Transcript Population evolution

Population evolution
Size
 Density
 Dispersion

Properties of Population

Fundamental and important property of
population but can be difficult to measure
directly.
◦ Often too abundant, mobile, or widespread to
count.
Population size

Population density is the quantity of
individuals living in a particular space.
Population Density
Population Dispersion
Clumped
Uniform
Random
Population Profile
AKA: Age Structure
What would
the data table
for this look
like?
Survivorship curves
Type 1
Type 2
Type 3
Relative Age
What does
each line
say about
the
population?
Type 1: ex: humans: chances of death
increase with age.
 Type 2: ex: certain species of birds:
probability of mortality does not change
through out the lifespan.
 Type 3: ex: sea turtles: chance of death is
higher at younger ages. If they make it
past this stage they stand a good chance
to make it to old age.

Survivorship curve
Measuring Populations
19.2
 Growth
= births – deaths
Increased life expectancy: childhood
immunizations, vaccines, medications
that prevent/maintain things like heart
disease and diabetes, improved health
care, etc.
This formula doesn’t take into account
another factor of population growth:
Immigration and emigration.
Mortality=death
Population Influences
 As
long as births > deaths the population will
grow
• Even once births < deaths the population will take
time to level off or decrease because of the base
number of individuals who are of reproductive age.
 Population
also grows faster if the start of
reproduction is at earlier ages.
 Once
the environment reaches the maximum
number of individuals it can support (K=carrying
capacity)the population will level off.
• Not true of human populations…they make choices
and can therefore change the dynamics of the graph.
Exponential Population Growth

Any factor such as space which will limit
the growth of an organism
◦ All populations are ultimately limited by their
environment.

The logistic growth model is similar to the
exponential growth model except that it
accounts for liming factors (carrying
capacity=K)
Limiting factor
Exponential growth with and
without “K”
Exponential growth
curve
K
Limiting
factor
Logistic
growth curve
Population Fluctuations
•
Predator populations follows close pattern to prey.
•If a new organism
(for example
another predator
that is capable of
eating the same
prey) were
artificially added the
natural predator can
be affected as can
the prey population.
•The new predator
may eat more or less
either dwindling the
prey or causing it to
“grow” out of
control.

Density independent: Reduce the
population by the same amount
regardless of the size of the population
◦ Fire, flood, weather.

Density dependent: an individual’s chance
of surviving or reproducing depends on
the number of individuals in the area.
◦ Resources such as food, nesting space.
Density Dependence

Small populations are more likely to be
affected or even wiped out by such
natural disasters as floods, fires, storms,
or disease outbreaks.
◦ Can lead to too few individuals to maintain the
population.
California Condor
Perils of small populations
Human Population
Growth
19.3

What scientists learned from this time
period:
◦ Small populations and high mortality rates lead
to slow growth.
◦ High infant and childhood mortality are
especially high factors in slowing population
growth because they never make it to
reproductive age.
Hunter/Gatherer Period

What happened during this period?
◦ Agriculture greatly increased and stabilized
food supplies.
◦ Human populations began to grow faster.
◦ People had more children
 Needed more hands to work the farm
 They weren’t as mobile so it made it easier to
have more children.
Agricultural revolution

After 1650:
◦ Sharp decline in death rates because of
improved sanitation, hygiene, control of
disease, increased availability of food.
◦ Birth rates remained high.
Industrial Revolution
Environmental Issues
Chapter 22 Section 2

What does this graph tell you?
•Shows a correlation
between CO2 and
global warming.
•Shows the
concentration of CO2
in the atmosphere
from 1880-2000.
Global Warming
Biological
Magnification
Evolution
Lesson 15.1

Supported the idea that populations
changed over time, but thought that
acquired changes would be carried to the
next generation.
◦ Does a deer who looses an antler in a fight
with another deer pass that “lost antler” trait
on to the next generation?
◦ Lemarck thought it did.

He also thought that individuals could
acquire traits within their lifetime due to
experience or behavior.
◦ If you need fins, are you going to grow them?
Lemarck

Proposed the theory of Natural selection
◦ Organisms may possess traits that make them
more suitable to their environment. Those
individuals survive, pass on those traits to
future generations. (survival of the fittest)
◦ Requires genetic variation within a species.
◦ Is the process that leads to evolution (natural
selection over many generations)
Darwin
Disruption of Genetic
Equilibrium
Lesson 16.2

Possible causes of disrupted genetic
equilibrium:
◦ Mutation
◦ Immigration/emigration (migration)
◦ Genetic drift
 Traits change as a result of random events or
chance
 Happens more in smaller populations than in
larger ones.
◦ Artificial selection
◦ Nonrandom mating
◦ Small population size
Causes of evolution

Many times mate selection is determined
by geographic proximity.
◦ May result in disorders caused by inbreeding.
Sometimes a mate is chosen because
they possess similar traits: assortative
mating.
 Sexual Selection: In order to be selected
by a mate, and leave offspring, an
individual must possess extreme traits
(like the plumage of a peacock)

Nonrandom Mating
The “average” individual is best fit.
 Consider the hypothetical situation of the
lizard…Large ones may be more easily
seen by predators, while small sized ones
may be to slow to escaper
predators…therefore it is the average
sized individuals which may be best suited
to the environment.

Stabilizing Selection

Individuals with the extreme variation of a
trait have a greater chance of survival
than the one with the average variation.
◦ Therefore individuals with short fat beaks and
those with long narrow beaks would survive,
but those with average length beaks die out on
an island with flowers and nuts.
Disruptive Selection

Individuals that display a more extreme
form of a trait have greater fitness than
an individual with an average trait.
◦ For example when anteaters feed, they push
their sticky tongue into the nest of termites.
The longer the tongue the more fit the
anteater.
Directional selection
Formation of Species
Lesson 16.3

The process of species formation that
results in closely related species.
◦ Some are very similar to their shared ancestor.
Speciation

Proposed by Mayr, a species is an
interbreeding population that cannot
breed with other groups.
Biological Species Concept

Geographic Isolation: Physical separation
of members of a population.
◦ When the original habitat becomes physically
separated.

Reproductive Isolation: May sometimes
arise through disruptive selection where
the two extremes are selected for and as
time passes, the two subpopulations can
no longer interbreed.
Isolation and Speciation
Rates of Speciation
Gradualism: speciation occurs at a
regular, gradual rate.
 Punctuated equilibrium: Speciation occurs
at a rapid pace.

◦ What is rapid in evolution?
◦ A few thousand years rather than a few million.

Two or more species become adapted to
each other’s presence over a period of
time
Coevolution

Divergent: one species becomes two
separate subpopulations.
◦ Artificial selection has been used by humans to
speed up this process.

Convergent: two species develop
similarities even though they come from
two very different ancestors.