Figure 5.1 An endangered southern sea otter in Monterey Bay,
California (USA), uses a stone to crack the shell of a clam
(insert). It lives in a giant kelp bed near San Clemente Island,
California (background). Scientific studies indicate that the
otters act as a keystone species in a kelp forest system by helping
to control the populations of sea urchins and other kelp-eating
species.
Slide 3
Core Case Study: Southern Sea Otters: Are They Back from the
Brink of Extinction? Habitat: giant kelp forest of Pacific Coast of
N.A. Habitat: giant kelp forest of Pacific Coast of N.A. Fast agile
swimmers that eat about their weight in shellfish: clams, mussels,
crabs, sea urchins, abalone and 40 other benthic animals. Fast
agile swimmers that eat about their weight in shellfish: clams,
mussels, crabs, sea urchins, abalone and 40 other benthic animals.
Hunted to near extinction by early 1900s Hunted to near extinction
by early 1900s Partial recovery from 1938 to 2007, pop. increased
from 50 to about 3000. Partial recovery from 1938 to 2007, pop.
increased from 50 to about 3000. Helped in part by ESA listing in
1977 Helped in part by ESA listing in 1977 Why care about sea
otters? Why care about sea otters? Ethics Ethics Keystone species
Keystone species Tourism dollars Tourism dollars
Slide 4
5-1 How Do Species Interact? Concept 5-1 Five types of species
interactions competition, predation, parasitism, mutualism, and
commensalismaffect the resource use and population sizes of the
species in an ecosystem.
Slide 5
Species Interact in Five Major Ways Interspecific Competition
Predation Parasitism Mutualism Commensalism These interactions have
significant effects on the resources use and pop. sizes of species
in an ecosystem Also influence the abilities of the interacting
species to survive, thus the interactions are agents of natural
selection.
Slide 6
Most Species Compete with One Another for Certain Resources
Competition is the most common interaction The greater the niche
overlap, the greater the competition. Competitive exclusion
principle no two species can occupy the exact same niche.
Competition would be too intense Humans are outcompeting other
species for space food and other resources as our ecological
footprint increases.
Slide 7
Most Consumer Species Feed on Live Organisms of Other Species
(1) Predation is when a member of species feeds directly on all or
part of a living organism of another plant or animal. Predator and
prey form a predator-prey relationship. Herbivores, carnivores, and
omnivores are predators. Methods of Prey Capture by Predators:
Herbivores walk, swim, or fly up to plants they feed on. Carnivores
Pursuit requires speed and agility on ground, in water, or in the
air Ambush predators use stealth and camouflage. Chemical warfare
Venom
Slide 8
Most Consumer Species Feed on Live Organisms of Other Species
(2) Prey escape/avoidance methods: Highly developed senses, sight
and smell (so do predators!) Flight response Run, swim, and fly
fast Protective armor Shells, bark, spines, thorns Camouflage to
hide Chemical warfare Poisons (oleander plants, toads), irritants
(poison ivy, bombardier beetle), foul odor (skunk, stink bug), bad
taste (monarch butterfly) Warning coloration Mimicry (viceroy
butterfly, milk snake) Deceptive looks Deceptive behavior Schooling
or herding behaviors
Slide 9
Most Consumer Species Feed on Live Organisms of Other Species
(3) At the individual level Predator benefits Prey species is
harmed At the population level Predation plays a role in natural
selection Predators take the sick, weak, old, and less fit members
of the prey species. Some people view predators with contempt. If
you were an ambassador for nature, what would you tell these
people?
Slide 10
Figure 5.2 Some ways in which prey species avoid their
predators: (a, b) camouflage, (ce) chemical warfare, (d, e) warning
coloration, (f) mimicry, (g) deceptive looks, and (h) deceptive
behavior.
Slide 11
Science Focus: Why Should We Care about Kelp Forests? Kelp
forests Restricted to cold, nutrient-rich, and fairly shallow
coastal waters. One of most biologically diverse marine ecosystems
supporting large numbers of marine plants and animals. Help reduce
shore erosion. Harvested as a renewable resource for algin found in
blades. Used in toothpaste, ice cream, and many other products.
