Endemic Salamanders of the<i> Plethodon Ouachitae</i> Complex


The complex is composed of three large woodland salamander species endemic to the forest communities of the Ouachita Mountains: the Rich Mountain salamander, Plethodon ouachitae; the Fourche Mountain salamander, P. fourchensis; and the Caddo Mountain salamander, P. caddoensis. Distribution is restricted to a narrow habitat gradient within a five-county region in western Arkansas and southeastern Oklahoma. As a result of isolation, coupled with great geologic age, evolutionary processes have influenced the distribution and genetic make-up of a distant Pliocene ancestor to give rise to five distinct geographic variants in terms of color pattern and size (Highton, 1995). The paper will focus on the existing pattern of distribution due to present and past conditions of the environment. Cartographic software will be used to create a seamless mosaic of DEMs overlayed with point data (salamander locations). The overall objective is to create a professional cartographic output to illustrate the influence of topography on species assemblages.

Rich Mountain Salamander
(Plethodon ouachitae)

Consists of three geographic variants that differ in coloration and maximum size (4 to 5 inches). The Rich Mountain variant is found on Rich and Black Mountains. It has a black ground color with chestnut markings down the back and variable white spots with bronze frosting down the sides and back. In some individuals the white spotting may fuse to form a continuous white band. The Winding Stair variant occurs on all of Winding Stair and Buffalo Mountains. It exhibits a significant reduction in the amount of chestnut on the back and in some individuals it may be absent or reduced to small flecks. The Kiamichi variant occurs on Lynn, Round, and Phillips Mountains and the eastern two-thirds of Kiamichi Mountain. This variant lacks all the chestnut pigment and bronze frosting on the back and sides. All variants are abundant on northwest-facing talus slopes beneath logs, bark, rocks, and ground surface debris (Petraka,1998; Sievert,1986).

Fourche Mountain Salamander
(Plethodon fourchensis)

The largest (4.5 to 6 inches) of the five variants occurs on Fourche and Irons Fork Mountains. It has two irregular longitudinal rows of large white spots or blotches along the back. Shares similar habitat characteristics with the Rich Mountain Salamander (Petranka, 1998)

Caddo Mountain Salamander
(Plethodon caddoensis)

The smallest (3.5 to 4 inches) of the variants is profusely marked with small white spots and brassy flecking on the back and sides. Distribuition is restricted to the Caddo Mountains of the Novaculite Uplift where it is locally abundant in or near north-facing talus slopes (Petranka, 1998).

Photographs courtesy of Suzanne Collins Center for North American Herpetology

Geologic background

The Interior Highlands Region is composed of two rather different provinces, the Ozark Plateau to the north and the Ouachita Province to the south. Both of these provinces form an isolated upland area of approximately 119,000 sq km that is surrounded by lowlands (Duellman, 1999). The Ouachita Mountains will be the focus of the project, however both of the provinces set the framework to understand the present distribution of flora and fauna.

The Ouachita Mountians are made up of folded and faulted Paleozoic age sedimentary rocks that were originally deposited in deep marine environments.

image source Rockhounding Arkansas

Historically, Arkansas was on the shore of a deep ocean, referred to as the Ouachita Basin. With millions of years passing the ocean floor accumulated deep layers of sediment from erosion of the North American continent. As continental plates moved, South America slowly advanced northward causing a significant reduction of the Ouachita Basin. As the plates converged the ocean became shallower and sediments were compacted and folded. This process is referred to as low angle thrust faulting which permitted large sheets of land to override the land to the north. Overtime, the marine sediment and rock accumulated to form the Ouachita-Appalachian mountain range. Eventually, the continental plates stopped advancing and South America separated from North America. The exposed and uplifted rocks began to feel the effects of water and wind erosion. The weathering leveled the tops of mountains which began to fill in the sea to form the delta (Rock Hounding Arkansas).

Erosion continued through the Tertiary slowly filling in the shallow sea. This was followed by Pleistocene glaciations of the Quaternary Era. The northern boundary of the Interior Highlands was the extent of glacial advances. However, the advance significantly altered climatic patterns and ancestral rivers deposited large amounts of glacial outwash to the eastern part of Arkansas.

