Ellie E. Dyer

No saturation in the accumulation of alien species worldwide

Although research on human-mediated exchanges of species has substantially intensified during the last centuries, we know surprisingly little about temporal dynamics of alien species accumulations across regions and taxa. Using a novel database of 45,813 first records of 16,926 established alien species, we show that the annual rate of first records worldwide has increased during the last 200 years, with 37% of all first records reported most recently (1970–2014). Inter-continental and inter-taxonomic variation can be largely attributed to the diaspora of European settlers in the nineteenth century and to the acceleration in trade in the twentieth century. For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time. This highlights that past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.

Global patterns of freshwater species diversity, threat and endemism

Aim Global-scale studies are required to identify broad-scale patterns in the distributions of species, to evaluate the processes that determine diversity and to determine how similar or different these patterns and processes are among different groups of freshwater species. Broad-scale patterns of spatial variation in species distribution are central to many fundamental questions in macroecology and conservation biology. We aimed to evaluate how congruent three commonly used metrics of diversity were among taxa for six groups of freshwater species. Location Global. Methods We compiled geographical range data on 7083 freshwater species of mammals, amphibians, reptiles, fishes, crabs and crayfish to evaluate how species richness, richness of threatened species and endemism are distributed across freshwater ecosystems. We evaluated how congruent these measures of diversity were among taxa at a global level for a grid cell size of just under 1°. Results We showed that although the risk of extinction faced by freshwater decapods is quite similar to that of freshwater vertebrates, there is a distinct lack of spatial congruence in geographical range between different taxonomic groups at this spatial scale, and a lack of congruence among three commonly used metrics of biodiversity. The risk of extinction for freshwater species was consistently higher than for their terrestrial counterparts. Main conclusions We demonstrate that broad-scale patterns of species richness, threatened-species richness and endemism lack congruence among the six freshwater taxonomic groups examined. Invertebrate species are seldom taken into account in conservation planning. Our study suggests that both the metric of biodiversity and the identity of the taxa on which conservation decisions are based require careful consideration. As geographical range information becomes available for further sets of species, further testing will be warranted into the extent to which geographical variation in the richness of these six freshwater groups reflects broader patterns of biodiversity in fresh water.

Global patterns of freshwater species diversity, threat and cross-taxon congruence

Aim Global-scale studies are required to identify broad-scale patterns in the distributions of species, to evaluate the processes that determine diversity and to determine how similar or different these patterns and processes are among different groups of freshwater species. Broad-scale patterns of spatial variation in species distribution are central to many fundamental questions in macroecology and conservation biology. We aimed to evaluate how congruent three commonly used metrics of diversity were among taxa for six groups of freshwater species. Location Global. Methods We compiled geographical range data on 7083 freshwater species of mammals, amphibians, reptiles, fishes, crabs and crayfish to evaluate how species richness, richness of threatened species and endemism are distributed across freshwater ecosystems. We evaluated how congruent these measures of diversity were among taxa at a global level for a grid cell size of just under 1°. Results We showed that although the risk of extinction faced by freshwater decapods is quite similar to that of freshwater vertebrates, there is a distinct lack of spatial congruence in geographical range between different taxonomic groups at this spatial scale, and a lack of congruence among three commonly used metrics of biodiversity. The risk of extinction for freshwater species was consistently higher than for their terrestrial counterparts. Main conclusions We demonstrate that broad-scale patterns of species richness, threatened-species richness and endemism lack congruence among the six freshwater taxonomic groups examined. Invertebrate species are seldom taken into account in conservation planning. Our study suggests that both the metric of biodiversity and the identity of the taxa on which conservation decisions are based require careful consideration. As geographical range information becomes available for further sets of species, further testing will be warranted into the extent to which geographical variation in the richness of these six freshwater groups reflects broader patterns of biodiversity in fresh water.

The global distribution and drivers of alien bird species richness

Alien species are a major component of human-induced environmental change. Variation in the numbers of alien species found in different areas is likely to depend on a combination of anthropogenic and environmental factors, with anthropogenic factors affecting the number of species introduced to new locations, and when, and environmental factors influencing how many species are able to persist there. However, global spatial and temporal variation in the drivers of alien introduction and species richness remain poorly understood. Here, we analyse an extensive new database of alien birds to explore what determines the global distribution of alien species richness for an entire taxonomic class. We demonstrate that the locations of origin and introduction of alien birds, and their identities, were initially driven largely by European (mainly British) colonialism. However, recent introductions are a wider phenomenon, involving more species and countries, and driven in part by increasing economic activity. We find that, globally, alien bird species richness is currently highest at midlatitudes and is strongly determined by anthropogenic effects, most notably the number of species introduced (i.e., “colonisation pressure”). Nevertheless, environmental drivers are also important, with native and alien species richness being strongly and consistently positively associated. Our results demonstrate that colonisation pressure is key to understanding alien species richness, show that areas of high native species richness are not resistant to colonisation by alien species at the global scale, and emphasise the likely ongoing threats to global environments from introductions of species.

