BIOL 4120: Principles of Ecology Lecture 15: Community Ecology

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BIOL 4120 Principles of Ecology Lecture 15
Community Ecology

• Dafeng Hui
• Office Harned Hall 320
• Phone [phone]
• Email dhui_at_tnstate.edu

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Outline (Chapter 16)Community structure
16.1 Species Diversity 16.2 Dominance 16.3
Keystone species 16.4 Food web 16.5 Functional
groups 16.6 Physical structure 16.7 Zonation 16.8
Boundaries between communities 16.9 Two
contrasting views of community
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16.1 Species diversity

• Biological structure of a community is defined by
  the mix of species, including both their number
  and relative abundance.
• Attributes of community structure
• Species richness number of species that occur
  within the community
• Relative abundance counting all individuals of
  each species in a number of sample plots within a
  community and determining what percentage each
  contributes to the total number of individual of
  all species.
• Table 16.1 and 16.2
• Rank-abundance diagram graphical way to show
  relative abundance
• Species eveness equitable distribution of
  individuals among species
• Gradual slope in the rank-abundance diagram

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Compared to 1st forest stand, this stand has less
species. Also, two species make up 83.5 of the
total tree density.
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Rank-abundance diagram
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Species diversity

• Attributes of community structure (cont.)
• Diversity indexes an index considering both the
  number and relative abundance of species within
  the community.
• Simpsons index (D) three definitions
• Definition
• Where ni is the number of individuals in species
  i n is the total number of individuals of all
  species
• D measures the probability that two individuals
  randomly selected from a sample will belong to
  the same species
• Range of D 0 to 1 (1 is no diversity)

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Species diversity
Attributes of community structure
(cont.) Simpsons index of diversity1-D Simpson
s reciprocal index 1/D also called Simpsons
diversity index Calculate Simpsons Index using
Tables 16.1 and 16.2
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16.2 Dominance
Dominants when a single or a few species
predominate within a community. Measurement
Simpsons index D D1 represent complete
dominant (only one species) Dominance typically
means the greatest in number But individual size
should be considered too. Consider both number
and body size. Dominate species are usually good
competitors (American chestnut tree before and
now).
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16.3 Keystone species
Keystone species a species that has a
disproportionate impact on the community relative
to its abundance. Keystone species could be
dominant. Remove of keystone species initiates
changes in community structure and results in
significant diversity loss. Role in community
create or modify habitats, or influence
interactions with others.
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Keystone species examples
Coral (Oculina arvbuscula) in the eastern coast
of US This coral has complex branch and provide
shelter of more than 300 species of
invertebrates
African elephants in the savannas of southern
Africa Elephants are destruct feeders, damage
trees, shrubs, but increase grass growths.
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16.4 Food webs describe species interactions
Species interaction predation, parasitism,
competition, mutualism Fundamental issue
(process) resource (food, nutrient or energy
acquisition) Food web describes species
interaction and is an important part of community
structure.
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Food webs describe species interactions
Food web and food chain An abstract
representation of feeding relationships within a
community. Food chain Grass ? grasshopper ?
sparrow ? hawk A series of arrow, each pointing
one species to another, representing flow of food
from prey to predator.
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Food webs describe species interactions
Food web Involve numerical food chains meshed
together.
Hypothetical food web Circle species Links
arrows from one to another Basal species feed on
no others, but are fed upon by others Intermediate
species feed on others, and are fed upon Top
predator not subjected to predator, but prey on
other species. Trophic levels
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More in next chapter.
A food web for a prairie grassland community in
the midwestern US
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16.5 Species within a community can be classified
into Functional groups

• Functional groups C3, C4, CAM
• Autotroph and heterotroph
• Trophic levels groups of species that derive
  their food energy in a similar way
• Herbivores, carnivores, omnivores
• Here subdivided each trophic level into groups
  according to exploit a common resource in a
  similar fashion----guilds.
• Guilds a ground of species utilizing the same
  resources in similar ways
• Examples seed-eating birds, insect-eating birds
  etc.
• Benefit instead study of individual species,
  focus on manageable subset of the community

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An example
Spider in major crops, Uetz et al. 1999
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16.6 Communities have a definitive physical
structure
Communities have both biological structure
(species richness, abundance, species
interactoins) and physical structure. Physical
structure reflects Abiotic factors such as
depth and flow of water in aquatic environments
Biotic factors such as spatial arrangement of
organisms (size and height of tree in forests
density and distribution of populations).
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Communities are often defined by vegetation
types Terrestrial Shrubs, trees, herbs or
Deciduous, conifers, broad-leave evergreen
etc Or dominant plant growth form physical
Forests, woodlands, grasslands Aquatic Seagrass
meadow, coral reefs
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Physical structure
Photic zone, aphotic zone benthic zone
Vertical sectional view of communities from
aquatic to terrestrial.
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Height (ft)
Vertical distribution of birds species within the
forest community on Walker Branch watershed, Oak
Ridge, TN
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16.7 Zonation is spatial change in community
structure

• Zonation (Arrangement or formation in zones)
• Changes in physical and biological structure of
  communities as moving across the landscape.
• Reflect patterns of spatial variation in
  community structure

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Changes in species composition of forest stands
along a topographic gradient in Virginia
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Patterns of zonation in a New England salt marsh.
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Life on a sandy ocean beach along Mid-Atlantic
Coast
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16.8 Defining boundaries between communities is
often difficult

• How to determine the community?
• Do you consider the forest from hilltop to
  bottomland as one or two communities?
• If two, how to separate?
• Sampling and data analysis

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Community similarity
Sorensens coefficient of community Based on the
species presence or absence
Example s124, s210, c9 CC29/(2410)0.529 CC
ranges from 0 to 1
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Community similarity
Another one is Percent Similarity (PS) Based on
the relative abundance PS add the lowest
percentage for each species that the communities
have in common
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PS29.74.74.30.447.2 PS ranges from 0 to
100
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An example of forest zonation
Topographic distribution of forest communities in
the Great Smoky? Mountains National Park
(west-facing) F Frazir fir SF spruce-fir S
Red spruce OCF Oak-chestnut forest H Helmock
forest GB grassy balds HBHeath balds
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Arrangement of community types according to
elevation and aspect
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Large scale zonation Distribution of deciduous
forest communities in the eastern United States
(Braun 1950)
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16.9 Two contrasting views of the community

• Community is defined as groups of species
  (populations) that occupy a given area,
  interacting with each other directly or
  indirectly.
• How do they interact? Two groups
• Organismic concept
• Individualistic (or continuum) concept

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• Organismic concept
• Distribution of species is discrete
  (associations)
• Association a type of community with
• relative consistent species
• a uniform general appearance
• a distribution that is characteristics of a
  particular habitats such as hilltop or valley
• Transitional between communities are narrow, with
  few species in common
• Suggest a common evolutional history and similar
  foundational response and tolerances for
  component species
• Mutualism and coevolution play important roles in
  the species that make up association.

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• Individualistic (or continuum) concept
• Relationship among co-existing species is the
  result of similarities in their requirements and
  tolerances, not the result of strong interactions
  or common evolutionary history.
• Gradual change in species abundance along
  environmental gradient (no associations)
• Transitions are gradual and difficult to detect.

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THE End
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