BIOL 4120: Principles of EcologyBIOL 4120: Principles of Ecology

Lecture 15: Community Lecture 15: Community EcologyEcology

Dafeng HuiDafeng Hui

Office: Harned Hall 320Office: Harned Hall 320

Phone: 963-5777Phone: 963-5777

Email: dhui@tnstate.eduEmail: dhui@tnstate.edu

Outline (Chapter 16)Outline (Chapter 16)Community structureCommunity structure

16.1 Species Diversity16.1 Species Diversity16.2 Dominance16.2 Dominance16.3 Keystone species16.3 Keystone species16.4 Food web16.4 Food web16.5 Functional groups16.5 Functional groups16.6 Physical structure16.6 Physical structure16.7 Zonation16.7 Zonation16.8 Boundaries between communities16.8 Boundaries between communities16.9 Two contrasting views of community16.9 Two contrasting views of community

16.1 Species diversity16.1 Species diversity

Biological structure of a community is defined by the mix of Biological structure of a community is defined by the mix of species, including both their number and relative abundance.species, including both their number and relative abundance.

Attributes of community structureAttributes of community structure1.1. Species richness: number of species that occur within the Species richness: number of species that occur within the

communitycommunity2.2. Relative abundance: counting all individuals of each species in Relative abundance: counting all individuals of each species in

a number of sample plots within a community and determining a number of sample plots within a community and determining what percentage each contributes to the total number of what percentage each contributes to the total number of individual of all species.individual of all species.Table 16.1 and 16.2Table 16.1 and 16.2

3.3. Rank-abundance diagram: graphical way to show relative Rank-abundance diagram: graphical way to show relative abundanceabundance

4.4. Species eveness: equitable distribution of individuals among Species eveness: equitable distribution of individuals among speciesspeciesGradual slope in the rank-abundance diagram Gradual slope in the rank-abundance diagram

Compared to 1st forest stand, this stand has less species. Also, two species make up 83.5% of the total tree density.

Rank-abundance diagramRank-abundance diagram

Species diversitySpecies diversity

Attributes of community structure (cont.)Attributes of community structure (cont.)Diversity indexes: an index considering both the number and Diversity indexes: an index considering both the number and

relative abundance of species within the community.relative abundance of species within the community.1.1. Simpson’s index (D): three definitionsSimpson’s index (D): three definitions

Definition: Definition:

Where ni is the number of individuals in species i; n is the total Where ni is the number of individuals in species i; n is the total number of individuals of all speciesnumber of individuals of all species

D measures the probability that two individuals randomly D measures the probability that two individuals randomly selected from a sample will belong to the same speciesselected from a sample will belong to the same species

Range of D: 0 to 1 (1 is no diversity)Range of D: 0 to 1 (1 is no diversity)

Species diversitySpecies diversity

Attributes of community structure (cont.)Attributes of community structure (cont.)

Simpson’s index of diversity=1-DSimpson’s index of diversity=1-D

Simpson’s reciprocal index =1/DSimpson’s reciprocal index =1/Dalso called Simpson’s diversity indexalso called Simpson’s diversity index

Calculate Simpson’s Index using Tables 16.1 and 16.2Calculate Simpson’s Index using Tables 16.1 and 16.2

16.2 Dominance16.2 DominanceDominants: when a single or a few species Dominants: when a single or a few species

predominate within a community.predominate within a community.Measurement: Simpson’s index DMeasurement: Simpson’s index D

D=1 represent complete dominant (only one D=1 represent complete dominant (only one species)species)

Dominance typically means the greatest in Dominance typically means the greatest in numbernumber

But individual size should be considered too.But individual size should be considered too.Consider both number and body size.Consider both number and body size.Dominate species are usually good competitors Dominate species are usually good competitors

(American chestnut tree before and now). (American chestnut tree before and now).

16.3 Keystone species16.3 Keystone species

Keystone species: a species that has a Keystone species: a species that has a disproportionate impact on the community disproportionate impact on the community relative to its abundance.relative to its abundance.

