Transcript Population - Lamar County School District

Populations
How Populations Grow
• Since 1930, the world’s human population has
nearly tripled. What causes populations to
grow? What determines how fast they grow?
What factors can slow their growths?
• Population – all the individuals of a species that
live together in one place at one time.
• Every population tends to grow. Limited
resources in an environment limit the growth of a
population. The statistical study of all
populations is called demography.
Demographers can predict how the size of a
population can change.
3 Key Features
Population size – the number of
individuals in a population. This can
affect the population’s ability to survive.
Very small populations are the most
likely to become extinct.
• Population density – the number of
individuals that live in a given area.
• Dispersion – the way individuals of the
population are arranged in space.
A population model is a hypothetical
population that attempts to exhibit the
key characteristics of a real population.
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Growth Rate and Size
• A population grows when more individuals are
born than die in a given period. So a simple
population model describes the rate of
population growth as the difference between the
birth rate and the death rate.
• An exponential growth curve is a curve in
which the rate of population growth stays the
same, as a result the population size increases
steadily.
Carrying Capacity- the number of organisms of one
species that an environment can support.
• When a population is below carrying capacity, the
growth rate is rapid. When a population reaches C.C.,
the death rates begin to rise and birthrates begin to
decline. So the rate of growth slows. In real-life, a
pop. may actually exceed the C.C. for a short time, but
the death rate will be high until the pop. goes back
down.
Biological Communities
How Organisms Interact in
Communities
• Coevolution – back and forth evolutionary
adjustments between interacting members of an
ecosystem.
– Predators and prey coevolve: predation is the act of one
organism feeding on another. Parasitism is when one
organism feeds on and usually lives on or in another
organism. Parasites do not usually kill their prey (host) bc
they depend on it for food and a place to live.
– Plants have defenses against herbivores. Virtually all plants
contain defensive chemicals called secondary compounds.
(sometimes like with mustard plants, backfires…yum! Dijon!)
Some animals are made to eat and be fine with these
specific plant chemicals. Ex. Some larvae enjoy only a
certain cabbage species bc of their chemicals.
Symbiotic Relationships and
Species
• Symbiosis – two or more species live together
in a close, long-term association. They can be
beneficial, harmful, or neutral. (we already
mentioned parasitism or (+,-)
• Mutualism – symbiotic relationship in which
both participating species benefit (+,+)
• Commensalism – symbiotic relationship in
which one species benefits and the other is
neither harmed nor helped (+,0)
Competition Shapes Communities
• When two species use the same resource, they
participate in a biological interaction called competition.
These resources include food, water, space.
• The functional role of a particular species in an
ecosystem is called its niche. A niche is how an
organism live, the “job” it performs within the ecosystem.
• The entire range of conditions an organism is potentially
able to occupy within an ecosystem is its fundamental
niche.
• The part of its fundamental niche that a species occupies
is called its realized niche.
• If two species are competing, the species that uses the
resource more efficiently will eventually eliminate the
other. This elimination of a competing species is
referred to as competitive exclusion.
Major Biological Communities
• Temperature – most organisms are adapted to
live within a particular range of temperatures and
will not thrive if temperatures are colder or
warmer.
• Moisture – all organisms require water. On land,
water is sometimes scarce, so patterns of rainfall
often determine an area’s life-forms.
• A major biological community that occurs over a
large area of land is called a biome.
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7 Biomes
Tropical rain forests – Rainfall is 80-180 in. per year. Richest
biome in terms of number of species (more than 2 million)
Deserts – Fewer than 10 in. of rain. Vegetation is
characteristically sparse.
Savannas – Dry climates with development of grassland.
Open landscape with widely spaced trees. (Lions, zebra,
etc.)
Temperate Deciduous Forests – Relatively mild climates and
plentiful rain promote forests. Warm summers, cold winters
with rain well distributed throughout the year. (deer, bear, etc.)
Temperate Grasslands – Often highly productive when
converted to farmland. Also called prairie. (bison, ground
hogs, etc.)
Taiga – Coniferous forests, with long, cold winters (moose,
elk)
Tundra – Open, sometimes boggy biome. Water is usually
unavailable bc it’s frozen. (foxes, lemmings, caribou)
Human Impact on the
Environment
Global Change
• Things you do can ultimately influence every ecosystem
on Earth.