The Ouachita Mountains are the southernmost subdivision of the Interior Highlands. It is a lens-shaped area having a width of 60 miles and a length of 225 miles extending from southeastern Okalahoma to the west central portion of Arkansas. This mountainous and geologically complex region is surrounded on the east and south by the coastal plain, and on the west by the dry, slightly elevated central lowlands. On the north, the low Arkansas River Valley separates the Ouachita Mountains from the mountainous Ozark region. The relief of the region is 2,381 feet with elevations ranging from 300 feet at Fourch-LeFave River to 2,681 feet at Rich Mountain. It is predominately made up of sandstone, limestone, and conglomerate along with metamorphic rocks such as shale and chert. The area receives more than 127 cm of precipitation annually. A majority of the area is still in forest with pines along the rideges and oak-hickory hardwoods in the basins (Fenneman,1938).


The topography and climate of the Ouachitas has created a unique complex of species that have adapted to specific environments. Dowling (1956), has compiled some possible explanations to account for the rich diversity of flora and fauna, particularly the endemic species of the region.

-unlike the Southwest, the region was not covered by shallow seas of the Creataceous period and it may have been above sea level since the Pennsylvanian
-may have served as a refuge for species whose northern relatives were destroyed by southward advancing glaciers of the Pleistocene
-during the late Cenozoic (perhaps Pliocene), the sediments that accumulated from the inland seas eroded sufficiently to define boundaries
-river systems were established during or before the Pleistocene may have given rise to distinct boundaries.

Many factors contribute in determining the present day distribution of species. It is obvious that topographic factors in conjunction with climate influenced the regions bidiversity. Through geologic time one type of habitat will decrease in extent, while another will increase. According to Blair (1965), Pleistocene climatic oscillations (temperature and moisture) may account for the disruption of ranges that may have lead to the onset of diversification. The evolution of distinct varieties or even species was brought about when populations of the ancestral lineage were isolated. These disjunct populations were subjected to genetic drift and after a long period of separation distinct varieties or even species evolved.

On the otherhand, Highton (1995) speculates that eastern Plethodon speciation may have occured somewhat earlier. Current genetic research conducted by Highton (1995) do not support the Pleistocene glaciation theory. Events of the last 2 Myr do not appear to be responsible for the subdivision of the Ouachiatae Complex. Although, it could have played a role in the interruption of gene flow between species. Recent data indicate that glaciation began in Greenland as early as the late Miocene and thus climatic effects initiating speciation in Plethodon may have been related to earlier glaciation events.

It is hypothesized that the dry periods of the Pliocene could have isolated many populations in wetter forested mountainous environments where speciation occurred in isolation. When wet climates returned, many species were only able to survive in their restricted mountian habitats. With the passing of geologic time these salamanders evolved isolating mechanisms. When favorable conditions returned some of the isolated populations were able to expand their range, whereas others were confined to a narrow habitat gradient. This scenerio of fragmentaion of ranges can be extrapolated to the Ouachitae complex that now have a restricted distribution.


1. Downloaded ninety-eight 7.5 minute (30m) DEMs from Data Depot to use as the base image for the salamander distribution map and one GTOPO30 (1km) DEM from the US Geological Survey to use as base image for the Interior Highlands map

2. 3DEM to open DEMS and create a shaded-relief seamless mosaic

3. GPS coordinate data overlay

4. Create professional cartographic output with Adobe Illustrator and Photoshop

5. Set-up interactive photo tour of geographic variants (will be updated in October)


When looking at the map it is apparent that topography plays a signifcant role in the maintenance and evolution of the Ouachitae Complex. The isolation of variants is evident. The Rich Mountian variant is found on both of the monoclinal ridges of Rich and Black Fork Mountains. A high gap exists that separates it from the Winding Stair variant. To the south the Kiamichi variant is secluded by a wide deep valley. It is only known from the eastern half of this very long ridge. The Fourche Mountain variant is considered a true species, although a narrow zone of hybridization occurs on the extreme western end of Fourche Mountain. This is the result of climatic and physiographic changes that may have broken down ecological barriers. To the southeast the Novaculite Uplift defines the range of the Caddo Mountain Salamander. Unlike the exposed Jackfork limestone of the previous mountains, the Carboniferous rocks have been eroded down to Devonian novaculite. The range is separated by river valleys: the Fourche and Black Fork mountains by the valley of the Ouachita River and the Rich and Kiamichi mountians are separated by the headwaters of the Mountain Fork River (Blair,1965). The interpretation of the biogeography was aided by creating a map with visible topographic feautures which helped correlate distribution, physiography, and climatic history.


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USGS physiographic provinces: Ouachita-Interior Highlands, World Wide Web homepage. URL: http://www.aqd.nps.gov/grd/usgsnps/province/inthigh.html

This webpage was created by Andy Schmidt to fullfill the requirements for the Spring 2002 Computer Mapping Systems (ES 551) at Emporia State University. For questions or comments contact Andy Schmidt at newt70@hotmail.com