CH5 Populations

Question 1

What are the factors that affect all the organisms living in an ecosystem.

Answer 1

• The intensity of energy flowing through the ecosystem varies.
• Biological cycles, such as the nitrogen cycle, vary the mineral availability
• Habitats change over time as succession occurs
• New species arrive and some species are no longer present

Question 2

What is the size of a population at a particular time determined by?

Answer 2

• Birth rate (hatching, reproduction by binary fission and all other ways organisms increase their numbers
• Death rate
• Immigration
• Emigration

Question 3

What are fugitive species?

Answer 3

Species that are poor at competition: instead they rely on a large capacity for reproduction and dispersal to increase numbers. They invade a new environment rapidly, e.g. algae colonizing bare rock and rose bay willow herb colonising soil cleared by fire

Question 4

What are equilibrium species?

Answer 4

Species control their population by competition within a stable habitat. Their usual pattern of growth is a sigmoid (s-shaped) curve called the one-step growth curve. Seen for example when bacteria are put into nutrient solution or when rabbits are newly introduced to an island.

Question 5

What is the lag phase?

Answer 5

A period of slow growth. A period of adaptation or preparation for growth, with intense metabolic activity, especially enzyme synthesis

Question 6

What is the exponential phase?

Answer 6

When numbers increase as long as there are no limiting factors. More individuals available for growth. Population doubles per unit time.

Question 7

What are the environmental resistance factors that slow down growth?

Answer 7

• Less food available
• The concentration of waste products becomes increasingly toxic
• There is not enough space or nesting sites

Question 8

what are the factors that limit growth?

Answer 8

• available food
• overcrowding
• competition
• accumulation of toxic waste

Question 9

what are some biotic factors that limit growth?

Answer 9

• predation
• parasitism and disease because increased population density allows infection to spread more rapidly
• competition

Question 10

name some abiotic factors that limit growth?

Answer 10

temperature and light intensity

Question 11

what is the stationary phase?

Answer 11

occurs when birth rate is equal to death rate and the population reaches its carrying capacity

Question 12

what is the carrying capacity?

Answer 12

the maximum number of individuals that an area can support

Question 13

what is the death phase?

Answer 13

when the factors that slow population growth at the end of the log phase become more significant population decreases

Question 14

how are the populations of predator and prey regulated?

Answer 14

negative feedback (prey increase so predator increase meaning that prey decrease until there aren’t enough prey to support the predators so predators decrease).

Question 15

why is a log scale used for population graphs of bacteria?

Answer 15

the population increase is very large

Question 16

what are density dependent factors?

Answer 16

environmental factors that have more effect if the population in a given area is larger (as they affect a greater proportion of the population).

Question 17

Name some density dependent factors?

Answer 17

they are biotic factors and include:

disease, parasitism and depletion of food supply

Question 18

why do density dependent factors have more effect depending on the density of the population?

Answer 18

if population s denser, parasites are transmitted more efficiently and a greater proportion of individuals are affected.
also if prey density is higher, predators encounter them more often and so predator population increases.

Question 19

what are density independent factors?

Answer 19

they are abiotic factors and there effect is the same regardless of the size of the population.

Question 20

how does negative feedback work?

Answer 20

if the population rises above the carrying capacity, a density dependent factor increases mortality or reduces breeding to such an extent that the population declines.
if the population falls below the carrying capacity, environmental resistance is temporarily relieved so that the population rises again.

Question 21

how is animal abundance assessed?

Answer 21

• capture-mark-recapture using the Lincoln index calculation

- kick sampling in a stream and counting aquatic invertebrates

Question 22

how is plant abundance measured?

Answer 22

• using a quadrat to calculate the number of individuals in a sample to estimate the total.
• estimating percentage cover of a plant in which individuals are hard to recognise
• estimating percentage frequency

Question 23

what is distribution?

Answer 23

the area or volume in which the organisms of a species are found.

Question 24

why is a transect useful in measuring non uniform distribution?

Answer 24

it displays the variation in organisms and the correlation this has with a changing abiotic factor

Question 25

what does a belt transect show?

Answer 25

the abundance data for a given area at measured distances along the transect.

Question 26

what is a habitat?

Answer 26

where an organism lives and gains its means of survival(e.g. food, temperature, pH)

Question 27

what is a microhabitat

Answer 27

a very small area that differs from its surroundings and has features that make it suitable for a particular species. (e.g. cabbage looper= lower surface of cabbage leaves)

Question 28

what is a community?

