Andrews, Pough - 1985 - Metabolism of Squamate Reptiles Allometric and Ecological Relationships

7/24/2019 Andrews, Pough - 1985 - Metabolism of Squamate Reptiles Allometric and Ecological Relationships

1/19

Division of Comparative Physiology and Biochemistry Society for Integrative and

Comparative Biology

Metabolism of Squamate Reptiles: Allometric and Ecological RelationshipsAuthor(s): Robin M. Andrews and F. Harvey PoughSource: Physiological Zoology, Vol. 58, No. 2 (Mar. - Apr., 1985), pp. 214-231Published by: The University of Chicago Press. Sponsored by the Division of ComparativePhysiology and Biochemistry, Society for Integrative and Comparative BiologyStable URL: http://www.jstor.org/stable/30158569.

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2/19

METABOLISM

OF

SQUAMATE

REPTILES:

ALLOMETRIC

AND

ECOLOGICAL RELATIONSHIPS'

ROBINM.

ANDREWS

AND

F. HARVEY

POUGH

Departmentof Biology,VirginiaPolytechnic nstituteand StateUniversity,Blacksburg,Virginia24061-0794;

and Sectionof

Ecology

and

Systematics,

Cornell

University,

thaca,New York

14853-0239

(Accepted9/20/84)

We

used

multiple

regression

analysis

to evaluate

the

relationship

between

metabolic

rate

and

three

independent variables-mass,

temperature,

and

standard or

resting

state-for

squamate

reptiles.

For

comparisons

among

adults

of

different

species,

mass

raised to the

.80

power

explains

88%

of the

variation

in

metabolic rate.

(The

.80

mass

exponent

is

significantly greater

than

the .75

predicted by

theoretical

considerations.)

A

further 8%

of the

variation

in

metabolic

rate

is

explained by

body

temperature

and

whether the

lizard

is

in

a

standard

or

resting

metabolic state.

Residuals

were

used to

determine whether

metabolic

rates

varied

as a function

of

phylogenetic relationship

or

ecological

grouping.

Familial associations

explained

16% of the variation in metabolic rate for

varanids,

lacertids,

iguanids,

colubrids,

scincids, xantusiids,

gekkonids,

and boids. More variation

(45%)

was

explained

when

lizards

were

partitioned

into

four

ecological

categories:

day-active

predators,

hervibores,

reclusive

predators,

and

fossorial

predators.

A

single

equation

relating

metabolic

rate to mass is

thus

inappropriate

to estimate the metabolism

of

squamates.

For

intraspecific

comparisons,

the

mass

exponents

of

the

relationship

between metabolic

rate and

mass

are

significantly

lower

than

.80 for 25 of 28 data

sets.

Estimating

the

metabolic

rates

of

juvenile

squamates

from

equations

based

on

comparisons

among

species

is

thus invalid.

Moreover,

there is

significant

variability

among

mass

exponents

among

the

14

species

that met the statistical

requirements

for

analysis

of

covariance,

and a

common mass

exponent

cannot be

assumed for

intraspecific

comparisons.

INTRODUCTION

Large

animals

use

more

energy

than

small

ones,

but

the

correct

expression

of

that

truism

has

long

been

a

subject

of

controversy.

The

relationship

between

metabolic rate

(MR)

and

mass

(M)

is

most

commonly

expressed

as a

power

(or

allo-

metric)

function of the

form MR

=

aMb,

where

a

and b

are the

mass

coefficient and

'

We

would

like

to

thank

Raymond

Huey,

Robert

Gatten,

and Kirk

Millerfor

their

helpful

comments

on

the

manuscript

nd

Jeffrey

Birch

of

the

Statistical

Consulting

Laboratory

t

Virginia

Polytechnic

nsti-

tute and

State

University

(VPI

&

SU)

and

Philip

Dixon for

advice

on

data

analyses.

We

are

grateful

to the

following

for

information

or

advice:

Jeffrey

Graham,

Virginia

Hayssen,

Hal

Heatwole,

Dennis

King,

Howard

Lawler,

Wilber

Mayhew,

Lee

Miller,

Charles

Myers,

Alan

Savitzky,

Lucia

Severinghouse,

and

Richard

Shine.

