Adaptations to the Physical Environment Chapter 3 Ecology: Evolution, Application, Integration...

Adaptations to the

Physical Environment

Chapter 3

Ecology: Evolution, Application, Integration

Ecology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press

Concepts

• 3.1 How Do Environmental Factors Limit Growth and Survival?

• 3.2 What Adaptations Avoid Harsh Conditions?

• 3.3 How Do Physiological Adaptations Alter the Organism’s Tolerance Limits?


How Do Environmental Factors Limit Growth and Survival?

Physical resources

The inorganic materials or energy

organisms require for existence

Physical (abiotic) factors

Physical conditions that affect growth

and survival


Shelford’s Law of Tolerance (1913)

• There are upper and lower limits to the physical factors an organism can tolerate.


Shelford’s Law of Tolerance

• Species differ in the factors that limit their growth and in their ranges of tolerance.

• Deleterious effects that occur outside the range of tolerance depend on the specific physical factor.

• Beyond the tolerance limits, organism’s fitness is compromised.– Often associated with an organism’s inability to

maintain homeostasis


Role of Evolution In Shaping The Tolerance Curves

• This tolerance curve represents the tolerance limit of the entire population.

• The tolerance curves of individuals vary and some of this variation is genetically determined.

• What implications does this have for evolution?


Role of Evolution In Shaping The Tolerance Curves

• If the environment changes, some individuals may be better able to tolerate the new range of conditions. – If these differences have

genetic basis, they will be selected for.

• Directional selection shifts the population tolerance limit.


Environmental Conditions Change in Time

• Some temporal variability is predictable (blue line)– Seasonal– Diurnal– Tidal

• Environmental conditions can also change unpredictably (orange line)

• Temporal variation in the physical environment poses a significant challenge to the organism’s fitness.

• It is much simpler to adapt to a constant environment than to a variable one.


The Principle of Allocation

• Adaptations to one challenge may preclude or reduce adaptations to others (Levins, 1968)

• Adaptation involves evolutionary trade-offs– There are costs and benefits to every

adaptive solution


Two Categories Of Adaptive Responses

Avoidance

• Behavioral avoidance• Migration

• Metabolic avoidance• Metabolic rate

depression• Hibernation• Estivation

Adaptations

• Traits that match the organism’s tolerance limits to the physical conditions it faces• Behavioral• Morphological• Physiological• Biochemical


Avoidance AdaptationsMetabolic Avoidance

• Dormancy– Seeds– Spores– In some unpredictable

habitats, dormancy can be indeterminate (until the conditions improve).

• Metabolic arrest• For example, brine shrimp,

water bears (tardigrades), rotifers

Slows down the biological clockEcology: Evolution, Application, Integration David T. Krohne Copyright © 2015 Oxford University Press


• Torpor• Usually in response to cold

and food deficiency• E.g., hummingbirds• Prolonged

torpor=Hibernation• E.g., bears, ground squirrels

• Estivation• Usually in response to

drought and heat• E.g., snails

Slows down the biological clock



• Must enter hibernation each year

• Accumulate significant fat reserves

• Metabolic rate and body temperature drop

• Heart rate and respiration slow down

• Kidney function often ceases

• Quickly enter a torpid state

• Quickly aroused by external stimuli.

• Drop in the metabolic rate and body temperature not as deep as in the obligate hibernators

Obligate hibernators Facultative hibernators


Benefits of Hibernation

• Avoidance of harsh conditions

• Protection against predators

• Survival of hibernators (orange) is higher than in physically and ecologically similar non-hibernators (blue)

• What may be the costs of hibernation?

Bats

Other mammals


Avoidance AdaptationsBehavioral Avoidance

• Migration—the seasonal movement from one region to another and back

• May be obligate or facultative • Advantageous when the abiotic challenges are

seasonal and predictable• External stimuli serve as cues for migration


Avoidance AdaptationsBehavioral Avoidance: Large Scale

• Migration—the seasonal movement from one region to another and back

• May be obligate or facultative

• Advantageous when the abiotic challenges are seasonal and predictable

• External stimuli serve as cues for migration


Benefits and Costs Of Migration

Benefits

• Avoid harsh environmental conditions

• Expand resource base by separating breeding and overwintering grounds

Costs

• Considerable energy cost

• High risk of mortality


Avoidance AdaptationsBehavioral Avoidance: Small Scale

• Behavioral thermoregulation– Moving to spots with more

favorable temperatures– Basking– Modifying posture

• Contact with the substrate• Affects heat exchange by

conductance and convection

• Local stress and predator avoidance– Burrowing– Nocturnal behavior


Adaptations to the Physical Environment Chapter 3 Ecology: Evolution, Application, Integration...

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