Download Prey is a term used to describe animals that are hunted and killed by

COEVOLUTION
Many of the subjects on midterm II relate to Coevolution – Symbiosis, predation strategies, prey
survival strategies.
Natural selection not only refers to genetic traits and physical appearance or abilities, but it also
refers to behaviors. If the behavior is beneficial for that species, it is highly likely that behavior
will persist (or continue) in future generations. The abundance of some genetic changes within
the gene pool can be reduced by natural selection (selected against), while other "more
favorable" mutations may accumulate and result in adaptive changes (selected for). As a result
of natural selection, beneficial strategies, or traits, persist in a population because such
characteristics make the individuals that possess them well suited to thrive and reproduce.
Genetic traits or behaviors that make the individuals that possess them poorly- suited to their
environment tend to disappear in a population.
Predators and prey are in a constant battle to gain an advantage that will help them survive.
Whenever a predator develops an advantage that helps them acquire prey, there is selective
pressure on the prey to adapt and find a way to avoid this new method of predation. The
organisms that most effectively adapt to and avoid predation will survive and reproduce. It
works in the opposite direction too. When prey organisms develop an effective defense against
predation, predators must adapt to the change and find a way around the defense, or find a
new organism to prey on. Predators that don't adapt and can't capture prey will starve to
death. The end result is that predators and prey evolve in response to interactions with each
other. These tight evolutionary relationships can result in coevolution, which is when two
species evolve in a coordinated fashion by adapting to changes in each other.
SYMBIOSIS
Symbiosis results from coevolution of Beneficial behaviors. Symbiosis is an example of coevolution - sometimes different species will evolve together creating long-standing relationships
that persists over many generations. In symbiosis, individuals of one species usually live in or on
or around the individuals of another species. At least one of the species—and sometimes
both—uses its partner’s resources. The partners of a symbiotic relationship, may benefit from,
be unaffected by, or be harmed by the relationship. Each of these types of symbiosis have
special manes.
There are 3 types of symbiotic relationship
1. Mutualism Both species benefit
2. Commensalism
One species benefits, but the other is not helped or harmed
3. Parasitism
One species benefits, but the other is harmed
MUTUALISTIC SYMBIOTIC RELATIONSHIPS
EXAMPLES – Sea Anemone and the Clown Fish
- SEA ANEMONES
 Are predators that attach themselves to rocks or coral
 They are immobile
 Eats fish by stinging it with its tentacles as it swims by
 These tentacles will shoot out a long poisonous thread.
 The toxins in this thread paralyze the prey.
- CLOWNFISH
 They are one of the only species that can survive the deadly sting of the Sea
Anemone.
 By making the anemone their home, clownfish become immune to its sting.
These fish will gently touch every part of their bodies to the anemone’s tentacles
until it no longer affects them. A layer of mucus then forms on the clownfish’s
body to prevent it from getting stung again.
- IN THE MUTUALISTIC SYMBIOTIC RELATIONSHIP BETWEEN THE SEA ANEMONE AND THE
CLOWNFISH…
 A sea anemone makes an ideal home for a clownfish.
 The Sea anemone’s poisonous tentacles provide protection to the clownfish by
warding off predators.
 The clownfish makes its meals from the anemone’s leftovers and feces!
 A clownfish can help an anemone catch its prey by luring other fish toward over
so that the anemone can catch them.
 Clownfish also eat any dead tentacles keeping the anemone and the area around
it clean.
PARASITISM –
The Tongue-Eating Louse (Cymothoa exigua) -
is a parasite that replaces the tongue of its
victims.
 The tiny, or tongue eating louse, enters its
victim through the gills.
 Once inside, the female latches onto the
base of the fish’s tongue, while the male
attaches behind her or on the gills.
 Through her
front claws, she
sucks the fish’s
blood, which
causes the
tongue to die
and drop off.
 She will then
re-attach, this
time to the tongue stub, effectively becoming its replacement.
 Each infested fish almost always has more than one mating pair in its
mouth; usually four to six. Courtesy of Matthew Gilligan
 After one of the males mates with the female, she gives birth to a brood
of live male parasites.
ZOMBIE ANTS – FUNGI PARASITIC RELATIONSHIP
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Zombie ants are ants
that have been
infected by parasitic
fungus known to
manipulate the brains
of ants turning them
into ‘slaves’.
