Ecology:Community Structure &

Ecosystem Services

David Mellor, PhDCitizen Science CoordinatorVirginia Master Naturalists

Overview of Ecology• Definition and Scope• Energy and Food Webs• Nutrient Cycles• Population Dynamics• Ecological Interactions• Community Structure• Ecosystem Services• Human Impacts

Community Structure

• Species Diversity• Keystone Species• Disturbance• Succession

Species Diversity

• Species Richness– The number of species in an ecosystem

• Relative Abundance– The amount of a species in a given ecosystem

• Species Diversity– Considers BOTH richness and abundance– There are many ways to measure diversity

Richness

Higher (3 species)

Lower (1 species)

Species Diversity

• Species Richness– The number of species in an ecosystem

• Relative Abundance– The amount of a species in a given ecosystem

• Species Diversity– Considers BOTH richness and abundance– There are many ways to measure diversity

Abundance

Higher

Low

Species Diversity

• Species Richness– The number of species in an ecosystem

• Relative Abundance– The amount of a species in a given ecosystem

• Species Diversity– Considers BOTH richness and abundance– There are many ways to measure diversity

High Richness, Low Abundance

High Abundance, Low Richness

Keystone Species

• An organism whose role in the environment is “critical.”

• Species Dominance– Role of organisms in an environment may not be

directly related to the number of individuals• e.g. Numerous understory trees may play less of a role

than a few canopy species that determine light levels.

Disturbance and Stability

• Stability– The tendency of a community to reach and

maintain an equilibrium, or relatively constant condition, in the face of disturbance

• Community resilience– The ability of a community to persist in the face of

disturbance

Disturbance

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

The change in community composition over time.– Primary succession: creating a new ecosystem, such

as after a volcanic eruption creates new land– Secondary succession: community change in an

existing habitat.– Pioneer species: Early to inhabit a new community– Seral stage: Each stage of the succession process, may

last months to decades– Climax community: A mature community that no

longer exhibits change in species composition

Ecological Succession

• Disturbance (e.g. abandoned farm)• Annual plants (“weeds”)• Perennial weeds and grasses• Woody Shrubs• Young pine forest• Mature hardwood forest

Tim

e

Succession

Intermediate Disturbance Hypothesis

Frequency of Disturbance Events

Biod

iver

sity

Question

Why does a community change over time following a disturbance?

Ecosystem Services

An ecosystem process that leads to a service from which humans benefit.

Ecosystem Services

Process Services Benefits

Nitrification Converting Ammonia or Nitrite to Nitrate

or Atmospheric Nitrogen

Clean Drinking Water

Decomposition Using non-living organic matter for

energy

Removing disease-spreading matter,

Soil creation

Pollination Growth of fruit or reproduction of

useful plants

Fruit, nuts, timber, seeds

Photosynthesis Capturing carbon dioxide, creating

sugars

Food production, Carbon capture, Breathable air

• Some ecosystem services could be replaced by humans.– Wastewater treatment plants

• All ecosystem goods and services have a value.– How much money are the food resources

worth?– How much is our soil worth?– How much money do we spend on recreation

in the outdoors?

Ecosystem Services

• Some ecosystem services could be replaced by humans.– Wastewater treatment plants

• All ecosystem goods and services have a value.– How much money are the food resources

worth?– How much is our soil worth?– How much money do we spend on recreation

in the outdoors?

Ecosystem Services

Ecosystem Services

Ecosystem Services

Included estimates of 17 services: Regulating gasses, climate, water;

soil formation, nutrient cycling, waste treatment, pollination, food

production, raw materials, recreation, etc.

Ecosystem Services

$16 - $54 trillion per year (World GDP = $18 trillion)

(Costanza et. al., 1997)US Dollars per Hectare per Year

Worksheet

Describe an ecosystem service that occurs in an natural area near your home.