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 CO 2 and water  Sunlight acts as energy source  O 2 is a by-product

In Chemistry notation… Energy from sunlight + CO 2 + H 2 O  CH 2 O + O 2

Chlorophyll, a necessary pigment

Pigments absorb light energy Pigments absorb light energy between  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

CO 2 must enter though stomata  stomata (sing., stoma) are tiny holes on the undersides of leaves  CO 2 enters and moisture is released  In hot, dry climates, this moisture loss is a problem

CO 2 is turned into sugar with RUBISCO  RUBISCO (short for Ribulose-1,5-bisphosphate carboxylase) is the most important enzyme on Earth  O 2 has an inhibitory effect upon photosynthesis because it makes RUBISCO perform PHOTORESPIRATION instead

C3 photosynthesis –CO 2 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 O 2: CO 2 ratio is high

C4 photosynthesis –Have a special enzyme that actively pumps in CO 2 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 CO 2  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 CO 2 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 consumers  heterotrophs that feed on consumers in trophic level below them (carnivores) –Detritivores  bacteria, 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 chainsFood 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 respiration plant growth/ total photosynthesis/ unit area/ unit area/unit time unit 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 increases  Energy 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