Chapter 3 Flashcards
Species richness varies with
PLOC
Productivity
Latitude
Other physical & biological variables
Climate
Earth’s species may
disappear due to:
(there are 6)
Habitat destruction
Overharvesting (particularly marine species)
Invasive species
Eutrophication
Global Climate Change
Other Human Activities
Naeem et al. (1994) & Tilman and Downing
(1994)
Two studies that paved the way to understand the relationships between
biodiversity and ecosystem functioning.
- see slides
effects of
biodiversity on four important ecosystem
functions: which are
“pinc”
Productivity
Invasibility
Nutrient use and nutrient retention
Community and ecosystem stability
Species richness had a strong, positive effect on
primary productivity
slide 19 not sure how to break up
Increasing species richness increases
biomass production in primary
producers.
question: Does higher species diversity lead to higher ecosystem
productivity?
For at least low-stature plant communities… YES!
A recent meta-analysis of 368 experiments found that manipulated primary
producers in a variety of ecosystems (i.e. terrestrial, freshwater, marine)
resulted in an increase in biomass when high plant species richness occurred.
But, some mathematical modeling has found that although the relationship is
positive,
it occurs at a decelerating rate. (diminishing returns)
Why might productivity increase with species richness?
two mech
Niche complementarity
Species selection
what is niche complementarity
When species differ in the way they
use limited resources.
If each species differs in their
niches, the use of resources within a
community becomes more efficient
and this can leader to higher
productivity.
what is species selection
Species Selection (a.k.a. sampling effect)
May lead to increased productivity with increased species richness if diverse
communities are more likely to contain more productive species that come to
dominate the community.
is the relationship between the extent of ecosystem
functioning and the degree of niche overlap between species npositive or negative ?
negative
Meta analyses
If species exhibit resource partitioning and niche complementarity, then
more diverse communities should use resources more efficiently and the
amount of unused resource in an ecosystem should decline as species
richness increases.
Most data in support of niche complementarity
comes from
terrestrial plants.
nitrogen availability limits
primary productivity.
Nitrogen
in above ground vegetation also correlated
positively with species diversity.
This means N uptake increased with increasing plant diversity.
Dijkstra et al. (2007)
an
increase in plant species richness reduced
that an
increase in plant species richness reduced leaching loss of dissolved inorganic nitrogen.
Cardinale et al. 2011
on polycultures
Found that species-rich polycultures reduced nutrient concentrations (mean
= 48%) more than monocultures
Little evidence that polycultures used resources more efficiently; standing
nutrient concentrations in soil/water were higher in polycultures than the
most efficient monocultures
Do polycultures use resources more efficiently
than the most efficient monocultures?
They Uptake it, but do they use it efficiently?
Simple Answer: it depends on the complexity
homogenous vs heterogeneous
biomass plays a role
heterogeneous streams increased algal richness dramatically reduced the
amount of dissolved nitrogen.
by increasing algal species richness in heterogeneous streams, water quality
was significantly increased due to niche complementarity.
Temporal Stability
Examines species abundance (usually measured in biomass) over time
Diversity had a strong, positive effect on the temporal stability of the total
plant community, but a negative effect on the stability of individual species
abundances.
The idea that increased species diversity leads to ecosystem stability has been
around a long time!
but does it
The answer seems to rest on how we view
stability.
Are more diverse communities more resistant to invasion by exotic species?
Overall, yes, but there are some important unanswered questions.
Elton (1958): “This resistance to newcomers can be observed in established
kinds of vegetation, due to competition for light and soil chemicals and
space.”
Fargione and Tilman (2005) – again using the Cedar Creek plots – found
both biomass and number of invading plants declined as richness of resident
plant community increased.
Increasing biodiversity negatively affects
invaders ability to survive
decreasing occupied space
decreases native species richness?
What traits make it more likely for species to go extinct?
strong, consistent effects of biodiversity loss on ecosystem functionality
Loss of particular species can significantly impact ecosystem functioning (keystone species)
Some traits such as population size, geographic range, body size, trophic level, low
fecundity can accurately predict probability of loss for some species.
How has biodiversity been affected by human activities?
It seems species richness can stay the same, but species turnover has risen in areas of high
human impact (i.e. invasive species taking over native species) - Thus, Beta diversity is high
while Alpha diversity remains similar.
Still need to better understand effects of species richness on ecosystem functioning
How do multiple interacting trophic levels
impact biodiversity?
trophic-level interactions are important for
ecosystem functioning
alterations in the number & kinds of top-level
consumers have cascading effects
number of species declines as we move from lower
to higher trophic levels, species extinctions tend to
occur towards the top
think pyramid
Why do areas of high native plant diversity also contain high numbers of
invading plant species when experimental manipulations find the opposite?
Hypothesis to address this:
Environmental factors that support high native plant diversity also support high exotic
plant diversity. Small-scale experiments seek to control environmental variation.
Experimental evidence overwhelming finds that biodiversity alterations
significantly impact ecosystem functioning, but some have questioned if
that impact in natural ecosystems is significant.
Here again we are seeing the pull between experimental data and what actually occurs
in natural systems.
Species richness varies with
Latitude
Climate
Productivity
Other physical & biological variables
what was biomass a measure of
productivity
Tilman and Downing (1994)
Showed a link between species richness, ecosystem
productivity, and ecosystem stability
Found that plots with high plant species diversity
were better buffered against the effects of a severe
drought.
four important ecosystem
functions:
Productivity
Nutrient use and nutrient retention
Community and ecosystem stability
Invasibility
‘Jena Biodiversity Experiment’
study above- and belowground productivity and nutrient use
efficiency.
Species richness had a strong, —— effect on primary producers
positive
Cedar Creek productivity (measured in biomass) increased rapidly in response to
the addition of a few plant species, but then
slowed (reached diminishing returns).
Positive effect of species richness on plant biomass….
increased over time.
how does increasing species richness affect biomass production in primary producers
Increasing species richness increases biomass production in primary
producers.
the relationship is
positive, it occurs at a decelerating rate. (diminishing returns)
richness-biomass relationship, and functional group richness-biomass relationship have _______ correlations
Positive
Two mechanisms productivity increase with species richness?
Niche complementarity
Species selection
Niche complementarity
If each species differs in their
niches, the use of resources within a
community becomes more efficient
and this can leader to higher
productivity.
Species Selection (a.k.a. sampling effect)
May lead to increased productivity with increased species richness if diverse
communities are more likely to contain more productive species that come to
dominate the community.
Transgressive overyielding
plots containing species mixtures yield more
biomass than any monoculture plot.
when does species selection tend to be dominant vs ncihe complementarity
Studies of terrestrial plant communities
suggest that species selection effects are
the dominant drivers of ecosystem
functioning EARLY in experiments
Niche complementarity effects
become stronger as communities
mature.