The fungus is
recognizes the brains
of specific ant species,
and releases its mindcontrolling chemical
cocktail only when in
its preferred host.
"Behavioral
manipulation” is very
rare in nature and it
only occurs when
there's a very close
coevolution between
pathogen and host.
Ophiocordyceps — so-called zombie ant fungi — need ants to complete their life cycle.
The fungus reproduction strategy is completely dependent on the infection and hostile takeover
of the ant!
The infection occurs when the ant is exposed to fungal spores while foraging. The fungus infects
the insect and quickly spreads throughout its body.
Once inside the host ant, the fungus in the ant's head release chemicals that CONTROL the
insect's central nervous system.
The fungus forces the ant to climb up vegetation and clamp down onto a leaf or twig before
killing its hapless drone.
It then grows a spore-releasing stalk out of the back of the victim's head to infect more ants on
the ground below.
LIFE CYCLE OF A BOTFLY PARASITE
Karl Weatherly/Photodisc/Getty Images
Botflies have a unique way of reproducing.
They require a human or mammal host in
order to complete their life cycle.

Adult female botflies lay their
eggs on blood-sucking insects, such as
mosquitoes or tick.
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When the blood-sucking insect
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lands on a human, it drops the eggs on its victim.
The warm body of the human triggers the bot fly to hatch from its egg.
The larvae (bot fly babies) may travel down hair follicles or through bite wounds and burrow into the
mammal's skin.
The larvae growing in the skin drop from the mammal host after a period of 30 days.
Predator/Prey Interactions
A predator is an animal that hunts and kills other animals for food.
Prey is a term used to describe animals that are hunted and killed by predators. We can also think of
herbivores as predators of plants and plants as prey of herbivores. Predation is a strong, selective pressure
that drives prey organisms to find ways to avoid being eaten.
Prey organisms that are difficult to find, catch or consume are the ones that will survive and reproduce.
The result is that over evolutionary time, prey organisms have developed a stunning array of strategies to
avoid being eaten.
Chemical defenses are common among animal prey. The South American poison arrow frog has poison
glands in its skin.
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Some insects developed the ability to tolerate milkweed toxins. As a result, they can eat
milkweeds without being poisoned, and they accumulate the toxins in their tissues, making themselves
toxic to predators
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Camouflage - Some animals blend into their surroundings to hide from predators. Camouflage,
also called cryptic coloration, is a defense or tactic that organisms use to disguise their
appearance, usually to blend in with their surroundings. Organisms use camouflage to mask
their location, identity, and movement. This allows prey to avoid predators, and for predators to
sneak up on prey•
The animal’s behavior often enhances such cryptic coloration.
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Plants cannot escape predators by fleeing, but they possess adaptations that protect them from
being eaten. The presence of spines, thorns, tough leathery leaves, or even thick wax on leaves
discourages foraging herbivores from grazing. Other plants produce an array of protective chemicals
that are unpalatable or even toxic to herbivores.
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Safety in numbers - Some animals live in groups—a herd of antelope, colony of honeybees,
school of anchovies, or flock of pigeons. This social behavior decreases the likelihood of a predator
catching one of them unaware; the group has many eyes, ears, and noses watching, listening, and
smelling for predators.
Some defensive strategies are pretty obvious, and top among the list of obvious strategies is
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Running away. Gazelle, deer, small mammals and lizards often rely on their speed
and quickness to escape predators, and many birds rely on flight as their primary
defensive strategy.
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Fighting back – defense - Some organisms, like armadillos, tortoises, porcupines and
thorny plants, use armor, quills and thorns to defend themselves against predators.
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Hiding – camouflage
PREY ADAPTATIONS
A. Camouflage
Squids, octopuses, and cuttlefishes are among the few animals in the world that can
change the color of their skin in the blink of an eye. These cephalopods—a group of
mollusks with arms attached to their heads—can change their skin tone to match their
surroundings, rendering them nearly invisible, or alternatively give themselves a pattern
that makes them stand out.
