Species Distributions

What is a population?

All organisms of the same species living in the same geographical area.

What is population density?

The number of individuals of a species within a unit area.

How is population density calculated?

Number of individuals divided by area.

What example illustrates grizzly bear population density?

Glacier National Park has about 230 grizzly bears across 1,500 square miles.

What population density is calculated for grizzly bears in Glacier National Park?

About 0.15 bears per square mile.

How much area does each grizzly bear need on average in the lecture example?

About 6.7 square miles per bear.

What is the range or distribution of a species?

The geographical area where that species can be found.

How can a species' range be mapped?

Map individual organisms and outline the area in which they occur.

Are species range boundaries sharp like international borders?

No. Species range limits are not sharp boundaries.

What is a historic range?

The geographical area a species occupied in the past.

What is a present range?

The geographical area a species occupies currently.

What does the grizzly bear range map illustrate?

The historic range was much larger than the present range.

What is an isolated population?

A population separated from other populations of the same species.

What is a discontinuous range?

A species distribution made up of separated patches rather than one continuous area.

What is an extirpated population?

A population that is extinct locally but whose species still exists elsewhere.

What are temporary populations in the lecture diagram?

Individuals present in an area that are not reproducing there.

What is a metapopulation?

A group of spatially separated populations of the same species that interact at some level.

What is another way to describe a metapopulation?

A population of populations.

Why is gene flow important to a metapopulation?

Gene flow connects populations genetically and is central to how they interact.

How can gene flow occur in a metapopulation?

It can be unidirectional or bidirectional, and continuous or sporadic.

What plant illustrates species distribution in the lecture?

White spruce (Picea glauca), a coniferous evergreen common across the North American boreal forest.

What does the white spruce distribution map show?

The geographical distribution of white spruce across parts of North America.

What is an environmental tolerance diagram?

A diagram showing how population density changes along an environmental gradient, such as temperature.

What is the zone of optimum?

The environmental range where conditions are most favorable and population density is highest.

What are zones of stress?

Conditions near the optimum where organisms can survive but experience stress and population density is lower.

What are zones of intolerance?

Environmental conditions so unfavorable that organisms cannot survive.

How does population density change across tolerance zones?

It is highest near the optimum and decreases toward zones of intolerance.

What is an environmental gradient?

A range of changing environmental conditions, such as low to high temperature.

What is the Principle of Limiting Factors, or Law of the Minimum?

Growth and survival are controlled by the scarcest resource or limiting factor, not the total amount of resources available.

What is a limiting factor?

A resource or environmental condition that restricts an organism's growth or survival.

Why might abundant resources not guarantee an organism's growth?

Another resource or condition may be scarce and act as the limiting factor.

What is a generalist species?

A species with a wide range of environmental tolerance.

What is a specialist species?

A species with a narrow range of environmental tolerance.

How do generalists and specialists differ?

Generalists tolerate a wider range of environmental conditions; specialists tolerate a narrower range.

What does the lecture say about successful survival and reproduction?

They have many requirements, and environmental factors are only one part of them.

How do adaptations relate to species distributions?

Adaptations allow organisms to survive, reproduce, and grow under particular environmental conditions.

Why might a species be absent from an area that seems suitable in one way?

Other environmental factors or requirements may be limiting; one favorable condition does not guarantee survival.

What is the difference between population density and species range?

Population density is individuals per unit area; species range is the geographical area where the species occurs.

What is the difference between a discontinuous range and a metapopulation?

A discontinuous range describes separated areas of occurrence; a metapopulation is separated populations that interact.

What is the difference between extirpation and global extinction?

Extirpation means a species has disappeared from one area but exists elsewhere; global extinction means it no longer exists anywhere.

How does geographic isolation affect populations?

It can separate populations into distinct patches, affecting whether and how gene flow occurs.

What does a range map show that a population-density value alone does not?

Where a species occurs geographically, rather than how many individuals occur per unit area.

What do the scissor-tailed flycatcher maps illustrate?

Ways to represent a species' range and the relative abundance of observations across locations.

What does the tolerance-zones diagram on page 25 combine?

A population-density curve across an environmental gradient with zones of optimum, stress, and intolerance.

What is the central idea of species distributions?

Where organisms occur and how abundant they are depend on environmental tolerances, limiting factors, population interactions, and adaptations.