Download Chapter 4: Populations and Communities

AP Environmental Science
Name: ________
Chapter 4: Populations and Communities
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 – Will be studied with populations later.
Population ecology; carrying capacity; reproductive strategies; survivorship
Key Terms and Vocabulary in this chapter:
Population, community, population growth, equilibrium, population growth rate, exponential increase, population
explosion, J-curve, rmax, r, carrying capacity (K), logistic growth, S-curve, biotic potential, mortality, k-strategists,
k-selected species, equilibrial species, r-strategists, population density, density dependent, density independent,
critical number, threatened, endangered, predator, prey, pathogens, keystone species, intraspecific competition,
territory, natural selection, interspecific competition, mutualism, commensalism, amensalism, symbiosis, selective
pressures, biological evolution, reproduction isolation, plate tectonics, tectonic plates, tsunami.
The tale of the Golden Frog, Atelopus zeteki.
What are the pressures that led to this organism almost becoming extinct?
–
habitat loss and overcollection for the pet trade
–
an introduced chytrid fungus deadly to amphibians
http://commons.wikimedia.org/wiki/File:Panamanian_golden_frog_01_2012_BWI_00395_zoom.jpg
AP Environmental Science Chapter 4.1. to 4.4.
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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.
•
•
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
4.3 Community Interactions
Population growth is a function of the dynamic interplay between Biotic potential and
environmental resistance
• Relationships between species may be positive (helpful), negative (harmful), or neutral
for each species
•
Predation: one member benefits, the other is harmed (+−)
Predation is the process by which individual of one species hunt, capture, kill and
consume individuals of another species, the prey.
Predator: the organism that does the feeding
• Prey: the organism that is fed upon
• Predator-prey interaction:
carnivores (meat eaters)
eat herbivores (plant eaters)
Predation includes parasitism, herbivory
• Parasites feed on hosts
Parasite: an organism (plant or animal) that feeds on its “prey,” usually without killing it
Host: the organism that is being fed upon
Examples:
tapeworms, disease-causing bacteria, viruses, fungi
Predation is a primary organizing force of community ecology (feeding relationships)
and sometimes drives cyclical population dynamics (increases and decreases in in the
population of one species driving increases and decreases of another, such as hare and
lynx populations.
Another example: Wolf and Moose on Isle Royale. Fig 4-7
AP Environmental Science Chapter 4.1. to 4.4.
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•
However Wolf predation is not the only factor affecting moose on the Isle Royale.
What else affected the moose population?
– Deep snow limited access to food for moose
– A tick infestation killed lots of moose.
– Hunters depleted the moose population
Read and make a good note on Regulation of Prey page 83 to 85.
AP Environmental Science Chapter 4.1. to 4.4.
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Comment on Plant – Herbivore interactions
If herbivores eat plants faster than they can grow
plants are depleted and the animals, then suffer.
Reindeer taken to St. Matthew Island were
healthy and well-nourished. With no predators, little
food and harsh weather, almost the entire herd
starved
• The billions of livestock animals are
overgrazing 20% of rangelands
• No population can escape the ultimate
limitations set by environmental resistance
Keystone Species
What is a keystone species? These species have a
crucial role in maintaining an ecosystem. Keystone species are species that play a
disproportionately large role in the prevalence and population levels of other species within their
ecosystem or community.
Why are they crucial?
•
play a crucial role in maintaining ecosystem biotic structure
prevent other species from taking over an area
allow other, less-competitive species to flourish
Examples:
•
Sea otters eat sea urchins in the U.S. West Coast
Removing sea otters allows urchins to eat kelp forests, affecting all species and reducing
diversity
AP Environmental Science Chapter 4.1. to 4.4.
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The wolves of Yellowstone https://www.youtube.com/watch?v=ysa5OBhXz-Q
Read this:
When the federal government set aside the Greater Yellowstone Ecosystem (GYE) as a national
park in 1872, about three to four hundred wolves were present, preying mostly upon large
hooved ungulates such as elk (Cervus canadensis, Figure 5) and bison (Yellowstone Association
1996). Fearing the wolves' impact on elk and bison herds as well as livestock owned by area
ranchers, the federal government began eradicating the wolf population. Bounty programs that
continued until 1965 offered as much as $50 per wolf. Wolves
were trapped, shot, dug from their
dens, hunted with dogs, and
poisoned. In Yellowstone National
Park, park rangers killed the last
two remaining pups in 1924. By
the 1930s wolves had been
effectively eliminated from the
contiguous 48 States and Mexico
and only remained in high numbers in Alaska.
With their primary predator eliminated, elk populations exploded, leading to the overgrazing of
plants, especially those found in riparian zones (Laliberte & Ripple 2004). Significant declines in
the populations of many plant species (e.g., aspen, willow) resulted, which in turn influenced
other wildlife, such as beaver and songbird populations (Ripple & Breschetta 2004, Hallofsky &
Ripple 2008). Intensive browsing of aspen (Populus tremuloides) stands, for example, led to a
rapid decline in the number of seedlings and root sprouts growing into saplings and trees. For
many stands of these trees, only large diameter trees (i.e., those that had matured before the
wolves were eradicated) remained.
Disappearance of these and other plant species not only caused the loss of habitat for many other
animals but also influenced other ecological factors (Smith et al. 2009), including stream bank
stability, the deposition of organic matter and fine sediment in riparian zones, water temperature
regulation via shading, and nutrient cycling. The removal of wolves thus led to the instability of
riparian and other environmentally sensitive areas.
After the United States Congress passed the original Endangered Species Preservation Act in
1966, the gray wolf made the original Endangered Species List. The subsequent Endangered
Species Act of 1973 called for their restoration. Consequently, the National Park Service
changed their policy to restore natural conditions within Yellowstone National Park, including
