Species diversity and ecological stability

Question 1

What is biotic potential?

Answer 1

the maximum possible rate of reproduction of a species under optimum conditions and unlimited resources
- evolved to exceed the death rate, must be high enough to have enough young to survive hard years

Question 2

What is environmental resistance?

Answer 2

the biotic and abiotic factors that prevent species or communities reaching the biotic potential i.e. factors causing some to die

Question 3

What is recruitment rate?

Answer 3

the measure of how many of a species survive from birth to become a juvenile

Question 4

Give an example of low and high biotic potential

Answer 4

PRIMATES = low BP but high recruitment rate e.g. most baby chimps survive

COD = very high BP, producing millions of eggs, but very low recruitment rate (most die)

Question 5

What factors control the death/mortality rate?

Answer 5

ENVIRONMENTAL FACTORS
- disease
- drought
- predation
- food shortage

• fighting
• accidents
• recruitment rate
• age profile of pop

Question 6

Why do populations stop growing?

Answer 6

homeostatic regulation
- they are at a stable, optimal level (carrying capacity)
- it slows due to limiting factors due to environmental resistance

Question 7

What is a r-selected species?

Give an example

Answer 7

species that can respond rapidly to low survival rates
- reach sexual maturity quickly
- produce many young
- disperse widely

e.g. mice, locusts, greenfly

Question 8

What is a k-selected species?

Give an example

Answer 8

species that recover slowly from a decline in population
- reach sexual maturity at an older age
- produce few young
- often live for a long time
- increase in death rate caused by a change in the habitat or by human exploitation may cause population crash
- low reproduction rate may make it impossible to replace the losses

e.g. whales, rhinos, elephants, whitetip reef shark

Question 9

Why is it important to understand population dynamics?

Answer 9

• important in monitoring survival of a species, its breeding success and to assess Maximum Sustainable Yield (MSY)

Question 10

What is MSY?

Answer 10

Maximum Sustainable Yield - an estimate of the greatest exploitation that is possible without causing unsustainable long-term population decline

Question 11

What variables are required to forecast a change in population size?

Answer 11

• current population
• number of births and deaths
• number of individuals immigrating/emigrating

Question 12

What are the two categories of factors affecting mortality rates?

Answer 12

Density dependent
Density independent

Question 13

What are the density independent factors that affect mortality rates?

Give examples

Answer 13

Factors where the population density has no effect on the chances of survival of an individual

e.g. drought, flood, volcanic eruption

Question 14

What are the density dependent factors that affect mortality rates?

Give examples

Answer 14

Factors where the chances of an individual surviving depends on the population density

• survival chances are usually higher when the population density is low and lower when the population density is high
• as the pop density increases the density dependent factors become more important until the combined mortality rate, caused by density dependent factors plus density independent factors, forms a long-term balance

e.g. food supply: intra-species competition for food is greatest when the population density is high
e.g. disease: spreads more easily between individuals when they are close together

• exception is ‘safety in numbers’

Question 15

What is ecological carrying capacity?

Answer 15

the maximum population of a species that can be sustainably supported within an environment

Question 16

What is homeostatic control of a population?

Answer 16

Populations in the wild do not remain constant in size but instead fluctuate about the carrying capacity and negative feedback keeps it under control

If a population increases or decreases from the equilibrium populations, the environmental resistance will change with it, to result in the opposite change to bring it back to the equillibrium

Question 17

What are some of the factors which stabilise or limit population size or carrying capacity?
Explain them

Answer 17

NUTRIENT IONS IN SOIL - become used up as plant pops increase, so limits population growth

COMPETITION/OVERCROWDING - increases at high densities

FOOD/PREY (OF ANIMALS) - becomes more difficult to get as population increases

PREDATORS - are able to catch/are attracted to higher density prey populations

PARASITES/DISEASE - spread between individuals more easily at high densities/immunity of stressed individuals weakened at high population density

Question 18

What is a plateau/stationary phase of a growth curve a result of?

Answer 18

1. competition/limiting factors for:
   - space
   - named nutrients
   - named respiratory gas
2. microorganism has been poisoned by
   - toxic waste
   - named waste
3. cell division = cell death/division rate slows or equals death rate
4. reached carrying capacity

Question 19

What are the phases on a growth curve?

Answer 19

lag phase
log phase
stable fluctuating phase

Question 20

Give an example of ecological carrying capacity

Answer 20

Elephants in Africa

• Conservation efforts in certain areas of Africa have been so successful that the elephant populations are now well above carrying capacity
• This has resulted in overgrazing, soil compaction, habitat loss, reduced species diversity and exhaustion of food sources
• As human pop density also increased, there has been increasing conflict with farmers as crops are eaten or trampled

In Western Africa, the population in 1980 was 14,000, but fell to 6,000 in 2004.

Question 21

Give an example of wider implications cased by exceeding carrying capacity

Answer 21

1. Population of herbivore is higher than carrying capacity
2. overgrazing/deforestation
3. reduced organic matter
4. decreased fertility
5. increased use of artificial fertilisers
6. increased fossil fuel use
7. increased global warming

So rabbits are causing global warming

Question 22

What are the implications of exceeding carrying capacity?

Answer 22

Can be localised

Or widespread and difficult to connect to the original cause

Question 23

How are predator and prey populations closely related?

Answer 23

Prey population rises = predator population rises = prey population falls = predator population falls = prey population rises etc etc etc

Question 24

What are some methods of artificial population control?
Why would they be needed?

Answer 24

Culling
Captive breeding and release programmes

• needed to enable the species or habitats to survive where natural control mechanisms no longer regulate the population

Question 25

Give some situations of where artificial population control is used

Answer 25

- the breeding rate of an endangered species is low, so a captive breeding and release programme is needed to maintain or increase the population - a non-indigenous species is introduced which reduces the populations of indigenous species because it is a predator, competitor, or pathogen - an indigenous predator has been removed so its prey species becomes over populated and needs to be culled to avoid the ecological damage it may cause by its impact on other species e.g. wolves in Scotland exterminated, so Red Deer must be culled to prevent their pop rising too high, which would lead to overgrazing

Question 26

What is the general equation for population size?

Answer 26

population size = starting population - death rate - emigrants + birth rate + immigrants