Life History and Ecology of the Five-lined Skink, Eumeces fasciatus Part 2

3:08 Boards used for shading adjusted back slightly so that _E. obsoletus_ is in sunshine.

3:08-1/2 _E. obsoletus_ moves back to cold end.

3:10 Young still at middle, but resting mainly over cooled metal with tail partly in sunshine.

3:10-1/2 Young moves out into sunshine at middle.

3:11 Female moves out into sunshine at middle. _E. obsoletus_ moves over cooled metal to its edge, coming to rest partly in sunshine.

3:12 Female moves back over cooled metal.

3:13-1/2 Air temperature 33.3C. _E. obsoletus_ shifts a short distance so that it is resting entirely over the cooled metal, with only part of its tail receiving sunshine.

3:17 Young moves about in sunshine, then comes to rest in shadow with half its body over cooled metal.

3:19 Young shifts so that more than half its body is in sunlight in middle section.

3:20 Young shifts away from sunlight, coming to rest with most of its body over the cooled metal.

3:21-1/2 Female moves from cooled metal to sunshine in middle strip.

3:23 Female moves out of sunshine, partly over edge of cooled metal.

3:30 Young moves off cooled metal, coming to rest over edge of warmed metal in narrow middle strip that is in shadow.

3:30-1/2 Young moves back away from warmed metal, pauses briefly, and then moves over cooled metal coming to rest there.

3:31 Female shifts so that about half her body is in sunshine in the middle.

3:32 Female shifts back into shadow, partly over cooled metal.

3:33 Boards providing shade readjusted so that female is in sunshine.

3:33-1/2 Female moves back into shadow over cooled metal.

3:38 Female moves to edge of cooled metal, resting partly in sunshine; sky is becoming slightly overcast.

3:40 Temperature of female 33.4C.

3:41 Temperature of young 32.8C.

3:43 Temperature of _E. obsoletus_ 32.4C.

3:45 Young moves to shaded edge of warmed metal. Finds a dead spider dropped there and eats it.

3:47 Temperature of female 32.3C.

3:48 Temperature of young 36.4C.

3:50 Temperature of _E. obsoletus_ 33.8C.

3:52 Sky partly overcast with thin layer of clouds; observations concluded.

Having once emerged from its hiding place a skink becomes more or less independent of the temperature of the air and substrate, as it is capable of thermoregulation through insolation. However, after a period of cooling and inactivity in dormancy, or merely resting for the night in temporary shelter, the skink is dependent on warmth from the air or substrate or both to become sufficiently activated so that it can emerge and take advantage of direct sunlight. About 10:00 a. m. on April 13, 1951, when the air temperature was a little less than 10C., a large adult male rustling among dry leaves attracted my attention. Obviously recently emerged from hibernation, he was caked with dried mud and his eyelids were nearly sealed shut. He had been sunning, however, and was active enough to elude my attempts to catch him, as he scurried into a deep crevice under the ledge. On the morning of March 24, 1951, while the temperature was still between 10 and 15C., a subadult skink, the first one of the season, was seen sunning itself at the entrance of a deep crevice under the ledge. This skink was still not fully active, and its movements were stiff, yet it was alert and wary, and it quickly retreated back into the crevice. During the first week of May, 1952, skinks were active in abundance and numbers were caught daily in funnel traps and pitfalls. On May 9, however, the maximum air temperature was 16.5C. with cloudy sky and occasional showers. Under these conditions skinks stayed under cover; none was seen in the open nor caught in a trap, and several found under rocks were slow and sluggish. On May 10 a terrarium with several adults was placed in dilute sunshine beside a window in an unheated room. After a period of basking the skinks were stimulated to activity, but were unable to attain normally high temperatures, and as a result their movements were like slow motion caricatures of the normal behavior. Males approached each other with menacing demeanor, with heads turned, snouts depressed, and forequarters standing high. Frequently one would edge up to another and bite hard at its flanks. The several males were s.e.xually aroused by the presence of the two females, but were capable of only the preliminary phases of courtship, in delayed and protracted form. The temperature of one was 18.2C. when the sun had nearly set and activity was tapering off, at an air temperature of 16.2C. At 16C. skinks in a terrarium with no access to sunshine for the most part showed no interest in food and kept out of sight under cover. When exposed their activity was directed almost entirely toward burrowing into the substrate or searching for objects beneath which to hide. One adult female was partly exposed by sc.r.a.ping away loose soil into which she had burrowed. A mealworm was then dropped just in front of her head. She tested it several times with her tongue and then ate it without emerging, her movements being much less brisk than they normally are in feeding. Probably this approximates the threshhold temperature for feeding behavior. At 19.5C. the several skinks in this terrarium were moving about in the open although they were not exposed to sunshine, and they accepted food avidly when it was offered, but were much slower than at optimum temperatures. On May 16, 1951, when a pair of skinks were put together in a terrarium in the laboratory at 21C., copulation ensued but it was of longer duration than in other observed instances, seemingly because of the relatively low temperature.

