3.5 population size and ecosystems Flashcards
population definition
the total number of organisms of a single species interbreeding within a habitat
what is the population size equation?
population size = birth size + immigration - death rate + emigration
the number of individuals in a population changes over time
immigration definition
the movement of individuals into a population
what happens to the number of organisms in the lag phase?
- there is a period of slow growth
(in sexually reproducing organisms e.g rabbits, this represent the time taken to reach sexual maturity and gestating young)
what happens to the number of organisms in the log phase?
- (growth phase)
- numbers increase logarithmically as there are no factors limiting growth
- this cannot be maintained indefinitely as environmental resistance reduces growth (e.g biotic + abiotic factors)
biotic factors definition
- a living factor that can influence the population
- e.g a predator or pathogen
abiotic factors definition
- a non-living factor which can influence the population
- e.g oxygen availability or air temperature
what are some examples of biotic factors that limit growth?
- predation
- competition
- parasitism
- disease
what are some examples of abiotic factors that limit growth?
- soil pH
- light intensity
- temperature
what happens to the number of organisms in the stationary phase?
- birth and death rates are equal
- the population has reached its maximum size/carrying capacity
- numbers will fluctuate around this in response to environmental changes
- this is often due to predator-prey relationships, where negative feedback regulates, i.e no. of prey decreases so there is less food so no. of predators decrease, which reduces predation, so prey number increases, and so on.
- these fluctuations exist over months, even years as population responses are slow
what happens to the number of organisms in the death phase?
- factors that have reduced population growth become more significant and the population size decreases
- death exceeds birth
- when writing about population growth, it is important to consider the organism
- bacteria are not born, mammals are
- the death phase in bacteria occurs largely due to build up of toxic waste products; which cannot be said about a population of rabbits
carrying capacity definition
- the maximum size/number/density of a population
- that can be sustained/maintained (indefinitely) by a particular environment
- (varies depending on biotic and abiotic factors)
negative feedback definition
- occurs in an equilibrium where the corrective mechanism is in the opposite direction to the direction change
- e.g if population numbers increase, negative feedback results in a decrease and vice versa
what is a log scale used for?
- used to show very large numbers which a linear scale would be unable to do
- with log10, the scale increases by a factor of ten times each time
what are density-dependent factors? examples?
- factors that have an increased effect on larger population sizes (denser population)
- are biotic factors
- e.g predation and disease. in larger populations, disease is more easily spread, and a predator can find more prey more easily
what are density-independent factors? examples?
- abiotic
- their effect is the same regardless of the population density
- e.g light intensity, temperature, fire
what is the abundance of a species?
- a measure of how many individuals exist in a habitat
- physical features like soil type, pH and temperature will influence the range of organisms that can live there
- where conditions are optimal, e.g warm, good rainfall, high sunlight intensity, then many plants will be found supporting many other animals
why should sampling be at random?
to eliminate sampling bias
(can be done by creating a square grid and generating random coordinates)
what are some methods to estimate the number of individuals of each species in a given area?
- mark-release-recapture
- kick sampling + simpson’s index
- quadrats + transects
what type of species does the mark-release-recapture technique work on?
terrestrial animals
what is the method for mark-release-recapture (lincoln index)?
- animals are captured and marked (important that they are not harmed or made more visible to predators) and then released
- once animals have had chance to reintegrate with the population, e.g 24hours, the traps are reset
- the total population size can be estimated using the number of individuals captured in sample 2, and the number in the sample that are marked (i.e caught before)
- pop size = (no. in sample 1 x no. in sample 2) / no. marked in sample
- have to assume that no births/death/immigration/emigration, have occurred during the time between collecting both samples