Chapter 8

What is a population?

The given number of a given species in a given area at a given time.

What does the word population refer to?

A group in general or the size/number of individuals.

What is density (when referring to populations)?

The number of individuals of the same species that live in a given area.

What is dispersion?

The pattern or distribution of organisms in a population.

What are the types of dispersion?

Even, clumped, and random.

When describing populations or predicting changes within them, what types of data are used?

Size, density, dispersion, and other properties.

What is growth rate?

An expression of the increase in the size of an organism or population over a given period of time.

What types of numbers can growth rate be represented by?

Positive, negative, and zero.

How would growth rate be zero?

Birth rate and death rate are equal.

How would growth rate be negative?

Death rate exceeds birth rate.

How would growth rate be positive?

Birth rate exceeds death rate.

Which growth rate do populations usually show? Why?

Zero. Various factors kill individuals before then can reproduce.

What is biotic potential?

The fastest rate at which a species’ population can grow.

What limits biotic potential?

Reproductive Potential

What is reproductive potential?

The maximum number of offspring a given organism can reproduce.

Reproductive potential increases when?

Individuals produce more offspring at a time, reproduce more often, and reproduce earlier in life.

What is generation time?

The average time it takes a member of a population to reach the age when it reproduces.

How does the size of the organism affect reproductive potential?

Large animals become sexually mature after a longer period of time and have longer gestations than small animals do.

What is exponential growth?

Logarithmic or growth in which numbers increase by a certain factor in each successive time period.

Why can populations not grow forever?

Natural conditions are neither ideal nor constant.

What is carrying capacity?

The maximum, equilibrium number of organisms of a particular species that can be supported indefinitely in a given environment.

Why is carrying capacity difficult to calculate exactly?

Ecosystems change.

How is carrying capacity estimated?

Average population sizes or by observing a population crash after a certain size has been exceeded.

When does a species reach carrying capacity?

When it consumes a particular resource at the same rate at which the ecosystem produces the resource.

What is a limiting resource?

The resource that determines the carrying capacity of an environment for a particular species.

What do all animals need?

Food, water, shelter, space, and a mate.

What is interspecific competition?

Competition between members of differing species.

What is competed for in interspecific competition?

Food, water, shelter, and space.

What is intraspecific competition?

Competition among members of the same species.

What is competed for in intraspecific competition?

Food, water, shelter, space, and a mate.

Causes of death in a population are classified into one of two types. What are the two types?

Density dependent and density independent.

What does density dependent mean?

Deaths occur more quickly in a crowded population than in a sparse population.

What density dependent things result in a higher rate of death in a population?

Disease, predation, migration.

What does density independent mean?

A certain proportion of a population may die regardless of the population’s density.

What density independent things result in death in a population?

Unusual weather, natural disasters, human involvement, seasonal cycles…

What is a niche?

The unique position occupied by a species, both in terms of its physical use of its habitat and its function within an ecological community.

How is a niche different from a habitat?

Habitat is a location, niche is pattern of use of the habitat.

How are interactions between species categorized?

At the level where one population interacts with another.

What are the five major types of species interactions?

Competition, predation, parasitism, mutualism, and commensalism.

What is competition?

The relationship between two species (or individuals) in which both species (or individuals) attempt to use the same limited resource such that both are negatively affected by the relationship.

Can species compete if they never come in contact with each other? Explain.

Yes. Using the same resources at different times.

What is niche restriction?

When each species uses less of the niche than they are capable of using.

What is predation?

An interaction between two species in which one species, the predator, feeds on the other species, the prey.

What is a parasite?

An organism that lives in or on another organism and feeds on the other organism.

What is an example of a parasite?

Tick, flea, tapeworm, heartworm, leech.

What is parasitism?

A relationship between two species, the parasite, benefits from the other species, the host, and usually harms the host.

What is the difference between a parasite and a predator?

A parasite spends some of its life in or on the host, and that parasites do not kill their hosts.

What is commensalism?

A relationship between two organisms in which one organism benefits and the other is unaffected.

What is mutuallism?

A relationship between two species in which both species benefit.

What is symbiosis?

A relationship in which two different organisms live in close association with each other.

What does coevolve mean?

The evolution of adaptations that reduce the harm or improve the benefit of a symbiotic relationship.