Relatively few temperature readings on gravid or brooding females under natural conditions were obtained as they were easily disturbed and tended to desert their nests at slight provocation. To avoid desertions handling was kept to a minimum. Occasionally gravid females were caught in the open, but most of them were in nest burrows under flat rocks.

These females found in nests were mostly cold to the touch, and the temperature readings taken on some of them usually approximated the air temperature, being either higher or lower (depending on whether the air was cooling or warming and whether the lizards were warmed by contact with rock or soil receiving sunshine). On May 23, 1952, 22 skinks were seen, four adult males, seven adult gravid females, and 11 young. Of these the adult females all were in nest burrows, and were cold and slow; consequently all of them were caught without difficulty. The males and young, however, were either fully warmed or warm enough to escape rapidly, so that only three of the young and no adult males were caught.

Temperatures of the females tested were 25.6, 23.6, 23.5, 22.3, and 19.4, and for the three young, 32.8, 28.4, and 28.4. Air temperature varied from 20.5 to 24.8. For the total of 30 females in nest burrows whose temperatures were taken in 1952, the average was 26.3C, ranging from 16 to 34. Gravid females, and those with nests and eggs were rarely seen in the open.

The five-lined skink is confined to a region where summer rains are frequent. It is evident that a regular supply of drinking water is one of the most critical ecological requirements. Bogert and Cowles (1947:19) found that an _E. inexpectatus_ experimentally kept at high temperature lost moisture at a more rapid rate than any other reptile tested (including two other kinds of lizards, four kinds of turtles, an alligator, and three kinds of snakes). They remarked that this rapid moisture loss presumably accounts for the inability of skinks to survive in containers when no moisture is readily available, and also accounts for their absence in truly arid habitats. The Natural History Reservation is situated near the western edge of the species' range in a climate that may be near the limit of its range of tolerance. However, on most summer mornings low woodland vegetation is copiously laden with dew, and this evidently fulfills the need for drinking water. Diminution of surface activity and retirement to underground retreats seem to be closely correlated with cessation of rains in late summer. After rainless periods in August and September, when morning dew is no longer available these skinks, especially the adults, are no longer regularly seen in the open. They have retreated to underground shelters where they spend nearly all their time. The time of disappearance varies from year to year and the correlation with varying weather conditions seems obvious. While no actual experiments were performed to determine the moisture requirements, it is evident that the need for moisture rises sharply with increased temperature. Skinks that are dormant in hibernation survive for periods of months without drinking, with but little loss of weight. In their underground shelters temperature is low and presumably relative humidity is high. At temperatures above their optimum of approximately 34C. the skinks are especially subject to rapid moisture loss, since evaporation of body moisture is resorted to as a device to keep the temperature below the lethal level. The skinks subjected to extremes of temperature in an experimental terrarium were seen to lap up condensed moisture on the cooled metal plate at intervals of a few minutes. After an hour or more in the experimental terrarium they seemed somewhat debilitated. Skinks brought from the study areas to the laboratory for weighing and other records, were ordinarily returned on the following day. When circ.u.mstances prevented adherence to this schedule in hot summer weather, mortality could be expected in the skinks kept in cloth bags or gla.s.s containers, unless water was provided. Dramatic weight loss of up to more than 30 per cent was recorded in some individuals, kept at the high temperatures which usually prevailed in the laboratory, over periods of days in the summer.

Skinks having access to drinking water often ingest amounts far beyond their immediate requirements, which may be stored in the bladder and drawn upon over periods of days as it is needed, or may be utilized to dampen the soil of the underground shelter and raise the humidity, as incubating females seem to do.

