The costs of becoming a predator - ScienceDirect

Pat Shipman Walker

& Alan

The costs of becoming a predator At some as-yet-unknown point during hominid evolution, a dietary shift occurred which involved incorporating a larger proportion offood derived from animal resources. Features of predatory and non-predatory mammalian species are compared in order to identify features or characteristics that would be expected to change as a consequence of this dietary shift. Tht record of hominid evolution is then reviewed to determine when these expected changes occurred, insofar as they are visible in the fossil record. Characteristics ofHono erectus are most congruent with those predicted for a species that has hecome significantly more predatory than its antecedents.

Department of CdlBiology and lnatomy, Johns Hopkins Cfniversi!v Srhool of .\fedicinc. 73 North Wolfe .Stwet Baltimore. A111 21X.5. c:..s.A. Received 5 September 1988 Revision recei\red 6 March, 1989 and accepted 6 March 1989

Kqwords: Diet; ecological carnivorr: CTtY tu.l

herbivore;

rules; Homo

Journal ofHuman Evolution (1989)

18,373-392

Introduction Determining

the

diet

paleoanthropology. the heart (Dart,

of several

1949,

important

(Isaac,

hypothesis

(Shipman,

1978),

question

theories

striding

raised

extent,

unusual elaborate

hypothesis

the

1981;

recognize

the immense

the basic

biology

scavenging Zihlman

&

importance

of any species.

in the hominid

as an enlarged

communication

of

have lain at

the food-sharing

1981)

(Zihlman,

traits-such

concerns

the hunting

the diet or diets of the species

estrus,

significant

effects

not only the diet of any extinct

changes

that the hominid

condition

theories

central

1968),

(Lovejoy,

hypothesis

to some

whether

to deduce

of any dietary

apparent

these

and,

including

& Lancaster,

hypothesis

gathering

ofvarious

concealed

origins,

of the

of early hominids

lineage

brain,

and symbolic

of The

upright,

expression,

technology.

It is important impact

the

the ecology

bipedalism,

of human

is one

practices

1975; Washburn

In essence,

to the evolution

sophisticated

species

the pair-bonding

1986),

is frequently

art‘ linked

present

the diet or dietary

1961,

1978), and others.

diet in determining

and

about

1957; Ardrey,

hypothesis Tanner,

of past

Ideas

during

lineage

on the biology

a lineage’s

underwent

a major

of our ancestors

that must have been largely

species

evolutionary dietary

and

but also the timing

history. transition

near-relatives.

or even excltisively

vegetarian,

In particular

and it is

that may have had From

an ancestral

hominid

diets shifted

towards substantial amounts of meat-eating. Whether this meat was obtained by hunting or scavenging is not the focus of this paper, though it is a controversial issue in the literature (e.g., Binford,

1981; Bunn,

1982, 1983, 1986; Bunn

1988; Potts,

1983, 1987, 1988; Potts

explore

the timing

here

& Shipman,

and consequences

& Kroll,

1986; Blumenschine,

1981; Shipman,

of this transition

1986a,b,

1983, 1986). Rather,

towards

we

meat-eating.

Many different approaches have been used to reconstruct the diets of extinct hominids. Here, we seek to determine some of the ecological “rules” (Walker, 1981: 58 flJ involved in and the consequences steps.

First,

categories: herbivorous

attendant

we compare

various

upon

becoming

attributes

predatory species, whether species, in the broadest sense

0017-?484/89/000373

+ 20$03.00/O

a predator. of living

true or of animals

This approach

mammals

in two

involves broad

three dietary

simply facultative carnivores; and with diets predominantly comprised 0

1989 Academic

Press

Limited

of plant

resources

dilIerences

of any

in ecology,

demands ofeach herbivores

type.

dietary regime. Second,

and carnivores

occurred

at the point

evolution.

