7.3 Populations in ecosystems

Question 1

define niche

Answer 1

how an organism fits into the environment; where it lives and what it does

Question 2

explain the advantage of species occupying different niches

Answer 2

less competition between different species for food, habitats, or mating partners

Question 3

define population size

Answer 3

the total number of organisms of one species in a habitat

Question 4

define carrying capacity

Answer 4

the maximum stable population size of a species that an ecosystem can support

Question 5

suggests five factors that can affect carrying capacity

Answer 5

1. number of predators and prey
2. diseases
3. presence of water
4. interspecific competition
5. intraspecific competition

Question 6

define interspecific competition

Answer 6

competition between different species for food, habitats or resources

Question 6

define intraspecific competition

Answer 6

competition between the species for food, habitats or resources

Question 7

what is a running mean?

Answer 7

when a new mean is calculated after each new sample. when the mean remains the same, you have enough data to give a representative estimate

Question 8

describe a method to follow to estimate the population size of a plant species [6]

Answer 8

• choose area and create grid using tape measure
• use random number generator to choose random coordinates
• place quadrat at coordinates and calculate percentage cover of the plant
• repeat
• calculate running mean
• multiply to give estimate for whole field

Question 9

explain the benefits of using a logarithmic scale for population numbers when plotting data on a graph

Answer 9

it is easier to distinguish between different points on the graph

Question 10

how could you investigate the population growth of bacteria?

Answer 10

nutrient broth
solution becomes murky
use spectrophotometer to measure absorbance

Question 11

what equation can be used to calculate the total population size when using the mark-release-recapture method?

Answer 11

total population size= (number caught in first sample x number caught in second sample) / number marked in second sample

Question 12

what four assumptions are made when using the mark-release-recapture method?

Answer 12

1. marked individuals have sufficient time to disperse and mix back in with the main population
2. the marking does not affect the survival rates of the marked individuals
3. the markings remain visible throughout the sampling and don’t rub off
4. the population size stays the same throughout the investigation period