lecture 4 ecology Flashcards
how have we defined ecosystem function so far
- species interactions
- energy and nutrient flow (how nutrients are cycled within ecosystems)
how ecosystems “work” – what is being altered
humans are altering ecosystem function
important questions we ask ourselves:
- what is a healthy ecosystem,
- does health = good function
- how does an ecosystem ‘function’
components of an ecosystem ( draw mapping)
living and non living componenets (living organisms, dead organisms) — biotic factors
(physical environment) – abiotic factors
in a sqaure (physical environment) top will be primary producers which are autotrophs, then we will have primary consumers (which consume the primary producers) then we will have secondary consumers (consume organisms further down into food web)
we will then have decomposers (feed on dead organic matter) and then we will have detritus (which is the dead organisms)
what are primary consumers examples of
herbivores
what are primary consumers, secondary consumers, and decomposers and example of
heterotrophs
what are the primary producers examples of
autrophs
what are autotrophs
organisms that make their own food/chemical energy
what re heterotrophs
organisms that get energy from consumer other organisms (living or non living)
living component – more detail definition
group of organisms that process energy and nutrients in SIMILAR ways
the compoenents are connectewd, what two ways does energy and nutrients flow – draw mapping of arrows.
between organisms and between evironment
red arrow = bw organisms
blue arrow = bw environment
– red arrow bw primary producer and primary consumer because primary consumer eats PP obtaining energy and nutrients from it.
– red arrow bw primary consumer and second consumer because second consumer eats and obtains energy from promary consumer
– red arrow between detritus and secondary because secondary die and vbecome dead organisms.
– red arrow between primary and detritus because they die and become dead organisms between decomposers and secondary because secondary also eat decomposers (some of them)
– two arrows between decomposers and detritus because decomposers can die and they also break down dead organsisms to obtain energy.
black arrows coming out of each thing and a black arrow from environmewnt to PP
how is the ecoysystem function characterized
by connenctions between components and flow of energy and nutrients
what are ecosystems powered by
majority powered by the sun
energy flow firsat step (sun, PP)
Primary producers capture radiants energy )photosynthesis) and store it as chemical energy (molecular bonds in orangic compounds (carbohydrate, sugars, ATP))
Energy flow second step (PP, PC)
Ecosystems transfer chemical energy through consumption (transfer to consumers) and Death (transfer to detritus)
detritus and consumptions –
not sonsumed directly, usually floats in ewaters, or falls to the ground, energy is locked up and decomposers will feed on the nutrients.
what is also happening as energy is entering the ecosysatem –
energy is also lost (heat Loss) through respiration – therefore the energy flow is not a perfect loop.
what direction is energy flow
irt is a one-way flow – enters as radiant energy, stored and transferred as chemical energy, and leaves as heat energy. – has to be a continued input of sunlight to maintain one-way energy flow
how can we compare ecosystem energy flow
- amount of energy reaching ecosystem
- efficiency of energy capture
- transfer rates
- rates of energy loss
ecosystem nutrient cycling
more of a closed loop
- we need nutrients in addition to sunlight to build new biomass.
- nitrogen compoinds
- flows from organisms to physical enviironment and back to ecosystem via the primary producers.
– circular flow of nutrients – nutrients mostly retained – cycle bw organisms and physical enviornment
CO2 in the cycle
plants get CO2 (gas) from atmosphere and convert it to organic carbon. Org. C is transfewrreed among components. CO2 is returned into atmosphere through respiration.
what component plays an important role in nutrient cycling
decomposers
– invertebrates, fungi, bacteria
– they obtain chemical energy and nutrients that qwere locked up in detritus and return some nutrients back to physical environmeny to keep flow of nutrients going
how can we compare ecosystem nutrient cycles - give examples for some
-nutrient stores in physicasl environment (soil [diff levels of nutrients])
- efficiency of nutrient uptake (macroalgae (high nutrient) vs corals (low nutrient)
- transfer rates
- retention of nutrients (retained within ecosystem)
little recap of nutrient and energy flow
– an ecosystem processes and transfers energy and nutrients
– fueled by energy from outside the ecosystem
– cycle and recylce nutrients from and to the physical enviornment
an ecosystem might be ‘unhealrthy’ ifg it is less able to
– obtain or transfer energy (decline in Primary Producers
– cycle or retain nutrients (losing key species [decomposers])
Measures of ecosystem function
- rate of primary production
- rate of secondary production
- rate of decompositionr
rate of primary production
how effectively sunlight is being tuerned into primary produced biomass.
– energy capture and nutrient uptake
– death rates
– plant respiration (heat loss)
– these are the factors it depends on
rate of secondary production
supported by primary consumers
– energy and nutrient transfer
– death rates
– respirationr
rate of decomposition
rate that inorganic nutrients are released from detritus
reasons to care about ecosystem health and function
– feeding ourselves
– natural ecosystems
– we are changing the rates
feeding ourselves
– primary production – how fast can we GROW food.
