Transcript Chthamalus

Ecology Part 2
Density-dependent-limiting factors (intra-specific) regulate population
growth because increasing population size reduces resource availability
and resource limitations ultimately limit population growth.
Intra-specific competition: the reliance of two or more individuals of the
same species on the same limited resource. Competition between
individuals of the same species increases as population size increases and
r or (b-d) is reduced in proportion to the intensity of the competition.
-Population growth declines because death rate increases, birth rate
decreases or both.
-Reduction in food may limit reproductive output. e.g. eggs or seeds
e.g. The
of seeds
with increase sowing density
The average
clutch size of
a sparrow
decreases with
increase in
-Territoriality is a behavioral mechanism that may reduce intraspecfic
competition since each individual protects its own area.
-Health and survivorship decreases as crowding results in smaller less
robust individuals.
-Predators take a greater percentage of prey, when prey population is
high. (density-dependent)
It can be concluded from this graph that
A) the population of plantains are increasing
B) an increase in the density of plantain plants
decreases the individual seed output.
C) Plantain seeds do not germinate when crowded
D) The more plantains planted, the more seeds that
This plant self regulates its
population by producing fewer seeds
when there are more mature plantains
in a given area.
Intrinsic factors may also play a role in limiting populations
-High densities may cause stress syndrome resulting in changes
hormones that delay sexual maturation, inhibiting reproduction
-High densities can also suppress the immune system with stress
-High densities can
reduce birth rates and
increase death rates. e.g.
The percentage of flour
beetles (Tribolium
confusum) surviving
from egg to adult
decrease at moderate to
high populations
densities, reducing the
adults in the next
It is possible for
populations to be
regulated by both
density-dependent and
density independent
Population may display short-term fluctuations due to densityindependent factors.
The population Dungeness Crab fluctuates due to densitydependent factors e.g. intra-specific competition and cannibalism
and density-independent factors e.g. changes in water temperature
due to ocean currents.
The Bobwhite quail's population fluctuates
with the depth of the snow. If the snow is
very deep, then many quail die. During years
that the snow depth is shallow, the fecundity
of these birds is related to their population
density. The population of these birds is
regulated by
A) density-independent factors
B) density-dependent factors
C) both density-dependent and densityindependent factors
D) inter-specific competition
In this example the population of birds is
controlled by the weather (densityindependent factor) and their fecundity
related to their population density
(density-dependent factor).
e.g.Bobwhite quail (southern Wisconsin)
survival varies with the depth of snow cover
(density-independent factor), but if the snow
depth is shallow then factors like reduction in
fecundity due to limited resources (densitydependent factor) regulates the population.
Together these interact to keep the population
Some populations show regular fluctuations in density in a cyclic
-Small herbivores (lemmings) 3-5 year
-Large herbivores (snowshoe hares)9-11 year cycle
Hypotheses for fluctuations
-Stress from high densities may alter hormone balance and
reduce fertility or may cause physiological changes
-High density may cause changes in the immune system,
Oscillation in
the population
of the hare
changes in the
lynx density.
This was once
considered to
be interrelated.
However, the hare shows such oscillations on
islands where the lynx is absent. The lynx
population oscillation may be the result of
hare population but not the other way around.
The emigration of a
species to reduce
populations can be
caused by crowding
which can cause
physiological changes.
e.g. Aphid population is mostly wingless
females, when the population increases, winged
females appear. Locusts when crowded will
grow longer wings, increase fat content, become
darker and emigrate very readily.
Generalizations-Populations can be K-selected
(equilibrium populations) or r-selected (opportunistic
-Maturation time
growth curve
-Death rate in young high
-Investment of
time in offspring
- # of offspring
per reductive episode
# reproductions
early in
late in
per lifetime
-Timing of first
Which of the following is considered
to be a characteristic of Kstrategists (K-selected)?
A) No investment of parental time
B) Reproduce later in life
C) Many offspring per episode
D) High mortality among offspring
A r-strategist is one that usually has
boom-bust growth pattern, many
offspring and many offspring per
episode, short life span,and lives in
unstable areas, whereas a k-strategist
usually exhibit a logistics curve growth
pattern, fewer offspring with fewer
per episode, a longer lifespan and lives
in more stable areas.
Which of the following is
considered to be a characteristic of
r-strategists (r-selected)?
A) long time to mature
B) few reproductive episodes
C) many offspring per reproductive
D) long life span
A r-strategist is one that usually has
boom-bust growth pattern, many
offspring and many offspring per
episode, short life span,and lives in
unstable areas, whereas a k-strategist
usually exhibit a logistics curve growth
pattern, fewer offspring with fewer
per episode, a longer lifespan and lives
in more stable areas.
