Flows of invasive ants worldwide to the United States

International trade and human movements have accidentally transported thousands of species worldwide at an unprecedented scale. The resulting biological invasions are among the greatest drivers of species extinctions and can cause enormous economic losses. Understanding how globalization affects the accidental transport of species is urgent to prevent new invasions. However, global trade networks have had mixed success so far in explaining intercontinental species movements. Here, we show that commonly used proxies of global trade flows such as general imports and agricultural imports differed greatly from flows of alien ants from their donor regions to the United States. The analysis of 97 individual commodity flows revealed instead that plants and fruit imports, which are a small subset of all agricultural commodities, were associated with invasion flows. All 95 other commodities differed from flows of alien ants, including most "agricultural" commodities which had extremely heterogenous geographic origins. This highlights the need to know precisely which commodities serve as introduction pathways for a particular taxonomic group in order to explain invasion flows and identify likely source regions of future invasions in a world of changing trade relationships.

国际贸易与人类迁移活动正以前所未有的规模，无意间将数千个物种扩散至全球范围内。由此引发的生物入侵，是造成物种灭绝的主要诱因之一，同时也会带来巨额经济损失。明晰全球化如何影响物种的无意间扩散，对于防范新的生物入侵至关紧迫。然而迄今为止，全球贸易网络在解释跨大陆物种迁移方面的表现喜忧参半。本研究表明，常用的全球贸易流量替代指标（如普通进口商品与农业进口商品），与外来蚂蚁从其源区域向美国的迁移流量存在显著差异。通过对97种单独商品流量的分析却发现，仅占全部农业商品极小一部分的植物与水果进口，与外来蚂蚁的入侵迁移流量存在关联。其余95种商品则均与外来蚂蚁的迁移流量无关，其中包括多数地理来源极为分散的“农业”类商品。这凸显出精准识别哪些商品可作为某一特定生物分类类群的入侵传入路径的必要性，以便在贸易关系不断变化的全球背景下，解释入侵迁移流量并预判未来生物入侵的潜在源区域。