Ecosystem ecology:
Pools and fluxes
So far this semester
- Dynamics of individual populations
- Keep track of individual organisms’ birth rate & mortality rate
- Dynamics of species interactions
- Keep track of overall types of iteractions, e.g. competitive, consumer–resource
- Species diversity over space and time
- Patterns over large and small scales
Now
- Ecology of ecosystems
Scope of ecosystem ecology
Patterns and drivers of major energy/substance fluxes
Net primary productivity across the globe
https://neo.gsfc.nasa.gov/view.php?datasetId=MOD17A3H_Y_NPP
Major drivers of global water cycle
https://www.usgs.gov/media/files/water-cycle-poster-pdf
Major drivers of global nitrogen cycle
Life: The Science of Biology
What defines an “ecosystem”?
- All the organisms in an area and abiotic matter/energy with which they interact
- When we study ecosystems, we consider them as ‘bounded’ systems
- Artificial boundary - but necessary for science
“The ecosystems we isolate mentally are not only included as parts of larger ones, but they also overlap, interlock, and interact with one another.”
- Arthur Tansley
Some questions that ecosystem ecology studies
- What determines the productivity of a system, and why is it so different across the globe?
- What controls the movement of chemicals and energy through a system?
- How do ecosystem process affect biodiversity, and how are they shaped by biodiversity?
Ecosystem Ecology: pools and fluxes
Approach to ecosystem ecology
What are the pools of energy or substance in the system?
What are the fluxes of the energy or substance in the system?
What happens when ecosystem processes are perturbed?
- e.g. Fertilization, Extended droughts, Warmer temperatures
How do these changes affect biodiversity and productivity?
Pools and Fluxes
Consider the global water cycle
What are the major pools?
What are the major fluxes?
https://labs.waterdata.usgs.gov/visualizations/water-cycle/index.html#/
Some questions that ecosystem ecology studies
- What determines the productivity of a system, and why is it so different across the globe?
- How are distinct global cycles linked with one another?
- What controls the movement of chemicals and energy through a system?
- How do ecosystem process affect biodiversity, and how are they shaped by biodiversity?
Some questions that ecosystem ecology studies
- What determines the productivity of a system, and why is it so different across the globe?
- How are distinct global cycles linked with one another?
- What controls the movement of chemicals and energy through a system?
- How do ecosystem process affect biodiversity, and how are they shaped by biodiversity?
What explains variation in net productivity across the globe?
First-order explanation: productivity is shaped by precipitation and temperature
The question then becomes, what shapes precipitation and temperature?
- Structural explanation
- Dynamic explanation
Structural factors behind temperature
- Latitudinal gradient in temperature
- Seasonal variation in temperature
Structural factors beind precipitation
- Distribution of water & patterns of temperature variation
Structural factors behind precipitation
Inter-tropical convergence zones
Structural factors behind precipitation
Rain shadow effect
Patterns of precipitation are not driven by “structural” factors alone
- Consider the fluxes in the water cycle
Patterns of precipitation are not driven by “structural” factors alone
- Consider the fluxes in the water cycle
- How much water does an “average” oak tree transpire annually?
Patterns of precipitation are not driven by “structural” factors alone
Landscapes with vegetation that transpire more water will have larger evapotranspirative flux, which moves water from the groundwater pool to the atmospheric pool
Depending on what happens to the atmospheric water, this can cause more rainfall somewhere
Human modified landscapes often have reduced rates of evapotranspiration
(fig. 2 from Spracklen et al. 2018, Annual Reviews of Environment and Resources)
Large reductions in rainfall expected due to land-use change
(fig. 2 from Spracklen et al. 2018, Annual Reviews of Environment and Resources)
Changes in rainfall can lead to “regime shifts”
A more subtle story of the water cycle in the Amazon basin
This analysis provides compelling observational evidence that rainforest transpiration during the late dry season plays a central role in initiating the dry-to-wet season transition over the southern Amazon
The fate of the southern Amazon rainforest depends on the length of the dry season.
The length of the dry season also depends on the rainforest.
Feedbacks at the ecosystem scale
Cloud seeding as a way to “trigger” more rain?
Why does this matter?
- Large-scale ecosystem processes are not just ‘set in stone’
- They are always in relationship with the biological processes that unfold
- This means that disruptions to the biology can have important consequences to the ecosystem as a whole
Next class
- Diving into the Nitrogen cycle.