Most insects are r-selected
species but honeybees have
a low r-max, producing
only "one" offspring a year
(queen) and invest in it
heavily to assure its
success. The progeny is a
queen and half of the
colony. Each worker
gorges itself on honey to sustain the new colony and
make honeycomb.
Interspecific interaction can also act as a
density-dependent limitation. Predation and
parasitism relationships can regulate
Predator-kills and eats the prey
Parasite-live on or in their hosts deriving
nutrients and energy. If the parasite kills the
host, then it is called a parasitoid.
Usually the predator and parasite population
fluctuates in direct proportion to changes in
the density of the prey.
Mites prey on Mites
The predator population mirrors the population of the prey with a lag
As the prey numbers increase, there is more food available for the
predator. So there will be a corresponding in increase in the predator.
This reduces the number of prey available with less food available for
the predator, there is a corresponding decrease in predator population.
Herbivory is also considered a type of predation. The interactions of
the herbivore and the plant can be complex.
e.g. Passion flower vines produce toxic chemical that help protect
leaves from herbivorous insects.
A counter adaptation has evolved in the butterfly, Heliconious: Its larvae
can feed on the leaves because they have digestive enzymes the break
down the toxic chemicals.
The females of these butterflies avoid laying eggs on passion flowers
leaves that already carry bright yellow egg clusters reducing intraspecific
The leaves of the passion flower have responded by growing yellow
nectaries that resemble eggs. The butterflies avoid laying eggs on these
leaves. These nectaries also attract ants and other insects that prey on
butterfly eggs.
Which of the following is a logical conclusion based on
the graph above?
A) The population of the prey is greater than that of
C) A decrease in the predator results in a decrease
of the prey
B) There is no lag time between increases in both the
predator and prey
D) An increase in the population of the prey, results
in an increase in the population of the predator
As can be seen from the graph, the
population of the prey is greater than the
population of predator. (note the scales
on the axes)
There are times when the relationship can be mutualistic (mutualism).
e.g. Ants live in acacia trees. The ants harvest the trees' nectar and
leaves, and they also burrow into the thorns and stems to make their
nests. The acacia trees benefit by fact that the ants keep the trees
relatively free from plant-eating insects and attack any mammals that eat
the tree. The ants also prevent vines from growing on the trees. The
acacia provides hollow thorns for the ants to live in and Beltian bodies
found at the tips of the leaves. These Beltian bodies provide a source of
protein for the ants.
What is the best description of the
relationship between ants and acacia
A) commensalism
B) Antagonism
C) Mutualism
D) enslavement
This is a case of mutualism as the acacia
tree provides food and habitat for the
ants and the ants protect the tree from
other herbivores.
Interspecific competition can be a
density-dependent limitation. The more
two species attempt to use the same
limited resource, the greater the
A niche refers to the functional role and position of an organism in an
ecosystem. Every aspect of an organism's existence helps define that
organism's niche. A niche, theoretically, can be quantified by graphing
two or more resources. For instance with the birds above, the density of
the branches for nesting, versus, temperature tolerance, versus food size.
Where these intersect would define (Hutchinson, G. E., 1957) the
hypervolume of the niche. Many more factors could be added to the
graph, giving more multidimensional enclosed space for the species.
When 2 species are competing for the same limited resource their
niche's are said to overlap. (some argue that no two species can occupy
the exact same niche)
The more similar two niches are, the more likely that both species will
compete for at least one limited resource. There is a limit on the
amount of niche overlap compatible with coexistence. Competition for
one most limited resource therefore usually leads to one or two of four
possible outcomes
1. One species will become extinct.
2. One species may become superior in some regions and the second in
other regions. Sympatry will disappear.
3. One species may be superior under normal conditions but at a
strong disadvantage under periodic crises, which will reduce the
population size of the superior species. Competition will then begin
anew as long as generations overlap and the periodic crises are
frequent enough to prevent the extinction of the inferior species.
4. Given enough time and slight differences in niche, selection may
act to produce character displacement, which reduces competition.
e.g. Paramecium cultures of 2 different species demonstrate #1. The
graphs shows the population growth of P. aurelia and P. caudatum by
themselves in a culture. They both exhibit typical logistics curves,
but when both are put together in a culture, P. aurelia outcompetes P.
caudatum. The growth of P. caudatum actually decreases.
The more that two niches overlap,
A) the more there is a decrease in the
amount of space available for the
B) the greater the competition.
