ecosystems, biogeochem & 1º production Flashcards
& energy transfer
how can all ecosystems be understood?
- in terms of transfer and transformation of energy and matter
- energy flows one way through ecosystem
- cycling of matter within ecosystem
First Law of Thermodynamics
- energy cannot be created or destroyed …
- only transferred / transformed
Second Law of Thermodynamics
entropy of a closed system always ↑ (or remains constant)
summary of energy in an ecosystem
- energy enters most ecosystems as solar radiation…
- and is transformed by p/s into chemical energy…
- which is transferred between trophic levels and everntually lost as heat
entropy
measure of disorder in a system
-ves of thermodynamics
conservation of energy law
- energy flows through ecosystems -> cannot be cycled / recycled
- energy transfer is inefficient between trophic levels –> energy used and some is always lost
law of mass conservation
- mass is neither created nor destroyed
- elements can be combined into molecules but cannot be created or transformed
- chemical elements (C, N, O, etc.) exist in env, can be incorporated into organisms, and can be recycled
how is recycling of chemicals facilitated?
by activity of detritivors and decomposers
- detritivors feed on dead organic material
- decomposers further break down organic material left behind by detritivors into simpler substances
- closed nutrient cycle -> nutrients recycled back into soil, then used by living organisms again
^without them, organic matter would pile up until available elements are exhausted
ecosystem
- ecological community
- and abiotic env with which it interacts
conservation of energy law
in an ecosystem
- refers to principle that energy is neither created nor destroyed within the system…
- but is instead transferred / transformed from one form to another
- this concept is derived from 1st law of thermodynamics: states that total energy in a closed system remains constant
weathering
- caused by atm (wind and water) and wildlife
- may be physical (heat, water, ice, pressure) or chemical (biological or atmospheric)
erosion
transportation and deposition of weathered material (e.g. by wind and water)
nutrient enrichment
- human activities (eg. in agriculture) can lead to movement of nutrients across diff parts of biosphere
- most biogeochemical cycles now disrupted/dominated by human activities
describe toxic effects of excess nutrients
eg. Mississippi River carries nitrogen pollution to Gulf of Mexico -> causing summer phytoplankton blooms
When phytoplankton die: their decomposition creates a “dead zone” with low oxygen levels along the coast
dead zone
- areas of water where aquatic life cannot survive …
- due to low oxygen levels
consequence of dead zones and efforts to reduce dead zone size
- disappearance of fish & other marine animals -> impacting economically important waters
- improved fertilizer use by farmers and wetland restoration in the Mississippi watershed
1º production
- amount of energy that autotrophs convert into usable chemical energy (organic compounds)
- determines amount of energy available for consumption by:
-> Herbivores
-> Carnivores
-> Detritivores
global energy budget
- 1º production driven by availability of solar energy
^ (approx. 1022 J of solar energy/day) -
not all solar radiation is available for p/s…
-> absorbed, scattered, reflected by clouds/dust, lands on non-photosynthetic surfaces - only 1% of visible light that strikes photosynthetic organisms is converted into chemical energy
- photosynthetic rates / light absorption dep. on photosynthetic accessory pigments (chlorophyll, carotenoids, phycobilins)
GPP
rate of conversion of light energy->chemical energy (i.e. biomass) by p/s
NPP
- rate of chemical energy (i.e. biomass) production after resp has been subtracted
- (NPP = GPP – Respiration)
- amount of energy available to consumers
NEP
net ecosystem production
GPP - community resp
estimating production
important diff between NPP & biomass of producers present at a given time (i.e. standing stock)
eg. forest standing stock > grassland standing stock but NPP of forests is typically smaller than NPP of grasslands
1º production in diff ecosystems & geographical locations
- Rainforests:
-> high NPP
-> large contribution to global NPP - Oceans:
-> low NPP
-> large contribution to global NPP - Deserts:
-> low NPP
-> small contribution to global NPP - Corals:
-> high NPP
-> small contribution to global NPP
1º production in aquatic systems is limited by…
light & nutrients
-> light availability limits production to surface waters in freshwater & marine ecosystems
Aquatic ecosystems
Geographic variation in 1º production is largely shaped by nutrients
- iron availability in central ocean gyres
- nitrogen limitation in marine coastal waters
- phosphate limitation in freshwater
-> many of these patterns changed by human activity…
eg. eutrophication from domestic, industrial & agricultural activity
terrestrial ecosystem
- on large scales, 1º production driven by climate: ↑ productivity in warm & wet areas
- on regional & local scales, production constrained by nutrient availability
-> plants have extensive adaptations to sequester nutrients (e.g. extensive roots, interactions with fungi & bacteria)
example of human activity/eutrophication impacting terrestrial ecosystems
Alpine meadows
- many plants mutualistic with microbes to survive low nutrient availability
- nutrient addition => switches plant-microbe interactions towards parasitism & ↓ production in some plant sp
Gross secondary production (GSP)
total energy taken in - excretion (food eaten - excretion)
Net secondary production (NSP)
amount of energy in consumers’ food that is converted to biomass (GSP - respiration)
Production efficiency
- calculate eff. as % of energy assimilated from food that is used for growth (i.e. new biomass)
- NSP ÷ GSP
- inefficiencies occur (never 100%) as not all of what organism eats can be digested & organisms use energy (i.e. energy resp)
trophic efficiency
% production transferred at each trophic step
- trophic efficiency < production efficiency (some portion of each trophic level is not consumed)
- trophic eff. typically ~10% (range from 5-20%)
where does all the energy go (in trophic efficiency)?
- decomposers: breakdown dead organic matter externally & then absorb nutrients (e.g. bacteria, fungi, protists)
- detritivores: eat/consume dead organic matter/detritus (e.g. earthworms, millipedes, slugs, termites)
- coprovores: organisms that consume & re-digest waste produced by other
Why is so much ‘food’ left uneaten?
- global terrestrial NPP ~6x10¹º metric tons/ year…
- of which herbivores consume < 20%
the green world hypothesis
top-down control of herbivores by predators allows plant biomass to accumulate
the bad tasting world hypothesis
plants evolve defenses that force herbivores to compete for limited amount of palatable food
-> bottom-up regulation
