Teaching about niches and the relationships between species

Back in October I started sharing Michigan species cards and promised that I would show how I used them in the classroom.  After much delay, here is an example of their use - I can use the cards to help students understand the relationships between species in a habitat.

If you think of an environment as a giant puzzle, species only fit in a certain place in the environment.  They have a role that they belong in.  In the same way that a puzzle piece from the edge will not fit into the center and vice versa, a species can only fit in a certain place in the environment.  That role or place that a species occupies in its environment is known as its niche.  A species locks into its niche by a series of connections with the species around it.  Some species will connect with many species while others will only connect with a few.

Let's start by exploring the relationships between two species.

Some species are connected by their shared needs.  They might compete for resources such as food, water, shelter, or space.  For example a Downy Woodpecker and an Eastern Grey Squirrel may both wish to occupy a hole in a Red Oak tree, but they will not share the space so this makes them competitors.  The woodpecker and squirrel might also compete over food as both eat fruit, seeds, and nuts.  In times of plenty this may not be an issue, but when foods are scarce there may not be enough for both species to survive.  So the relationships between the two species (form the squirrel's perspective) are as follows.

• The squirrel competes for shelter with the woodpecker.
• The squirrel competes for food with the woodpecker.

We could also state this from the perspective of the woodpecker as thus:

• The woodpecker competes for shelter with the squirrel.
• The woodpecker competes for food with the squirrel.

In addition to competition, species may be connected by food in other ways.  To continue using the Eastern Grey Squirrel as an example, this species eats fruit, nuts, seeds, fungi, insects, bird eggs, birds, and very small mammals.  Although not listed on the card above, this species will also feed on leaf and flower buds and tree sap.  The squirrel might consume the eggs or young from the woodpecker's nest - another relationship between the two species.  If we think of it from both perspectives there are two relationships:

• The squirrel receives food (eats) the woodpecker.
• The woodpecker provides food (is eaten by) to the squirrel.

The squirrel also gets food from the Red Oak tree in which it lives.  At different times of the year the squirrel may consume leaf and flower buds, acorns, or sap from the tree.  Again two relationships can be identified if viewed from both perspectives.

• The squirrel receives food from the oak.
• The red oak provides food to the squirrel.

I have already mentioned another relationship between the squirrel and the oak tree.  Squirrels find shelter in trees.  They live in holes in trees, but they also construct nests made of leaves high in the canopy.  

• Squirrel receives shelter from the oak.
• Oak provides shelter to the squirrel.

In addition to the relationships involving food and shelter, the squirrel is connected to the oak tree by a pair of chemical relationships.  As a plant capable of producing its own food through the process of photosynthesis, the oak produces oxygen (O₂) as a waste product.  The squirrel needs that oxygen to survive.  Conversely, the tree needs carbon dioxide (CO₂) to perform photosynthesis and the squirrel creates carbon dioxide through the process of respiration (breathing).  

• Squirrel receives  O₂ from the oak.  
• Squirrel provides CO₂  to the oak.

Or from the perspective of the tree:

• Oak provides O₂  to the squirrel
• Oak receives CO₂  from the squirrel.

The squirrel and oak tree have another potential chemical relationship.  The squirrel's urine and dung contain nutrients that the oak tree may need.  The urine (diluted by groundwater) may be taken up directly by the oak tree's roots.  The dung must be broken down by decomposers before it can taken in by the tree.

• The squirrel provided nutrients to the oak.
• The oak receives nutrients from the squirrel.

A final relationship between the squirrel and the oak involves seed dispersal.  The squirrel consumes the seeds (acorns) of the oak tree, but the squirrel cannot eat them all at once.  To prevent competitors (other squirrels, deer, turkeys, jays, mice, etc.) from consuming the acorns, the squirrel will hoard them to consume later.  The Eastern Grey Squirrel is a "scatter hoarder"; it buries acorns in scattered locations throughout the woods.  Not all of these acorns are recovered.  Some will sprout and develop into new trees.  The tree actually counts on this dispersal, that is why the tree will create so many acorns in a given year, by ensuring an overwhelming supply at least every few years there will be enough seeds to regenerate the forest.

• The squirrel disperses seeds for the oak tree.
• The oak tree's seeds are dispersed by the squirrel.

