Lecture 18 Patterns of Biodiversity Flashcards
What is Biodiversity?
> 1.7 million species on Earth!
(Estimates up to 10 million)
More diverse communities are
generally:
* more productive
* better able to withstand and
recover from environmental stress
* more stable from one year to the
next
* more resistant to invasive species
slide 3-4
Quantifying Biodiversity
- Abundance: total number of organisms
- Richness: number of species
- Relative abundance: proportion of
individuals of different species - Diversity: incorporates both relative
abundance AND richness
slide 5 and 6
Quantifying Biodiversity: Alpha Diversity
Slide 7-8
Quantifying Biodiversity: Beta Diversity
slide 9
Quantifying Biodiversity: Gamma Diversity
slide 10
Quantifying Biodiversity: Diversity Indices
slide 11-13
Quantifying Biodiversity: Diversity Indices
slide 14-15
Simpson’s Diversity Index
slide 16-23
Shannon-Weiner Diversity Index
slide 24-31
Diversity from eDNA
Environmental DNA (eDNA) can help detect
species presence and relative abundance
when you can’t find them!
slide 32
Patterns of Biodiversity
slide 33
Latitudinal Gradient
- Area: larger
area can fit
more species - Climate: more
primary
productivity,
more stability - Evolution: more
time for new
species to arise,
speciation rates
higher
slide 34-36
Geographical Area Hypothesis
- More surface area at the Equator
- Larger areas hold more species
slide 37
Geographical Area Hypothesis
slide 38
Geographical Area: Species-Area Curve
- Area effects are scale dependent:
weak at global scale, but on smaller
scales strongly correlated - Species-area curve: larger geographic
areas contain more species - More area = more diversity of
habitats and more resources - Is it unlimited? NO. Number of
species approaches asymptote at
largest sizes
Why an asymptote?
* Resources are finite
* Microhabitats are finite
* Regional pool of species
is finite
slide 39-40
Species-Energy Hypothesis
- Amount of available environmental energy limits richness
- Greater solar energy (and abundant precipitation) = higher primary productivity
- Plant species richness positively correlates with primary productivity
- Amount of available environmental energy limits richness
- Greater solar energy (and abundant precipitation) = higher primary productivity
- Plant species richness positively correlates with primary productivity
- Animal species richness positively correlates with plant diversity & NPP
slide 41-43
Climate Stability Hypothesis
- Fluctuating environments
increase extinction rates and
limit specialization - Stable environments allow
specialization on predictable
resources - Long-term stability = more time
to evolve & more specialization - Species at higher latitudes have
to tolerate a wider range of
conditions (Rapoport’s Rule)
slide 44
Elevational Gradient
- Species richness decreases with elevation
- Hypotheses similar to latitudinal trends: energy, climate
slide 45
Ecosystem Change
- Are ecological communities in equilibrium?
- Disturbance changes communities by removing organisms or altering resource
availability - Type, frequency, and severity of disturbance affect organisms differentially
- Non-equilibrium model: communities are changing constantly in response to
disturbance
slide 46
Succession
- Ecological Succession: transition of species composition over time as new
species colonize and modify the environment
Succession: Primary Succession
- Primary Succession occurs on barren land
- Ecosystem pioneers help develop a layer of soil
- Early arriving species may facilitate or inhibit colonization by subsequent species
- Once soil is present, grasses, shrubs, and eventually trees sprout, transferred by wind and animals
- Process can be VERY LONG! Hundreds to thousands of years
Surtsey island formed off of
Iceland from 1963-1967
from volcanic eruption
slide 48-50
Succession: Secondary Succession
- Secondary Succession occurs where existing vegetation has been disturbed or destroyed
- Remaining vegetation is gradually replaced by other species
- Early arrivers are typically herbaceous from wind or animals or from seed beds
- The area may return to something like its original state
slide 51-53
Succession: Climax Community
- Climax community:
the final stage of
succession, a stable
and self-sustaining
ecological community - Organisms are well- adapted to the
environment - Can persist in this
state for a very long
time if environmental
conditions remain
stable
slide 54
Intermediate Disturbance Hypothesis
Intermediate Disturbance
Hypothesis: disturbance fosters
diversity by opening up habitats for
less competitive species
* Too much reduces diversity by
creating stress that exceeds
tolerance or disturbing so
frequently that slow growing
species are excluded
* Too little reduce diversity by
allowing competitive species to
dominate
Large-scale disturbances can be integral parts of functioning ecosystems
Small-scale disturbance creates patches of habitat diversity
slide 55
Key Points to Understand
- What are the main ways of calculating biodiversity
and what do they mean? - Alpha, beta, gamma diversity
- Simpson’s diversity index
- Shannon-Weiner diversity index
- What is the latitudinal pattern of biodiversity and
the major hypotheses to explain the pattern? - Geographical area hypothesis
- Species-energy hypothesis
- Climate stability hypothesis
- How does ecosystem change impact biodiversity?
- Primary succession
- secondary succession
- intermediate disturbance hypothesis
slide 57