• Coal that we burn for electricity is rich in sulfur.
Scientists have discovered that the sulfur introduced into
the atmosphere by smokestacks combines with water
vapor in the air to produce sulfuric acid. Rain and snow
carry the sulfuric acid back to the earth’s surface. This
acidified precipitation is called acid rain.
• In 1985, someone noticed that the ozone levels (protect
us from the sun) were 30% less than they were 10 yrs
ago. ??? This means more U.V. rays hitting Earth
causing skin cancer, and cataracts. In fact, the # of
cases of melanoma (bad bad skin cancer) has doubled
since 1980.
What’s Destroying the Ozone?
• The major cause of ozone destruction is a class of
chemicals called chlorofluorocarbons (CFCs).
• Throughout the world, CFCs are commonly used as
coolant in refrigerators and air conditioners, as aerosol
propellants in spray cans, and as foaming agents in the
production of plastic-foam cups.
Global Warming
•When fossil fuels are burned, carbon atoms of the
fuel molecules combine with oxygen atoms from air,
yielding carbon dioxide (CO2)
•The chemical bonds in CO2 absorb solar energy,
trapping heat within the atmosphere. The warming
of the atmosphere that results from greenhouse
gases is known as the greenhouse effect.
Ecosystem Damage
• In many countries, modern agriculture
introduces large amounts of chemicals into the
global ecosystem. These chemicals include
pesticides, herbicides, and fertilizers. Some
industrialized countries (like the U.S.) try to
monitor/eliminate these chemicals.
Unfortunately, most toxic chems are still
available.
• Ex. DDT was a pesticide that was taken up by
the roots of plants. They are then stored by the
fatty acids of animals that ate the plants. As this
toxin passes up the food chain, it accumulates
(high concentration). This process is called
biological magnification. DDT was hurting the
bald eagle pops by making the egg shells weak
(no new offspring).
Loss of Resources
• The U.S. is one of the most productive agricultural countries on
Earth, largely bc of its fertile soils. These rich topsoils have
accumulated over thousands of years and cannot be replaced
and it’s being lost at a rate of several centimeters each decade.
Turning over soil to eliminate weeds, overgrazing and practicing
poor land management all allow wind and rain to remove the
topsoil.
• We also cannot replace ground water. Much of our drinking
water is stored in aquifers (porous rock reservoirs). Much of it
is wasted by washing cars, watering lawns, and leaky faucets
and toilets. Not to mention all the nonpoint source pollution
(changing the oil in your car and not properly disposing of it,
pouring out paint thinner, etc.
• And our population is still growing. Will we choke ourselves
out????!!!
Real Pop.s and Growth Patterns
• Density-independent factors – environmental
conditions (weather, climate, etc.) Ex. Mosquito
pops grow in the summer bc it’s warm but
decrease in the winter.
• R-strategists – grow exponentially when
environmental conditions allow them to
reproduce. Temporarily large populations. They
reproduce early in life and have many offspring
that need little or no parent care. (Type III
survivorship)
• K-strategists – grow slowly. Pop density is
usually near the c.c. These organisms have a
long life span, few young that are slow maturing
and reproduce late in life. (Type I survivorship)
16.2, How Populations Evolve
• After Mendel’s pea plants, biologists wondered if
dominant alleles spontaneously replaced recessive
alleles within populations.
• Using algebra and a simple application of
probability, they showed that the frequency of
alleles in a population and the ratio of heterozygous
to homozygous individuals do not change unless
the pop is acted on by things that favor the allele.
• Ex. If a dominant allele is lethal, it will not become
more common just bc it is dominant. It will actually
become more rare as the dominant individuals die.
• Hardy-Weinberg principle – the frequencies of
alleles in a population do not change unless the
evolutionary forces act on the population.
Other Issues…
• Mutation – mutation rates are very slow. They
are rare and usually result in death.
• Gene flow – the movement of alleles into or out
of a pop. (from immigrants adding new alleles,
and emigrants taking alleles away.)
• Nonrandom mating – some individuals prefer
to mate with others nearby or that are their own
phenotype. Inbreeding is a type of nonrandom
mating that causes a lower frequency
• Genetic drift – in small populations, the
frequency of an allele can be greatly changed by
a chance event. (ex. Fire killing most of the pop.)
• Natural selection – causes deviations by
directly changing the frequency of alleles.