Many thousands of color-changing cells called chromatophores just below the surface
of the skin are responsible for these remarkable transformations. The center of each
chromatophore contains an elastic sac full of pigment, rather like a tiny balloon, which
may be colored black, brown, orange, red or yellow. If you squeezed a dye-filled
balloon, the color would be pushed to the top, stretching out the surface and making the
color appear brighter—and this is the same way chromatophores work. A complex array
of nerves and muscles controls whether the sac is expanded or contracted and, when
the sac expands, the color is more visible. Besides chromatophores, some cephalopods
also have iridophores and leucophores. Iridophores have stacks of reflecting plates that
create iridescent greens, blues, silvers and golds, while leucophores mirror back the
colors of the environment, making the animal less conspicuous.
The most obvious reason such a soft-bodied animal would change color is to hide from
predators—and octopuses are very
good at this. They can change not only
their coloring, but also the texture of
their skin to match rocks, corals and
other items nearby. They do this
by controlling the size of projections on
their skin (called papillae), creating
textures ranging from small bumps to
tall spikes. The result is a disguise that
makes them nearly invisible; can you
even see the octopus in the video
above? Color changing is just one tool
in an octopus’s arsenal of defenses,
however; it can also spray ink, and
make a quick escape through any hole
it can get its hidden bony beak
through.
http://ocean.si.edu/ocean-news/howoctopuses-and-squids-change-color
The Mimic Octopus (Thaumoctopus mimicus) has a unique way of camouflaging. Rather than
blending in with the seafloor, it changes its skin color and how it moves its tentacles to take
on the shape of other sea creatures. It has been known to impersonate more than 15 different
marine species, including flounders, lionfish, and sea snakes.
WOLVERINE FROG (HAIRY FROG)
The hairy frog actively breaks its own bones to produce claws that puncture their way out of the frog’s
toe pads, probably when it is threatened. When the
frog does not feel threatened, it only has claws on
the hind feet only, are nestled inside a mass of
connective tissue. A chunk of collagen forms a bond
between the claw’s sharp point and a small piece of
bone at the tip of the frog’s toe. The other end of
the claw is connected to a muscle. When the animal
is attacked, it contracts this muscle, which pulls the
claw downwards. The sharp point then breaks away
from the bony tip and cuts through the toe pad,
emerging on the underside.
Horned lizards
Horned lizards are able to
squirt a stream of blood
from the corners of their
eyes as a defense against
predators. This blood
squirt can reach a
distance of up to 5 feet!
They do this by restricting
the blood flow leaving the
head, thereby increasing
blood pressure and
rupturing tiny vessels
around the eyelids. This
not only confuses
predators, but also the blood tastes foul to canine and feline predators. It appears to have no effect
against predatory birds.
PREDATORS
The Gray Wolf
There used to be a large population of gray wolves in North America. This population dwindled by 1960
and the gray wolf was added to the Endangered Species List in 1974. This means that there were less
than 250 mature males in the gray wolf
population!
In 1995, the U.S. Fish and Wildlife Service
(FWS) relocated a small number of gray
wolves from Canada to Yellowstone
National Park in Wyoming. The population
thrived and has increased to several
hundred individuals in the Yellowstone
area.
One of the reasons ecologists thought that
Yellowstone would be a good place for the
gray wolf, is because Yellowstone was being
overrun by Elk!
Once the wolves were relocated
to Yellowstone, the wolves had
plenty of elk to eat.
Also, the wolf packs helped to
reduce elk population. This was a
great benefit to the ecosystem,
because when elk numbers are
not managed properly, they
overgraze their habitat (eat too
many of the plants), and
thousands starve during hard
winters.
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More wolves led to less elk. Less elk led to more plants. More plants led to more herbivores
(plant-eaters). More herbivores led to more small predators.
Conservation Efforts Saved the Gray Wolf from Possible Extinction. Today there are more than 5,500
wolves in the continental United States. The gray wolf has been taken off of the Endangered Species List.
The wolf population is carefully monitored and guarded in some states to ensure the wolf population
continues to thrive.
Niches and Competition
The role that an organism plays in nature is called its ecological niche. Organisms carve out their
own unique niches that they specialize in, and it is extremely unusual to find two organisms with the
same exact niche
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Every organism is likely to face competition from other species. The most direct form of
competition comes from those organisms that try to make a living in almost the exact same
way. This direct form of competition for an ecological niche is called interspecific
competition.
