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1

The Problem with Giants

wild

fact

.com

Livyatan melvillei

2

Gigantism – Giants Defined

• Largest species in an ecological community

• Largest species in an ecological guild

• Largest species in a clade

skyw

alke

r.co

chis

e.ed

u

3

Nonrandom Distribution of Giants

• Cope’s Rule – within a lineage, body size increases through time

4

Nonrandom Distribution of Giants

• Gigantism through timeV

erm

eij (

2016

)

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2

5

Evolution of Large Size

• Large size must have advantages• Relatively lower food requirements

• Obtain a higher proportion of available resources

• Lower locomotion costs (b = -0.2 to -0.4)

• Less vulnerable to predators

mfood = mbody3/4

i.telegraph.co.uk

• Transport in directed systems

6

Supply-Demand Dynamics

B = m3/4

B = (m(rs/rd))D/(D+1)metabolic

rate

supply rate demand rate

dimension

mass

Which simplifies to…

Banavar, et al., 2002

7

Supply-Demand Dynamics

equa

tion-

of-t

he-m

onth

.blo

gspo

t.co

m

b = 0.73

8

Supply-Demand Dynamics

• Scaling of heart rate with heart mass M

achi

da a

nd A

ohag

i (20

01)

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3

9

Types of Allometric Scaling

• Structural scaling(b ~ ⅓ multiples) –based on A-V processes

• Metabolic scaling(b ~ ¾) – based on fractal processes

• Frequency scaling(b ~ -¼) – based on fractal processes

••• • ••

www.buriedtreasurefossils.com

•

= nutrient foramen

•• Pagel’s ‘everyanimal’

• Using present to reconstruct past – constrains past to be like present

• Overreliance on lines of best fit produces ‘average’ animals

• Sequential extrapolations compound averaging in reconstructions

10

Through a Glass, Darkly

ww

w.e

dge.

org

• Size-related changes in scaling• Running speed in quadrupedal mammals

11

Through a Glass, Darkly

Iria

rte-

Día

z(2

002)

cursorial

non-cursorial

30 kg

• Size-related changes in scaling• Swimming speed in bony fishes (□) & cetaceans (▲)

12

Through a Glass, DarklyIr

iart

e-D

íaz

(200

2)

6/8/2019

4

• Size-related changes in behavior• Acceleration in bony fishes (□) & cetaceans (▲)

13

Through a Glass, Darkly

Iria

rte-

Día

z(2

002)

14

Through a Glass, Darkly

15

Upper Limits on Size

• Factors affecting maximum size1. Skeletal support & locomotion

2. Metabolism & thermoregulation

3. Feeding mode & trophic level

4. Environment

www.unexplained

‐mysteries.com

16

1. Skeletal Support & Locomotion

• Skeletal mass must increase faster than body mass• Positive

allometry for bone diameter

Sch

mid

t-N

iels

en (1

984) b = 1.13

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5

2. Metabolism & Thermoregulation

• Thermal strategies• Endotherms (red area)

• Heterotherms/Mesotherms (gray area)

• Ectotherms (green area)

17Ferrón et al. (2017) 18

3. Feeding Mode & Trophic Level

• General trend – animal body size increases at higher trophic levels• Needed to subdue prey

• BUT… are largest animals always top carnivores?• Prey become rarer &

less predictable at higher trophic levels –requires movement over longer distances

19

3. Feeding Mode & Trophic Level

• Giant animals should occur where prey are abundant & incapable of escaping

redm

ehra

pens

min

.blo

gspo

t.co

m

en.wikipedia.org

4. Environment – Aquatic

• Filter-feeders are largest marine animals –carnivores consistently smaller

• Thermal constraints at largest sizes?

• Role of productivity

20carnivoraforum.com

www.north-slope.org

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6

21

4. Environment – Land (Herbivores)

Ullm

ann

et a

l. (2

017)

Hen

ders

on (

2013

)

en

.wik

ipe

dia

.org

22

4. Environment – Land (Carnivores)

en

.wik

ipe

dia

.org

Gar

land

(19

83)

23

4. Environment – Aerial

Sato, et al. (2009)

en.w

ikip

edia

.org

• Scaling relationships = models for expected changes in shape as size increases

• Intrinsic factors • Skeletal support

& locomotion

• Metabolism & thermoregulation

• Feeding mode & trophic level

• Extrinsic factors• Environment &

productivity24

Summary

iliketowastemytime.com

Titanoboa