Ecosystem Productivity and Diversity

Transcription

1 Ecosystem Productivity and Diversity Many Ecologists productivity has a pervasive influence on diversity Primary Focus of Ecosystem Ecology --> examine the exchange of ENERGY MATTER All Ecosystems Radiant Energy Producers - have 3 basic components Autotrophs / Primary Producers Heterotrophs / Consumers Abiotic Components CO 2 O 2 H 2 O Nutrients Leaf Litter Decomposition Translocation Consumption CO 2 O 2 H 2 O Nutrients Abiotic Elements Deposition Consumers Three measure that can be used to define relative importance: Studying Ecosystems First Step --> determine the food web - defines the qualitative movement of ENERGY and NUTRIENTS Then --> decide significance of various species to movement of ENERGY and NUTRIENTS 1) BIOMASS Mass of standing crop of each species Rate of production of new biomass (YIELD) 2) Flow of Chemical Materials Superorganism analogy useful here view community as taking in, processing, re-using, discarding nutrients eg P molecule: soil--> grass--> grasshopper --> feces -->bacteria--> soil 3) Flow of Energy transform solar energy and transfers it to green plants, consumers most is lost as heat, requires constant input

2 Most ecologists use energy - chemicals are often tied up in peculiarities of organisms Primary Production Photosynthesis - solar energy ----> chemical energy - energy is not recirculated (easier to measure) 12 H 2 O + 6CO 2 + solar energy --> C 6 H 12 O 6 + 6O 2 + 6H 2 O - reduces diverse communities to calories Carbohydrates Energy enters almost all ecosystems via solar radiation, and is fixed by the process of photosynthesis Primary Production Photosynthesis - solar energy ----> chemical energy 12 H 2 O + 6CO 2 + solar energy --> C 6 H 12 O 6 + 6O 2 + 6H 2 O Compensation Point - P synthesis = Respiration --> no new production Gross Primary Production --> energy fixed during photosysnthesis Respiration - opposite of P synthesis C 6 H 12 O 6 + 6O 2 --> 12 H 2 O + 6CO 2 + energy for work and heat Net Primary Production --> energy fixed in photosynthesis - energy lost due to respiration How do you measure these 2 aspects of Primary Production? Terrestrial Systems --> measure change in CO 2 or O 2 concentrations around a plant Daytime P syn and Resp occurring CO 2 uptake measures NET production Nighttime only Resp occurring CO 2 output measure respiration Daily patterns of CO 2 assimilation in Douglas fir during spring and summer Temperature/ Light Net CO 2 Assimilation

3 Can determine the energetic equivalent using: 12 H 2 O + 6CO kcal --> C 6 H 12 O 6 + 6O 2 + 6H 2 O Absorption of 6 moles of CO 2 indicates absorption of 709 kcal Alternative methods --> measure uptake of radioactive Carbon ( 14 C) --> 14 CO 2 of known concentration around plant --> harvest plant at later time --> determine amount of 14 C in plant tissues Method is difficult to do in the field. But can do easily in lab Measure concentration of Chlorophyll --> know how much carbon is assimilated per gram of chlorophyll produced One way, --> collect plant tissue and extract Chlorophyll, determine how much chlorophyll per gram of tissue Another way, --> satellite imagery --> use reflectance of light from plants --> different reflectance patterns depending on how much cholorphyll is present Simplest Method --> measure amount of plant material present at 2 times B = B 2 -B 1 B 1 = Plant Biomass at time 1 B 2 = Plant Biomass at time 2 B = change in Biomass from time 1 to time 2 LOSSES occur due to death (L) consumption (G) If you know death rate and consumption rate Net Primary Production = B + L + G Can apply this method to individual plants, or above ground production or below ground production, or all plants of one species or of all plants... Convert Biomass to Energy --> determine caloric equivalent of plant material in bomb calorimeter Mean of 57 species (cal/g dry wt) (J/g dry wt) Leaves 4,229 17,694 Roots 4,720 19,748 Seeds 5,065 21,192

4 Aquatic Systems - P syn measured in much the same way as in terrestrial But easier to look at CO 2 changes Most aquatic primary producers don t require remaining rooted in order to function Use a light bottle - dark bottle technique Light bottle - Dark bottle method Water samples (containing the primary producer) --> placed in two bottles --> one bottle transparent (light bottle) --> one bottle opaque (dark bottle) --> measure CO 2 and O 2 in each bottle at various times Net primary production --> light bottle Gross primary production --> light bottle + dark bottle Prod (g/m 2 /yr) Ecosystem Area Range Mean World Net (t/yr) Tropical Rainforest Temperate Coniferous Temperate Deciduous Temperate Grassland Desert Wetlands Lakes Open Ocean Continental Shelf Estuaries Efficiency of Primary Production How efficient are plants at converting solar energy to biochemical energy? Efficiency = Energy fixed by plant / energy in incident solar radiation Phytoplankton usually < 0.5% Forest plants % Factors that Limit Primary Productivity in Ecosystems Marine Systems di/dt = -ki LIGHT - obvious factor - water absorbs solar radiation - 1/2 is absorbed in first metre % reaches 20m in very clear water Relative Light Intensity k=0.1 k=0.02 Depth (m)

