Global flows of insect transport and establishment: the role of biogeography, trade, and regulations

Aim: Non-native species are part of almost every biological community worldwide, yet numbers of species establishments have an uneven global distribution. Asymmetrical exchanges of species between regions are likely influenced by a range of mechanisms, including propagule pressure, native species pools, environmental conditions, and biosecurity. While the importance of different mechanisms is likely to vary among invasion stages, those occurring prior to establishment are difficult to account for. We used records of unintentional insect introductions to test 1) whether insects from some biogeographic regions are more likely to be successful invaders, 2) whether the intensity of trade flows between regions determines how many species are intercepted and how many successfully establish, and 3) whether the variables driving invasion success differ pre- and post-introduction. Location: Canada, mainland USA, Hawaii, Japan, Australia, New Zealand, Great Britain, South Korea, South Africa. Methods: To disentangle processes occurring during the transport and establishment stages, we analysed border interceptions of 8,199 insect species as a proxy for transported species flows, and lists of 2,076 established non-native insect species in eight areas. Results: During transport, the largest species flows generally originated from the Nearctic, Panamanian and Neotropical regions. Insects native to eight of twelve biogeographic regions were able to establish, with the largest flows of established species on average coming from the Western Palearctic, Neotropical, and Australasian/Oceanian regions. Both the biogeographic region of origin and trade intensity significantly influenced the size of species flows between regions during transport and establishment. The transported species richness increased with Gross National Income in the source country and decreased with geographic distance. More species were able to establish when introduced within their native biogeographic region. Main conclusions: Our results suggest that accounting for processes occurring prior to establishment is crucial for understanding invasion asymmetry in insects, and quantifying regional biosecurity risks.研究目的：外来物种几乎是全球各类生物群落的组成部分，但全球物种定殖数量的分布却并不均衡。区域间物种交换的不对称性可能受到多种机制的影响，包括繁殖体压力（propagule pressure）、本地物种种库（native species pools）、环境条件与生物安全（biosecurity）。尽管不同机制的重要性可能随入侵阶段而异，但定殖前发生的过程往往难以纳入考量。本研究利用无意引入昆虫的记录，开展三项检验：1）是否来自某些生物地理区域的昆虫更易成为成功入侵物种；2）区域间贸易流量强度是否决定了截获物种数量与成功定殖物种数量；3）驱动入侵成功的变量在引入前后是否存在差异。 研究区域：加拿大、美国本土、夏威夷、日本、澳大利亚、新西兰、英国、韩国、南非。 研究方法：为厘清转运与定殖阶段的相关过程，本研究以8199种昆虫的边境截获记录作为物种转运流的替代指标，并分析了8个区域内2076种已定殖外来昆虫物种的名录。 研究结果：转运阶段中，规模最大的物种流通常源自新北界（Nearctic）、巴拿马区（Panamanian）与新热带界（Neotropical）。源自12个生物地理区域中8个区域的昆虫均可成功定殖，平均定殖物种规模最大的类群则来自西古北界（Western Palearctic）、新热带界与澳大拉西亚/大洋洲界（Australasian/Oceanian）。生物地理起源区域与贸易强度均显著影响了转运与定殖阶段区域间的物种流规模。转运物种丰富度随来源国国民总收入（Gross National Income）升高而增加，随地理距离增大而降低。当引入至其原生生物地理区域内时，更多物种可成功定殖。 主要结论：本研究结果表明，厘清定殖前的相关过程，对于理解昆虫的入侵不对称性与量化区域生物安全风险均至关重要。