GEOGRAPHIC RANGE AND THE DECIDUOUS FOREST HABITAT

EUMECES FASCIATUS corresponds in its distribution with the original hardwood forests of eastern North America, as mapped by Braun (1950:cover folder) and the "Oak-Wild Turkey Biome" of Shelford (1945:240). Few species of vertebrate animals have ranges that coincide more closely with this extensive area (exclusive of the northern edge, that part characterized by Braun as the Hemlock-White Pine-Northern Hardwoods). This latter is a mixed forest which actually is transitional between the more typical deciduous forest farther south and the Taiga Biome (or Formation) to the north, which is dominated entirely by conifers. At the northern edge of its range _Eumeces fasciatus_ is much less generally distributed than it is farther south. Although it is well established and even may be locally numerous in South Dakota, Minnesota, Wisconsin, northern Michigan, Ontario, northern New York, and Connecticut, the locality records from these states are few, and seemingly represent isolated and widely separated colonies that are able to persist because of favorable combinations of environmental factors not of general occurrence in the surrounding regions. Figure 6 shows the extent of the hardwood forests as mapped by Braun (excluding the transitional Hemlock-White Pine-Northern Hardwoods a.s.sociation) with specific locality records of _E. fasciatus_ included in all outlying portions of the range. The locality records are those published by Taylor (1936:206-212) supplemented by other marginal records, more recently published, by Hamilton (1947:64) for New York, Breckenridge (1944:97) for Minnesota, Hudson (1942:42) for Nebraska, Smith (1950:185) for Kansas, Brown (1950:116) for Texas, Neill (1948:156) for Georgia, and Neill and Allen (1950:156) for Florida. Along the northern edge of its range, the skink invades the Hemlock-White Pine-Northern Hardwoods a.s.sociation, in Ma.s.sachusetts, New York, Pennsylvania, Ontario, Michigan, and Wisconsin, but does not penetrate far into it anywhere.

Correspondence of its northern limits with those of the Oak-Chestnut, Maple-Ba.s.swood, Beech-Maple and Oak-Hickory a.s.sociations is remarkably close, considering the fact that the boundaries of these climax a.s.sociations are not sharply defined; rather they merge by gradual stages into the northern coniferous forests, with outlying peninsulas and islands where conditions are favorable.

The outlying northern localities where _E. fasciatus_ occurs within the Hemlock-White Pine-Northern Hardwoods a.s.sociation are all within the region of Pleistocene glaciation, which 20,000 years ago, or even more recently, were covered with the continental ice ma.s.s during Wisconsinan time. Yet the localized northern populations of skinks evidently are relicts from a time when favorable conditions were more widespread in the general region. Braun (_op. cit._:464-465) indicates five successive postglacial stages in the trends of climate up to the present, as revealed by bog pollen profiles: (1) Cool and moist; (2) warm and dry; (3) warm and humid; (4) warm and dry; (5) cool and moist. Stages 2 and 4 would have been most favorable for encroachment of the skink into glaciated regions, whereas stages 3 and 5 might have caused retrenchment of its populations. In view of the localized habits of individuals, and the lack of any mechanism for rapid dispersal, the time available seems no more than adequate for the distance of 200 miles or more northward that the skinks must have moved since the final retreat of the ice sheet. This northward movement involved crossing of formidable barriers such as the Great Lakes. Even minor barriers such us small rivers and creeks, might be expected to halt population movements for long periods.

[Ill.u.s.tration: FIG. 6. Geographic distribution of _Eumeces fasciatus_ as indicated by published records (marginal and near-marginal records shown, excluding those of doubtful validity). (1) Distribution of the Deciduous Forest Formation of eastern North America, as mapped by Braun (1950), but excluding the Hemlock-White Pine-Northern Hardwoods a.s.sociation that is transitional to the more northern coniferous forests. (2) The shaded area in Kansas that is outside the Deciduous Forest Formation comprises the Kaw River District, Cherokee Prairie District, and southern Osage Savannah Biotic District (c.o.c.krum, 1952).]

