Download Mutualism

Name: _______________________________________________
Date: ________________________________________________
Flynt - _____ Period
_____th Grade Science
Essential Question: How important are interrelationships to the survival of an ecosystem?
Types of Ecological and Symbiotic Relationships:
 Symbiosis—the close relationship of two dissimilar organisms.
 Mutualism—a symbiotic relationship where both organisms benefit.
 Commensalism—a symbiotic relationship where one organism benefits while the other organism—
typically called the host (but not always)—neither benefits nor is harmed!
 Parasitism—a symbiotic relationship where one organism benefits while the other organism—typically
called the host— is harmed.
 Ecological/Co-Evolutionary Relationships: Generally not considered symbiotic, but there is a definite,
close, significant relationship that requires co-evolution to avoid extinction.
 Predation—behavior of one animal feeding on another; one organism benefits while the other is killed.
o If a new adaptation appears in either the predator or the prey species that provides an advantage
in obtaining prey or avoiding predators, there is almost always a corresponding population drop
(at least initially) followed by a period of adaptation in the other species.
 Competition—when two or more organisms rely on and compete for the same environmental resource.
o While competition always occurs between organisms of the same species, in this case, we are
referring to competition between two unique populations (two different species).
Overview
Animals and plants that live close together in an ecosystem have many interrelationships. Some of these
relationships benefit both organisms, some harm one or both organisms. You’ve already studied some of these
relationships---for example, predator-prey relationships. In a predator-prey relationship, the predator benefits,
and the prey is harmed. Many other relationships can benefit or harm organisms, but their effects often aren’t
as dire as the death of one organism.
The chart below shows the different types of relationships that organisms might have, based on the benefit or
harm to each organism. This reading will talk about each of these different kinds of relationships.
Parasitism
In parasitism, one organism lives on or in another organism at the expense of this organism, In parasitism, one organism lives on or in another organism at the expense of this organism, which is called the host. Parasites may destroy the host. The hookworm is a good example of a parasite. Hookworms may live in the intes-
tines of human beings and other animals. Hookworms eat the food that the animal has ingested, essentially
stealing nourishment from that animal. At the same time, the hookworm can cause discomfort and illness in the
animal. Thus, the hookworm benefits by getting food, and the animal is harmed by losing nutrients in the food
it eats, as well as suffering discomfort and possible illness.
An example of parasitism from the upland ecosystem is found in those insects that insert their larvae into the leaves and stems of young oak trees. The larvae feed on the plant, then mature and move on, leaving
holes in the plant. If an infestation is bad enough, this can harm or kill the tree, or at the very least, leave it vulnerable to disease.
Commensalism
Commensalism is an association between organisms in which one benefits from the presence or the activities of another, without the other being affected (either positively or negatively). The word commensal
means “sharing a table,” and refers to the primary types of commensal organisms that utilize waste food.
Consider the example of cattle in field whose grazing disturbs the insects that live in that field. As the
cattle walk around, they force insects off the grass and into the air, where they are preyed upon by birds. In this
case, the birds are benefiting by the cattle's activities, but the cattle are not greatly affected. The birds’ success
in finding insects to eat depends largely on the presence of these cattle.
Commensalism is not confined to the animal kingdom. Many plants and fungi benefit from the presence
or activities of animals. The non-feeding activities of many animals can benefit plants. Large grazing animals,
such as cattle, often disturb the ground, exposing bare earth. This exposed soil is readily colonized by a variety
of opportunistic plants. The same is also true of the soil exposed or unearthed by moles and rabbits.
Some examples of commensalism in the Upland Ecosystem in Florida include:
 Gopher tortoises dig burrows that are later abandoned. Snakes, frogs, birds, fox, opossum, rabbit,
and armadillo use those burrows for shelter. In fact, tortoise burrows afford refuge to more than 360
animal species.
 Panthers use saw palmetto plants as shade and hiding places for their young while the adults hunt.
 Wiregrass is an important location for bird nesting, as well as nests for squirrels, rabbits and mice.
 Birds collect threads from the palmetto plant to build their nests.
Mutualism
In mutualism, both parties in the relationship benefit from it. Mutualism is a positive reciprocal relationship between two species. Through this relationship both species enhance their survival, growth, or fitness. For
example, certain kinds of ants live in thorny acacia plants. The plants provide food and nesting sites for ants. In
return, the ants protect the plant from other insects that might feed on and injure it. Mutualism also occurs
when algae and fungus grow together---to form lichen. The fungus, which cannot produce its own food, gets its
food from the alga. In return, the fungus helps the algae get water.
Mutualism can be divided into three functional categories: trophic, defensive, and dispersive:
Trophic mutualism involves partners specialized to obtain energy and food from each other. An example is
the algae and fungus.
Defensive mutualism involves species that receive food or shelter from their partner in return for defending
the partner against predators or parasites. An example is the ants and the thorny plants. Other examples of
defensive mutualism include:
 Frogs finding shade and cooler temperatures among the leaves of the palmetto. They also eat spiders
and crickets that might damage the plant.
 Birds nesting in oak trees, and feeding on the caterpillars that would otherwise eat the oak leaves.
Dispersive mutualism involves animals transporting a plant’s pollen and receiving, in turn, a nectar or other reward. It also includes animals that disperse seeds in the process of eating or digesting the nutritional
fruits or nuts that contain those seeds. Often, the seeds pass through an animal's gut (many seeds actually
require that the coat of the seed is softened by digestion before they can germinate), but sometimes the animals just carry the fruits away, tear them apart and scatter the seeds in the process. Either method is effective and helps the seeds reach a suitable place to sprout, away from the parent plant. Fruits intended for animal dispersal are usually rich in nutrients and low in toxins, unlike the regular plant parts, though some
fruits are poisonous to the “wrong” animals (those that don’t disperse them). Most plant species in the
world, and in most forests, use animals at some stage in their life cycle, either for pollination, seed dispersal,
or both.
A few examples of dispersive mutualism in the Florida upland ecosystem include:
 Birds, like the Florida scrub jay, that bury surplus oak nuts for winter. If the nuts/seeds aren’t dug up
by the bird, they eventually grow into trees.
 Beetles and flies that act as pollinators for pawpaw plants in exchange for parts of the flower they
eat.
 Gopher tortoises that eat the fruit of the palmetto and pawpaw plants. The seeds pass through the tortoise and are dispersed to other parts of the ecosystem.
Other (Less Significant) Ecological Relationships: Amensalism and Neutralism
In a relationship of this type, one species suffers and the other is unaffected. For example, an animal
goes to a pond to drink. In its approach to the pond, it tramples the pond-side vegetation. Although the plants
may not be killed, their fitness will be affected. The animal gains no benefit and suffers no harm.
Neutralism is a situation in a community in which there are two species populations that have absolutely
no impact on each other’s survival or fitness. It is unlikely that there are many, if any, such species pairs. To be
true, this would require minimal interaction between the two and no competition for ANY resources.
Analysis Questions:
1. Fill out the following chart for ecological relationships and research real-world examples.
Relationship
Description/Definition/Significance
Parasitism
Mutualism
Commensalism
Predation
Competition
2. How are the three types of mutualism similar? How are they different?
Real-World Examples
3. Can you think of any parasitic, mutualistic, or commensal relationships among any organisms in the area
where you live?
4. Answer the essential question: How important are interrelationships to the survival of an ecosystem?