The

BiologyDepartment

f VPI

& SU

supported

F.H.P.

during

a

sabbatical

eave.

The

research

was

supported,

n

part,

by

a

VPI

&

SU

small projectsgrantto R.M.A.and by Hatch funds

(project

no.

412)

from

Cornell

University

o F.H.P.

Physiol. Zool.

58(2):214-231.

1985.

1

1985

by

The

University

of

Chicago.

All

rights

reserved.

0031-935X/85/5802-8403$02.00

mass

exponent, respectively.

Kleiber

(1961)

and

Hemmingsen

(1960) thought

that

the

mass

exponent

should

equal .67,

as

pre-

dicted

by

the ratio of surface to

volume

of

geometrically

similar

figures.

However,

interspecific

comparisons

for a

wide

variety

of taxa

produced

higher

mass

exponents.

Thus,

Kleiber

(1961)

advocated

the

adop-

tion of .75

as the true

scaling

factor of

the

relationship

between

MR

and M

because

it

provided

the best fit for data that he

analyzed

and because of

its convenience

for

taking

logarithms

with

a slide

rule.

Subsequently,

theoretical

arguments

have

been advanced

to

support

Kleiber's

rule.

A

mass

exponent

of

.75

can

be

derived

from

principles

of the mechanics

of

loco-

motion

(McMahon

1973)

and

from

the

geometry

of

four dimensions

(Blum

1977).

Recently,

the mass

exponent

of

.67

has

reemerged

as

the

predicted exponent

for

comparisons of different-sized individuals

of

a

single

species

(Heusner

1982).

More-

over,

Feldman

and McMahon

(1983)

argue

from

their

reanalysis

of the

data

used

by

Heusner

(1982)

that

both

.75

and .67

are

214

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3/19

ALLOMETRY

OF REPTILIAN METABOLISM

215

statistically

valid

mass

exponents

for the

relationship

between

MR and

M;

the

for-

mer

is

appropriate

for

comparisons

among

species

and the latter for

comparisons

within

species.

Do .75 and .67 represent generally ap-

plicable

scaling

factors for the

relationship

between

metabolic rate

and mass for

com-

parisons

among

and

within

species,

re-

spectively?

This

question

has

been

ad-

dressed for

interspecific

comparisons

among

mammals

(Hayssen

and

Lacy

1984)

and for

selected families of

mammals

(Kenagy

and

Vleck

1982;

Hinds and

MacMillen

1984).

These authors found

values of b that

ranged

from

.55

to .69.

Moreover, Hayssen and Lacy (1984) found

significant

variation

in

b

among

phyloge-

netic

lineages

of

mammals.

For

mammals

at

least,

the use of

the mass

exponent

of

.75

as a

baseline for metabolic

comparisons

among

species appears

to

be invalid.

The

only

taxon

for which

the

relation-

ship

between

MR

and

M

has

been

evalu-

ated

as a basis of

comparisons

within

species

is mammals

(Heusner

1982).

Whether

these results are

generalizable

to

other taxa, or even to all mammals, is

unknown. Mammals

are not

a

particularly

good

group

for

intraspecific comparisons

because the

range

of

body

size

of

individ-

uals

after

weaning

is

relatively

low.

Heus-

ner

(1982)

circumvented this

difficulty

by

comparing

domestic

species

that have

been

selected for

high

variance

in adult

size.

The

object

of

this

paper

is

to

review

the

relationship

between

MR

and

M

for

the

squamate

reptiles.

We

will

address

two

questions: (1) Are mass exponents of .75

and

.67

appropriate

as

general

models

describing

the

metabolism

of

squamates

for

inter- and

intraspecific

comparisons,

respectively?

(2)

Can the variation

in

MR

of

squamates

be

attributed to

phylogenetic

or

ecological

differences

among

species?

We restrict

our

analyses

to

standard and

resting

metabolism

of the

squamate reptiles

(lizards, snakes,

tuataras,

amphisbaenians),

which

comprise

over 90%

of

living

reptiles.

