Ch 19- Populations Notes
A population is a group of the same species in the
same area at the same time.
The proper way to indicate a population is to list
Common name and Scientific (Species) name, give a
well -defined location, date or date range and number
as specifically as can be determined. Examples below;
The Grey Wolf (Canis lupis) population in Yellowstone
Park in 2014 was 104.
The Wild Turkey (Meleagris sylvestris) population in
New Hampshire, as of April 1990 was estimated at
2,500.
Populations have 3 main properties;
1- Population size- how many individuals are in
the population.
2- Population density- how many individuals there
are in a certain area.
3- Population dispersion- how the organisms
arrange themselves in the population. There are 3
types of dispersion (also known as distribution).
a- Random distribution- organisms are
randomly dispersed in an area
b- Uniform distribution – organisms are in an
arranged and orderly distribution
c-Clumped/aggregated distribution- organisms
are found in small clumps/groups within the
population
Survivorship Rates/Curves- Different species have a
different chance of survival at different times in their
lives. A survivorship curve is a graph showing the
number or proportion of individuals surviving to each
age for a given species or group (e.g. males or
females). Survivorship curves can be constructed for a
given cohort (a group of individuals of roughly the
same age) based on a life table.
Type I- Small clutch sizes, most offspring live- death usually occurs at old
age. Ex- Elephants & Humans
Type II- Medium clutch sizes, Death rate is more constant throughout it’s
lifetime- chance of dying young, middle aged or old is the same. Expigeons, squirrels
Type III- Large clutch sizes, High chance of dying at an early age, but
usually life a long life if survive. Ex- spiders, octopus
Growth Patterns
Two types
1- Exponential growth- When the resources availability is unlimited in
the habitat, the population of an organism living in the habitat
grows in an exponential or geometric fashion. The population is in
an environment that has enough resources (food, water, space lack
of predators etc) to allow the population to grow quickly – usually
represented by a “J” Shaped curve or “Hockey Stick” on a graph. In
theory- as long as there is unlimited resources- the population
should continue to climb forever.
2- Logistic Growth- In reality- “J” shaped curves cannot last foreversome natural resource will ultimately limit the population from
growing any further (we call these Limiting Factors) and the “J”
shaped curve levels off- creating what we call an “S” shaped curve.
Logistic population growth occurs when the growth rate decreases
as the population reaches carrying capacity.
This leveling off of the population represents the maximum number of
organisms this environment can hold. We call this the Carrying Capacity
or “K”,
The Carrying Capacity can change if the environment changes- i.e. a new
predator is introduced etc.