BIOL 4120: Principles of Ecology Lecture 18: Ecosystem Ecology Dafeng Hui Room: Harned Hall 320 Phone:

Ecosystem Definition: biotic community and abiotic environment functioning as a system. Includes organism-complex and whole complex of physical factors. Ecosystem ecologist: Forest is a system composed of autographs, heterographs, and abiotic environment, each component processing and exchanging energy and matter. Inputs: exchanges from the surrounding environment into the ecosystem Outputs: exchange from inside ecosystem to the surrounding environment Closed ecosystem: an ecosystem with no inputs and outputs Open ecosystem: an ecosystem with inputs and outputs Ecosystem ecology: exchanges of energy and matter between ecosystem and environment and among components within the ecosystem (energy flow and nutrient cycling).

Outline (Chapter 20) Ecosystem Energetic

20.1 Energy fixed in the process of photosynthesis is primary production Flow of energy through a terrestrial ecosystem starts with the harnessing of sunlight by autotrophs. Rate at which light energy is converted by photosynthesis to organic components is referred to as primary productivity. Gross primary productivity (GPP): Total rate of photosynthesis Net primary productivity (NPP): rate of energy as storage as organic matter after respiration NPP=GPP-R

Standing crop biomass: amount of accumulated organic matter in an area at a given time Biomass is expressed as g organic matter per square meter (g m-2) Productivity is the rate at which organic matter is created by photosynthesis (g m-2 yr-1)

How to measure? Terrestrial ecosystem: Change in standing crop biomass over a given time interval (see Hui & Jackson 2006 for grasslands) Aquatic ecosystem: Wrong again?

20.2 Temperature, water, and nutrients control primary production in terrestrial ecosystems Net primary productivity for a variety of terrestrial ecosystem as a function of mean annul precipitation (MAP) and mean annual temperature (MAT) as well as length of growing season Deciduous forest in N. America

Warm temperature and adequate water supply for transpiration that gives the highest primary productivity. (Remember that photosynthesis and transpiration are coupled processes)

Global map of primary productivity Patterns of productivity reflect global patterns of temperature and precipitation. High NPP in equatorial zone and coastal region.

Primary production varies with nutrient availability Different forest ecosystems RO, red oak; RP, red pine; SM, sugar maple, Hem, hemlock; WP, white pine 20 oak savanna in Minnesota

20.3 Temperature, light, and nutrients control primary production in aquatic ecosystems Changes in available light, respiration, NPP with water depth Compensation depth: Depth that available light is equal to the light compensation point (NPP=0 or GPP=R)

Effects of nutrient addition on marine phytoplankton growth rate in 303 experiments John downing, Iowa State Conducted 303 experiments Nitrogen addition stimulated phytoplankton growth the greatest, follow closely by Fe, addition of P showed no effect Effect of P addition varied among different ecosystems. In polluted areas, show negative effect

Geographic variation in primary productivity of world’s oceans High productivity is along coastal regions 1.Great transport of nutrient from bottom to top 2.Nutrient from terrestrial ecosystems

20.4 Primary production varies with time Park Grass, Rothamsted Experimental Station in England Climatic variation Disturbance Stand aging

Aboveground stem biomass, LAI, and aboveground NPP for stands of boreal needle- leaf evergreen conifer of different ages.

20.5 Primary productivity limits secondary production Net primary production is the energy available to the heterotrophic component of the ecosystem Either herbivores or decomposers eventually consume all plant productivity, but often it is not all used within the same ecosystem. Secondary production: net energy of production of secondary consumers Energy stored in plant material, once consumed, passes through the body as waste products. Of the energy assimilated, part is used as heat for metabolism (respiration) Reminder is available for maintenance – capturing or harvesting food etc, and lost as heat Energy left over from maintenance and respiration goes into production, including growth of new tissues and production of young Secondary productivity: secondary production per unit of time

Secondary production depends on primary production for energy Sam McNaughton 69 studies for terrestrial ecosystems (from Arctic tundra to tropical forests)

Similar relationship in lake ecosystems 43 lakes+12 reservoirs Tropic to Arctic Bottom-up and top- down control

20.6 Consumers vary in efficiency of production Energy use is a complex process. Not all consumers have the same efficiency A simple model of energy flow through consumer I: food ingested by a consumer A: a portion is assimilated across the gut wall W: remainder is expelled from the body as waste products R: of the energy assimilated, part is used for respiration P: reminder goes to production (new growth and reproduction) Based on these data, we can calculate: Assimilation efficiency A/I, ratio of assimilation to ingestion measure the efficiency with which consumer extracts energy from food Production efficiency P/A, ratio of production to assimilation measure the efficiency with which the consumer incorporates assimilated energy into secondary production.

Secondary producers are not necessarily highly efficient

Assimilation efficiency Vary widely among animal groups Endotherms are much more efficient than ectotherms Carnivorous animals (even ectothermic ones) have high assimilation efficiency than herbivores (meat vs veg)

Production efficiency varies mainly according to taxonomic class

20.7 Ecosystem have two major food chains Food chain and food web review Food chain is a flow of energy Feeding relationships within a food chain are defined in terms of trophic or consumer level 1 st level: Autotrophs or primary producer 2 nd level: herbivores (1 st level consumers) Higher level: carnivores (2 nd level consumers) Some consumers occupy more than one trophic level

Within any ecosystem, there are two major food chains Difference 1. Source of energy for herbivores 2. Energy flow direction 3. interconnected

20.8 Energy flow through tropic levels can be quantified Energy flow within a single trophic compartment Consumption efficiency: I n /P n-1

20.8 Consumption efficiency determines the pathway of energy flow through the ecosystem In terrestrial ecosystems and shallow water ecosystems, with their high standing biomass and relative low harvest of primary production by herbivores, the detrital food chain is dominate. In deep water aquatic ecosystem, with low biomass, rapid turnover and high rate of harvest, grazing chain may be dominate.

20.9 Energy decreases in each successive trophic level

Energy pyramid

End

Normally ecosystems have two major food chains Terrestial grazing chain not very important Only 2.6% of primary production Insects very important Detrital chain is very important 35% of primary production Food chains are interconnected Energy flows through trophic levels Energy decreases with each tropgic level

Assimilation efficiencies vary widely among endotherms and ectotherms Pattern of flow varies

20.1 Laws of thermodynamics govern energy flow Energy Potential energy: stored energy; capable of and available for performing work Kinetic energy: energy in motion. It performs work at the expense of potential energy Work: at least two kinds: the storage of energy and the arranging or ordering of matter First law of thermodynamics: Energy is neither created nor destroyed. Exothermic and Endothermic Second law of thermodynamics When energy is transferred or transformed, part of the energy assumes a form that cannot pass on any further Entropy increases As energy is transferred from one organism to another in the form of food, a portion is stored as energy in living tissue, whereas a large part of that energy is dissipated as heat.

Biomass and productivity

Trophic Dynamic View of Ecosystems Lindeman (1942) concluded the ecosystem concept is fundamental to the 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. 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.