Ch. 56 Ecosystems

Ecosystem

• Sum of all organisms living in a given area and the abiotic factors with which they interact
• Abiotic factor- chemical and physical properties of an environment
• Sunlight, soil type, rainfall, temperature
• Ecosystem ecology studies interactions between living organisms and two main abiotic factors:
• Energy – originates from sunlight and chemosynthesis
• Nutrients – originate from soil, water, and atmosphere

Energy Flows and Chemical Cycles

• Both move through an ecosystem via the organisms in the system
• Each trophic level plays a role in cycles
• Primary producers- autotrophs that receive solar energy and convert it to chemical energy (photosynthetic species)
• Primary (1⁰) consumers- heterotrophs that consume autotrophs (herbivores)
• 2⁰, 3⁰, and higher consumers- eat other heterotrophs (carnivores)
• Decomposers- heterotrophs that eat detritus (non-living organic material…dead stuff)

• Energy flows and chemicals cycle through the ecosystem
• Energy is not a closed cycle because some of it is constantly lost (heat) and added (sun)
• 10% moves to next level, other 90% lost as heat

Global Energy Production

• Ecosystems can only use energy that is received and absorbed by photosynthetic primary producers
• Primary production- amount of light converted to chemical energy by autotrophs during a given time period
• Primary production sets the “energy budget” for an area
• Higher production means more energy available and more life that can be supported by the system
• Primary productivity has a predictable geographic pattern

• Terrestrial production is controlled by rainfall and temperature

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• Aquatic production is controlled by nutrient availability and light penetration

Limitations of Ecosystems

• Many ecosystems have an abundance of most resources needed for growth but lack one or a few resources needed for increased growth
• Limiting factor- an environmental variable that limits or slows the growth/activity of organisms in a given area
• Sunlight, water, nest site locations, food, competition, predation, nutrients
• Limiting Nutrient- element that must be added for primary production to increase
• Commonly the problem in terrestrial ecosystems

Limiting Factors of the Prairie Ecosystem?

Eutrophication

• Process of ecosystem change initiated by an increase in nutrients consumed by phytoplankton, cyanobacteria, and algae in aquatic systems
• Results in algae population explosions (blooms)
• Algae die after bloom and decompose
• Results in oxygen deficiency (hypoxia) that leads to a cascade of organismal death from hypoxia
• “Dead zone” like the Gulf of Mexico

• Fertilizer runoff into Mississippi River leads to eutrophication of Gulf of Mexico
• “Dead zone” with little marine life because of hypoxic zones

Energy Movement in Ecosystems

• Once primary productivity introduces chemical energy to an ecosystem, movement of energy through the trophic structure is known as secondary production
• Source of energy for organisms and ecosystems that is derived from the consumption of organic compounds produced by other organisms
• Secondary production broken into:
• Assimilation efficiency – proportion of ingested biomass that consumers assimilate by digestion
• Production efficiency – proportion of assimilated biomass used to produce new consumer biomass

Nutrient Cycling Involves Chemical and Biological Transformations

Decomposer Roles in Cycling

• Decomposers play a critical role in recycling nutrients
• Rate of decomposition controlled by temperature, water availability, and nutrient availability
• Areas of high decomposition rate tend to be warm and wet
• Tropical forests: decomposition takes a few months to a few years
• Temperate forests: 4-6 years

• Researchers placed identical samples of organic matter in 21 locations
• Returned to collect everything left 3 years later
• More mass remained at cold, dry locations
• Decomposition occurs more rapidly in warm, moist locations

Biogeochemical Cycles

• Any of a number of chemical cycles which involve both biotic and abiotic components of ecosystems
• While energy is continually added to the system (from sun), other nutrients like carbon, nitrogen, oxygen, and sulfur are cycled through the ecosystem and reused

General Model

• Nutrients flow among reservoirs, get locked in pools for periods of time, and get freed to reenter cycle
• Exact process different for each nutrient

4 Major Cycles

• In each cycle, remember two characteristics about each reservoir
• The nutrients in each reservoir are organic or inorganic
• The nutrients in each reservoir are available or unavailable
• Some nutrients can be locked away for millions of year and others cycle very quickly from one reservoir to another

• Reservoirs: Oceans 97%, ice caps 2%, lakes, rivers, and ground 1%
• Processes: evaporation, precipitation, transpiration

WATER

• Reservoirs: fossil fuels, soil, aquatic sediments, plant/animal biomass, and atmosphere
• Processes: photosynthesis, cellular respiration, consumption, burning of fossil fuels, outgassing, dissolution

CARBON

Figure 55.14c

• Reservoirs: Atmosphere 80%, soils and sediments of lakes, rivers, and oceans
• Processes: nitrogen fixation (inorganic to organic), industry input (fertilizers), legume crops, industrial production of reactive nitrogen

NITROGEN

Figure 55.14d

Runoff

• Reservoirs: marine sedimentary rock, soil, oceans
• Processes: weathering of rock, eaten by consumers, returned to soil via decomposition or defecation

PHOSPHORUS