Biology 205 7

Biology 205Ecology and Adaptation

Energy and

nutrient relations

Dr. Erik D. Davenport

Outline

Review of the lecture 6: water relations

What are the energy sources?

Plants take in energy: Photosynthesis in

Ecology!!!

What environmental factors regulate the

intakes of energy and nutrients for plants

and animals?

Animals take in energy: Optimal Foraging

Water Concentration

Water is not pure in

the environments.

There are many

substrates could

dissolve into water.

Which could dilute

water (less water

concentration)

Water availability

What determine whether an organism tends

to lose water or gain water from the

environment?

The tendency of water to move down water

concentrations, Water will move from high water

concentration place to low water concentration

place.

How is the water content of air measured?

The quantity of water vapor in the air is expressed conveniently in

relative terms:

Relative humidity = (x 100)

Water vapor density is measured as the amount of water vapor per

unit volume of air (how much water in the air).

Saturation water vapor density is measured as the quantity of water

vapor air can potentially hold (how much water the air can hold).

Temperature strongly influence the relative humidity -- Warm

air hold more water vapor than cold air!!!!

density or water vapSaturation

densityr water vapo

Relative Humidity

Which color

represents water

vapor density

Which color

represents

saturation water

vapor density?

True or False?

If the water content (water vapor density) in the air is

constant. Increasing the air temperature will cause

an increase of relative humidity.

This statement is True or False?

Water and salt balance in aquatic environments

Marine and freshwater organisms use complementary mechanisms for water and salt regulation.

Most marine invertebrates maintain an internal concentration of solute equivalent to that in the seawater around them. (isosmotic organisms)

Sharks, skates generally elevate the concentration of solutes in their blood to levels slight hyperosmotic to seawater. So they slowly gain water through osmosis, and had to excrete excess water through urine.

In contrast to most marine invertebrates and sharks, marine bony fish have body fluids that are strongly hypoosmotic (less salts) to the surrounding medium.

They will lose the water to the environments.

Marine bony fish make up this by drinking.

However, they have the specialized cell at the gill to excrete the excess salts to the surrounding seawater.

Other Marine fishes -- Marine

bony fish

How is energy and nutrients acquired ??

Energy sources

Organisms use one of the three main energy sources: light, organic molecules, and inorganic molecules.

We can group organisms by how they obtain energy (trophic biology):

– Autotrophs (use inorganic sources of both carbon and energy)

Photosynthetic: use CO2 and light. (plants)

Chemosynthetic: use inorganic molecules as sources of carbon and energy. (some bacteria)

– Heterotrophs: use organic molecules as a source of carbon and energy.

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Trophic diversity across biological kingdoms

Figure 6.2

6-1

Using light and CO2

The solar powered biosphere:

Light travel through space as a wave, so it has the frequency and wavelength.

The visible light (the light we can see by eye), is called photosynthetically active radiation (PAR), with the wavelength between about 400nm to 700nm.

Ecologists measure PAR as photon flux density (is the number of photons striking a square meter surface each second).

Solar - Powered Biosphere

Photon: Particle of light bears energy.

– Infrared (IR) Long-wavelength, low energy.

Interacts with matter, increasing motion.

– Ultraviolet (UV) Short wavelength, high energy.

Can destroy biological machinery.


Photosynthetically active radiation

Figure 6.3

6-2 Source: Larcher 1995, after Kairiukstis 1967

Landscapes, water, and organisms can all change the amount and

quality of light reaching an area.

Photosynthetic pathways

C3 photosynthesis: CO2 first combines with a 5-carbon compound called RuBP, then is catalyzed to a three-carbon acids.

Most plants and all algae.

To fix carbon, plants must open stoma to let in CO2

Photosynthetic pathways

C4 photosynthesis: fix and store CO2 in acids containing four-carbon atoms.

Usually in arid environments.

The carbon fixation and other light-depended photosynthesis is separated into two different cells

Photosynthetic Pathways

C4 Photosynthesis

– Reduce internal CO2 concentrations.

Increases rate of CO2 diffusion inward.

Need fewer stomata open.

– Conserving water, why??

– Acids produced during carbon fixation diffuse to

specialized cells surrounding bundle sheath.

Photosynthetic Pathways

CAM Photosynthesis

– (Crassulacean Acid Metabolism)

– Limited to succulent plants in arid and semi-arid

environments.

Carbon fixation takes place at night.

– Reduced water loss.

Low rates of photosynthesis.

Extremely high rates of water use efficiency.

CAM Photosynthesis

Using organic molecules

Hetertophic organisms use organic

molecules both as source of carbon and an

energy, which ultimately, on the carbon and

energy fixed by autotroph.

– Herbivores: eat plants

– Carnivores: eat meats

– Detritivores: feed on nonliving organic matter

Chemical composition and Nutrient Requirements

Chemical composition of organisms is very similar:

Five important elements: carbon, oxygen, hydrogen, nitrogen,

and phosphorus, these element consist up to 93% to 97% of

total biomass.

C:N ratio could be an important indicator of protein contents

A high C:N ration indicate a low nitrogen content, also a low

protein content.

