Changing weather, and other factors that vary from year to y_Life History and Ecology of the Five-Lined Skink, Eumeces fasciatus

marked differences in the dates of important events in the annual cycle,

and in the stage of development at any given date. Data are available

for five successive annual broods of young, those of 1948, 1949, 1950,

1951, and 1952, and each brood differs from the others to some extent,

as shown in Figures 11 to 13. In 1949, for instance, young hatched

relatively early, and probably most of them were active by the middle of

July. They made rapid growth in August, averaging larger than young

hatched in other years on any given date in late summer. However, they

retired into dormancy early in the fall. Cool and dry weather in early

September ended their activity for the season. In 1950, young hatched,

on the average, at least three weeks later, about the first of August,

but they remained active until late in September, and by hibernation

time had partly caught up to the stage of development attained by the

young of 1949. Most young of 1951 hatched late in the first half of

August, and at first were smaller than those of 1950 and much smaller

than those of 1949 on corresponding dates, but favorable weather in the

early fall hastened their development. By early September they had

caught up and passed the stage of development of young of 1950 and by

the time they retired to dormancy in late September, they had reduced by

half the size-advantage of the young of 1949 at the time these latter

retired into hibernation. The young of 1951 appeared to be few in

numbers, and a lack of competition may have been a factor in their rapid

early development.

[Illustration: FIG. 15. Records of growth in another group of

recaptured young that grew less rapidly than those of Fig. 14.]

The young of 1948, first sampled after their emergence from their first

hibernation in mid-April of 1949, were then somewhat intermediate in

size as compared with those of 1949 and 1950 at the same times of year.

Their subsequent development was rapid; by late May they had caught up

and passed the stage reached by the 1949 young at the same time of year.

The young of 1950 after having a late start, were further set back by

cold weather in April 1951 delaying their emergence from hibernation. As

a result they were still unusually small in late April and May. Even

though they grew rapidly subsequently, they were consistently smaller

than those of other broods on corresponding dates. Favorable fall

weather prolonging the 1951 growing season into late September beyond

the time of retirement in other years may have permitted many of them to

attain adult size.

[Illustration: FIG. 16. Records of immature individual skinks marked

and recaptured within the same growing season, showing the trend of

rapid growth, and differences in growth rate between individuals.]

The varying fortunes of the several annual broods studied were closely

correlated with weather trends, and suggest possible effects of slight

changes in climate. An unfavorable sequence of weather might bring about

drastic reduction of the population without causing any direct

mortality. A late spring in two successive years would have cumulative

effect in delaying emergence and breeding of adults the first year, and

delaying in the second year emergence of the young, already retarded by

the lateness of their hatching. If this sequence were followed by onset

of unusually cool and dry weather in early September, or even in late

August, the young might be "caught short," and forced to hibernate

while still in the 50-60 mm. size class. Emerging the following spring,

they might have failed to mature sexually, reducing by perhaps half the

number of productive adults. At the northern extreme of the species'

range, length of growing season may be more critical than extremes of

temperature in limiting the numbers and distribution. Growing seasons

that average long enough and warm enough to permit attainment of

maturity by onset of the second hibernation period may be essential to

the species. While no two annual broods of young in the same locality

come under exactly the same weather influences, extremes of retardation

or acceleration continuing throughout development are relatively rare.

Retarding effects of unfavorable weather causing delayed breeding and

hatching, may be offset by prolongation of warm weather in the fall thus

delaying hibernation, or by warm spring weather hastening emergence from

hibernation.

Under favorable conditions an adult female produces about ten offspring

annually of which about half are females. It is calculated that if all

survived, after ten breeding seasons, the progeny of an original female

might have increased to a population of more than 97,000, under the

climatic conditions of eastern Kansas, permitting attainment of breeding

maturity late in the second year of life. In the same ten year period

under climatic conditions delaying maturity until late in the third year

of life (as seems normally to occur in _E. septentrionalis_ and _E.

skiltonianus_, and probably in _E. fasciatus_ at the northern edge of

its range) the original female would have produced a population of

somewhat less than 7,800 assuming that all survived. With a long growing

season such as occurs in the southern part of the range, it seems

theoretically possible (though not probable) that individuals might

mature before the end of their first year, in time to participate in the

next breeding season. If this should occur the original female might

produce a population of more than 120 million by the end of the tenth

breeding season.