C) the more offspring each species will
D) The more there is a decrease in the
death rate due to altruistic behavior.
The greater the niche overlap, the
greater the competition between two
species as they have more factors in
e.g.#2 Joseph Connell carried out studies using barnacles. He cleared
a rocky area and observed repopulation patterns of 2 species.
Semibalanus by itself lived in the lower regions of the tidal zone. It
can not survive the periodic drying out in the upper part of the tidal
zone. When Chthamalus lived by itself it could exploit both the upper
and lower tidal zones however when both species were living
together, whenever the Chthamalus ventured in the lower tidal zone
of the Semibalanus, it was crushed by the Semibalanus. So that being
the case the Chthamalus restricted itself to the upper tidal zone and
the Semibalanus was found in the lower tidal zone.
Which of the following is NOT a result
of two species that have considerable
niche overlap?
A) One species may go extinct.
B) One species may migrate to another
C) The two species may fuse and
become one species.
D) There may be character
This leads to the concept of a fundamental niche vs. a realized niche.
A fundamental niche is the full environmental range that a species
can occupy if there is no direct competition. A realized niche is a
niche that is narrowed from the fundamental niche due to
Competitive exclusion principle- No two species can occupy exactly
the same niche at the same time
Balanus can only live in low tide regions, but Chthamalus can
in both the high and low tide region. When both live in the
same area, Chthamalus lives only in the high tide region.
Which of the following is a logical conclusion?
A) The realized niche of Chthamalus is equal to its
fundamental niche
C) The realized niche of Balanus is greater than its
fundamental niche
B) The realized niche of Chthamalus is greater than its
fundamental niche
D) The fundamental niche of Chthamalus is greater than its
realized niche
The diagram shows that the
fundamental niche of the Chthamalus is
greater than its realized niche. This is
due to the competition present from
Balanus barnacle which reduces the
niche of the Chthamalus.
Communities where competition occurs between species are
characterized by resource partitioning, meaning that every species uses
a different aspect of the resource.
Three different species of warbler occupies the same spruce tree but they
are found in different areas of the tree.
Social organization often plays an important
role in limiting the size of populations
Sociality carries the cost of increased competition and
the benefit of increased food supply through cooperative
hunting, cooperative defense of food territory against
predators and sharing of information about food
Dominance pays an important role in access to
resources, particularly resources critical to breeding.
Male-contest sexual selection has a profound effect on
gene frequency, since certain phenotype are more likely
to succeed than others
Natural Selection has a profound effect on gene frequency, since
certain phenotype are more likely to succeed than others. By
hunting together, these African wild dogs can capture a much larger
prey (wildebeest) than an individual could take on its own.
These bees cooperate to regulate the internal temperature of
the hive. They fan air out of the hive entrance, drawing
cooler air in else-where. When the internal temperature is
even higher, bee collect water and spread it on the comb
then fan it to cool the hive evaporatively.
Symbiosis are two organisms living and interacting together.
1. Mutualism-Both species benefit .
2. Commensalism-One species benefits and the other is
neither harmed or benefits.
3. Parasitism-One species benefits and the other is harmed.
4. Enslavement-One species controls the reproduction and
destination of another for its own benefit.
Which of the following states-No two
species can occupy exactly the same
niche at the same time?
A) Mutualism
B) Natural selection
C) Competitive Exclusion Principle
D) Commensalism
Competitive exclusion principle states
that no two species can occupy exactly
the same niche at the same time.
The yellow-billed oxpecker are birds
that remove parasites from large
herbivores such as rhinoceroses. The
term that is most descriptive of this
relationship is
A) symbiosis
B) Commensalism
C) Parasitism
D) Enslavement
E) mutualism
Both organisms are benefitting from
the relationship, so the most
descriptive term is mutualism.
Symbiosis is a broader term
encompassing the other terms.
Forming communities from populations
The species of a community interact with each other and
with the physical environment.
The biotic community they form can be considered a unit of
life, with its own characteristic structure and functional
Species diversity and complexity of interaction influence
community stability.
-A simple community may respond more violently to a
disturbance but often recovers quickly.
-The complex community may sometimes respond less
dramatically but may continue to show effects over a longer
-A diverse physical environment seems to favor community
-The number of species in a particular area varies.
-The rule of thumb, the closer the environment is to the
equator, the greater the species diversity.
The relationship between a tapeworm
and a dog it lives in is best described
A) Symbiosis
B) Mutualism
C) parasitism.
D) commensalism
E) enslavement
The tapeworm benefits from the
nutrition provided by the gut of the
dog. The dog is weakened by the
presence of the tapeworm