Removing invasive species

Whether it involves the use of chemical treatment, physically uprooting plants, or introducing biological controls, there are numbers projects in place to remove invasive species e.g.1, 2, 3. However, invasives are persistent and removal is expensive (Pimentel et al., 2000) so should not be done light heartedly. I found it particularly interesting that removing invasives may also have unexpected ecosystem wide effects (Zavaleta et al., 2001).

Macquarie Island is a natural heritage site, home to a variety of native plant species and seabird colonies. The story of what happened on this Island describes what can wrong if conservationists do not consider ecosystem processes and food web structure before removing invasive species…

Cats were unfortunately introduced to the island in the early 1800’s and rabbits were later introduced by sealing gangs in 1878. When the rabbits arrived they were preyed on by the cats and populations were kept at equilibrium. Despite this the population size was still large enough that rabbit grazing activity had an extremely negative impact on the vegetation. As a result the European Rabbit Flea was introduced to the island to further reduce the rabbit population and protect the native vegetation. The flea was effective and the population size decreased. However, the conservationists did not consider the implications that this would have on the cats, which developed an appetite for seabirds in the absence of rabbits! In response to this the cats were shot on the island, which obviously lead to an increase in rabbits! (Bergstrom et al., 2009)

This is not the only case where eradication has been hard. The Giant African Snail recently featured on BBC News for this exact reason. 

For those of you against invasives it therefore seems that prevention is more beneficial than eradication. Methods of preventing invasives can be read about here, and interestingly investment in prevention could save money in the long term (Leung et al., 2002)

This adds to the debate of whether or not we should allow invasive species that are moving north as a consequence of human induced climate change to establish or not. After all, invasive species can have a positive effect on the environment, but if we don't prevent them will it be too late to find out?

In the new year I’ll be posting my opinion on invasive species and climate change – in the mean time have a fabulous time celebrating the start of 2014!

Elena