population growth Flashcards
r
The difference between the birth rate and death rate per individual is called the per capita rate of increase. If the per capita birth rate is greater than the per capita death rate, then r is positive and the population is growing. Opposite if the per capita death rate exceeds the per capita birth rate.
Intrinsic rate of increase rmax
È when conditions are optimal for a particular species – meaning birth rates per individual are as high as possible and death rates per individual are as low as possible – then r reaches this maximal value. When this occurs, a population’s growth rate is expressed as change in N divided by change in t equals rmaxN
Exponential population growth
occurs when r does not change over time. Growth rate does not depend on the number of individuals in the population. This type of population growth is density independent. Rate of increase is the same, but the number of individuals added is not.
Exponential growth is common in two circumstances, but it is not possible for exponential growth to continue indefinitely:
- A few individuals found a new population in a new habitat.
- A population has been devastated by a storm or some other type of catastrophe and then begins to recover, starting with a few surviving individuals.
Carry capacity K
defined as the maximum number of individuals in a population that can be supported in a particular habitat over a sustained period of time.
Logistic population growth
described by the logistic growth equation; changes in growth rate that occur as a function of population size.
Density-independent factors
alter birth rates and death rates irrespective of the number of individuals in the population, and they usually involve changes in the abiotic environment— variation in weather patterns, or catastrophic events such as cold snaps, hurricanes, volcanic eruptions, or drought.
Density-dependent factors
change in intensity as a function of population size, and they are usually biotic. When trees crowd each other, they have less water, nutrients, and sun- light at their disposal and make fewer seeds.
lambda
called the finite rate of increase. Lambda equals N1/N0. Only applies to populations that breed seasonally. If a population is growing, then its lambda is greater than one. The population is stable when lambda is 1.0 and declining when lambda is less than 1.0.
Net reproductive rate (R0)
can be calculated directly from life-table data, but is dependent on generation time.
Instantaneous rate of increase (r)
more difficult conceptually, but is the most useful expression for growth rate because it is independent of generation time and is relevant for species that breed either seasonally or continuously.
