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Categorizing
Relationships |
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Our houseplants might live on their own, isolated in a planter, but in natureand in
our gardensplants form close relationships with other organisms. These relationships
are often complex and many-layered. Slugs and snails, for example, are the nemesis of many
gardeners, devouring favorite plantings seemingly overnight. Yet these disdained creatures
help in the critical task of breaking down organic matter and returning vital nutrients to
the soil.In this section we are going to look at
some examples of relationships between plants and other organisms. Well start
"small," with plant-microbe relationships, then move to plant-insect,
plant-plant, and, finally, plant-animal relationships. Although its somewhat
artificial to isolate and analyze individual relationships like this, the exercise should
help us, in the end, view the garden more
holistically"whole"-isticallyby making us more aware of the many
individual players and connections.
As usual, lets begin by defining a few terms. You
probably know by now that scientists like to categorize and name things! Here are some
useful terms and definitions. (Dont worry too much about the individual terms;
its more important to understand the variety of possible relationships.)
| When two (or more) different organisms live in close
association, they are said to be living in symbiosis
(Gr. syn = together with, bios = life). |
| If both organisms benefit from the association, the
relationship is called mutualism, or mutualistic symbiosis. |
| If one organism benefits, and the other remains unaffected,
the relationship is called commensalism. |
| If one organism lives on or in another living organism,
from which it derives nutrients, it is called a parasite, and the provider is called the
host. |
| If one plant grows on the body of another plant, but is not
parasitic, then it is called an epiphyte. |
| If an organism fills its nutrient needs from dead and
decaying organic matter, it is called a saprophyte. |
Another important concept when talking about relationships
among organisms is the specificity of
the relationship. This refers to how "choosy" an organism is when it comes to
forming a relationship. Some relationships arent very specific at all. Some ivies,
for example, will climb up any type of treethe species of tree doesnt matter.
On the other hand, relationships involving very close, cell-to-cell contact tend to be
very specific; that is, the two organisms involved must be fully compatible. For example,
certain strains of nitrogen-fixing bacteria will form root nodules on specific types of
legumes, but not on others.
Now well begin our look as some relationships. As
you read these isolated accounts, however, keep in mind that the natural world is made up
of complex systems and relationships.
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