by: Tony Dongarra

With the 1994 release of his book, The Reptiles of Virginia, Dr. Joseph C. Mitchell joins a distinguished list of herpetologists who discount the autonomy of the coastal plains milk snake (Lampropeltis triangulum temporalis) by describing populations of triangulum from the mid-Atlantic Coastal Plains as intergrade between the eastern milk snake, (L. t. triangulum) and the scarlet kingsnake, (L. triangulum elapsoides).. Since L. t. temporalis can be described as intermediate to these forms, this would seem logical; nevertheless, strong evidence can be presented to challenge this conclusion.. The purpose of this discussion is to present ecological concepts that apply to this issue from a macroscopic perspective.. From a broader view, the conclusion can be made that L. t. temporalis is a valid designation, and that these serpents from the mid-Atlantic Coastal Plains are the nominate form of the species Triangulum..

By accepting narrowly defined characteristics for L. t. elapsoides, Dr. Mitchell effectively extended its zone of integration with L. t. triangulum further south to include the portion of North Carolina, north of the Pamlico Sound and east of the Blue Ridge Mountains. This extension significantly adds to an already broad range.. According to mainstream herpetological thought, populations of Triangulum intermediate to those of L. t. triangulum and L. t. elapsoides range from southern New Jersey and southeastern Pennsylvania, through central Maryland, the Delmarva Peninsula, eastern Virginia and well into northeastern North Carolina.. With a cool climate to the north, an ocean to the east, mountains to the west and an ecological barrier to the south (to be discussed latter) this is most certainly a discrete range.

DISTINCTIVENESS
Kenneth Williams in his landmark work, The Systematics and Natural History of the American Milk Snake, identified 25 sub-species of Triangulum (Williams excluded L. t. temporalis).. Both he and Mitchell recognize that L. t. elapsoides and L. t. triangulum differ from one another to a greater degree than perhaps any other two races of Triangulum.. The primary features considered in this comparison are size, head shape, pattern and color.

L. t. triangulum, is the larger of the two races ranging from 24 - 36 inches with a moderately defined head and a dark pattern consisting of, on average, 33 blotches.. Though this race utilizes a wide variety of habitats, it is most commonly found on rocky slopes where the dominant vegetative pattern is deciduous forest.. Prey preference is for warm-blooded prey with the dietary bulk consisting of appropriately sized rodents.. In direct contrast, L. t. elapsoides is a relatively small animal ranging from 14 - 20 inches with a poorly defined head and a brightly colored ringed pattern consisting of, on average, 16 triads.. Though not restricted to the coniferous forests of the coastal southeastern United States, population densities indicate that this is the preferred habitat.. Prey usually consists of small lizards and snakes however, insects and occasional small rodents are also taken.. Because of the vast differences between these races, it is questionable that they would integrate.. Indeed, these forms are sympatric (inhabiting the same area) in eastern Tennessee and south-central and eastern Kentucky, yet, on the mid-Atlantic Coastal Plains extensive integration is proposed.. This inconsistency is noted by Williams when he states, "If the differences between the two forms are examined, the fact that they are sympatric is not surprising; their integration on the Atlantic Coast becomes the unusual aspect."

Since the two races fail to integrate in other areas where their ranges overlap, the series of populations found on the mid-Atlantic Coastal Plains exhibiting intermediate traits must logically be considered genetically distinctive.. Given the discrete range inhabited by these genetically distinctive populations of Triangulum, L. t. temporalis should be considered a valid sub-species in accord with Wilson's definition.

TEMPORALIS AS THE NOMINANT FORM OF TRIANGULUM
In describing residents of various biologically diverse environments, Wilson also writes, "Some resident species are individually specialized for narrow niches and limited to small geographical ranges.. Their dispersal ability is poor ....... At the opposite extreme, other species possess flexible food habits and are excellent dispersers.. They form new populations readily and evolve quickly into new niches...."

Possessing traits intermediate to those of the two most divergent forms of triangulum, L. t. temporalis is an example of an excellent disperser.. Being flexible in its habitat and dietary preferences, it is able to adapt and form new populations.. In his 1943 study, Roger Conant recognized L. t. temporalis as well as areas of integration with L. t. triangulum and L. t. elapsoides.. These areas of integration can easily be viewed as adaptation zones where populations exist in highly dynamic states poised for sub-speciation.. By observing characteristics of the 25 recognized geographic races of Triangulum, two patterns of adaptive radiation emanating from L. t. temporalis are noted.. These dispersion patterns are discussed as the southern and northern expansions.

