Biol 208: Lecture 24 - Ecological Communities

Community define

An association of interacting species inhabiting a defined area at a particular scare over a particular span of time

Guild, Life form + Functional groups.

• Define + Examples

• Which are used by animal researchers and which by plants?

Groups of association in Communities

Guild = species living in a similar way (eg. use the same resources) - Zooplankton

• Used by Animal ecologists

Life form = species that have similar growth form (eg. trees, vines grass algae etc.)

• Used by PLANT ecologists

Functional group = species with a similar ecological function or attribute eg. Trees, carnivores, herbivores, etc.

• Used by both animal + plant ecologists

How communities are described:

• what are the 3 attributes of a communities structure?

• Which of the 3 is the most SPECIFC?

1. Relative abundance of species within a community

2. Number of species + diversity

3. Species composition (most specific)

Define Species ABUNDANCE:

• 3 ways it can be measured

• When to use each type of measurement

• give examples

Number of individuals (Count):

• distinct entities eg. Bird (not useful for clonal organisms (like aspen)

Species cover (%):

• Visual ESTIMATION. Quick + Less destructive But Less Precise

• Individuals are not clearly distinguishable (Eg. algae + plants)

Species Biomass (mass/weight):

• Quantifiable as FRESH or DRY. Slow + Destructive but precise

• Individuals not Distinct or Countable

Species Dominance

• How many species are dominant?

• Species abundance distribution

Dominant species = one that is much more COMMON than others

Few species are Dominant or Rare

Most species occur in MODERATE abundance

• Bell curve Distribution

Are Abundance curves always ideal? Why?

NO

• Depends on HOW MUCH YOU SAMPLE

Rare species are often overlooked → the more you sample the more likely you will find the rare species + the closer the abundance distribution will match the bell curve

Community structure #2: DIVERSITY

• Species Diversity

  • Species richness

  • species Evenness

Define each

Diversity = a metric of community composition that combines species richness + species evenness

• Richness = How many (number of) species in a community

• Evenness: the relative abundance of species in a community

What type of community is more stable?

Diverse community

Three different scales of measuring species Diversity

1. Gamma = TOTAL diversity within a region or landscape (largest scale) eg. # of species in central parkland region of Alberta

2. Alpha = Diversity within a locality within a region or landscape eg. Number of species in a 20×20m plot in a forest

3. Beta = Measure of diversity AMONG locations within a region eg. compare B between a forest + a field patch

What does this equation represent?

• How to compare + interpret Beta

Beta Diversity = measures species Richness

• Diversity among locations within a region

• Comparing diversity between Alpha’s

The more similar 2 different Beta are the lower the difference between the 2 locations

What does this equation represent/ what does it measure

• what do all the symbols represent?

• How to interpret?

Shannon Wiener diversity Index H’ = measures BOTH Richness + Evenness (takes evenness into account)

• Pi = Proportion of species i

• ln = natural log

• s = number of species in community

The HIGHER the number the greater the diversity

What is the lowest H’ (Shannon wiener diversity) you can get? What does this mean?

0

= means only ONE SPECIES

What does this equation represent/ what does it measure

• what do all the symbols represent?

• How to interpret?

Pielou’s J = Measuring JUST Evenness

• H’ = Shannon wiener

• ln(s) = natural log of species richness (total # of species)

Closer to 1 = More even

Closer to 0 = less even

What is a Rank Abundance Curve?

• How to interpret species evenness

• How to interpret species richness?

Assessing evenness graphically

• Plot of relative abundance of species against their rank in abundance (rank species based on abundance)

• High Abundance is plotted on the LEFT side

Evenness = How FLAT the line is (more flat = more even)

Richness = How LONG the line is (more long = more rich)

What are 4 factors that Increase/Decrease Biodiversity?

1. Time: more uninterrupted time to evolve/colonize = more diversity

2. Complexity: More complex the environment = more diversity

3. Exploitation + Limitation: Limitations that decrease competition + increase biodiversity

4. Global Change: Pollution, habitat loss, invasive species = decrease diversity

Relationship between Environmental Complexity + species Diversity:

• What is included in complexity

• What does a homogenous vs. heterogenous environment look like?

More Complex/ heterogenous = more diversity

Complexity = Vertical structures (Trees), Water movement (current), nutrient, light etc. etc.

Homogenous = Few factors that influence organism → Few Niches

Heterogenous = Many factors that influence organism → Many Niches

Species Composition

• Define

• Importance

Composition = The species that occur in each community at a given time (WHAT TYPE/FLAVOURS OF SPECIES)

• Changes and differences between communities are not only indicated by the number of species + the evenness of those species but the species themselves

• Two communities can have the same species richness but different species composition.

Importance:

1. Species + species group identity influence ecosystem functioning

2. Composition can indicate shifts due to environmental or anthropogenic effects

Biotic Invaders

• Define

Non-native/ invasive species that establish in new range + proliferate, spread + persist to the detriment of the environment

• Shift in species COMPOSITION = alters community attributes + ecosystem processes