Lecture 18 Patterns of Biodiversity

Question 1

What is Biodiversity?

Answer 1

> 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

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Question 2

Quantifying Biodiversity

Answer 2

• Abundance: total number of organisms
• Richness: number of species
• Relative abundance: proportion of
  individuals of different species
• Diversity: incorporates both relative
  abundance AND richness

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Question 3

Quantifying Biodiversity: Alpha Diversity

Answer 3

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Question 4

Quantifying Biodiversity: Beta Diversity

Answer 4

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Question 5

Quantifying Biodiversity: Gamma Diversity

Answer 5

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Question 6

Quantifying Biodiversity: Diversity Indices

Answer 6

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Question 7

Quantifying Biodiversity: Diversity Indices

Answer 7

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Question 8

Simpson’s Diversity Index

Answer 8

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Question 9

Shannon-Weiner Diversity Index

Answer 9

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Question 10

Diversity from eDNA

Answer 10

Environmental DNA (eDNA) can help detect
species presence and relative abundance
when you can’t find them!

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Question 11

Patterns of Biodiversity

Answer 11

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Question 12

Latitudinal Gradient

Answer 12

1. Area: larger
   area can fit
   more species
2. Climate: more
   primary
   productivity,
   more stability
3. Evolution: more
   time for new
   species to arise,
   speciation rates
   higher

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Question 13

Geographical Area Hypothesis

Answer 13

• More surface area at the Equator
• Larger areas hold more species

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Question 14

Geographical Area Hypothesis

Answer 14

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Question 15

Geographical Area: Species-Area Curve

Answer 15

• 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

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Question 16

Species-Energy Hypothesis

Answer 16

• 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

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Question 17

Climate Stability Hypothesis

Answer 17

• 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)

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Question 18

Elevational Gradient

Answer 18

• Species richness decreases with elevation
• Hypotheses similar to latitudinal trends: energy, climate

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Question 19

Ecosystem Change

Answer 19

• 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

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Question 20

Succession

Answer 20

• Ecological Succession: transition of species composition over time as new
  species colonize and modify the environment

Question 21

Succession: Primary Succession

Answer 21

• 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

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Question 22

Succession: Secondary Succession

Answer 22

• 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

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Question 23

Succession: Climax Community

Answer 23

• 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

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Question 24

Intermediate Disturbance Hypothesis

Answer 24

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

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Question 25

Key Points to Understand

Answer 25

• 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

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