EST 4 THE LIVING WORLD

CHAPTER 9

Populations and Communities

(pp. 291 –309)

1 Studying Populations

A population is a group of individuals of the same ______, living in a ______space at a specific ______in time.

Examples:

  • Green frogs in a marsh
  • Balsam fir on a mountainside
  • ______

Why do ecologists study populations?

______

Three main characteristics that describe a population:

  1. ______
  2. ______
  3. ______

1.1 POPULATION SIZE

Population size refers to the ______of individuals in a ______.

Why is it useful to know the size of a population?

______

Over time, the size of a population may ______, ______or remain ______.

FOUR FACTORS AFFECTING POPULATION SIZE

Factor / Description
Births / Births of individuals within a population
Deaths / Deaths of individuals within a population
Immigration / Arrival among the population of individuals from other regions
Emigration / Departure of individuals to other regions

What two factors increase population size? Births & Immigration

What two factors decrease population size? Deaths & Emigration

  • If the births and immigration rates are greater than the death and emigration rates, then the population ______.
  • If the births and immigration rates are less than the death and emigration rates, then the population ______.
  • If the births and immigration rates are equal to the death and emigration rates, then the population ______.

METHODS OF MEASURING THE SIZE OF A POPULATION

  1. Counting individuals
  2. Counting by sample area

This method consists of counting the individuals in ______selected ______of the study area and estimating the total population size with the following equation:

What are quadrats? ______

For what types of populations are quadrats a useful counting technique?

______

  1. Mark and recapture

This method is commonly used to count populations of very ______animals, such as, ______, ______, ______and ______.

It consists of the following stages:

  • Installing ______or nets in the populated region
  • Counting the ______animals and ______them with ______, ______, ______or ______
  • ______the marked animals
  • Reinstalling ______or ______
  • Counting the captured individuals again, with a separate count for ______individuals
  • ______the size of the population using the following calculation:

1.2 POPULATION DENSITY

Population density refers to the number of individuals per unit of ______or ______.

Some factors affecting population density

  • Good supply of food and water
  • ______
  • Presence of ______, ______or ______
  • Natural or human-caused ______

1.3 POPULATION DISTRIBUTION

Population distribution is the way in which individuals are ______within their ______.

There are three main patterns of population distribution

  1. ______distribution

Example: Many ______move around in ______.

  1. ______distribution

Example: Northern ______space their nests at regular ______.

  1. ______distribution

Example: ______in a field

1.4 ECOLOGICAL FACTORS

An ecological factor is an aspect of a habitat that can affect the ______living there and thus the population ______.

There are two types of ecological factors:

  1. ______(non-living) factors: These are ______or ______aspects of the environment.
  1. ______(living) factors: These are related to the ______of living organisms in a habitat.

EXAMPLES OF ABIOTIC FACTORS

Abiotic Factors / Biotic Factors
Disease
Terrain
Competition
Air Humidity

A ______FACTOR is an ecological factor that causes the density of a population to decrease.

Examples:

  • Exposure to ______is a limiting factor in the growth of rose bushes.
  • Amount of ______in the ground is a limiting factor in the growth of cacti.
  • The size of the ______is a limiting factor for the snake population.

1.5 BIOLOGICAL CYCLES IN POPULATIONS

The biological cycle of a population consists of the alternating periods of ______and ______in its size. These periods are of ______duration and are ______continually.

The most commonly studied biological cycles in Quebec are those of the lynx and the snowshoe hare. (See figure 9.14 on p. 302)

  • When the hare population rises, the lynx have ______food, so they become healthier and ______more causing their population to ______.
  • When the number of lynx increases, they hunt ______hares causing the hare population to ______. With fewer hares to hunt, the lynx population will eventually ______as well.
  • Finally, as the lynx population decreases, fewer hares will be hunted, so the hare population will ______again and the whole cycle ______.

2 Studying Communities

A community is a set of ______of different ______sharing the same ______.

The squirrels, fungi, trees and mosquitoes in the forest are thus part of the same ______.

2.1 BIODIVERSITY

Biodiversity describes the variety of ______living in a ______.

There are two components to consider when measuring the biodiversity of a community:

  1. ______: the number of species in the community.
  1. The relative ______of each species.

The biodiversity of a community is high when two conditions are met:

  1. The number of species is ______.
  1. The relative abundance of different species is ______.

What is the IUCN?

______

Of the 41415 species identifies in the 2007 IUCN survey, how many are threatened with extinction? ______

How are species protected from extinction?

______

2.2 INTERACTION BETWEEN INDIVIDUALS IN A COMMUNITY

There are four main types of interaction that may occur between individuals of a community:

  1. ______
  2. ______
  3. ______
  4. ______

COMPETITION

Competition is the interaction between living organisms that seek access to the ______in their habitat.

There are two types:

  • ______competition: occurs between individuals of the same species.
  • ______competition: occurs between individuals of different species.

PREDATION

Predation is the interaction between living organisms in which one ______on the other.

The individual that feeds on another living organism is called the ______.

The individual being eaten is called the ______.

Parasitism is a form of ______. The parasite feeds of the ______and in turn, the ______is ______in some way. (Examples include: ______, ______, & ______)

MUTUALISM

Mutualism is the interaction between two living organisms that ______both organisms. (Example: ______and ______)

COMMENSALISM

Commensalism is the interaction between two living organisms in which one organism ______while the other remains ______.

Example: A warblers nest in a ______tree.

THE EFFECTS OF INTERACTION BETWEEN POPULATIONS ON THEIR DENSITIES

Type of Interaction / Effect on population A / Effect on population B
Competition / /
Predation and Parasitism / /
Mutualism / /
Commensalism / /

END OF CHAPTER 9

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