Objective 3: How do interactions among organisms and their environment help shape ecosystems?

Section 1: Symbiotic Relationships: Who’s Playing Nice?

Symbiotic Relationships Some organisms play nice. Some don’t. Some play nice with certain organisms while playing not so nice with others. Regardless, many organisms have close living relationships that can be characterized.

Relationships of Superman Lois Lane loves Superman and protects his secret while Superman loves and protects her—a mutualistic relationship. Lex Luthor is always looking to attack and hurt Superman—a predator- prey like relationship. We all know Superman’s weakness is kryptonite, which pulls away his power and can, with long-term exposure, kill him—a parasitic relationship. Lastly, Lois Lane and Lex Luthor share a relationship where Lex benefits because he can use Lois to draw in Superman, serving as a benefit for Lex, but neither help nor harm Lois—a commensalistic relationship.

Symbiotic Relationships Symbiosis is a close relationship between two species in which at least one species benefits. The relationship may be positive, negative or neutral. There are three basic types of symbiosis: Mutualism Commensalism Parasitism

Mutualism Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish and shrimp. The nearly blind shrimp and the fish spend most of their time together. The shrimp maintains a burrow in the sand in which both the fish and shrimp live. When a predator comes near, the fish touches the shrimp with its tail as a warning. Then, both fish and shrimp retreat to the burrow until the predator is gone. From their relationship, the shrimp gets a warning of approaching danger. The fish gets a safe retreat and a place to lay its eggs.

Commensalism Commensalism is a symbiotic relationship in which one species benefits while the other 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 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 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. 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.

Think like an Ecologist 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. Define mutualism and commensalism. Explain why most parasites do not kill their host. Why is it in their own best interest to keep their host alive? Use complete sentences.

Section 2: Predator-Prey: Who’s in charge here?

Predator-Prey Relationships Predation is another mechanism in which species interact with each other. It 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 Predator-prey (relationship where one species, the predator, eats or consumes another species, the prey) relationships are essential to maintaining the balance of organisms in an ecosystem. There are different types of predation, including: Predation (true predation) Grazing Parasitism

Predation (True Predation) Predation is when a predator kills and eats its prey. Predators may hunt actively for prey, or they may sit and wait for prey to get within striking distance.

Grazing In grazing, the predator eats part of the prey but does not usually kill it.

Predator-Prey Relationship Importance Predators play an important role in an ecosystem. 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.

Predator-Prey Model

Think Like a Field Ecologist How do you determine which organism is the prey and which one is the predator? What are some of the effects predation has on ecosystems and ecosystem dynamics? What is the difference between a lion’s predation and a cow’s predation? The amount of prey has increased in a population, what will happen to the amount of predators? Why? Explain in one paragraph using full sentences.

Section 3: Competition: Does there have to be a winner?

Competition 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 (a relationship between organisms that strive for the same resources in the same place) can be for resources such as food, water or space. Does there have to be a winner? When animals compete, yes.

Competition There are two different types of competition: Intraspecific competition: occurs between members of the same species. 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 Interspecific competition often leads to extinction of species that share a niche. Specialization occurs when competing species evolve different adaptations.

Think Like an Ecologist Create a list of at least 4 resources that lead to competition of organisms. Is competition always between different species? How does competition affect the niche of a species? Describe an example of interspecific competition. You are a science teacher. You have a student who is having difficulty understanding intraspecific competition. Write him a letter that explains intraspecific competition in simple terms and give at least one example.