C.5 Population ecology Flashcards
What are the four factors that determine the change in the size of a population?
Natality
Immigration
Mortality
Emigration
What is the population size equation?
population size = (immigration + natality) - (mortality + emigration)
How does natality affect population size?
Increases through reproduction
How does immigration affect population size?
Increases population size from external populations
How does mortality affect population size?
Decreases as a result of death
How does emigration affect population size?
Due to loss to external populations
What is a population?
All the individuals of a given species living in the same area at the same time
What are populations subject to?
Continual change
When are populations not impractical to count?
When the species is large and the target area is small
What does population sampling involve?
Identifying individual numbers in small areas and then extrapolating to estimate population totals
When population sampling what must be done to avoid selection bias?
Sampled areas must be chosen randomly
What would selection bias cause?
A misrepresentation of the population size
What does more samples taken mean?
That the more accurate population estimates are likely to be
When are different sampling techniques used for?
Non-motile and motile species
How can non-motile species be sampled?
Using quadrats
How can motile species be sampled?
Using the capture mark release recapture method
When marking a species what must marking not be?
Easily removable or affect the animals survival prospects
What is the first half of capture mark and release technique?
Area is defined and a selection of individuals are captured counted are marked and released
When is a second capture made in the capture mark release method?
After sufficient time to allow marked individuals to reintegrate in the population
What is counted in the second capture of the capture mark release method?
Unmarked individuals and marked individuals
What are the three values generated in the capture mark release method?
1st collection of marked individuals
2nd capture of both marked and unmarked individuals
2nd capture of just the marked individuals
How is an estimated population size derived from the capture mark release method?
The Lincoln index
How can you increase the accuracy of the Lincoln index?
- increasing the size of the capture samples
- taking repeated samples
What is the equation of the lincoln index?
(n1 x n2) / n3
What assumptions must be true for the lincoln index to require?
- all individuals in a given area have an equal chance of being captured
- that marked individuals are randomly distributed after release
- that marking individuals will be randomly distributed after release
When will exponential population growth occur?
In an ideal, unlimited environment
When will a logistic population growth occur?
When environmental pressures slow the rate of growth
In an environment of exponential growth what will there be none of to place limits on rate of growth?
No competition
Why will population growth initially be slow in an exponential population growth?
As there is a shortage of reproducing individuals that may be widely dispersed
What is the maximal growth rate for a given population known as?
Its biotic potential
Where can exponential growth be seen?
In populations that are very small or in regions that are newly colonised by a species
In an exponential growth, what will increase as population numbers increase?
The rate of growth
What is the carrying capacity?
The maximum number of a species that can be sustainably supported by the environment
What is population numbers approaching in a logistic population growth?
Carrying capacity
What happens when a population approaches carrying capacity?
Environmental resistance occurs
When does the graph plateau on logistic population growth?
At carrying capacity
Where will logistic growth eventually be seen?
In any stable population occupying a fixed geographic space
What are limiting factors?
Environmental conditions that control the rate at which a process can occur
What two types of environmental factors can population growth can be determined by?
Density dependent factors and density independent factors
What type of environmental factors are influenced by the relative size of a population?
Density dependent environmental factors
What are density dependent factors? (panda)
Predators
Availability of resources
Nutrient supply
Disease
Accumulation of wastes
What are density independent factors? (paw)
Phenomena
Abiotic factors
Weather conditions
What do stable populations occupying a fixed geographic space demonstrate?
A sigmoidal population growth curve
What are the three stages of a sigmoidal population growth curve?
Exponential growth phase
Transitional phase
Plateau phase
Why will natality greatly exceed mortality in the exponential growth phase?
As there is a rapid increase in population size
Why is mortality low in the exponential growth phase?
Because there are abundant resources and minimal environmental resistance
What causes competition for survival in the transitional phase?
As the population grows resources eventually become limited
What begins to fall during the transitional phase?
Natality rates
What rises during the transitional phase?
