ecosystems, biogeochem & 1º production Flashcards

& energy transfer

1
Q

how can all ecosystems be understood?

A
  • in terms of transfer and transformation of energy and matter
  • energy flows one way through ecosystem
  • cycling of matter within ecosystem
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2
Q

First Law of Thermodynamics

A
  • energy cannot be created or destroyed …
  • only transferred / transformed
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3
Q

Second Law of Thermodynamics

A

entropy of a closed system always (or remains constant)

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4
Q

summary of energy in an ecosystem

A
  1. energy enters most ecosystems as solar radiation
  2. and is transformed by p/s into chemical energy…
  3. which is transferred between trophic levels and everntually lost as heat
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5
Q

entropy

A

measure of disorder in a system

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6
Q

-ves of thermodynamics

conservation of energy law

A
  • energy flows through ecosystems -> cannot be cycled / recycled
  • energy transfer is inefficient between trophic levels –> energy used and some is always lost
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7
Q

law of mass conservation

A
  • 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
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8
Q

how is recycling of chemicals facilitated?

A

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

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9
Q

ecosystem

A
  • ecological community
  • and abiotic env with which it interacts
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10
Q

conservation of energy law

in an ecosystem

A
  • 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
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11
Q

weathering

A
  • caused by atm (wind and water) and wildlife
  • may be physical (heat, water, ice, pressure) or chemical (biological or atmospheric)
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12
Q

erosion

A

transportation and deposition of weathered material (e.g. by wind and water)

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13
Q

nutrient enrichment

A
  • 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
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14
Q

describe toxic effects of excess nutrients

A

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

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15
Q

dead zone

A
  • areas of water where aquatic life cannot survive
  • due to low oxygen levels
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16
Q

consequence of dead zones and efforts to reduce dead zone size

A
  • disappearance of fish & other marine animals -> impacting economically important waters
  • improved fertilizer use by farmers and wetland restoration in the Mississippi watershed
17
Q

1º production

A
  • amount of energy that autotrophs convert into usable chemical energy (organic compounds)
  • determines amount of energy available for consumption by:
    -> Herbivores
    -> Carnivores
    -> Detritivores
18
Q

global energy budget

A
  • 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)
19
Q

GPP

A

rate of conversion of light energy->chemical energy (i.e. biomass) by p/s

20
Q

NPP

A
  • rate of chemical energy (i.e. biomass) production after resp has been subtracted
  • (NPP = GPP – Respiration)
  • amount of energy available to consumers
21
Q

NEP

net ecosystem production

A

GPP - community resp

22
Q

estimating production

A

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

23
Q

1º production in diff ecosystems & geographical locations

A
  • 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
24
Q

1º production in aquatic systems is limited by…

A

light & nutrients

-> light availability limits production to surface waters in freshwater & marine ecosystems

25
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
26
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)
27
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
28
Gross **secondary** production (GSP)
total energy taken in - excretion (**food eaten - excretion**)
29
Net secondary production (NSP)
amount of energy in consumers’ food that is converted to biomass (**GSP - respiration**)
30
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**)
31
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%)
32
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 cons**ume & re-digest waste** produced by other
33
Why is so much ‘food’ left uneaten?
- global terrestrial NPP **~6x10¹º** metric tons/ year... - of which herbivores consume **< 20%**
34
the **green** world hypothesis
**top-down** control of herbivores by predators **allows plant biomass to accumulate**
35
the **bad tasting** world hypothesis
plants evolve defenses that force herbivores to **compete** for **limited amount of palatable food** -> **bottom-up** regulation