Community Dynamics Ecosystem Ecology

1
Community Dynamics Ecosystem Ecology

• Part II Mechanisms
• Chapin, Matson, Mooney
• Principles of Terrestrial Ecosystem Ecology

2
11/2/03
Earth is in midst of 6th major extinction event
in history of life Caused by human activities We
dont know the ecosystem consequences
3
Second biotic change of global proportions

• Introductions of exotic species
• e.g., California grasslands
• Has become an issue in Alaska in last decade

4
Impact of organisms on ecosystems depends on
D. Species interactions
5
(No Transcript)
6
Species effects on other slow variables
determines ecosystem consequences
7
Species effects on resource supply Invasion of
exotic N fixer augments N cycling
8
Deep-rooted species access more water Augments
water available to support NPP
9
Deep-rooted species access more
resources Enhanced NPP Alters ecosystem
structure and functioning
10
Relative growth rate is key trait with strong
ecosystem impacts Determines NPP Influences
nutrient requirement and litter quality
11
Plant species differ predictably in litter
quality High-resource-adapted leaves decompose
quickly Enhance nutrient cycling rates
12
Species effects are an important affect most
ecosystem processes
13
Species effects on nitrogen mineralization Associ
ated with differences in litter quality
14
Species effects on N mineralization
15
Species effects on climate in tropical forests
16
Foley et al. 2003
17
Tropical deforestation causes net warming
Bala et al. 2007
Converse Tropical afforestation causes net
cooling
18
Response to drought
19
Clearing for agriculture in W. Australia altered
climate 30 less ppt over farmlands 10 more
ppt over heathlands Why?
Photo S. Chambers
20
Land clearing changes energy balance Higher
albedo (less energy absorbed) More ET from
irrigation (cools surface) Less sensible heat
(less convective uplift
21
Species effects on climate in boreal forest
22
(No Transcript)
23
1949
1949
Shrub density has increased
2000
Sturm
Chandler River, 50 miles S. of Umiat Sturm,
Racine and Tape Fifty Years of Change in Arctic
Alaskan Shrub Abundance
24
Climate feedbacks from shrub expansion
Sturm
25
(No Transcript)
26
Energy budget feedbacks to regional summer climate

• Feedbacks from vegetation change
• Tussock to shrub transition 3.9 W/m2
• Tundra to forest transition 5.0 W/m2
• 2 change in solar constant 4.6 W/m2
• (glacial to interglacial change)
• Doubling atmospheric CO2 4.4 W/m2

Chapin and McFadden
27
Simulated increase in July temperature due to
shrub expansion
Chapin , Lynch et al.
28
Species effects on disturbance

• Many animals are ecosystem engineers
• Soil disturbance (gophers, ants)
• Landscape disturbance (beavers)
• Plants influence disturbance
• Fire probability
• Stabilize soils (e.g., sand dunes)

29
(No Transcript)
30
(No Transcript)
31
Boreal conifer forests are born to burn After
fire are replaced by less flammable deciduous
forests
32
Species interactions modify effects of individual
species

• Mutualisms
• e.g., mycorrhizae
• microbial consortia
• pollinators

33
Species interactions modify effects of individual
species

• Mutualisms
• Trophic interactions
• e.g., herbivory, predation
• Trophic cascades

34
(No Transcript)
35
Herbivores magnify differences among ecosystems
in NPP and energy flow
36
Species interactions modify effects of individual
species

• Mutualisms
• Trophic interactions
• Facilitation
• e.g., N fixation
• Shading
• Organic matter accumulation

37
Nitrogen fixers add the nitrogen that supports
primary succession 70 of total N inputs arrive
in 15 years!
Tanana River, interior Alaska
38
Species interactions modify effects of individual
species

• Mutualisms
• Trophic interactions
• Facilitation
• Competition
• Alters abundance and activity or organisms
• This determines what traits are actually
  expressed in ecosystem

39
Effects of species diversity

• Enhance efficiency of resource use?
• Stabilize ecosystem processes in variable
  environment
• Insurance against radical ecosystem changes

40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
Global distribution of biodiversity
44
(No Transcript)