The impacts of introduction bias on the composition and invasion status of Australia’s alien flora

Student thesis: Doctoral ThesisDoctor of Philosophy


Human-mediated translocation of species to locations beyond their native biogeographic ranges is of global concern for ecological integrity. Introduction of alien (non-native) species beyond their native biogeographic ranges forms the initial stage of alien species biological invasions. Once introduced, alien species have the potential to become naturalised, and once naturalised, to become invasive. At this stage, species can cause far-reaching ecological, environmental and socio-economic impacts in non-native ranges.

Despite well-known impacts, introduction of alien species is intensifying worldwide with socio-economic human-activities, specifically globalisation. Introduced species form a non-random subset of species that are available for introduction; the subset of species introduced is biased by human-activities that can select for species with certain traits (e.g. functional traits such as height). This selection can result in introduction biases where the characteristics of species introduced form a specific compositional sub-set of all non-native species that could be introduced. Any introduction biases in the pool of introduced alien species will potentially propagate through to subsequent stages of invasion (naturalisation and invasion). However, introduction biases in introduced plants are not known, partly due to the difficulty in obtaining comprehensive data on introduced plants over time. For this reason there are limitations in our understanding of how human-activities affect alien flora and its characteristics, and how any introduction biases may filter through later invasion stages. The aim of this thesis is to determine how human-mediated introduction of plant species affect the numbers and types of alien species introduced and how the characteristics of introduced species affected their invasion status (i.e. introduced, naturalised, invasive). This thesis focuses on 34,650 vascular plant species and uses Australia as a case study due to its long history of biosecurity and subsequent availability of species introductions data. This thesis is based on a comprehensive dataset of introduced species and their characteristics, compiled as part of the research. The dataset allowed for novel research where introduced species characteristics could be compared: (1) across invasion stages, (2) over time with socio-economic drivers, and (3) to species characteristics globally using the tree growth form.

Overall this thesis shows that: (1) functional traits alone cannot be used to predict a species’ risk of becoming invasive. Rather, evidence suggests that characteristics of species introductions—specifically, a longer time-lag since first introduction and more pathways of introduction—define the relative risks of species moving through invasion stages; (2) socio-economic human activities affect the numbers and composition of introduced species over time; (3) introduced non-native (alien) species were selectively introduced and do not form a random subset of all non-native species, though they do represent the functional trait-space occupied by tree species globally, and (4) introduction debt can indicate characteristics of potential future non-native introductions.

The findings of this thesis are of use for understanding ecological and invasion biology processes, and for biosecurity measures. In particular, where reflecting changing demands and increases in trade and transport, alien species source pools are expanding and diversifying such that new types of species are being introduced to new areas. The human-mediated introduction of new species poses a problem for biosecurity, which relies on information about trait profiles of species that are known to have become invasive. Therefore, existing biosecurity risk assessment can fail to identify new ‘high risk’ species when new species with different traits to those introduced previously, are introduced to new locations.
Date of Award1 Sept 2023
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorJane Catford (Supervisor) & Tim Blackburn (Supervisor)

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