5 60 Clear Lk Rate of P synthesis in Three CA Lakes 50 Castle Lk ---> zone of primary productivity at surface 40 8 Lk Tahoe % 50% 30% If you know: --> extinction coefficient, k Depth (m) % 10% Relative light intensity Average values for tropical marine locations --> amount of solar radiation --> amount of chlorophyll present ---> Rate of P synthesis P = (R/k) * C * Gross production (3.7 - average value - g C fixed by 1 g chl in 1 hour under light saturation) P = rate of photosynthesis - g C fixed / m 2 ocean / day R = relative rate of P synthesis for amount of light entering water k = extinction coefficient per metre C = grams of chlorphyll per cubic metre Relative rate of P synthesis, R Example from Gulf of Alaska solar radiation = 229 cal/cm 2 /day k = 0.1/m chlorophyll = g/m 3 water R = 14.5 P = 14.5/0.1*0.0025*3.7 = 1.34 g C/m 3 /day Measured rate is 1.5 g C/m 3 /day --> so formula does good job predicting Total daily surface radiation, kcal/m 2

6 Solar radiation varies greatly globally --> so should primary productivity Summer Fall 20 June Potential productivity Sept 5 Dec North Latitude Winter (mg/m3) Spring Why are tropical regions under productive when light intensity is good year round? Something else must be limiting P synthesis. --> nutrients N and P Nitrogen in bays on Long Island Duck farms were common - source of nutrient input P and N --> increased P observed in bays, but not N --> N taken up right away by algae --> oceans typically low in N and P at surface Nutrient Enrichment in Sargasso Sea Low productivity despite good sun Addition of Nutrient combinations to algal cultures Nutrients Added N+P+metals N+P N+P+metals (no Fe) N+P+Fe Uptake of 14 C (% relative to controls) Freshwater Ecosystems --> solar radiation limits 1 o prod n --> Nutrient limitation also operates Addition of Fe alone stimulated Primary P tion for short time

7 Addition of nutrients to Algonquin Lakes (Langford) Experimental Lakes Area (ELA) Fertilizer - Nitrogen, Phosphorus, Potassium 2 years Average # of large zooplankton per litre Lake Pre-Fertilization Post-Fertilization Brewer Kearney McCauley Dillon and Ringler 1974 Phosphorous and Primary productivity Lake fertilized annually with phosphate and nitrogen Algal biomass (mg chla/m 3 ) Phosphorous (mg/m 3 ) Lake split with impermeable barrier P, C and N on one side, C and N on the other. Phytoplankton Biomass (mg/m 3 ) Year

8 Primary Productivity in Terrestrial Systems Solar radiation vs temperature --> tightly linked in aquatic systems AET - Actual Evapotranspiration - moisture into atmosphere --> evaporation from ground --> transpiration from plants --> but, in terrestrial --> large range of temps among areas with same solar radiation eg Arizona - desert to alpine Function of --> solar radiation --> temperature --> rainfall Net Primary Production Net Primary Production Wisconsin Massachussetts New York Tennessee North Carolina AET Length of photosynthetic period Boreal coniferous Deciduous Pine Temperate Coniferous Gross Primary Production Net primary production Evergreen Broadleaf Leaf area duration

9 Solar radiation, temperature and moisture Local? --> good for predicting global patterns of primary produciton --> nutrients --> fertilizer increases yields in crop plants Old Growth Forests and Salmon --> nutrient input --> black bears consume tonnes of salmon each year --> 8 dragged 1600kg each from river to forest --> up to 100m away --> consume only fraction of each carcass --> feces --> up to half of N in samples originated in ocean Secondary Production Energy from Plant Biomass from plants Not Used Consumed Detritus Herbivory Feces Digested Urine Metabolizable Energy Resting E Activity Growth Reproduction Maintenance Production How can you estimate secondary production in an animal community? Gross energy intake --> watch the animal Assimilated energy --> gross E in minus e in urine and feces Assimilated = Respiration + Production Estimate Respiration - measured in a lab Basal metabolic rate --> not really a good estimate Maintenance and activity rates can be much higher than basal --> temperature is very important

10 Ecological Efficiencies Net Production --> growth of individuals in a population --> Population size Production Efficiency = Net productivity at trophic level n (P) Assimilation at trophic level n (P+R) Production = Growth + Birth BIOMASS --> calories Group Insectivores Birds Small mammals Other Mammals Fish and social insects Other Invertebrates Herbivores Carnivores Detritivores Nonsocial Insects Herbivores Detritivores Carnivores Production Efficiency No. of Studies Birds and mammals --> 97-99% of assimilated energy --> RESPIRATION Production efficiency --> not constant within a species Proportion to Respiration Food Consumption Community Level Efficiency Lindeman s = Consumption = Assimilation at trophic level n Assimilation at trophic level n-1 Intake at trophic level n Net productivity at trophic level n-1 Efficiency Lindeman s Consumption Trophic Level Trophic Level