Ecology Lecture 5 & 7

What is Physiological ecology?

The study of interactions between organisms and their physical environment, and how these interactions influence their survival and determine their geographic range.

How does the physical environment influence an organism’s ecological success?

• availability of energy and resources

• extreme conditions can exceed tolerance limits

what are psychological ecologists trying to understand?

The impact that the physical environment has on defining the geographic distribution of a species

What factors determine aspen distribution, and how is it predicted?

Aspen distribution is limited by low temperatures and drought. A computational approach called environmental niche modeling predicts a potential distribution that is larger than the actual distribution 🌲🌍

What is the difference between potential and actual species distribution?

• Potential distribution: where climate and resources are suitable

• Actual distribution: reduced by biological factors (competition, herbivory, etc.)

• Population abundance is highest where conditions are most favorable 📈

What is a tolerance curve and what does it represent?

A tolerance curve shows how an individual’s physiological rate (e.g., metabolism, photosynthesis) responds to an abiotic factor. It has an optimum, where performance is highest ⚡🌡

Why are tolerance curves important for population persistence?

At the optimal conditions, individuals can survive, grow, and reproduce. For populations to persist, many individuals must experience conditions near this optimum 👥🌱

What is physiological stress?

Stress occurs when environmental conditions deviate from the optimum, causing a decrease in the rate of physiological processes and lowering the potential for survival, growth, or reproduction.

What is acclimatization?

Acclimatization is a short-term, individual-level physiological adjustment that minimizes stress caused by environmental change. It can result in temporary, unregulated changes in homeostasis.

What is hypoxia and how does it affect the body at high altitudes?

Hypoxia occurs at high elevations (typically above 8,000 feet) due to lower partial pressure of oxygen, reducing oxygen delivery to tissues. This can cause altitude sickness, decreased exercise capacity, and impaired cognitive function.

How does the body acclimatize to high elevations?

Acclimatization includes increased breathing rate, increased production of red blood cells and hemoglobin, and increased pulmonary blood pressure to improve oxygen delivery. These changes are reversible when returning to lower elevations.

What is adaptation and how does it occur?

Adaptation is a long-term, genetic response of a population to environmental stress. Natural selection favors individuals with traits that reduce stress, causing those traits to become more common over generations.

What is an example of adaptation to low oxygen conditions?

Andean populations, living at high elevations for ~10,000 years, show adaptations such as higher red blood cell production and greater lung capacity, improving oxygen delivery compared to non-native populations.

How is adaptation different from acclimatization?

• Adaptation: long-term, genetic, population-level change

• Acclimatization: short-term, physiological, individual-level response
  Both reduce stress, but only adaptation increases genetic fitness across generations.

What are ecotypes and how can they lead to speciation?

Ecotypes are populations adapted to specific abiotic or biotic environments. Over time, divergence in physiology and morphology can lead to reproductive isolation and the formation of new species.

Why is temperature important for organisms?

Survival depends on internal temperature, which is controlled by energy gained and lost to the environment. Organisms must tolerate or regulate temperature.

How does temperature affect metabolism and enzymes?

Higher temperature increases metabolism up to a limit. Enzymes work best in a narrow temperature range and denature at high temperatures.

How do organisms adapt enzymes to different temperatures?

Some species make isozymes, enzymes with different temperature optima, allowing acclimatization.

How does temperature affect membranes and water loss?

Cold temperatures stiffen membranes and reduce function; warm temperatures increase membrane leakiness and water loss. Cooler-climate organisms have more unsaturated membrane lipids.

What determines energy balance in some animals?

Energy transfer processes plus metabolic heat.

Which animals generate heat internally?

Birds and mammals.

Why is internal heat generation an advantage?

It allows animals to maintain a constant internal temperature near the metabolic optimum.

How does internal heat generation affect geographic range?

It allows animals to survive in a wide range of external temperatures.

What is evaporative heat loss?

Cooling that occurs when water evaporates from the body surface.

Which animals commonly use evaporative cooling?

Humans (sweating) and dogs (panting).

How do some animals use water for cooling?

By getting wet or licking to increase evaporation.

What is conduction?

Heat transfer through direct contact between objects.

What is convection?

Heat transfer through moving air or water.

What is evaporation?

Heat loss when liquid water changes to gas.

What is radiation?

Heat transfer through infrared radiation without direct contact.

What is solar radiation?

Heat gained from sunlight

What are endotherms?

Animals that generate heat internally to maintain a constant body temperature.

What is the advantage of being an endotherm?

It allows body temperature to stay in the optimal range despite changes in the external environment.

Which animals are endotherms?

Mostly birds and mammals.

what are ectotherms?

Animals that regulate body temperature through energy exchange with the environment.

How do ectotherms regulate body temperature?

By gaining or losing heat from their surroundings.

How does temperature tolerance differ between ectotherms and endotherms?

Ectotherms generally tolerate greater variation in body temperature than endotherms.

How do ectotherms in temperate and polar regions deal with freezing temperatures?

They either avoid freezing or tolerate freezing.

How do some ectotherms tolerate freezing?

By limiting ice formation to outside the cells and reducing cellular damage.

What adaptations allow some animals to tolerate freezing?

Ice-nucleating proteins control ice formation outside cells, and solutes like glycerol and glucose lower the freezing point inside cells, as seen in the wood frog.

What advantage do endotherms have in cold environments?

They can remain active at subfreezing temperatures.

What is the main cost of being endothermic?

A high energy (food) demand to support metabolic heat production.

What is the thermoneutral zone (TNZ)?

The range of environmental temperatures where endotherms maintain a constant basal metabolic rate.

How do metabolic rates of ectotherms compare to endotherms?

