Conservation 4- Effects of Biodiversity loss

What does biodiversity do for us?
1. 1. Pollination
  1. 2/3 of all food crops benefit from pollination
  2. US $153-- Global annual value
2. 2. Climatic regulation
  1. Destruction of tropical forests accounts for at least 1/4 of all anthropogenic Carbon emission
  2. Kyoto protocol-- international carbon market--- REDD-- reducing emissions from deforestation and degradation
3. 3. Hydrological regulation
  1. High % of precipitation in montane regions is directly onto vegetation
  2. Essential for supply of water to lower altitudes--- agricultural land
What's the relationship between species richness and ecosystem functioning?
1. 3 possible relationships between species richness and ecosystem function
  1. Redundancy-- reduce species richness with very little effect
  2. Rivet-popping-- Reduce species richness-- at first nothing much, reach threshold, ecosystem function then drops to new stable level, repeats
  3. Idiosyncrosy-- might be no relationship at all between richness and function--- loss of predator but increase in another species
2. Evidence supports positivity with some evidence of reduncy
  1. Plant species richness and total plant cover--- positive correlation but levels off between 12 and 23 species
  2. Plant species and microbial biomass--- positive correlation--- but only 3 data points
  3. Number of Mycorrhizal fungal species increases shoot biomass
  4. Number of species and Co2 flux-- positive correlation
  5. Number of consumer species and autotrophic biomass-- negatively correlated
3. Possible mechanisms
  1. Sampling-- larger sample-- more likely to contain one or more species which contribute a lot
  2. Species complimentary--- difference in resource use-- more species-- more thorough use of resources
  3. Positive interactions--- more species leads to more mutualistic interactions
4. Does reduncy mean that there are lots of spare species in terms of ecosystem fucntion?
  1. 1. We need insurance-- a pool of species that can buffer a system against environmental uncertainty
  2. 2. We need a longer view-- long-term relationships, not just short-term
5. Loss of pleistocene megafauna
  1. Fruit too large and tough for any living species to disperse their seeds--- often restricted to riverbanks
  2. Dispersal relied on megafaunal species that went extinct at the end of pleistocene
Trophic cascades and co-extinctions
1. 1. Barro Colorado Island- bottom up
  1. Small island in Panama: formed when River Chayres dammed to provide water for Panama canal
  2. At time of isolation, several large predators-- all disappeared soon after
    1. Pumas
    2. Jaguars
    3. Harpy Eagles
  3. Disappearance resulted in 2-10 fold increase in medium sized predators and omnivores
    1. Cotimunids
    2. Pacas
    3. Monkeys
  4. By 1970s-- 45 species of bird has disappeared-- all ground nesting species-- nest predation
    1. Wood-Quail
    2. Ground-Cuckoos
    3. Ant-thrushes
2. 2. Venezuela- top down
  1. Set of islands created by hydroelectric impoundment
  2. Small islands (>1 ha)-- no predators of vertebrates
  3. Lack of predators led to densities of seed predators and herbivores-- 10-100 times greater than on nearby mainland
    1. Rodents
    2. Howler monkeys
    3. Iguanas
    4. Leaf-cutter ants
  4. Density of seedlings and saplings of canopy trees severely reduced
  5. Forest is being stopped from regenerating
3. 3. Alaska- Mixed top down and bottom up
  1. Over hunting of sea otters reduced once complex kelp forest to a 2 trophic layer system of sea urchins grazing on algae
  2. Sea otters-- major predator of sea urchins, sea urchin pop increased-- over grazed and reduced algae
  3. Relaxation of hunting pressure restored the system in some places
  4. Problem is predation by Orcas-- normally prey on larger seals and sea lions-- decline in these due to decline in fish stocks due to climate change
  5. System is mainly top-down control, but with increasing bottom-up effects
4. 4. Coextinction-- Plants and pollinators
  1. Recent stud of Bees and hoverflies in Britain and the Netherlands-- revealed a casual connection between local extinctions of plants and pollinator species
  2. In Hawaii-- Several plant species in genus Hibiscadelphus were pollinated exclusively by individual species of honeycreeper-- honeycreeper extinct-- plant species now extinct or citically endangered
Does the stability of ecosystems vary with species richness?- Two opposing views
1. 1. Species- rich communities are more stable
  1. More complex food webs with more cross-linking
  2. Losses can be absorbed
  3. Losses have less impact on remaining species
  4. Relevant view up until 1970s
2. 2. Species-rich communities are less stable
  1. With more species-- each species is less abundant (fixed amount of resources)--- more risk from extinction processes
  2. Consequences propagate more widely through multiple trophic connectionsL prevalent view during 1970s-1990s
  3. *May's paradox*
    1. Species-rich communities have lower constance
      1. Ability of an ecosystem to retain the number of species present
      2. More likely to lose species
    2. Species rich communities have higher resilience-- they are more likely to continue functioning normally despite lower constancy
    3. Evidence from experimental grasslands
      1. Plots with higher species richness had not only higher average productivity but also less variable productivity over a period of 10 years
      2. At the same time, species-rich plots varied much more in terms of the relative abundance of species
      3. Stable biomass was maintained not because of steady populations but despite a more unstable dynamic system where there were more species present
      4. Logging in tropical forests had much larger impact on species richness than on trophic structure
Recent data suggests that weak trophic interactions may in fact play a vital role in stabilising food-webs and species rich food webs probably contain weak interactions-- Herring gull and Dog whelk feed on common mussel
1. Common mussel declines and the herring gull and dog whelk both decline
2. Insertion of weak trophic link-- stabilised all 3 pops
3. If mussels start to decline-- gulls switched diets to Dog whelk
4. Mussels recover without decline in gulls and whelks decline less than before
5. In presence of weak trophic interaction all 3 populations and whole system remain stable

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Conservation 4- Effects of Biodiversity loss

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	Created by jackharney93 over 10 years ago