Lecture XXI: Ecosystems Flashcards
Recall: Ecosystem
All of the living organisms in a given area (the community or biotic component of an ecosystem)
Plus,
The physical environment (abiotic factors) they interact with.
Biomes
A biome is any of the world’s major ecosystem types.
What characterizes Biomes
Terrestrial biomes are typically characterized by the predominant vegetation and the adaptations seen in organisms to thrive in the specific environment. Examples of terrestrial biomes are: dessert, tropical rainforest, savanna, temperate grassland, northern coniferous forest etc..
Aquatic Biomes
Aquatic biomes are characterized by the physical environment and the adaptations that organisms have to survive within it. Lakes, rivers, wetlands, intertidal zones, oceanic pelagic zone, coral reefs and marine benthic are examples of aquatic biomes.
Biotic Components of Ecosystems
Primary Producers (autotrophs)
Consumers (heterotrophs)
Decomposers (heterotrophs)
Primary Producers
The only group that can utilize simple carbon molecules (CO2) and convert it into biomass in the form of complex organic macromolecules.
Many are photoautotrophic, meaning they have the ability to convert radiant energy from the sun into chemical bond energy through photosynthesis.
They form the base of all ecosystem food chains (webs).
Consumers:
Consumers unlike producers are heterotrophic, they must acquire carbon through the consumption of food (organic compounds).
Most consumers are chemoheterotrophic, they also acquire their energy from the food they ingest.
Primary Consumers - Ingest producers as their carbon and energy source. Herbivores Secondary, Tertiary….. Consumers Ingest other consumers Omnivores/Carnivores
Decomposers
Decomposers like consumers are heterotrophic, they must acquire carbon from organic molecules. They differ from consumers in the way that they acquire it.
Instead of ingesting food like consumers, decomposers secrete digestive enzymes into the external environment and then absorb small organic molecules as they become available.
Ecosystem Trophic Levels
Within each ecosystem there is a different feeding relationship between the organisms that exist there. Energy and nutrients pass from one organism to the next. Each link in the chain is called a trophic level.
What type of abiotic factors could limit the number and type of species that can live within an ecosystem?
The number of trophic levels found within an ecosystem is strongly influenced by the abiotic environmental factors that exist there.
Amount of sunlight
Nutrient availability (water, phosphorous, carbon, nitrogen)
Temperature
Ecosystems with more sunlight (energy) and nutrients available can support a greater number of living organisms (more biomass) and will have greater species diversity than ecosystems with low sunlight and nutrient availability.
Food Web:
A Food Web
In nature simple food chains are uncommon.
More complex interactions occur forming a food web between trophic levels.
Generally, each species feeds on, or is fed upon by, more than one species.
Energy Flow
Radiant Energy from the sun
Primary Producers
Capture less than 10% of radiant E in photosynthesis
Convert it into chemical E (stored in bonds of organic molecules)
Primary Consumers
-Herbivores
Ingest producers
Break bonds of organic molecules in cellular respiration producing ATP. Other molecules used to build up their tissues.
Secondary and Tertiary Consumers
-Omnivores/ Carnivores
Ingest consumers.
Organic molecules used the same way as primary consumers.
Energy is lost at each trophic level in the form of heat.
Energy flow is linear
Energy is lost with each trophic level.
All levels are connected to decomposers.
Energy Budget
The total amount of energy available for an ecosystem
Based on Primary Production, the amount of radiant energy that is converted into chemical energy by primary producers.
The greater the primary production in an ecosystem the greater the ecosystem’s energy budget is.
Primary Production: Gross vs. Net
Gross Primary Production (GPP) = Total primary production in an ecosystem (radiant E → chemical E)
However, plants need to use some of that energy for their own metabolism (R).
What is left over and stored in the plants tissues is the energy available to consumers:
Net Primary Production or NPP (E available to consumers)
NPP = GPP - R
Evatranpirations rate
Primary Production is for the most part determined by the amount of available sunlight. However, in Terrestrial Ecosystems it is also influenced by Water, Temperature, and Availability of other Nutrients.
Primary production in terrestrial ecosystems is correlated with the evapotranspiration rate that occurs there.
The evapotranspiration rate is a measure of the amount of water entering the atmosphere from the ground through the process of evaporation and through transpiration from plants, so it is a measure of both temperature and available water.
Secondary Production
Is the amount of chemical E ingested by primary consumers (Herbivores) that is converted into their own tissue growth (biomass).
Bioaccumulation and Biomagnification of Toxins within Ecosystems
So far, we have considered how energy flows through ecosystem food chains (webs). An issue that faces organisms today is the tendency of certain toxins to accumulate or build up within food chains.
When a toxin is present in the environment it may begin to appear in the tissues of living organisms. This is called bioaccumulation.
When the toxin is passed from one trophic level to the next and increases in concentration it is called biomagnification.
How are nutrients cycled?
Unlike energy, nutrients are in a closed system and are never lost. Nutrients are, however cycled between abiotic and biotic components in ecosystems.
Rate of Nutrient Cycling
The rate of nutrient cycling is closely linked to the number of decomposers active within an ecosystem.
Eutrophication
The process by which elevated nutrient levels lead to an overgrowth of algae and the subsequent depletion of water oxygen levels in aquatic ecosystems. Cultural eutrophication refers to the enrichment of water with nutrients derived from human activities such as fertilizer use and sewage dumping.
Phosphorous is usually the limiting nutrient in aquatic ecosystems, so when it is added, primary production increases dramatically.
The Phosphorous Cycle
Reservoirs: Sedimentary rock Soil Ocean Living organisms
Primary producers uptake (assimilate) phosphate and then pass it up the food chain.
Carbon Cycle
Primary Reservoir is the atmosphere, but also sediments, soil, fossil fuels, plant and animal biomass.
Photosynthesis removes substantial amounts of carbon from the abiotic environment. Called Carbon fixation.
Carbon returns to the abiotic environment through Respiration, Combustion and Decomposition.
Carbon is essential to build the backbone of all macromolecules (proteins, lipids, carbohydrates and nucleic acids.
The Water Cycle
Reservoirs: -Oceans 97% Glaciers and ice caps 2% Fresh water bodies 1% Living organisms
Processes: Evaporation Condensation Precipitation Transpiration
Nitrogen Cycle:
Nitrogen (N2)is in abundance in the atmosphere, but most living organisms cannot use it in this form.
They must rely on nitrogen fixing bacteria to convert nitrogen into a usable form.
Once N2 has been converted into nitrate, producers can assimilate it and pass it up through the trophic levels.