Crocodilians and chelonians were excluded

because

relatively

few data exist for these

groups,

particularly

for

intraspecific

com-

parisons

of

metabolic rate. We focused on

standard and

resting

metabolism

because

information about the

intraspecific

allom-

etry

of MR

and

M

during

activity

is

essentially

nonexistent,

and the

informa-

tion

dealing

with

species comparisons

of

activity

metabolism

has

recently

been

re-

viewed

by

Bennett

(1982).

MATERIAL

AND

METHODS

Bennett and Dawson's

(1976)

review

of

the metabolism of

reptiles

was used

as

the

major

source of data

on MR and

M

for

papers

published

before

1976,

and

the

recent literature

was

searched

for

addi-

tional

reports.

Inclusion of data

was

based

on the

following

considerations:

1. Animals had to be

fasted and

inac-

tive.

We considered that a two-

or

three-

day fast insured that small species were

postabsorptive

but that a

longer

period

would be

necessary

for

larger

species

(Coulson

and

Hernandez

1980).

2. Metabolism

had to be measured

un-

der

standard

or

resting

conditions.

Reptiles

exhibit

daily rhythms

of metabolism

that

may

persist

even

under

conditions of

con-

stant

light

or dark

(Wood

et al.

1978;

Heusner and Jameson

1981).

We

therefore

categorized

metabolism as

resting

when

it

was measured for fasting individuals during

the

period

of normal

activity (daytime

for

most

squamates)

and as

standard when

it

was

measured

for

fasting

individuals

during

the

period

of normal

inactivity

(night

for

most

squamates).

3.

Temperature

had to

be

within

the

range

of

normal

activity.

This

range

was

20-30 C for most

species.

Higher

temper-

atures

were included

only

for those

species

with

correspondingly

high

selected

body

temperatures. For example, the upper limit

for

Sceloporus

was 35

C and

for

Dipsosau-

rus,

Cnemidophorus,

canthodactylus,

nd

Varanus

40

C.

4. The

period

of

acclimation

to

exper-

imental

temperatures

varied

considerably

among

the

studies

cited.

At the

extremes,

acclimation

periods

ranged

from

several

hours to several

weeks.

Because

daily

fluc-

tuation

in

temperature

and

light

is

neces-

sary

to elicit

normal

behavior

(Regal 1980),

acclimation at a constant temperature for

periods

of

more

than

a few

days

is

probably

not

biologically

realistic.

Moreover,

long

periods

of acclimation

at a

high tempera-

ture are

stressful

(Marion

1982).

Given

the

variability

in

the

literature,

we

consid-



4/19

216

R. M. ANDREWS AND

F. H.

POUGH

ered

for our

purposes

that 2-3

h

of accli-

mation was

sufficient

for

small

species

but

that

large

species

should

have

been accli-

mated

for

several

days.

5. When

more

than one data set

was

available per species, we selected the best

in

terms

of

experimental

rigor

as

judged

by sample

size,

specification

of

experimen-

tal

conditions,

etc.

Thus,

no

species

was

represented

more than once at

any

one

temperature

and

metabolic

state.

Unless

specified,

all

statistical tests

were

conducted with SAS software

(Ray 1982).

INTERSPECIFIC

ALLOMETRY OF

METABOLIC RATE

We

included

only

measurements of

me-

tabolism of adults in our analysis of the

interspecific

relationship

between MR

and

M. We

used

published

values of

mean

metabolic rate

(ml

02

h-W

STPD)

and

mean mass

(g)

of

individuals

in

each

data

set.

For

reports

in

which metabolic

rates

of

adults were

taken

from

ontogenetic

series,

we used

the metabolic rate

asso-

ciated with

the

largest

individual.

Although

mean adult mass

would

have

been

the

most consistent

index of

species

size

for

all our analyses, this datum was seldom

given

in

the

cited

studies.

However,

be-

cause

species

size

in

our

analyses spanned

almost five

loglo

units,

greater precision

in

the index of

adult

mass

for

each

species

would not have

altered

any

of

the

reported

results.

Stepwise

multiple

regression

(maximum

R2

improvement

technique)

was

used

to

evaluate

the

influence of

temperature,

metabolic

state

(standard

or

resting),

taxon

(snake or lizard-the sphenodontid and

the

trogonophid

being arbitrarily

coded as

lizards),

and mean

adult

mass

(loglo

MR

in

ml

02

h-').

