(DAPTF). This task force is the central communica-
tion point for scientists investigating amphibian de-
clines. It awards seed grants for promising research
projects and publishes a newsletter (Froglog). Small
working groups—some organized by region, others by
topic—carry out much of the task force's activities.For an update of recent meetings and progress, see
Wake (1998). Those desiring more information about
DAPTF or wishing to receive Froglog should contact
W. Ron Heyer, Chairman, DAPTF Board of Directors,
c/o Biodiversity Programs, NHB 180, Smithsonian
Institution, Washington, D.C. 20560 USA.HOW DO MEADOW TREEFROGS DECIDE WHERE TO LAY EGGS?
Martha L Crumpmphibians are choosy about where they lay
eggs. As comparisons among species show,
aquatic-breeding frogs and toads prefer cer-
tain bodies of water over others. Some species breed
only in streams; others are pond breeders. Of the lat-
ter, some breed in temporary ponds, and others in
permanent ones. Within these broad patterns, a fe-
male might be choosy about details that can affect
her offspring's chances of survival. A pool that is too
warm might cause developmental abnormalities. One
with the wrong kind of vegetation might be asso-
ciated with high densities of predators, competitors,
or parasites.
To examine how female Meadow Treefrogs (Hyla
pseudopuma) on Monteverde's upper Pacific slope
decide where to lay eggs, I performed experiments
along the margins of a seasonal pond shortly after it
had filled (Crump 1991a). These frogs lay eggs in tem-
porary pools of various sizes. Although a single female
might lay up to 2500 eggs, she typically lays them in
several clusters (each with fewer than 500 eggs) at dif-
ferent places within the habitat. My earlier studies had
revealed two important sources of mortality: drying of
pools before larval development was completed, and
cannibalism of eggs and hatchlings by older tadpoles
(Crump 1983,1990,1991b). I designed experiments to
determine whether water depth and the presence or
absence of conspecific tadpoles influence a female's
choice of sites. I predicted that females would prefer
relatively deep water and pools lacking tadpoles.
In four experiments, I used plastic bowls to pro-
vide artificial pools in which I manipulated these
variables. In experiment I, I asked whether females
prefer to lay eggs in pools lacking conspecific tad-
poles. I placed 20 bowls, each containing water 3.5
cm deep, in pairs around the edge of the pond. In one
bowl of each pair, I put twenty 8-day-old tadpoles
(hatched from eggs taken from a nearby pond that had
filled earlier). As predicted, the female frogs preferredthe bowls without tadpoles. In experiment II, I asked
whether females prefer to lay eggs in deep, rather than
shallow, water. All bowls lacked tadpoles, but one in
each pair contained shallow water (1.0 cm instead
of 3.5 cm deep). As predicted, the females preferred
bowls with deeper water. In experiment III, I asked
whether females choose between two unfavorable
options; deep water with tadpoles and shallow water
without tadpoles. I found no evidence that females
chose one option over the other. Apparently prefer-
ring the adjacent pond, they laid few eggs in any of
the bowls. In experiment IV, I asked whether females
change their preferences over the course of an evening
as pools become loaded with eggs, I used a design
similar to that of experiment II (deep vs. shallow
water), but after putting out the bowls (13 pairs) early
in the evening (1900 hr), I checked them late the same
evening (2300 hr) and the following morning (0800
hr). During the first part of the evening, females laid
eggs preferentially in bowls with deep water. Later,
when these containers became crowded with eggs,
females preferred shallow water that contained fewer
eggs.
These experiments showed that females are choosy
about where they lay eggs. Their preferences in ex-
periments I and II were appropriate in light of what
we know about natural sources of mortality of em-
bryos and larvae. The avoidance of sites with heavy
egg loads (experiment IV) suggests that overcrowding
of pools is another source of mortality, but this has
not been studied in Meadow Treefrogs. Choice of
oviposition sites affects both individual reproductive
success and the structure of communities. Future
studies should examine interactions between factors
such as water depth and vegetation structure and the
impact of potential competitors (e.g., Pin-striped
Treefrogs at high elevations in the Monteverde area),
predators (e.g., aquatic insects), and other possible
enemies.173 Amphibians and ReptilesA