Population Growth Flashcards
Why is the study of population growth important? (3)
For conservation management
Food supply (i.e: fish stocks)
Understanding causes of population changes
To make predictions about future growth/ decline
When will exponential growth occur? Give an example
Occurs when there are optimal conditions and an unlimited environment
- When individuals colonise new habitats with lots of resources
e.g. introduced species
- When populations recover
E.g. over hunted species are allowed to recover
- Bacteria in a petri dish!
How do bacteria reproduce?
Binary fission
What is exponential growth?
Rapid population growth
What is binary fission an example of?
Exponential growth
Why do populations not generally demonstrate exponential growth for long? (3)
Resources usually limited
Conditions vary and may not be optimal
Effected by interactions with other organisms and the environment
Give two case study examples of exponential growth
Whopping cranes - only 15 existed in 1941 but by 2004 population reached over 300
American Bison in Yellow Stone National Park - 21 individuals in 1902, 250 by 1915
Why were the growth of American Bison in Yellow Stone National Park so successful
- hunting band = few predators
- plenty of food availability
- they were isolated (= no migration)
What does an exponential growth curve look like?
a J shape (hockey stick)
What is the difference between exponential growth and linear growth?
Exponential = constant growth by number of individuals added increases (multiplies) - i.e: population doubles, then triples etc
Linear = population growth is consistent over time - i.e: population grows by 2 individuals each year
When does geometric population growth occur?
When populations reproduce periodically (i.e: at the same time each year)
Gave an example of an animal that has geometric population growth
Bison - only give birth in spring to early summer time each year (when the population grows)
Give 5 limiting factors of bison population growth
Diseases Predation Habitat loss and fragmentation Human intervention Harsh winters/ climatic conditions
Before the 1800s, how many bison existed?
15-100 million
How did human intervention control bison population growth?
Herd management - individuals were removed from population
Which 4 factors define population size
Birth rates (natality)
Death rates (mortality)
Immigration (new individuals)
Emigration (removing individuals
How do you calculate the change in population?
(Births + Immigration) - (Deaths + Emigration)
Total individuals added) take away (total individuals removed
What does the symbol for population change over time look like?
triangle N over triangle t
Which letter represents the population size in equations?
N
Which letter represents the growth rate in equations?
r
What does the triangle represent in equations?
‘Change’ - i.e: change in t / population size etc
How do you calculate growth rate of a population?
Change in population size divided by change in time
If growth rate is consistent, why does the growth curve get steeper?
Because there are more individuals per unit time
what does r represent?
Growth rate
What does N represent
Population size
What does a triangle represent?
Change
What does ‘r max’ mean
The maximum per capita rate of population growth
How do you calculate the maximum population growth rate?
Change in population size / change in time = maximum population growth rate
what is the range of r max?
1 - 0
What is the max rate of population growth for a species?
1
What can a triangle symbol also be represented by?
d - for delta
What does an r maxN rate more than 0 mean?
there will be fast exponential growth
What conditions are needed for exponential growth
unlimited resources
What is the carrying capacity (K)
The maximum population size that a habitat can sustain
What is the name for the maximum population size that a habitat can sustain
Carrying capacity (K)
What factors limit carrying capacity (3)
Space
Food
Water
Which letter represents carrying capacity
K
What affect does carrying capacity have on a population
it can limit the number of individuals
What 2 main types factors can affect population size
Density-DEPENDENT factors
Density INDEPENDENT factors
Name 3 density dependent factors
Increased predation
Disease
Competition
Name 3 density independent factors
Pollution
Natural disasters
Extreme weather/ climatic conditions
(Stochastic events)
Which factors affect a population more as it approaches the carrying capacity
Density-dependent factors - because the population becomes more dense
What happens to birth rates if resources decrease
Birth rates decrease
What happens to death rates if disease increases
Death rates increase
What does a logistic growth curve show?
Natural population changes
What is a logistic growth curve also called? And which shape is it
Sigmoidal curve
S shape
What does an S shape curve show?
logistic growth of a natural population
In a logistic growth curve, what does the levelling off indicate?
That carrying capacity has been reached - has limiting factors restricting population growth
What are the 5 stages of sigmoidal population growth curves
The establishment stage The increase stage, The inflection stage, The deceleration stage The maximum sustained density stage.
Which stage comes just before the levelling off in a sigmoidal curve?
The deceleration stage
Which stage shows the most growth in a sigmoidal curve?
The inflection stage (Middle, steepest part of the S shape)
What happens to population size when is it nearing carrying capacity?
It fluctuates
Why do populations fluctuate near the carrying capacity ?
Because seasonal or environmental cycles can cause changes - plus other density dependent factors
What is the difference between an exponential growth curve and a logistical growth curve?
Exponential = J shaped curve
Logistical = S shaped curve
What is the equation for exponential growth?
dN / dt = rN
Change in population size / change in time = growth rate of population
If the r is more than 0 what happens to the population?
it grows
What is the equation for logistic growth?
dN/ dt = rN (K-N / K)
K= carrying capacity