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The principle that allows one organism to completely exclude another through competition
is competitive exclusion.
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An ideal niche that would exist in the absence of competition from other species is called a
species' fundamental niche.
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However, most organisms are generally forced to play a more limited role thanks to
competition. The actual niche that a species fills in the face of interspecific competition is
called its realized niche.
Competition may make things difficult for organisms, but it is also a major driving
force in evolution. Many organisms get better at what they do because other species forced them to.
For example, a gazelle evolved its speed and maneuverability not because it has to chase down
plants, but because it gets chased down by lions and other predators. Many species on Earth owe a
great deal of their characteristics and lifestyle to competition from other species.
The density of a population within an ecosystem is determined by a
number of factors, including the amount of habitat, food, water and shelter that are available, as well
as the rates of predation, disease and reproduction that are occurring within the population.
Some of these factors become more limiting as the population increases. These factors are
called density-dependent factors. Some examples of density-dependent factors are the amounts
of habitat, food, water and shelter that are available. In most species, reproductive rate is also
density-dependent. This has been experimentally proven for many species.
Some population-limiting factors are not affected by population size. These are called densityindependent factors. Some examples of density-independent factors are climate changes.
Ecosystems contains a rich variety of animal and plant life (biotic factors = living things) as well
as abiotic factors, or nonliving things - environmental factors like climate, elevation, soil type and
sources of water.
Every type of organism in an ecosystem has a niche, or a specific role that it plays within the
ecosystem. Other factors, like habitat, the types of animal-animal or animal-environment interactions
also define a NICHE.
The density of a population within an ecosystem is determined by a number of factors. Some
are density-dependent factors, or population-limiting factors that become more limiting as the
population increases. Some examples of density-dependent factors are reproductive rate and the
amounts of habitat, food, water and shelter that are available. There are also density-independent
factors, or population-limiting factors that are not affected by population size. Some examples of
density-independent factors are climate change.
A.
What Is an Ecological Niche?
An ecological niche is the role and position a species has in its environment; how it meets its needs
for food and shelter, how it survives, and how it reproduces. A species' niche includes all of its
interactions with the biotic and abiotic factors of its environment. Biotic factors are living things,
while abiotic factors are nonliving things. It is advantageous for a species to occupy a unique niche
in an ecosystem because it reduces the amount of competition for resources that species will
encounter.
B. Individuals' Ecological Niches
Every living thing on Earth has a role to play in its environment. In fact, you are filling a niche right
now as you read this lesson. Whether you are a student, have a full time job, or are a mother or
father, these are parts of the niche you fill. Your niche also includes where and how you obtain food
and all of the things you do in order to survive.
If you closely look at a typical habitat in the environment, you will see many organisms living and
working together, fulfilling their ecological niches. For example, imagine you are walking through
the forest where there are leaves scattered on the ground and an old rotting log sitting on the forest
floor. If you look closely, you could probably find earthworms just under the soil feeding on decaying
organic matter. There could also be centipedes eating small beetles and other organisms as well as
a colony of ants that work and feed on dead insects. You may even find a couple of millipedes
strolling around feeding on decaying leaves.
In this small section of the vast forest, all of these organisms are filling an individual ecological niche.
To some degree, their niches may overlap, but if you look into all aspects of their lives, including
where they live, how they survive, and how they reproduce, you will see that they are each truly
individual niches. You could think of each ecological niche as parts of a puzzle that go together to
make the environment successful.
C. Importance of Unique Niches
It is important to note that an organism has a greater chance for a successful life if their ecological
niche is unique. Consider the mighty polar bears that inhabit arctic regions of the planet. While most
organisms, including humans, would find the idea of living an isolated life in the vast cold tundra very
unappealing, it works quite well for polar bears. They fill a unique ecological niche. Due to the harsh
environment, they face very little competition. They are able to hunt and fish in relative peace and
are an important part of their ecosystem.
As you can see, an ecological niche is the way an organism fits into its environment. Every living
thing has its own niche and is a crucial part in providing stability to its ecosystem. After reading this
lesson, maybe you can sit back and think about your own ecological niche and the many roles you
play as you live your life.