CHANGES IN PATTERN

Progressive alteration of the color pattern is more rapid in males than

in females and is synchronized with growth. During the first year of

life changes in the pattern are gradual, and consist chiefly of loss in

vividness. The blue of the tail is slightly dulled. The light lines

become suffused with brown and the dorsolateral dark areas become paler,

with light brown areas appearing on the corners of the scales and

gradually spreading to replace the original black. In skinks that are in

the second year of life the striped pattern although still conspicuous

is made up of two shades of brown instead of the earlier black and white

markings.

[Illustration: FIG. 17. Records of another group of immature skinks

marked and recaptured within the same growing season.]

Even in hatchlings, the dorsal part of the rostrum and the inter-nasals

are of a somewhat neutral brownish color, matching neither the light

lines nor the dark interspaces of the striped body pattern. With

advancing age this neutral brown color gradually spreads posteriorly on

the head so that the striking lyrate marking of the bifurcated dorsal

stripe on the head in the juvenile become obscured by the time the skink

has grown to small adult size, at 21 months. The top of the head is then

dull brown, with a slightly mottled appearance caused by the different

intensity of pigmentation in different areas. The stripes though still

discernible, are faint and inconspicuous. Dorsally, on the body, the

stripes are still conspicuous, but are dull and lacking in contrast. At

this stage, the dark lateral area is retained with intensity of

pigmentation scarcely diminished.

Table 13. Normal Range of Variation in Dorsal Striping of Head

and Body, and in Color of Tail According to Age and Sex.

===================+================================+============================

| Condition of stripes | Color of tail

Age, Size and Sex |-----+--------+----+-----+------+--------------+-------------

-------------------+-----+--------+----+-----+------+--------------+-------------

body | X | | | | | |

head | X | | | | | |

| | | | | | |

body | X | | | | | |

head | X | X | | | | |

| | | | | | |

body | X | X | | | | | to brown

head | | X | X | X | | |

| | | | | | |

head | | | X | X | X | |

| | | | | | |

| | | | | | |

| | | | | | |

body | | | X | X | X | occasional |

| | | | | | |

body | | | | | X | |

head | | | | | X | |

-------------------+-----+--------+----+-----+------+--------------+-------------

In tracing the gradual ontogenetic changes in the striped pattern, from

the vividly contrasting colors of hatchlings to the dull, patternless

coloration of old adult males, five descriptive terms have been applied

to the successive stages: "sharp," "distinct," "dull," "faint," and

"absent." To most individuals below minimum adult size, the term "sharp"

is applicable, although there is some loss in vividness in the larger

young, as compared with hatchlings. Fading of the original striped

pattern proceeds more rapidly on the head than on the body. Upon

emergence from their second hibernation at an age of about 21 months,

the skinks, mostly grown to adult size, and ready to mature sexually,

still show but little sexual difference. They retain the hatchling

pattern essentially unchanged, but with colors dulled and contrasts

reduced. Within a few weeks the newly matured males undergo relatively

rapid color change as the breeding season progresses. The stripes tend

to fade and blend into the dark areas adjacent to them. In the

two-year-old males stripes are distinct to dull on the body and faint or

absent on the head, while in females of the same age group, body stripes

are sharp or distinct.

Table 13 refers to adult pattern and coloration as they appear in the

breeding season. After the breeding season, in late spring and early

summer, when the red suffusion of the head and neck has faded in adult

males, the original striped pattern, after having been almost completely

suppressed may again become discernible. Individuals of the same size

differ in extent of pattern change, and the color descriptions made of

individuals were not sufficiently detailed to show fully the changes

occurring between successive dates of capture. However, most large adult

males taken later than mid-June had at least some trace of the striped

body pattern and many of them had become so much like females in

appearance that close scrutiny was necessary to determine their sex.