Mortality rates
What does the decrease in natality rates and increase in mortality rates cause?
Slowing of population growth
What is the plateau phase?
When the mortality rate equals the natality rate
What has been reached at the plateau phase?
The carrying capacity
What is not constant at the plateau phase?
The population size
What keeps the population stable in the plateau phase?
Limiting factors
How can the exponential growth phase be summarised?
N + I»_space;> M + E
How can the transitional phase be summarised?
N + I > M + E
How can the plateau phase be summarised?
N + I = M + E
What simple organisms can be used to model population growth curves?
Yeast or duckweed
Where is yeast grown?
On agar plates
Where is duckweed grown?
In cups of water
Why is using yeast or duckweed good for modelling population growth?
- organisms are small and can populate small easy to store containers
- nutritional requirements are low
- experiments inexpensive to conduct
- reproduce rapidly so results generated quickly
What will yeast and duckweed demonstrate?
The phases of a sigmoidal growth curve
What are the two ways limiting population factors can exert their influence?
Either top down or bottom up control
What are top down factors?
Pressures applied by a higher trophic level to control the population dynamics of the ecosystem
What does the top predator do to its prey to limit its rate of population growth?
Suppresses the abundance of its prey or alters its behaviour to limit its rate of population growth
What does top down control result in?
Oscillating trophic cascade
What commonly exerts top down control by preventing lower trophic levels from monopolising essential resources?
Keystone species
What are bottom up factors?
Pressures that limit the availability of resources to lower trophic levels
What suppresses the abundance of organisms at higher trophic levels?
A lack of resources at lower trophic levels
Why will population growth be reduced for all higher levels in bottom up control?
As the suppression of the bottom restricts energy supply to the top
What can inadvertently exert bottom up pressure on an ecosystem?
Human activity
What causes algal blooms?
Eutrophication
What is an algal bloom?
A rapid increase in the population of algae in a water system
What can algal blooms be limited by?
Measures that exert bottom up or top down control
What type of control would be the most successful?
Bottom up and top down control
How can algal blooms be reduced?
By limiting the supply of nutrients like nitrogen and phosphorus
How can you implement bottom up control in algal blooms?
Reducing the use of fertilisers for agricultural practices
How can you implement top down control?
Introducing fish eating fish into the aquatic ecosystem
How does introducing fish eating reduce algal bloom?
They eat zooplanktivores and they eat the algae
Why should you be careful when introducing piscivorous into the aquatic environments?
As they have unintended consequences
What is sustainability?
The capacity for a biological system to remain diverse and productive indefinitely
What is a sustainable yield?
The amount of a natural resource that can be taken from an ecosystem without reducing the base stock
What is the maximum sustainable yield (MSY) in fishing?
The highest proportion of fish that can be removed from the total population without jeopardising the maximum yield in the future
What should the MSY be?
Half the carrying capacity of the species
Why should the MSY be half the carrying capacity of the species?
This is the stage when population growth is highest
What does the MSY represent?
The optimum balance between reproductive growth rates and losses to harvesting and death
What will harvesting above the MSY do?
Reduce the possible sizes of future yields
What are the three ways commercial stock can be estimated?
Capture mark release recapture
Echo sounders
Analysing Fish Catch Data
How may fish be captured in the capture mark release recapture method?
Electro shocking
Where would you use and not use the capture mark release recapture method?
Use in rivers and lakes but not in oceans
What is echo sounding?
The transmission of sound waves in water to identify the sizes of schools of fish via sonar
Why is echo sounding good?
It is a non-invasive way of collecting data
When can you use echo sounding?
If the species of fish form shoals
What can data collected from fish catches be used to estimate?
Population size
What are the factors that must be considered when developing and implementing sustainable fishing practices?
Population size
Age
Reproductive status
If a population is growing will the the relative proportion of older fish be higher or lower?
Lower
If a population is in decline, will the relative proportion of older fish be higher or lower?
Higher