Log

transformation

of

MR

and

M

linearizes

the

relationship

between

these two

variables

for

regression analysis.

Other

variables

used in

the

stepwise

anal-

ysis

were

not

transformed. This

procedure

implies

an

exponential

relationship

be-

tween

these

independent

variables

and the

dependent

variable.

That

relationship

is

appropriate for temperature because it

provides

a

Qio

of '-2

(Robinson, Peters,

and

Zimmermann

1983).

For statistical

comparisons

among

fam-

ilies and

ecological

groupings,

standardized

residuals were used rather than

the ob-

served metabolic

rates. Standardized

(Stu-

dent)

residuals

were calculated as

being

(observed

MR

-

expected

MR)/Sy,

where

the

expected

MR

is the MR

predicted

by

the multiple regression equation and

Sv

is

the standard

error

of the

expected

MR

at

a

given log

M. Because

of the

loglo

trans-

formation

of

observed

metabolic

rate,

the

residuals

are

in

loglo

units.

Comparisons

based on residuals

reflect both the

direction

(positive

or

negative)

and

magnitude

of

deviations from

the

expected oxygen

con-

sumption

and

are

independent

of

the

ab-

solute

magnitude

of

observed values.

In

order to reduce

potential

bias

associated

with the differing numbers of observations

per

species,

the

mean standardized

residual

for each

species

was

used

in

comparisons

of families or

ecological groups.

The

resid-

uals for all

observations,

for

individual

families,

and for

ecological

groups

were

normally

distributed

(Kolmogorov

D

tests).

INTRASPECIFIC ALLOMETRY OF METABOLIC RATE

Analysis

of

covariance

was used

to

eval-

uate the

relationship

between

loglo

MR

and loglo M for comparisons within spe-

cies. Data sets

for

each

species

had

to

include

both

juveniles

and

adults.

Because

hatchling

size is

smaller relative to adult

size

in

large

than

in

small

species (Andrews

1982),

we

used as

a

guideline

the rule

that

our observations

should include

juveniles

as small as 10% and 30% of the mean

adult mass of

large

and

small

species,

respectively.

Because of statistical and

ex-

perimental problems

associated with

re-

peated-measures designs, we did not use

data sets that

represented

multiple

mea-

surements

of

the same

individuals.

Data

for

most

species

were obtained

by

projecting

transparencies

of

published

plots

of

loglo

MR

versus

loglo

M

on

log-log

paper

so

that the

values could be

read

directly.

The

analysis

of covariance

was

based on

only

one

set

of observations

per

species.

When

several

data

sets were

avail-

able for

the same

species (e.g.,

for

different

temperatures), the set in which the agree-

ment between our

calculation of

a

and b

and the

published

values was

the

greatest

was used in the

analysis.

For two

species,

the

original

observations were used as

they



5/19

ALLOMETRY OF REPTILIAN

METABOLISM

217

were either

presented

in

the

publication

(Graham

1974)

or obtained

from the

au-

thors

(Bakker

and Andrews

1984).

RESULTS

INTERSPECIFICCOMPARISONS

A

total

of 226

observations

of

107

spe-

cies

of

squamates

was used

to

evaluate

the

relationship

between

metabolic

rate and

the

independent

variables

(table

1).

Mass

entered

at the

first

step

of

the

stepwise

multiple regression

analysis

and accounted

for

88%

of the

variation

in

metabolic

rate.

Temperature

entered

at

the second

step

and

accounted

for

an

additional

8%

of the

variation

in

metabolic

rate.

Metabolic

state,

although

as

significant

as the preced-

ing

independent

variables

(P

.50).

None

of the interaction

terms in

multiple

regression

models

was

significant

(P

>

.05).

Therefore,

the

rela-

tionship among

MR,

adult

mass,

temper-

ature

(C),

and state

(0

=

standard,

1

=

resting)

was

expressed

in

terms

of the

multiple regression equation

loglo

MR

=

-1.87

+

.800

loglo

M

+

.038

temperature

+

.140 metabolic state

(1)

(F3,225

=

1656.5,

P

.05

by

Tukey

test;

Zar

[1984]),

no further tests

were

conducted.

