Physiological Ecology Outline Physiological Ecology Physiological ...

Physiological Ecology

Physiological Ecology v

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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


Nutrient and Energy Transfer

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Endothermy and Ectothermy

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Climate

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Current Climate Change

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Introduction to Ecology

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Evolution and Natural Selection

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Physiological Ecology

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Behavioural Ecology



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Endothermy and Ectothermy

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Climate

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Current Climate Change


Ch. 6.1 – 6.6, Bush

Outline

Outline

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Basics of energy

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Basics of energy

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Photosynthesis

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Photosynthesis

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Trophic Levels

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Trophic Levels

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Efficiency of Energy Transfer

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Forms of Energy v

Energy transfer

Fuel (chemical bond energy): – nutrients, such as carbohydrates – needed for everything a species does – e.g., growth, movement

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

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Light: – needed by plants to create fuel

Energy source

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

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Basics of energy

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Photosynthesis

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Trophic Levels

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Photosynthesis v

What is it?

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Chlorophyll, a necessary pigment

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Variations in photosynthesis

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The fate of carbohydrate

In Chemistry notation…

Photosynthesis v

Synthesis of carbohydrates from CO2 and water

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Sunlight acts as energy source

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O2 is a by-product

Chlorophyll, a necessary pigment

Energy from sunlight + CO2 + H2O ⇒ CH2O + O2

Pigments absorb light energy

Why are leaves green? v

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

Pigments cannot absorb light in the green wavelength region

The “Green Gap”

Why are some plants not green? v

Fall colour

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

Why is chlorophyll necessary? v

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the production of chlorophyll requires sunlight and warm temperatures in many plants, chlorophyll production stops in fall and other pigments become visible

Variations in photosynthesis

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

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

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

CO2 must enter though stomata v

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

C4 photosynthesis

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CO2 enters and moisture is released

CAM photosynthesis

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

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C3 photosynthesis

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CO2 is turned into sugar with RUBISCO v

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

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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: v water loss in hot, arid regions vphotorespiration where O2 :CO2 ratio is high

The global distribution of C4 plants in today's world

C4 photosynthesis – Have a special enzyme that actively pumps in CO2 and delivers it to RUBISCO enzyme so: v (1) stomata do not have to be open for long v (2) photorespiration is reduced – Energetically costly – 1-4% of plant species use C4 photosynthesis.

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

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

– used by species that live in hot, sunny environments with low CO2 v E.g. tropical grasses

CAM photosynthesis

Unrelated species with similar physiology -Photosynthetic pathways show CONVERGENT EVOLUTION

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

-CAM found in at least 12 different families

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

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

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

Euphorbia (Africa)

Why photosynthesize? v

sugars created from photosynthesis are necessary for: – chemical reactions – plant functions – e.g., conduction of water and nutrients up the stem

– growth (biomass)

Outline

Energy transfer

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Basics of energy

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Photosynthesis

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Trophic Levels

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Two types of organisms v

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

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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 v

Tropic level refers to how organisms fit in based on their main source of nutrition – Primary producers v autotrophs (plants, algae, many bacteria, phytoplankton) – Primary consumers v heterotrophs that feed on autotrophs (herbivores,zooplankton) – Secondary, tertiary, quaternary consumers v heterotrophs that feed on consumers in trophic level below them (carnivores) – Detritivores v bacteria, fungi, and animals that feed on decaying organic matter

Trophic levels examples

How many trophic levels?

Exceptions to the rule?

Food chains versus food webs

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Carnivorous plants capture and digest animal prey

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

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

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

~600 spp. of carnivorous plants have been described

Food chains versus food webs

Food chains

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Food web

Outline v

Basics of energy

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Photosynthesis

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Trophic Levels

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The energy budget

Efficiency of Producers

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

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

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

Coniferous versus deciduous forest

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”

Efficiency of photosynthesis v

Plant biomass – a fraction of total energy v

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

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

Primary productivity v

Gross Primary Productivity (GPP): – total amount of photosynthetic energy captured in a given period of time.

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Net Primary Productivity (NPP): – the amount of plant biomass (energy) after cell respiration has occurred in plant tissues.

NPP = plant growth/ unit area/ unit time

GPP – total photosynthesis/ unit area/unit time

Plant respiration

Secondary Productivity v

Pyramid of productivity

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

Productivity pyramid

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Energy content of each trophic level

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Pyramid has large base and gets significantly smaller at each level

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

Calculating Ecological Efficiency v

Lindeman Efficiency: -can be seen as the ratio of assimilation between trophic levels = energy (growth + respiration) of predator energy (growth + respiration) of food species

Calculating efficiencies

Efficiencies

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

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

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

The “Lost” energy v

What happens to the rest of the energy?

First Law of Thermodynamics:

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– energy cannot be created or destroyed it can only change form v

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Second Law of Thermodynamics:

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– as energy changes form it becomes more disorganized. I.e., ENTROPY increases vEnergy quality index:

decomposers eventually get this!

– light>chemical bond>movement,heat

Detritivores and decomposers

used to do work (cell processes, activity) “Lost” as heat (entropy) not consumed or not assimilated:

Summary v

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

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Photosynthesis converts light energy into chemical energy

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All other trophic levels depend on photosynthesis for life

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