Finally,

that

predictions

carnivory

lirst

which are found to differ Iretween

concerning

became

for a species can

be

record,

that has newly adopted

expected some

to

may

leave

serve

that must havc~

significant

in human

record for changes which match

predatory

recognizable

as markers

changes

rcolo,gically

we inspect the fossil and archaeological

such

archaeological

those attributes

then become

those predicted changes

These comparisons hi,ghli,ght general or largt,-scalt, or life history that are rclatcd to the constraints and

behavior,

behavior.

signatures

alerting

in

\Vhilc not all the

li)ssil

ot

us to the timing

of this

in the fossil record

to the

transition. Gaution

must be used in attributing

adoption of a predatory

observed

dealt with in this paper will arise onl_yq‘carnivory

the types of changes

we are faced with the sometimes is an exaptation

the changes

lifestyle. Similar changes may occur for different reasons and lew of’ difftcult issue ofdetermining

or an adaptation

(Gould

& Vrba,

is practiced.

Thus,

whether the trait in question

1982).

For clarity, we will define precisely what we mean by various terms used to describe diets or dietary vertebrate

categories. By carnivory or predation, we mean a dietary regime in which flesh forms a large portion of the diet. Neither carnivory nor predation is meant

to indicate

how animal resources

scavenging

are the same if both yield comparable

are acquired;

for the purposes of this paper, hunting and proportions

of animal resources.

As used

here, carnivory is distinct from insectivory. Herbivory is used here to indicate a predominantly vegetarian dietary regime. ‘l’his term and its derivatives are not used in the restricted

sense of grass-eater; such as grass,

indicates

a mixed diet that may include

invertebrates. simplistic general

leaves,

they imply

resources

Classifying

but perhaps

differences

only a heavy

seeds, shoots,

all dietary

appropriate

both animal

regimes in studies

carnivory

point to be considered

appears

upon

plant

food

buds and fruits. Omnivory

and plant resources,

into these three very broad

in addition

to

categories

is

such as this one where only lar,ge-scale,

are sought.

Dietary transitions One significant

dependence

bark, flowers,

to be a relatively

and evolution

at the outset is that the transition rare evolutionary

event,

from herbivory

unlike the transition

to

from

either ofthese dietary regimes to omnivory. It is likely (Ewer, 1973) that the true carnivores and perhaps many of the facultative carnivores evolved from insect-eating forms. Thus, the behaviors

of hunting and catching

caught-were

already

cases of non-hominid transition

in parallel

established. mammals

live prey-and

the abilities

to eat and digest prey oncr

It would be useful to examine

that had apparently

with the hominid

lineage,

undergone

to determine

with special

care any

a herbivore-to-carnivore

which features or traits were

particularly liable to change. A partial model of this type can be found among the rodents. One of the few lineages that appears to have evolved from a vegetarian ancestral stock into carnivory is the grasshopper mouse. The grasshopper mouse is any one of two closely-related murid species within the genus, O&~om_vs: 0. leucogaster and 0. torridus are widely-accepted

species. A third species,

0. arenicolu, is listed by Nowak & Paradiso (1983), but its distinctness is problematic (Carleton & Eshelman, 1979). These mice are fairly common and widespread in the central and western United States and resemble deer mice in appearance and size.

THE

Behaviorally,

grasshopper

small groups

at night,

COSTS

OF BECOMING

mice are ferocious predators

taking small vertebrates

377

A PREDATOR

in miniature.

including

They hunt in pairs OI

lizards and other rodents,

and

insects nearly as large as themselves (Bailey & Sperry, 1929; Egoscue, 1960; Flake, 1973; of wolves, Horner et ul., 1965; Langley, 1978, 1981, 1986). I n a behavior reminiscent grasshopper mice put their noses up into the air and howl when near conspecifics or before making a kill (Hafner & Hafner, 1979). A careful comparison between grasshopper mice and herbivorous carnivory

mice may point up characteristics

that can be expected

that are dictated

to parallel the changes

by the transition

that must have occurred

to

in our o\%II

lineage. ‘I‘he reverse transition-from features of a carnivorous carnivory

carnivory

to herbivory-is

species turned vegetable-eater

are most readily relaxed or abandoned.

also of interest.

