Transcript Chapter 6 Population Biology

Chapter 6 Population Biology
APES 2012
Outline
• Dynamics of Population Growth
• Factors that Increase or Decrease Populations
• Factors that Regulate Population Growth
• Conservation Biology
Lecture #1
Dynamics of Population Growth
Population - all the members of a single species living in a
specific area at the same time
dN/dt = rN
The change in the number of individuals (dN) per
change in time (dt) equals the rate of growth (r) times
the number of individuals in the population (N). r is
often called the intrinsic capacity for increase.
Population balance
For an ecosystem to be stable over a long period of time, the
population must remain more or less constant in size and
geographic distribution.
Population balance occurs when there is an equilibrium between
births and deaths
Problems can occur if a population is out of balance.
• Example: not enough resources for all
Biotic Potential
Biotic Potential- The number of offspring that a species
may produce under ideal conditions
Biotic potential varies among the different species.
Examples:
Mice = can breed every 6 weeks.
Some plants = many millions in a year
(Biotic potential cont)
• Biotic potential refers to unrestrained biological
reproduction.
• Biological organisms can produce enormous numbers
of offspring if their reproduction is unrestrained.
Things that limit populations (Constraints) include:
– Scarcity of resources
– Competition
– Predation
– Disease
To have any effect on the size of future generations the young
must survive and reproduce
Recruitment - Survival through the early growth
stages to become part of the breeding population
Survivorship is determined by the percentage of a cohort that
survives to a certain age
r and K Selected Species
There are differences in biotic potential and recruitment.
This brings about two different reproductive strategies.
• r selected species rely upon a high reproductive rate to
overcome the high mortality of offspring with little or no
parental care.
– Example: A clam releases a million eggs in a lifetime.
– This strategy results in low recruitment.
• K selected species have few offspring but more parental
care.
– Example: An elephant reproduces every 4 or 5 years.
– This strategy results in high recruitment
Reproductive Strategies
Exponential Growth
If the biotic potential of a species is realized, the resulting growth
would be exponential.
Exponential Growth - growth at a constant rate of increase
per unit time (geometric) ; has no limit
• Number of individuals added to a population at the beginning of
exponential growth is relatively small. But numbers increase
quickly because a % increase leads to a much larger increase as the
population grows.
• J curve when the equation is graphed
• Exponential growth is a simple, idealized model. In the real world
there are limits to growth.
Carrying Capacity
• Carrying capacity - limit of sustainability that an
environment has in relation to the size of a species
population
• Overshoot - population exceeds the carrying capacity
of the environment and death rates rise as resources
become scarce
• Population crash - growth becomes negative and the
population decreases suddenly
• Boom and bust - population undergoes repeated
cycles of overshooting followed by crashing
Growth to a Stable Population
• Logistic Growth - growth rates regulated by internal
and external factors until coming into equilibrium
with environmental resources
– dN/dt = r N (1 - N/K)
– Terms have the same definitions as previous slide,
with K added to indicate carrying capacity.
– Growth rate slows as population approaches
carrying capacity.
– S curve when the equation is graphed
Logistic Growth Curve or S Curve
Link to video clip
files/multimedia/lesson36/lessonp.html?show
Topic=1
Population Crash (hippocampus)