Major threats to kelp forests Sea urchins Pollution from water
run-off Global warming
Slide 12
Figure 5-A Purple sea urchin in coastal waters of the U.S.
state of CA.
Slide 13
Predator and Prey Species Can Drive Each Others Evolution To
survive, predators must eat and prey must avoid being eaten
Predators and prey populations exert intense natural selection
pressures on one another. Coevolution occurs when populations of
two different species interact over such a long period of time,
changes in the gene pool of one species can lead to changes in the
gene pool of the other species.
Slide 14
Figure 5.3 Coevolution. A Langohrfledermaus bat hunting a moth.
Long-term interactions between bats and their prey such as moths
and butterflies can lead to coevolution, as the bats evolve traits
that increase their chances of getting a meal and the moths evolve
traits that help them avoid being eaten.
Slide 15
Some Species Feed off Other Species by Living on or in Them (1)
Parasitism occurs when one species (the parasite) feeds on the body
of, or the energy used by, another organism, usually by living on
or in the host. Parasites rarely kill host, but may gradually
weaken them. Endoparasites, some pathogenic Tapeworms, liver fluke,
Trypanosoma Ectoparasites Mosquitoes, fleas, ticks, mistletoe, and
sea lamprey Other forms of parasitism: Brood parasitism and klepto-
parasitism
Slide 16
Some Species Feed off Other Species by Living on or in Them (2)
At the individual level For host, parasites are harmful. Parasites
benefit. But at the population level Parasites can promote
biodiversity by increasing species richness. Help keep a hosts
population size in check. Parasite-host relationship may lead to
coevolution
Slide 17
Figure 5.4 Parasitism: (a) Healthy tree on the left and an
unhealthy one on the right, which is infested with parasitic
mistletoe. (b) Blood-sucking parasitic sea lampreys attached to an
adult lake trout from the Great Lakes (USA).
Slide 18
In Some Interactions, Both Species Benefit Mutualism occurs
when two species behave in ways that benefit both by providing each
with food, shelter, or some other resource. Flower s and their
pollinators Nutrition and protection Gut inhabitant mutualism
Slide 19
Figure 5.5 Examples of mutualism. (a) Oxpeckers (or tickbirds)
feed on parasitic ticks that infest large, thick-skinned animals
such as the endangered black rhinoceros. (b) A clownfish gains
protection and food by living among deadly stinging sea anemones
and helps protect the anemones from some of their predators.
Slide 20
In Some Interactions, One Species Benefits and the Other Is Not
Harmed Commensalism is an interaction that benefits one species but
has little, if any, effect on the other. Epiphytes Birds nesting in
trees
Slide 21
Figure 5.6 In an example of commensalism, this bromeliadan
epiphyte, or air plant, in Brazils Atlantic tropical rain
forestroots on the trunk of a tree, rather than in soil, without
penetrating or harming the tree. In this interaction, the epiphyte
gains access to water, other nutrient debris, and sunlight; the
tree apparently remains unharmed.
Slide 22
5-2 How Can Natural Selection Reduce Competition between
Species? Concept 5-2 Some species develop adaptations that allow
them to reduce or avoid competition with other species for
resources.
Slide 23
Some Species Evolve Ways to Share Resources Resource
partitioning occurs when species competing for similar scarce
resources evolve specialized traits that allow them to use shared
resources at different times in different ways in different places
Niche overlap can be reduced when natural selection reduces broad
and overlapping niches. Species become more specialized.
Slide 24
Figure 5.7 Competing species can evolve to reduce niche
overlap. The top diagram shows the overlapping niches of two
competing species. The bottom diagram shows that through natural
selection, the niches of the two species become separated and more
specialized (narrower) as the species develop adaptations that
allow them to avoid or reduce competition for the same
resources.
Slide 25
Figure 5.8 Sharing the wealth: resource partitioning of five
species of insect-eating warblers in the spruce forests of the U.S.
state of Maine. Each species minimizes competition for food with
the others by spending at least half its feeding time in a distinct
portion (shaded areas) of the spruce trees, and by consuming
different insect species. (After R. H. MacArthur, Population
Ecology of Some Warblers in Northeastern Coniferous Forests,
Ecology 36 (1958): 533536.)
