Introduction to Ecology –
Most of the material covered in our ecology unit will include the material covered in Chapter 16, with additional information coming from our freshwater ecology project and bits from other chapters. The term ecology literally translates as ‘house,’ a useful concept to understand why we study the unit. Just as certainly as we live within a physical house, we also live within our local and global environment. For example, just one generation ago we would have one or two students in a class of 25 with notable cognitive problems due to lead poisoning. Our local environment now has greatly reduced levels of lead, and one result is fewer cases of mental impairment in our children.
In common usage, ecology is the study of environmental issues. Generally, this unit is a favorite of students as we get to study the effects of local landscapes and practices on local rivers and lakes. Ecology is a challenging field as it studies connections within our world; how the use of fertilizer affects streams and how this in turn affects fish and other animals reliant upon the stream.
Chapter 16: Ecosystems
What is an Ecosystem?
1. Ecosystem – A system in which the abiotic (nonliving) and biotic (living) factors interacts through nutrient cycles and energy flow.
I spend much of my summer ‘vacation’ studying at Montana State University in Bozeman, MT. The town is just north of Yellowstone National Park and thus a great place to study ecology. YNP is currently engaged in a huge debate in regards to how the park should be managed. The land and park are owned and managed by the federal government, and surrounding lands are owned and controlled by private individuals, state governments and federal agencies. If YNP were a complete ecosystem, the federal government would be able to manage the park on their own as all food, nutrients, minerals and living critters that use the park would exist within the park boundaries. But the "Yellowstone Ecosystem" extends well beyond the park. For example, in the winter hundreds of bison migrate over 100 miles north of the park in search of food, while elk (wapiti) will migrate greater distances to the south to Jackson Hole, WY. When these animals leave the park, they can be hunted (state of Montana shoots hundreds of bison every year) or feed hay in crowded areas where disease transmission is greatly accelerated (as happens every winter in Jackson Hole, WY).
To fully understand the issues surrounding Yellowstone National Park, we need to cover a few terms:
2. Key Terms associated with ecosystems:
a. Habitat – The physical location in which a population lives.
b. Population – A group of individuals of the same species that can
interbreed. (in YNP, all bison)
c.Community – The living things living within a given habitat (in YNP,
the bison, elk, bears, plants, wolves, etc.).
Obviously, it is difficult to define the limits of an ecosystem. When DDT was commonly used to control bugs such as mosquitoes, researchers were able to detect levels of the chemical in penguins in Antarctica! To define the limits of an ecosystem, we must come up with reasonable limits.
3. Succession – The (pretty much) regular and predictable process in which communities replace one another as a habitat matures.
The physical environment in which an animal lives is known as its habitat. The type of habitat that exists in an area is dependent upon many factors: rainfall, temperatures (maybe), soil, and many other factors. One other important factor is time: many habitats require a great deal of time to develop. The change in communities within a habitat over time is known as succession.
Consider what happens to a new house being built in Brandon: the field is dug up during the process and a large lot of black dirt is left. But this dirt will not remain empty for long as plants such as crabgrass and thistles will quickly colonize it. Over time, other plants, even trees such as cottonwoods, will replace these plants. This is secondary succession, as the community is colonizing an area that had been previously filled with life (the field that existed before the development began).
In contrast, primary succession involves life forms filling in an environment that previously hadn’t supported any life. In the classroom there is a picture of a lupine growing in the ash left from Mt St Helens. No life had existed in this area before, so this is considered to be an example of primary succession. The first organisms to inhabit such an area are likely to be mosses, lichens, bacteria and small plants.
In YNP, succession is a poorly understood concept. In the summer of 1988 (still known as Hell’s summer is the area), large wildfires burned large parts of YNP (and the West). While many beautiful forested areas were destroyed, too few visitors recognize this as a necessary, natural case of succession. Older trees are prone to disease and many animals in the park rely upon an alteration of habitats for survival. Immediately after the fire, populations of elk and bison boomed (they grazed on the open fields of grass) and new, healthy trees are now recolonizing the area.
