Invasive species in Guam

From the seventeenth through nineteenth centuries, the Spanish introduced the Philippine deer (Rusa mariannus), black francolins, and carabao (a subspecies of water buffalo), which have cultural significance. Herds of carabao obstruct military base operations and harm native ecosystems. After birth control and adoption efforts were ineffective, the U.S. military began culling the herds in 2002 leading to organized protests from island residents.^[7] Other introduced species include the giant African snail (an agricultural pest introduced during World War II by Japanese occupation troops).

Guam has no native amphibian species, but now a total of nine amphibian species have been established in Guam. Litoria fallax (native to the eastern coast of Australia) has been present in Guam since 1968, and Rhinella marina (the cane toad) was brought to the island in 1937. The other 7 amphibian species, namely Sylvirana guentheri (native to mainland Asia), Microhyla pulchra (native to mainland Asia), Polypedates braueri (endemic to Taiwan), Eleutherodactylus planirostris (native to the Caribbean), Fejervarya cancrivora (the Guam variety being most closely related to F. cancrivora found in Taiwan), Fejervarya limnocharis (native to Southeast Asia), have been in Guam since 2003 ^[8] and the Eleutherodactylus coqui also commonly known as the coquí frog native to Puerto Rico that may have arrived from Hawaii, have led to fears that the noise could threaten Guam's tourism.^[9] Many species were likely inadvertently introduced via shipping cargo, especially from Taiwan, mainland China, and Southeast Asia.

Introduced feral animals such as pigs and deer, over-hunting, and habitat loss from human development are also major factors in the decline and loss of Guam's native plants and animals.

Feral chickens (Gallus gallus domesticus) are found in the forests^[10] although they are not significantly integrated into the food webs in most areas.^[11]

Invading animal species are not the only threat to Guam's native flora. Tinangaja, a virus affecting coconut palms, was first observed on the island in 1917 when copra production was still a major part of Guam's economy. Though coconut plantations no longer exist on the island, the dead and infected trees that have resulted from the epidemic are seen throughout the forests of Guam.^[12]

During the past century, the dense forests of northern Guam have been largely replaced by thick tangan-tangan brush (Leucaena leucocephala). Much of Guam's foliage was lost during World War II. In 1947, the U.S. military is thought to have planted tangan-tangan by seeding the island from the air to prevent erosion. Tangan-tangan was present on the island before 1905.^[13]

In southern Guam, non-native grass species dominate much of the landscape. Although the colorful and impressive flame tree (Delonix regia) is found throughout the Marianas, the tree on Guam has been largely decimated.

The Coconut rhinoceros beetle (CRB) infestation has become an epidemic event of palm tree damage on Guam. The CRB infects palm trees by burrowing into the tips of the palms, effectively killing the plant by destroying the shoot apical meristem during the process. While the grubs and larvae of CRB do no actual harm to palms, they populate and grow within the damaged crowns of the palm trees, which is a specific mating habit of Guam CRBs.

A possible solution to the crisis, which has been ecologically analyzed in Western Samoa, would be the introduction of CRB predators. Centipedes, Scolopendra Morsitans, have been found to seek out and eat the larvae of the beetle in logs and other breeding grounds.^[14] Manual insertion of the centipedes, or introduction of volatile attractors within the plant, may cause a significant dent in Guam's CRB mortality. The introduction of terpene, fatty acids, or other nitrogenous compound metabolites may allow palm trees to attract CRB-predators such as the centipede through an indirect defense response,^[15] which is triggered by mechanoreceptors activating secondary metabolite transcribers via an action potential pathway.

A secondary solution could be introducing metal hyperaccumulation into the palm population on Guam's beaches. Plants that accumulate extra inorganic minerals, such as iron, nickel, or zinc, indirectly deter herbivory by depositing excess materials in certain sections of the plants.^[16] While the excess inorganic materials may not directly affect adult CRBs (as minerals would not be deposited in the meristem sections of the plant), it may create an inhospitable and toxic environment for the immature CRBs that are growing in the trees.