Lecture 3Hope organisms cope（应对） with

their environment

Principles of EcologyEben Goodale

College of Forestry, Guangxi University

Last week’s comprehension test and some thoughts

• Rather than read lecture notes after class, let’s read them before.

• By Thursday / Sunday afternoon, lecture notes will be available on web.

• Still working on readings; eventually these may replace the lecture notes.

• Tuesday March 30, I am away; my wife will fill in.• Apr 4 we will have another comprehension test, this

time worth participation points.

Today’s class

• How do organisms cope with variation（变化） in the environment? Species’ responses and ranges

• Species responses to variation in – Temperature– Water

• How species obtain energy

Review of last time

• Biomes（生物群落） are broad categories of communities that allow us to understand the diversity of climates and vegetation in a simple way.

• We “toured” the diversity of biomes.• How do organisms live in some of these

extreme environments?• The case of the frozen frogs.

The organism’s range

• An organism has two solutions to coping with difficult conditions: to “tolerate（忍受）” or to move.

• The non-solution: to die!

The organism’s range

• So each species has a range of（范围） environmental conditions over which it can live.

• It’s realized range 实际范围 (where it actually occurs) might be different from its fundamental range 理论范围 (where it could occur)

How does an organize cope with its environment?

• An individual can acclimatize（适应） during its lifetime. Example: people getting used to high altitudes.

• Or a population can adapt（适应） through natural selection:– Some individuals have a trait that makes them better

suited than others to the environment. They survive and reproduce better.

– This trait is hereditable, and over time comes to spread in the population.

• Note that an individual doesn’t adapt.

Temperature• Temperature is an important determinant of

an organism’s survival and reproduction.• Enzymes work at a certain range of

temperatures and denature when overheated.• Freezing can disrupt and puncture cells.

Gaining and losing heat• Conduction: heat moves from colder to

warmer body by direct contact.

• Convection: the water or air moves across the surface of a body (occurs in a fluid).

• Radiation: transfer of heat through electromagnetic waves.

• Evaporation: change in the state of water from fluid to gas reduces (uses) heat.

• In living things, heat can also be made through metabolism (break down of food)

Tea cup gets hot.

Loss of heat from tea to air

Micowave tea.

Water turns to steam.

Hs = Hm ± Hcd ± Hcv + Hr - He

For plants• Plants mostly lose heat

by being able to lose water through their leaves (specialized type of evaporation called transpiration)

• Have special cells in the bottom of their leaves called stomates（气孔） that allow water out.

• But with loss of heat comes loss of water.

Hs = Hm ± Hcd ± Hcv + Hr - He

Desert and artic plants

Hs = Hm ± Hcd ± Hcv + Hr - He

Hs = Hcd - Hcv + Hr

Plant trying to lose heatwithout losing water

Away from ground decreases conductionOpen structure increases convection

Leaves are reflective to decrease radiation Dark or light pigment?

Leaves are parallel to sunlight to decrease radiation

For deserts

Textbook gives example of pubescence (little white hairs) increasing reflectance in desert plant.

Desert and artic plants

Hs = Hm ± Hcd ± Hcv + Hr - He

Hs = Hcd - Hcv + Hr

Plants trying to gain heat

Close to ground increases conduction Low surface area decreases convection

Leaves are absorptive to increase radiation dark or light pigment?

Leaves are perpendicular to light

For artic plants

For animals• Some animals are

endoderms（内胚层） and regulate temperature through internal heat generation.

• Rest of animals are ectotherms（变温动物） , regulate body temp through energy exchange with environment

Hs = Hm ± Hcd ± Hcv + Hr - He

Which animals?

For animalsSmall animals have large surface-area-to-volume ratio

1 m

2 m

Surface area: 6 m2

Volume:

Surface area to volume:

1 m3

6 m2

1 m3= 6

1m

24 m2

8 m3

24 m2

8 m3= 3

1m

Surface area:

Volume:

Surface area to volume:

So do you expect endotherms to be big or large?

What other adaptations do endotherms have to retain heat?

Some endothermic animals undergo torpor（麻木） or hibernate

• Especially important for small animals like rodents and hummingbirds.

