Transcript Biodiversity, Species Interactions, and Population Control

Biodiversity, Species
Interactions, and Population
Control
Big Idea #2
 Populations cannot grow indefinitely
because resource are limited and there is
competition for those resources
Population Dynamics
 The study of how
 Distribution
 Age structure
 Population Size
 Population Density
These things change in response to
changes in the environment
Some species count more than others
 Changes in the growth rate of
 Invasive species
 Keystone species
 Ecosystem engineers
 Has a greater impact on the biodiversity
of an area than other species
Distribution
Population Dynamics
 For example:
 How disease affects a population
 How the introduction of a nonnative species affects a
population
 How the presence of chemicals like pesticides affect
populations
 Studying these things helps us identify keystone
species
Population Distribution
 3 basic patterns:
 Clumped
 Uniform
 Random
Clumped Distribution
 Most common in both plants and
animals
Why clump?
1.
2.
3.
4.
5.
Cluster where there are resources
More likely to find resources if they
work together
Protection from predators
Teamwork to catch prey
Mating group and/or help raising
young
Uniform
 Especially in plants
 Secrete chemicals that prevent others
from growing nearby
 Increases chances of getting the water and
soil nutrients it needs
Random
 Pretty rare
 Occurs when there is no good reason for
the other types
Random, uniform,
clumped? Why?
Population Size
Population Size
 4 variables
 Birth rate (natality) +
 Death rate (mortality)  Immigration rate +
 Emigration rate  Let’s try some math!
Biotic Potential
 A population’s capacity for growth
under ideal conditions
 General rule of thumb:
 Big things have low biotic potential
 Little things have high biotic potential
Blue whale &
calf
ants
E. O. Wilson
studied ants
mostly
Intrinsic Rate of Increase (r)
 The rate at which a population
would grow if it had unlimited
resource
 Species with high “r” usually:
 Reproduce early in life
 Have short generations
 Can reproduce often
 Have lots of offspring each time
So what’s the difference between biotic potential and
intrinsic rate of increase?
Reproductive Strategies
 r-selected species
 High biotic potential
 Lots of offspring
 Little or no parental care
 Usually opportunist species
Reproductive Strategies
 K-selected species
 Low biotic potential
 Few offspring
 Lots of parental care
 Usually competitive species
9 mo. Gestation,
8 years between
births
22 mo. Gestation, 5
years between births
Most fall somewhere in the middle
Species can’t keep growing and
growing…
 There are limiting factors that prevent
this
 Competition for resources
 Predators
 Disease
How do you feel about what you
are learning?
A. Happy
B. Bored
C. Suspicious
D. Love-struck
E. Confused
F. Overwhelmed
G. Other? _________________
Signal all that apply
Population Density
Population Density
The number of individuals in
a given volume
Density-Dependent Controls
• Competition for resources
• Predation
• Parasitism
• Disease
• Poisoning
• Human Harvesting
Density-Independent Controls
• Natural disasters
• Global warming
• Ozone depletion
Environmental Resistance
 The combination of all the factors that limit the
growth of a population
 Together these factors determine the carrying
capacity (K) of the population
 The maximum number of a species that can survive in a
given area
Alphabet Soup
What are the letter symbols we’ve learned
and what do they stand for?
Genetics and Population
Dynamics
Genetic Diversity
Difference in genes among
members of a population
A very important factor in
the long term health and
survival of a population
The Founder Effect
 Founder Effect - a small
group of individuals
becomes separated from
the larger population.
 They may have less
genetic diversity than the
larger population
The Bottleneck Effect
 When only a small
group survives some
change in the
environment
 Lack of variation
means less
adaptability
 Humans sometimes
create bottlenecks in
other species
Small populations may experience
genetic drift
 Fluctuations in gene frequencies in a
small population from one generation
to the next
 The smaller the size of the population,
the more likely there is to be a major
shift in allele frequencies
Example
 If I flip a penny 100 times, how
many heads should I get?
 If I flip a penny 10 times, would
it seem really weird that I got 7
heads and only 3 tails?
 Why not?
Inbreeding
 Individuals in a small population
mate with each other
 Increase the frequency of defective
genes
Minimum viable population
 The minimum number of individuals
needed to maintain a species for the
long term (so no inbreeding!)
How do you feel about your knowledge
of genetics and population dynamics at
this point?
0 – not even with prompting can I explain
this topic
1 – with some prompting I could explain
some of it
2 - I get the basics
3 – I understand it beyond just basic info
without help
4 – I can apply what I know to a test
question
Population Growth Patterns
Stable
 Fluctuates a little above and below
carrying capacity
 Found in stable ecosystems like rain
forests
Irruptive
 Population explodes,
then stabilized at a
lower level; often tied
to the seasons
Cyclic
 Boom and bust; like lynx and hare -
every few years/generations
LE 52-18
Irregular
Moose population size
2,500
Steady decline probably
caused largely by wolf
predation
2,000
1,500
1,000
Dramatic collapse caused by severe
winter weather and food shortage,
leading to starvation of more than
75% of the population
500
0
1960
1970
1980
Year
1990
2000
Age Structure
Age Structure
Quick Think
 What are the pros and cons of:
 Rapid population growth?
 No population growth?
 Declining population?
Choose 1:
Would you rather…
 Sleep in a bed of rats.
 Catch a porcupine thrown from a 2nd story
window.
 Be sprayed by a skunk.
 Let a rattle snake slither across your body.
 Let bumble bees cover you from head to feet.
 Let a tarantula walk across your face.
 Give a speech to the student body with only
your underwear on
 Shave off your head hair and eyebrows for
the rest of the semester
Stump the class
• Work in teams of 2-3
• Each person write one multiple choice
or short answer question on your index
cards from Ch. 4 or 5
• Question on one side, answer on the
other
• Share your questions with your team
and revise if necessary
• Give your cards to Beck to share with
the class