the reintroduction of the gray wolf (Smith & Bangs 2009). In 1995, the federal government
began reintroducing gray wolves into the GYE. Initially, fourteen wolves were captured in
Canada and relocated to one-acre acclimation pens where they were held for ten weeks before
AP Environmental Science Chapter 4.1. to 4.4.
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being released into the GYE. This process was repeated in 1996 and 1997 with an additional
seventeen wolves from Canada and ten pups from Montana (Smith et al. 2009). For the most
part, wolf populations have continued to grow at a rapid rate, averaging 17% per year (Smith &
Bangs 2009). At the end of 2009, there were between 96 and 98 wolves in Yellowstone, with 14
packs, 1 non-pack grouping, and 2 loners (Figure 6). Park staff recorded 365 prey animals killed
by wolves, most of which were elk (302).
Despite some setbacks (e.g., disease outbreaks within the fledgling wolf packs), recovery efforts
in the GYE have greatly surpassed expectations. Since their reintroduction, wolves have
overwhelmingly targeted elk over other prey. This has coincided with an increase in willow
heights in several areas. This may indicate that a wolf-elk-willow trophic cascade has been
reestablished within the GYE. Furthermore, investigators believe that restoration of willow
populations has led to a ten-fold increase in beaver populations (Smith 2004) as well as a
significant songbird rebound (Baril & Hansen 2007).
Halofsky & Ripple (2008) found that aspen browsing by elk had ceased in areas burned during
the historic 1988 fires but continued in unburned areas. These results were attributed to the
increased risk of wolf predation in burned areas. The authors proposed that a recoupling of fire
with increased predation risk from wolves may help improve aspen restoration. The results also
suggest that much more research needs to be conducted to determine the effects of wolf
reintroduction into the GYE
Competition: occurs when multiple organisms seek the same limited resource
both species are harmed (− −)
Interspecific competition: between different species
Examples:
Intraspecific competition: between the same species
Examples:
How are the following terms involved in the description of competition?
A fundamental Niche is the full niche of a species
The Realized niche is the niche which is displayed when, as a result of competition, an individual
plays only part of its role or uses only part of its resources.
• Resource partitioning is the evolutionary process by which species adapt to competition
by using slightly different resources and/or using them in slightly different ways, the
division of a resource and specialization in different parts of it.
• Competitors in the same area have different niches
Woodpeckers eat insects; other birds eat seeds
AP Environmental Science Chapter 4.1. to 4.4.
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Space can also be a resource
Intense competition divides resources even further
By limiting competition, species can put more energy into reproduction
Examine Fig 4-12 and 4-13 on page 87 and understand them.
Also look at resource partitioning in plants on page 90 – plants with short roots get their water
and minerals from different areas in the soil to deep tap roots.
Territory: an area defended by an individual or group
Most defense is intimidation—serious fights are rare
Protected areas for: nesting, a harem, food
A lack of suitable territories is a density-dependent factor
How does Competition impact Species
•
Survival of the fittest: one of the forces in nature leading to evolutionary changes in a
species
Individuals in a competing group that survive and reproduce show superior fitness to the
environment
•
Every factor of environmental resistance is a selective pressure
Individuals who survive and reproduce have the genetic endowment to cope with their
environment
Mutualism: both species benefit (++)
Examples:
Pollinators (e.g., bees) receive nutrition while plants receive pollination
Fungi on roots: the fungus gets nutrition while the plant takes up nutrients more easily
Lichens are made of a fungus and an alga
The anemone fish protects the anemone from predation and the anemone protects the fish
AP Environmental Science Chapter 4.1. to 4.4.
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•
Commensalism: one benefits, the other is not affected (+0)
Examples:
Buffalo stir up insects that cattle egrets eat
Orchids live on trees but do not harm them
•
Amensalism: one is unaffected, the other is harmed (0−) (I see this more as a protection
from the organism for it’s survival)
Examples:
Usually accomplished by natural chemical compounds
Black walnut tree chemicals can kill other plants
Marigolds exude chemicals which chase damaging nematodes in the soil.
• Symbiosis: two species live close to each other
Can be beneficial (mutualism) or harmful (parasitism)
Evolution as a force for change.
I have called this principle, by which each slight variation, if useful, is preserved, by the term
Natural Selection.
Charles Darwin, The Origin of Species
Evolution is a genetic change in a population that occurs over time in response to
environmental pressures that cause change. Species respond to these pressures and to
changes in the environment by adapting, migrating, or dying. Adaptation of a species in
response to environmental (selective) pressures comes about through a process called
natural selection which is a constant selection and “modification of a species’ gene pool
toward features that enhance survival and reproduction within the existing biotic
community and environment.”
•
The gene pool of a population is continually tested by the selective pressures exerted by
environmental resistance.
Provide examples of selective pressures!
• environmental resistance factors
that affect survival and reproduction
Predators, parasites, drought, lack of food
• Organisms with traits that protect
them or allow them to escape can survive
and reproduce
AP Environmental Science Chapter 4.1. to 4.4.
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Predators function as a selective pressure: traits that let prey escape are favored.
Food is a selective pressure: predators with keen eyesight, cryptic colors, or swift
speed survive
In Mastering Environmental Science
4.3 Community Interactions
Activity: Overview of Macroevolution
4.4 Evolution as a Force for Change
Activity: Causes of Evolutionary Change
Activity: Evolution and Genetics
Activity: The Bottleneck Effect
Animation: Global Geography Through Geologic Time
BioFlix: Mechanisms of Evolution
AP Environmental Science Chapter 4.1. to 4.4.
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What is Natural Selection?
Survival of the species with the best adapted traits

