Biodiversity and Ecosystem function


How many species are needed to make an ecosystem work?

Why should we conserve species?

  • Theocentric-most religions comment on caring for nature, stewardship, part of creation.
  • Biocentric- ethical arguements: living organisms have the right to exist and future generations the right to see organisms we experience now.
  • Anthropocentic- Species are fundamental to the ecosystem processes that enrich our lives.


What is the evidence that biodiversity is important for sustaining ecosystem processes?

Natural Capital: Stocks- Flow - Benefit

e.g. Capital stock of soils and trees = Timber, drugs, Clean Water, Aesthetics, Shelter 

Environmental degradation changes the stock and reduces the flow.

Bees and pollination

Wildflowers/field/crops- Bee pollination- Apples. citrus, tomatoes, peach, melons, straberries, apricots, cherries, almonds, mangoes, cotton.

Service valued at $112 billion worldwide

Populations are declining dramatically in recent decades- due to pesticide use? disease?

Which species do we need to save?

Models of biodiversity: ecosystem functioning

Model 1- Linear relationship: all species are equally important- if we loose any-direct loss of services.

Model 2- Loss of species has a random effect on a process. Effect on processes is highly dependent on species identity and the order in which they are lost.

Model 3- Many species can be lost before a process is affected-therefore some species are not necessary to fulfilling a process- redundancy.

Which model is most relevant?

The Ecotron (Imperial College 1993/4)

Highly controlled growth chamber- soil, plant, decomposers. herbivores…


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