Frogs of the genus _Ptychohyla_ are ecologically associated with
mountain streams at elevations between 650 and 2200 meters; in the
geographic region where these frogs occur the vegetation between those
elevations consists of cloud forest or pine-oak forest. In some places
the frogs have been found in a mixture of oak and semi-deciduous scrub
forest. At Vista Hermosa, Oaxaca, _P. leonhardschultzei_ and _P.
ignicolor_ were found in cloud forest, whereas at Agua del Obispo,
Guerrero, the former species was found in pine-oak forest. _Ptychohyla
schmidtorum_ is known only from cloud forest; _P. euthysanota
euthysanota_ and _P. spinipollex_ generally are found in cloud forest,
but in some places they live in pine-oak forest. _Ptychohyla
euthysanota macrotympanum_ has been found in pine-oak forest and in a
mixture of oak and semi-deciduous scrub forest. With the possible
exception of the members of the _Ptychohyla schmidtorum_ group, which
has been found only in cloud forest, it seems as though the type of
vegetation is not the controlling factor in the ecological
distribution of these frogs.
_Ptychohyla_ has been found only where there are clear, cascading
streams overhung by vegetation, on which adults and young perch at
night, or even by day. The presence of these streams, in which the
tadpoles live, seems to be an important factor in the distribution of
_Ptychohyla_. As has been shown previously, the tadpoles of
_Ptychohyla_ are adapted for existence in torrential streams, where
the water is cool, and the amount of oxygen is high. Clearly these
tadpoles are unsuited for life in ponds or sluggish streams in the
lowlands, where the temperature of the water is high, a layer of silt
on the bottom is deep, and the amount of oxygen is low. The tadpoles
cling to rocks on the bottom of the streams; there they move slowly
across the rocks, apparently feeding on the thin covering of algae.
Tadpoles were not observed on rocks having a thick covering of algae
or moss. The tadpoles were observed to swim against the current in
torrential streams, in which no fishes were found. Therefore, it seems
as though the presence of the stream-habitat for the tadpoles is a
significant factor in the ecological distribution of the species of
_Ptychohyla_.