Transcript Population Biology - Miss Galegar's Biology Class

Populations

 Populations—large and small—change over time
 Meaning, they are DYNAMIC
 Humans face similar problems as small or large
populations that other organisms do
 BUT humans also have an advantage
 What is our advantage?
We know populations interact…

Prey
Herbivore-carnivore
populations
mayBay
increase,
LynxPrey
and Hare Pelts
Sold to the Hudson’s
Company
followed by
increases in predator populations,
Number of organisms(in thousands)
 followed by decrease in prey populations, followed by decrease
in predator populations
Times (in years)
Predators

Results in the fates of predator and prey
populations being intimately intertwined.
Population size fluctuates due to this relationship
Preying most successfully on the
 Slowest
 Weakest
 Least fit members of their target population
Predators affect populations

 Preventing excess population growth
 Allowing successful traits to become dominant
in the prey population (and the predators)
 Sounds like…unscramble the phrase below
 TAURALN TNIOLEESC
Predation may lead to extinction
 Seen with introduced species.
Two categories of predator-prey relationships.
 Intraspecific and interspecific…more later
Herbivore vs. Producer

Herbivores have developed adaptations to deal with
fluctuations in available food supplies:
 Put on extensive layers of fat during seasons of
abundance.
 Some will migrate to where food is available.
 Others hibernate during seasons of hardship.
 Respond to seasons of scarcity by making do with foods
of relatively low nutritional value.
Plants are Prey too…
Plants respond to herbivores
by:
 Producing enough
tissue for herbivores
and still survive
 Produce distasteful
chemicals that deter
further feeding
 Produce chemicals
that affect
herbivores’
physiology
Herbivore-Carnivore Interactions

 Compared to plant material, animal material is
 Easier to digest
 Energy and nutrients are more concentrated
 Drawback:
 Herbivores are mobile
 Dangerous when cornered
 Mimicry
Competition
 Intraspecies—arising or occurring within a species;
involving the members of one species

INTRA—
m
o
n
g
u
s
Remember—hyenas compete with each other
for rank (hierarchy), food, mating rights and
territory
Plants have developed mechanisms to
cope with intraspecific competition.

 Seedlings unable to germinate in the shady
conditions created by parent plants.
 Plants disperse seeds to other sites by water, air, or
animals.
 Plants secrete substances that inhibit the growth of
seedlings near them.
Animals have developed mechanisms to
cope with intraspecific competition.
 Varied life cycles

 different habitats and feeding
 in juvenile and adult invertebrates
 Occupy different ecological niches.
 Territoriality: intense intraspecific competition
 define an area surrounding their home site/nesting site
 defend it.
How would this help the population
(increase survival)???

 Help allocate resources of an area by spacing out the
members of a population
 Promote dispersal into adjacent areas
Competition
 Interspecies—existing or occurring between species
b
INTER—
t
w
e
e
n
2
When Populations Compete, Both are
Harmed
Law of competitive exclusion:

 no two species will occupy the same niche
 cannot compete for exactly the same resources in the same
habitat for very long
One species will have a competitive edge
 gain a larger share of resources.
Other species will migrate to a new area, become
extinct, or change its behavior in a way to minimize
competition.
Competition may
cause competitive
exclusion, the
elimination of one
species in a
community.
Examples:
•Paramecium
•Wasps
•Barnacles

Factors That Influence
Population Size

 Population growth rate
 Determined by:
 Natality or birth
rate
 Death rate
 Also influenced by
immigration and
emigration.
 Expressed
mathematically:
r = (b-d) + (i-e)
When Studying Populations…
Count up all the
individuals in the
population.
Why is that impractical?
More frequently used is
density.
 The number of individuals
per unit area.
Labs… Random Sampling

 A method of selecting a
sample
 Random means
 Sample means
 How does it work?
 BEST for STATIONARY
POP (pic of or plants!!!)
Mark and Recapture
 Sample
 where animals are
caught alive and
tagged and then
returned (unharmed)
to their habitat
 over time animals
from the pop are
trapped and those
with marks/tags are
counted
mathematical
formula
estimates the
pop size
Next
 How do scientist collect data on population size?
Population Growth
J-Curve
Exponential
Growth
 Unchecked
growth
 As a
population
gets larger it
grows faster
Population Growth
S-Curve
Carrying capacity
 Number of
organisms the
environment can
support
 Limiting factors
 Biotic
 abiotic
What often happens…
Population Size
Assumptions
 Perils of Small
Populations
 low genetic
diversity
 subject to
inbreeding
 less likely to adapt
to environmental
changes

