7.4 - Populations in ecosystems

Question 1

size of ecosystems

Answer 1

varies from very small to very large

Question 2

define habitat

Answer 2

an area where one or more organisms live

Question 3

define carrying capacity

Answer 3

certain size of population of a species which an ecosystem can support

Question 4

why do population sizes of species vary?

Answer 4

• effect of abiotic factors
• interactions between organisms i.e interspecific and intraspecific competition, predation

Question 5

name two ways the size of a population can be estimated

Answer 5

• slow moving/non-motile organisms: randomly placed quadrants or quadrants along a belt transect
• motile organisms: mark-release-recapture

Question 6

how can species abundance be measured for slow-moving/motile organisms?

Answer 6

percentage cover or frequency

Question 7

describe how you could estimate a population size of a non-motile species

Answer 7

• use a grid
• use a random number generator to obtain coordinates

using % cover
- divide total % by number of quadrats

using frequency
- count frequency of organisms from species in a quadrat
- use a large sample size and calculate mean
total population size = mean no. organisms of that species per quadrant x number of quadrats

Question 8

name assumptions made when using the mark-release-recapture method?

Answer 8

• marked individuals from first capture distribute randomly
• no marks rub off
• mark is not toxic and does not reduce chance of survival
• few, if any, births or deaths in population
• no immigration in or emigration out of population
• proportion of marked to unmarked individuals in second sample is representative of individuals in population as a whole

Question 9

describe procedure of mark-release-recapture method

Answer 9

• collect sample of known number, mark (non-harmful) and release in same area they were caught
• allow organisms to randomly distribute before collecting second sample of known number and record number of these that are marked
  estimated population size = number in first sample x total number in second sample /number marked in second sample

Question 10

give 3 features of a climax community

Answer 10

• same species present over long time
• abiotic factors constant
• populations are stable

Question 11

which abiotic factors affect population growth?

Answer 11

• temperature
• light intensity
• pH
• water + humidity

Question 12

name factors that individuals of the same species compete for (most apply to organisms of other species)

Answer 12

• food sources
• water
• mates
• shelter
• minerals
• light

Question 13

when does interspecific competition most commonly occur?

Answer 13

when two species occupy the same niche

Question 14

define predation

Answer 14

one species is caught by another species

Question 15

describe the predator-prey relationship

Answer 15

• when prey is eaten by predator, prey population decreases
• so predator population increases, but this means more prey is consumed
• so prey population decreasing means increased competition for prey between predators
• lack of food for predators = predator population decreases so less prey eaten
• allows prey population to recover and cycle occurs over in an oscillating manner

Question 16

define succession

Answer 16

the change of one community of organisms into the other

Question 17

describe and explain how primary succession occurs

Answer 17

• colonisation by pioneer species which is adapted to survive in harsh conditions
• pioneer species changes the environment (organisms die so they are decomposed by microorganisms which adds humus, leading to soil formation)
• this makes environment less hostile for new species with different adaptations (could cause environment to become less suitable for previous species)
• over time soil becomes more mineral rich
• increase in biodiversity
• climax community established

Question 18

what is a climax community?

Answer 18

a self-sustaining and stable community of organisms

Question 19

how could the formation of a climax community be stopped?

Answer 19

controlled burning of land

Question 20

describe how secondary succession occurs

Answer 20

• previously colonised area where an existing community has been cleared e.g after forest fires
• soil layer already present so succession begins at later stage

Question 21

define conservation

Answer 21

human management of the Earth’s resources
typically involves managing succession