Examining

tht

may indicate which adaptations

Such an analysis

to

may also help idcntif!.

those features that are not genuinely linked to predatory behavior. That is, such a species should not show an adaptation that is causally linked to the predatory lifestyles unless it is such a fundamental of the C:arnivora

biological

attribute

are omnivores,

animals

and insects,

notable

exception,

few have become

and an interesting

case to consider

foods. Only a tiny proportion

food at all (Ewer,

1973; Morris

& Morris,

Herbivore Adaptations

and features

are predicted carnivory-fall

foods, eggs, smail

vegetarian.

The

most

hpre, is the giant panda, .4ilzuopdu comprised

of their diet includes

1966: Schaller.

and carnivore

that distinguish

to have occurred into three general

ofvegetable

fully and almost exclusively

In the wild, giant panda diet is predominantly

ntelanoleuca.

other vegetable

position

that it is difficult to change. While man)- mcmhers

and may eat a combination

ofbamboo

stalks and

any animal

or insect

1981 i .

comparisons

carnivores from herbivores-and dietary transition from

during a categories:

food-procurement;

the mechanics

of obtaining

that therefore herbivory to

food-processing

and

in the food web.

Food-procurenmt ‘I’hcb first type of change because

of the different

example,

although

are common.

vertebrate

passive

Thus,

important

and animals

must acquire

and physical

defenses,

draws near. C:apturing

plant foods. Obviously,

that were unnecessary

to enhance

1).

For

such as leaf toxins and

to be the major task. In contrast,

can use alarm calls to warn of a predator’s

adaptations

(Table

of taking evasive action once thcv have

food items appears

once the predator

to harvest

food, which arc din‘erent

as food items

task here and it is obvious that different behaviors

from those needed success)

chemical

locating

prey move around,

have escape mechanisms

species

of plants

plants are sessile, quiet, and incapable

been located, thorns,

concerns attributes

presence,

are need to capture li1.e prev

then, a newly-evolved

prey capture

and

food items is the most

(i.e.,

to maximize

predator) huntin,:

for herbivores.

Two factors apparently account for much of the variability in hunting success rate (Bertram, 1979; Houston, 1979) among African predators, for which there art qood ethnological data. The first important factor is maximum speed of pursuit. As a ,group, these predators are not significantly faster than their prey species (Figure 1: student’s / = 0.19, P > 04 for a one-sided test; P > 0.8 for a two-sided test). However, there is a statisticall),

significant

correlation

between

maximum

reported

hunting

SLICWSS

01‘ ;t

376 Table

P.

1

Stereotypical

SHIPMAN

AND

A.

WALKER

features of plants and animals as foods

Plants Unwary Sessile Passive defense mechanisms Low protein’ High fiber Few calories/unit food2 Pm-ingestion processing Fermentation needed

needed

Prg animals War) Mobile Passive and active defense mechanisms High protein’ Low fiber Many calories/unit food’ Pre-ingestion processing needed Fermentation unnecessary

’ While some particular plant foods are high in protein, most are significantly lower in protein per unit volume than meat. 2 A unit of food as applied to a plant is the particular portion that is eaten, such as an individual leaf, flower, nut, or fruit; a unit offood as applied to a prey animal is the entire individual.

predator-that is, the number of hunts that end in the capture of a prey-and maximum reported speed (r = 0.814,4 d.f., P< 0.05). In other words, in general predators may not be faster than prey, but the faster predators are more successful in hunting. Inspection of the residuals in Figure 2 suggests the second factor that strongly influences hunting success. The three carnivores that have success rates that fall on or below the regression line are solitary species: leopard, cheetah, and striped hyena. The three species that have better-than-expected success rates are all social: lions, Cape hunting dogs, and spotted hyenas. In short, two adaptations that would enhance the hunting success of a newly-evolved predatory species are anatomical adaptations for speed and behavioral adaptations for sociality. However, many herbivores and nearly all higher primates are social, so it is difficult to determine whether this is an adaptation or exaptation in any particular herbivore-turned-carnivore. Another aspect of the acquisition of food is the time expended in the task. Although plant food items are readily obtained once located, they tend to occur in small units such as leaves, buds, or fruits, each of which is of relatively low nutritional value. Despite the difficulty of chase and capture, mammalian food items tend to come in relatively larger, more nutritious units (whole animals). Thus, though both plant and animal foods contain calories, protein, fats, and so on, the net gains are different. One way to evaluate the efficiency of these two dietary regimes is to look at the time species spend in feeding. Figure 3 shows a semi-log plot of the percentage of 24 h spent feeding (including time spent searching for food) for herbivorous and carnivorous species as a function of the log body weight ofan adult. For plant-eaters, the percentage of the day spent feeding correlates closely with total body size; bigger animals spend more time getting food (r = 0.98,6 d.f. P < 0.001). A similar and also statistically significant trend is seen among carnivores (r = 0.84, 6 d.f., P < 0.02). The slope of the regression line for herbivores is much steeper and intercept is higher than those of the regression line for carnivores. In other words, if body size is controlled for, an animal must spend much more time feding if the food is derived from plants rather than animals. Therefore, one of the apparent benefits of becoming a predator is that the amount of time spent feeding drops dramatically. For example, a species of about 35 kg-roughly the size of early hominid species-would be predicted to spend about 6 h in feeding on plants or only about 2 h in feeding on animal foods.