A. What Is Intraspecific Competition?
Imagine two oak trees growing next to each other. While it may not seem like it, these two trees are
in a constant competition. They both need sunlight, water, and nutrients, and because they are
growing so near to each other, they have to fight over those same resources for survival. This
competition between members of the same species is called intraspecific competition. This is
different from interspecific competition, which is the competition for resources between individuals
of different species.
In intraspecific competition, members of the same species may compete for food, shelter, water,
and mates. This competition provides a type of control on the population size. If the population
grows but the amount of resources stays the same, the resources become limiting. This means that
the population can no longer increase in size.
B. Examples of Intraspecific Competition
Intraspecific competition can be silent, as with the trees mentioned above, or it can be observed in a
variety of ways.
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Bird songs sound very pretty to us, but they are often signals to other birds that they are not
welcome in that area. Bird songs are often used to defend territories that contain breeding
areas, shelter, and food.
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Other territory signaling may be in the form of marking. Many wild canine and feline species
mark their territories with scent. This tells other members of the same species in that area
that they have claimed the territory and all of the resources within it.
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Ornamental features are a form of intraspecific competition. Intraspecific competition for
mates can be quite dramatically observed through ornamental features. For example, male
peacocks display beautiful plumage to attract females. Male deer fight each other for mates
with their large antlers - the larger set of antlers usually wins this competition.
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Resources are limited, and this forces members of the same species to compete for them,
which is called intraspecific competition. The resources may include food, shelter, water,
and mates. The struggle may be visible or silent, but this limited amount of resources is an
important factor in controlling population size.
What happens when two similar species that consume the same resources occupy the same space?
Interspecific competition, that's what! Watch our video lesson to learn about the outcomes of this
ecological battle.
C. Interspecific
Exclusion
competition and Competitive
When two species are subject to competitive exclusion, or when one species outcompetes another
in a part of its habitat so well that the second species is excluded from that part.
There are Three possible outcomes of strong interspecific
competition
1. Competitive exclusion is one possible outcome of strong interspecific competition.
2. Local extinction, which is when one species is outcompeted by another so effectively
throughout the entire local habitat, that it becomes extinct in that area. For instance, in our
example of the bird species, what if species A did not have an advantage at higher elevations,
and instead, species B had an advantage at all elevations? In this situation, species B would
likely outcompete species A to extinction in that local area.
3. Niche differentiation – this is when similar species with similar niches become specialists
in specific areas and create more than one specific niche, which allows both species to
coexist.
You see, most species do not actually use all of the resources they are potentially capable of using.
So, we can define a theoretical or fundamental niche for each species, which contains all of the
resources that a population is theoretically capable of using.
However, if we want to look at the actual resources a population uses, then we can look at that
population's realized niche, which contains only the resources that a population actually uses.
When niche differentiation occurs, each different species becomes specialized to best exploit a
small subset of resources within the fundamental niche and creates a much smaller realized niche.
In this way, several different species that share a common fundamental niche can coexist together.
Let's review.
Interspecific competition is when two or more species in a community are competing for
resources. Limited interspecific competition for resources often occurs between multiple species in
the same ecosystem. However, when two species are so similar that interspecific competition for
limiting resources is high, these two species are unlikely to be able to coexist - presumably because
this type of intense competition is unlikely to be balanced and therefore it is also unlikely to be
sustainable.
three potential outcomes can result from strong interspecific competition: competitive
exclusion, local extinction and niche differentiation.
Competitive exclusion occurs when one species outcompetes another in a part of its habitat so
well that the second species is excluded from that part.
Local extinction is a more severe outcome and occurs when one species is outcompeted by
another so effectively throughout the entire local habitat, that it becomes extinct in that area.
Yet, another possible outcome to strong interspecific competition is niche differentiation, or
when similar species with similar niches become specialists in specific areas and create more than
one specific niche, which allows both species to coexist.
Herbivores
Animals that have a diet composed entirely of plants are known as herbivores.
In nature, there are many different types of diets for animals. Plants are found in every habitat, and
often come in a wide variety of shapes, sizes, and colors. Due to their abundance, plants are the
most readily available source of food on Earth.
Some herbivores are selective and only consume part of the plant, such as the fruit, leaves, nectar,
seeds, sap, roots, or bark.
Other herbivores are less selective and consume multiple plant components. Commonly recognized
herbivores include deer, rabbits, cows, sheep, goats, elephants, giraffes, horses, and pandas.