The more species that I add, the better I can define the niche that the squirrel occupies.  For example, if I add a Red Fox to the equation, what relationships or connections would that fox have to the squirrel?  The fox is an omnivore.  It easts fruit, nuts, seeds, birds, eggs, amphibians, reptiles, insects, small to medium-sized mammals, and carrion (dead animals).  Based on food alone, the fox has two possible connections to the squirrel both as a competitor and as a predator.

• The squirrel competes with the fox for food.
• The squirrel provides food to (is eaten by) the fox.

Or these can be expressed from the fox's perspective as:

• The fox competes with the squirrel for food.
• The fox receives food from (eats) the squirrel.

If I expand my thinking beyond the squirrel, I can define how all the other species in the habitat relate and see other degrees of interconnectedness.  For instance it may be difficult to see the relationships that exist between the Red Fox and a Black-capped Chickadee, but by digging deeper a couple of relationships emerge - they eat some of the same foods such as fruit, berries, and insects.  This makes them competitors (on a small level).  

• The fox competes with the chickadee for food.
• The chickadee competes with the fox for food.

Both species will also eat carrion (dead animals).  However, a chickadee can only eat carrion if a larger animal has first "opened" the carcass. 

For example, if the fox finds a dead White-tailed Deer it can chew through the deer's hide to get to the meat.  Once the hide has been opened the chickadee can then begin to feed on small bits of meat and fat.  The fox has therefore made the food accessible to the chickadee (and other small birds such as the Downy Woodpecker).  Some of the relationships that can be described here include:

• The fox scavenges the remains of the deer.
• The deer provides food (in the form of carrion) to the fox.
• The fox makes food accessible to the chickadee.
• The chickadee scavenges the remains of the deer.
• The chickadee scavenges the remains of the fox's meal.
• The deer provides food (in the form of carrion) to the chickadee.

If look at the deer while it's alive, I can find several other connections in the ecosystem. 

• The deer competes with the squirrel for food.
• The deer competes with the fox for food.
• The deer competes with the chickadee for food.
• The deer competes with the woodpecker for food
• The deer receives food from (eats) the oak.
• The deer receives oxygen from the oak. 
• The deer provides carbon dioxide to the oak.
• The deer provides nutrients to the oak.

Finally, let's add fungi into this model ecosystem that we have created.  Some fungi like the Fly Agaric mushroom have symbiotic relationships with trees such as the Red Oak.  The fungi coat the roots of the trees and send out hyphae (roots) to collect water and minerals that they share with the tree.  In exchange, the tree shares sugar with the fungi.  Other species of fungi such as the Gem-studded Puffball act as decomposers, breaking down organic matter that is then recycled by plants such as the oak tree.  This organic matter might include wood, leaves, other plant debris, animal dung, and even animal parts.  These fungi might then be eaten by animals in the habitat.  Despite the toxicity of the Fly Agaric mushroom, the Grey Squirrel is able to eat it with no ill effects

A couple of the relationship of the Fly Agaric include:

• The Fly Agaric provides nutrients to the oak tree.
• The Fly Agaric provides food to (is eaten by) the squirrel.
• The Fly Agaric receives food from the oak tree.

The Gem-studded Puffball has some of the following relationships:

• The puffball receives food (decomposes) the oak.
• The puffball provides food to (is eaten by) the squirrel.
• The puffball receives food from (decomposes) the squirrel's dung.
• The puffball receives food from (decomposes) the deer's dung.
• The puffball provides nutrients to the oak.

So how can all of this information be shown graphically?  The way that I use in the classroom is with a puzzle as a graphic organizer.  In this example, I have picked the Grey Squirrel to be the central piece in the puzzle.  All of the other pieces are described by their relationship(s) to the squirrel.  This method could be used with any of the species shown above - I could have the Red Oak be the central species in this puzzle, or the Downy Woodpecker, or any of the other species.  The goal of this activity is to get students to realize that species are connected on many different levels.

 Instead of using the puzzle pieces, I could also do this with a honeycomb arrangement of hexagons.  This allows me to expand beyond one species and the relationships between many species.

In this example I haven't listed every relationship between species, but only a couple that connect any two species together.  This activity can be as simple or complex as you want to make, but either way it meets the goal of demonstrating to students the relationships that exist between species in a habitat.