Comparing determinants of alien bird impacts across two continents : implications for risk assessment and management

Invasive alien species can have serious adverse impacts on both the environment and the economy. Being able to predict the impacts of an alien species could assist in preventing or reducing these impacts. This study aimed to establish whether there are any life history traits consistently correlated with the impacts of alien birds across two continents, Europe and Australia, as a first step toward identifying life history traits that may have the potential to be adopted as predictors of alien bird impacts. A recently established impact scoring system was used in combination with a literature review to allocate impact scores to alien bird species with self-sustaining populations in Australia. These scores were then tested for correlation with a series of life history traits. The results were compared to data from a previous study in Europe, undertaken using the same methodology, in order to establish whether there are any life history traits consistently correlated with impact across both continents. Habitat generalism was the only life history trait found to be consistently correlated with impact in both Europe and Australia. This trait shows promise as a potential predictor of alien bird impacts. The results support the findings of previous studies in this field, and could be used to inform decisions regarding the prevention and management of future invasions.

Long after the event, or four things we (should) know about bird invasions

The most significant single event in the study of alien bird invasions occurred in 1981, with the publication of John L. Long’s seminal book “ Introduced birds of the world” (full title: Introduced birds of the world: The worldwide history, distribution and influence of birds introduced to new environments”; David & Charles Ltd., Newton Abbot, UK). The significance of this book derives not just from its content, but also from its timing, coincident with the 1982 Scientific Committee on Problems of the Environment (SCOPE) programme on the ecology of biological invasions. It was not long before studies started to appear that exploited the data in Long’s book to address the questions posed by SCOPE regarding alien invasions. As a result, we arguably have a more complete understanding of the invasion process for birds than for any other taxon. Nevertheless, there are still some key issues in the study of bird invasions where understanding is not all it should be. The aim of this review is to highlight four of these issues by arguing that (1) we do not know half so much about bird invasions as we think; (2) propagule pressure promotes invasions; (3) colonization pressure matters; (4) there is no evidence that escape from parasites promotes alien (bird) invasions. We expect some of the views expressed to be controversial, and others less so, but either way we hope this paper will stimulate others to provide better evidence for—or against—our propositions.ZusammenfassungDer wichtigste Moment in der Erforschung der Vogelinvasionen war das Erscheinen John L. Long’s Buches „Eingeführte Vögel der Welt“ 1981 [Titel in Englisch: Introduced birds of the world: The worldwide history, distribution and influence of birds introduced to new environments”; David & Charles Ltd., Newton Abbot, UK]. Die Bedeutsamkeit dieses Buches ist nicht nur dem Inhalt geschuldet, sondern auch dem Zeitpunkt. 1982 begann der wissenschaftliche Beirat der Umweltprobleme [Englisch: Scientific Committee on Problems of the Environment (SCOPE)] mit seinem Programm über die Ökologie biologischer Invasionen. Kurz danach erschienen die ersten Studien, die Long‘s Daten nutzten um einige der Fragen zu biologischen Invasionen aus dem SCOPE Programm zu beantworten. Auch resultierend daraus haben wir heute unbestreitbar ein weitaus tieferes Verständnis der Invasionsprozesse von Vögeln als für irgendeine andere Artengruppe. Trotz allem gibt es immer noch Lücken im Verständnis von Vogelinvasionen. Das Ziel dieser Übersichtsarbeit ist es vier dieser Lücken zu adressieren, indem wir argumentieren, dass (1) nur halb so viel über Vogelinvasionen wissen, als wir denken; (2) Propagulendruck Invasionen unterstützt; (3) Kolonisierungsdruck eine Rolle spielt; (4) es keine Beweise gibt, dass die Abwesenheit von Parasiten(Vogel-)Invasionen unterstützt. Wir hoffen, dass unsere mehr oder weniger kontroversen Ansichten andere Forscher anregen weitere Beweise für oder gegen unsere Behauptungen zu liefern.

The global avian invasions atlas, a database of alien bird distributions worldwide

The introduction of species to locations where they do not naturally occur (termed aliens) can have far-reaching and unpredictable environmental and economic consequences. Therefore there is a strong incentive to stem the tide of alien species introduction and spread. In order to identify broad patterns and processes of alien invasions, a spatially referenced, global dataset on the historical introductions and alien distributions of a complete taxonomic group is required. Here we present the Global Avian Invasions Atlas (GAVIA)—a new spatial and temporal dataset comprising 27,723 distribution records for 971 alien bird species introduced to 230 countries and administrative areas spanning the period 6000BCE—AD2014. GAVIA was initiated to provide a unified database of records on alien bird introductions, incorporating records from all stages of invasion, including introductions that have failed as well as those that have succeeded. GAVIA represents the most comprehensive resource on the global distribution of alien species in any major taxon, allowing the spatial and temporal dynamics of alien bird distributions to be examined.