Download Biological populations and communities

AP Environmental Science: Populations
Name: ________
Where does this fit?
I. The Living World
Ecosystem Structure
Biological populations and communities; ecological niches; interactions among
species; keystone species; species diversity and edge effects;
Ecosystem Diversity
Biodiversity; natural selection; evolution;
Natural Ecosystem Change
Species movement;
II. Population
A. Population Biology Concepts
Population ecology; carrying capacity; reproductive strategies; survivorship
Chapter 4 Learning Objectives:
1. Dynamics of Natural Populations: Explain the three model ways populations grow, and
describe the graph that would illustrate each.
2. Limits on Populations: Explain factors that limit populations, including those that increase as
populations become denser (such as predation and resource limitation) and factors that are
unrelated to the population density.
3. Community Interactions: Define the types of interactions that can occur between species in a
community and the effect of those interactions on each species.
4. Evolution as a Force for Change: Describe the major ideas in the theory of evolution, such as
inheritance and natural selection, and list examples of adaptations organisms have for
survival.
5. Implications for Human Management: Describe at least three ways in which humans alter
features in the environment to change population growth patterns.
Key Terms:
population ecology
population density
birth rate (b)
death rate (d)
growth rate (r)
natural increase
dispersal
immigration
emigration
biotic potential
intrinsic rate of increase
exponential population growth
environmental resistance
carrying capacity (K)
survivorship
density-dependent factor
density-independent factor
zero population growth
demographics
highly developed countries
developed countries
infant mortality rates
developing countries
moderately developed countries
less developed countries (LDCs)
doubling time
replacement-level fertility
total fertility rate
demographic transition
preindustrial stage
transitional stage
industrial stage
postindustrial stage
age structure
age structure diagram
population growth momentum
Baby Boom
Immigration and Nationality Act
Immigration Reform and Control Act
(IRCA)
Chapter 4.1: Dynamics of Natural Populations
The tale of the Golden Frog, Atelopus zeteki.
What are the pressures that led to this organism almost becoming extinct?
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habitat loss and overcollection for the pet trade
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an introduced chytrid fungus deadly to amphibians
http://commons.wikimedia.org/wiki/File:Panamanian_golden_frog_01_2012_BWI_00395_zoom
.jpg
Dynamics of Natural populations.
Ecosystems and the organisms within them are constantly changing. These changes occur
because living organisms within the ecosystem face varying stresses from both living and
non-living factors in the environment. Living things must respond to those stresses and
their response changes not only the affected population but many others that are tied in
some way to the affected population.
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Again, what is a
Population: a group of members of the same species living in an area
Community: populations of different species living together in an area
Populations grow with births and immigration
They decline with deaths and emigration
Change in population number = (Births + Immigration) – (Deaths + Emigration)
• Population growth is a change (rate) in population size = r
• Equilibrium: (births + immigration) = (deaths + emigration)
Often, population growth is not zero
• Population growth rate: amount the population has changed divided by the time it had
to change
A. Population Growth Curves
• Population growth curves graph how populations grow and are used to determine:
how fast a population could grow
the population size now and in the future
There are three basic scenarios that any given population may find itself in at any
given point in time:
What are these?
exponential increase, logistic growth, and constant growth.
1.
Constant growth is virtually never seen in nature. See Figure 4-1.
Constant population growth rate: adding a constant number of individuals over
each time period is the simplest type of growth to model. Is not generally found in
nature but it’s a good comparison to other growth patterns
Population number at the start + (A constant * Time)
= Population number at the end
(Ex: start with 2 individuals and a constant growth rate of 2 per week: at the end
of 24 weeks you would have 50 individuals)
2. Exponential Increase—J-curve growth. When does this occur? Ppt 7
growth at a constant rate of increase
Elaborate on Exponential growth.
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the doubling time remains constant
(Ex: it takes 2 days to go from 8 to 16 individuals, as well as from 1,000 to 2,000
individuals)
• r (or rmax) = the number of offspring individuals can produce in a given time if
resources are unlimited
• the number of times you multiply e by itself
Starting population x constant (e) multiplied by itself
a given number of times = Ending population
• Under unlimited conditions, organisms with a high r have rapid population
growth
• Such growth is called an “explosion”
but it cannot continue indefinitely
• The population continues to grow and then dies off
• Carrying capacity (K): the maximum population of a species a habitat can support
without being ruined. In exponential growth carrying is exceeded.
3. Logistic Growth—S curve growth. When does this occur?
This occurs when a population is at equilibrium and the number of births +
immigration = the number of deaths + emigration.
Logistic growth: some process slows growth so it levels off near carrying capacity results in
an S-shaped curve
• As the population approaches K, growth slows
the population remains steady and growth = 0
the maximum rate of population growth occurs halfway to K
Starting population + (reproductive capacity (r) * population * a number
showing how far the population is from K) = Ending population
What growth do the curves below represent?
Use the graph below to explain real life growth.
