chapter 58 Dynamics of Ecosystems. Flashcards
Biogeochemical Cycles
Ecosystem
Includes all the organisms that live in a particular place, plus the abiotic environment in which they live and interact
Biogeochemical cycles
Chemicals moving through ecosystems
Biotic and abiotic processes
Biogeochemical cycles usually cross the boundaries of ecosystem
One ecosystem might import or export chemicals to another
Carbon cycle
Carbon is a major constituent of the bodies of organisms
Carbon fixation: metabolic reactions that make nongaseous compounds from gaseous ones
Aerobic cellular respiration releases CO2
Methanogens: produce methane (CH4) by anaerobic cellular respiration
Over time, globally, the carbon cycle may proceed faster in one direction
This can cause large consequences if continued for many years
Earth’s present reserves of coal, and other fossil fuels were built up over geological time
Human burning of fossil fuels is creating large imbalances in the carbon cycle
The concentration of CO2 in the atmosphere is going up year by year
Water Cycle
All life depends on the presence of water
60% of the adult human body weight is water
Amount of water available determines the nature and abundance of organisms present
It can be synthesized and broken down
Synthesized during cellular respiration
Broken down during photosynthesis
Basic water cycle
Liquid water from the Earth’s surface evaporates into the atmosphere
Occurs directly from the surfaces of oceans, lakes, and rivers
Terrestrial ecosystems: 90% of evaporation is through plants
Water in the atmosphere is a gas
Cools and falls to the surface as precipitation
Groundwater: under ground water
Aquifers: permeable, underground layers of rock, sand, and gravel saturated with water
Important reservoir: 95% of fresh water used in United States
Two subparts:
Upper layers constitute the water table
Lower layer can be tapped by wells
Changes in the supply of water to an ecosystem can radically alter the nature of the ecosystem
Deforestation disrupts the local water cycle
Nitrogen Cycle
Nitrogen is a component of all proteins and nucleic acids
Usually the element in shortest supply
Atmosphere is 78% nitrogen
Availability
Most plants and animals cannot use N2 (gas)
Use instead NH3 (ammonia), and NO3– (nitrate)
Nitrogen fixation: synthesis of nitrogen containing compounds from N2
Nitrification: N2 → NH3 → NO3–
Denitrification: NO3– → N2
Both processes are carried out by microbes: free or living on plant roots
Nitrogenous wastes and fertilizer use radically alter the global nitrogen cycle
Humans have doubled the rate of transfer of N2 in usable forms into soils and water
Phosphorus cycle
Phosphorus is required by all organisms
Occurs in nucleic acids, membranes, ATP
No significant gas form
Exists as PO43– (phosphates) in ecosystems
Plants and algae use free inorganic phosphorus; animals eat plants to obtain their phosphorus
Limiting nutrient
Weak link in an ecosystem; shortest supply relative to the needs of organisms
Nitrogen and phosphorus can also be limiting nutrients for both terrestrial and aquatic ecosystems
Iron is the limiting nutrient for algal populations in about 1/3 of world’s oceans
Flow of Energy in Ecosystems
Energy is never recycled Energy exists as: Light Chemical-bond energy Motion Heat First Law of Thermodynamics: energy is neither created nor destroyed; it changes forms
Second Law of Thermodynamics: whenever organisms use chemical-bond or light energy some is converted to heat (entropy)
Earth functions as an open system for energy
Sun is our major source of energy
Earth’s incoming and outgoing flows of radiant energy must be equal for global temperatures to stay constant
Human activities are changing the composition of the atmosphere
Greenhouse effect: heat accumulating on Earth, causing global warming
Trophic levels: which level an organism “feeds” at
Autotrophs: “self-feeders” synthesize the organic compounds of their bodies from inorganic precursors
Photoautotrophs: light as energy source
Chemoautotrophs: energy from inorganic oxidation reactions (prokaryotic)
Heterotrophs: cannot synthesize organic compounds from inorganic precursors
Animals that eat plants and other animals
Trophic levels Primary producers: autotrophs Consumers: heterotrophs Herbivores: first consumer level Primary carnivores: eat herbivores Secondary carnivores: eat primary carnivores or herbivores Detritivores: eat decaying matter Decomposers: microbes that break up dead matter
Productivity: the rate at which the organisms in the trophic level collectively synthesize new organic matter
Primary productivity: productivity of the primary producers
Respiration: rate at which primary producers break down organic compounds
Gross primary productivity (GPP): raw rate at which primary producers synthesize new organic matter
Net primary productivity (NPP): is the GPP less the respiration of the primary producers
Secondary productivity: productivity of a heterotroph trophic level
Fraction of incoming solar radiant energy captured by producers
Something around 1% per year
Primary producers capture this in chemical bond energy
Carry out their own respiration
Losses to heat
Heterotrophs have only chemical-bond energy left in primary producers
Amount of chemical-bond energy decreases as energy is passed from one trophic level to the next
50% of chemical-bond energy is not assimilated and is egested in feces
33% of ingested energy is used for cellular respiration
17% ingested energy is converted into insect biomass
Some is available to next consumer
Ecologists figure as a rule of thumb that the amount of chemical-bond energy available to a trophic level over time is about 10% of that available to the preceding level over the same period of time
hey
Biodiversity and Stability
David Tilman: species richness may increase stability of an ecosystem
Plots with more species showed less year-to-year variation in biomass
Drought: decline in biomass negatively related to species richness
Tilman’s conclusion not accepted by all ecologists
Critics question the validity and relevance:
When more species are added to a plot, the greater the probability that one species will be highly productive
Plots would have to exhibit “overyielding”
Species richness is influenced by ecosystem characteristics
Primary productivity
Habitat heterogeneity
Accommodate more species
Climatic factors
More species might be expected to coexist in seasonal environment
Tropical regions have the highest diversity Species diversity cline: biogeographic gradient in number of species correlated with latitude Reported for plants and animals Evolutionary age of tropical regions Increased productivity Stability/constancy of conditions Predation Spatial heterogeneity
jack