They were especially like females in having the dark lateral area

extending forward onto the cheek and setting it off sharply from the

paler temporal region above it. In breeding males the head has no such

dark markings and is suffused with red.

GROWTH AND REGENERATION OF THE TAIL

Even among those skinks which have never broken their tails there is a

wide range of variation in relative length of tail. This is partly a

matter of relative growth since the proportions change during the course

of development. Also there may be slight sexual difference and there is

much individual variation. In fetuses still well below hatching size,

the tail length is less than the snout-vent length. For instance, an egg

in a natural nest 12 days short of hatching contained a fetus that had a

snout-vent length of 14 mm. and tail length of 12 mm. (Figure 18). In

the late stages of fetal development the tail growth is relatively

rapid. At hatching, the tail is considerably more than half the total

length. In a large series of young with snout-vent lengths from 30 mm.

down to hatching size of 25 mm. or less, the tail length averaged 130.8

per cent of snout-vent length. In larger young, up to a snout-vent

length of 40 mm. or more, the tail continues to lengthen more rapidly

than the body. In skinks that are about two thirds grown, the tails

average relatively longer than in either larger or smaller individuals.

In the sample representing the size class 50-54 mm. snout-vent length,

the tails average 163.3 per cent of the snout-vent lengths, whereas in

groups of adults of various sizes and both sexes, the tail length is

near 155 or 156 per cent of the snout-vent length. Sexual dimorphism in

tail length is slight if it exists at all; in adult males, tails

averaged a little longer than in adult females.

[Illustration: FIG. 18. Diagram showing relative tail-length (as a

percentage of snout-vent length) in skinks of different size

groups that retain their original tails unbroken; in the early

stages of growth the tail becomes relatively longer as size

increases, but the trend is reversed before adult size is attained.

For each series the mean, standard error, standard deviation,

and extremes are shown.]

When a skink's tail is broken, there is almost no loss of blood. The

fractured surface is rough and irregular, with exposed muscle masses

protruding on the detached end and corresponding concavities on the end

of the stump tail retained by the lizard. The concavities are soon

filled with oozing blood, and a thick scab forms. As healing begins, the

broken end presents a flat, slightly irregular surface. When the scab is

sloughed off, a slightly convex surface of delicate, pale-colored new

skin of the regenerating tail, is exposed. At first, no scale structure

is discernible. As growth proceeds, the new tail takes on a bluntly

conical shape. During the early stages of growth, it is well set off

from the original portion by the abrupt taper at the point of contact

and by its paler coloration and different texture, with no scales

discernible at first, and later with fine and granular scalation. The

new tail elongates until the more abrupt taper beyond the point of the

break is no longer noticeable, and the coloration, surface texture and

scalation match that of the original portion so closely that it is

difficult to determine where the break occurred or even to ascertain

that there has been one. On the regenerated tail, however, the scales

are less uniform in size and less regular in shape. The regenerated

tail, being different from the original in internal structure, with a

cartilaginous rod replacing the vertebral column, is less fragile and

subsequent fractures are most likely to be on the part proximal to the

regeneration. Nevertheless, fractures of regenerated tails occur

occasionally. In old skinks especially, the tail eventually may consist

of three or more distinct segments including the basal remnant of the

original tail and the successive regenerations. When a break in the

regenerated tail occurs, the detached portion is relatively inert, and

is capable of only feeble twitching movements in contrast with the

lively wriggling normally displayed in a newly detached tail that

includes part of the central nervous system.

[Illustration: FIG. 19. Relative lengths of original and regenerated

portions of tails in skinks which have had their tails broken and

regenerated; for each individual, length of each part of the tail

is expressed as a percentage of the snout-vent length.]

Rate of growth in the regenerating tail is controlled by a variety of

factors, such as age, condition, and activity of the individual, and

site of the fracture. A break occurring early in the skink's lifetime

results in regeneration more complete than occurs in an adult sustaining

the same type of injury. The regenerated tail eventually may be longer

and thicker than the lost part if the lizard is young and still growing.

But the regenerated tail is never so long as the original one would have

been. Regeneration is most extensive in those tails broken near the

base. The farther from the base the break occurs the shorter is the part

regenerated. As a result, tails that have had time to regenerate do not

differ greatly in total length regardless of where the break occurred.

