7C :Populations in Ecosystems

What is a community?

Populations of different species in a habitat

What is a population?

A group of organisms of the same species living in a particular place at a particular time and potentially able to interbreed

Competition occurs within and between these populations for the means of survival. Within a single community, one population is affected by other populations, the biotic factors, in its environment. Populations within communities are also affected by, and in turn affect, the abiotic (physicochemical) factors in an ecosystem.

What is an ecosystem?

All the organisms living in a community and the abiotic conditions of the environment

What are biotic conditions?

Living features of an ecosystem e.g. predators/food

What are abiotic conditions?

Non-living features of an ecosysrem e.g. temperature, soil pH

True or False

Ecosystems are always large in size

False

Ecosystems can be any size

What is a niche?

The role of a species within its habitat

What does a niche a species occupies include?

Biotic interactions

Abiotic interactions

Each species has its own unique niche

True or False

True

A niche can only be occupied by one species

What is a habitat?

The place where an organism lives

What happens when two species try to occupy the same niche?

They compete with each other

One species will be more successful

Only one species will survive

What is the carrying capacity ?

The maximum stable size of a population of a species which that ecosystem supports

What can cause the carrying capacity to vary?

Biotic factors

Abiotic factors

What will happen to the size of a population if the abiotic factors are ideal for that species?

It will increase

How can biotic factors cause population size to vary?

1. Competition

2. Predation

What are the two types of competition?

Interspecific

Intraspecific

What is the difference between interspecific and intraspecific competition?

Interspecific competition is between organisms of different species

Intraspecific competition is between organisms of the same species

What is competition?

Organisms compete with each other for the same resources

How are carrying capacity and intraspecific competition linked?

The population of a species will increase when resources are plentiful

This increases the competition for the same resources

The resources will become limiting

If the population grows beyond the carrying capacity, the population will decline (Not enough resources)

Cycle repeats

How are the population sizes of predators and prey linked?

Population of the prey increases

Causes population of predator to increase as more food

Population of the prey decreases

Causes population of predator to decrease as less food

Repeats

Why is it unlikely that predator-prey relationships are simple?

There are many other factors involved

e.g. availability of food for prey

What is species abundance?

The number of individuals of one species in a particular area

What are 3 methods of measuring species abundance?

Counting number of individuals in sample

Frequency- count number of samples a species is in

Percentage cover - Count what percentage of the area is covered by a species

When is percentage cover used?

Non-motile species

Slow-moving species

How should samples be chosen?

Random sampling

Use calculator to generate random numbers

Use numbers as coordinates

Why is it important to take many samples?

Reduces probability that results due to chance

How can you estimate the number of individuals in a whole area from number of individuals in a sample?

Multiply up mean of individuals in sample area to get total area size

Find mean of percentage cover

What does the distribution of species mean?

Where a particular species is in the area (i.e how spread out)

How do you work out the best number of samples to use?

Take a running mean of the samples

When the mean has stabilised, there is no point in taking more samples

Mean now gives realistic estimate for whole area

When are quadrats and transects used?

Investigating non motile or slow moving organisms

When are traps, nets appropriate for sampling?

When studying motile organisms

e.g. insects

What can a quadrat be used to measure?

Species frequency

Percentage cover

How can areas with large plants/trees be samples?

Using very large quadrats

What is a belt transect?

Quadrats placed next to each other along a transect

Or in an interrupted belt transect, places at regular intervals

What is a belt transect used for?

Working out species frequency and percentage cover

What are transects used for?

Find out how organisms are distributed across an area

What is the calculation for total population size? (from-mark release-recapture)

(Number caught in sample 1 x number caught in sample 2) / number marked in sample 2

What are the 6 steps for mark-release-recapture?

1. Capture a sample of a species using appropriate technique and count

2. Mark in harmless way e.g. spot of paint/ID tag

3. Release into habitat

4. Wait until organisms have rejoined and redistributed among population

5. Take second sample and count number marked

6. Use Total population size equation

What is mark-release-recapture used for?

Measuring abundance of mobile species

What 4 assumptions does the accuracy of mark-release-recapture depend on?

1. Marked sample has enough time to mix back with population

2. Marking hasn't affected chance of survival

3. Marking still visible (not rubbed off)

4. No births, deaths, migration changing population size

Why is it important to minimise stress to animals in mark-release-recapture?

Reduces their chance of survival/they avoid trap in future

Changes population size

Estimate not accurate

ALSO unethical

How do you minimise stress to animals in mark-release-recapture?

Handle and keep as little as possible

Why does monoculture decrease plant diversity?

One species of plant grown

Herbicides or weeding

Crop better competitor for e.g. Light or carbon dioxide

Why does monoculture decrease diversity of animals?

Fewer species of plant

Less variety of food sources

Less habitats or niches

Pesticides used