Slide 26
Figure 4.13 Specialized feeding niches of various bird species
in a coastal wetland. This specialization reduces competition and
allows sharing of limited resources.
Slide 27
Figure 5.9 Specialist species of honeycreepers. Evolutionary
divergence of honeycreepers into species with specialized
ecological niches has reduced competition between these species.
Each species has evolved a beak specialized to take advantage of
certain types of food resources.
Slide 28
5-3 What Limits the Growth of Populations? Concept 5-3 No
population can continue to grow indefinitely because of limitations
on resources and because of competition among species for those
resources.
Slide 29
Populations Have Certain Characteristics (1) Populations differ
in Distribution Numbers Age structure Density Population dynamics
is the study of how characteristics of populations change in
response to changes in environmental conditions.
Slide 30
Populations Have Certain Characteristics (2) Changes in
population characteristics due, for example, to: Temperature
Presence of disease organisms or harmful chemicals Resource
availability Arrival or disappearance of competing species
Slide 31
Most Populations Live Together in Clumps or Patches Three
general patterns of population distribution or dispersion in a
habitat. Clumping, most common as resources are also clumped.
Uniform dispersion, when resources is even and scarce. Random
dispersion, not as common. Why clumping? Species tend to cluster
where resources are available. Groups have a better chance of
finding clumped resources. Protects some animals from predators.
Packs allow some to get prey. Temporary groups for mating and
caring for young.
Slide 32
Figure 5.10 Generalized dispersion patterns. The most common
pattern is clumps of members of a population scattered throughout
their habitat, mostly because resources are usually found in
patches. Questions: Why do you think the creosote bushes are
uniformly spaced while the dandelions are not?
Slide 33
Populations Can Grow, Shrink, or Remain Stable (1) Population
size governed by Births Deaths Immigration Emigration Population
change ( N) = (births + immigration) (deaths + emigration)
Slide 34
Populations Can Grow, Shrink, or Remain Stable (2) How fast a
population grows or declines depends on its age structurethe
proportions of individuals at various ages. Prereproductive age:
not mature enough to reproduce. Reproductive age: those capable of
reproduction. Postreproductive age: those too old to
reproduce.
Slide 35
No Population Can Grow Indefinitely: J-Curves and S-Curves (1)
Biotic potential is the capacity for population growth under ideal
conditions. Low, usu. in species with large individuals High, usu.
in small species. Intrinsic rate of increase (r) is the rate at
which the population of a species grows if it had unlimited
resources. Individuals in populations with high r Reproduce early
in life Have short generation times Can reproduce many times Have
many offspring each time they reproduce
Slide 36
No Population Can Grow Indefinitely: J-Curves and S-Curves (2)
Size of populations is regulated by limiting factors. Water Space
Nutrients Exposure to too many competitors, predators or infectious
diseases
Slide 37
No Population Can Grow Indefinitely: J-Curves and S-Curves (3)
Environmental resistance is the combination of all factors that act
to limit the growth of a population. Biotic potential and
environmental resistance determine carrying capacity (K)the maximum
population of a given species that a particular habitat can sustain
indefinitely without being degraded. Exponential growth growth at a
fixed rate relative to the population size, e.g. 2 % annually.
Curve shape, J Logistic growth rapid growth followed by a steady
decrease as a population encounters environmental resistance. Curve
shape, S (or sigmoid)
Slide 38
Figure 5.11 No population can continue to increase in size
indefinitely. Exponential growth (left half of the curve) occurs
when resources are not limiting and a population can grow at its
intrinsic rate of increase (r) or biotic potential. Such
exponential growth is converted to logistic growth, in which the
growth rate decreases as the population becomes larger and faces
environmental resistance. Over time, the population size stabilizes
at or near the carrying capacity (K) of its environment, which
results in a sigmoid (S-shaped) population growth curve. Depending
on resource availability, the size of a population often fluctuates
around its carrying capacity, although a population may temporarily
exceed its carrying capacity and then suffer a sharp decline or
crash in its numbers. Question: What is an example of environmental
resistance that humans have not been able to overcome?
Slide 39
Figure 5.12 Logistic growth of a sheep population on the island
of Tasmania between 1800 and 1925. After sheep were introduced in
1800, their population grew exponentially, thanks to an ample food
supply. By 1855, they had overshot the lands carrying capacity.
