BISC 121 - Community Ecology Part 2 - Midterm 4

What did most ecologists once favor about communities?

The view that communities are in a state of equilibrium (stable, balanced states, regulated by internal factors like competition and carrying capacity (a "balance of nature"))

Who supported the equilibrium view?

F. E. Clements.

What did F. E. Clements suggest?

That species in a climax community function as a superorganism.

Which ecologists challenged whether communities were at equilibrium?

A. G. Tansley and H. A. Gleason.

What has recent evidence led to?

A nonequilibrium model.

What does the nonequilibrium model describe?

Dynamic, constantly changing systems influenced by disturbances (like fires, floods, predators, climate shifts) rather than steady, balanced states.

What is a disturbance?

An event that changes a community, removes organisms from it, and alters resource availability.

What is fire in most terrestrial ecosystems?

A significant disturbance.

What is fire often in some communities?

A necessity.

What does the intermediate disturbance hypothesis suggest?

That moderate levels of disturbance can foster greater diversity than either high or low levels of disturbance.

What do high levels of disturbance do?

Exclude many slow-growing species.

What do low levels of disturbance do?

Allow dominant species to exclude less competitive species.

What did the 1988 Yellowstone fire demonstrate?

That communities can often respond very rapidly to a massive disturbance.

What is ecological succession?

The sequence of community and ecosystem changes after a disturbance.

What is primary succession?

Succession that occurs where no soil exists when succession begins.

What is secondary succession?

Succession that begins in an area where soil remains after a disturbance.

How may early-arriving species and later-arriving species be linked?

In one of three processes.

What is the first possible process linking early and later species?

Early arrivals may facilitate appearance of later species by making the environment favorable.

What is the second possible process?

They may inhibit establishment of later species.

What is the third possible process?

They may tolerate later species but have no impact on their establishment.

What provides a valuable field-research opportunity for observing succession?

Retreating glaciers.

Where is succession on glacial moraines studied?

Glacier Bay, Alaska.

What does succession in Glacier Bay follow?

A predictable pattern of change in vegetation and soil characteristics.

What are the four succession stages?

Pioneer, Dryas, Alder, Spruce (in this stage).

What is succession the result of?

Changes induced by the vegetation itself.

How does vegetation affect soil on glacial moraines?

Vegetation lowers the soil pH and increases soil nitrogen content.

What has the greatest impact on biological communities worldwide?

Humans.

What does human disturbance usually do to communities?

Reduces species diversity.

What else do humans often prevent?

Naturally occurring disturbances that can be important to community structure.

What example is given of human-caused disturbance?

Trawling to capture fish near the sea floor.

What two key factors affect a community’s species diversity?

Latitude and area.

What happens to species richness along an equatorial–polar gradient?

Species richness generally declines as you move from the equator to the poles.

Where is species richness especially great?

In the tropics.

What two key factors probably drive equatorial–polar gradients in species richness?

Evolutionary history and climate.

What may partly account for the greater species richness of the tropics?

The greater age of tropical environments.

What is likely the primary cause of the latitudinal gradient in biodiversity?

Climate.

What climatic factors correlate with biodiversity?

Temperature, solar energy, and water availability (on land).

How can these climatic factors be considered together?

By measuring a community’s rate of evapotranspiration.

What is evapotranspiration?

Evaporation of water from soil plus transpiration of water from plants.

What does the species–area curve quantify?

The idea that a larger geographic area tends to have more species.

Why do larger areas tend to have more species?

Because of the inclusion of new niches and new isolated patches as the examined area increases.

What supports the species–area relationship?

A species–area curve of North American breeding birds.

What does the figure for the species–area curve show?

Area (hectares) vs number of species on a logarithmic scale.

What does species richness on islands depend on?

Island size, distance from the mainland, immigration, and extinction.

What does the equilibrium model of island biogeography maintain?

That species richness on an ecological island levels off at a dynamic equilibrium point.

What do studies of species richness on the Galápagos Islands support?

The prediction that species richness increases with island size.

How are ecological communities universally affected?

By pathogens.

What are pathogens?

Disease-causing microorganisms, viruses, viroids, and prions.

What can pathogens do to communities?

Alter community structure quickly and extensively.

What effects can pathogens have on communities?

They can have dramatic effects.

What example is given of pathogen damage?

Some coral reef communities being decimated by white-band disease.

What other example is given involving keystone species?

Many sea stars being affected by a wasting disease.

What are human activities doing to pathogens?

Transporting pathogens around the world at unprecedented rates.

What is community ecology needed for?

To help study and combat them.

What are zoonotic pathogens?

Pathogens transferred from other animals to humans.

How can transfer of pathogens occur?

Directly or through an intermediate species called a vector (can be multiple species).

What is noted about emerging human diseases?

Many of today’s emerging human diseases are zoonotic.

What example of a zoonotic disease is given?

West Nile Virus.

How was West Nile Virus dispersed?

Widely via birds and humans, and host-to-host by mosquitoes.

Where did West Nile Virus have outbreaks before reaching the Western Hemisphere?

Algeria 1994, Romania 1996.

When did West Nile Virus reach New York?

1999.

How dangerous is West Nile Virus for humans?

Though 80% of infected humans show no symptoms, it killed 286 Americans in 2012.

What virus is being monitored as another zoonotic threat?

Avian Flu.

What is avian flu?

A highly contagious virus of birds.

What could make avian flu a deadly global epidemic of humans?

If recombined with human flu.

What fact about flu viruses increases this risk?

Flu genome is segmented so recombination is common.

Which animals are studied for potential spread of avian flu?

Migrating birds from Asia to North America.

How many humans have contracted the H5N1 avian flu strain so far?

Very few, with high fatality.

How far has human-to-human transmission of H5N1 gone?

It has not gone past a single transfer.

What would pose a major threat?

If a strain develops efficient human-to-human transfer ability.

Where is recombination of human and avian flu strains most likely to occur?

In pigs.

What is recombination in pigs thought to have caused?

Major pandemics in 1957 and 1968.

How else can avian flu become able to infect humans?

By mutation.

What pandemic is this thought to explain?

The 1918 pandemic that killed about 50 million people.