D. Physical Adaptations of Herbivores
Herbivores have developed several physical adaptations that better enable them to survive
and thrive as plant eaters.
One major physical adaptation is the unique design of the herbivore's head, including its
eyes, ears, and teeth.
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SPECIALIZED EYES - Most herbivores have eyes located on the side of their head.
This adaptation makes it possible for herbivores to have a wider field of vision. Due
to their eye placement, these animals can see almost all the way around their bodies
without moving their heads. -- Why would these animals want to have such a wide
field of vision? Many herbivores are prey for carnivores, meat-eating animals, and
their visual adaptation makes it possible for them to notice a predator before being
attacked, and, hopefully, escape unharmed.
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SPECIALIZED EARS - Due to their role in the food chain, the sequence of who eats
whom in an environment, herbivores have also developed well-designed ears to
avoid predation. The ears of many herbivores are large, which increases the volume
of the sounds they hear and makes it possible for herbivores to hear the otherwise
low volume noises of an approaching predator. With eyes on the sides of their heads
and large ears, herbivores increase their chances of avoiding predation and surviving
to graze another day.
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SPECIALIZED TEETH - Herbivores also have specially designed teeth for their diet
of plants. The average herbivore mouth is full of molars, which are flat and round
teeth. These teeth are designed to grind up plant materials into smaller pieces so
that the herbivore can more easily digest the material they consume.
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SPECIALIZED STOMACHE - Some herbivores have developed a unique digestive
system to process the large amounts of plant material they ingest. Several animal
species, such as cows and leaf-eating monkeys, have bacteria in their stomachs that
help digest plant materials. The bacteria break down the plant material into a more
easily digestible product for the herbivore. Without the bacteria, the herbivore would
not be able to effectively break down the plant material and would not gain any
energy from the food they consumed.
SOCIAL ADAPTATION - In addition to physical adaptations, some herbivores have also developed
behavioral adaptations to increase their survival. The most noticeable behavioral difference between
carnivores and herbivores is how social they are. Carnivores tend to travel and hunt alone, while
many herbivore species travel and eat in groups. This social behavior increases survival because
the members of the group watch each other's backs and can protect each other from predators.
Herbivory is a term used to describe critters that are vegetarians. More specifically, herbivory is
when animals eat plants or plant-like organisms, and a
Herbivore is a type of animal that eats plants or plant-like organisms. , herb means
'plant,'
Carnivores, on the other hand, are animals that eat meat carn means 'flesh,'
Omnivores are animals that eat plants and meat. omni means 'all' in Latin.
In biology, many of the vocabulary words originate from Latin or Greek root words. For exampleCan
you think of other words that have these roots? Herbicides are things that kill plants; chili con carne
is chili with flesh (meat), and if someone is omnipresent, they are 'always' present.
E. Adaptations for Herbivory
Eating plants requires special adaptations including different teeth, a different skull, and even a
different stomach!
F.
Teeth
Animals can have molars, premolars, canines, and incisors. The molars and premolars are in the
back, the canines are the fang-type teeth seen in carnivores, and the incisors are the front teeth.
Herbivores have flat molars and premolars to grind up plants. Some herbivores have a diastema, or
space between the back molars and front teeth, which is used to carry plant material. Herbivores
usually do not have canine teeth, and incisors may be absent as well. If they do have incisors, they
are used to break off plant material.
Look at this skull of a herbivore. Notice the flat molars and the space between the molars and the
front teeth. The incisors on the top are not present, and the eyes are on the side of the skull.
G. Skull
Animals that practice herbivory are often prey to carnivores. To minimize the chance of being eaten,
herbivores have eyes on the sides of their head allowing them to have a better view of what is
around them. Carnivores have eyes facing forward, which allows them to have improved depth
perception, improving their ability to catch prey.
H. Digestion
Eating and digesting plant material takes a lot of work, so animals that practice herbivory require a
special digestive system.
Ruminants are herbivores that have a rumen. A rumen is a large vat located between the
esophagus and stomach that houses microbes, such as bacteria, fungi, and protozoa. These
microbes actually breakdown the plant material and then the ruminant regurgitates, re-chews,
swallows, and the process continues until the plant-material is digested. If you have ever watched a
cow or moose, it is always chewing. That is because it is a ruminant! Ruminants are also known
as foregut fermentators. Animals with rumen include cows and deer.