Their numbers then stabilized and fluctuated around a carrying
capacity of about 1.6 million sheep.
Slide 40
Science Focus: Why Are Protected Sea Otters Making a Slow
Comeback? Low biotic potential Prey for orcas Cat parasites
Thorny-headed worms Toxic algae blooms PCBs and other toxins Oil
spills Figure 5.B Population size of southern sea otters off the
coast of the U.S. state of California, 19832007. According to the
U.S. Fish and Wildlife Service, the sea otter population would have
to reach about 8,400 animals before it can be removed from the
endangered species list. (Data from U.S. Geological Survey)
Slide 41
When a Population Exceeds Its Habitats Carrying Capacity, Its
Population Can Crash Carrying capacity is not fixed. Reproductive
time lag may lead to overshoot of K. The time lag is the period
needed for the birth rate to decrease and the death rate to
increase in response to resource overconsumption. Dieback, or crash
Damage from overconsumption/use may reduce areas carrying
capacity.
Slide 42
Figure 5.13 Exponential growth, overshoot, and population crash
of reindeer introduced to the small Bering Sea island of St. Paul.
When 26 reindeer (24 of them female) were introduced in 1910,
lichens, mosses, and other food sources were plentiful. By 1935,
the herd size had soared to 2,000, overshooting the islands
carrying capacity. This led to a population crash, when the herd
size plummeted to only 8 reindeer by 1950. Question: Why do you
think this population grew fast and crashed, unlike the sheep in
Figure 5-12?
Slide 43
Species Have Different Reproductive Patterns Natural capital:
generalized characteristics of r-selected (opportunist) species and
K-selected (competitor) species. Many species have characteristics
between these two extremes.
Slide 44
Figure 5.14 Positions of r-selected and K-selected species on
the sigmoid (S-shaped) population growth curve.
Slide 45
When does death come? Survivorship curves for populations of
different species, show the percentages of the members of a
population surviving at different ages. Most members of a late loss
population (such as elephants, rhinoceroses, and humans) live to an
old age. Members of a constant loss population (such as many
songbirds) die at all ages. In an early loss population (such as
annual plants and many bony fish species), most members die at a
young age. These generalized survivorship curves only approximate
the realities of nature.
Slide 46
Genetic Diversity Can Affect the Size of Small Populations When
a population becomes so reduced, reduced genetic diversity can
affect the overall survival of the population. Genetic drift random
changes in gene (i.e., allele) frequencies in a population that can
lead to unequal reproductive success; occurs more often in small
populations. Founder effect when a few members of a population
colonize a new area and become geographically isolated. Demographic
bottleneck occurs when only a few member of a population survive a
catastrophic die-off. Inbreeding occurs when individuals of small
population mate with each other increase in the freq. of defective
genes. Minimum viable population size the number of individuals a
population needs for long-term survival.
Slide 47
Random Effects on Allele Frequency in Small Populations
Under Some Circumstances Population Density Affects Population
Size Population density the number of individuals in a population
found in a particular area or volume. Density-dependent population
controls Predation Parasitism Infectious disease Competition for
resources Density dependent factors tend to regulate a population
at a fairly constant size, often near carrying capacity of an area.
Density independent factors are often abiotic Severe freeze,
hurricanes, fires, pollution, habitat destruction, wetland
loss.
Slide 51
Several Different Types of Population Change Occur in Nature
Stable Hovers around K. Characteristic of species that live in
undisturbed tropical rain forests. Irruptive Increase to a high
peak and then crash Algae and insects display this type of
population changes Linked to seasonal changes in weather and
nutrient availability Cyclic fluctuations, boom-and-bust cycles
Changes occur in regular cycles Examples: Lemming populations rise
and fall every 3-4 years Lynx and snowshoe hare every 10 years
Top-down population regulation Bottom-up population regulation
Irregular Changes in pop. size with no recurring pattern.
