Coping with Environmental Variation:
Temperature and Water
Photo of differential drought stress tolerance in 2 genotypes of Arabidopsis thaliana from
http://www.riken.jp/en/research/rikenresearch/highlights/7320/
The Ecological Niche
Key niche dimensions include:
Energy availability
Availability of other resources
Physical conditions (e.g., pH)
Figure from Bruno et al. (2003) Trends in Ecology & Evolution
Generalists & Specialists
Two species with the same niche breadths along both niche axes
Water Availability
(resource & physical condition)
Species 1
Species 2
Temperature (C)
Generalists & Specialists
Species 1 has a narrower niche breadth along both niche axes
Water Availability
(resource & physical condition)
Species 1
(Specialist)
Species 2
(Generalist)
Temperature (C)
Generalists & Specialists
Individuals with much narrower niche breadths
than their respective populations
Water Availability
(resource & physical condition)
Species 1
Specialist?
Species 2
Generalist?
Individual
Temperature (C)
Stress Tolerance
Range of environmental tolerances helps determine
potential geographic distribution
(fundamental niche)
Photo of saguaro in Sonoran Desert and range map from Wikimedia Commons
Tolerance & Avoidance of Stress
To reduce exposure to, or consequences of, environmental stress:
physiological changes, e.g., drought deciduousness
Photo of dry season Tabebuia aurea from Wikimedia Commons
Tolerance & Avoidance of Stress
To reduce exposure to, or consequences of, environmental stress:
behavioral/physiological changes, e.g., dormancy (highly reduced metabolic
activity), torpor (reduced met. & temp. in animals), hibernation (extended
torpor); winter sleep / denning (extended sleep with slight reduction in temp.)
Hibernating northern bat in Norway from Wikimedia Commons
Tolerance & Avoidance of Stress
To reduce exposure to, or consequences of, environmental stress:
behavior, e.g., migration
Migration routes for some champion avian migrants from Wikimedia Commons
Acclimatization
Usually reversible physiological, morphological or behavioral
adjustment by individuals to reduce stress
(under lab conditions = acclimation)
Photo of Mt. Everest base camp from https://studentadventures.co.uk/adventures/everest_base_camp_trek
Adaptation
Ecotypes are populations adapted to local conditions
Image re Clausen, Keck & Heisey’s (1948) classic study from http://www2.nau.edu/~gaud/bio300w/ecotype.htm
Temperature
Enzymes have physical optima
Isozymes’ optima differ
Denature at high temp.
Lower activity limit  -5 C
Image from https://wikispaces.psu.edu/pages/viewpage.action?pageId=112526688&navigatingVersions=true
Temperature
Influences the properties of biological membranes
Image of cell membrane from Wikimedia Commons
Thermal Energy Balance (Plants)
Energy input vs. energy output determines an object’s
heat energy change (and internal temp.)
Hplant = SR + IRin – IRout  Hconv  Hcond – Het
Cain, Bowman & Hacker (2014), Fig. 4.8
Thermal Energy Balance
Boundary layer lowers convective heat loss
Cain, Bowman & Hacker (2014), Fig. 4.11
Thermal Energy Balance (Animals)
Ectotherm – regulates temp. through
energy exchange with environ.
Hectotherm =
SR + IRin – IRout  Hconv  Hcond
Endotherm – relies primarily on
internal heat generation
Hendotherm =
SR + IRin – IRout  Hconv  Hcond + Hmet
Photos of basking snake and weasel from Wikimedia Commons
Thermal Energy Balance (Animals)
Cain, Bowman & Hacker (2014), Fig. 4.16 A
Properties of Water
Maximum density at 3.98 C
High heat capacity – ratio of change in heat
energy to change in temperature
Photo of water in 3 physical phases from Wikimedia Commons
Properties of Water
Universal solvent for biologically important solutes
“Water is the medium in which all biochemical reactions
necessary for physiological function occur”
Quote from Cain, Bowman & Hacker (2014), pg. 98; photo of bacteria grown from Lake Whillans (beneath
Antarctic ice sheet) from http://www.nature.com/news/lakes-under-the-ice-antarctica-s-secret-garden-1.15729
Water and Biology
Organismal water content for normal physiology
60% to 90% of body mass
