habitats: the Stream Anole, the Common and Emer-
ald Basilisks, and the Tropical Seep Snake. Frog-
eating snakes, however, often hunt in these areas. Rep-
tiles not ordinarily found near bodies of water may
be associated with them in some parts of their range.
The Cloud Forest Anole, for example, was previously
widespread in Zones 3 and 4 and extended into Zone
2 (to 1400 m) along forested watercourses. Because
this species has disappeared from the drier, western
parts of its distribution (Zone 2 and part of Zone 3;
see Sec. 5.4.1), it would be valuable to examine
whether surviving populations in Zone 3 have be-
come dependent on streams.
5.6.2. The Disturbance Mosaic
Although many species require undisturbed, closed-
canopy forest, others thrive in gaps. Fitzinger's Rain
Frog, for example, may be found in undisturbed
forest but is most common in open grassy areas
(J. A. Pounds, unpubl. data). The chronically dis-
turbed margins of rivers and swamps may be its pri-
mary natural habitat in the area. The Terciopelo, the
area's largest pit viper, is also most abundant in grassy
clearings, possibly because of a high density of rodent
prey. Over much of Costa Rica, the Black-tailed Cribo
is found below an elevation of 1000 m (Scott 1983b).
On Monteverde's Pacific slope, however, it ascends
to 1540 m, where it basks in clearings. The availabil-
ity of open areas for basking also appears to limit the
upper altitudinal range of the Green Spiny Lizard.
Thermobiology in relation to canopy cover like-
wise influences the distribution of anoline lizards
(Fitch 1972, 1973, 1975, Pounds 1988). Whereas
Cloud Forest Anoles, Ground Anoles, and Blue-eyed
Anoles inhabit the shaded understory and allow
their body temperatures to track ambient tempera-
tures, Montane Anoles (Fig. 5.5) and Gray Lichen
Anoles inhabit gaps and bask to raise their tempera-
tures. Nonbasking anoles in highland forests tend
to be relatively inactive. For example, Cloud Forest
Anoles averaged 8.9 movements/hr, compared to 14.4
movements/hr by heliophilic Montane Anoles at the
same elevation (Pounds 1988, J. A. Pounds and K.
Masters, unpubl. data). The former also captured prey
less frequently. Sticky traps captured 94% more
arthropods in open areas than in the shaded forest
understory, so feeding rate appeared to be correlated
with prey availability. The low-energy strategy of
Cloud Forest Anoles (low gain, low expenditure) is
probably important to their ability to exploit a cool
environment. Trade-offs include slow growth and
maturation (see Sec. 5.4) and reduced running speeds
(Van Berkum 1986). Also, because of physiological
adaptations that permit these anoles to operate at low
body temperatures, they are extremely heat sensitive;
a few minutes in direct sun can be lethal. The po-
tential vulnerability of these and similarly adapted
cloud-forest species to unusually warm weather
should be studied.
Future research should also examine how climate
change affects the spatial pattern of the disturbance
mosaic and hence the distribution and abundance of
species. Long-term trends in atmospheric pressures—
a consequence of warm oceanic conditions in the
tropical Pacific in recent decades—suggest a strength-
ening of the trade winds over Costa Rica (Brenes and
Saborio 1994, Graham 1995). If this trend continues,
the frequency of tree falls may rise, increasing the
prevalence of gaps and altering tree size and age
distributions.5.6.3. Habitat Strata
If tree-fall rates increase, the vertical profile of vege-
tation structure and microclimate will change, with
important consequences for animal communities.
Anoline lizards, for example, are behaviorally and
morphologically adapted for particular subsets of the
available strata (Pounds 1988, 199lb). The vertical
distribution of most amphibians and reptiles is poorly
known. For a broad comparison, I assigned species to
three categories: (1) subterranean, (2) ground and leaf
litter, and (3) aboveground vegetation (Miyamoto 1982,
Hayes et al. 1989, Guyer 1994; Appendix 8). The cae-
cilians are burrowers. Salamanders are discussed be-
low in relation to epiphyte use. Of the remaining taxa,
snakes are most strongly associated with the forest floor
and litter, whereas frogs and lizards include greater
proportions of climbers (Table 5.5).5.6.4. Epiphytes
Many species of amphibians and a few species of rep-
tiles are associated with epiphytes. Tropical sala-
manders are the group of vertebrates most closely
associated with these plants (Wake and Lynch 1976,
Wake 1987). In the cloud forests of Mexico, Hondu-
ras, and Guatemala, salamanders mainly inhabit bro-
meliads. In the cloud forests of Costa Rica and west-
ern Panama, they exhibit a variety of microhabitat
specialties and make greater use of moss mats (Wake
1987). The Moss Salamander specializes in the use
of moss mats but occasionally inhabits bromeliads.
Poelz's and Highland Worm Salamanders are typi-
cally found in moss mats covering downed vegeta-
tion and soil banks, where they also burrow. The
Monteverde Salamander appears to be mostly asso-
ciated with bromeliads. It thus differs from its close
relative, the Mountain Salamander (Bolitoglossa sub-168 Amphibians and Reptiles