Chapter 16 Species Abundance and Diversity

1st Question of the Day

Define the term “Community”

1st Question of the Day

Define the term “Community”

An association of interacting species inhabiting some defined area.

Chapter 16 Species Diversity

Objectives:1. Identify the abundance distributions of species in

a community

2. Determine objective measures of species diversity

3. Determine how many species there exist in the world

4. Identify trends in species diversity distribution

5. Relate the concepts of diversity and stability

Log-Normal Pattern of Species Abundance In Communities

Very few species have extremely high relative abundance

Why ?

Low ◄ Abundance ► High(Log Scale)

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Log-Normal Pattern of Species Abundance In Communities

Very few species have extremely high relative abundance

Very few species have extremely low relative abundance

Most species are moderately abundant

Plants

Birds

Low ◄ Abundance ► High(Log Scale)

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Species Abundance

Log normal distributions are thought to be a consequence of species in a community subdivided niche space.

What does this mean?

Species Richness

How many species exist in the world?

• E. O. Wilson found 1.4 million classified

• Most ecologist agree 3-10 million

• E. O. Wilson estimates 100 million

Problem!!!!

Hard to measure (or find) the dang critters!!!

Species Richness

Terry Erwin:

Tropical rain

forest insects

Species Richness

30 - 40m

Species Richness

Bug Bomb to

the tree tops----

Species Richness

Bug Bomb to

the tree tops----

Funnels to catch

Insects as they

fell---

Terry Erwin

Species Diversity

Erwin’s results

• 163 species of beetles in one species of tree Luehea seemannii

• Estimated 50,000 tropical tree species

• If this typical - then 8,150,000 canopy dwelling tropical beetles

• Beetles represent 40% of arthropods

Species Diversity

• In tropical canopy - 20 million species arthropods

• Twice as many arthropods in canopy as on the ground - 30 million tropical species

Conclusions:

From 163 beetles - expanded to 30 million arthropod species in tropical rain forests

Species Diversity

Stork - Similar techniques to Erwin

Indonesia

• 10-80 million species on earth

Species Richness

How many species exist in the world?

• E. O. Wilson found 1.4 million classified

• Most ecologist agree 3-10 million

• E. O. Wilson estimates 100 million

Species Diversity

Bacteria:

Pinch of soil -

• Quarts grains

• decaying organic matter

• free nutrients

• 10 billion bacteria

Species Diversity

Pinch of soil -• 1/1,000,000 of the pinch• Spread out on agar plate and grow - expect

10,000 bacterial colonies• How many do we see? 10-100 colonies

Species Diversity

Bacteria:

Bergey’s Manual of Systematic Bacteriology

4,000 species of bacteria

How many exist? Unknown, and limited by technology to grow them.

Species Diversity

Definition:

1. A measure of the number of species (species richness) and

2. The relative abundance (evenness) within a community.

Species Diversity

Low Diversity:

either few species or highly uneven abundances

High Diversity:

large number of species or very even abundances

Fig. 16.5

Species Diversity

AAAA ABCD ABCD

AAAA AAAA DCBA

AAAA AAAA BCAD

AAAA AAAA CDAB

Species Diversity

AAAA ABCD ABCD

AAAA AAAA DCBA

AAAA AAAA BCAD

AAAA AAAA CDAB

Lowest Highest

Diversity DiversityShannon-Weiner Index

Pages 374-375Table 16.1

Species Diversity

Some Assumptions -Species Diversity Indices

1. All species have equal impact on the community

2. No account made for variation within a species (e.g., larvae or adult)

Species Diversity

Some Assumptions -Species Diversity Indices

3. Species accounts can be taxonomically difficult

4. Cannot compare different communities (e.g., plankton and fish, tree and insect)

Species Diversity

OK-- We can’t measure all the species in the world (at least not at the moment)

But!!!

Can we get some guidance or hints where biodiversity is greatest???

Species Diversity

More land area to develop and no barriers to spread of species

Biodiversity Hotspots

Latitudinal Trends at Different Latitudes

8 40 72Latitude

Number of

species

75

50

25

QuadrupedalMammals

(4 legged furry things!)

Muncie

Species Diversity

Why?

Three reasons----------

Species Diversity

1. With environmental (habitat) heterogeneity, species diversity increases, compared to uniform environments - greater niche differentiation and resource partitioning

Species Diversity

Environmental heterogeneity: can be defined as "with parts that are different".

Resource partitioning: avoidance of, or reduction in, competition for similar resources by individuals of different species occupying different nonoverlapping ecological niches

Foliage Height and Bird Species Diversity

MacArthor’s warblers

Fig. 16.9

Species Diversity

Variant nutrient (and moisture) availability

Variation in Nitrate and Soil Moisture

Different plant species are the superior competitor under different soil conditions. Complex environment prevents competitive exclusion.

Variation in Soil Conditions Is Associated With Variation In Species Composition of Plant

Communities.

Fig. 16.14

Species Diversity

2. Nutrient Availability: High species diversity occurs in environments with LOW nutrient availability.

In high nutrient environments, competition for LIGHT dominates. Competitive exclusion is more likely to drive some species extinct.

Soil Fertility and Plant Species Diversity(Rain Forest in Ghana, Africa)

Species Diversity

3. Disturbance:

Question for the Day!

What level of disturbance (e.g., fire, drought, local condo development, etc.) would be associated with the highest and lowest diversity levels? Pick from low, medium, and high disturbance levels. Of course, defend your answer---------

Fig. 16.18

Species Diversity - Who Cares?

Principle of Community Ecology:

Diversity and stability are causally related.

More StableLess Stable

Species Diversity

Why?

1. Increasing species diversity leads to more complex interactions: e.g., more species, more predation, more competition, more parasitism

2. Complex systems are more stable: changes in a single species have less impact

Stability

Two parts:

1. Resistance - the ability of a system to resists perturbation

2. Resilience - the ability of a system to return to normal following disturbance

Species Diversity

What if----

An exotic species enters a community. (Presumably) it would immediately increase species richness, but would it increase species diversity overall???????????????

Kudzu

Zebra Mussels

EuropeanStarling

Nile Perch

Summary for Today!

1. Determined abundance distributions and species richness

2. Determined species diversity is a mix of abundance and eveness

3. Identified reasons for levels of species diversity

4. Diversity and stability are related concepts

Species Diversity

• Intermediate Levels of Disturbance -

# of Species

Frequency or intensity of disturbance

Low High