The Importance of Biodiversity

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  • Created by: sikemi__
  • Created on: 22-05-21 16:28

Ecosystem functioning and ecosystem services

Ecosystem functions - "The ecological processes that control the fluxes of energy, nutrients and organic matter through an environment" Cardinale, et al. (2013) e.g. primary production, nutrient cycling, decomposition

Ecosystem services - - "The suite of benefits that ecosystems provide to humanity" Cardinale, et al. (2013). These services are the flows of mineral, energy and information from natural capital stocks which combine with manufactured and human capital services to produce human welfare.

  • Millenium Ecosystem Assessment (2005) - introduced four particular ways we can look at ecosystem services
    • Provisioning services e.g. provision of food, bioenergy, building materials (such as timber) etc.
    • Regulating services e.g. climate sequestration, pest control.
    • Supporting services e.g. primary production, nutrient cycling, soil formation.
    • Cultural services e.g. spiritual, education, recreational in terms of the benefits that we take from them.
  • Must remember that not all species have the same functions within their ecosystems
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Functional diversity

  • The role that a species performs within its ecosystem
  • To measure the importance of that species we often use NPP (for vegetation)
    • e.g. Mediterranean grassland communities in Lesvos, Greece
    • Compared prodductivity of plots which only contained annual grasses vs perennial grasses (latter had greater NPP)
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Keystone species

  • No precise definition, making use of the term diffcult
  • But can be used to describe species that if not present in an ecosystem, the ecosystem will be dramatically different or even cease to exist
  • E.g. worms - if removed from the soil it will become much more waterlogged, meaning that air pockets will fill up and soil will not be aerated, so plant species might die and animal species that are dependent on the plant species too
  • Gannon & Bovard (2016) describe how bats might be keystone species
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Trophic cascades

  • Term first used scientifically by Paine in the 1980s
  • Ripple et al (2016)described trophic cascades as being'indirect species interactions that originate with predators and spread downwards through food webs', where indirect means the influence of one species on another is mediated through the presence of other species
  • Term describes how predators can structure entire communities through interactions with their prey (regarded as a top-down model)
  • An alternative to an opposite view that ecosystems are controlled by nutrient availability and therefore quality of the vegetation (autotrophs) which is regarded as a bottom-up model
  • Now both top down and bottom up are regarded as working simultaneously
  • The cascade does not have to start with the apex (top) predator and does not have to stop at the bottom with autotrophs
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What happens when an ecosystem breaks down?

1. When top predators are removed from an ecosystem

  • Example - Lake Guri
  • Creation of a dam on the Caroni River, Venezuala in 1986 led to river valleys being submerged and hilltops being left as islands
  • Smallest islands lost 75% of their original species, largest islands retained most
  • But within 4 years they had all lost their top predators (jaguars, pumas, harpy eagles)
  • As habitat area shrank, fewer species could be supported so ecological release occurred, removing other species competiting for the same resources
  • Population numbers no longer kept in check by top predators
  • Populations of remaining species increased and they became more abundant on small islands than they would on larger, more species rich islands
  • Trophic cascade effect - unpalatable species become dominant - plants assert control on grazers as they lose their preferred plants - population crash eventually
  • Details given in Terborgh (2001) and Moore (2006)
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Wolves in Yellowstone Natural Park

  • Wolves were extirpated (made locally extinct) from Yellowstone in mid 1920s as they were preying on cattle which were the ranches livelihood
  • Led to ecological release and huge increase in population of Rocky Mountain Elk
  • Elk browse on deciduous tree species e.g. alder so vegetation cover declined. This impacted water levels in streams flowing through the park
  • Between 1995 and 1996, wolves were reintroduced from Canada. Elk populations declined and vegetation recovered (good as it brings benefits to other species and to ecosystem processes and services e.g. nitrogen fixing, cover for fish, shade for temp modification)
  • Example of trophic cascade, or were there other drivers of elk population changes?
    • Hunting (allowed as a sport at the time)
    • Drought in 2000-2007
    • Cold winters e.g. severe winters of late 90's, might have affected young or older elk
    • Carnivores other than wolves e.g. bears
    • Competition for grazing from other mammals
    • But, number of elks steadily reduced after re-introduction of wolves
  • Results of tests on alder showed that it was likely that a wolf-elk-alder trophic cascade
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Links between biodiversity and ecosystem services

  • Sufficient evidence that biodiversity either directly influences (experimental evidence) or is strongly correlated with (observational evidence) certain provisioning and regulating ecosystem services
  • Avoid sweeping statements that biodiversity always benefits society
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