DISCUSSION

GENERAL

NTERSPECIFIC

OMPARISONS

Metabolic

rate

is

typically

expressed only

as a function of mass. Because metabolism

is

simultaneously

affected

by

other

vari-

ables,

univariate

analyses

limit

compari-

sons

among

taxa

to

studies

conducted

under

the

same

conditions.

Our

approach

~a

a

a

.au

1,t,

a

n

o ..... . .o o

.

oA

Doact

v

,a

s

,

0.0

a

cca

.t.0

....

Fo.......

0

0

0

a

0

-2.0

-o0e 0o

2:4

3:2

4.0

LOG1o

MASS

(G)

FIG.

1.-Metabolic

rates

of lizards

in four

ecological

categories

as a

function

of

body

mass.

Each

species

is

represented

by

the mean standardized

residual

of

the

relationship

between metabolic

rate

and

three

independent variables (mass, temperature, and stan-

dard

or

resting

metabolic

state).

See

Material

and

Methods

for details.

The

ecological

categories

are

day-active

predators

(A),

herbivores

(A),

reclusive

predators

(0),

and

fossorial

predators

(0).

Means

for

each

category

are

indicated

by

arrows

on the

vertical

axis.



14/19

TABLE

3

MASS

COEFFICIENTS

AND

EXPONENTS

FOR

INTRASPECIFIC

REGRESSIONS

OF

METABOLIC

RATE

AND

BODY

MASS

IN

VARIOUS

SQUAMATE

SPECIES

Mass

Mass

Body

Mass

Metabolic

Temperature

Species

Coefficient

Exponent

(g)a

State

(C)

Source

Ophidia:

Helicops

modestus

.317

.585

196

R

20

Abe

and

Mendes

(1980)

H.

modestusb

.411

.560

196

R

25

Abe

and

Mendes

(1980)

H.

modestus

.488

.585

196

R

30

Abe

and

Mendes

(1980)

Liophis

miliaris

.150

.753

401

R

20

Abe

and

Mendes

(1980)

L.

miliaris

.338

.674

401

R

25

Abe

and

Mendes

(1980)

L.

miliaris

.257

.802

401

R

30

Abe

and

Mendes

(1980)

Pelamis

platurusb

.198

.729

116

S

30

Graham

(1974)

Lampropeltis

getulusb

.333

.650

1,217

R

26

Davies

(1982)

Spalerosophis

cliffordiib

1.2c

.62

500

R

30

Dmi'el

and

Borut

(1972)

Elaphe

guttata

1.21

.70

800

R

25

Smith

(1976)

Sauria:

Chalcides

ocellatusb

.208

.647

25

S

30

Bakker

and

Andrews

(1984)

C.

ocellatus

.313

.626

25

R

33

Pough

and

Andrews

(1984)

Sceloporus

occidentalisb

.23

.67

20

S

25

Heusner

and

Jameson

(1981)

Lacerta

viviparab

.17

.78

4

S

30

Cragg

(1978)

Varanus

exanthematicush

.88

.57

7,500

S

25

Wood

et

al.

(1978)

V.

exanthematicus

3.39

.51

7,500

S

35

Wood

et

al.

(1978)

Sceloporus

graciosus

.145

.694

5

R

25

Mueller

(1969)

S.

graciosus

.249

.682

5

R

30

Mueller

(1969)

S.

graciosus

.394

.785

5

R

35

Mueller

(1969)

Scincella

lateralisb

.

.

.306

.633

1.5

R

30

Hudson

and

Bertram

(1966)

Hemidactylus

frenatush

.128

.685

2

S

27

Feder

and

Feder

(1981)

Cosymbotus

platyurusb

.139

.744

3.5

S

27

Feder

and

Feder

(1981)

Anolis

bonairensis

.201

.548

12

S

27

Bennett

and

Gorman

(1979)

A.

bonairensisb

.430

.554

12

R

33

Bennett

and

Gorman

(1979)

Cnemidophorus

murinus

.168

.761

85

S

27

Bennett

and

Gorman

(1979)

C.

murinusb

.680

.705

85

R

40

Bennett

and

Gorman

(1979)

Gonotodes

antillensis

.127

.753

1.8

S

27

Bennett

and

Gorman

(1979)

G.

antillensisb

.199

.695

1.8

R

34

Bennett

and

Gorman

(1979)

NOTE.-Abbreviations

are

those

given

in

table

1.

a

Largest

individual

observed

in

each

study.

b

Used

in

an

analysis

of

covariance

(see

Material

and

Methods).

