HOW TO BECOME A SUCCESSFUL INVADER

Most invasive species hitchhike on human transportation, and their close associations with human activity increase their chances of uptake. Once aboard, potential invaders have to survive the journey, and those with traits such as being a general feeder or tolerance to a wide range of environmental conditions tend to survive the transportation better. Similar traits are generally considered to also aid their establishment in new habitats, but studies showed that the propagule pressure, not any of the species-specific traits, is the most important factor contributing to their successful establishment. Higher propagule pressure, i.e., repeated invasions of larger numbers of individuals, reduces Allee effects and aids the population growth of invasive species in alien lands. Coined as the invasive bridgehead effect, repeated introduction also selects a more invasive population that serves as the source of further invasions to other areas. Invasive species is the consequence of homogenocene (our current ecological epoch with diminished biodiversity and increasing similarity among ecosystems worldwide) that began with the Columbian Exchange of the 15th century and possibly the Pax Mongolica of the 13-14th century. Anthropogenic movement of goods among major cities will only accelerate, and the heightened propagule pressure will increase the number of invasive species for as long as the current practices of global commercial activities continue.