Review species interactions

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Review species interactions

• Species can coexist when
• A) Interspecific competition is stronger than
  intra-
• B) Intraspecific competition is stronger than
  inter-

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Review species interactions

• Does the following example meet the strict
  criteria for character displacement?
• Sticklebacks are a marine fish that sometimes
  become established in freshwater. Sometimes there
  is one generalist form with moderately spaced
  gill rakers. Sometimes there are 2 forms
  on-bottom with wide gill rakers, and mid-water
  with narrow gill rakers. The gill rakers
  determine the particle size eaten by the fish.

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Wolves and humans hunt moose in
Alaska Interspecific competition
Interference? Resource Exploitation?
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Chapter 16Abundance and Diversity
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What are your current ideas?

• How is biological diversity measured?
• How is biological diversity maintained? What are
  important ecological approaches to studying how
  species coexist?
• How does biological diversity contribute to the
  functioning of ecosystems (provision of goods
  and services)? What happens as species are lost
  (when) does it matter?
• What are major threats to biodiversity?

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Mike Siegel, Seattle Times photos 1/21/09
Ecology News-of-the-Week Why are amphibians
dying? 1/21/09 article by L. Mapes in Seattle
Times

• Worldwide declines may be due to toxins or
  climate change animals with permeable skin are
  very susceptible
• Local declines due to habitat loss? And roads?

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Mike Siegel, Seattle Times photos 1/21/09
A real King County ecologist at work, sampling
for amphibians in breeding ponds
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Mike Siegel, Seattle Times photos 1/21/09
Wetland habitats are protected from development,
but amphibians may travel 1-5 km away
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Mike Siegel, Seattle Times photos 1/21/09
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Mike Siegel, Seattle Times photos 1/21/09
Biodiversity (biological diversity) variety of
life, often measured at the species level (How
many species are present at what abundance?)
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• Important Terms
• Community Association of interacting species
  inhabiting some defined area. (assemblage)
• Community Structure includes attributes such as
  number of species, relative species abundance,
  and types of species.
• Guild Group of organisms that all make their
  living in the same fashion.
• Life Form Combination of structure and growth
  dynamics.

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Guild generally refers to animals.
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Life-form generally refers to plants.
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• Two challenges
• 1 Describe the number of species and their
  relative abundance
• 2 Determine controls on diversity why are
  there so many species (and not more or less) in a
  particular place?

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• Two challenges
• 1 What is diversity?

Number of different species and Their relative
abundance (most species are very rare and
therefore contribute little to this component of
diversity)
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• Two factors are used to measure
• species diversity
• Species Richness
• Number of species in the community.
• Species Evenness
• Relative abundance of species.

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Species Diversity
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Ecological community data
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• Two descriptions
• 1 Numerical Shannon-Wiener diversity index
  (for instance)
• 2 Graphical log-normal distribution OR
  rank-abundance curve

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Quantifying Species Diversity

• Shannon-Wiener Index
• H
• H value of SW diversity index
• pi proportion of the ith species
• loge(pi) natural logarithm of pi
• s number of species in
• community

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Ecological community data
H 1.37
Total 33
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Graphing diversity 1

• Lognormal Distributions the abundance of
  species graphed as frequency distributions.
• X-axis Categories of abundance (log scale)
• Y-axis number of species in each category
• Result Bell-shaped curves.
• Only a few species are very abundant.
• Often, the bell-shaped curve lacks its left tail,
  because rare species are missed entirely.

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Lognormal Distribution
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Lognormal Distribution
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Graphing diversity 2

• Rank-abundance curves the abundance of
  species graphed by rank.
• X-axis Species rank ordered
• Y-axis number of individuals per species (log
  scale)
• Result Downward sloping lines.
• Different slopes show different evenness.
• Length of line shows species richness.

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Rank Abundance Curves
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Review 2 ways of displaying community structure

• What are the axes?
• What relationships indicate high vs. low
  diversity?
• Why would you report data each way?

Frequency Distribution
Rank-Abundance
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Review 2 ways of displaying community structure

• What are the axes?

