BODY SIZE
Basic conditions for life
8. Non-eccentric
orbits to avoid
collisions
1. Source of
constant and
stable energy
7. Carbon
and oxygen
2. A terrestrial
planet
4. Need a
satellite
star
5. Near
circular
orbit
6. The right place in the galaxy
A basic principle:
Energy
BIOMAS
SPECIES
Body size
Number of
species
Abundance
Ecological /
Evolutionary
forces
Why a species has the
body size it does?
Optimum
trade-off
Cost
Benefit
Body size
Evolutionary forces: source availability
Large individuals use ↑ Resources
Small individuals use ↓ Resources
Environment’s role
Resource available ↓
Resulting body size ↘
Resource available ↑
Resulting body size ↗
Evolutionary forces: source availability evidence
41,000 y BP
12,000 y BP
Extinct 9,500 y BP
Individuals 25% smaller were
found in a small island
Fossils dated 7,000–4,000 yr BP
No humans
Russia
Alaska
No glaciation
Dwarfing most likely due to
limited resources
Vartanyan et al., Nature 1993
Evolutionary forces: ecological forces
PREDATION
PREY
Expected size
PREDATOR
Smaller is
better
Bigger is
better
Evolutionary forces: ecological forces
Distribution of organisms
Competition
Time
Time
Resource variation
By specializing, species use a
smaller spectrum of available
resources… so they have to
compromise either their size
or their abundance
Evolutionary forces: ecological forces
Competition: Soule 1966 classic work
Smaller is
better…
…or
rather
smaller is
forced
Types of competition: by interference & by exploitation
BY INTERFERENCE: one species prevent other species of accessing a limiting resource.
Example: Territorial damselfishes
competing for benthic algae
How will body size change
over time under this type
of competition among
species?
Competition
BY EXPLOITATION: two o more species have free access to a limiting resource
and variation among species in competitive abilities will
determine variations in species performance: eg. growth,
reproduction.
Such sort of competition is common among species that compete
for resources that are not defensible spatially.
Example: Damselfishes of the genus Chromis competing for plankton
How will body size change
over time under this type
of competition among
species?
Evolutionary forces: ecological forces
Competition and the Taxon Cycle (E. O. Wilson 1961)
Abundance
Body size
Evolutionary forces: climate
Clarke & Jonhston, J. Ani.Ecol. 1999
Energy required to maintain metabolisms increase
with increasing temperature
In laboratory experiments, for every 2
degrees the scientists cranked up the
temperature, various types of fruit flies
decreased anywhere from 3 to 17
percent. For fish, the shrinking was even
more pronounced, from 6 to 22 percent
A male frog specimen from Mount Kinabalu in
Malaysia
1980s
2008
Everything else being equal
Body size should reduce with increasing
temperature
Sheridan & Bickford, Nature Climate Change 2011
Evolutionary forces: hunting
40,000 years
Wallaroo
Tasmanian devil
Koala
Flannery Book 1994
Nothing explains this reduction in body size better than the fact that humans colonized the
islands some 40,000 years ago and that humans liked bigger animals
Selection on the fittest
Evolutionary forces: fishing
1957
1980
2007
MacClanaham Conservation Biology 2009
Jackson et al, Science 2001
Geographical variations in body size: Bergmann's rule
Body size increases with colder temperatures
2
2
Mass=8
Area=24
Area/Mass=3
A lower area/mass ratio helps
to conserve heat which is
very adaptable in cool
temperature
2
Roberts DF (1978) Climate and human variability
1
1
1
Mass=1
Area=6
Area/Mass=6
A higher area/mass ratio
helps to dissipate heat
which is very adaptable in
warm temperature
Geographical variations in body size: Allen's rule
Limbs and other appendices are shorter and more compact in individuals living
in colder temperatures
The greater the exposed surface area, the greater the loss of heat and therefore energy
Mass=8
Area=24
Area/Mass=3
Will conserve more heat, which is better
in colder environments
Mass=8
Area=28
Area/Mass=3.5
Will dissipate more heat, which is better
in warmer environments
Geographical variations in body size: Cope's rule
Lineages tend to increase in body size over evolutionary time
Size benefits survival, mating
success and fecundity (Hone &
Benton, Trends Ecol. Evol. 2005)
Geographical variations in body size: Island rule
Insular body size of terrestrial mammal as percentage of
body size of the species on the mainland (Sm)
Small
species get
larger
Ecological
release
Large
species get
smaller
Resource
limitation
Why shall we care about patterns in body size?
Because body size influences the risk of becoming extinct
Forero et al., Biota Neotrop 2009
Why is this important
Mammalian body mass by
current extinction risk
Davidson A D et al. PNAS 2009;106:10702-10705
Why is this important
Rapid body size decline in Alaskan Pleistocene
horses before extinction
Guthrie, Nature 2009
Current declines in body size are
worrisome sings of extinction
In summary
Resources
Interactions: predation, competition
Determinants
Climate
Human driven evolution
Body size
Bergmann's rule: Body increase with
latitude
Patterns
Allen's rule: Limbs and other appendices get
shorter in colder areas
Cope's rule: Body increase with evolutionary
time
Island rule: On islands large species get
smaller and vice versa