Transcript 2.6_Ecosystem Changes

Snowshoe Hare and Canada Lynx
Population Growth
 Population: a group the same species that live in the same
place at the same time
 Resources: food, water, shelter, space and mates
 In theory populations can grow to an infinite size, but they
are limited by resources
 This causes individuals to compete for resources (remember
intraspecific and interspecific competition!).
Factors that Control Populations
 There are 4 main factors
controlling population
sizes:
 Natality - births increase the
population
 Mortality - deaths decrease
the population
 Immigration - movement of
individuals into an area
increases the population
 Emigration - movement of
individuals out of an area
decreases the population
Carrying Capacity
 Carrying capacity: maximum number of individuals of a
species that can be sustained indefinitely in a given space
 No population can grow indefinitely! Resources = Limited!!
Limiting Factors of Populations
 Factors (biotic or abiotic) which prevent population
numbers from growing too large and overrunning an
ecosystem.
 Example:
 Disease/ parasites
 disasters
 hunting & predation
 competition for resources
 (food, oxygen, nutrients)
Patterns of Population Growth
 “J” population growth curve
 Exponential growth = starts out slow and then
proceeds faster and faster
 Occurs when a population has few resource limitations
 Sudden collapse
('diebacks')
Patterns of Population Growth
 “S” growth curve
(S for sigmoid)
 Initially shows
exponential growth then
levels off at the carrying
capacity.
 Occurs when a
population has limited
resources.
 Results in stable
population
J Curve vs. S Curve
Population Dynamics
 A look at the factors that tend to increase or decrease the size
of a population
 The population size is determined by the interplay of biotic
potential and environmental resistance.
 Biotic potential- growth rate with unlimited resources
 Environmental resistance - all the factors acting jointly to
limit population growth
Biotic Potential vs. Environmental Resistance
Biotic potential
(Growth Factors)
 Favorable light,




temperature
High reproductive rate
Adequate food supply
Ability to migrate
habitats
Ability to adapt to
environmental change
Environmental resistance
(Decrease Factors)
 Too much or too little




light and temperature
Low reproductive rate
Inadequate food supply
Inability to migrate
habitats
Inability to adapt to
environmental change
Biotic Potential vs. Environmental
Resistance
Density Dependent Factors
 Density dependent factors
 Depend on the size of the population
 Effects of the factors increase as the population grows
 Act as negative feedback
 Tend to be biotic
 Two categories:
 Internal factors = Within a single species
limited resources
 reduced fertility rates
 External factors = between species
 populations of predators or prey
 diseases spread more easily in densely-populated areas

Density Independent Factors
 Do NOT depend on the size of the population
 Tend to be abiotic
 Effect the population regardless of its size
 Examples:
 1. Weather
 2. Earthquakes
 3. Floods
 4. Fires
 R-strategists are most
affected by these factors
Reproductive Strategies
r
Unstable environment
K
Stable environment
 Small size
 Large size
 Many offspring are produced
 Few offspring produced
 Early maturity
 Late maturity (long parental
 Short life span
 Each individual reproduces

once
 Type III survivorship curve
 Affected by density
Independent



care)
Long life span
Individuals reproduce more
than once
Mostly type I survivorship
curve
Affected by density
dependent
Survivorship Curves
 Type I - high survival rate of the young, live most of
their expected life span and die in old age. (ex.
Humans)
 Type II - relatively constant death rate, could be due to
hunting or diseases. (ex. coral, squirrels, honey bees
and many reptiles)
 Type III - have many young, most of which die very
early in their life. (ex. plants, oysters and sea urchins).
Survivorship Curves
Pop Quiz
 What does parental care have to do with the shape of these
curves?
 What density dependent factor will always affect the
population of white tailed deer in Wisconsin? (Only at
certain times in the year)
 What do you think the survivorship curve would be for a
white-tailed deer population?