Posted by Delayn Fritz @WildOptic

Progress and technological advancement allows us the brilliant capability to receive goods from the other side of the planet in only a matter of days. This is a good thing for the delivery men who just 100 years ago would have had to suffer an arduous journey just for the yearly supply of salt. However, this decrease in vectoring time has meant that survivorship of stowaway critters has increased, as well as an overall increase in the amount of trade volume. In fact, it has been shown that the amount of trade may be the biggest indicator of how many invasive species are established in a given country, and this trade has steadily been increasing.

So this may leave you wondering how do species become invasive, and move from the initial ’transport stage’ and proliferate into an invasive species. A unified framework for this process has been widely accepted and explains several stages from transportation, to establishment, to spread. This is important because between each stage are biological barriers that may inhibit species from moving to the next stage. Species can overcome these barriers, through increased propagule pressure (i.e. the amount of individuals being introduced), by being pre-adapted to the climate of the new environment, and perhaps by possessing certain biological characteristics.

The unified framework proposed by Blackburn et al. 2011

Why should we care about the process and not just focus on eradication? The associated effort and cost to remove a species increases as it occupies more area. The fruit fly incursion responses in 2012 and 2014 both cost around $2 million, and that was just the size of a suburb. The real goal and money saver while getting the best results would be to prevent a species from establishing and/or spreading in the first place, this is best done in conjunction with understanding the invasion pathway and bolstering the natural barriers that already exist.

The invasion curve refined by Harvey and Mazzotti

This is where my MSc project comes in. I am studying a data set spanning 60 years of interception data at the border, and records of spread within New Zealand to try and understand the reasons that non-native ant species have either been successful in establishing and spreading or why they have failed. In starting to really understand how these barriers affect success of species we can improve chances of successful prevention through risk assessment.

Nylanderia spp. in the urban garden (Image credit: Delayn Fritz)

 Delayn Fritz is an MSc student in the Centre of Biodiversity  and Biosecurity, School of Biological Sciences, University of Auckland. He is interested in the invasion process of ants (Hymenoptera: Formicidae) in New Zealand. He is supervised by Darren Ward and Eckehard Brockerhoff (Scion, B3).