Natural selection occurs on the individual level by determining which organisms have
adaptations that allow them to survive and reproduce and be able to pass those adaptive
traits onto their offspring.

New genes enter the gene pool through mutation.

Natural selection occurs over successive generations.

Evolution works on the species level by describing how the species attains the genetic
adaptations that allow them to survive in a changing environment.

Without a changing environment neither evolution nor natural selection would exist.
There are four observations of the natural world that allow for Natural Selection.
1. Overproduction – more offspring are born than can survive.
2. Variation – Within a species there must be a good variation of genes in the gene pool.
There are introduced by mutation.
3. Struggle for Existence- This is essentially competition for food, water, space, mates,
home.
4. Differential reproductive success – Selection via sexual reproduction, strongest, smartest,
-------- able to win a mate in order to pass on genes.
Natural selection operates in three ways.
It may be stabilizing, directional or disruptive.
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Extreme phenotype
Differentiate between Natural Selection and Artificial Selection and discuss briefly how these
affect each other.
AP Environmental Science Chapter 4.1. to 4.4.
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Adaptations to the Environment—Include coping mechanisms, adaptations for
obtaining food, adaptation for escaping predation, adaptations for pollination,
adaptations for finding and attracting mates, and adaptations for seed dispersal. See
Figure 4-18. Excellent visual page 91
What is Fitness in an evolutionary sense?
features (traits) that adapt an organism for survival and reproduction
A population’s gene pool is tested by selective pressures exerted by environmental resistance
• If a trait increases survival and reproduction
it is maintained through natural selection
1. The Limits of Change—If a species faces new selective pressure it will either :
 Adapt through natural selection
 Migrate move to an area with suitable conditions
 or become extinct. If the first 2 options are not possible
Some individuals have traits (alleles) that allow them to survive and reproduce
under the new conditions
o Alleles: variations or new combinations of genes
Four variables affect species survival:





Geographical distribution,
specialization to a given habitat or food supply,
genetic variation within the population,
and reproductive rate relative to the rate of environmental change.
 The less vulnerable species are r-strategists
 The more vulnerable species are K-strategists
Rapidly reproducing species can be vulnerable if the environment changes
too rapidly or too much
AP Environmental Science Chapter 4.1. to 4.4.
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ii. Genetic Change—Genetic variation is the norm in living things and will
occur over generations in a population. Mutations and sexual
reproduction produce the essential genetic variation upon which natural
selection acts.
2. The Evolution of Species—Over time the result of adaptations can lead to the
formation of new and unique species.
i.
Two Species from One, this is macroevolution or speciation—
Prerequisites include reproductive isolation of individuals in the
species and differing selective pressures for each new population.
See Figure 4-20. Page 93 of the Arctic Fox and Gray fox evolution.
Reproductive isolation can be
a. Geographic = Allopatric speciation
b. Or a non-geographic barrier that prevents reproduction. =
sympatric speciation
Drifting Continents—The drifting of continents over time certainly provided for the geographical isolation and
differing selective pressures that separated populations would have needed to undergo speciation.
See Figure 4-21. On page 95
http://www.youtube.com/watch?v=cQVoSyVu9rk Continental drift
Briefly account for the variation in species in Indonesia. Page 95.
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