Topic 14 Flashcards
Life tables can be used to..
determine if a population grows from one generation to the next
Population growth models are used to..
estimate population size many generations in the future.
Imagine a closed population
- no immigration
- no emigration
- births increase population
- deaths decrease population
To determine a change in population size (N) from one point in time to sometime later =
N (later) = N(now) + Births - Deaths
Geometric model assumes..
discrete breeding
Geometric model
population only grows during the breeding season.
Average number of offspring left by an individual during one time interval
greek symbol upside down Y (same as R0)
Population increases by…
factor of upside down Y ^ of breeding interval
Exponential model assumes..
continuous breeding
Exponential model
population grows continuously through the year. population increases by factors of e^r
r =
= b - d
exponential growth rate of the population between time 0 and time t (not the same as R0)
e =
base of natural logarithm
Rate of change in a population size over a specific time person is equal to the..
average birth rate minus the average death rate multiplied by the number of individuals in the population at the start of the time period
dN/dt =
slope of population growth curve at a particular point in time
Rate of population growth directly effects the ..
size of the population (increased exponentially)
Intrinsic rate of increase
r is considered to be an instantaneous rate of increase
Underlying principles of intrinsic rate of increase
- r is individual or “per capita” contribution to population growth
- dN/dt varies in direct proportion to N at that instant
- r is constant through time
Geometric vs exponential
curves depicting geometric and exponential population growth can be superimposed there is direct relationship between them
Exponential model assumptions
- all individuals have the same average b and d rates
- b and d are constant through time
- b and d occur continuously
- no migration (I or E) the population is closed
- resources are unlimited
When population size is low..
no competition (resources are unlimited). populations grows at the intrinsic rate of increase r (exponential growth = highest growth potential)
When population size is high..
competition increases (resources become limited). population size levels off and r = 0
1 underlying assumptions violated
all individuals have the same average b and d rates. (diff age classes generally have diff b and d rates)
2 underlying assumptions violated
b and d (r) are constant through time.
Populations rarely have constant b and d because
- age distribution of a population changes through time
- environmental conditions change through time and continuously influence b, d and r (=b-d)
Consider r the highest growth rate that the population have potential to achieve if
- the population have a stable age distriubtion
- b and d remain constant over time
3 underlying assumptions violated
no migration (I or E) the population is closed
4 underlying assumptions violated
resources are unlimited
A large population with a relatively low growth rate can still.
greatly increase in size
Universe is limited to ..
10^80 atoms
A single E. Coli with its high growth rate (r) would otherwise reach a population size of 10^80 individuals in just..
6 days
Resources are never truly ..
unlimited!