Population Ecology Flashcards
What is ecology?
- the study of the interactions of organisms with their physical and biological environments
- and how these determine the distribution and make-up of populations within an ecosystem
What is population ecology?
- population ecology is concerned with fluctuations in the size of a population and the factors, both physical and social that regulates these fluctuations
What is the biosphere?
- the part of the earth where living organisms are found
What is an ecosystem?
- made up of groups of different species of organisms that interact with each other and with the environment
What is an organism?
- an individual form of life, composed of a single cell or a complex of cells that are capable of growing and reproducing
What is a community?
- a group of different species that inhabit and interact in a particular area
What is a species?
- a group of closely related organisms that are very similar to each other and are usually capable of interbreeding and producing fertile offspring
What is an individual?
- a single organism capable of independent existence
What is a population?
- a group of organisms of the same species that occupy the same area and can breed freely with each other
What is population size?
- the total number of individuals in a population
What factors affect the size of a population?
- natality
- mortality
- immigration
- emigration
What is natality?
- the birth rate in animals or the production of seeds in plants
What is mortality?
- the death rate
What is immigration?
- individuals move into a population and stay
What is emigration?
- individuals leave a population and do not return
What is the birth rate in humans?
- the number of births per 1000 people in a year
What is the death rate in humans?
- the number of deaths per 1000 people in a year
When do populations grow?
- when birth and immigration exceed death and emigration
When do populations decline?
- when death and emigration exceed birth and immigration
When do populations remain stable?
- when birth and immigration approximately equal death and emigration
When does the number of individuals increase exponentially?
- if a few individuals enter an unoccupied area where there is no shortage of food or other resources and no predators, they will reproduce
What does exponential mean?
- increasing more and more rapidly
What builds up environmental resistance?
- as the numbers increase, more demands are made on the available resources and this builds up environmental resistance
What does environmental resistance cause?
- the birth rate/immigration rate to decrease
- and the death rate/emigration rate to increase
What happens when a balance is reached?
- the population stabilises at a particular size or number
What is the carrying capacity?
- the population density that the environment can support
What does the population fluctuate around?
- around the carrying capacity until the environment changes again
When does population size fluctuate?
- seasonally and annually
- depending on the resources available
What kind of regulation does population size possess?
- population size in an ecosystem is self-regulating
What are limiting factors?
- the factors that help to regulate the growth of a population
What kinds of limiting factors are there?
- density independent factors
- density dependent factors
What are density independent limiting factors?
- factors that limit the growth of a population as a result of natural factors and not because of the density or number of the organisms
What are the types of density independent factors?
- physical factors
- catastrophic events
What are some examples of density independent physical factors?
- rainfall
- temperature
- humidity
- acidity
- salinity
What are some examples of density independent catastrophic events?
- floods
- fire
- drought
- volcanic eruptions
- tsunami
- earthquakes
What are density dependent limiting factors?
- factors that have a greater effect when the population density is high
What happens when organisms are more crowded (density dependent factors)?
- compete more for resources
- are more easily found by predators
- spread disease and parasites more readily
What are some examples of resources that organisms compete for when they are more crowded?
- food
- light
- oxygen
- water
- space
- shelter
What is a stable population?
- one in which numbers decrease when its size exceeds the carrying capacity
- but increase again when numbers fall below the carrying capacity
- i.e. one that fluctuates around the carrying capacity
When does an unstable population develop?
- if the population far exceeds the carrying capacity
What happens to the habitat of an unstable population?
- deteriorates rapidly, leading to a lowering of the carrying capacity
- eventually not able to support the population, which will decrease rapidly and possibly become extinct
What do direct methods involve?
- counting every single individual in a population - this is called a census
What are the types of methods used to estimate population size?
- direct methods
- indirect methods
When can direct methods be used?
- for populations where organisms are large enough to be seen
- where the area in which the animals are being counted is not too large
For what kind of individuals can direct methods be used?
- slow moving (e.g.
- stationary (e.g. plants)
- usually stay in a fixed position (e.g. barnacles)
What can be used if the area is too large to count every individual at one time?
- aerial photographs can be used to show the whole area in which the population occurs
- helicopters can be used to count larger animals
What do indirect methods involve?
- counting a sample number of the population and then using simple calculations to estimate the total size of the population
What are some examples of indirect methods?
- quadrat method
- mark-recapture method
What does the quadrat method involve?
- involves counting the number of individuals in small measured areas (quadrats)
- and then using these numbers to calculate the population size of the total area with the aid of the quadrant formula
What is the formula for the total population when using the quadrant method?
[numbers in sample x size of whole habitat] ÷ size quadrat
What is the purpose of using a quadrat?
- to enable comparable samples to be obtained from areas of consistent size and shape
What is important to do when using quadrats?
- quadrats should be distributed at random
Why is random sampling important?
- as the distribution of individuals may not be uniform throughout the area
- it is important to sample as many quadrats of the total area as possible
- to achieve a true reflection of the distribution
What does the mark-recapture method involve?
- a known number of individuals is caught and marked and then released
- after a suitable time period another sample is captured and the number of marked individuals counted
What is the formula used in the mark-recapture method?
P = (M x C) ÷ R
What does the P symbolise in the mark-recapture method formula?
P = estimated population
What does the M symbolise in the mark-recapture method formula?
M = total number of marked animals
What does the C symbolise in the mark-recapture method formula?
C = total number of animals caught in the second sample
What does the R symbolise in the mark-recapture method formula?
R = total number of animals marked in the second sample (i.e. recaptured)
What precautions must be taken for a reliable result in terms of time?
- only a short time should pass between the first and second sampling
- so that no births and deaths can occur
What precautions must be taken for a reliable result in terms of repetition?
- sampling should be repeated several times and an average population calculated
What precautions must be taken for a reliable result in terms of the actual marking?
- the marking must not damage the individual or affect its movement or behaviour
What precautions must be taken for a reliable result in terms of the marked animal?
- the marked animal must mix freely with the rest of the population before a new sample is taken
What precautions must be taken for a reliable result in terms of immigration and emigration?
- no immigration or emigration is allowed
- i.e. the population must be closed
What is the significance of all living organisms within an ecosystem being interdependent?
- this means that changes in the population size of one species can drastically affect that of another
What is predation?
- a biological interaction where one species kills and eats another species
What does the role that predators play in their environment do?
- helps to create and maintain greater diversity within an ecosystem
How do predators create and maintain greater diversity within an ecosystem in terms of regulation?
- by regulating the abundance and distribution of prey species
- as the predator population increases, the prey population decreases
How do predator and prey evolve in relation to one another?
- they evolve together and are part of the same environment
How do predators create and maintain greater biodiversity within an ecosystem?
- by increasing the biodiversity of communities by preventing a single species from becoming dominant
How do predators create and maintain greater diversity within an ecosystem in terms of genetics?
- by keeping the prey population genetically fit by removing sick, injured and weak individuals
How do predators create and maintain greater diversity within an ecosystem in terms of food?
- by providing vital food sources for scavengers
What does the feeding relationship between the predator and the prey determine?
- determines the size of the two populations by means of a negative feedback mechanism
What happens to the predator population as the prey population decreases due to predator killing?
- the food available for the predators is less
- and so their numbers subsequently decline