Transcript Populations and Communities

Do now- Monday

 Information: Tropisms are plants responses to stimuli.
Stimuli can include sunlight, gravity, elevation, and many
other factors by which a plant needs to respond by
growing differently. Cypress trees grow in higher
elevations where a lot of water is available.
 Scenario: I was at a music festival in the hill country of
Texas. Expecting to see a lot of grassland and cacti, we
were actually in the woods surrounded by tall cypress
trees.
 Questions:
 1. Why do you think cypress trees were able to grow there?
 2. What kind of elevation do you think we were at?
 3. How would the different trees affect other organisms in
the same food web?
Thought Question

 In the last century, the piney woods of northwestern
and central Louisiana were logged extensively by
timber companies. A once vast forest was left with
only a few areas intact, while all around, timber
wasteland lay open with its wildlife decimated. In
the 1930s, the US Forest service began purchasing
what would amount to 604,000 acres of piney woods
spread out across 5 management districts. The Forest
Service dedicated the land to ecosystem restoration.
 Describe how the land area changed after the
restoration effort. Be specific.
The effects of preservation
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Ecology

 The branch of biology that studies the relationships
of species with each other and their environment.
 Biology is a subcategory of ecology.
Biome

 An ecosystem
with the same
climate,
ecosystem
Ecosystem

 The biotic
factors in a
biome
Community

 Group of
populations
living in a
geographic
area
Population

 All of the
individuals
of a species
that live
and
reproduce
in a given
area
Individual

 One
organism
in a
particular
population
Thought Question

 Describe your status in the different spheres (starting
at individual and working outward).
Thought Question 1

 Describe some biotic and abiotic facts in the
Kisatchie National Forest. Use the Forest’s website as
a resource.
Habitat versus niche

 Habitat= The environment in which a population
lives and provides the four things all species need to
survive: food, water, shelter, and space
 Niche= The place where a population lives and the
jobs that is performs within a community and a
habitat
Thought Question 2

 Predict what would happen if two species began
competing directly for resources within the same
niche.
Competition

 When two or more organisms need to use the same
resource at the same time.
 Can occur between two species and within members
of a population.
Predation

 When one animal pursues and uses another animal
as a source of food.
Symbiosis

 More complex interaction taking place between
species
 Parasitism
 Mutualism
 Commensalism
Parasitism

 One organism benefits as the other organism is
harmed
Mutualism

 Both organisms benefit
Commensalism

 One organism benefits and the other organism is
neither harmed nor helped
Limiting Factor #1
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 Predation
Thought Question

 In the early twentieth century, the US government
wanted to increase the deer population of the Grand
Canyon. To accomplish this, government officials
wiped out the Grand Canyon’s wolf population.
Describe two effects that this action most likely had
on the deer populations.
Limiting factor #2

 Food supply
Other limiting factors
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Population Density

 Population density refers to the concentration of
individuals living within an area.
 Divide the number of individuals in an area by the
total area.
Thought Question

 A garden that is 50m2 is plagued by a population of
roughly 2,500 caterpillars. Calculate the population
density of the caterpillars in numbers per square
meter.
 Explain how the size of a population in a habitat
differs from the density of the population in a
habitat.
Scientific Method

 Scientists can count the number of individuals in a
population
 Or they can count the number of individuals in a
small area then multiply that figure to estimate the
total number of individuals in a habitat.
Thought Question

 When does it make more sense to estimate the
number of individuals in a population rather than
counting them all?
Changes in population
size

 Population size is never constant
 Mortality refers to the death rate
 Natality is the birth rate
Thought Question

 In the US, the mortality rate for humans is about 2.4
million per year. The natality rate for humans is
about 4 million per year. According to the mortality
and natality rates, is the human population
increasing or decreasing?
 In addition to mortality and natality rates, what
processes could be changing the human population
in the US?
Other populationchanging factors

 Immigration= individuals moving into a habitat
(remember In)
 Emigration= individuals leaving a habitat
(remember Exit)
Thought Question

 Suppose that over the course of a year, a population
of rabbits experiences the following changes in its
population: 25,000 individuals die, 20,000
individuals are born, 15,000 individuals emigrate,
and 20,000 individuals immigrate. By how much did
the population of rabbits change in one year?
Invasive species
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 New species that enter a community and don’t “fit in
well” with the other species