European colonial empires accelerated ant invasions

Abstract

Between the 16th and the 20th centuries, European countries established vast colonial empires on all continents. These empires triggered profound environmental, demographic and economic transformations. It is likely that many non-native species have benefited from the newly emerged trade network between European countries and their colonies to spread to new regions, leading to an increase in invasions across countries that belonged to these empires. However, this hypothesis has not been tested, and it is still unknown whether colonial empires influenced non-native species richness and invasion dynamics over the last centuries. Here, we show that prior to 1960, countries that belonged to a colonial empire received more than twice as many non-native ant species than those that did not. During that period, ant species native to parts of an empire spread preferentially to other countries within the same empire. However, after 1960 former colonial ties had no longer an effect on ant introductions. We also found that colonized countries were the most important source of non-native ants, contradicting the ‘Imperialist dogma'. Overall, our findings show that ant invasion dynamics were shaped by the rise and fall of European colonial empires, transitioning from empire-centered invasions before 1960 to a truly global spread of species in the more recent decades.