THE

COSTS

OF BECOMING

Predatory

RdFr

GrFx

JCkl

cyte IncreasIng

species

wolf

WDog

body

Herbivorous

?=67.1&1

377

A PREDATOR

ttyeflo

Chth

Lprd

Lion

stze --+

species

l-2

1

T(502 Ggoz Deer Wthg lncreaslng

HI1st

Wbst

body

Topi

Zbro

Elnd

Grf

Bflo

size --+

Figure 1. Maximum reported speed (in kph) of various predatory and herbivorous (prey) species (data from Howell, 1944; Schaller, 1972; Bertram, 1979; and Kruuk, 1972, 1976). Rdfx = red fox; GFx = grey fox; Jckl = jackal; Cyte = coyote; WDog = wild or Cape hunting dog; Chth = cheetah; Lprd = leopard; TGaz = Thompson’s gazelle; Ggaz = Grant’s gazelle; Wthg = warthog; Hbst = hartebeest; Wbst = wildebeest; Zbra = zebra; Elnd = eland; Grf = giraffe; Bflo = African buffalo.

Food-processing The second predictable and chemical

properties

well as placing

type of change occurs because animal food has different physical from plant food. Meat requires a different sort of preparation

different demands

on digestion.

Therefore,

as

jaws and teeth of predatory

378

P.

SHIPMAN

ANI)

‘1. M’ALKEK

801 +

0

+ L 1 /

+

/

0

0

0

kb-ek

Ll

40

50

Maximum

60

70

80

90

IO0

speed

Figure ‘2. Maximum reported speed (in kph) of various mammalian, African predators plotted against hunting success (data from Bertram, 1979). Hunting success is measurrd as the percentage of pursuits that end in a prey capture. + = social species (lion, spotted hyena, wild or Cape hunting dog): 0 = solitary species (cheetah, leopard, striped hyena). The correlation is statistically significant (r = 0.811. -1 d.f., P < 0.05).

species may evolve to permit slicing up of meat and other animal tissues. More predatory species

show restricted

shearing

stout grasping Ewer,

rotational

mobility

blades and reduced grinding canines

(e.g.,

1973). The proportions

herbivores

must ferment

at the temporomandibular

areas on the molars,

Van Valkenburgh, of the digestive

relatively

joint,

elongated

smaller incisors,

1984; Van Valkenburgh

& Ruff,

and 1987;

tract alter, too. Both grazing and browsing

their food, either through adaptations

of the foregut (e.g., sloths.

langurs, bovids) or through adaptations of the midgut (e.g., zebras, elephants, etc.). Foregut fermentation is accomplished through the development of a rumen or other structure from the stomach; in midgut fermenters, the proximal part of the colon and the cecum are elaborated. Facultative or true carnivores tend to have a relatively longer small intestine, where the digestive and absorption of animal product occurs, and a relativeI) shorter

large intestine

and cecum

(Ewer,

1973; Chivers

& Hladik,

1984; Martin

et al.,

1985). The relaxation of the dental adaptations for carnivory can be seen clearly in the panda, which has broad selenodont teeth with crests that are used for slicing bamboo rather than for meat-slicing (Ewer, 1973). The adaptation for eating bamboo is a simple one of greatI>

