Physiological Ecology. Outline Introduction to Ecology Evolution and Natural Selection ...
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Transcript of Physiological Ecology. Outline Introduction to Ecology Evolution and Natural Selection ...
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