Physiological Ecology

Outline

Introduction to Ecology

Evolution and Natural Selection

Physiological Ecology

Behavioural Ecology

Physiological Ecology

study of species’ needs and tolerances that determine their distribution and abundance

species need lots of things: e.g., carbon, nitrogen, amino acids, etc.– we will discuss species needs and

tolerances with regards to ENERGY

Physiological Ecology

Nutrient and Energy Transfer

Endothermy and Ectothermy

Climate

Current Climate Change

Physiological Ecology

Nutrient and Energy Transfer

Endothermy and Ectothermy

Climate

Current Climate Change

Nutrient and Energy Transfer

Ch. 6.1 – 6.6, Bush

Outline

Basics of energy

Photosynthesis

Trophic Levels

Efficiency of Energy Transfer

Outline

Basics of energy

Photosynthesis

Trophic Levels

Efficiency of Energy Transfer

Forms of Energy

Fuel (chemical bond energy):– nutrients, such as carbohydrates– needed for everything a species does

– e.g., growth, movement

Heat:– needed for all chemical reactions– by-product of reactions

Light:– needed by plants to create fuel

Energy transfer

Energy source

The ultimate energy source for (most) life on earth is the sun

Outline

Basics of energy

Photosynthesis

Trophic Levels

Efficiency of Energy Transfer

Photosynthesis

What is it?

Chlorophyll, a necessary pigment

Variations in photosynthesis

The fate of carbohydrate

Photosynthesis

Synthesis of carbohydrates from CO2 and water

Sunlight acts as energy source

O2 is a by-product

In Chemistry notation…

Energy from sunlight + CO2 + H2O CH2O + O2

Chlorophyll, a necessary pigment

Pigments absorb light energy

Pigments absorb light energy between 400-700 m-energy in this range is termed Photosynthetically Active Radiation (PAR)

Why are leaves green?

Pigments cannot absorb light in the green wavelength region

The “Green Gap”

Why are some plants not green?

Chlorophyll is missing from some cells, making the reflectance of other pigments visible

Fall colour

the production of chlorophyll requires sunlight and warm temperatures

in many plants, chlorophyll production stops in fall and other pigments become visible

Why is chlorophyll necessary?

Other pigments pass on the energy they absorb to a chlorophyll molecule

When chlorophyll is in an energized state, it is able to turn light energy into chemical bond energy

This chemical bond energy passes through a number of different molecules and then rests within a carbohydrate (glucose) molecule

Variations in photosynthesis

C3 photosynthesis

C4 photosynthesis

CAM photosynthesis

CO2 must enter though stomata

stomata (sing., stoma) are tiny holes on the undersides of leaves

CO2 enters and moisture is released

In hot, dry climates, this moisture loss is a problem

CO2 is turned into sugar with RUBISCO

RUBISCO (short for Ribulose-1,5-bisphosphate carboxylase) is the most important enzyme on Earth

O2 has an inhibitory effect

upon photosynthesis because it makes RUBISCO perform PHOTORESPIRATION instead

C3 photosynthesis

– CO2 enters passively so stomata have to be open for long periods of time

– Majority of plant species use this variation of photosynthesis

– C3 plants experience high rates of: water loss in hot, arid

regions photorespiration

where O2:CO2 ratio is high

C4 photosynthesis

– Have a special enzyme that actively pumps in CO2 and delivers it to RUBISCO enzyme so:

(1) stomata do not have to be open for long

(2) photorespiration is reduced

– Energetically costly

– 1-4% of plant species use C4 photosynthesis.

– used by species that live in hot, sunny environments with low CO2

E.g. tropical grasses

The global distribution of C4 plants in today's world

C4 grasslands (orange) have evolved in the tropics and warm temperate regions where C3 forests (green) are excluded by seasonal drought and fire.

C3 grasses (yellow) remain dominant in cool temperate grasslands because C4 grasses are less productive at low temperatures.