 Problems being a Large
population
 Increase food shortages
& diseases
 Decrease in space, clean
water
 Live at carrying
capacity so can
experience huge crash
 Adaptable with greater
genetic diversity
Population Density

 Population density is total population size per unit of
area.
 Population densities depend on:




Interactions within the environment
Quality of habitat
Density dependent factors
Density independent factors
Dispersion Patterns Within
Populations

Three common patterns of population distribution are:
Population
Density
Uniform
Clumped
Random
Population Density
Densitydependent factors





Disease
Competition
Predators
Parasites
food

Densityindependent factors






Volcanoes
Temperature
Storms
Floods
Drought
Habitat disruption
Population Stress

As populations increase in size = variety of
stress symptoms
aggression, decrease in parental care,
decreased fertility, and decreased resistance
to disease.
become limiting factors for growth and keep
populations below carrying capacity
Patterns

 Reproductive pattern = life-history pattern
 Variety of patterns
 Two extremes
Patterns
Rapid life-history
patterns
 Changing or
unpredictable
environment
 Small
 Mature rapidly
 Reproduce early
 Short life span
r-selected Reproductive
Strategy
r-selected Species:
 have high
reproductive
rates
 tend to occur in
unpredictable
environments
 typically have
type III
survivorship
curves
Patterns
Slow life-history
pattern
 Large species
 Stable environments
 Reproduce slowly
 Matures slowly
 Long life span
 Stay at or near carrying
capacity
K-selected Reproductive
Strategy
 K-selected Species:
 occur near
carrying capacity
 experience effects
of population
density
 have low
reproductive rates,
high parental care
 have type I
survivorship
curves.
Survivorship in Populations

Reproductive Strategies
r- Selected (maximum growth
rate, below carrying capacity)
 Early reproduction
 Short life span
 High mortality rate
 Little or no parental care
 Large investment in
producing large numbers
of offspring
 Below carrying capacity
 Examples:
 Bony fish
 Grasshoppers
K-Selected (maximizes
population size near carrying
capacity)
 Late reproduction
 Long life span
 Low mortality rate
 Extensive parental care
 Greater investment in
maintenance and survival
of adults
 At or near carrying
capacity
 Examples:
 Sharks
 Elephants

Other population
factors
Predation
Competition
Age Structures
and
Human Growth
Human Population
Growth

 Human population growth does not currently show
density effects that typically characterize natural
populations.
 In natural populations, per capita population growth
rate decreases with population size, whereas global
human population growth rate has a positive
relationship.
Population Age
Structure
 Differences in environmental conditions and past history may
cause populations to differ in their age distributions.
 The future growth of a population depends on its current age
distribution.
Age Structure

 A population’s age structure indicates the percentage
of individuals at each age.
 The right side shows females; the left, males
 The x-axis is number is populations size
 Usually in millions
 The y-axis is age ranges usually 0-4, 5-9, 10-14, etc…

US Dynamic Age Structure
me
Ya’ll
History of Human Population
Growth

• The Development of Agriculture
– About 10,000 to 12,000 years ago, the
development of agriculture increased the
growth rate of the human population.
What happened in the
1600s?
The Population Explosion
 Around 1650, improvements in hygiene, diet, and
economic conditions further accelerated population
growth.
 After World War II, the human population grew at
the fastest rate in history, largely because of better
sanitation and medical care in poorer countries.
Advances in Human Technology =
Growth

1. What is the
difference between
linear growth and
exponential growth
as plotted on a
graph?
2. Explain the graph of
linear growth
shown.
4. Why don’t populations of organisms grow
indefinitely?
5. What is the relation ship of births to deaths in
a population
before the population reaches the
environment’s carrying capacity?
6. What happens when the population exceeds
the carrying capacity?
7. What are some limiting factors that can curb
population growth?

 Human population growth rate has been growing
more than exponentially.
 Limited resources eventually will cause human
population growth to slow, but global human
carrying capacity is not known.