Wednesday, January 14, 2009

However you skin them, cats have important ecosystem consequences

For disclosure’s sake, I was the editor who handled this paper, and much of this post comes from an editorial I wrote for this paper.
Islands experience the greatest impacts from the invasion of non-indigenous species and are also at the forefront of efforts to eradicate problematic species and mitigate negative impacts. Bergstrom et al. elegantly studied the habitat and ecosystem consequences from the eradication of feral cats from Macquarie Island, a subantarctic island and a world heritage site administered by the state of Tasmania, Australia. This island has undergone a series of invasions and both cats and rabbits were introduced in the 19th century. Cat predation resulted in drastic declines in seabird populations, likely causing two extinctions, and thus a cat eradication programme began in 1985 with the last cat killed in 2000. The authors recognized that the feral cats had become fully ingrained in the island food web, and they show that despite the introduction of the Myxoma virus prior to the cat eradication, rabbit populations exploded after the cat removal. These large rabbit populations caused pervasive vegetation changes. The authors sampled plots before and after the eradication and found that vegetation in these plots shifted from large, long-lived plants to smaller, faster growing species, some of which are themselves non-indigenous to the island. Further, satellite imagery revealed that more than one-third of island has since undergone vegetation change, likely resulting in large-scale habitat alterations.

What these results show us is that the consequences of species eradication may be complex with unintended results. Non-indigenous predators and meso-predators can become important components of island food webs –so important that their subsequent removal can have repercussions felt throughout the entire food web. While trying to protect seabird populations is undoubtedly worthy of management action (including eradication programmes), adequately predicting ecosystem-level consequences should be the basis directing such activities. Planning for such management activities must include information gained through experimentation, modeling and natural history. By using all available tools and knowledge, management activities can have a better chance of succeeding and harmful unintended consequences minimized.

Dana M. Bergstrom, Arko Lucieer, Kate Kiefer, Jane Wasley, Lee Belbin, Tore K. Pedersen, Steven L. Chown (2009). Indirect effects of invasive species removal devastate World Heritage Island Journal of Applied Ecology, 46 (1), 73-81 DOI: 10.1111/j.1365-2664.2008.01601.x

1 comment:

Christine Buckley said...

I noticed this paper as well and was boggled by the number of large-scale, dramatic interactions among large vertebrates on this island. And yet this system is really quite simple compared to the complexity of many trophic cascades, which are difficult to work out even in the absence of invading animals. I blogged about it on the ESA blog, EcoTone:

I do not envy the scientists trying to model species interactions in such systems, nor the policymakers and managers figuring out the best course of action!