Maintaining a water balance

• Lack of water clearly a problem for terrestrial organisms.

• But maintaining water also difficult as we will see for freshwater animals whose internal fluids have more solutes than the water around them.

Water balance in plants• We all know that water flows

downhill, away from high gravitational potential energy levels.

• Water also flows to where it is less concentrated, away from “high osmotic”, or more generally, “high water” potential.

• Such flow explains “turgor pressure（膨压）” of plant cells: water flows in because cell has more solutes, putting pressure on the hard cell walls.

How can we tell when a planthas low turgor pressure?

Water balance in plants

• Remember that plants need to transpire to lose heat.

• The water that’s lost makes the water potential of the leaf higher than the air, and this causes water to continue to leave.

• This is called “transpirational pull”.

Water balance in plants

• Water also has the property that molecules stick to each other chemically.

• Hence a column of water is pulled out of the leaves from the roots and soil.

• Even for a 75 m Sequioa tree (think of pull of gravity that is offset)!

Water balance in plants

The drier the environment, the more plants invest in roots to extract water.

Water balance in animals

• Teleost fish (96% of living fish) developed in freshwater.

• In freshwater they have the problem of being hyper-osmotic 高渗透压 (more salt inside than out), and need always to excrete water.

• In the ocean, they are hypo-osmotic低渗透压 , and need to continually drink water.

Anadromous fish have unique problem in moving between fresh and salt water

Anadromous fish … live mostly in sea, buttravel up rivers to spawn. Young fish are hatch in freshwater, than travel to the sea.

Young fish go through dramatic physiological changes as they enter salt water for first time called “smoltification”

Physiological changes involve the Na+-K+ ATPase in fish gills, which increasesas fish prepare to enter ocean

Water balance in animals

• Many animals have hard coverings to retain water.

• The kangaroo-rat lives in deserts and minimizes water loss: it never drinks!

Water balance in animals

• It gets water from metabolism.

• It has very concentrated urine, as do other animals that conserve water.

Kangaroo rat

Respiration + energy (ATP)C6H12O6 + 6O2 6CO2 + 6 H2O

Why is there a need to have urine at all?

One of the products of metabolism is nitrogen, often NH3, a poison.

Some organisms can withstand desiccation干燥 (drying out)

• Some organisms, both plants (especially seeds) and animals, become dormant with very low levels of water inside them, then recover from dehydration when water is plentiful.

• Similar to the idea of torpor in low temperatures.

Today’s class

• How do organisms cope with variation in the environment? Species’ responses and ranges

• Species responses to variation in – Temperature– Water

• How species obtain energy

Trophic levels

• Definition of trophic:

• Autotrophic: fix carbon into organic molecules. Can be photosynthetic or chemosynthetic.

• Heterotrophic: consume the organic molecules made by autotrophs.

Organic moleculeconsists of more thanone carbon atomlinked togetherin a chain or ring.

Of or relating to nutrition.

Chemical autotrophs• Some organisms make sugars by

using energy in inorganic compounds.

• For example, some bacteria in deep sea trenches use H2S as source of energy (gives electrons).

• Not just in strange places – also in “nitifying” bacteria, which fix nitrogen, and are very important symbionts (mutualistic partners) of plants.

Chemosynthetic bacteriaIn sulfur hot spring

Photosynthesis: Intro to Light

Light like a wave（波浪） …

And also like a particle…

PAR = Photosynthetically active radiationWavelengths of light that chlorophyllis capable of absorbing.

What colors doeschlorophyll appear to us and why?

Photosynthesis

• Overall:6CO2 + 6 H2O

C6H12O6 + 6O2

+ energy (solar)

2 types of reactions

Light reactions – uses light to make ATP (energy)

Dark (light-independent) reactions – uses ATP to fix carbon

+ energy (ATP)

C6H12O6 + 6O2

6CO2 + 6 H2O

So it’s the opposite of metabolism:

Light reactions

Chloroplasts – organelles with own DNA

Light reactionsoccur insidethylakoid stacks

Light reactions

The electron transport chain produces a proton gradient acrossThylakoid(内囊体 ) membrane. Protons move across that gradient through ATP synthase, producing ATP.

