7.2 Food Webs and Species Interdenpendencies

Question 1

What are autotrophs?

Answer 1

Plants and phytoplankton which make their own food, including glucose through the process of photosynthesis or chemosynthesis, and are always at the start of the food chain.

Question 2

What are heterotrophs?

Answer 2

All organisms other than plants and phytoplankton, such as animals and insects, which feed by consuming other organisms or their products.

Question 3

List the 6 types of organisms which are heterotrophs:

Answer 3

• Herbivores
• Carnivores
• Scavengers
• Parasites
• Detritivores
• Decomposers

Question 4

Name the 2 producers in the food chain:

Answer 4

• Autotrophs

- Heterotrophs

Question 5

What is a detritus? Give some examples:

Answer 5

• Consumes organic waste, including faeces and dead tissues.
• Differ to decomposers as they do not break down materials outside their bodies
• Physically break down litter into small particles to make it easier for decomposer to then work
• Eg. Worms, snails, dung beetles

Question 6

What are decomposers?

Answer 6

Break down complex molecules of the organic material in or on which they live.

Question 7

What are food webs?

Answer 7

The feeding patterns within an ecosystem which appear web-like when shown as a diagram.

Question 8

Why is it important that we understand food webs?

Answer 8

Because changes to one species with impact other species.

Question 9

What is the principle of food webs? Give an example:

Answer 9

The simpler the food chain, (eg. The Giant Panda only eats one type of food), the more sensitive it will be to changes.

Question 10

What is a keystone species? Give 2 examples:

Answer 10

A species that plays a critical role in maintaining the structure of their ecosystem.
Eg. Keeping population numbers of other species in check, or influencing the habitat (eating trees/shrubs).

Question 11

List the 3 features of population dynamics:

Answer 11

• Population size
• Total abundance
• Population density

Question 12

What is population size?

Answer 12

The total number of organisms in an area.

Question 13

What is total abundance?

Answer 13

The total number of organisms on the planet.

Question 14

What is population density?

Answer 14

When it is difficult to calculate the number of individuals, the size is measured by biomass (how much matter is present in a certain area).

Question 15

List the 4 parts population size:

Answer 15

• Population growth rate
• Natality (birth rate)
• Mortality (death rate)
• Migration

Question 16

What is population growth rate?

Answer 16

The change in the total population per unit time.

Question 17

What is natality (birth rate)?

Answer 17

The number of organisms born per unit of time

Question 18

What is mortality (death rate)?

Answer 18

The number of organisms dying per unit of time.

Question 19

What are the 2 features of migration?

Answer 19

• Immigration: Organisms moving into a population

- Emigration: Organisms moving out of the population

Question 20

What is exponential growth?

Answer 20

Rapid increase in the size of a population, which is only sustained when there is no environmental resistance.

Question 21

What do species with exponential growth tend to have?

Answer 21

• Short generation time

- Large numbers of offspring

Question 22

What is logistic growth?

Answer 22

• When population size is below the carrying capacity, the growth is rapid
• As the population size approaches carrying capacity, growth slows and stops

Question 23

List the 4 abiotic factors which influence tolerance range:

Answer 23

• Temperature
• Soil/water pH
• Rainfall
• Wind

Question 24

List the 2 types of major changes to the environment and give an example for each:

Answer 24

• Natural disasters (Eg. Fire, drought, volcanic activity)

- Human caused changes (Eg. Construction, pollution)

Question 25

What is tolerance range?

Answer 25

Where for most conditions, species require a variable (eg. Temperature) to remain within that range ‘Goldilocks zone’.

Question 26

What are the 3 density dependant factors?

Answer 26

• Food supply (Increased density = compete for resources)
• Disease (Increased density = Spread diseases and parasites more readily)
• Predation (Increased density = More easily found by predators)

Question 27

What is carrying capacity (K)?

Answer 27

Maximum population that can be sustained before organisms run out of environmental resources.
-Total carrying capacity will change as conditions change