THE

Relationship

Table 2

COSTS

OF

BECOMING

between feeding

time and body weight’

increased

cheek-tooth

that

the

discrepancv Apparently, their The

size from that seen in more omnivorous

any new cusp pattern

the panda

LI.hen

of gut

shorter

length

to body

than length

or carnivorous

1964) that

Davis

bears

and not

( 1964) also showed

of more

carnivorous

is examined

bears.

allometricall~.

the

howc\,er-. much

from

condition.

intestinal

tract

of a

dtavelopment

interpreted

of grasshopper

pronounced

indigestible

fragments

serves

to

them

protect associated in human

mammals.

4a,b). Since

has been

fundic

pouch,

when

from

chewed.

damage.

grasshopper cuttin,g:, cheek

mice

et al. ( 1965), who

by Horner

slicing among

Oydon;ys

predator)-,

were scqucstercd. which

of all glands shows

intestinal

mice than

like those

are not present

this only shows is not imperative.

man)

is not one likeI\- to bc

of omnivorous canines

yield

to the pouch

a distinct

but that adaptation

or enlarged

carnivores

glands

arthropods,

restriction

like those

crests

are highly

teeth

The

diet,

all gastric

chitinous

Thus.

mice are more

Sharp

studied

in which

to eating

with its carnivorous evolution.

ofgrasshopper

The teeth carnivorous

mice

proportions of different parts of the tract. ‘I’hcy considered to be “typical for a cricetid” (p. 520) except for the

this as an adaptation

sharp,

have sharp,

(Davis,

the proportions of pandas and other bears is diminished, , between the gross proportions of the gut of giant pandas have not changed

ancestral

adaptation paralleled

for ursids

has a gut proportionateI>,

relationship

unfortunately did not measure the @l&o~_~,~ digestive tract They

Feeding time

BOd> weight (kg)

Species

one that involves

37’)

A PREDATOR

that

the tendenq

‘I’he diffcrcncr

bcacome more

out resemblances hypsodont through

between time-and

to

may be

due to the fact that much of the live prey taken by Orychomys is arthropod. not vcrtebratc. I‘he sharp slicing incisors typical of most rodents, including grasshopper mice, apparent]) suffice for despatching and dismembering their prey. Additionally, Carleton & Eshelman

(1979 : 42) point

01

(Fi,guw

the high-cusped molars of Oychom_w--which those insectivores or insccti\,ororls I)ats.

380

P.

0

0.5

SHIPMAN

I.0

AND

A.

2.0

I.5

WALKER

2-5

Log body weight

3.0

3.5

4.0

(kg)

Figure 3. Log body weight (in kg) plotted against feeding time, measured as the percentage of 24 h spent in feeding activities (data from Scott, 1978; Clough & Hassam, 1970; Owen, 1970; Jarman & Jarman, 1973; Spinage, 1968; Wyatt & Eltringham, 1974; Goddard, 1967; Waser, 1975, 1977; Grimsdell& Field, 1976; Scott, 1978; Guggisberg, 1975; Mech, 1970; Smith, 1978; Kruuk, 1972, 1976; Schaller, 1972; 1983). 0 = herbivorous species; + = Malcolm, pers. comm.; Dunbar, 1977; Nowak and Paradiso, carnivorous species. The relationship is statistically significant for both herbivores (P < 0.001) and carnivores (P < 0.02).

Ecological position The

third

type of change

Carnivores

other plant-food-eaters. Eltonian

or trophic

Initially, tissues

has to do with broader

ecological

occupy a different position in the ecosystem As a simple,

pyramids

first approximation,

(Odum,

costs energy.

issues.

ecosystems

can be modeled

or as

197 1).

all energy on earth comes from sunlight.

of an organism

and physiological

and food web than do herbivores

Thus,

But transforming

as energy

is transformed

this energy into the from sunlight

to

primary producers (plants) and then to primary consumers (herbivores) and finally to secondary consumers (carnivores), there is a tremendous net energy loss. It has been estimated that each transformation, represented diagrammatically as a step on the pyramid, uses up 80-90% of the energy available from the next lower trophic level (Odum, 197 1, p. 63). For this reason, food chains or pyramids are usually limited to four or five steps. The cost of energy transformation steadily decreasing biomass.

thus dictates

that the different

trophic

levels have

381

THE COSTS OF BECOMING A PREDATOR

A

Figure 4. Dental adaptation of grasshopper mice (after Carleton & Eshelman, 1979). (A) Occlusal view of the molars of 0. hogaster; (B) lateral view of left mandible of 0. leucogaster. Note that the elongated canines and sharp carnassial crests typical of carnivores are not present.

