The Amphibians and Reptiles of Sinaloa, Mexico - Smithsonian ...

60 UNIVERSITY OF KANSAS PUBLS., MUS. NAT. HIST.
lizards, for example, exhibit the least diversity in Sinaloa; they are
more numerous in Michoacan than in Arizona but constitute a
larger percentage of the herpetofauna in the latter region, In
contrast, the number and percentage of turtles are lowest in Michoacan
and highest in Sinaloa. Both frogs and snakes follow the
expected pattern, increasing in number from Arizona to Michoacan.
It is interesting to note that while snakes increase in number
from north to south, their percentage of the total fauna is nearly
the same in all three areas.
Distribution Within Habitats
The distribution of amphibians and reptiles in the five vegetation
zones in Sinaloa is summarized in Table 2. Each species and
subspecies has been designated as being abundant (A), moderately
abundant (M), apparently rare (R), or absent (—) in each
habitat. Locality records that we consider questionable are designated
(P). The altitudinal distribution is based primarily on
locality data associated with specimens examined, rounded off to
the nearest 100-meter interval. If specimens lacked data as to
elevation of capture, the locality is designated by the nearest of
the following altitudes: 300, 900, 1500, 2100 meters (see Fig. 1).
Records on or very near the boundary between the two vegetation
zones generally were assigned to a zone on the basis of total
distributions. For example, a species which is moderately abundant
in the Tropical Semiarid Forest and recorded from the Tropical
Thorn Woodland only at a border locality is not included in the
Tropical Thorn Woodland herpetofauna. This procedure compensates
for the transition and interdigitation of borders between
two vegetation zones and emphasizes the ecotonal nature of each
boundary line.
Tropical Thorn Woodland.—Thorn woodland forest occurs in
the most arid parts of Sinaloa along the northern Pacific coast.
Sixty-one species and subspecies of amphibians and reptiles are
known from this zone; of these 16 are considered abundant. They
include: Scaphiopus couchii, Leptodactylus occidentalis, Bufo Jcelloggi,
B. marinus, B. mazatlanensis, Rana pipiens, Holbrookia
maculata, Sceloporus clarkii boulengeri, Urosaurus ornatus latemlis,
Cnemidophorus costatus griseocephalus, Leptodeira punctata, Masticophts
flagellum piceus, M. striohitus, Natrix v. valida, Thamnophis
cyrtopsis collaris, and Crotalus b. bas&iscus.
Many species characteristic of this area have exploited the new