POPULATIONS, COMMUNITIES, AND ECOSYSTEMSChapter 2

LIVING THINGS INTERACT

All the organisms of the same species living together that live in a specific ecosystem are called a population

The individuals in the population compete with one another for food, nesting space, and mates.

LIVING THINGS INTERACT

All of the populations of different species of animals and plants that live and interact together in an area is a community

The different populations in a community depend on each other for food, shelter, and many other things

LIVING THINGS INTERACT

Each community depends on its environment. The nonliving, or abiotic, parts of an environment combine with the living, or biotic, things in a community to make up an ecosystem.

Abiotic things include soil, air, temperature, precipitation, and many more.

Looking at p.34 in your textbook, identify two biotic and two abiotic factors in Figure 2-1.

Biotic1. ______________________________________2. ______________________________________

Abiotic1.______________________________________2. ______________________________________ When you’re finished, pair up with someone

beside you and share what you wrote down.

In the next slide box, draw an ecosystem of your choice. Include at least 5 populations as well as biotic and abiotic factors. Below your picture write

Populations:

Community:

Ecosystem:

Tell me what from your picture is included in each of the vocabulary words.

CHARACTERISTICS OF POPULATIONS

1. Population density- the number of organisms per unit of living space

It’s NOT just the number of organisms in the population.

POPULATION DENSITY

Look at Figure 2-3 on p.36. Each population is made up of the same number of oak trees.

Trees in population I are spread over 10 km2 while those in population II occupy only 1 km2.

Which of these populations has greater population density?

What are the population densities for each?

Sometimes populations are spread over a large area while in other cases a population is clumped together in a small area.

Look at Fig.2-4. Those birds are evenly spread throughout the marsh where they live.

-Why do you think they spread out evenly?

CHARACTERISTICS OF POPULATIONS

2. Size- which is constantly changing

Populations can increase in size through reproduction of organisms. They can also decrease in size due to the death of organisms.

The birthrate and death rate need to be considered together to see their actual effect on population size.

LOOKING AT BIRTHS AND DEATHS

Population of rabbits lives in a 1 km2 field. At the beginning of the year the population is 225 rabbits. The end of the year population count shows there are now 310 rabbits.

Does this mean that there were 85 rabbits born that year?

Not necessarily. Although the population increased by 85, perhaps 150 rabbits were born and 65 rabbits died.

LOOKING AT BIRTHS AND DEATHS

Let’s take a look at that same rabbit population the following year. The total population goes from 310 to 400 rabbits.

Births: 150 Deaths: 75 Net gain: 75 rabbits

Where did the other 15 rabbits come from?

COMING AND GOING

The other 15 rabbits might have immigrated to the ecosystem.

Immigration: when new members join a population

Emigration: when members of a population leave

Mice Cats

Original Population 45 6

Births 105 4

Deaths 95 1

Immigration 6 2

Emigration 16 0

Which population has the greatest density at the beginning of the year?

At the end of the year?

Which population was larger at the end of the year?

INTERACTIONS WITH THE ENVIRONMENT

Most living things produce more offspring than will survive. For example, a female frog might lay hundreds of eggs in a small pond.

In a few months, the population of frogs in that pond will be about the same as it was the year before.

Why isn’t the pond overrun with frogs?

LIMITING FACTORS

Populations cannot grow indefinitely because the environment only contains so much food, water, living space, and other needed resources.

When one or more of those resources becomes scarce, it is called a limiting factor.

For example, food could become a limiting factor when a population becomes too large for the amount of food available.

Any single resource can be a limiting factor for population size.

CARRYING CAPACITY

The largest population that a specific environment can support over a long period of time is called the environment’s carrying capacity.

When a population grows larger than its carrying capacity, limiting factors in the environment cause the population to get smaller.

What kinds of limiting factors might act on a population of tropical fish living in an aquarium?

RELATIONSHIPS BETWEEN POPULATIONS

Most common is the predator-prey relationship.

Predator is an animal that hunts and eats other animals

The animal eaten by a predator is its prey

Examples: lion-zebra, bird-worm

Parasitism is a relationship between two types of organisms in which one organism benefits while the other one is harmed

Parasite is an organism that lives in or on another organism and is harmful to that organism

The infected organism is the host

EXAMPLES OF PARASITISM

Athlete’s foot-Parasite: fungus-Host: human’s foot

Other common examples are fleas, ticks, lice, and mosquitoes. These animals live off the blood of the host.

The parasite doesn’t want to kill the host though. If the host dies, this normally results in the death of the parasite as well.

OTHER RELATIONSHIPS

Commensalism: one organism benefits while the other is not affected Examples: clown fish and sea anemone from p.32-33

Mutualism: both organisms benefit Example: termite and protozoan in termite’s gut