University of Guam, Western Pacific Tropical Research Center - Research for Guam's Future
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Fields of Study

Invasive Species

Islands are extremely vulnerable to invasive species due to their isolation. Native plants and animals have evolved with out the need for defenses against these newly introduced plants, animals or organisms that make their way into the ecosystem. When these invaders are highly competitive, voracious eaters or in other ways harmful to native flora and fauna it can mean the end for many local species. The Global Invasive Species Database lists 100 of the world’s most invasive species and Guam has become the adopted home for 20 species on that list.  

The most recent invasive species to arrive on island is the coconut rhinoceros beetle (CRB) which poses a major threat to the palm trees of Guam. The coconut rhinoceros beetle eradication project, a cooperative project being run by the Guam Department of Agriculture, the United States Department of Agriculture, and the University of Guam was organized last year when an infestation of the coconut rhinoceros beetle was detected in Tumon. 

This large scarab beetle is a major pest of coconut and other palms. Adult beetles bore into the crowns of palm trees to feed on sap and once a beetle bores through the growing tip, the tree will die. Several young coconut palms have already been killed by CRB in the Guma Trankilidat area and many mature trees have been mortally wounded throughout Tumon. The growing tips of these trees have been destroyed and they will eventually die when their existing fronds age and fall to the ground.

At the top of the invasive list for most destructive behavior is the brown tree snake (Boiga irregularis), which has caused the forests of Guam to fall silent through the loss of nine out of twelve native bird species. Accidentally introduced to Guam in the 1940’s, the brown tree snake has found the ideal vacation spot. With no natural enemies and a defenseless bird population that provided effortless dinners the snakes multiplied. Currently, research has shown the tiny island of Guam has approximately 13,000 snakes per square mile, more snakes per square mile than anywhere else in the world. Doing the math gives a total of 2,756,000 snakes living on Guam. Is it any wonder that there are so few birds left on the island?

Nine out of twelve species of native birds are no longer found on Guam due to predation by the brown tree snake. Photo:

The loss of birds has allowed insect populations to thrive, which can have a negative impact on agricultural crops and native flowering plants. Certain plants depend on birds and bats for pollination and propagation. Birds and bats eat fruit and disperse the seeds throughout the island, without the birds and bats how will the seeds be spread? A single introduced predator like the brown tree snake can have an exponential effect on the biodiversity of the island. Guam has also lost two of its eleven native lizards due to the snake’s omnivorous nature and the population of fruit bats has been in decline since the arrival of the brown tree snake. 


The following researchers are involved with this Field of Study:

James  McConnell - Publications

Gadi VP Reddy - Publications

Aubrey  Moore - Publications

Ross H Miller - Publications

George C Wall - Publications

Thomas E Marler - Publications

Robert L. Schlub - Publications


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