0198566123.pdf

The species–area relationship overestimates species
extinction threat in the Lesser Sundas, and this was
suggested by Brooks et al. (1997) to be because the
natural vegetation of these islands is deciduous mon-
soon rather than moist tropical forest. Most endemic

birds are found in this deciduous monsoon habitat

and they speculate that these birds may adapt better

to secondary growth and scrub than do the moist for-

est species. In contrast, in the Philippines, 78% of the

endemic birds are confined to the accessible lowland

304 ANTHROPOGENIC LOSSES AND THREATS TO ISLAND ECOSYSTEMS

eventually be released back into the wild, once

the snake is controlled or eradicated.

Furthermore, two out of the three species of

native mammals: the Pacific sheath-tailed bat

(Embollonura semicaudata) and the little Marianas

fruit bat (Pteropus tokudae), as well as 5 of the

10 species of native lizards: the snake-eyed skink

(Cryptoblepharus poecilopleurus), the azure-tailed

skink (Emoia cyanura), Slevin’s skink (Emoia

slevini), the island gecko (Gehyra oceanica), and

the Micronesian gecko (Perochirus ateles) have

also been extirpated. It is not possible to be

certain that all these losses are solely attributable

to the snake, but careful assessments of the

evidence suggest that it has had a major role

(Roddaet al. 1999), especially for birds and

lizards, as shown in the figure.

The ecological (and socio-economic)

consequences go beyond this immediate

biodiversity loss. A trophic cascade can be

considered to be under way, due to the loss of

birds and bats that acted as pollinators and

dispersers of trees, and there are concerns that

there may be consequent outbreaks of insect

populations that are no longer subject to

predation by insectivorous birds and lizards

(Roddaet al. 1999). In recent years, large

populations of mosquitoes have propagated

dengue fever among the people of Guam (Fritts

and Leasman-Tanner 2001). Economic damage

due to the brown tree snake includes electrical

outages every third day, including island-wide

blackouts, that have been costed at $1–4 million

a year. Finally, the central role of Guam in the

Pacific transportation network has facilitated the

further extension of the brown tree snake range

to other oceanic islands, such as several Mariana

islands (Saipan, Rota, Tinian), Okinawa, Pohnpei,

Oahu, and even Diego García in the Indian Ocean.

Considerable efforts are under way to alert people

to the danger of introducing this species to other

islands.

Due to snake

Extirpated Due to snake

Due to snake

Extirpated

Endangered

Endangered

Endan

gered

Safe

Safe

Extirpated

Status of Guam’s native forest vertebrates (as present in 1950), with estimates of the degree to which their decline may be attributed to the

introduction of the brown tree snake (black segments). The central pie graph represents the vertebrates, and the small pie graphs represent

the degree of responsibility for the declines suffered by mammals (upper right), lizards (lower right), and birds (left); heavy lines delineate

those major taxa in the central graph. (Redrawn from Fig 2.13 of Rodda et al. 1999.)