Populations Flashcards
Distribution
Geographical extent; may refer, for example, to a family, genus, species, or a particular population of a species.
Define: population
All of the individuals of a species that live together in one place at one time.
Demography
The statistical study of populations. It is used to predict how the size of a population will change.
Sustainable
Able to be maintained, may describe an ecosystem in which the organism can reproduce and their offspring become established and grow, thus the biological community continues over time, even with a level of disturbance.
Key features of populations
Population size
Population density
Dispersion
Population size
Is the number of individuals in a population.
Has an important effect on the ability of the population to survive.
A small population is more likely to become extinct.
A small population is more likely to become extinct when…
In the case of random events or natural disaster.
Due to inbreeding where the population is more genetically alike and recessive traits are more likely to appear.
With reduced variability it is harder to adapt to changes.
Population density
The number of individuals in a given area.
If they are too far apart they may only rarely encounter one another resulting in little reproduction.
Dispersion
The way in which the individuals are arranged.
Population size is limited by…
Density-dependent factors and density-independent factors
Density-dependent factors include…
Disease Competition Predators Parasites Food Crowding
The greater the population, the greater effect these factors have. Eg: Black Death in the Middle Ages- more deaths in cities.
Density-independent factors include…
Most are abiotic factors Volcanic eruptions Temperature Storms Floods Drought Chemical pesticides Major habitat disruption
Predicting population growth
Nearly all populations grow exponentially as long as there are resources available.
What are two of the most basic factors that affect the rate of population growth?
Birth rate and death rate
r(rate of growth)= ?
r(rate of growth)= birth rate- death rate
The exponential growth curve shows…
The population growth plotted against time.
What does exponential growth show?
That as a population gets larger, it also grows at a faster rate.
This is the maximum population growth under ideal circumstances.
Includes plenty of room for each member, unlimited resources (food, water) and no hindrances (predators).
Logistic model
This model accounts for the declining resources available to populations as they grow.
It assumes the birth and death rates are not constant.
As the population grows, births decline and death rises.
Eventually birth= death, so the population stops growing.
What is the carrying capacity (K)?
The number of organisms of one species that an environment can support indefinitely.
When does the exponential curve occur?
When there is no limit to population size.
What does the logistic curve show?
The effect of a limiting factor.
Population growth strategies include?
r-strategists
K-strategists
Two ways a population can prosper are?
Depends on the rate of growth (r).
Influenced by the carrying capacity (K).
r-strategists
r= rate of growth
Characterised by exponential growth, which results in temporarily large populations, followed by sudden crashes in population size. Eg: insects, bacteria, some plants.
Live in unpredictable and rapidly changing environments.
Reproduce quickly when conditions are favourable.
Many offspring: small, mature rapidly, no parental care.
