habitat-related choices made by individuals occupying these landscapes are often difficult to explain, as the cues they use may be decoupled from the ecological context in which they evolved. Here, we investigated nesting habitat selection in a ground-nesting raptor breeding mainly in wetlands, which, unlike many other species occupying farmlands, has experienced a population increase in some agricultural regions. We used multivariate analysis to assess the extent to which habitat characteristics, human disturbance or proximity to other occupied sites influenced nesting-site occupancy. Our results indicate that Marsh harriers occupied breeding sites according to habitat cues obtained at two complementary spatial scales (i.e. the breeding site and the foraging area). This study indicates that a raptor species that uses human-made structures such as ponds for breeding while exploiting their surrounding crops for hunting can take advantage of agricultural intensification. Environmental disturbances are often viewed only in terms of their harmful impacts on the affected species. However, human activities are causing many types of alterations in natural landscapes that can be exploited by certain species with positive responses towards these transformations. The adaptation of some raptors to human-altered environments, such as the Marsh harrier in our study area, raises doubts regarding the appropriateness of using such species as indicators of natural habitat quality.

According to niche theory, mechanisms exist that allow co-existence of organisms that would otherwise compete for the same prey and other resources. How seabirds cope with potential competition during the non-breeding period is poorly documented, particularly for small species. Here we investigate for the first time the potential role of spatial, environmental (habitat) and trophic (isotopic) segregation as niche-partitioning mechanisms during the non-breeding season for four species of highly abundant, zooplanktivorous seabird that breed sympatrically in the Southern Ocean. Spatial segregation was found to be the main partitioning mechanism; even for the two sibling species of diving petrel, which spent the non-breeding period in overlapping areas, there was evidence from distribution and stable isotope ratios for differences in habitat use and diving depth.

Wildlife trade is currently the most important and increasing source of vertebrate invasive species. However, exhaustive analyses of potential side effects of trade regulations on this pathway of introduction are lacking. We addressed this by combining environmental niche models and global trade data on parrots (Psittaciformes), one of the most widely traded and worldwide invasive taxa. We used the wild bird trade bans of United States (1992) and Europe (2005) as case-studies. Results showed that regional bans can generate geographic redirections in trade, with important consequences on worldwide invasion risk. While the amount of parrots traded internationally remained largely constant, changes in trade destination occurred. Consequently, the world surface predicted at risk of parrot invasions increased with successive bans. Of concern, a redirection of trade toward developing countries was observed. Attention should be paid on the mismatch between the global requirements of invasion management and the regional scales governing trade regulations.

a b s t r a c tIdentifying the factors that affect the spatial distribution of marine biodiversity is a central issue to ecology. This knowledge is crucial to evaluate biodiversity patterns, to predict the impact of environmental change and anthropogenic activities, and to design accurate management programs. Here, we investigated the degree to which environmental features, human activities and spatial constraints interact and influence spatial gradients in marine biodiversity using the Western Mediterranean Sea as a model system. Our results revealed that a large fraction of the variability in biodiversity metrics of most marine groups analysed is accounted for by the joint effect of environment and human activities, environment and spatial variables or between all three groups of variables. In other words, major environmental variables and human activities have a collinear spatial structure, and thus an important part of the variation in biodiversity metrics can be attributed to these three groups of explanatory variables. Among pure effects, deviance partitioning results showed that the effect of environmental variables was more evident than the effect of human or spatial variables. The effect of single environmental and human variables considered in the analyses was different for different marine groups. This study contributes to the knowledge of the effects of ecological factors on the spatial distribution of marine biodiversity in the Mediterranean Sea, which is important in the development of more complex spatial analyses. Our results support the hypothesis that the joint effect of different predictor sets can be highly relevant in spatial patterns of biodiversity due to spatial collinearity. Thus, the simultaneous analysis of the relative effect of ecologically important predictor sets is important in preventing misinterpretations of the ecological mechanisms that explain spatial distribution of marine biodiversity.

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International wildlife trade is a major source of current biological invasions. However, the power of trade regulations to reduce invasion risks at large, continental scales has not been empirically assessed. The European wild bird trade ban was implemented in 2005 to counter the spread of the avian flu. We tested whether the ban reduced invasion risk in two European countries, where 398 nonnative bird species were introduced into the wild from 1912 to 2015. The number of newly introduced species per year increased exponentially until 2005 (in parallel with the volume of wild bird importations), and then sharply decreased in subsequent years. Interestingly, a rapid trade shift from wild‐caught birds to captive‐bred birds, which have lower invasive potential than wild‐caught birds, allowed the maintenance of bird availability in markets. Our results demonstrate the effectiveness of a trade ban for preventing biological invasions without impacting the ability to meet societal demands.