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.
Aim Determining the causes of range size variation in the distributions of alien species is important for understanding the spread of invasive species. Factors influencing alien range size have been explored for some species at a regional level, but to date there has been no global analysis of an entire class. Here, we present such an analysis for birds, testing for the effects of introduction event, location and species-level variables on alien range sizes. Location Global. Methods We used a novel dataset on the global distributions of alien bird species to test for relationships between alien range size and colonization pressure, residence time, extent of the global climatic niche, native range size, body mass and specialization, using a statistical approach based on phylogenetic generalized least squares models. We performed this analysis globally, and for separate biogeographical realms. Results Approximately half of the variation in alien bird range size is explained by colonization pressure in univariate analysis. We identified consistent effects of higher colonization pressure at global and realm levels, as well as support for effects of native range size and residence time. We found less support for effects of body mass, specialization or extent of the global climatic niche on alien range size. Main conclusions Alien bird range sizes are generally small relative to their native range sizes, and many are continuing to expand. Nevertheless, current variation is predictable, most strongly by the event-level factor of colonization pressure. Whether a species is widespread is a better predictor of alien range size than whether a species could be widespread (estimated by global climatic niche extent), while we also find effects of residence time on alien range size. These relationships may help to identify those alien species that are more likely to spread and hence have greater environmental and economic impacts where they have been introduced. KeywordsAlien, avian ecology, bird, body mass, geographical range size, global climatic niche extent, number of introductions, residence time, specialisation.2009), but there remain significant gaps in our understanding. Most notably, apart from a few case studies (e.g. Liversidge, 1962;Silva et al., 2002), the processes determining the geographical spread of alien bird species, and their resulting geographical range sizes, have largely been ignored (Mack et al., 2000;Blackburn et al., 2009). Geographical range size
17Living in groups comes with many potential benefits, especially for juveniles. Naïve individuals may learn 18 how to forage, or avoid predators through group vigilance. Understanding these benefits, however, 19 requires an appreciation of the opportunities juveniles have to associate with (and learn from) others. 20Here we describe social groups in terms of residency, movement, relatedness, and social associations 21 from the perspective of juvenile hihi, a threatened New Zealand passerine bird. Over three years, we 22 identified individuals in groups, their relatedness, and behavioural interactions. Using multistate 23 analysis, we compared movement and residency of adults and juveniles and found that groups were 24 composed predominately of juveniles which remained at group sites for longer than more transient 25 adults. Movement of juveniles between groups did occur but was generally low. There was no evidence 26 that siblings and parents were likely to be seen in groups together. With an initial understanding of group 27 structure, we next asked what characteristics predicted assortment in social network associations. By 28 identifying groups of co-occurring juveniles from time-stamped observations of individual hihi and 29 building a social network, we found that juveniles were most likely to associate with other juveniles. 30Associations were also predominantly based on locations where hihi spent the most time, reflecting 31 limited movement among separate groups. We suggest groups are best described as "gangs" where 32 young hihi have little interaction with adults. These spatially-separated groups of juveniles may have 33 consequences for social information use during the first few months of independence in young birds. 77between juveniles only, interactions can include "social play" (documented in species such as ravens 78 (Heinrich and Smolker, 1998)), where at least two individuals engage in a reciprocated behaviour and 79 alternate between roles, and potentially share information (Diamond and Bond, 2003). However, the 80 presence of many naïve individuals in gangs could increase the risk of associating with misinformed 81 peers, especially if some individuals are more social than others (Pruitt et al., 2016). Across the animal 82 kingdom, genetically-related groups such as crèches promote associations between parents and 83 offspring (Balda and Balda, 1978; Clayton and Emery, 2007) that allow for learning (e.g. European shags 84 Phalacrocorax aristotelis: Velando, 2001; ravens Corvus corax: Schwab et al., 2008; vervet monkeys 85 Chlorocebus pygerythrus: van de Waal, Bshary and Whiten, 2014) and can even facilitate teaching (e.g. 86 meerkats Suricata suricatta (Thornton, 2006; Thornton and Raihani, 2010)). Alternately, some studies 87 suggest associations with non-kin can still be beneficial as these individuals may have a different range 88 of experiences (Hatch and Lefebvre, 1997). Describing group structures and understanding how these 89 affect associations should therefore help us to understand...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.