Biology Reference
In-Depth Information
were individually naive to bullfrogs. Thus, behavioral avoidance appears to have a
genetic basis. Juvenile
Pseudacris regilla
from ponds inhabited by
R. catesbeiana
also showed avoidance of chemical cues from the latter species, whereas juveniles
from ponds lacking the alien frog did not (Chivers et al., 2001). In this last case,
although evolution of avoidance behavior may be involved, the study design did not
exclude the possibility of learning.
Until the extirpation of most birds and mammals from Guam brown treesnakes
were primarily nocturnal in behavior. With the loss or extreme depletion of these
nocturnal food sources during the 1980s, the snakes switched to largely feeding on
diurnal lizards, and that prey switch is reflected in a major change in activity patterns
for the snakes, with diurnal activity approaching 50% of all snake activity in the
1990s (Fritts and Rodda, 1998). Similarly, prior to 1988 the brown treesnake was
primarily arboreal in behavior; during the 1990s, ground-level activity became the
mode for some populations on Guam (Rodda, 1992b; Fritts and Rodda, 1998). It is
uncertain whether these changes have a genetic basis or merely represent behavioral
plasticity in the species. The latter seems more likely but it does highlight the degree
to which behaviors that are thought to be typical for a species (in this case arboreality
and nocturnality) may change in short order as circumstances require.
Social Effects
Economic
Economic effects from alien herpetofauna have been little considered, but those of the
brown treesnake in Guam have been recognized as considerable. From 1978-1997,
this species caused >1,600 power outages on Guam (Fritts et al., 1987; Fritts and
Chiszar, 1999), including many of island-wide scope. Incurred costs are conserva-
tively estimated to be from US$1-4 million/year (United States Geological Survey,
2007) and include (1) damage to electrical-distribution equipment, (2) increased
maintenance and emergency-repair costs, (3) damage to electrical products due to
voltage surges, (4) loss of revenues during outages, (5) loss of business by consumers
during outages, and (6) investment in backup generators and transformers to ensure
stable power availability (Savidge, 1987b). Occasionally, power outages have resulted
in loss of water to some parts of the island for periods up to one week (Savidge,
1987b). Outage durations have risen from an average of 1 hour every 3-4 days in
1997 to 1.5 hour every two days in 2003 (Burnett et al., 2006). Power outages
on a very localized level have also been attributed to Cuban treefrogs (
Osteopilus
septentrionalis
) taking refuge in transformers in Florida (S. Johnson, University of
Florida, personal communication, 2007), but no quantification of costs is available.
Brown treesnakes are significant predators of domestic chickens and their eggs
on Guam. Although the dollar value of this predation was not determined,
approximately 80% of chicken farmers surveyed reported predation, and 45% of