Energy FLOW in Ecosystems
Within an ecosystem, energy flows from the sun to primary producers (such as plants and algae). We need plants and algae primarily for their value in trapping energy that can be used by consumers (such as animals). A grazing animal that feeds only on producers is known as a primary consumer, or herbivore. If an animal feeds on primary consumers, they are known as secondary consumers. The next level is tertiary consumer, followed by quaternary consumers. If an animal feeds exclusively on other animals, they are known as carnivores. Most animals are omnivores, feeding on many different types of food.
Above, I highlighted the term FLOW. Energy is not like aluminum that can be continually recycled. It flows in one direction, from the sun to the producers to the consumers. The energy is not lost, but is becomes useless to living things. Thus, if the sun were to stop shining, we would quickly run out of useful energy.
In general, very little energy (around 10%) is passed on from one level of a food chain to the next. For this reason, it is rare to find 3rd or 4th level consumers (such as eagles). Why? Where does the energy go? Think of a cow eating 10 kg of grass. Of the energy contained within the grass, the cow uses some for heating its body, it burns energy as it walks and digests food, and some energy is lost in waste products. On average, only 10% of the energy will be converted into tissue that can be eaten by a secondary consumer.
A food pyramid is a diagram of the organisms within a given ecosystem. At the base (or lowest trophic level) are the producers. Next are the consumers, getting narrower as you move to the 2nd level, 3rd level due to the reduced amount of energy. An energy pyramid sounds easy, right? Actually, they can be difficult as most living things are part of a food web, meaning we feed on many different levels. We place living things at the level they usually feed.
Nutrient Cycling in Ecosystems
Energy flows into an ecosystem, constantly being replenished by the sun. Other nutrients cycle, or are continually reused and recycled. We will study three cycles: Water cycle, carbon cycle, and nitrogen cycle.
4. Water cycle: Water commonly cycles as follows: Ocean water evaporates, creating mist and clouds, which travel great distances, dropping water on land. When this water enters lakes and rivers, it evaporates (or is released by life) to create clouds and carry the water across great distances,
restarting the cycle.
5. Carbon cycle: You are exhaling carbon dioxide right now, and it might be taken in by plants, which will store it as food, which we eat and turn back into carbon dioxide. Additionally, great stores of carbon dioxide are stored in fossil fuels and in our oceans, which we seem to be releasing at a great rate at present.
6. Nitrogen cycle: Nitrogen is all around us (78% of our air) but it is in short supply for plants. Why? It must be converted into a usable form by bacteria. We often supplement nitrogen with applications of fertilizer in agriculture. One reason our local waters are so green is because we have thrown off the nitrogen cycle, adding too much to our local waters.
Interactions between Species
When two species exist in close contact with each other, the relationship is known as a symbiotic relationship. We commonly recognize four types of symbiosis:
1. Mutualism: both species benefit (like a clown fish living in an anemone).
2. Commensalism: One species benefits, the other is unaffected (bird building a
nest in a tree)
3. Parasitism/Predation: One species directly harms or kills the other (Lynx and
snowshoe hares).
4. Competition: Two species fight over the same food, habitat, or resource.
Additional Notes for Freshwater Lab:
I. Chemical Tests for Water Quality:
A. Dissolved Oxygen: Measures how much oxygen is available for organisms to breathe. Increased by factors such as wind, low temperatures, aquatic life and low altitude.
B. Turbidy: Measure clarity of water. High turbidity can indicate excessive runoff and erosion. Problems may include blocking sunlight and may clog gills of inverts requiring high dissolved oxygen levels.
C. Total Dissolved Solids: Like sugar dissolved in tea, excessive fertilizer and other solids in runoff dissolve in stream water. No water is pure, but excessive dissolved solids may indicate a problem with runoff.
D. Nitrates: This is the form of nitrogen used by plants as a fertilizer. Many of our local lakes and streams contain excessive nitrate levels, leading to green water due to excess algae growth. This comes from lawns, parks and agricultural sources.
Ecosystem Questions:
Consider the river tank in the room. Is this an ecosystem? Explain.
Name one abiotic factor in the tank.
Name one biotic factor in the tank.
Construct a food web of ten living things (any 10 things, your choice).
Construct an energy pyramid consisting of the same ten living things.
a. Give an example of a herbivore:
b. Define herbivore:
a. Give an example of a producer:
b. Define producer:
Consider the population tank at the back of the room.
a. How many populations exist within the tank?
b. How many communities exist within the tank?