chapter 8.1: Population Ecology & Population Growth

population biologists

Scientists who study the interactions that occur between living things.

individual

The simplest level of biological organization. Each individual is a member of a population.

population

A group of individuals of the same species that occupy the same environment and interact with each other.

community

Many different populations together make up a community.

ecosystem

Many different populations together make up a community, and many different communities interact with one another in an ecosystem.

biome

A group of ecosystems that share temperature and moisture conditions.

biosphere

All the biomes on the globe make up the Earth's biosphere.

Levels of complexity of living organisms on earth

The levels of complexity are: 1. Individual 2. Population 3. Community 4. Ecosystem 5. Biome 6. Biosphere.

population size

The number of individuals that make up a population.

population density

The number of individuals (population size) in relation to the area they inhabit.

population distribution

Indicates where the individuals are located across the environment they occupy.

sex ratio

The number of males versus females (or vice versa) in a population.

age structure

Describes how many individuals fall into different age classes. Some populations consist mainly of young individuals, while others include individuals spread across many ages.

Factors that control or limit the growth of populations in natural systems

1. Density-dependent factors 2. Nondensity-dependent factors.

Density-dependent factors

The influence of individuals on a population changes as the size of the population changes.

Example of density-dependent factors

As individuals die, the population size decreases, leaving more food for survivors.

Nondensity-dependent factors

Factors that affect populations no matter how large or small the populations are.

Two models to describe how populations grow over time

1. The exponential growth model 2. The logistic growth model.

Two concepts that underlie both models of population growth

1. Carrying capacity 2. Limiting resource.

Carrying capacity

The number of individuals that the available resources of an environment can successfully support.

Limiting resource

A resource that organisms must have in order to survive and that is available only in limited quantities in their environment.

Function of limiting resource

A limiting resource functions to limit the population.

Common limiting resources for animals

Food and water are common limiting resources for animals.

Exponential growth model

Population increase over time is a result of the number of individuals available to reproduce without being limited by environmental resources.

Exponential growth pattern

The population size increases at an exponential rate over time, continuing upward.

J-curve

A graph that shows how quickly a population can grow when it does not face any limiting resources. The line creates a shape like the letter J.

Exponential growth model equation

dN/dt = rN.

Meaning of exponential growth model equation

The change (d) in the number of individuals (N) over a change (d) in time (t) equals the rate of increase (r) in number of individuals (N).

Logistic growth model

A model that illustrates how a population may increase exponentially until it reaches the carrying capacity of its environment.

Population at carrying capacity in logistic growth

When a population's number reaches the carrying capacity, population growth slows down or stops altogether.

Logistic growth and density-dependent factors

This model applies in particular to populations that respond to density-dependent factors.

S-curve

The logistic growth model looks like the letter S, which is why it is often called an S-curve.

Logistic growth model equation

dN/dt = rN(1 - N/K).

Meaning of logistic growth model equation

The change (d) in number of individuals (N) over a change (d) in time (t) equals the rate of increase (r) in number of individuals where population size (N) is a proportion of the carrying capacity (K).

Overshoot and collapse

A pattern where fast-growing and reproducing populations exceed carrying capacity and then decline because of insufficient resources.

Cause of overshoot and collapse

As populations approach carrying capacity, more offspring are born than current resources can support, causing the population to exceed the carrying capacity. When resources become insufficient, individuals die off and the population collapses.

Reproductive strategies

Strategies that populations exhibit to increase or maintain population size.

K-selected species

Species that often keep their populations at or near carrying capacity.

Characteristics of K-selected species

They usually have a long lifetime with few opportunities to reproduce and few offspring, maintaining a fairly level population size.

r-selected species

Species that do not stay close to carrying capacity in terms of population size. Instead, they grow rapidly and exhibit extreme patterns of overshoot and die-off.

K-selected and r-selected species

Many species exhibit characteristics of both K-selected strategies and r-selected strategies.