EEB 2244: Adaptations to the Environment

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Adaptation to the Environment

Overview:

Adaptation to terrestrial environments

Variable environments and phenotypic plasticities

Environmental stressors threaten to disruption an organism's homeostasis

Water (lack of)

Heat

Cold

Food and nutrients

Not mutually exclusive

Physical Properties of Environments Dictate Stresses

In what biome. would. we most expect a combination of cold and water stress to affect the organisms living there?

- Tundra

Water Stress

Conserve

Eliminating salts and other toxins (NH3) often involves water intake and urine excretion

Water loss is reduced through:

production of concentrated urea or. ureic acid (containing NH3)

Large specialized kidneys and other salt excreting organs

Water acquisition and transport

driven by evapo-transpiration through stomata

cohesion and tension "pull" water through plant

Water loss can be minimized by closing or sheltering (underneath hair or in pits) stomata

Role of Soils

Water availability impacted soil properties

Small particles--> more surface area, cohesion and adhesion

Small: more held, but tightly

Large: loosely held, but less

Soils with a good mix often best for plants:

Loam: 40% sand, 40% silts, 20% clay

Tolerate

Tolerating air embolisms in dry environments can help plants survive

Smaller leaves with more major veins reduce the impact of air embolism

Tolerate: allow to happen while dealing well with or minimizing. the consequences

Alternate Pathways for Photosynthesis

C3 photosynthesis (most plants)

use of rubisco--> energy loss when stomata are closed--> need to keep open more often

Not good in hot, dry environments

C4 & CAM photosynthesis increase water-use efficiency:

Different enzyme: PEP (phosphenol pyruvate)

Separate photosynthesis into different cells (C4) or different times of the day (CAM)

Store

Storing water for a "non-rainy day" can be an important adaptation in dry environments

Heat Stress:

Reduce Input/ Evade/Avoid

Thermoregulation: ability to regulate temperate

Endotherm:

Ectotherm:

Behavioral avoidance of heat stress

Morphological adaptations (waxy cuticle, hairs reflect heat)

Dissipate

Increasing surface area--> increased exchange of heat energy with the environment

Bergmann's rule: smaller size organisms in warmer environments at lower latitudes (higher surface area to volume ratio)

Tolerate

Homeotherm:

Poikilotherm:

Cold Stress:

Tolerate

Many amphibians can avoid tissue damage while "freezing solid"

Willow tit tolerates-lower body temperature at night (nocturnal hypothermia)

Hibernation

Individuals reduce energetic costs by lowering heart rate and decreasing body temperature; common in mammals

Nutrient Stress:

Many strategies for coping with nutrient stress involve biological interactions

fungal and bacterial associates aid in nutrient acquisition (typically in exchange for carbon products)

Root Structure

Food Stress: Storage

Plants store carbohydrates in roots and stems

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Variable Environments and Phenotypic Plasticities

Phenotypes

Influenced by genotype and the environment

Fixed or variable over time and space

Phenotypic Trade-offs

A phenotype well-suited to one environment may be poorly suited to others

Phenotypic Trade-off: higher fitness is achieved by different phenotypes different environments

Phenotypic Plasticity

The ability of a single genotype to produce multiple phenotype

Depends on the "honest" environmental cues

One genotype, multiple "options"

Predator cues ---> long tail

No predator cues ---> short tail

Detecting and responding to cues takes energy

Non-variable (stable) environments favor fixed phenotypes

Variable environments and phenotypic trade-offs favor plasticity

Responses to:

Biotic variation (enemies, competition, etc..)

Abiotic variation (temperature, water, salt, oxygen, etc..)

Rapid responses often reversible (behavior, physiological acclimation)

Slower responses (morphology, life history) often irreversible

Plastic Foraging Behavior

Different feeding strategies represent different behavioral phenotypes

Changes in diet composition, foraging locations, time spent foraging

Optimal Foraging Theory:

Central Place Foraging

Costs=travel, search, handling times

Benefits= energy gained

Organisms should. maximize the ration of times

Diminishing returns: benefits decrease as patch is depleted

Risk Sensitive Foraging

Risk of predation can be a cost

Foraging influenced by the presence of predators

Higher risks cane offset by higher food benefits

Strategies to Survive Extreme Environmental Variation:

Scale of variation influences response type

Strategies to survive extreme. variation include storage, migration, and dormancy

Migration

Seasonal movement from on region to another

Conditions so severe that individuals cannot acclimate (or necessary changes would be too costly)

Dormancy

Reduce metabolism due to conditions that prevent normal functioning

Diapause- partial or complete physiological shutdown

Hibernation- dormancy during winter in response cold or difficulty finding food

Torpor- brief period of dormancy to deal with cold conditions

Aestivation- dormancy during the summer in response to hot or dry conditions