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 Nutrient and Energy Transfer Endothermy and Ectothermy Climate Current Climate Change 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 Energy transfer 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 source Outline The ultimate energy source for (most) life on earth is the sun Basics of energy Photosynthesis Trophic Levels Efficiency of Energy Transfer
Photosynthesis Photosynthesis What is it? Chlorophyll, a necessary pigment Variations in photosynthesis The fate of carbohydrate Synthesis of carbohydrates from CO 2 and water Sunlight acts as energy source O 2 is a by-product In Chemistry notation Chlorophyll, a necessary pigment Energy from sunlight + CO 2 + H 2 O CH 2 O + O 2 Pigments absorb light energy Why are leaves green? Pigments cannot absorb light in the green wavelength region Pigments absorb light energy between 400-700 µm -energy in this range is termed Photosynthetically Active Radiation (PAR)
The Green Gap Why are some plants not green? Chlorophyll is missing from some cells, making the reflectance of other pigments visible Fall colour Why is chlorophyll necessary? the production of chlorophyll requires sunlight and warm temperatures in many plants, chlorophyll production stops in fall and other pigments become visible 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 C3 photosynthesis 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 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 The global distribution of C4 plants in today's world 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 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 Energy transfer Basics of energy Photosynthesis Trophic Levels Efficiency of 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 Outline Basics of energy Photosynthesis Trophic Levels Efficiency of Energy Transfer Food chains Food web
The energy budget Efficiency of Producers 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 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 Calculating efficiencies Efficiencies Herbivores are generally more efficient than carnivores (7% versus 1%) e.g., grasshopper: Efficiency: =1,000 J / 10,000 J =10% efficient 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) 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