Population Biology: Population Dynamics
Unit 2 Ecology / Ch. 5 / Sec. 5.1
How & why do populations grow?
Methods of investigating:
A. Placing a microorganism, such as a bacterium or yeast cell,
into a tube or bottle of nutrient solution, & observing how
rapidly the pop grows.
B. Introducing a plant or animal species into a new
environment that contains abundant resources, & observing
the pop growth of that species
1. Population growth:
The change in the size of a population with time
Pops of organisms do not experience a liner growth;
rather they produce a J-shaped curve.
Initial increases in the # of organisms is slow b/c the #
of reproducing organisms is small; they will soon grow
rapidly b/c the total # of potentially reproducing
organisms increases
2. Exponential growth:
Explosive population growth in which the number of
reproducing individuals increases by an ever-increasing
rate
Results in a pop explosion (Fig 5.3 / pg 115)
3. Carrying capacity:
The number of organisms of a population a particular
environment can support over an indefinite period of;
Maximum, stable population size an environment can
support over time
Often represented by letter K; S-shaped curve
(Fig 5.4)
When pops are under the carrying capacity of a particular
environment, births will exceed deaths until the carrying
capacity is reached; when above, deaths exceed births
until the carrying capacity is reached
4. Density-dependent factor:
Factors that limit population density; examples include
predation, disease, & competition for food, water, &
territory
Ex: Disease spreads more quickly in a pop whose
members live close together than in smaller pop
whose members live farther away
5. Density-independent factor:
Most often weather-related occurrences such as storms
& floods that affect populations, regardless of their
density
Most are abiotic factors like temp, storms, floods,
drought, & habitat disruption
No matter how many earthworms live in a field, they will
all drown in a flood