C

ecalculated

from

figured

values.



15/19

ALLOMETRY

OF

REPTILIAN METABOLISM

227

has

been to use

multivariate statistics as

a

means to

express

metabolism

as a

function

of the three

independent

variables that

are

most

important

in

studies of

squamate

reptiles. Thus,

equation

(2)

expresses

the

relationship between MR and M over a

temperature

range

of

20-40

C

and

for

individuals

under either

standard or

resting

conditions.

Our

predictions

of

metabolism

based

on

multivariate

analysis

agree

closely

with

the

results of

univariate

analyses

(Bennett

and

Dawson

1976).

For

example,

with the

appropriate

substitutions for

temperature

and

metabolic

state,

our

equation

(2)

re-

duces to

MR =

.103

M.80

(resting,

20

C)

and MR = .248 M.80(resting, 30 C).

For

reptiles

in

general

(mostly squa-

mates),

Bennett

and

Dawson

(1976)

ex-

pressed

the

relationships

as

MR

=

.102

M.80

(resting,

20

C)

and MR

=

.278

M 77

(resting,

30

C).

In

our

analyses,

metabolic rate

scales to

mass

by

a

power

of

.80.

The

metabolism

of

free-living iguanid

lizards also

scales

to

mass

to the .80

power

(Nagy 1982).

These

results

are

not

in

accord

with

theoretical

predictions (McMahon 1973; Feldman and

McMahon

1983)

of

a

.75

scaling

factor.

Thus,

metabolic

rates of

squamates

in-

crease faster

with

mass than

expected,

and

they

also increase

faster

with

mass than

has been

observed for a

class-wide

analysis

of

the metabolic rates

of

mammals

(Hays-

sen and

Lacy

1984).

Equation (2)

provides

a

flexible

esti-

mator

of

the

metabolic

rates of

squamate

reptiles

that

is

useful

either for

comparisons

of the vertebrateclasses (e.g., Pough 1980)

or

for

other

general

uses in

which

the

magnitude

of the

intergroup

difference

greatly

exceeds the

magnitude

of

the

vari-

ation

within

groups.

Equation

(2)

is not

suitable for

comparisons

among

squa-

mates,

however,

because

significant

vari-

ation

exists

among

taxonomic and

ecolog-

ical

groupings.

INTERSPECIFIC COMPARISONS:

PHYLOGENY

AND

ECOLOGY

Metabolic

rates of

squamate reptiles

vary

as

a function

of

both

phylogenetic

relationship

and

ecology. Considerably

more variation

in

metabolism

was

ex-

plained

by

ecological

groupings (45%)

than

by family

(16%).

That

relationship

suggests

that some

families are

ecologically

diverse

and

that this

diversity

is

associated

with

intrafamilial

variation

in metabolic

rates.

Families

that

are

ecologically

homoge-

neous

have

low

intrafamily

metabolic

variation. This point is illustrated in table

2

by

the contrast

of the coefficients

of

variation

for the standardized

residuals

of

ecologically

diverse

families

(colubrids,

scincids,

and

iguanids)

and those

of

eco-

logically homogeneous

families

(varanids,

xantusiids,

gekkonids,

and

boids). (Our

characterization

of

families

as

ecologically

diverse or

homogeneous

in this context

is

based on the

species represented

in

our

sample,

which do

not

necessarily

reflect

the characteristicsof the family as a whole.)

Sorting

skinks and

iguanids

by

ecological

characteristics

reduces the

variance,

ap-

parently by producing

more

homogeneous

groups.

It thus

appears

that

ecology

is

more

important

than

phylogeny

in

deter-

mining

levels

of

resting

and

standard

me-

tabolism

among

squamate

reptiles.

INTRASPECIFIC

COMPARISONS

The theoretical prediction that the re-

lationship

between MR

and M for

com-

parisons

within

species

should

differ

from

comparisons

among

species

was

supported

only

in

a

very general sense,

but

not

in

specific

details

of the

prediction.