CAM photosynthesis

– open stomata at night when the air is cool and more humid, thereby reducing water loss

– store the CO2 in tissues to be used during the day

– storage space is a potential constraint, thus many CAM plants are succulent (e.g. cacti)

Unrelated species with similar physiology

-Photosynthetic pathways show CONVERGENT EVOLUTION

-CAM found in at least 12 different families

-Recent studies say C4 has independently evolved over 45 times in 19 families of angiosperms

Cacti (Americas) Euphorbia (Africa)

Why photosynthesize?

sugars created from photosynthesis are necessary for:– chemical reactions– plant functions

– e.g., conduction of water and nutrients up the stem

– growth (biomass)

Outline

Basics of energy

Photosynthesis

Trophic Levels

Efficiency of Energy Transfer

Energy transfer

Two types of organisms

Autotrophs (producers)– organisms which can manufacture their own food – e.g., plants

Heterotrophs (consumers)– “other feeders” – organisms which must consume

other organisms to obtain their carbon and energy– e.g., animals, fungi, most protists, most bacteria

Trophic Levels

Tropic level refers to how organisms fit in based on their main source of nutrition– Primary producers

autotrophs (plants, algae, many bacteria, phytoplankton)

– Primary consumers heterotrophs that feed on autotrophs (herbivores,zooplankton)

– Secondary, tertiary, quaternary consumersheterotrophs that feed on consumers in trophic level below them

(carnivores)

– Detritivoresbacteria, fungi, and animals that feed on decaying organic matter

Trophic levels examples

How many trophic levels?

Exceptions to the rule?

Carnivorous plants capture and digest animal prey

They are able to grow without animal prey, albeit more slowly

~600 spp. of carnivorous plants have been described

Food chains versus food webs

Food chain – the pathway along which food is transferred from trophic level to trophic level in an ecosystem

Food web – the feeding relationships in an ecosystem; many consumers are opportunistic feeders

Food chains versus food webs

Food chains Food web

Outline

Basics of energy

Photosynthesis

Trophic Levels

Efficiency of Energy Transfer

The energy budget

The extent of photosynthetic activity sets the energy budget for the entire ecosystem

Of the visible light that reaches photosynthetic land plants, 1% to 2% is converted to chemical energy by photosynthesis

Aquatic or marine primary producers (algae) convert 3-4.5% - this difference accounts for why aquatic and marine food chains tend to be longer

Efficiency of Producers

One difference among ecosystems is their reflectance. Broadleaf forests reflect up to 20% of visible radiation. Conifer forests reflect only about 5%.

Ecosystems with low leaf area (e.g. deserts) absorb very little light. Conifer forests with very high leaf area index can absorb almost 95% or more of the “incident light”

Coniferous versus deciduous forest

Efficiency of photosynthesis

Of the energy that is actually absorbed by chloroplasts, at best about 20% is converted into sugars

Plant biomass – a fraction of total energy

Of the solar energy that is converted into organic molecules in photosynthesis, about 40-50% is lost in the processes of respiration

Primary productivity

Gross Primary Productivity (GPP): – total amount of photosynthetic energy captured in

a given period of time. Net Primary Productivity (NPP):

– the amount of plant biomass (energy) after cell respiration has occurred in plant tissues.

NPP = GPP – Plant respirationplant growth/ total photosynthesis/ unit area/ unit area/unit timeunit time

Secondary Productivity

Secondary productivity – the rate at which consumers convert the chemical energy of the food they eat into their own new biomass

Pyramid of productivity

Energy content of each trophic level

Pyramid has large base and gets significantly smaller at each level

Organisms use energy for respiration so less energy is available to each successive trophic level

Productivity pyramid

Calculating Ecological Efficiency

Lindeman Efficiency:-can be seen as the ratio of assimilation

between trophic levels

= energy (growth + respiration) of predator

energy (growth + respiration) of food species

Simplifying Ecological Efficiency

Production Efficiency:-can be seen as the ratio of biomass production

between trophic levels

= energy (growth + respiration) of predator

energy (growth + respiration) of food species

Calculating efficiencies

e.g., grasshopper: Efficiency: =1,000 J / 10,000 J =10% efficient

Efficiencies

Herbivores are generally more efficient than carnivores (7% versus 1%)

Ectotherms are more efficient than endotherms (up to 15% versus 7%)

The “Lost” energy

First Law of Thermodynamics:– energy cannot be created or destroyed it

can only change form

Second Law of Thermodynamics:– as energy changes form it becomes more

disorganized. I.e., ENTROPY increasesEnergy quality index:

– light>chemical bond>movement,heat

What happens to the rest of the energy?

used to do work (cell processes, activity, reproduction)

“Lost” as heat (entropy)

not consumed or not assimilated:

decomposers eventually get this!

Detritivores and decomposers

Summary

Virtually all energy comes from the sun; this energy is never destroyed, it just changes form

Photosynthesis converts light energy into chemical energy

All other trophic levels depend on photosynthesis for life

Organisms vary in their ability to extract energy from the trophic level below them but most efficiencies are below 15%, leaving much for detritivores