Slide 52
Figure 5.15 Population cycles for the snowshoe hare and Canada
lynx. At one time, scientists believed these curves provided
circumstantial evidence that these predator and prey populations
regulated one another. More recent research suggests that the
periodic swings in the hare population are caused by a combination
of top-down population controlthrough predation by lynx and other
predatorsand bottom-up population control, in which changes in the
availability of the food supply for hares help determine hare
population size, which in turn helps determine the lynx population
size. (Data from D. A. MacLulich)
Slide 53
Humans Are Not Exempt from Natures Population Controls Ireland
Potato crop in 1845 Bubonic plague Fourteenth century AIDS Global
epidemic So far, technological, social, and other cultural changes
have extended the earths carrying capacity for humans.
Slide 54
Case Study: Exploding White-Tailed Deer Population in the U.S.
1900: deer habitat destruction and uncontrolled hunting 1920s1930s:
laws to protect the deer Pop no 25-30 million Current population
explosion for deer In some forests, they are consuming native
ground cover making way for non-native invaders. Lyme disease
Deer-vehicle accidents Eating garden plants and shrubs Ways to
control the deer population
Slide 55
5-4 How Do Communities and Ecosystems Respond to Changing
Environmental Conditions? Concept 5-4 The structure and species
composition of communities and ecosystems change in response to
changing environmental conditions through a process called
ecological succession.
Slide 56
Communities and Ecosystems Change over Time: Ecological
Succession Types and numbers of species change in a biological
community over time. Mature forests and other ecosystems do not
spring up from bare rock. Instead they go through changes in
species composition over long periods of time. Ecological
succession Primary succession Secondary succession
Slide 57
Some Ecosystems Start from Scratch: Primary Succession Primary
succession begins with a lifeless area where there is No soil in a
terrestrial system No bottom sediment in an aquatic system Early
successional plant species, called pioneer, or colonizing species.
Lichens and mosses Midsuccessional plant species Herbs, grasses and
shrubs, and later trees Late successional plant species Other trees
Can also occur in ponds.
Slide 58
Figure 5.16 Primary ecological succession. Over almost a
thousand years, plant communities developed, starting on bare rock
exposed by a retreating glacier on Isle Royal, Michigan (USA) in
northern Lake Superior. The details of this process vary from one
site to another. Question: What are two ways in which lichens,
mosses, and plants might get started growing on bare rock?
Slide 59
Some Ecosystems Do Not Have to Start from Scratch: Secondary
Succession (1) Secondary succession begins in an area Disturbed
Removed Destroyed Some soil remains in a terrestrial system Some
bottom sediment remains in an aquatic system
Slide 60
Figure 5.17 Natural ecological restoration of disturbed land.
Secondary ecological succession of plant communities on an
abandoned farm field in the U.S. state of North Carolina. It took
150200 years after the farmland was abandoned for the area to
become covered with a mature oak and hickory forest. A new
disturbance, such as deforestation or fire, would create conditions
favoring pioneer species such as annual weeds. In the absence of
new disturbances, secondary succession would recur over time, but
not necessarily in the same sequence shown here. Questions: Do you
think the annual weeds (left) would continue to thrive in the
mature forest (right)? Why or why not?
Slide 61
Some Ecosystems Do Not Have to Start from Scratch: Secondary
Succession (2) Primary and secondary succession Tend to increase
biodiversity Increase species richness and interactions among
species Are accompanied by succession of faunal species Primary and
secondary succession can be interrupted by Fires Hurricanes
Clear-cutting of forests Plowing of grasslands Invasion by
nonnative species
Slide 62
Science Focus: How Do Species Replace One Another in Ecological
Succession? Facilitation is when one set of species makes an area
suitable for species with different niche requirements. Inhibition
is when some early species hinder the establishment and growth of
other species. Some plants produce allopathic compounds. Tolerance
may be observed when late successional plants are largely
unaffected by plants at earlier stages because they are not in
direct competition with them for key resources. For example, shade
tolerant trees.
Slide 63
Succession Doesnt Follow a Predictable Path Traditional view
Balance of nature and a climax community Current view Ever-changing
mosaic of patches of vegetation Mature late-successional ecosystems
State of continual disturbance and change
Slide 64
Living Systems Are Sustained through Constant Change Inertia,
or persistence Ability of a living system to survive moderate
disturbances Resilience Ability of a living system to be restored
through secondary succession after a moderate disturbance Tipping
point