What does this moving down a concentration gradient remind you of?

Dark reactions: C3

The C3 model

RuBP

PGA

Uses enzyme RuBisCoLow affinity for CO2

Calvin Cycle

Infact about 1/3 of the timetakes O2 instead of CO2

This is called photorespiration（光呼吸 );It lowers the efficiency of photosynthesis.

Dark reactions occur in stomaMaking larger strings of carbons

Different forms of photosynthetic pathway do better in certain

environmental conditions

• Photorespiration is a major problem for photosynthesis at high temperatures (> 27°C).

• One solution of plants is C4 photosynthesis（光合作用） (compared to normal “C3” photosynthesis).

• Another solution is known as “CAM pathway（景天酸代谢途径）” .

Dark reactions: C4

PEPPEP hashigh affinityfor CO2

CO2 low in mesophyll…Released Inbundlesheath

RuBP

CO2

Bundle sheathseparate,high CO2

environmentfor Calvin Cycle(in which RuBisCoInvolved)

Dark reactions: CAM

Runs the dark reactions only at night, sowater loss with CO2 uptake is low. Reactions

prepare 4 C chain like C4.

Water loss: C3: 380-900 g of H2O per g of tissueC4: 250-350CAM: 50

Disadvantages of C4 and CAM

C3 is the most efficientprocess biochemically …It doesn’t waste energy gettingthe carbon ready for the CalvinCycle. So when temperaturesare low it is more productive.

C4 and CAM are examples of convergent evolution

What is convergent evolution?

C4 and CAM evolved independently in different plant families; C4 may be as many as 30 different times.

Corn: C4

Pineapple: CAM

Saxaul tree: C4

Heterotrophs

• Consume organic compounds already produced by autotrophs. Different kinds:– Herbivores– Parasites– Predators– Detrivores

Eat other organism without killing

Kill their prey

Eat already dead organism

Much of ecology is about what you eat and who eats you!

Heterotrophs• 3 stages of eating:

– Finding and obtaining food– Consuming food– Absorbing the energy in the food.

• Tradeoff（平衡） between the quality of the food and how easy it is to find.

Bacteria: stays in place and ingests low quality food

Cheetah: high quality food,but a lot of energy to catch

How do foods differ in their quality?

• Plant materials have a high amount of cellulose（纤维素） (kind of fiber) and secondary compounds that make them difficult to ingest.

• Carbohydrates and fats high amount of energy

• Proteins have important nutrient nitrogen

The diversity of tools to consume food

Red-crossbillappears to be speciesin process of speciation(breaking apart into different species)

5 subspecies that differ in beak morphology and eat different cone types

The diversity of tools used to absorb food

• Some bacteria (single celled organisms) have organelle called vacuole where food is broken down

• Multi-cellular organisms vary greatly in their digestive systems.

• Because herbivores have low quality food, they have much surface area in digestive systems, and unique ways of re-processing（在加工） .

Cow chews “cud”Rabbits eat feces“coprophagy”

Some animals even make tools to capture, consume food

Chimpanzee termite fishing

New Caledonian crowChapter 5 Case study

From Gavin and Hunt2003

Dolphin with sponge on rostrum

The story of New Caledonian crows

What is the general idea of this figure?

From Rutz et al. 2010

What is the general idea of this figure?

From Rutz et al. 2010

Homework

• Review: Lecture 3 notes.• Problem solving: Problem on C3/C4 plants:http://sites.sinauer.com/ecology3e/problem05.html

• Primary literature: Benkman 2003.• By Thurday night:

– Lecture 4 powerpoint with notes.– Be prepared for quiz on Saturday.

Key concepts• Organisms cope with

variability in temperature and water by acclimitizing (in individual’s lifetime) or through adaptation (population level), and these factors determine species’ ranges.

• Water balance and temperature is maintained by exchange between organism and the external environment.

• Autotrophs are organisms that capture energy to make carbon-carbon bonds; photosynthesis is the powerhouse for life on earth.

• Heterotrophs eat autotrophs and differ among themselves in how they find, consume and absorb food.