Download Relationships: Predation, Competition, Symbiosis

Relationships: Predation,
Competition, Symbiosis
Brian Blake
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Printed: September 10, 2013
AUTHOR
Brian Blake
www.ck12.org
C ONCEPT
Concept 1. Relationships: Predation, Competition, Symbiosis
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Relationships: Predation,
Competition, Symbiosis
Standard 1, Objective 3: Describe how interactions among organisms and their environment help
shape ecosystems.
Objective:
• Explain the different types of interactions among organisms including symbiosis, predator-prey, and competition.
Predation
FIGURE 1.1
Praying Mantis eating a grasshopper.
Who is the predator and who is the prey?
Can insects hunt for food? When you think of an animal hunting for its food, large animals such as lions may come
to mind. But many tiny animals also hunt for their food. For example, this praying mantis is eating a grasshopper.
To eat the grasshopper, the praying mantis first had to catch the grasshopper, which is a form of hunting.
Predation is another mechanism in which species interact with each other. Predation is when a predator organism
feeds on another living organism or organisms, known as prey. The predator always lowers the prey’s fitness. It
does this by keeping the prey from surviving, reproducing, or both. Predator-prey relationships are essential to
maintaining the balance of organisms in an ecosystem.
There are different types of predation, including:
• true predation.
• grazing.
• parasitism.
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True predation is when a predator kills and eats its prey. Some predators of this type, such as jaguars, kill large
prey. They tear it apart and chew it before eating it. Others, like bottlenose dolphins or snakes, may eat their prey
whole. In some cases, the prey dies in the mouth or the digestive system of the predator. Baleen whales, for example,
eat millions of plankton at once. The prey is digested afterward. True predators may hunt actively for prey, or they
may sit and wait for prey to get within striking distance.
FIGURE 1.2
This example of a true predator shows a
pair of lions actively hunting prey.
In grazing, the predator eats part of the prey but does not usually kill it. You may have seen cows grazing on grass.
The grass they eat grows back, so there is no real effect on the population. In the ocean, kelp (a type of seaweed)
can regrow after being eaten by fish.
Predators play an important role in an ecosystem. For example, if they did not exist, then a single species could
become dominant over others. Grazers on a grassland keep grass from growing out of control. There are species
that can have a large effect on the balance of organisms in an ecosystem. For example, if all of the wolves are
removed from a population, then the population of deer or rabbits may increase. If there are too many deer, then
they may decrease the amount of plants or grasses in the ecosystem. Decreased levels of producers may then have a
detrimental effect on the whole ecosystem.
SUMMARY
• Predation happens when a predator organism feeds on another living organism or organisms, known as prey.
EXTENSION
Use the resources below to answer the questions that follow.
Traces of Early Animal Life at Shape of Life http://shapeoflife.org/video/scientist/whitey-hagadorn-paleontologis
t-traces-early-animal-life (6:11)
1. What does the fossil record suggest about how predation affected the diversity of life? Can you think of a
reason, other than predation, for the pattern in the fossil record?
2. How many years were sessile organisms the dominant life form on Earth? What factors do you think contributed to the shift away from the dominance of sessile life forms?
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Concept 1. Relationships: Predation, Competition, Symbiosis
3. Is it possible for sessile life forms to be predators? How does this situation relate to your answer to question
2?
4. What sort of systems allow an organism to develop directed movement?
Dragonfly Larva Hunts Newt at Shape of Life http://shapeoflife.org/video/behavior/arthropods-dragonfly-larva-hun
ts-newt(2:06)
1. Notice the dragonfly larva’s movements. How deliberate do its movements appear to be?
2. Given that this is a young individual, what sort of behavior do you think this represents, innate or learned?
Explain your reasoning.
3. What predation-related attributes or adaptations do you see in the newt and the dragonfly larva?
4. What sort of predation occurs between the dragonfly larva and the newt?
REVIEW QUESTIONS:
1. What’s the difference between grazing and true predation?
2. What are some of the effects predation has on ecosystems and ecosystem dynamics?
Competition
FIGURE 1.3
Competition:
Two Kangaroos fighting.
Does this remind you of you and your
sibling fighting for the last cookie?
Does there have to be a winner? When animals compete, yes. Animals, or other organisms, will compete when both
want the same thing. One must "lose" so the winner can have the resource. But competition doesn’t necessarily
involve physical altercations.
Competition is a relationship between organisms that strive for the same resources in the same place. The resources
might be food, water, or space. There are two different types of competition:
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• Intraspecific competition occurs between members of the same species. For example, two male birds of the
same species might compete for mates in the same area. This type of competition is a basic factor in natural
selection. It leads to the evolution of better adaptations within a species.