Answer 28

interacting populations of different species in the same habitat at the same time.

Question 29

what is a saprobiont?

Answer 29

a micro-organism that obtains its food from dead or decaying remains.

Question 30

what's the difference between detritivores and decomposers.

Answer 30

- detritivores- organisms like earthworms which feed on small fragments of dead material. - decomposers are microbes like bacteria and fungi which complete the process started by detritivores.

Question 31

what is the calculation for photosynthetic efficiency?

Answer 31

light energy in product/energy falling on the plant x 100

Question 32

what is Gross Primary Productivity (GPP)?

Answer 32

the rate of production of chemical energy in organic molecules by photosynthesis in a given area in a given time (KJ/m^2/y)

Question 33

What is Net Primary Productivity (NPP)?

Answer 33

the energy in the plants biomass which is available to primary consumers (KJ/m^2/y)

Question 34

what is the NPP equation?

Answer 34

GPP - RESPIRATION = NPP

Question 35

what are the common figures for GPP and NPP?

Answer 35

GPP- 1% | NPP- 0.5%

Question 36

what is primary productivity?

Answer 36

the rate at which producers convert energy into biomass.

Question 37

what is secondary productivity?

Answer 37

the rate at which consumers accumulate energy from assimilated food in biomass, in their cells or tissues

Question 38

how is energy lost at trophic levels.

Answer 38

- egestion of undigested material - heat energy from processes fueled by respiration e.g. muscle contraction - energy remains in parts of the animal not eaten (horns fur and bones)

Question 39

what is primary succession?

Answer 39

the sequence of changes in the structure and species composition of a community over time in an area that has not previously been colonised.

Question 40

explain what a sere is?

Answer 40

the sequence of communities with different species and structures. - a sere in a very dry environment is called a xerosere. - each seral stage changes the environment and makes it more suitable for other species.

Question 41

what is the sequence of a xerosere?

Answer 41

pioneer species - herbs and grasses - shrubs and small trees - large trees

Question 42

what is a climax community?

Answer 42

a stable self-perpetuating community that has reached equilibrium with its environment and no further change occurs.

Question 43

what are the characteristics of a climax community?

Answer 43

- has great species diversity - has a complex food web - is dominated by long-lived plants

Question 44

what are the species of a climax community dependent on?

Answer 44

climate | climatic climax community

Question 45

describe the diversity at climax community?

Answer 45

animal diversity is at its highest -plant diversity is lower than its pre-climax state because the tree canopy limits the intensity of light reaching the woodland floor.

Question 46

what does the climax community have equilibrium between?

Answer 46

- GPP and respiration - energy used from sunlight and released by decomposition - uptake of nutrients from the soil and their return by decayed plant and animal remains - new growth and decomposition, so the quantity of humus is constant.

Question 47

what are the changes as a xerosere progresses?

Answer 47

increases are seen in: - soil thickness and availability of water, humus and minerals - biomass - biodiversity - resistance to invasion by new species - stability to disruption by environmental challenges, e.g. abnormal weather.

Question 48

What is secondary succession?

Answer 48

the recolonisation of a habitat previously occupied by a community, but disturbed by factors such as fire and tree felling.

Question 49

what do the species in a secondary succession depend on?

Answer 49

the conditions prior to the disturbance e.g. soil thickness, mineral and humus content

Question 50

what will assist in the colonisation of the habitat?

Answer 50

- the dispersal of plants and migration of animals | - the presence of seeds, spores and organs of vegetative reproduction in the soil.

Question 51

what is disclimax?

Answer 51

a stable community maintained by human activity.

Question 52

Explain how human interference can prevent the development of a climatic climax community.

Answer 52

- grazing maintains grassland and prevents the shrubs and trees of normal succession from growing. - farming removes all except deliberately introduced species and great effort is expended in excluding all others. - deforestation removes a community of large trees.

Question 53

How is the life cycle of heather important to the growth of red grouse?

Answer 53

1. adult grouse feed mainly on young heather shoots 2. the main form of management is burning the heather every 12 years usually in the autumn. this causes a secondary succession. 3. the pioneer stages supplies the best food for the grouse 4. the building phase provides the best shelter for nesting

Question 54

what would happen to red grouse if heather were not managed?

Answer 54

the heather would pass through the mature to the degenerate phase and conditions would become unsuitable for the breeding of grouse.