However, the nearer the break is to the base, the shorter is the total

tail-length after regeneration (Figures 19 and 20). If only the tip of

the tail is lost, regeneration may not occur. In the skinks examined

that had regenerated tails the proportions varied over a wide range.

Presumably, in many, growth of the regenerated portion was still

incomplete.

[Illustration: FIG. 20. Diagrams showing typical extent of tail

regeneration in skinks having tails broken at different points,

x approximately 2/3. Original parts of the tails are at the right.]

Table 14. Records of Regeneration of the Tail in Individual Skinks

Marked and Recaptured.

=================+==================+==========+========================

| |Snout-vent|

Age and Sex | Date |length | Tail length

| |in mm. | in mm.

-----------------+------------------+----------+------------------------

No. 1. |June 1, 1951| 73 | 38 (newly broken)

Adult male |June 26, 1951| 73 | 38 + 14

|August 17, 1951| 76 | 40 + 45

|April 29, 1952| 76 | 40 + 45

| | |

No. 2. |May 28, 1949| 51 | 46 (newly broken)

Immature |October 15, 1949| 69 | 51 + 21

| | |

No. 3. |June 11, 1950| 49 | 49 (newly broken)

Immature |September 2, 1950| 63 | 63 + 31

| | |

No. 4. |August 10, 1950| 62-1/2 | 60 (newly broken)

Immature female|June 14, 1951| 68 | 62 + 17

| | |

No. 5. |August 14, 1950| 67-1/2 | 77 + 4-1/2

Adult male |September 3, 1950| 68-1/2 | 77 + 6-1/2

|April 27, 1951| 69 | 78 + 9

| | |

No. 6. |April 7, 1950| 67 | 38 (newly broken;

Adult male | | | separated end 66)

|July 27, 1950| 71 | 39 + 47-1/2

| | |

No. 7. |May 28, 1951| 70 | 18 (newly broken;

Adult male | | | separated end 100)

|June 14, 1951| 71 | 18 + 1

|September 22, 1951| 76 | 19 + 29 + 7-1/2

| | |

No. 8. |June 12, 1951| 72 | 33 (recently broken)

Adult male |July 28, 1951| 76 | 36 + 31

| | |

No. 9. |May 2, 1951| 45 | 47 + 1

Juvenile |May 14, 1951| 45 | 47 + 3

|May 19, 1951| 45 | 47 + 5

| | |

No. 10. |June 7, 1952| 64 | 51 (recently broken)

Subadult female|June 24, 1952| 64 | 51 + 11

| | |

No. 11. |August 19, 1949| 42 | 40 (newly broken)

Juvenile |June 13, 1950| 58-1/2 | 58 + 28

|August 5, 1950| 63 | 62 + 31

| | |

No. 12. |May 17, 1951| 78 | 20 (newly broken)

Adult male |June 12, 1951| 78 | 20 + 13

-----------------+------------------+----------+------------------------

Under favorable conditions regeneration occurs at a relatively rapid

rate. After a period of healing the new tail grows with a sudden spurt,

making most of its gain in length within a few weeks. Then growth

abruptly slows or ceases altogether. In young similarly rapid growth of

the regenerating tail occurs, but subsequently the increase is more

gradual corresponding to the over-all growth of the lizard. In numerous

adult skinks marked, and recorded as having well-regenerated tails, the

proportions recorded at subsequent captures months or years later were

still just the same, demonstrating that extent of regeneration is not

proportional to elapsed time. Those adult skinks having unusually long

regenerated tails presumably are individuals in which the original tail

was lost early in life, and the potentiality for regeneration is

probably somewhat less in older individuals, especially those that have

stopped growing.

Successive records of selected individuals are listed in Table 14 to

illustrate trends in regeneration of the tail. In those instances in

which the tail is referred to as "newly broken" the separation usually

occurred as an accident at the time the lizard was captured, while in

those designated as "recently broken" separation had already occurred in

some earlier accident but regeneration was not yet perceptibly underway.

