 |
Leafy spurge (invasive species)
|
Land of Many Opportunists
Background
Many exotic species can easily take advantage of a wide range of
required resources (water, food, shelter, space, etc.), because
they are living in an ecosystem that is not their native one. Exotic
animals may feed off of a broad range of foods and have no native
predators existing to control their populations. Invasive exotic
plants may be successful in a variety of soils and environmental
conditions. Exotic plants and animals may not be affected by native
diseases, which normally act in the ecosystem to regulate and maintain
normal populations. Ecologists consider any species that can take
advantage of a broad spectrum of resources opportunistic.
On the other hand, sensitive native species tend to have evolved
very specific environmental needs. This makes survival
difficult when unexpected changes—biological or environmental—occur.
An example of a highly specialized native species is an alpine plant.
If the climate gets slightly warmer, trees take over the habitat.
If the climate gets colder, rock and ice begin to dominate. When
nonnative species move into a habitat, they can modify and impact
the ecosystems they invade. Those native species with specific habitat
requirements may lose their ability to compete with opportunistic
intruders.
If the exotic species is highly aggressive, it may even be able
to create a monoculture and keep native species from re-colonizing
the habitat. Fortunately for the natives, nature has built-in regulatory
systems which make monocultures extremely unstable in the natural
world. Agricultural researchers are continuously battling this natural
'regulatory system' with pesticides, because their own monocultures
of agricultural plants are so often under relentless attack by disease.
So it is possible that through nature's tendency to balance itself
out, a natural 'remedy' would develop against invasive monocultures
to keep exotics at bay.
 Procedure
In this relay game of tag there are four teams: red bean, black
bean, pinto bean, and invasive (exotic). The goal of each team is
to gather as many of their resources (beans) as they can and make
a pile at their team's cone.
The course is laid out with a ten-foot diameter rope circle in
the center. About 100 beans of each type are scattered in the circle.
Four team cones or home base makers are set equidistant around the
circle, about fifteen feet from the rope's edge.
Each of the five or more game sessions lasts for only three minutes.
After each session, the bean count for each team will be graphed
on graph paper and all the beans will be re-scattered into the center
of the circle. The team with the least number of beans after each
session will be required to move their cone ten feet farther away
from the circle, representing the weakening of a population due
to strengthening competitors. (If the team that moved ten feet back
in a previous session collects the most beans during subsequent
sessions, they may return their cone to its previous position.)
The first session begins by establishing a baseline. Only the three
bean teams will compete. One student per team will run to the rope
enclosure and collect five of their team's bean resources (pintos
are collected by the pinto team, reds by the red team, etc.), return
to their cone, and place the beans in a pile  next
to the cone. Then the next member of their team will be allowed
to go and collect beans. When the three minutes are up, the game
will be stopped and beans will be counted and graphed. Team members
that are not actively collecting beans must be touching their team's
cone.
The second session is played similarly to the first, with the addition
of the invasive team. Since the members of the invasive team are
opportunists, they may collect up to ten beans of any color with
each member's turn to go to the circle.
The third and fourth session are played identically to the second.
Remember to move the cone of the team with the least beans back
ten feet after each session.
In the fifth session, the invasive team is allowed to be an 'aggressive'
invasive species (without being physically or verbally aggressive).
When they approach the center, they can either collect beans or
acquire another person's beans by tagging someone within the circle.
At the end of the game, discuss the outcomes which are visually
displayed on the graph. With older students, be sure to discuss
these questions:
- Native species usually play an important role in supporting
their ecosystem. Since the reds, blacks, and pintos have been
reduced in numbers and are not able to play their supporting role
in the local ecology, how will the invasive species cope with
a weakening ecosystem?
- It is usually the case in ecosystems that a consumer actually
plays a role in supporting the producer on which it depends.
A) What may happen to the populations of native producers (beans)
when their biological consumers/supporters (students) diminish
in population? And since invasive species have not evolved naturally
in conjunction with the native producers,
B) will the invasive species be able to support the native producers
or will they destroy the integrity of the resources on which they
have become dependent?
- What might happen to the invasive species if it becomes a monoculture
and entirely displaces the native consumers?
|
|
