Molles: Ecology 2 nd Ed. PRIMARY PRODUCTION AND ENERGY FLOW Chapter 18

Molles: Ecology 2 nd Ed. Chapter Concepts Terrestrial Primary Production limited by temperature and moisture Aquatic Primary Production limited by nutrient availability Consumers can influence rates of primary production in terrestrial and aquatic ecosystems Energy losses limit the number of trophic levels found in ecosystems

Molles: Ecology 2 nd Ed. Fundamental Concepts Primary Production Fixation of energy by autotrophs in an ecosystem Or, conversion of inorganic energy (light) into organic forms (chemical potential energy)

Molles: Ecology 2 nd Ed. Rate of Primary Production Amount of energy fixed during period of time  Gross PP – Total amount of energy fixed  Net PP – Amount of energy leftover after autotrophs have met their metabolic needs (subtract plant respiration)  This is amount left over for consumption by herbivores

Molles: Ecology 2 nd Ed. Fundamental Concepts Trophic Level  Position in food web determined by number of energy transfers from primary producers to current level:  Primary producers = first level  Primary consumers = second level  Secondary consumers = third level  Tertiary consumers = fourth level

Molles: Ecology 2 nd Ed.

Evapotranspiration and Terrestrial Primary Production Rosenzweig (1968)  Estimated influence of moisture and temperature on rates of primary production  Plot annual net primary production and annual actual evapotranspiration (AET)

Molles: Ecology 2 nd Ed. Plot annual net primary production and annual actual evapotranspiration (AET)  AET – annual amount of water that evaporates and transpires  Cold dry ecosystems tend to have low AET Fig 18.2

Molles: Ecology 2 nd Ed. Evapotranspiration and Terrestrial Primary Production  Positive relationship between net primary production and AET  Sala found east-west variation in primary production correlated with rainfall

Molles: Ecology 2 nd Ed. So? Rainfall or, rainfall and temperature  Predict net primary productivity in terrestrial ecosystems

Molles: Ecology 2 nd Ed. Soil Fertility and Terrestrial Primary Production Soil fertility is important too! Shaver and Chapin  Arctic net primary production twice as high on fertilized plots compared to unfertilized plots

Molles: Ecology 2 nd Ed. Bowman  N is main nutrient limiting net primary production in a dry tundra meadow;  N and P jointly limit production in a wet meadow

Molles: Ecology 2 nd Ed. Fig 18.5

Molles: Ecology 2 nd Ed. Patterns of Aquatic Primary Production Several studies found quantitative relationship between phosphorus and phytoplankton biomass – nutrient availability controls rate of primary production in freshwater ecosystems

Molles: Ecology 2 nd Ed. Figure 18.9

Molles: Ecology 2 nd Ed. Global Patterns of Marine Primary Production Highest primary production by marine phytoplankton –  in areas with higher levels of nutrient availability = continental margins  Nutrient run-off from land  Sediment disturbance Open ocean tends to be nutrient poor  Vertical mixing main nutrient source

A Comparative Analysis of Annual Primary Production (Kcal / m 2 /yr) 0.29 (29%) 0.44 (44%) 0.61 (61%) 0.62 (62%) NPP / GPP (1.86%) (0.58%) (0.58%) (1.17%) GPP / Total Solar Radiation 13,0005,0007,50015,200 Net Primary Production 32,0006,4004,7009,200 Respiration 45,00011,40012,20024,400 Gross Primary Production 2,415,0002,091,000 Total Solar Radiation Mature Tropical Rain Forest Middle-Aged Oak Forest Young Pine Plantation Alfalfa Field

Summary of Comparisons of Ecosystem Primary Production Efficiency of primary production is reduced by drought or freezing-induced dormant seasons (sun light going to waste) Efficiency of primary production is reduced by high temperatures that increase respiration w/o increasing photosynthesis. Efficiency of primary production is reduced by large amounts of non-photosynthetic plant biomass (increase respiration w/o increasing photosynthesis).

Association b/t Plant Biomass and Primary Production Ocean Upwelling Zone 4700Savanna (Grass + Trees) 20800Boreal Conifer Forest 22000Algal Beds & Coral Reefs Swamps & Marshes Tropical Rain Forest Plant Biomass Net Primary ProductionEcosystem } } (There isn’t one)

Molles: Ecology 2 nd Ed. Consumer Influences Bottom-Up Controls  Influences of physical and chemical factors of an ecosystem Top-Down Controls  Influences of consumers

Molles: Ecology 2 nd Ed. Lake Primary Production Carpenter et al. (1985)  Piscivores + planktivorous fish can cause significant deviations in primary productivity Carpenter and Kitchell (1988)  Influence of consumers on lake primary productivity propagate through food webs  = Trophic Cascade Hypothesis

Molles: Ecology 2 nd Ed. Fig 18.11

Molles: Ecology 2 nd Ed. Fig

Molles: Ecology 2 nd Ed. Carpenter + Kitchell Whole lake experiments N. Wisconsin / UP Michigan

Molles: Ecology 2 nd Ed. UNDERC Three lakes: Peter, Paul, Tuesday 1985: reciprocal transplants of fish