Ectotherms have much lower metabolic rates across ambient temperatures than endotherms.

How does ambient temperature affect metabolic rate in endotherms?

Below the lower critical temperature and above the upper critical temperature, metabolic rate increases.

what factors influence metabolic rate?

External temperature and rate of heat loss.

What determines the rate of heat loss in animals?

Surface area-to-volume ratio.

Why do small endotherms have higher metabolic rates than large endotherms?

They have a larger surface area-to-volume ratio and lose heat more quickly.

Why do small endotherms need more food relative to their size?

Higher heat loss requires more energy and higher feeding rates.

Why is insulation important for endotherms?

It helps retain metabolically generated heat and makes endothermy efficient.

What types of insulation do animals have?

Fur, feathers, and fat, which limit conductive and sometimes convective heat loss.

How do animals adapt insulation to different climates or seasons?

Arctic mammals keep thick fur; some animals grow thicker fur in winter and shed it in summer.

Why do small mammals in cold climates have high metabolic energy demands?

They have thin fur and little fat, so they lose heat quickly below the lower critical temperature.

What is torpor and how does it help small mammals?

Torpor is a temporary decrease in metabolic rate (50–90% lower than basal), which lowers body temperature and conserves energy.

How much can body temperature drop during torpor?

Up to about 20 degrees Celsius.

When do small endotherms use torpor?

They may undergo daily torpor to survive cold nights, while longer torpor (hibernation) occurs in animals with enough energy reserves.

What is an example of an animal that hibernates?

The yellow-bellied marmot, which engages in long-term torpor during winter with regular periods of arousal.

Why is water important for life?

It is the medium for all biochemical reactions and a universal solvent for biologically important solutes.

What must organisms balance to maintain proper function?

Uptake and loss of water and solutes, primarily salts.

What is the typical range of body water content for proper physiological functioning?

Between 60–90% of body mass.

Which organisms face the greatest challenge in maintaining water balance?

Freshwater and terrestrial organisms.

Why do marine organisms rarely face water balance problems?

They seldom gain or lose too much water, and most marine invertebrates rarely have issues with water and solute balance.

How do terrestrial and freshwater organisms differ in water challenges?

Terrestrial organisms lose water to the dry atmosphere, while freshwater organisms may gain water and lose solutes to their environment.

What is water potential?

The potential for water to do work; water flows from high to low water potential.

What is gravitational potential and when is it important?

Energy due to gravity; important in very tall trees as water flows downhill.

What is osmotic potential?

Energy change when solutes are dissolved in water; water flows into areas with more solutes.

What is pressure (turgor) potential?

Energy from water moving from high to low pressure; can be positive (push) or negative (tension/pull).

What is matric potential?

Energy from attractive forces on surfaces of large molecules or soil particles; usually negative.

What units are used to measure water potential?

Megapascals (MPa).

What is the typical water potential of an aqueous system?

Usually negative; water flows from less negative to more negative water potentials.

How does atmospheric humidity affect water potential?

Air with relative humidity below 98% has very low water potential, creating a large gradient with terrestrial organisms.

Why would terrestrial organisms lose water rapidly?

Without barriers, the high water potential gradient would cause rapid water loss.

What is resistance in the context of water movement?

Any force that impedes water movement along an energy gradient, such as skin or waxy cuticles.

What does hyperosmotic mean?

more saline in the environment than the organism (organism loses water)

What does isoosmotic mean?

Same salinity as the organism.

What does hypoosmotic mean?

Less saline than the organism.

Why is water balance not a problem for marine organisms?

They live in an isoosmotic environment.

What challenges do freshwater organisms face?

They lose solutes and gain water from their hypoosmotic environment.

What challenge do terrestrial organisms face?

They lose water to the dry atmosphere.

Why must multicellular animals maintain water balance?

Because specialized organs for gas exchange, excretion, and other functions create local areas of water and solute exchange.

How can most animals help maintain water balance?

By being mobile and moving to different environments.

what is an organism’s life history?

it consists of major events related to its growth, development, reproduction, and survival.

Why do scientists study variation in life history traits?

To understand how traits interact with the environment and affect population growth.

What is a life history strategy?

The overall pattern of growth, reproduction, and survival in a species.

What shapes a species’ life history strategy?

How energy and resources are divided among growth, reproduction, and survival.

Why do individuals within a species differ in life history traits?

Due to genetic variation, environmental differences, or both.

How can genetically influenced traits be recognized?

They are more similar within families than between families

what is an example of heritable life history traits?

In bluegrass, siblings have similar age at first reproduction, growth rate, and number of flowers

why is heritable variation in life history traits important?

it is the raw material on which natural selection acts

how does natural selection act on life history traits

it favors individuals whose traits increase survival and reproduction

what is fitness in life history theory?

the genetic contribution of an organism’s descendants to future generations

why don’t organism have perfect life histories?

because constraints and trade-offs prevent unlimited reproduction and survival

what is phenotypic plasticity?

The ability of a single genotype to produce different phenotypes under different environmental conditions.

how does temperature commonly affect growth and development?

growth and development increase with temperature up to a point, then slow due to heat stress

What does allocation mean in life history biology?

how an organism divides energy or resources among different functions.

how does environment affect allocation in ponderosa pine trees?

Trees in cool, moist environments allocate more biomass to leaves; trees in hot, dry environments are shorter and stockier with fewer leaves

what is an example of discrete phenotypic plasticity?

Spadefoot toads develop either an omnivorous or carnivorous morph depending on food availability.

Is phenotypic plasticity always adaptive?

no, it must be shown to increase survival or reproduction; sometimes it is just a physiological response