SOUTHERN EXPANSION
The southern expansion has its origin to the south of the mid-Atlantic Coastal Plains.. In this region, an ecological barrier, in the form of dense populations of eastern kingsnakes, Lampropeltis, getula getula, exists.. The historical presence of this large and powerful competitor favored survival of L. t. temporalis populations exhibiting slightly distinct heads suited for a fossorial existence.. By adapting into a non-competitive niche, these populations expanded their range southward by avoiding contact with the dominant form of Lampropeltis.. Their expansion along the Atlantic seaboard likely proceeded unchanged until predation patterns were altered due to the presence of the venomous eastern coral snake, Micrur fulvius.. With this change, a brightly colored ringed pattern would have been afforded an additional survival advantage.. Once populations exhibiting these traits became firmly established, gene flow would carry the influence beyond the range of M. fulvius until environmental factors favored another color scheme.

From the southeast United States the dispersion pattern of milk snakes with predominantly ringed patterns and poorly to slightly distinct heads continues into the gulf States, through Latin America and into South America.. Races of Triangulum from the southern end of this expansion do not share the diminutive size of L. t. temporalis and L. t. elapsoides and are greatly enlarged in response to their tropical environments.. The one exception to the brightly colored ringed pattern is the black milk snake, L. t. gaigeae.. This animal, however, inhabits moist environs from relatively high elevations where its dark coloration assists in thermoregulation.. Additionally, vestiges of its ringed pattern are visible in juveniles as well as some adults.

NORTHER EXPANSION
The northern expansion has its origin in the Piedmont Physiographic Province, west of the range of L. t. temporalis where thin rocky soils would inhibit the expansion of smaller fossorial snakes.. Due to the relative scarcity of kingsnakes, L. g. getula, in this region, L. t. temporalis experienced ecological release and was able to expand as the dominant form of the genus.. In this setting, animals exhibiting larger body size and pronounced heads were better able to exploit rodent populations as a food source.. A darker heat absorbent coloration provided an improved ability to thermoregulate in the cooler northern and elevated parts of the range.. All of these traits are associated with the race L. t. triangulum.

The northern expansion continued throughout the northeast and into the central United States where the races of triangulum are primarily blotched with moderately distinct heads.. While many races of milk snake from the western end of this expansion exhibit brighter colors and or patterns that lean towards banding, this could easily be due to environmental influences that allow for extensive integration between the two expansions in the lower Mississippi River Valley.

Dual branches of adaptive radiation would also explain the simpatric association of L. t.triangulum and L. t. elapsoidies in areas west of the Appellations.. While both forms reached these areas, they arrived by different routes over a period of time.. Along the way, both had to adapt to vastly different sets of ecological influences.. In this case, the end result of time, distance and natural selection is near complete reproductive isolation.

At times it seems that nature refuses to be neatly placed into the little classification system we've devised for it.. All at once these two races of milk snake exist as a nominate form on the coastal plains, as sub-species within their preferred habitats and as totally different species at the extremes of their range.

In conclusion, the presence of an intermediate race (L. t. temporalis) of the two most divergent forms of Triangulum (L. t. triangulum and L. t. elapsoides) provides a logical starting point for an analysis of the species.. Inhabiting a discreet range with a cool climate to the north, the Appellation Mountains to the west, the Atlantic Ocean to the east and an ecological barrier (dense populations of L. g. getula,) to the south, L. t. temporalis initiated two branches of adaptive radiation discussed as the northern and southern expansions.. The northern races are described as having moderately distinct heads and primarily blotched patterns and those of the southern expansion as having slightly distinct heads and bright ringed patterns.

The technical classification of milk snakes, or any species for that matter, requires a microscopic view.. From such a close perspective, researches are absorbed with the tedious tasks of counting scales and triads, measuring body to tail length ratios and computing streams of statistical data.. While the importance of this line of study is beyond refute, the macroscopic view should not be ignored.. From this broader perspective, the many races of Triangulum are seen as a continuum, a species bent by physical and biotic elements of diverse ecosystems, and woven like a thread through the tapestry of life.

The factors mentioned in this discussion as influencing the races of Triangulum are presented as mere elementary observations.. The study of ecology as yet, is in its infancy.. The quest to understand the mechanisms driving speciation will likely span generations and test the limits of human comprehension.. Along the way both the curiosity and wonder of a child and the probing mind of the research scientist will be required.. Let us hope that in our stewardship of the planet we have the foresight and courage to preserve enough natural processes to delight and challenge those professional and amateur naturalist as yet unborn.