4: Populations and Succession

Question 1

What is an ecosystem?

Answer 1

all the interacting biotic and abiotic features of a specific area

Question 2

What is a population?

Answer 2

a group of organisms of one species in a habitat

Question 3

What is a community?

Answer 3

all the populations of different organisms living in a particular place at the same time

Question 4

What is a habitat?

Answer 4

a place where a community of organisms lives

Question 5

What is a niche?

Answer 5

all the abiotic and biotic factors required for an organism to survive

Question 6

When deciding on how many quadrats to lay, how would you know when to stop sampling?

Answer 6

when the running mean is no longer changing

Question 7

Why is it important for sampling to be random?

Answer 7

to avoid bias

Question 8

What is the mark-release-recapture formula?

Answer 8

estimated population size = (number in 1st sample x number in 2nd sample) / number of marked

Question 9

What assumptions does the mark-release-recapture technique rely on?

Answer 9

• no immigration or emmigration
• no births or deaths
• the marked individuals are distributed evenly among the population
• the marker does not make the individual more susceptible to predation
• the marker does not rub off

Question 10

What is an abiotic factor? Give examples.

Answer 10

a non-living factor

E.g. - temperature, light intensity, pH, water/humidity

Question 11

What is a biotic factor?

Answer 11

a living factor

E.g. - competition, predation

Question 12

What is intraspecific competition?

Answer 12

Competition between individuals of the same species for resources such as food and water

Question 13

Describe the effect of the predator-prey relationship on population size

Answer 13

• predators eat their prey, prey pop reduces
• with fewer prey available the predators are in greater competition with each other
• the predator population is reduced as some individuals are unable to obtain enough prey to survive
• With fewer predators, fewer prey are eaten
• The prey population increases
• With more prey now available as food, the predator population in turn increases

Question 14

Factors affecting death rate

Answer 14

age profile (more elderly = higher death rate), food supply (good diet reduces death rate), access to clean water, good sanitation, medical care quality, natural disasters, war

Question 15

Describe the process of succession

Answer 15

• colonisation by pioneer species
• these species change the environment by forming humus/soil containing organic matter and nutrients
• this enables other species to colonise
• environment becomes less and less hostile
• more and more species can colonise which increases biodiversity
• the stability of the environment increases until a climax community is reached

Question 16

What are the features of an area undergoing succession?

Answer 16

• environment becomes less hostile
• number and variety and habitats and food souces increases
• more complex food webs
• increased biodiversity
• more niches
• increased biomass

Question 17

Why does soil nitrate concentration increases durning succession?

Answer 17

Increase in dead organisms/humus/decomposition
Leading to nitrification
And nitrogen fixation

Question 18

Pioneer species seeds are often adapted to germinate in fluctuating temperatures.Why is this an advantage?

Answer 18

Lots of exposed soil at start of succession

Bare soil temperatures fluctuate

Question 19

What is secondary succession?

Answer 19

This happens on land that’s been cleared of all the plants, but where the soil remains e.g. After a forest fire or where a forest has been cut down by humans

Question 20

What is the climax community called when succession is stopped artificially?

Answer 20

Plagioclimax

Question 21

Describe how mowing a lawn prevents succession

Answer 21

A regularly mown grassy field won’t develop shrubs and trees, even if the climate of the ecosystem could support them. Lawn mower cuts off growing parts of woody plants so plants can’t establish themselves. The longer the intervals between mowing, the further succession can progress and the more diversity increases. But with more frequent mooring, succession can’t progress and diversity with be lower - only the grasses can survive being mowed

Question 22

What is conservation?

Describe two methods of conservation?

Answer 22

Sometimes involves preventing succession in order to preserve an ecosystem in its current seral stage
Animals allowed to graze
Managed fires are lit, leads to secondary succession

Question 23

Why is conservation important?

Answer 23

Species are resources that may be useful in the future
Ethical issues, species have a right to exist
Attractive to look at, bring joy to people
Helps prevent climate change e.g. Prevents trees being burnt
Prevents the disruption of food chains

Question 24

5 ways different species can be conserved

Answer 24

Seed banks for plants
Fishing quotas for fish
Captive breeding programmes for animals
Relocation - any organism 
Conserve habitats using protected areas

Question 25

Define adaptation

Answer 25

A feature that members of a species have that increases their chance of survival and reproduction

Question 26

What happens if two species try to occupy the same niche?

Answer 26

They will compete with each other. One species will be more successful than the other, until only one of the species is left

Question 27

What three bits of data might you be able to take using quadrat?

Answer 27

% cover
abundance
frequency

Question 28

How do abiotic factors affect population size?

Answer 28

When temperature of a mammals surroundings is significantly lower or higher than optimum body temperature, they have to use a lot of energy to maintain homeostasis . This means less energy available for growth and reproduction, so their population size will decrease

Question 29

What biotic factors affect population size?

Answer 29

Interspecific and intraspecific competition

Predation

Question 30

Why does a population exhibiting intraspecific competition fluctuate?

Answer 30

population increases when resources are plentiful
as pop increases, more organisms competing for the same resources, there isn’t enough so population begins to decline
a smaller population means less competition so population starts to grow again

Question 31

units of birth rate

Answer 31

Number of births per year per 1000

Question 32

How to calculate life expectancy from a survival curve

Answer 32

Read of age when 50% survivors as this is the average age at which people die

Question 33

Factors affecting birth rate

Answer 33

economic conditions
cultural and religious backgrounds
social pressures and conditions
birth control
political factors

Question 34

Factors affecting death rate

Answer 34

age profile
life expectancy at birth
food supply
water and sanitation
healthcare
natural disasters
war