lecture 22: ecosystem processes Flashcards
What are ecosystems?
Multiple populations of organisms that live in an area + Abiotic components (soil, water, atmosphere)
What arethe ecosystem processes?
Biotic + abiotic components of ecosystem are linked by:
1. FLOW of energy: energy dissipates as it flows through ecosystems
2. CYCLING of nutrients: nutrients cycle within ecosystems
—> Food webs: primary producers, decomposers, consumers (primary, secondary…)
Gross (GPP) vs Net primary production (NPP)
Total incoming solar energy —> Gross primary production (GPP) 0.8% of total solar energy
- Small percentage because:
1. Not all light hist photosynthetic tissue & pigments in photosynthetic tissue cannot capture all wavelengths
2. Rate of photosynthesis can decrease du to environmental conditions
—> Net primary production (NPP) 45% of GPP
- NPP = GPP - R (energy used for maintenance of primary producers; cellular respiration, released as heat)
GPP = Total primary production in an ecosystem
NPP: energy invested in production of biomass; converted into organic materials
Why si NPP so important?
Sets ecosystem’s energy budget
Represents amount of energy AVAILABLE to consumers and decomposers as BIOMASS
What limits primary production in terrestrial ecosystems?
- Temperature: high T = better, more active
- Moisture: more water = better, more active
High quantity of primary production: tropical rainforests
Low: deserts, arctic regions
What limits primary production in aquatic ecosystems?
- Inorganic nutrients: limited nutrients
- Sunlight: filtered, only certain wavelengths of light are available underwater
High quantity of primary production: coral reefs, algal beds, coast lines
Low: open ocean
What is eutrophication?
Large increase in populations within a trophic level —> bloom in growth of primary producers (algae or cyanobacteria)
- Excess nitrogen or phosphorus nutrients
- Natural cause or human induced
- Change in color
- Red Tides —> oxygen dead zones/accumulation of toxins —> too much biomass, all O2 used by decomposers, not enough O2 for fish —> eutrophication in lakes —> lead to loss of many fish species
What is secondary production?
Amount of chemical energy in consumers’ food that is converted to new biomass
What is an organism’s production efficiency?
Percentage of energy assimilated by an organism that becomes incorporated into new biomass
- Need to remove energy used for cellular respiration, maintenance of organism
- Vertebrates have LOWER PRODUCTION EFFICIENCIES than invertebrates —> because need MORE energy for cellular respiration and to maintain body
Describe an ecosystem’s pyramid of production
- Energy transfer between trophic levels
- Total biomass = greatest at the lowest trophic level (primary producers) and declines at higher levels
- Trophic-level transfer efficiency = only 5-20%
- Pyramid: less and less biomass/energy, but organisms get larger and larger —> Stop at tertiary/quaternary consumers bc cannot support another trophic level
Why doesn’t all the energy get transferred between trophic levels? (2)
- Energy in food consuemed = used/lost and not transferred for secondary production —> lost as heat
- Used for maintaining life activities via cellular respiration
- Lost in undigested material (feces) - Not all of the biomass in lower trophic level is consumed by next trophic level
Consequence of low efficiency transfer? (2)
- Production can only support 3-4 upper trophic levels
2. Major limitation of food chain length
What is biomagnification?
- Chemical pollutants (persistent organic pollutants; POPs) produced by humans = NOT broken down & accumulate in fatty (lipid) tissues of animals
- POPs increase in concentration (bc less biomass) as they are transferred between trophic levels —> BIOMAGNIFICATION
- High concentrations of POPs can poison upper level consumers + humans that eat them
What is nutrient cycling?
Biogeochemical cycle (phosphorus, sulfur, water, carbon, nitrogen cycles) = moving of elements from abiotic environment through organisms and back again
- Nutrients can be;
1. Inorganic or organic
2. Available or unavailable - Compounds can be transformed and moved from one reservoir to another
What is global cycling?
- Cycle with elements with gaseous phases, globally: carbon, oxygen, nitrogen, sulfur cycle
- Cycle with elements with no gaseous phase: phosphorus, potassium, calcium (less mobi;le, cycle locally in terrestrial systems but more broadly when dissolved in aquatic systems)
What is the carbon cycle?
- Biological importance: carbon-based organic molecules are essential to all organisms
- Forms available to life: photoautotrophs (photosynthesis) convert CO2 to organic molecules that are used by heterotrophs
- Reservoirs: biomass, fossil fuels, soils, sediments, solutes in oceans, atmosphere, rocks
- Processes: carbon compounds are transformed in photosynthesis, cellular respiration and decomposition, volcanic activity and burning of fossil fuels contribute to CO2 to the atmosphere, deforestation (burn wood = more CO2)
- COS is transported as a gas in atmosphere and dissolved in water
What is the nitrogen cycle?
- Biological importance: amino acids and nucleotides contain nitrogen, nitrogen mineral nutrients are often limiting in primary production
- Forms available to life: primary producers assimilate inorganic forms (ammonium NH4+ and nitrate NO3-) and some organic forms (amino acids), various bacteria can uses all these + nitrite (NO2-) —> IN NITROGEN FIXATION, animals can only use organic forms
- Reservoirs: main = atmosphere 80% or N2, need NITROGEN FIXATION (N2 —> NH3) to be used in ecosystem, other reservoirs of inorganic and organic compounds = soils, sediments of lakes, rivers, oceans, biomass of living organisms
- Processes: assimilation, consumption, decomposition, nitrogen fixation, ammonification (organic nitrogen —> NH4+), nitrification (NH4+ —> NO3-), denitrification (NO3- —> N2)
—> Most conversions carried out by BACTERIA (part of their metabolisms)
Human impacts in carbon cycle?
“Locked away” carbon —> mine them and use them
- Gas for cars so more CO2
Human impacts in nitrogen cycle?
Agriculture: fertilizers —> create N gases —> then end up in water —> algal and cyanobacteria blooms
Why conserve biodiversity? (4)
- Prevent extinction: humans depend organisms for food, medicine, industrial products, tools in research
- Maintain healthy (stable and productive, can withstand changes) and diverse ecosystems: humans depend on essential ecosystem services clean air, water)
- Culture (parks), leisure
- Ethical responsibility to protect other life forms
What is extinction? 2 types?
- Natural process that has been documented throughout history of life
1. Background extinction: ≈ 1-2 species extinct every 100 years
2. Mass extinctions: 5 documented from fossil record
Why are we in a biodiversity crisis right now?
- Past 100 years: several species have gone extinct
- Today: >20 000 species are threatened with extinction
- We are experiencing a 6th mass extinction that is human-induced
How are we causing extinction?
- Climate change
- Pollution
- Exploitation: largely reducing populations
- Habitat degradation
- Invasive species and disease: introduced to new habitat, but environment is not made for it (human-induced)
How is genetic drift a concern for conservation biology?
- Many pop. = getting reduced in size by habitat destruction/fragmentation
- Small pop. = Subject to MORE genetic drift
- Pop. become LESS FIT as “low fitness” alleles become fixed by chance (random)
- Pop. with lower fitness = MORE subject to EXTINCTION