As far as mammals that the number

are concerned,

of individuals

on the step below it. For example, show that carnivores While

comprise

there is a tendency

animals,

the cost of energy transformation

at most

l-2%

in such censuses

the figure is sufficiently

consistent

of the individuals

to underestimate

is obvious;

from that

game parks

(Potts,

1982).

of small-sized or guideline.

if predators

are too

they will consume their prey faster than the prey can reproduce and the predators

to be an immutable

ecological

rule. Indeed,

upon body size in both herbivores East

counted

the numbers

to serve as a general expectation

(prey) to predator

will quickly starve. Thus, the low densities of carnivorous

carnivores

markedly

census data from various modern African

The reason for such ratios of herbivore numerous,

also usually means

at each trophic level or step decreases

the absolute

(1984)

has

allometrically

population

shown

that

with increased

species in any ecosystem

(Damuth,

size is lower when body size is held constant. herbivores

rainfall;

appears

population density is inversely dependent 1981) and carnivores (Mohr, 1940), but in and

carnivores

both

the slopes are almost parallel,

increase

Similarly, in density

but carnivores

have a

lower intercept. Another

way of expressing

different dietary regimes. ethnological

the same fact is in terms of the home range size of species of‘

Since the area of a species’ home range is frequently

studies, more data are available

found to vary allometrically

with body size (mass)

1984, pp. 290-294

for a review).

relationship

according

vary

from the literature.

trophic

consideration. Thus, for example, Calder (1974) scales with mass (M, in kilograms) as follows:

level

of the

reports

equations mammalian

(2)

species

this under

P

Home range = 4.7 MI.O~

Secondary

expressing

that home range area in hectares

Primary consumers: (1)

o&4

3:

0.00 1

consumers:

Home range = 66.8

M”22

in

in a wide range of studies (see Calder,

It is clear that the allometric

to the

measured

Home range size has been

0.956

8

0.00 1

Different

studies

reported

use d’ff 1 erent

mammalian Nonetheless, Harestad

exponents.

finding in that carnivorous

samples, so thcrc & Bunnell (1979)

species (secondar),

consumers)

Primary consumers: (3) Home range = 2.3 Secondary consumers: (4)

~I-02

Home range = 13.2

MI-:~‘)

In terms of dietary transitions

from herbivory

is sonic’ variabilic\ ill [ht. report a generaIl>. similar

have much larger hon~t~ranges:

r

?I

I’

0.866

28

0.004

0.900

20

WOOI

to carnivory,

this density rule predicts that

almost any species that moves from the primary consumer or herbivore trophic level to that of secondary consumer or carnivore will face a density dilemma. To wit: since carnivores must be much scarcer

than herbivores,

a species transformed

from herbivory

to carnivor)

is likely to be much too densely distributed. There are four possible solutions predictions. density

for a herbivore,

undergo a reduction area. Third,

to this dilemma

First, the species undergoing thus obviating

in total numbers

the problem sufficient

altogether.

constant

cause a net expansion

Second,

IOL+

the species can per unit

selection can operate to favor smaller

home range size scales allometrically

hold its numbers

rules or

may be of unusually

to result in far fewer individuals

the species can reduce its body size-i.e.,

individuals-since

with body size. Fourth,

the species

but expand its home range size, which, in turn, must eventually

in its total geographic

range. Only two of these theoretical

are likely to be readily visible in the fossil record: geographic

that can be used as ecological

such a transformation

reduction

options

of body size or expansion

01

range.

