Life depends on the fact that energy can be converted from one form to another
energy transformations
- Laws of physics govern energy transformations
Two laws govern energy transformations
- First Law of Thermodynamics
- total amount of energy in the universe remains constant
- Second Law of Thermodynamics
- disorder (or entropy) in the universe is continuously increasing
- heat is one form of disorder
- Global energy budget
- we can potentially trace all the energy
- from
- its input as solar radiation
- to
- its release as heat
- energy
- enters "earth system" as
- visible light, infrared, UV radiation
- undergoes transformations
- degrade its form to heat
- leave "earth system" as heat
Trophic structure is a key factor in ecosystem dynamics
- Feeding relationships between organisms of an ecosystem
- determine routes of energy flow and chemical cycling in an ecosystem
- Ecosystems include
- producers (autotrophs
)
- consumers (heterotrophs)
- producers (autotrophs
)
- usually photosynthetic
- CO2+H20 ---> C6H12O6 +O2
- includes
- plants, algae, some bacteria, some protists
- consumers (heterotrophs
)
- organisms that must obtain organic molecules synthesized by autotrophs
- includes
- animals
- fungi
- most protists
- most bacteria
- several levels of consumers exist
- primary consumers
- secondary consumers
- decomposers
- Energy transformations in an ecosystem
- can be followed by grouping the species in a community into trophic levels
- food chain
- a stepwise flow of energy and nutrients
- from plants (producers)
- to herbivores (primary consumers)
- to carnivores (secondary and higher-level consumers) as one organism feeds on another, energy flows through the series
- food chain
- in general, from one level to the next
- amount
of total energy passed on decreases
- number
of organisms decreases
- total biomass
decreases
- food web
- interacting food chains
- defines feeding relationships among organisms
- passage of energy through ecosystems
- relatively small percentage of energy ingested at one trophic level reaches next trophic level
- ~10% on average
- ~5% for carnivores
- ~20% for herbivores
- Energy in food chains
- stepwise energy loss
- limits most food chains to 3 - 5 levels
- Community energy budgets
- example seen in study of flow of energy in freshwater ecosystem at Cayuga Lake
- Ecological pyramids
- Graphic representations of the relative energy amounts at each trophic level
- 3 types of Pyramids
- Pyramid of Energy
- Pyramid of Biomass
- Pyramid of Numbers
- Ecological pyramids
- inverted pyramids
- occur in some aquatic ecosystems
- biomass of consumers can exceed that of producers
- Ecosystem productivity
- An ecosystem’s energy budget depends on primary production
- Primary production
or primary productivity
- amount of organic matter produced from solar energy by autotrophs in a given period of time
- gross versus net primary productivity
- gross primary productivity
(GPP)
- total amount of light energy that is converted into chemical energy in a community in given time
net primary productivity (NPP)
- amount of organic matter produced in a community in a given time that is available for heterotrophs
- NPP = GPP – R
- biomass
- net weight of all organisms living in an ecosystem (or trophic level)
- increases as a result of net production
- Net primary productivity varies among ecosystem types
- Net primary productivity by ecosystem type
- tropical forests ~1500-3000 g/m2/yr
- wetlands ~1500-3000 g/m2/yr
- temperate forests ~1200-1300 g/m2/yr
- savanna ~900 g/m2/yr
- deserts ~90 g/m2/yr
- Major limits to primary productivity
- in terrestrial ecosystems
- temperature, moisture, nutrients
- in aquatic ecosystems
- Secondary productivity
- rate of production by heterotrophs
- amount of chemical energy in consumers’ food that is converted to their own new biomass during a given time period
- One way to understand
secondary production is
to examine the
process in
individual
organisms.
Energy flow vs. Matter Cycling
- energy flows through the earth system
- Matter cycles through the earth system
Matter cycles within ecosystems
- Organisms depend on the ability to recycle basic "components" of life
- Matter cycles through both biotic and abiotic components of ecosystems
- called biogeochemical cycles.
- cyclic pathways involving biological, geological and chemical processes
- There are many biogeochemical cycles
- unified by the involvement of the four reservoirs of earth system through which matter cycles
- lithosphere (rocks and soils)
- atmosphere
- hydrosphere(oceans, surface waters, groundwaters, glaciers)
- biosphere (living organisms)
- Chemicals in these reservoirs have different average times of storage or cycling
- depending on two main determinants
- chemical reactivity of the substance
- whether it has a gaseous phase at some point in cycle
- Generalized average times of storage or cycling based on reservoir
- long
- lithosphere (rocks and soils)
- intermediate
- hydrosphere(oceans, surface waters, groundwaters, glaciers)
- biosphere (living organisms)
- short
- 3 main categories of biogeochemical cycles
- Hydrologic
- Gaseous
- Sedimentary
- Gaseous
- involves exchanges among the atmosphere, biosphere, soils and oceans
- include
- Carbon Cycle
- Oxygen Cycle
- Nitrogen Cycle
- Sedimentary
- Involve materials that move from land to oceans and back
- include
- Phosphorous cycle
- Sulfur cycle
- Main biogeochemical cycles
- water cycle
- carbon cycle
- oxygen cycle
- nitrogen cycle
- phosphorous cycle
- Energy flow s through ecosystems
- ecosystems
- global energy budget
- physical laws governing energy transformations
- energy transformations in ecosystems
- trophic levels, food chains, food webs, primary and secondary production
- Matter Cycles through ecosystems
- types of cycles
- types of reservoirs
- major cycle (names)
The End