• Interspecific competition occurs between members of different species. For example, predators of different
species might compete for the same prey.
Interspecific competition often leads to extinction. The species that is less well adapted may get fewer of the
resources that both species need. As a result, members of that species are less likely to survive, and the species
may go extinct.
Instead of extinction, interspecific competition may lead to greater specialization. Specialization occurs when
competing species evolve different adaptations. For example, they may evolve adaptations that allow them to use
different food sources. The Figure below describes an example.
FIGURE 1.4
Specialization lets different species of
anole lizards live in the same area without
competing.
SUMMARY
• Competition is a relationship between organisms that strive for the same resources in the same place.
• Intraspecific competition occurs between members of the same species. It improves the species’ adaptations.
• Interspecific competition occurs between members of different species. It may lead to one species going
extinct or both becoming more specialized.
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Concept 1. Relationships: Predation, Competition, Symbiosis
EXTENSION
Use this resource to answer the questions that follow.
Go to: http://www.hippocampus.org/Biology
Select “Non-Majors Biology”
Search: Interactions Within Communities
1.
2.
3.
4.
5.
6.
What are the three general types of interactions within a community?
Define competition.
What are some of the resources organisms compete for?
What is the main outcome of competition? (Hint: affects the niche)
Describe an example of interspecific competition.
Why might intraspecific competition occur?
Competition at http://www.concord.org/activities/competition.
REVIEW QUESTIONS
1. What is competition?
2. Compare and contrast the evolutionary effects of intraspecific and interspecific competition.
Symbiosis
Do interactions between species always result in harm?
As commensal shrimp they neither bring a benefit nor have a negative effect on their host.
Symbiosis is a close relationship between two species in which at least one species benefits. For the other species,
the relationship may be positive, negative, or neutral. There are three basic types of symbiosis:
• Mutualism
• Commensalism
• Parasitism
Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish
and shrimp (see Figure below).
Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected. One
species typically uses the other for a purpose other than food. For example, mites attach themselves to larger flying
insects to get a “free ride.” Hermit crabs use the shells of dead snails for homes.
Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the host)
is harmed. Many species of animals are parasites, at least during some stage of their life. Most species are also hosts
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FIGURE 1.5
A commensal shrimp on another sea organism, possibly a sea cucumber.
FIGURE 1.6
The multicolored shrimp in the front and
the green goby fish behind it have a mutualistic relationship.
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Concept 1. Relationships: Predation, Competition, Symbiosis
to one or more parasites. Some parasites live on the surface of their host. Others live inside their host. They may
enter the host through a break in the skin or in food or water. For example, roundworms are parasites of mammals,
including humans, cats, and dogs (see Figure opposite).
FIGURE 1.7
Parasitic Round Worm: Often found in the
intestines of Mammals
The worms produce huge numbers of eggs, which are passed in the host’s feces to the environment. Other individuals
may be infected by swallowing the eggs in contaminated food or water.The roundworm above, found in a puppy’s
intestine, might eventually fill a dog’s intestine unless it gets medical treatment.
Some parasites kill their host, but most do not. It’s easy to see why. If a parasite kills its host, the parasite is also
likely to die. Instead, parasites usually cause relatively minor damage to their host.
SUMMARY
•
•
•
•
Symbiosis is a close relationship between two species in which at least one species benefits.
Mutualism is a symbiotic relationship in which both species benefit.
Commensalism is a symbiotic relationship in which one species benefits while the other species is not affected.
Parasitism is a symbiotic relationship in which one species (the parasite) benefits while the other species (the
host) is harmed.
EXTENSION questions
Use this resource to answer the questions that follow.
Go to:
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http://www.hippocampus.org/Biology
Select “Non-Majors Biology”
Search: Interactions Within Communities
1.
2.
3.
4.
What are the three types of symbiotic relationships?
Describe the three symbiotic relationships.
Describe an example of a symbiotic relationship involving humans.
Describe a symbiotic relationship involving plants and bacteria.
REVIEW QUESTIONS
1. Define mutualism and commensalism.
2. Explain why most parasites do not kill their host. Why is it in their own best interest to keep their host alive?
References
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4.
5.
6.
7.
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. CC BY-NC-SA
hunting lions. CC BY-NC-SA
Fighting Kangaroos. CC BY-NC-SA
Anole Lizards. CC BY-NC-SA
Shrimp on a Sea Cucumber. CC BY-NC-SA
Commensalism. CC BY-NC-SA
Parasitic Round worm. CC BY-NC-SA