Salt balance is intimately tied to water balance
Infra-red camera trap photo of bat at Peruvian mineral lick from
http://news.mongabay.com/2008/0714-hance_bats_atbc.html
Water Potential
Flows along potential energy gradients (high to low)
Gravitational potential – owing to gravity
o = Osmotic potential – negative, owing to solutes
p = Pressure (turgor) potential – positive, owing to pressure
(negative if under tension)
m = Matric potential – negative, owing to attractive forces on
surfaces (e.g., large molecules, soil particles)
Water potential = o + p + m
Resistance – force that impedes movement of water
(its reciprocal is conductance)
Water Potential & Transpiration
Daytime – decreasing water potential gradient from soil,
through terrestrial plant, to atmosphere
Cain, Bowman & Hacker (2014), Fig. 4.20
Allocation Tradeoff
Root-shoot ratio
Cain, Bowman & Hacker (2014), Fig. 4.22
Water & Salt Balance in Teleost Fishes
seawater < teleost < freshwater
Hypoosmotic
Cain, Bowman & Hacker (2014), Fig. 4.24
Hyperosmotic
Water & Salt Balance in Terrestrial Animals
Exchange gases in dry environment (low water potential)
Some adaptations to lower evaporative loss & water stress:
High skin resistance
Habitat selection (sufficient water to replace losses)
Metabolic water
High renal efficiency
Image of camels in Chad from Wikimedia Commons
Scaling
Many scaling relationships can be expressed as power laws:
Y = c Xs
X is the independent variable – measured in units of a
fundamental dimension; c is a constant of proportionality;
and s is the exponent (or “power” of the function)
The relationship is a straight line on a log-log plot:
Log10(Y) = Log10(c) + s  Log10(X)
…and by rearranging, this is the form of the familiar equation for a straight line:
y = mx + b
Scaling
Consider the scaling of squares & cubes as functions of the
length of a side (the fundamental dimension)
Area = Length2
Area  Length2
Surface area = 6 * Length2
Surface area  Length2
Volume = Length3
Volume  Length3
Scaling
120
2
Y = X2 y = x
100
(accelerating
function)
Area
80
60
40
20
0
0
2
4
6
Length
8
10
12
Scaling
120
2
Y = X2 y = x
100
(accelerating
function)
Area
80
60
40
20
0
0
2
4
6
Length
8
10
12
Scaling
120
2
Y = X2 y = x
100
(accelerating
function)
Area
80
60
40
20
0
0
2
4
6
Length
8
10
12
Scaling
3.5
120
2
Y = X2 y = x
(accelerating
function)
Area
80
Y = 2X
3
Log10(Area)
100
60
40
20
2.5
y = 2x
2
1.5
1
0.5
0
0
0
2
4
6
8
10
0
12
Length
0.2
0.4
0.6
0.8
Log10(Length)
Etc…
1
1.2
Scaling
700
Log10(Surface Area)
3
2
Y = 6 * yX=26x
Surface area
600
500
(accelerating
function)
400
300
200
100
= 2x + 0.7782
Y = y2X
+ 0.778
2.5
2
1.5
1
0.5
0
0
0
2
4
6
8
10
0
12
Length
0.2
0.4
0.6
0.8
Log10(Length)
Etc…
1
1.2
Scaling
3.5
1200
3
Y = X3 y = x
(accelerating
function)
800
600
400
2.5
2
1.5
1
200
0.5
0
0
0
2
4
Y = 3Xy = 3x
3
Log10(Volume)
Volume
1000
6
8
10
0
12
Length
0.2
0.4
0.6
0.8
Log10(Length)
Etc…
1
1.2
Scaling
Consider the ways in which surface area & volume
of a sphere scale with its radius
Surface area = 4  r2
Surface area  r2
Volume = 4/3  r3
Volume  r3
Scaling
Surface-to-volume ratio:
Surface area  r2
Volume  r3


Surface area1/2  r
Volume1/3  r
Surface area1/2  Volume1/3

Surface area  Volume2/3
Scaling
Slope = 1
1400
Log10(Surface area)
Y=4.83 * X
1200
Surface area
3.5
y = 4.8352x0.6667
0.667
1000
800
600
(decelerating
function)
400
200
y = 0.6667x* +X0.6844
Y=0.667
+ 0.68
3
2.5
2
1.5
1
0.5
0
0
0
1000
2000
3000
4000
0
5000
Volume
1
2
3
Log10(Volume)
Etc…
Volume increases
proportionately faster
than surface area
4
Scaling
Slope = 1
1400
Log10(Surface area)
Y=4.83 * X
1200
Surface area
3.5
y = 4.8352x0.6667
0.667
1000
800
600
(decelerating
function)
400
200
y = 0.6667x* +X0.6844
Y=0.667
+ 0.68
3
2.5
2
1.5
1
0.5
0
0
0
1000
2000
3000
4000
0
5000
Volume
1
2
3
Log10(Volume)
Etc…
This simple fact has
myriad important
implications for biology
(e.g., heat exchange)
4
Scaling
Assuming ecotothermy and environmental ceteris paribus,
which one (dino or frog) warms up (or cools down) fastest?
Paedophryne amauensis
Image of dinosaurs and world’s smallest known vertebrate from Wikimedia Commons