ecosystems, biogeochem & 1º production

Question 1

how can all ecosystems be understood?

Answer 1

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

Question 2

First Law of Thermodynamics

Answer 2

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

Question 3

Second Law of Thermodynamics

Answer 3

entropy of a closed system always ↑ (or remains constant)

Question 4

summary of energy in an ecosystem

Answer 4

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

Question 5

entropy

Answer 5

measure of disorder in a system

Question 6

-ves of thermodynamics

conservation of energy law

Answer 6

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

Question 7

law of mass conservation

Answer 7

• 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

Question 8

how is recycling of chemicals facilitated?

Answer 8

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

Question 9

ecosystem

Answer 9

• ecological community
• and abiotic env with which it interacts

Question 10

conservation of energy law

in an ecosystem

Answer 10

• 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

Question 11

weathering

Answer 11

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

Question 12

erosion

Answer 12

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

Question 13

nutrient enrichment

Answer 13

• 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

Question 14

describe toxic effects of excess nutrients

Answer 14

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

Question 15

dead zone

Answer 15

• areas of water where aquatic life cannot survive …
• due to low oxygen levels

Question 16

consequence of dead zones and efforts to reduce dead zone size

Answer 16

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

Question 17

1º production

Answer 17

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

Question 18

global energy budget

Answer 18

• 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)

Question 19

GPP

Answer 19

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

Question 20

NPP

Answer 20

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

Question 21

NEP

net ecosystem production

Answer 21

GPP - community resp

Question 22

estimating production

Answer 22

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

Question 23

1º production in diff ecosystems & geographical locations

Answer 23

• 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

Question 24

1º production in aquatic systems is limited by…

Answer 24

light & nutrients

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

Question 25

Aquatic ecosystems **Geographic variation** in 1º production is largely shaped by **nutrients**

Answer 25

- **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

Question 26

terrestrial ecosystem

Answer 26

- 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)

Question 27

example of human activity/**eutrophication** impacting terrestrial ecosystems

Answer 27

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

Question 28

Gross **secondary** production (GSP)

Answer 28

total energy taken in - excretion (**food eaten - excretion**)

Question 29

Net secondary production (NSP)

Answer 29

amount of energy in consumers’ food that is converted to biomass (**GSP - respiration**)

Question 30

Production efficiency

Answer 30

- 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**)

Question 31

trophic efficiency

Answer 31

% 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%)

Question 32

where does all the energy go (in trophic efficiency)?

Answer 32

- ***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

Question 33

Why is so much ‘food’ left uneaten?

Answer 33

- global terrestrial NPP **~6x10¹º** metric tons/ year... - of which herbivores consume **< 20%**

Question 34

the **green** world hypothesis

Answer 34

**top-down** control of herbivores by predators **allows plant biomass to accumulate**

Question 35

the **bad tasting** world hypothesis

Answer 35

plants evolve defenses that force herbivores to **compete** for **limited amount of palatable food** -> **bottom-up** regulation