N_{1} = number of species in the first fauna.
N_{2} = number of species in the second fauna.
R = degree of relationships (when R = 1.00, the faunas are
identical; when R = 0, the faunas are completely different).
The herpetofauna of southern El Peten has been compared with that in the
Tikal-Uaxactun area (Stuart, 1958), that in the humid lowlands of Alta
Verapaz (Stuart, 1950, plus additional data), and that in the Mexican
state of Yucatan (Smith and Taylor, 1945, 1948, and 1950). The
herpetofaunas of lowland Alta Verapaz and Yucatan are the largest,
having respectively 94 and 91 species, where as there are 78 species
known from southern El Peten and 64 from the Tikal-Uaxactun area. An
analysis of faunal relationships (Table 2) shows that the faunas of the
rainforests of southern El Peten and lowland Alta Verapaz are closely
related. The relationships between these two areas and the
Tikal-Uaxactun area in northern El Peten is notably less. Apparently
the biggest faunal changes take place between southern El Peten and the
Tikal-Uaxactun area, and between the latter and Yucatan. As stated by
Stuart (1958:7) the Tikal-Uaxactun is transitional between the humid
rainforests to the south and the dry outer end of the Yucatan Peninsula.
The transitional nature of the environment is exemplified by a rather
depauperate herpetofauna consisting of some species of both dry and
humid environments and lacking a large fauna typical of either.
Contrariwise, the continuity of the environment from southern El Peten
to the lowlands of Alta Verapaz is reflected in degree of resemblance of
the herpetofaunas.
TABLE 2.--INDEX OF FAUNAL RELATIONSHIPS BETWEEN SOUTHERN EL PETEN AND
OTHER REGIONS.
======================+==========+==========+==========+==========
| Lowland | Southern | Tikal- |
| Alta | El | Uaxactun | Yucatan
| Verapaz | Peten | Area |
----------------------+----------+----------+----------+----------
Lowland Alta Verapaz | | .85 | .61 | .43
----------------------+----------+----------+----------+----------
Southern El Peten | .85 | | .64 | .41
----------------------+----------+----------+----------+----------
Tikal-Uaxactun Area | .61 | .64 | | .63
----------------------+----------+----------+----------+----------
Yucatan | .43 | .41 | .63 |
----------------------+----------+----------+----------+----------
Most of the species of amphibians and reptiles found in southern El
Peten are found in humid tropical forests from the Isthmus of
Tehuantepec southeastward on the Atlantic lowlands well into Central
America.