Data on grasshopper via range expansion. those of similar-sized lower densities

mice suggest that they faced this density dilemma Oryhomys

species have home ranges significantly

herbivorous

than similar-sized

1979; Nowak Sr Paradiso,

species;

as a consequence,

herbivorous

species (Blair,

they occur in significantl!. 1953; Carleton

1983). W’hether their overall geographic

mice

do not appear

to have

and resolved it

larger in area than

unclear.

Grasshopper

resolved

reducing

overall body size. The living species are approximately

& Eshelman,

range has increased

the density 20-30

dilemma

is I,!

g (0. torridus) and

40-50 g (0. leucogaster) in weight. As summarized by Carleton & Eshelman ( 1979). the fossil record of grasshopper mice goes back to the late Hemphillian or very early Blancan (approximately 4 m.y. ago). The two lineages, leading to the modern 0. leucogaster and 0. torridus, increase in size from their first appearance to the late Blancan, remain stable in size through much of the Pleistocene, Their

present,

and

apparently

and then diminish original,

body

to close to their original

size is roughly

(inferred)

comparable

size.

to that

of

non-carnivorous rodents such as Peromyscus. The data on giant pandas are more- dificult to interpret. M’e compared the size of the giant panda’s home range with that of the American black bear (lJr.ws nmericanus), which is more carnivorous

and of similar body size. There are considerable

black bears. For example, hectares-but

published

variations

in the data

on

home ranges for black bears are as small as 235-505

these figures arc for an island population

where space is limited (Lindzey

Meslow, 1977, cited in Nowak & Paradiso, 1983) -to as large as Idaho (Amstrup & Beecham, 1976, cited in Nowak & Paradiso, pandas, as herbivores, would be expected to have smaller home black bears. Indeed, the reported home range size for giant pandas

&

1600-13,030 hectares in 1983). In contrast, giant ranges than carnivorous is 250 hectares, or about

THE

equal

to the smallest

the prediction What the

home

range

home

ranges,

about

is difficult

in numbers

to factor

since

Another

the

total

Giant

factor

considerably,

BECOMING

reported

for black

home

bears.

Thus,

this

giant

conli)rm

is the effect of the overall geographic

is that

home

pandas

to

decline

may well have been even smaller

in their

comparison

pandas’

giant

way.

pandas

ranges

of individuals

in

and

on giant

pandas’

3H3

A PREDATOR

but only m a general

number

complicating

sometimes

OF

into the data

of this species.

past

COSTS

black

ranges

today

range bear

was

itt

higher.

ranges

overlap.

are not overlapping.

]JI

giant pandas must leave their home ranges to seek out other pandas during their mating season (Chorn & Hoffman, 1978, cited in Nowak & Paradiso, 1983, p. 976).

ht,

Since

the point

hominid

evolution,

of comparing

1982, 1984, for reviews size, is also related Martin

(1981)

metabolic altricial

has proposed

brains.

extended

developed Altricial

period

suc~h species,

litters

diet.

(set Slartin.

size, like home

though

on fetal brain

to maternal

is to illuminate

attention

Brain

pyramid,

constraint

rangc~

not so dirrctly~.

growth

Carnivores

is matcrrntf

typically

periods.

having

small

bodies,

eyes and ears, and relativcly~

frequently

keep

are long;

closed

Altricial

ha\e

brief gestation

In contrast.

periods

here).

in the trophic

related

in this paper

also warrants

after

at birth, species

carnivores

discussed

the major

large

ofdependency.

gestation

position

is in turn

in fairly

and

size and growth

of the points

that

which

born

us11al1y poorly small

of many

to a species’

turnover, young.

herbivores

the issue of brain

their

young

in nests

precocial

young

typify hcrhivorous

litter

sizes are small;

or dens

young

\~un,g

a~‘(’

during

are born

their

spuk.

I II

larger

\vith

larger brains; neonates are physically advanced and can often carry out adult litnctiotrs such as feeding and walking shortly after birth. The relationships between neonatal tjraitr weight (E,,) and adult brain weight (E,) reported by Martin (1981. p. 58) arc: J

N

f’

(5) log E;, = 0.99 log E, + 0.42 Altricial mammals:

0.99

71