The over-all geographic range is approximately square, roughly a thousand miles across, from north to south and from east to west. On the east and south it is limited by the Atlantic Ocean and the Gulf of Mexico. On the north and west its limits correspond with those of the hardwood forests. On the northwest, it reaches southwestern Minnesota and the southeastern corner of South Dakota, extending far out into peninsular extensions of the Oak-Hickory a.s.sociation which penetrate westward into the prairies along the main river valleys.

In Kansas it occurs over the eastern one-fourth, west to the Flint Hills, and a little farther west in peninsular extensions of the forest along some of the main river valleys. In Braun's map the Deciduous Forest Biome is shown to reach only the eastern edge of Kansas along the Kaw River and Missouri River at and near their junction, the Osage (or Marais des Cygnes) River valley near the Missouri border, and the southeastern corner of Kansas. However, for almost 100 miles farther west from the Missouri border, the country has the aspect of a savannah with scattered groves of trees on hillsides and along streams, providing suitable habitat. The distribution of the five-lined skink in eastern Kansas corresponds well with certain "Biotic Districts" as mapped by c.o.c.krum (1952:12), namely the Kaw River, Osage Savannah (southern part), and Cherokee Prairie. Conversely the skink is excluded from the Short Gra.s.s Plains and Mixed Gra.s.s Plains Biotic Districts which occupy nearly all of the western three-fourths of the state. There are two specimens in the University of Kansas Natural History Museum, labelled Ranson, Ness County. This locality, in the western third of the state, more than 150 miles from any other recorded station, may represent an isolated colony; however Smith (1950:185) states that the record needs verification, and it is not included in the map, Figure 6.

In Oklahoma the distribution records fit fairly well the portion of the state mapped by Braun as the Oak-Hickory a.s.sociation of the Deciduous Forest, but extends a little farther west in the northeastern part of the state. A game type map published by the Oklahoma Game and Fish Department, Division of Wildlife Restoration, in 1943 shows in more detail distribution of the main vegetation types within the state. The locality records for the skink fall almost entirely within three of the fifteen vegetation types mapped, namely, the oak-pine, and oak-hickory forest of the state's eastern edge and the post oak-blackjack oak type of the eastern and central parts. The locality records extend almost throughout the area occupied by these three types but not in attenuate westward extensions of the post oak-blackjack type that occur along several of the main stream courses. In Texas likewise the recorded localities fall mainly within the area mapped as deciduous forest, but with several slightly beyond its boundaries. In a detailed map of the "game regions" of Texas (Anonymous, 1945:1), some of these outlying localities fall into the coastal prairie area, and the remainder into the post oak and blackland prairie belts, which grade into each other and the oak-hickory forest.

The former distribution of the five-lined skink may be postulated on the basis of the fossil record of its community a.s.sociates since it is a primitive and conservative type. Taylor (1936:56) explained the present discontinuous distribution of the genus on opposite sides of the world on the basis of a former northern connection of the continents. He wrote: "I regard migration from North America to Asia as having taken place via land bridges joining the Alaskan peninsula with Asia either at Bering Straits or via the Aleutian Island arc to Kamchatka, or both. One would need postulate but slight climatic changes since the present climate of this coastal region is probably no more rigorous than that of southern Canada which has three species of the genus." However, such former northward distribution, while entirely probable, would have been possible only in a climate much milder than that which prevails at present. In Asia, _tunga.n.u.s_ on the mainland and _latiscutatus_ on the island of Hokkaido extend north to about lat.i.tude 43, and in North America, _fasciatus_ extends slightly farther north. In order to have crossed between Alaska and Asia on presumed land bridges these skinks would have had to extend their ranges about 20 degrees north of their present limits, into what is now a cool climate. The winter climate of the Bering Sea is perhaps not much beyond the range of tolerance of the more cold-adapted forms of _Eumeces_, but the cold, cloudy, wet, and changeable summer climate is far beyond the range of tolerance of _Eumeces_ or any other lizard.

It is highly improbable that the fossil record will yield direct evidence for the existence of a northern ancestral _Eumeces_ of the _fasciatus_ group. The characters by which the various forms are recognized are to be found mainly in details of pattern and scalation; the skeleton is so conservative that specific characters are ill defined or lacking even in well preserved fossil material. This hypothetical ancestor probably was a member of a deciduous forest community having components in common with the modern forests where the American and Asiatic species occur, along with types now extinct, and others which, though existing at the present time, have become separated from their original a.s.sociates and occur in other regions.