– secondary production – how fast can we turn plants into animals
– decomposition – nutrient supply for growing plants
without these factors, we would not have any food.
Natural ecosystems
– primary production – plant/tree abundance and recovery after disturbance
– secondary production – animal diversity and abundance
– decomposition – nutrient suopply
we are changing the rates
– deforestation – primary production impacted
– use of fertilizers – packing up nutrients
– green house gas emissions and climate change – affects nitrogen cycle
Net primary productiion NPP
– rate that biomass increases in an ecosystem (measureing how much plant biomass is being produced in an ecosystem)
energy coming in - energy that is lost
biomass definition
amount (mass) of organic matter present in an ecosystem
gross primart production GPP
total light energy captured by plants
autotrophic respiratiopn (Ra)
energy lost due to PLANT respiration (hence autotrophic)
Net Ecosystem Production NEP
Energy (biomass) accumulated in ALL ecosystem COMPONENTS
total respiration (Rt)
heat lost from all componnents
NEP <0
ecosystem is losing biomass
– ecosystem releases MORE CO2 than it absorbs
– contributes to increasing atmospheric CO2
NEP >0
ecosystem biomass is increasing
– ecosystem absorbs more CO2 than it releases
– helps lower atmosphereic CO2 (climate change)
what limits NPP in terrestrial ecosystems
temperature, and light
- latitude
- elevation
m,oisture (water availability)
– soil nutrients
– limiting nutrient (nitrogen) – why we add fertilizers (to overcome limitation)
The nitrogen cycle – things to know
Nitrogen is essential for life
– forms of nitrogen
– pathways – where they go
– biotic components (where locked up in terms of biology)
– physicasl reservoirs
– how humans have altered pathways and flow rates
What do bacteria do in terms of the nitrogen cycle
bacteria drives the nitrogen cycle
– theres essentially three types of bacteria translating diff forms of nitrogen
1st step in nitrogen cycle
nitrogen fixation (N2 –> NH4+) N2 is abundant in our atmosphere – inert so it cannot be used, therefore needs to be converted to ammonium (by nitrogen fixing bacteria either free living or in symbiosis w another organism)
2nd step of nitrogen cycle
Nitrification (NH4+ –> NO3-) (by nitrifying bacteria)
3rd step of nitrogen cycle
denitrification (by denitrifying bacteria) (NO3- –> N2) back into the atmpshere as nitrogen gas
what are the physical reservoirs for nitrogen cycle
soil water and atmosphere.
decomposition vs assimilation nitrogen cycle
decomposition from detritus (organic N locked up) (organic –> NH4+)
assimilation
– NH4+ –> organic N
– NO3- –> organic N
draw diagram of nitrogen cycle, adding plants decomposition and assimilation
starts – N2 in atmosphere – N-fixation by bacteria – NH4+ – in soil water – Nitrification – NO3- – denitrification – N2 back in atmosphere
Detritus – decomposition – NH4+ – assimilation – plants
NO3- – assimilation – plants
in simple terms, what is assimilation relative to the nitrogen cycle
when plants absorb nitrogen from the soil in the form of organic Nitrogen
terrestrial plant growth : nitrogen limited
Pristine (natural) – N-fixation N2 –> NH4+ (85 Tg/yr) mostly by N-fixing bacteria, some by lightning
Human input (220 Tg/yr) – mostly by agriculture, some by burning fossil fuels
how does agriculture increase the rates of N-fixation
- growing legumes (soybeans, peas, beans) – they have the symbiotic relationship with nitrogen fixing bacteria (60 Tg/yr)
- manufacturing fertilizer (135 Tg/yr)
consequences of applying N fertilizer
– long term impacts of excessive nitrogen inputs
- High nitrate (NO3-) levels in soil water – can be toxic
- loss of nutrients from soil (e.g., calcium)
- pollution of aquatic ecosystems (increase of nutrients in aquatic ecosystem drives increase in macroalgae growth)
what limits NPP in marine ecosystems
light, depth, nutrients
– increase is nutrients can lead to eutrophication which is excessive primary production (algal growth) ex: macroalgae
– phytoplanktons are decomposers, they use a lottt of oxygen if many of them – fish dye as a result.
what is eutrophication
excessive primary production due to overload of nutrients
what is the dead zone
low O2 levels, fish and others die
fertilizer summary
– fertilizer converts N2 to forms that plants can use (NH4+ and NO3-)
– overuse leads to increase NO3- levels in soil water
– excess nitrogen ends up in aquatic ecosystems
– eutrophication and oxygen-depletion in fresh water and coastal habitats
fossil fuel use
burning fossil fuels adds nitrogen to atmosphere
– nitrogen is deposited back into ecosystem
Humans impact sumary
through application of fertilizer and burning fossil fuels, humans have hugely increased amount of available nitrogen.
secondary legume crops – N2–> NH4+
primarily fertilizer – N2 –> NH4+ + NO3-
thirdly fossil fuels – Org N –> NO3-