Heusner

(1982) proposed

that

mass

exponents

for

comparisons

within

species

should

be

lower

than the

mass

exponent

for

com-

parisons

among

species.

He

further

sug-

gested

that

the

relatively high

mass

expo-

nent for comparisons among species was

an

artifact

of

inappropriately

fitting

a

regression

line

through

independent

sets

of data with

common

slopes

but

different

intercepts.

Heusner's

contention

that

the

mass

ex-

ponents

for

comparisons

within

species

should

be less than the

mass

exponents

for

comparisons

among

species

is

correct

for

squamate reptiles.

All

but three

of

the

28

mass

exponents

for

intraspecific

data

sets (table 3) are significantly smaller than

.80,

the mass

exponent

for

comparisons

among

species

(P

.05

by

Tukey

test;

data from table

1).

PREDICTING ETABOLICATES

OF

SQUAMATES

The

limited data available to

Bennett

and

Dawson

(1976)

indicated

that

com-

parisons

within and

among

species

had

the

same

mass

exponent.

Thus,

the

me-

tabolism of

juvenile squamates

is

com-

monly

estimated

from

general equations

that

relate

MR

to

M

for

interspecific

com-

parisons

of adults

(e.g.,

Andrews

1979;

Porter and James

1979;

Thompson

1981;

Troyer

1984).

Our

analysis

shows

that this

procedure

is

invalid,

because

most

mass

exponents

for

comparisons

of

ontogenetic

changes

in

metabolism within

species

are

significantly

lower

than the value

of

.80

that

applies

to

interspecific comparisons

of

adults.

Unfortunately,

the

heterogeneity

of

mass

exponents

for

intraspecific

rela-

tionships

of MR and M means that there

is

no

easy

alternative method of

estimating

the

metabolism

of

juvenile

squamates.

An

accurate

description

of

energy require-

ments

of

juvenile

squamates requires

that

the

relationship

between

MR and M

be

measured

for the

species

in

question.

The metabolism of

adult

squamate

rep-

tiles

can

be

described

by

equation

(2),

which relates

MR

to

body

mass,

temper-

ature,

and metabolic state.

Despite

the

ease with which this

equation

can be

used,

variation

among

taxonomic and

ecological

groupings of squamates limits its applica-

tion. For

lizards,

nearly

one-half

of

the

variance

in MR

can

be attributed

to

some

combination of

behavior, habitat,

and diet.

If

that information

is available

for

the

species

in

question,

the estimate of

metab-

olism

provided

by equation (2)

can

be

improved

by

using

the mean

untrans-

formed residuals

in

table

2 to

adjust

the

intercept

of

equation

(2).

This

procedure

assumes

that the

value

of

b

for

the

groups

is identical.

CONCLUSIONS

The

pattern

and

extent of variation in

standard

and

resting

metabolic rates

of

lizards and snakes

are far from

being

clearly

revealed

by

our

analysis

because

the

taxonomic

and

ecological

diversity

of

the

group

has

scarcely

been

sampled.

Only

16

of the

approximately

34

families of

squamates

are

represented

by

observations

of

MR,

and

only eight

of

these are

repre-

sented

by

observations

of five or more

species.

The number of

comparisons

of

ecologically

homogeneous

groups

of

spe-

cies is

similarly

limited.

For

example,

the

prediction

that

carnivorous lizards would

have

higher

metabolic rates than

would

herbivorous

lizards

(Pough

1983)

could be

tested

only

by

a

comparison

of

five

species

of

varanids

with

four

species

of

iguanines

and

two scincids.

Not

only

are

more

ob-

servations of these

taxa

necessary,

but

the

comparison

would

profit

from observations

of

ecologically

similar

but

phylogenetically

distinct

groups.

For

example,

measure-

ments of the

large

carnivorous

teiids Cal-

lopistes

and

Tupinambis

and of

the

lacertid

Lacerta

lepida

or

of

the

herbivorous

sincid

Corucia

and the

agamids

Uromastix

and

Hydrosaurus

would be

especially

valuable.

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Documents

Andrews, Pough - 1985 - Metabolism of Squamate Reptiles Allometric and Ecological Relationships