Trace metals are also essential for plant and animal nutrition,

such as calcium, sulfur, zinc, copper, etc…


Ratio of carbon to nitrogen

Figure 6.7

6-6 Source: Spector 1956

herbivores

Herbivores had to overcome the physical and chemical defense of plants.

Physical defense: – thorns

Chemical defense: – tough tissue with large amount of cellulose and

lignin.

– higher C:N ratio for low nutrition value

– Some toxin or digest-reducing substrates


Variation in C:N ratios in pine forest

Figure 6.9

6-7 Source: Klemmedson 1975

Detritivores

Consume food rich in carbon and energy, but

poor in nitrogen.

– Dead leaves may have half nitrogen content of

living leaves.

Fresh detritus may still have considerable

chemical defenses present.

Carnivores

Most of the preys developed defense

mechanisms:

– Camouflage.

– Defensive spines, shell, repellents, and poisons.

– Run fast.

– Take refuge in burrows.


Predators as agents of natural selection

Figure 6.14

6-11


Size of pumas and

their prey

6-13 Source: Iriate et al. 1990

Size-selective predation:

predator select the prey based on its own size.

Energy limitation

The rate at which organisms can take in energy is limited.

– The external energy could be limited to organisms.

– Even the external energy sources is not limited in the environments, organisms energy intake is limited by internal constrains.

– Limits on potential rate of energy intake by plants have been demonstrated by studying response of photosynthetic rate to photon flux density. Limits on potential rate of energy intake by animals have been demonstrated by studying relationship between feeding rate and food availability

Photo influx and photosynthesis curves

Pmax and Isat

Photon Flux and Photosynthetic Response Curves

Rate of photosynthesis increases linearly

with photon flux density at low light

intensities, rises more slowly with

intermediate light intensities, and tends to

level off at high light intensities.

Response curves for different species

generally level off at different maximum

photosynthesis rates.

“sun” and “shade” plants

“Shade” plants:– Low Pmax, the rates of photosynthesis level off at low

levels.

– Low Isat, photosynthesis saturate at low light intensity, use light more efficiency.

– High light will damage the plants.

“Sun” plants:– High Pmax at high light intensity.

– High Isat, photosynthesis saturate at high light intensity.

– However, the photosynthesis rates are lower than “shade” plant at very low light environments.


Contrasting photosynthetic response curves

Figure 6.20

6-17 Source: Ehleringer, Björkman, and Mooney 1976, after Nobel 1977

Response curves

for different

species generally

level off at

different maximum

photosynthesis

rates.

Food density and animal functional response

Functional response: when you gradually

increase the amount of food availability to a

hungry animal, its rate of feeding increases

and then levels off at certain food density.

Three types of functional response.


Theoretical functional response curves

Figure 6.21

6-18

Type 1: feeding increases

linearly as food density

increases - levels off at

maximum

Type 2:Feeding rate rises

in proportion to food

density.

Type 3: Feeding rate

increases most rapidly at

intermediate densities

(S-shaped).

Type 2 functional responses are most popular

Optimal foraging theory

Optimal foraging theory attempts to model how organisms feed as an optimizing process

When organisms have limited access to energy, the natural selection is likely to favor individuals within a population that are more effective at acquiring energy.

Organisms can not simultaneously maximize all of their life functions, for example, allocation of energy to one function, such as growth or reproduction, will reduce the energy to other functions, such as defense.

A compromise of energy demands.

Attributes that affect intake of energy

The number of the prey (abundance of a potential food items), it is expressed as the number of prey encountered by the predator per unit of time: Ne

The amount of energy, or costs, expended by the predator while search for prey: Cs

The time spent processing prey in activities such as cracking, shells, fighting, and is expressed as handling time: H

Model for prey choice

Rate of energy intake of

a predator is

represented as: E/T, E

is intake energy, and T

is time:

(intake rate 1)

111

11

HNe

CsENe

T

E

Ne1 is the number of prey 1 encountered per unit of time

E1 is the energy gained by feeding on one prey 1 minus

the cost of handling.

Cs is the cost of searching prey.

H1 is the time required for “handling” one prey 1.

How about selection of prey?

When predator feed on two prey:

(intake rate 2)

22111

)22()11(

HNeHNe

CsENeCsENe

T

E

22111

)22()11(

HNeHNe

CsENeCsENe

T

E

If intake rate 1> intake rate 2,

predator will feed on prey 1.

otherwise, will feed on prey 2


Optimal foraging theory

Figure 6.24

6-21 Source: Werner and Mittelbach 1981

Bluegill Sunfish

Optimal Foraging By Plants

Limited supplies of energy for allocation to

leaves, stems and roots.

Bloom suggested plants adjust allocation in

such a manner that all resources are equally

limited.

– Appear to allocate growth in a manner that

increases rate of acquisition of resources in

shortest supply.


Soil fertility and ratio of root:shoot biomass

Figure 6.25

6-22 Source: Setälä and Huhta 1991


Root:shoot ratios along nitrogen availability gradient

Figure 6.26

6-23 Source: Tilman and Cowan 1989

Education

Biology 205 7