Log number individuals
Number of species
Species, ranked
Log Number of Individuals
Frequency Distribution
Rank-Abundance
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Review 2 ways of displaying community structure

• What are the axes?
• What relationships indicate high vs. low
  diversity?

Number of species
Log Number of Individuals
Frequency Distribution
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Review 2 ways of displaying community structure

• What are the axes?
• What relationships indicate high vs. low
  diversity?

Log Proportion individuals
Species, ranked
Rank-Abundance
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• Two challenges
• 1 Describe the number of species and their
  relative abundance
• 2 Determine controls on diversity why are
  there so many species (and not more or less) in a
  particular place?

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Key question in ecologyWhat allows species to
coexist?
Hey! Whats the difference between a fundamental
and realized niche?

• Equilibrium explanations (fluctuation-independent)
  Species occupy different niches spatial
  variation in the environment
• Non-equilibrium explanations (fluctuation-dependen
  t) Conditions change and therefore favor
  different species through time temporal
  variation in the environment

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Equilibrium explanation Environmental
complexityincreases species diversity
Which habitat is likely to be more biodiverse?
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West coast of Washington wet Complex structure
to vegetation
West coast of Namibian dry Very little
vegetation
Namibia from space with sulfur eruption
Washington from space with Columbia river plume
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Namib Desert contains few species, but high level
of endemism (10-20 of species are found only
there)
Picture of Washingtons big trees
West coast of Namibia 3 mm rain
West coast of U.S. 3 m rain
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Which habitat is likely to be more biodiverse?
Native eelgrass
Native burrowing shrimp
Introduced, commercially valuable oysters
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• G.E. Hutchinson
• The Paradox of the Plankton
• Phytoplankton communities live in relatively
  simple environments and compete for the same
  nutrients, yet many species coexist without
  competitive exclusion.

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Paradox resolved Even aquatic environments are
heterogeneous
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Different plankton species perform best in
different nutrient ratio niches
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• Nutrient Availability
• and Autotroph Species Diversity
• Adding nutrients to water or soils generally
  reduces diversity of plants and algae by reducing
  the number of limiting nutrients.

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Non-equilibrium explanation Disturbance
influences diversity
Where/ when will be most biodiverse?
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Disturbance and Diversity

• Wayne Sousa defined disturbance
• Discrete, punctuated, killing, displacement, or
  damaging of one or more individuals that directly
  or indirectly creates an opportunity for new
  individuals to be established.
• White and Pickett defined disturbance
• Any relatively discrete event in time that
  disrupts ecosystem, community, or population
  structure and changes resources, substrate
  availability, or the physical environment.
• Two major characteristics
  Frequency
• Intensity

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Intermediate Disturbance Hypothesis

• Joseph Connell
• Both high and low levels of
• disturbance reduce diversity.
• Intermediate levels promote higher diversity.
• Sufficient time between disturbances allows
  wide variety of species to colonize, but not long
  enough to allow competitive exclusion.

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Competitive exclusion occurs
Few species can withstand the frequent removal
associated with disturbance
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(No Transcript)
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What are the probable life history
characteristics of the dominant species at high
disturbance vs. low disturbance?
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Biodiversity and ecosystem functioning

• What are ecosystem functions?
• What are your ideas about the relationship
  between biodiversity and function?

Functioning
Biodiversity
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Biodiversity and ecosystem functioning

• What are ecosystem functions?
• Provisioning (food, fiber, etc.)
• Regulating (atmospheric gas concentrations, water
  purification, soil build-up)
• Cultural (esthetic, religious, etc.)
• Supporting (pollination, resources for
  economically important species)

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Biodiversity and ecosystem functioning

• What are ecosystem functions?
• What are your ideas about the relationship
  between biodiversity and function?

Depends on which species disappear
Functioning
Functioning
Functioning
Biodiversity
Biodiversity
Biodiversity
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Take-home messages

• Diversity measures include information about
  species number AND evenness (and additionally
  taxonomic distinctness)
• Diversity can be maintained by spatial
  heterogeneity (local habitat differences) or
  temporal heterogeneity (disturbance interrupts
  competitive exclusion)
• Relationship between diversity and ecosystem
  function is an active area of ecological research