Unlike ruminants, hindgut fermentators have a digestive system that is similar to humans, except
their large intestines are more complicated and larger. Like ruminants, hindgut fermentators depend
on assistance from microbes to digest plant-material; however, these microbes are housed in the
large intestine, and they do not have a rumen. Rodents, rabbits, and horses are examples of
herbivores that practice hindgut fermentation.
You may have noticed that fermentation was in the name of both types of digestion. The
word fermentation, in this case, refers to breaking down of plant material by microbes into
substances the animal can utilize.
I.
Examples
Animals that practice herbivory come in many shapes and sizes from enormous elephants to the
small chinchilla. Some are slow moving, like the sloth of South America, and some are fast, like the
quick-moving deer of North America. They are found in many animal families as well including
Bovidae (the buffalo, cows, and sheep), Equidae (the horses).
Herbivory is a verb and describes what herbivores do, which is eat plant material or plant-like
organisms. Herbivores have specific adaptations that allow them to digest plants, like molars made
for grinding and specialized microbes in their gut that allow them to break down the plants.
Herbivores are often prey for predatory animals, like wolves, tigers, and bears, so they have
adaptations that allow them to be aware of their surroundings, like eyes on the side of their head.
Herbivory can be found in many animal families including bovids (like cows and buffalo) and rodents
(like rabbits and chinchillas).
We have many ways by which to defend ourselves against enemies. Plants also have quite a few
ways in which they fight off herbivores and pathogens, some of which this lesson discusses.
A. Attacks on Plants
Poor plants! Plants get eaten by caterpillars, by cows, by people, and everything in between. They
are constantly infected with all sorts of microorganisms, like viruses. Plants just can't catch a break
and are picked on by everyone because they make up the foundation of the food chain.
Of course, they don't just take things lying down, or standing up, as the case may be. Plants have
defensive mechanisms against herbivores, plant-eaters, and pathogens, disease-causing agents,
which this lesson seeks to flush out.
B. Defenses against Herbivores
Some plant defenses against herbivores are really obvious, like physical defenses. This includes the
use of trichomes, fine outgrowths like hairs from the surface of a plant and, of course, thorns as
well.
Every rose has its thorn, just like many plants have their poison. No, not the band, but chemical
compounds that can either kill an animal that eats the plant or seriously harm the animal. Other
chemical substances that plants produce may not seriously harm or kill an herbivore but they make
the plant so distasteful that the herbivores just don't bother trying to eat it.
Some plant are even cleverer. They actually recruit animals to help fight off other animals. For
instance, if a caterpillar starts munching away on a plant, the plant may release a compound that
attracts parasitoid wasps. These wasps then inject their eggs into the caterpillar, the larvae (or baby
wasps) then eat the caterpillar from the inside out as they make their way out of the caterpillar. That
should teach caterpillars a lesson once and for all!
Chemicals released by damaged plants can also signal to nearby plants of the same species that
they need to beef up their defenses before they're attacked as well. For instance, lima bean plants
attacked by spider mites release signals to nearby healthy lima bean plants. These healthy plants
then release volatile chemicals of their own to attract another species of mite that kills off the spider
mites!
C. Defenses against Pathogens
Plants also need to defend themselves against pathogens like viruses, bacteria, and fungi. People
have skin that acts as a barrier against these same general types of organisms. Plants also have a
superficial layer that acts much like our skin for the same purpose. However, pathogens still make it
inside us and inside plants through various ways, thus a secondary line of defense must exist
against a pathogen.
In people, it's the immune system that attacks and kills off invading pathogens as a secondary line of
defense. In plants, the hypersensitive response and systemic acquired resistance are its secondary
line of defense.
The hypersensitive response is a defense mechanism utilized by plants that causes the cells and
tissues around the infection site to die off to prevent the spread of a pathogen. Basically, the cells
around the infection site release chemicals that kill off the pathogen, seal off the infected area, and
kill themselves off in the process. This way, the pathogen cannot use a living cell or tissue to
propagate its way throughout the entire plant.