Hollick (1936:11) has described a rich early Tertiary Alaskan flora strikingly different from that of the same region at the present time.

Composed of genera now characteristic of warm-temperate to subtropical climates, it was remarkable in having many types of plants that are now most characteristic of the North American hardwood forests in the southeastern part of the continent. Besides such widespread genera as _f.a.gus_, _Betula_, _Ulmus_, _Plata.n.u.s_, _Castanea_, _Corylus_, _Carpinus_, _Crataegus_, _Spiraea_, _Myrica_, _Smilax_, _Pinus_, _Picea_, and _Abies_, this flora included others now characteristic of both warm-temperate southeastern North America and Eastern Asia, as _Magnolia_, _Nyssa_, _Sa.s.safras_, _Persea_, _Benzoin_, _Hamamelis_, _Liquidambar_, _Celastrus_, _Nelumbo_, and _Onoclea_. It included genera _Carya_, _Taxodium_ and _Comptonia_ that now are limited to SE North America, _Sequoia_, now limited to western North America, and also included several genera which at present are limited to southeastern Asia: _Ginkgo_, _Glyptostrobus_, _Cinnamomum_, _Hausmannia_, _Artocarpus_, _Dillenia_ and _Koelreuteria_. This fossil flora provides strong evidence that in the early Tertiary climatic and habitat conditions as far north as Alaska were favorable for the existence of an ancestral _Eumeces_ similar to the modern _E. fasciatus_, which might have given rise to both North American and Asiatic members of the _fasciatus_ group.

There is abundant evidence for the existence of an Eocene land connection between Alaska and northeastern Siberia, permitting free interchange of faunas between the two continents, as shown by the almost simultaneous appearance of various mammalian groups in the fossil records of Asia and North America. Simpson (1947:627) has summarized the evidence that such intermigrations were occurring throughout most of the Tertiary, with occasional interruptions as in middle Eocene, and in middle and late Oligocene, and with increasing selectivity, chiefly a progressive tendency toward screening out of the groups less tolerant of cold (judged on the basis of their modern representatives). In the late Tertiary, and especially in the Pleistocene, animals known to have made migrations between North America and Asia were types now characteristic of boreal climates (_e. g._ pika, hare, vole, lemmings, marmot, jumping mouse, fox, wolverine, bear, moose, caribou, sheep, bison, camels, mammoth). Simpson believes that there was fairly strong climatic selectivity even in the Miocene interchanges, and he indicates several important groups that were non-migrants in the Miocene, most of them remaining so through the Pliocene and Pleistocene--the primates, Rhizomyidae, Gliridae, Viverridae, Hyaenidae, Dicerorhininae, Suidae, late Anthracotheriidae, Hippopotamidae, Tragulidae, Muntiacinae, Lagomerycidae, Giraffidae, and Bovidae. He states that there is good evidence that these are all mainly warm-climate animals which are not likely to have ranged in any force into a cold-temperate or boreal environment. In view of these conclusions it seems doubtful whether _Eumeces_ or other reptiles could have crossed the Alaskan-Siberian land connection so late as the Miocene.

On the contrary, the climate and habitat conditions with which _Eumeces_ might have been a.s.sociated, although present as far north as Alaska in the Eocene, evidently had shifted far to the south by mid-Tertiary time.

Axelrod (1950:230) has described a Miocene forest of the Columbia Plateau and northern Great Basin indicative of a uniform temperate climate and an average rainfall of thirty-five to sixty inches. This forest included: (_a_) various genera now characteristic of the southeastern hardwood forest or confined to it--_Carya_, _Castanea_, _Comptonia_, _f.a.gus_, _Liquidambar_, _Nyssa_, _Taxodium_; (_b_) other genera at present more characteristic of the western United States--_Sequoia_, _Lithocarpus_, _Pseudotsuga_, _Mahonia_, _Thuja_, _Gaultheria_, _Amelanchier_; (_c_) wide-ranging genera including _Alnus_, _Acer_, _Betula_, _Populus_, _Quercus_, _Picea_, _Pinus_, _Tsuga_, _Cornus_, _Ribes_, _Rosa_, _Hydrangea_; (_d_) modern east Asian genera, including _Ginkgo_, _Ailanthus_, _Glyptostrobus_, _Keteleria_, _Koelreuteria_, _Metasequoia_, _Pseudolarix_, _Pterocarya_, _Zelkova_, which were eliminated from the North American flora in the latter part of the Tertiary. In short, this western Miocene forest was remarkably similar in many respects both to the presumably ancestral early Tertiary Alaskan forest and the modern southeastern hardwood forest. The extent of this Miocene forest is unknown but judging from the sites where it has been recorded, it had progressed about halfway, both in lat.i.tude and in actual distance, from Alaska to the area occupied by the modern southeastern deciduous forests. Several other reptilian genera have distributions similar to that of the _fasciatus_ group, with representatives in southeastern Asia and southeastern North America that probably have parallel histories of distributional divergence from early Tertiary northern ancestors similar to contemporary species (Schmidt, 1946:148-150). _Alligator_, _Natrix_, _Ancistrodon_, _Scincella_, _Elaphe_, _Opheodrys_, and within the genus _Eumeces_, the _obsoletus_ group, all provide excellent examples.