• J-shaped explosions are often followed by crashes
• J-shaped growth results from unusual disturbances
introduction of a foreign species, the elimination of a predator
a suddenly changed habitat, arrival in a new habitat
• Other populations show an S-curve
In populations controlled by complex relationships between species
Cycles of lower and higher numbers around K
B. Biotic Potential Versus Environmental Resistance
Create a note
Biotic potential is “the number of offspring (live births, eggs laid, or seeds or spores
set in plants) that a species may produce under ideal conditions.” A species’ biotic
potential remains constant despite environmental pressures. Species are not often
allowed to reach their biotic potential because of environmental resistance.
– Measured by r (the rate at which organisms reproduce)
– Varies tremendously from less than 1 birth/year (some mammals) to millions/year
(plants, invertebrates)
• Recruitment: survival through early growth stages to become part of the breeding
population
Young must survive and reproduce to have any effect on population size
See Figure 4-3.
What is Environmental Resistance?
—is “the combination of all the abiotic and biotic factors that may limit a
population’s increase”. Resistance may increase or decrease depending on
population size and it controls a population’s size.
– Prevents unlimited population growth
Biotic: predators, parasites, competitors, lack of food
Abiotic: unusual temperatures, moisture, light, salinity, pH, lack of nutrients, fire
• Environmental resistance can also lower reproduction
loss of habitat, pollution, changed animal migration
A stable population results from interactions between factors that increase and decrease
population]
Reproductive Strategies—
R-strategists (r-selected species) “produce massive numbers of young, but then leave
survival to the whims of nature”.
– results in low recruitment
– rapid reproduction, rapid movement, short life span
– adapted to a rapidly changing environment
– “boom-and-bust” populations
– “weedy” or “opportunistic” species, usually small
– a housefly, dandelion, and cockroach are examples
On the other hand, K-strategists (K-selected species) “have a much lower
reproductive rate (that is, a lower biotic potential), but then care for and protect
the young until they can compete for resources with adult members of the
population”. See Discussion Topic #2 and #3.
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care for and protect young
live in a stable environment already populated by the species
larger, longer lived, well-adapted to normal environmental fluctuations
their populations fluctuate around carrying capacity
also called equilibrial species
an elephant and California condor are examples
Create a table to compare r and K strategists.
What is the Life history of an organism?
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progression of changes in an organism’s life
age at first reproduction, length of life, etc.
visualized in a survivorship curve
Explain the three types of survivorship curve!
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I.
Type I survivorship: low mortality in early life
most live their full life span (e.g., humans)
Type III survivorship: many offspring that die young
few live to the end of their life (oysters, dandelions)
Type II survivorship: intermediate survivorship pattern (squirrels, coral)
Limits on Populations
What is the difference between carrying capacity and actual population size?
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What factors limit population size?
Population density: number of individuals per area
Density-dependent factor: increases with increased population density
• Disease, predation, food shortages, competition for food and space
• Environmental resistance increases mortality
• The more dense a population is the more resistant factors affect growth
rate.
Density-independent factor: its effects are independent of the density of the population
• Spring freeze, fire
• Is not involved in maintaining population equilibrium
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factors include an unusual heat wave or hard freeze, severe weather and
natural disasters. If a particular limiting factor moves outside an
organism’s range of tolerance, then the organism dies irrespective of how
many individuals there are in the population
Mortality in a population may be related to either density dependent factors (related to
population size per given area) or density independent factors (not related to population
size per given area). In either case, when a population faces stress that leads to mortality,
a critical number of individuals in that population are necessary for that population to
survive in an ecosystem.
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Regulating a population’s size
Only density-dependent factors can regulate a population (keep it in equilibrium)
• Top-down regulation: control of a population (species) by predation
• Bottom-up regulation: control of a population occurs as a result of scarcity
of a resource (i.e. food)
Factors controlling a population determine the effects of adding or removing a species to
an area
• Removal of a species can even affect species that don’t directly interact
with it
What is the Critical Number of a population? —
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the minimum population base allowing the survival and recovery of a population
a pack of wolves, flock of birds, school of fish
• The group is necessary to provide critical interactions between members
protection and support
• If a population falls below this number
surviving members become more vulnerable
breeding fails
extinction is almost inevitable
If the number of individuals in a population drops below the critical number, density
independent factors become very important. It is very difficult to pre-determine what
the critical number for a particular population is because of the complexity of
ecosystems.
What is the connection between biodiversity loss and humans?
• Human activities are responsible for the decline and extinction of species
Humans change habitats, introduce alien species, pollute, hunt, etc.
• Human activities are not density dependent
they can even intensify as numbers decline
Differentiate between the terms critical number and carrying capacity. What is density
dependence?
Critical number is the minimum size of a population below which it will not reproduce. The
survival of the species is unlikely below the critical number. The carrying capacity is a
characteristic of an ecosystem and “is the upper limit to the population of any particular species
that an ecosystem can support....” Therefore, the critical number is the smallest number of
individuals within a species that is required for the species survival while the carrying capacity is
the largest number of individuals within a species that an ecosystem can support. Carrying
capacity is a characteristic of an ecosystem, while critical number is a characteristic of the
species.