In the "Tail length" column, plus signs separate the original portion of

tail, on the left, from the regenerated portion, on the right.

As in many other kinds of lizards, the tail in the five-lined skink

serves as a reservoir for fat, which may be drawn upon for nutrition in

time of food scarcity. An individual that is in good condition has a

plump and rounded tail. Fat comprises much of its bulk. Upon emergence

from hibernation this fat supply is not noticeably depleted. Brooding

females in the latter part of the incubation period have the supply of

caudal fat most noticeably depleted, and their tails may appear

emaciated, with kinks on the terminal portion. It is my impression that

in adults the capacity for storage of fat is most developed in the

females, and that their tails vary in proportions more than do those of

males. The capacity to shed the tail easily seems somewhat inconsistent

with this function of fat storage. Loss of the tail sometimes involves

loss of a large amount of reserve fat. Many detached tails that were

broken accidentally at the time of the skinks' captures were weighed. In

those that were broken off near the base and were not previously

regenerated, weights were usually 16 to 20 percent of the lizards' total

weights.

Movements

Data obtained concerning the movements of these skinks demonstrated that

individuals tend to limit their activities to small areas thoroughly

familiar to them, and wander but little. Although the nature and extent

of movements in reptiles in general, and in lizards especially, are

poorly known, my findings are perhaps what might be expected from the

studies of earlier workers on various other species of reptiles.

Goin and Goin (1951:29) observed that _Eumeces laticeps_ in Florida

lives in hollow stumps, each individual excluding other adults from its

stump but tolerating young. Movements have not been studied in detail in

any member of the Scincidae, however. The observations of Goin and Goin,

and those of other authors, seem to indicate that _E. laticeps_ is

territorial, and that each individual centers its activities about a

tree or snag, regularly using the same hollow as a shelter and home

base. In contrast, _E. fasciatus_ is not territorial and has no regular

home base.

The iguanid genus _Sceloporus_ is perhaps better known than any other

kind of lizard as regards its movements. Studies by Newman and Patterson

(1909), Stebbins and Robinson (1946), and Fitch (1940) on three

different species have shown that individuals of _Sceloporus_ keep to

small individual areas, and that territoriality is well developed, in

some species at least.

Among other reptiles, turtles are much better known, as detailed studies

of movements have been made on several species, of which the life

histories and ecology have been thoroughly investigated (Nichols, 1939;

Cagle, 1942 and 1944; Woodbury and Hardy, 1948; Stickel, 1950). They

have been found to have well-defined and fairly extensive home ranges,

which are not defended as territories. Studies of movements in several

different kinds of snakes, by Blanchard and Finster (1933), Stickel and

Cope (1947), Fitch (1949), Lowe and Norris (1950), and Carpenter (1952)

have shown that these reptiles usually have definite home ranges, which

may be several or many acres in extent. Their home ranges are not

defended as territories against other members of the species. In

general, turtles and snakes have been found to occupy home ranges that

are much larger than those of lizards.

Most information concerning movements of _Eumeces fasciatus_ has been

obtained from the recapture of marked individuals. Actual distances of

travel, and the time, frequency and motivation of movement was

uncertain. A skink marked, recorded, and subsequently recaptured at a

second location may have wandered widely in the meantime, visiting

points relatively remote from either location of capture. The two points

of capture may be within a home range regularly or occasionally covered

by the individual in the course of its routine activities; or the second

point may have been recorded only after a permanent shift of activities

away from the area within which the original point was located. Various

types of movements probably were involved.

Interpretation of the records is difficult because of the paucity of

direct observations on the behavior and movements of skinks under

natural conditions. Often when one is alarmed, it will run as much as 30

feet, in a fairly direct course, to a tree or bush or rock where it can

find refuge. Undisturbed individuals move about slowly and circuitously.

It is difficult to keep one under observation for any length of time

because of the secretive habits causing it to keep under cover, as much

as possible while moving about, and to hide in response to any slight

disturbance.

Life History and Ecology of the Five-Lined Skink, Eumeces fasciatus · 第 9 / 16 段

Changing weather, and other factors that vary from year to year cause