EFFECT OF CLIMATIC FACTORS

Accounts of the habits and habitat, by various authors, indicate versatility in behavior, and adaptation to a variety of habitat conditions in different climates and plant a.s.sociations. Some of the differences evidently result from the skink's tendency to maintain itself in surroundings of favorable temperature and humidity, which obviously are to be found in different types of situations at different extremes of the range. Hence even though the skink itself may remain unchanged, it tends to behave somewhat differently under diverse environmental conditions. Such environmentally enforced differences in habits would be difficult to distinguish from those having a genetic basis. Although no subspecies of _Eumeces fasciatus_ have been recognized, local populations undoubtedly differ somewhat in size and other characters that have a genetic basis.

At the northern edge of its geographic range, _fasciatus_ occurs in isolated colonies and seems to be restricted to open, rocky situations which receive the maximum amount of sunlight. Breckenridge (1944:96) wrote that at the two Minnesota localities representing the northwestern corner of the known range, the skinks were found at granite outcrops, and he mentions one found in western Wisconsin, at Taylor Falls, under an 18-inch slab of a basalt outcrop in spa.r.s.e oak woods. Patch (1934:51) described a habitat at Arden, Ontario, among ma.s.sive granite-gneiss domes, with spa.r.s.e vegetation. At Point Pelee, Ontario, the species is common in the drier, more spa.r.s.ely wooded situations, hiding beneath loose bark of stumps and logs.

Ruthven (1911:264) found _E. fasciatus_ in the vicinity of sandy beaches in the Saginaw Bay region of Michigan. Elsewhere in its range it is more characteristically an inhabitant of hardwood forests, preferring the better drained and more rocky situations, according to the testimony of numerous authors. In eastern Illinois, Smith (1947:33) found it confined to the area south of the Shelbyville moraine, and not ranging into a prairie habitat. Near Elkville, Illinois, Cagle found the species abundant in higher and drier areas within spa.r.s.e stands of oak in second growth woods, but it was absent from the low swampy areas adjacent to streams. Conant (1951:30, 210), describing the habitat in Ohio, stated that the species does not occur in swamps and areas that are subject to spring floods nor on dry hillsides, but is abundant in some areas where there are rotting stumps and logs remaining from former patches of swamp forest, and usually is found in low, moist situations, in wooded valleys or even at the edges of swamps and bogs. Lynn (1936:49) wrote that in Virginia, it is most often seen on steep, boulder-strewn hillsides and old sawdust piles. In the central Ozarks of Missouri, Owen (1949:49) found it abundant and saw it almost daily on rocky ledges, fallen timber, and fence rails, while _E. laticeps_ was seen only once. Taylor (1936:59) wrote that _E. fasciatus_ occurs where there is timber and is often found about fallen trees and rotting stumps, or about old sawmills where wood refuse has acc.u.mulated. Smith (1950:187) wrote that in Kansas the species is commonly found in wooded areas in moist situations about stones, leaves and rotten logs. Gloyd (1928:120) wrote that in Franklin County, Kansas, _E. fasciatus_ occurred in upland situations and was the most abundant lizard where there were rocks, brush, or decaying wood. Gloyd (1932:401) also recorded it as abundant in the Pigeon Lake area, Miami County, Kansas, in wooded areas of sufficient elevation to be out of the river flood-plain.