3.7 genetics, populations, evolution and ecosystems

Question 1

population size can vary as a result of

Answer 1

• the effect of abiotic factors
• interactions between organisms ; intraspecific and interspecific competition and predation

Question 2

2 types of competition

Answer 2

• intraspecific
• interspecific

Question 3

competitive exclusion principle

Answer 3

• when 2 species are competing for limited resources, one will typically have a competitive advantage and outcompete the other
• this may be avoided if one or both species have adapted to utilise other resources or a different area of the habitat

Question 4

size of a population can be estimated by using:

Answer 4

• randomly placed quadrats, or quadrats along a belt transect,
  for slow-moving or non-motile organisms
• the mark-release-recapture method for motile organisms. The
  assumptions made when using the mark-release-recapture
  method.

Question 5

define exponential growth of a population and state why this is not possible in real life

Answer 5

exponential growth of a population is the continuous growth in population size.
- exponential growth is only possible where there is an infinite supply of resources.
- in real ecosystems, this is not the case, hence exponential growth is not possible

Question 6

how might temperature affect population size

Answer 6

• extreme temperatures can affect enzyme action
• can directly affect the survival & distribution of a species. Species adapted to thrive in specific temperature ranges will form larger populations in these areas
• ff the temperature of a habitat is significantly lower/higher than the organism’s optimum temperature, the organisms in that habitat cannot grow as efficiently.
• more energy will be spent maintaining body temperature which means less energy will be available for growth and reproduction, limiting the population size (and the opposite for idea temperature conditions)

Question 7

how might light affect population size

Answer 7

• low light levels = less photosynthesis = smaller, slower growing, fewer plants = reduced food for primary consumers = knock on effect for all trophic levels
• opposite in high light levels: more food for primary consumers, carrying capacity increases

Question 8

how might pH affect population size

Answer 8

• extreme pHs affects enzyme action
• All enzymes have an optimum pH. The population is larger when the optimum exists and smaller when the pH is different.
• The pH of water can also affect the aquatic organisms that are found there. Different species have evolved to survive at different pH levels found within water

Question 9

how might water and humidity affect population size

Answer 9

• where water is scarce, populations are small and consist of a few well-adapted species.
• Humidity can affect transpiration and evaporation rates.
• Many plants cannot survive in waterlogged soils. Their roots are unable to respire, they rot and the plant dies.
• Other plants, such as pitcher plants, grow best in bogs where the moisture levels are high.

Question 10

how might intraspecific competition affect population size

Answer 10

• when resources are abundant, the population size increases. This increases intraspecific competition since resources will need to be shared between more organisms, which causes population size to decrease.
• this pattern causes population numbers to fluctuate around the carrying capacity (the maximum number of organisms that an ecosystem can support).
• species that have adaptations that allow them to gain resources better than other species are more likely to survive and reproduce

Question 11

how might interspecific competition affect population size

Answer 11

• interspecific competition means that resources have to be shared between the different species so there will be less available to both.
• this means both species will have less energy for growth and reproduction, so population numbers of both species will decrease.
• for example, leopards and lions show interspecific competition since they both feed on the same prey.

Question 12

define succession

Answer 12

the gradual change in a community/ecosystem (all the organisms of different species) over time. There are 2 types: primary and secondary

Question 13

why does succession occur?

Answer 13

succession occurs because the conditions (abiotic and biotic) in a habitat are gradually changed by the existing species living in it.
- the new conditions are less hostile and so more suitable for a different combination of species and less suitable for the previous species, causing the previous species to be outcompeted.

Question 14

define primary succession

Answer 14

• primary succession is when an ecological community develops in the absence of organisms and soil (i.e. from bare rock).
• this may happen after a volcanic eruption which results in the formation of new rock or if the sea level lowers and exposes new land, glaciers retreating and depositing rock

Question 15

define secondary succession

Answer 15

• when an ecological community develops from a barren landscape in which soil is present, with some organisms living in it, including spores and seeds, but the existing community has been destroyed so the soil is bare.
• e.g. after a forest fire, on an abandoned agricultural land. due to the presence of some soil and organisms, secondary succession occurs much faster than primary

Question 16

what equation is used in mark-release-recapture to calculate population size?

Answer 16

(total no. of individuals in first sample x total no. of individuals in second sample) / number of marked individuals recaptured.

Question 17

state and explain methods used to conserve habitats and species

Answer 17

• Managing succession: managing succession in a way that prevents change to the next stage, so the climax community is not reached
• Seed banks: prevent species of plants from going extinct
• Captive breeding: encourages endangered animals to breed and increase the numbers that exist e.g. pandas
• Fishing Quotas: prevents fishes from being overhunted. maintains biodiversity of the sea
• Protected Areas: maintains the natural diversity of the land e.g. National Parks. Protects landscapes and habitats from being destroyed

Question 18

ecosystem

Answer 18

a community of living organisms and the abiotic factors that affect them

Question 19

niche

Answer 19

the role an organisms has in an ecosystem, including where it lives and what it eats (biotic and abiotic factors)

Question 20

carrying capacity

Answer 20

when an ecosystem supports a certain size of population of a species
- maximum stable population number

Question 21

food chain

Answer 21

a linked series of living organisms each of which is the food for the next level, showing energy flow through the ecosystem

Question 22

food web

Answer 22

the complex interactions between food chains in an ecosystem

Question 23

producers

Answer 23

an organisms producing its own food from simple inorganic materials e.g by photosynthesis

Question 24

autotrophs

Answer 24

green plants and some bacteria that makes their own food

Question 25

consumers

Answer 25

heterotrophs, which obtain nourishment by feeding on other organisms

Question 26

heterotrophs

Answer 26

an organism obtaining food by feeding on complex organic matter i.e consumer

Question 27

trophic level

Answer 27

the position an organism occupies in a food chain

Question 28

gross productivity

Answer 28

total energy fixed during photosynthesis

Question 29

net productivity

Answer 29

energy available for the next trophic level after respiration

Question 30

biomass

Answer 30

the dry mass of organisms

Question 31

population

Answer 31

all the organisms of the same species living together in a particular habitat

Question 32

habitat

Answer 32

a place within an ecosystem where a population lives

Question 33

abiotic factors

Answer 33

physical and chemical features of the environment that have an effect on a population of organisms

Question 34

biotic factors

Answer 34

biological features of the environment that have an effect on a population of organisms

Question 35

intraspecific competition

Answer 35

individuals of the same species attempt to make use of the same scarce resources

Question 36

interspecific competition

Answer 36

individuals of more than one species attempt to make use of the same scarce resources

Question 37

pioneer

Answer 37

a plant species found in the early stage of succession

Question 38

sere

Answer 38

name given to each stage in a succession

Question 39

climax community

Answer 39

end stage in a succession