Molles: Ecology 2 nd Ed. Carpenter and Kitchell experiment Three experimental lakes  Two w/bass  One winterkill lake; Tuesday – no bass  Many planktivore fishes = minnows

Molles: Ecology 2 nd Ed. Experiment:  Remove 90% bass from Peter lake  Put into Paul lake  Remove 90% planktivores from Paul lake  Put into Peter lake  Third lake = control (Tuesday)

Molles: Ecology 2 nd Ed. Lake Primary Production Carpenter and Kitchell  Fewer planktivorous fish led to reduced rates of primary production  No planktivorous minnows resulted in more predator invertebrates  Abundant, large herbivorous zooplankton increased, phytoplankton biomass and primary productivity

Molles: Ecology 2 nd Ed. Fig Summary

Molles: Ecology 2 nd Ed. Primary Production in the Serengeti  25,000 km 2 grassland  Millions of large mammals still present

Molles: Ecology 2 nd Ed. McNaughton (1985)  Serengeti grazers consume average of 66% of annual primary production  Rate of primary production in Serengeti positively correlated with rainfall quantity

Molles: Ecology 2 nd Ed. Primary Production in the Serengeti Found that grazers can increase primary production  Increased growth rate =  Compensatory Growth is plant response  Lower respiration rate due to lower biomass  Reduced self-shading  Improved water balance due to reduced leaf area

Molles: Ecology 2 nd Ed. Fig 18.14

Molles: Ecology 2 nd Ed. Primary Production in the Serengeti In addition, McNaughton found compensatory growth highest at intermediate grazing intensities  Light grazing insufficient to produce compensatory growth  Heavy grazing reduces plant’s capacity to recover

Molles: Ecology 2 nd Ed. Fig

Molles: Ecology 2 nd Ed. Trophic Dynamic View of Ecosystems Lindeman (1942)  Ecosystem concept fundamental to study of energy transfer within an ecosystem  Suggested grouping organisms within an ecosystem into trophic levels  Each feeds on level immediately below  As energy is transferred from one trophic level to another, energy is degraded

Molles: Ecology 2 nd Ed. Trophic Dynamic View of Ecosystems  As energy is transferred from one trophic level to another, energy is degraded:  Limited assimilation  Consumer respiration  Heat production  Energy quality decreases with each successive trophic level – Pyramid-shaped energy distribution

Molles: Ecology 2 nd Ed. Fig

Trophic Pyramids Why are big, fierce animals (top carnivores) rare ? Because there is not enough energy to support large populations at the highest trophic levels. Bio-magnification

Human Trophic Pyramid

How Will We Feed a Growing Human Population ?

After 30 Years of Increase, Grain Production per Person Has Stabilized Green Revolution Agricultural production increases faster than human population Agricultural production just keeping pace with human population growth

What was the “Green Revolution” Genetic improvement of crop species to increase grain yields and resistance to pests, disease, wind damage. Increased use of fertilization, herbicide, pesticide, and irrigation. All the “easy” gains in production have been obtained. Further gains will come slowly, if at all. Negative effects of fertilization, pesticides and irrigation are beginning to affect production The human population continues to grow

Acreage of Productive Farmland Is Declining In the USA From 1992 – 1997 six million acres of farm land were converted to developed use. We lost farm and ranch land 51% faster in the 1990’s than in the 1980’s. Prime agricultural land is being converted 30% faster than non-prime rural lands. We must depend more on food production from marginal land that requires more irrigation and fertilization. “Farming On the Edge” (American Farmland Trust)

Losing Farm Land (USA) 25% of U.S. food supply comes from the California Central Valley

Losing Farm Land (Indiana) Wasteful land use is the problem, not growth itself.

Losing Farm Land (Indiana) Wasteful land use is the problem, not growth itself. From the U.S. population grew by 17%, while urbanized land grew by 47%.

Losing Farm Land (Indiana) Wasteful land use is the problem, not growth itself. From the U.S. population grew by 17%, while urbanized land grew by 47%. Over the past 20 years, the acreage per person for new housing almost doubled.

Losing Farm Land (Indiana) Wasteful land use is the problem, not growth itself. From the U.S. population grew by 17%, while urbanized land grew by 47%. Over the past 20 years, the acreage per person for new housing almost doubled. Since 1994, 10+ acre housing lots have accounted for 55% of land developed.

Energy Flow In the Human Food Chain Energy In Corn Grain (8.2 million Kcal) Energy Assimilated by Feedlot Cattle (7.0 million Kcal) Energy in the Body of Mature Feedlot Cattle (1.2 million Kcal) Energy in Meat from Feedlot Cattle (0.4 million Kcal) 5% of Energy in Corn is Available In Beef Not assimilated by cow Respiration Waste in meat processing Maybe humans should just eat the corn

Meat Production Continues to Rise All Endothermic Animals

More Efficient Meat Production ???Farm-grown Fish 2Chicken 4Pork 7Beef Pounds of Grain per Pound of Meat ProducedType of Meat

How to Feed a Growing Human Population With a Finite or Shrinking Agricultural Land Base Increase the proportion of calories in the diet provided by grains. Increase the proportion of protein in the diet provided by energy-efficient animals (poultry and fish). Protect prime farm land from development.

The End