Essay 10 due this Friday

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Essay 10 due this Friday Clarification final
is May 6thats a Wednesday, 7 PM Today
Faculty course questionnaires at 1040.
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Earth is in midst of 6th major extinction event
in history of life caused by human
activities. We dont know the ecosystem
consequences
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The relationship between species and ecosystems
is interesting at two different levels
Number of species
Ecosystem function (e.g., NPP)

• The first is how species diversity is
  controlled by
• ecosystem processes

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The second, and more recent, is how species
control ecosystem function
Ecosystem function (e.g., NPP)
Number of species
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Quantifying Dominance and Diversity Community
characteristics Species Richness species
Species Evenness how species partition
space/resources
Species Diversity index of both
richness and evenness Be aware that richness
and diversity are Sometimes used synonymously
Dominance 1/evenness
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Example Two ecosystems, each with four
species __________________________________ Species
Number of individuals
Ecosystem 1 Ecosystem 2 __________________
_________________ A 97
25 B
1 25 C
1 25 D
1 25 ________________
___________________ same results can be obtained
using cover rather than numbers.
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Community characteristics Species richness
same (4 each) Evenness very different
(max dominance vs max evenness) Species diversity
(Shannon index) Ecosystem 1 lower
(0.34) Ecosystem 2 higher (1.38)
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What determines species richness and species
diversity for a given area?
How many species Per unit area?
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There are evolutionary and ecological
explanations for local, regional and global
diversity. Factors that operate over
evolutionary time 1) productivity 2)
competition 3) environmental stability 4)
age of biome (production and competition can
be shown to be negative over
short-term) Immediate factors 1) area 2)
habitat complexity 3) intermediate disturbance 4)
top-down control (to limit competition)
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?
How important is biological diversity to
ecosystem functions such as NPP, carbon storage,
evapotranspiration, N cycles, etc?
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Ecosystem processes such as NPP are related
to the interaction of abiotic and biotic
processes. If we hold the abiotic
processes
constant, how important are the biotic
processes?
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Forests absorb more radiation (lower
albedo) Forests transfer more sensible heat to
atmosphere
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Deep-rooted species access more
resources Enhanced NPP Alters ecosystem
structure and functioning
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Species effects on climate in tropical forests
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Life form effects on climate in boreal forest
But these are life form comparisonshow about
species?
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Cedar Creek Biodiversity/invasion Experimental
site
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Richness appears to reduce nitrate leaching
(higher nutrient retention/use)
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Grass species effects on nitrogen
mineralization Associated with differences in
litter quality
OK Individual Species matter But what About
richness?
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Ecosystem Process
Richness or diversity
Resources
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Microcosm studies
Many field studies
C
B
Ecosystem Process
A
Richness or diversity
A?B Plt.05 B?C ns
Resources
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Specific shape/inflection point
controlled by other variables
Ecosystem process

Richness or diversity
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Empirical studies report different outcomes
depending upon initial conditions.
B
C
Ecosystem Process
D
A
A?B, Plt.05() A?C, Plt.05 () A?D, ns B?C ,
ns B?D, Plt.05(-) C?D, ns (-)
Richness or diversity Resources
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• To date, our studies have shown
• Productivity, per seis NOT correlated
• with species diversity
• (e.g., Spartina marsh vs tropical rain
  forest)
• (upland prairie (high diversity) vs lowland
• prairie (low diversity)

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A near monoculture of big blue at an annually
burned site on Konza Prairie..
(the dominant plant hogging the very restricted
resources of an annual burn!)
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Biodiversity and Ecosystem Function The Debate
Deepens J. P. Grime Science 1997
These studies all show that it is actually the
specific features of the species in an
ecosystem that determine its function--not their
number

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Since ecosystem processes are generated by
interaction effects, Can the importance of biota
really be measured by homogenizing the
abiotic components of the experiment? Do such
experiments have generality? Do their results
help us see what patterns exist on the
landscape?
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• Diversity effects on ecosystems
• Can be important to NPP on small
• scales, but not likely important at
• landscape or regional scales.
• Similar effects on biogeochemistry.
• b) Importance to ecosystem resistance/
• resilience probably KEY contribution
• c) Why preserve biodiversity?
• NEVER THROW AWAY THE PARTS!

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Effects of biodiversity on ecosystem
functioning a consensus of current knowledge
D. Hooper, F.S. Chapin III 13 others
Ecological Monographs 2005 we are certain
that 1. Species functional characteristics
influence ecosystem processes. 2.
Species changes (invasions, extinctions)
have altered ecosystem goods and services.
3. Effects of species loss or changes can
differ among ecosystem types.
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Species impose their effects on ecosystem
processes a) in terms of their functional
attributes b) these functional attributes
include direct impacts on energy and
nutrients and their indirect effects via
impacts on other organisms and the
environment. (one has to convert the
dimensions of species richness into the
dimensions of ecosystem ecology, e.g.
species numbers conversion factor
ecosystem structure/function
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• Some ecosystem properties are initially
• insensitive to species loss because of
• a) redundancy, b) lack of contribution by
  species,
• c) abiotic controls on process.
• More species are needed to insure a stable supply
• of ecosystem goods and services.
• We have high confidence that
• Certain combinations of species enhance
• productivity and nutrient retention.
• 2. Susceptibility to invasion is influenced by
• species diversity.
• 3. Diversity provides resistance to abiotic
  changes.

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Uncertainties remain with 1.Relationship
between taxonomic diversity, functional
diversity, and community structure. 2. Roles of
trophic level dynamics (trophic cascade effects)