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.