Snake Plague

Having received my new issue of Geographical today, I read a short article that stirred my interest. The article was about the dramatic increase in spider population on the Pacific island of Guam. What was fascinating was that the single accidental introduction of the brown tree snake 60 years ago, managed to wipe out 12 species of native bird. As a result, the island lost almost all its insect-eating birds allowing spider populations to thrive (Rogers et al. 2012).

Brown tree snake

I don't know about you, but I find it astonishing how a few snakes can eliminate almost an entire islands indigenous bird population in such a short space of time?

I suppose, Guam can be described as a text book example of what alien invasive species can inflict on an ecosystem. When the snakes were first introduced to Guam, the indigenous birds did not fear snakes and there were no predators to maintain the snake population. The island was a snake "paradise".

I delved further into the snake situation and discovered that there are an estimated 3,000 brown tree snakes per square mile on the 30 mile long island (National Geographic 2012).

A new research paper published in PLOS ONE (an open access paper, yay!) is one of the first papers to examine the impact of bird loss on the scale of an entire forests. Biologists from the University of Washington, Rice University and the University of Guam, lead by Haldre Rogers,  compared the density of spiders webs on Guam with the density of webs on the nearby Marianas Islands. They discovered that Guam has 40 times more spiders than any of the surrounding islands! Such astonishing results highlight how previous, small-scale studies underestimated the impact of bird loss on spider density as demonstrated by Guam- a large-scale natural experiment.

           Map of the Mariana Islands

(All forest birds are functionally extinct on the island of Guam, whereas relatively healthy bird populations remain on three nearby islands of Saipan, Tinian and Rota.)

 

 

 

It seems unbelievable that the effect of one invasive species can change the way in which biologists study and understand alien species interaction with ecosystems.  

So if you have arachnophobia I would not recommend a holiday to Guam!