At localities where two species of _Ptychohyla_ occur sympatrically
(_P. ignicolor_ and _P. leonhardschultzei_ at Vista Hermosa, Oaxaca,
and _P. euthysanota euthysanota_ and _P. schmidtorum schmidtorum_ at
Finca La Paz, Depto. San Marcos, Guatemala) effort was made to
determine what, if any, ecological interspecific relationships
existed. Although adults of the sympatric species were found on
adjacent leaves or branches of bushes overhanging the streams at both
localities, segregation at the time of breeding seems to be maintained
by the notably different breeding calls in sympatric species (see
discussion of breeding calls). Thus, as has been shown by Blair
(1956), Fouquette (1960), and others working on a variety of
pond-breeding frogs and toads, the breeding call in _Ptychohyla_ acts
as an important reproductive isolating mechanism.
At no locality were _Ptychohyla_ and associated species of hylids
found so abundantly as were species of pond-breeding hylids in the
lowlands. Apparently reproductive activity is not concentrated in a
short breeding season, and it is highly doubtful if the populations of
these frogs are as large as those of the lowland pond-breeders. The
continual humid conditions and abundance of insect food throughout the
year in the cloud forest are perhaps indicative of little
interspecific competition among adults of _Ptychohyla_ and other
sympatric hylids.
At Finca La Paz, Guatemala, tadpoles of two species of _Ptychohyla_
were ecologically segregated. The tadpoles of _P. euthysanota
euthysanota_ were found in riffles in the streams, whereas those of
_P. schmidtorum schmidtorum_ were found in slower water, chiefly in
small pools in the streams. At Vista Hermosa, Oaxaca, tadpoles of _P.
leonhardschultzei_ were found in riffles, and tadpoles of the
sympatric _P. ignicolor_ were found in a small pool in a stream.
Similar ecological relationships were observed for several species of
Costa Rican hylids. Throughout the range of _Ptychohyla_ east of the
Isthmus of Tehuantepec, members of the genus occur with species of
_Plectrohyla_, all of which are larger than _Ptychohyla_, and all of
which have tadpoles that live in torrential streams. Tadpoles of
_Ptychohyla spinipollex_ have been found in streams inhabited by the
tadpoles of _Plectrohyla guatemalensis_ and _P. quecchi_; tadpoles of
_Ptychohyla euthysanota euthysanota_ and _P. schmidtorum schmidtorum_
were found in streams inhabited by tadpoles of _Plectrohyla
guatemalensis_, _P. matudai_, and _P. sagorum_. In some streams great
numbers of tadpoles occur. The habitat is rather restricted, and the
food supply is limited. Consequently, interspecific competition among
the various species of hylids whose tadpoles live in the torrential
streams probably is highest during the larval stage. Unfortunately,
this aspect of salientian population ecology has received no intensive
study.