Keystone species could be dominant. Keystone species could be dominant. Remove of keystone species initiates changes Remove of keystone species initiates changes

in community structure and results in in community structure and results in significant diversity loss.significant diversity loss.

Role in community: create or modify habitats, Role in community: create or modify habitats, or influence interactions with others.or influence interactions with others.

Keystone species examplesKeystone species examples

Coral (Oculina arvbuscula) in the eastern coast Coral (Oculina arvbuscula) in the eastern coast of USof US

This coral has complex branch and provide This coral has complex branch and provide shelter of more than 300 species of shelter of more than 300 species of invertebratesinvertebrates

African elephants in the African elephants in the savannas of southern savannas of southern AfricaAfrica Elephants are destruct Elephants are destruct feeders, damage trees, feeders, damage trees, shrubs, but increase grass shrubs, but increase grass growths.growths.

16.4 Food webs describe species 16.4 Food webs describe species interactionsinteractions

Species interaction: predation, parasitism, Species interaction: predation, parasitism, competition, mutualismcompetition, mutualism

Fundamental issue (process): resource (food, Fundamental issue (process): resource (food, nutrient or energy acquisition)nutrient or energy acquisition)

Food web describes species interaction and is Food web describes species interaction and is an important part of community structure.an important part of community structure.

Food webs describe species Food webs describe species interactionsinteractions

Food web and food chainFood web and food chainAn abstract representation of feeding An abstract representation of feeding

relationships within a community.relationships within a community.

Food chainFood chainGrass Grass grasshopper grasshopper sparrow sparrow hawk hawk

A series of arrow, each pointing one species to A series of arrow, each pointing one species to another, representing flow of food from prey another, representing flow of food from prey to predator.to predator.

Food webs describe species Food webs describe species interactionsinteractions

Food web:Food web:Involve numerical food chains meshed Involve numerical food chains meshed

together.together.Hypothetical food web:Hypothetical food web:

Circle: speciesCircle: speciesLinks:Links: arrows from one to arrows from one to anotheranotherBasal species:Basal species: feed on no feed on no others, but are fed upon by others, but are fed upon by othersothersIntermediate species: Intermediate species: feed feed on others, and are fed uponon others, and are fed uponTop predator:Top predator: not subjected not subjected to predator, but prey on other to predator, but prey on other species.species.Trophic levelsTrophic levels

A food web for a prairie grassland community in the midwestern US

More in next chapter.

16.5 Species within a community can be classified into Functional groups

Functional groups: C3, C4, CAM Autotroph and heterotrophTrophic levels: groups of species that derive their

food energy in a similar way Herbivores, carnivores, omnivoresHere 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

An example

Spider in major crops, Uetz et al. 1999

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).

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

Physical structure

Vertical sectional view of communities from aquatic to terrestrial.

Photic zone,

aphotic zone

benthic zone

Vertical distribution of birds species within the forest community on Walker Branch watershed, Oak Ridge, TN

Heig

ht

(ft)

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

Changes in species composition of forest stands along a topographic gradient in Virginia

Patterns of zonation in a New England salt marsh.

Life on a sandy ocean beach along Mid-Atlantic Coast

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

Community similaritySorensen’s coefficient of community

Based on the species presence or absence

Example: s1=24, s2=10, c=9

CC=2*9/(24+10)=0.529

CC ranges from 0 to 1

Community similarityAnother one is Percent Similarity (PS)

Based on the relative abundance

PS= add the lowest percentage for each species that the communities have in common

PS=29.7+4.7+4.3+…+0.4=47.2

PS ranges from 0 to 100

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 HB:Heath balds

An example of forest zonation

Arrangement of community types according to elevation and aspect

Large scale zonation

Distribution of deciduous forest communities in the eastern United States (Braun 1950)

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:

Organismic concept: Distribution of species is discrete (associations) Association: a type of community with 1. relative consistent species; 2. a uniform general appearance; 3. 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.

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.

THE End