It's like fighting fire with fire. If you burn off an area of forest, the wildfire can't use the wood there
anymore to spread anywhere else because everything is destroyed already! The hypersensitive
response is limited to only one specific area of the plant. And so, the plant needs a systemic, or
body-wide, response to deal with the potential for infection throughout the plant.
Before the cells that seal off an area in the hypersensitive response die, they release important
chemicals that travel throughout the plant. Once these chemicals reach other cells in the plant, they
activate signaling pathways that force these distant cells to produce molecules that protect the plant
against all sorts of pathogens for several days. This process is known as systemic acquired
resistance.
Think of it as a signal to beef up security for a few days in a city if there's a threat of terrorism.
Everything will be placed on high alert for a few days. The signal to beef up security is called
methylsalicylic acid. It is carried from the site of infection to other parts of the plant where it is
converted to salicylic acid, which then activates a signal transduction pathway that confers an
acquired resistance to pathogenic attack.
D. Lesson Summary
Pathogens are disease-causing agents like viruses and fungi, and herbivores are plant-eaters.
Plants have defenses against both of these threats.
Defense mechanisms range from trichomes, which are fine outgrowths like hairs from the surface of
a plant and thorns, to poisons that kill an animal, to chemical signals to attract other animals that kill
off a munching caterpillar.
When it comes to pathogens, plants use their epidermis, or skin-like layer as a primary defense
barrier against infection. If infected, the plant can mount a hypersensitive response, which is a
defense mechanism utilized by plants that causes the cells and tissues around the infection site to
die off to prevent the spread of a pathogen.
The cells that die off release a signal that eventually causes plant cells far away from the infected
area to beef up their defenses against a multitude of pathogens for several days in a process
called systemic acquired resistance.
A. A Look at Prey
You have likely seen this scenario on TV: a lion stalks an unsuspecting antelope, a chase ensues,
the lion catches the antelope and has a very large meal to eat. In this situation the lion is the
predator and the antelope is the prey. Predation is a biological interaction between predator and
prey, but it is not always as clear, or as dramatic, as in this example.
B. Types of Prey
There are many types of predation and prey, and the example of the lion hunting the antelope is
called carnivory. Predation can also occur as parasitism, in which the prey is a host that supports a
parasite, such as a virus. In this case, the prey may be harmed but not killed outright like the
antelope. When the prey is the same species as the predator, this is called cannibalism.
Plants can also be prey, and this is called herbivory. When a deer eats grass, the plant is the prey
and the animal the predator. Herbivory is interesting because it highlights how sometimes an
organism can be predator or prey depending on the situation. As a mouse is prey as it runs from an
attack by a hawk, but becomes predator as soon as it eats some tasty sunflower seeds.
Humans can also be both predator and prey. Without weapons, humans are very vulnerable to
carnivory by larger animals, such as alligators and lions. However, when they have weapons, such
as guns, traps, and bows and arrows, they quickly turn the tables and can make the predator the
prey.
Additionally, organisms do not have to be larger than their prey to be successful predators.
Venomous snakes are able to take advantage of a variety of large prey items because an injection of
venom can be quite fatal.
C. Adaptations
Many species have developed adaptations to prevent being preyed upon. Some animals have
chemical defenses that help keep predators away, such as skunks. Getting sprayed with that awful
smell makes a predator weigh that choice very carefully.
Other organisms have developed physical characteristics that keep predators at bay. Porcupines
have painful quills all over their body that not only helps defend against a predation attack, but also
warns predators well ahead of time that it is very risky for them to even try.
Many animals are poisonous and have brightly colored bodies to indicate this. Poison dart frogs and
monarch butterflies both have very distinctive markings to warn predators that they are a very bad
prey choice because they will do great harm by eating them.
Mimicry is another way prey species can avoid predation, and this is when the prey has markings
on its body or acts in a way that mimics an unrelated species. The Io moth has markings on its
underwings that look like an owl's eyes. When it feels threatened it opens its wings and reveals
these markings, which startles the predator and allows the moth more time to escape.
D. Lesson Summary
Predation is a biological interaction between a predator and its prey. However, prey can quickly
become predator in the right circumstances. Prey are not always killed, but are usually harmed in
some way, and many organisms have adaptations that help them avoid predation, which reduces
their chances of becoming prey.