c.5- population ecology

Question 1

what is the use of sampling techniques?

Answer 1

estimating population size- involves determining the population size in a small area and using this to estimate the entire population

Question 2

describe how the Lincoln index is used

Answer 2

capture-mark-release-recapture used to estimate population size

1. capture as many individual as possible in area occupied by animal population using netting, trapping or careful searching
2. mark each individual, without making them more visible to predators
3. release all the marked individuals and allow them to settle back into their habitats
4. recapture as many individuals as possible and count how many are marked and how many unmarked
5. calculate estimated population size by using Lincoln index

Question 3

Lincoln index

Answer 3

n1 x n2
/ n3

n1- no caught and marked initially
n2- no caught on second occasion
n3- no recaptured

Question 4

draw and describe time-number population curve for fish, and sustainable yield curve as well

Answer 4

page 644

Question 5

evaluating methods used to estimate the size of commercial stock of marine resources - random sampling

Answer 5

most fish species are highly mobile and unevenly distributed

Question 6

evaluating methods used to estimate the size of commercial stock of marine resources - capture-mark-release-recapture

Answer 6

useful in lakes and rivers, but the numbers of recaptured fish are usually too small in the open ocean for reliable estimations

Question 7

evaluating methods used to estimate the size of commercial stock of marine resources - fish can be temporarily stunned then counted with an electric shock

Answer 7

possible in lakes and rivers but not in oceans

Question 8

evaluating methods used to estimate the size of commercial stock of marine resources - echo sounders

Answer 8

can be used to estimate size of shoals of fish, but many species do not form shoals

Question 9

evaluating methods used to estimate the size of commercial stock of marine resources - data obtained from fish catches

Answer 9

age structure of landed fish can be used to estimate population size - spawning rates can be deduced, from which estimates of the total c an be made. however, violators of regulations designed to control the age of fish landed do not report what they land

Question 10

draw and describe a J shaped population growth curve

Answer 10

exponential growth pattern than occurs in an ideal, unlimited environment §

Question 11

draw and describe an S shaped population growth curve

Answer 11

when a population colonises a new habitat, there will be a low level of environmental resistance initially, causing the population to grow exponentially. as the environment begins to offer resistance, the population reaches a transition point where the growth rate begins to slow until it reaches the carrying capacity

Question 12

annotate an S curve

Answer 12

1. exponential phase- natality exceeds mortality
2. transitional phase- mortality rates begin to increase until natality rate approaches mortality rate. This is due to limiting factors
3. carrying capacity reached

Question 13

4 factors that influence population size

Answer 13

• natality
• mortality
• immigration
• emigration

Question 14

k

Answer 14

the variable that represents the maximum size of a population that an environment can support - carrying capacity

Question 15

how are booms or busts brought back to normal

Answer 15

higher rates of mortality will return the population to the carrying capacity of the environment or the population may crash well below this

Question 16

Limiting population factors can exert their influence via either

Answer 16

top down or bottom up control

Question 17

top down control

Answer 17

Top down factors are pressures applied by a higher trophic level to control the population dynamics of the ecosystem
The top predator either suppresses the abundance of its prey or alters its behaviour to limit its rate of population growth
Top down control results in an oscillating trophic cascade (suppression at one level increases numbers at the next level)
Keystone species commonly exert top down control by preventing lower trophic levels from monopolising essential resources

Question 18

bottom up control

Answer 18

Bottom up factors are pressures that limit the availability of resources to lower trophic levels (e.g. producers)
A lack of resources at lower trophic levels suppresses the abundance of organisms at higher trophic levels
Population growth will be reduced for all higher levels as the suppression of the ‘bottom’ restricts energy supply to the ‘top’
Human activity can often limit resource availability and hence inadvertantly exert bottom up pressure on an ecosystem

Question 19

bottom up control using algae

Answer 19

Algal blooms can be reduced by limiting the supply of nutrients such as nitrogen and phosphorus in the water
This may involve reducing the use of fertilisers for agricultural practices to limit the nutrient input from surface runoff
Nutrient reduction can be expensive to implement and difficult to police, as it requires a concerted community effort

Question 20

Top Down Control using algae

Answer 20

Algal blooms can be reduced by introducing piscivorous (fish-eating) fish into the aquatic ecosystem
The piscivores will feed on zooplanktivores – and by reducing their numbers, will increase the number of zooplankton
Zooplankton (such as Daphnia) feed on algae, and hence will reduce the population of algae via herbivory
Introducing piscivores can have unintended consequences on food webs and should be done with caution