wk 6: carrying capacity/ecological footprint

biological definition of carrying capacity K

• carrying capacity K is max population size of species that the environment can sustain indefinitely given the habituate, water and other necessities required

• production environment can sustain larger pop

ecological definition

• difference btw exponential growth and an ecologically more realistic growth pattern that is constrained by environmental conditions

• expo growth 100% (doubles every time step) (j curve)

• logistic growth: population slows down as it gets closer to carrying capacity

• growth stops at carrying capacity

overpopulation

• population over carrying capacity

• resource depletion

• detoxication system insufficient

• leads to population crash

• depending severity of overshoot

  • slight: pop will fluctuate around carrying capacity → stabilize

  • significant: high potential for environment to become severely damage and permanently reduces ability to be sufficient for pop.

biological definition—applies to humans?

• doesn’t speak about the standard of living the population needs to be sustained indefinitely

earths carrying capacity for humans

• max population that can be sustained at the minimum standard of living necessary for survival

• determined by

  • ecological constraints

  • human choices: economics, environment, culture (values and politics), demography

• k is not static number bc needs change

challenges of carrying capacity approach

• prediction about future of a complex system is difficult

• limited understanding of all the resource system components and interactions

• calculations require massive assumptions about the future influence of technology and societal choices

• predictions associated with large uncertainty, makes it hard to use for planning

ecological footprint: definiton—simple accounting system

• deposits and withdrawals

• deposits: biocapacity—reps planets current biologically productive areas that provide resources and can also absorb waste we generate

• withdrawals: ecological footprint—how much land/water area populations need to produce resources it consumes and to absorb its co2 emissions based on current tech

EF calculations for a person

• unit of measure (currency): global hectare

• 1 global hectare represents 1 hectare of land where the average productivity of the biologically productive land that we have in year

• pastures, fisheries, ecosystems that absorb co2

• bio capacity: 12.2 billion gha in total

• ecological footprint 2.4 billion gha in total

world footprint

• global overshoot: when humanity’s demand on nature exceeds the biosphere’s supply, or regenerative capacity

• to use resources sustainably we can only use the new stuff that is grown every year

  • exceeding means we are getting into old stock (not living off interest but into savings)

earth overshoot day

• calendar day on which we used up the ecological resources and services that nature can regenerate in one year

country comparison

• creditor country: putting in more than it is taking out

  • small EF

  • low pop density

  • large biocapacity

• debtor country: taking out more than it is putting in

  • large EF

  • high op density

  • lowbiocapacity

pros and cons of ecological footprint approach

• accounting system does not require any assumptions regarding future:

  • per capita resource consumption

  • standard of living and ‘wants’

  • productivity of biosphere

  • advances in technology

• method relies on accurate assessments of ecosystem functions, vary spatially and are in state of continual change —bc of continuous damage

resilience

• capacity of a system to absorb shocks and remain without current state without losing its integrity

• limits to how far you can push to system, if pushed too far can exhibit entirely different characteristics

• has been stable for last 1000 years

planetary boundaries—nine planetary systems

• 3 big systems: (valley locations)

  • climate change

  • stratospheric ozone depletion

  • ocean acidification

• regulate the capacity of the resilience of the planet (depth of valley)

  • nitrogen and phosphorus cycle

  • land use change

  • rate of biodiversity loss

  • fresh water use

planetary boundaries—safe operating space

• state that atmospheric concentration of co2 should not go beyond 350 ppm etc etc

• risk of flip to inhabitability happening increases considerably

• rostram et al says we have exceeded thresholds 3 of 9 systems (co2 concentration, nitrogen cycle, extinction rate of species/loss of biodiversity)