Populations and communities

Question 1

Define population

Answer 1

A group of organisms of the same species living in a particular area.

Question 2

What four factors affect a population?

Answer 2

Birth, death, immigration, emigration

Question 3

Describe the features of bacterial growth in a nutrient medium in closed conditions

Answer 3

Sigmoidal shaped curve:

1. Lag phase - Nutrient assimilation, activating genes and producing necessary enzymes
2. Exponential phase - Bacteria divide exponentially, no restriction to growth
3. Stationary phase - A factor becomes limiting e.g. food, waste, space
4. Decline phase - Death rate exceeds birth rate

Question 4

What is the biotic potential?

Answer 4

The maximum rate of growth as seen by the exponential phase - The reproductive rate of a population under optimum conditions and unlimited resources

Question 5

What is environmental resistance?

Answer 5

The restriction by the environment on the population reaching its max growth rate and its biotic potential. e.g. nutrient shortage or accumulation of waste.

Question 6

What is the carrying capacity?

Answer 6

The max number of a population an ecosystem can support, determined by the resources available.

Question 7

Draw a J shaped curve.

Answer 7

in book

Question 8

What are J shaped curves representative of?

Answer 8

Characteristic of many protoctistan species

Question 9

What are the two types of competition?

Answer 9

Interspecific and intra-specific

Question 10

What is the competitive exclusion principle?

Answer 10

No two species can occupy the same ecological niche, therefore one species loses out.

Question 11

What type of curve do you get with a predator prey graph?

Answer 11

Oscillating with the predator peaks and troughs lagging behind the preys, with the number usually lower than the number of prey.

Question 12

What is the equation for population growth?

Answer 12

(Births + Immigration) - (Deaths + emigration)

Question 13

What are the two types of species we deal with?

Answer 13

r-selected species and k-selected species

Question 14

What are r selected species?

Answer 14

Opportunistic and grow very quickly, usually boom bust patterns of growth e.g bacteria and protoctistans

Question 15

What are k selected species?

Answer 15

Have more stable populations and population size usually remains at carrying capacity. Emphasis on survival. e.g. humans

Question 16

Features of r and k selected species?

Answer 16

in book.

Question 17

What are the three types of population interactions?

Answer 17

1. Mutualism - +/+ - both species gain, interaction necessary for both
2. Predation - +/- - The predator gains and the prey loses
3. Competition - -/- - Both species lose while interacting, species most affected is eliminated from its niche.

Question 18

What is parasitism and how does it differ from predation?

Answer 18

Parasite - an organism that lives in or on another organism benefitting from it an causing it harm over a period of time. +/-, the difference is predators kill their prey to obtain nourishment, parasites do not.

Question 19

Describe mutualism and give an example

Answer 19

Both species gain +/+, e.g. nitrogen fixing bacteria receive nutrients and protection inside the root nodules of leguminous plants. Lichens harbour green algae among their hyphae, the fungi absorbs water and nutrients used by the plant.

Question 20

What is a pest and what is biological control?

Answer 20

Pest - A species that damages a commercial crop and causes economic damage
Biological control - Deliberately introducing an organism that will target and cause harm to the pest e.g. a predator, competitor

Question 21

What are some benefits of biological control?

Answer 21

1. Reduce the need for chemical pesticides/herbicides
2. No bioaccumulation of waste in foods
3. Development of resistance is unlikely
4. If successful needs little additional action

Question 22

What are the downfalls of biological control?

Answer 22

1. Pest resurgence can occur
2. Pest is unlikely to be totally eliminated
3. Only works if the species can adapt and thrive
4. Important the introduced species does not outcompete the native species

Question 23

What is a community?

Answer 23

The total of all the populations in a particular area - The biotic component of an ecosystem

Question 24

What is an ecosystem?

Answer 24

The abiotic and biotic component

Question 25

What is succession?

Answer 25

The changes in an ecosystem over time, both biotic and abiotic.

Question 26

Where does primary succession occur?

Answer 26

It occurs on newly formed, harsh and hostile barren substrates that have not been previously colonised e.g. The lava fields after a volcanic eruption

Question 27

Describe primary succession.

Answer 27

Pioneer species (usually r strategists) are able to survive the hostile conditions. Over time the lichen degrade the rock and embryonic soil forms. This results in a change in community which further alters the abiotic environment. This process continues through a number of seres, until a final stage the climax community.

Question 28

What are the two types of climax community?

Answer 28

Climatic climax - Composition of the climax community determined by the climate
Biotic climax - Composition of the climax community determined by a biotic factor

Question 29

What are the trends in succession?

Answer 29

1. The soil develops - increases in depth and proportion of organic content (humus)
2. The height and biomass of vegetation increases
3. The abiotic environment becomes less hostile
4. Communities become more complex
5. Increased biodiversity
6. Communities in later seres more stable than communities in earlier ones

Question 30

What can interrupt a succession?

Answer 30

Fire, flooding, wind damage, human interference

Question 31

Describe secondary succession

Answer 31

Secondary succession does not usually begin with lichens as the soil is already formed, therefore it is much quicker than primary succession. Occurs after an existing ecosystem has been disturbed