Community Structure and Ecosystems
Important Vocabulary
Biogeography - the study of the geographic distribution of plants and animals.
Biome - a major regional community characterized by the dominant forms of plant life and the prevailing climate; also known as a vegetation zone.
Ecotone - areas when the vegetation and animal forms are a mixture of two different vegetation zones or biomes.
Water holding capacity - the capacity of a soil to hold onto water when the water is available.
Species diversity - the variety of life forms found on earth.
Diversity index - a mathematical measure of species diversity in a community. Diversity indices provide more information about community composition than simply species richness; they also take the relative abundances of different species into account. Simpson's Index (D) is a type of diversity index.
Species richness - the number of species present.
Evenness - the same number of individuals in each species.
Environment is defined by the Oxford English Dictionary as "The conditions under which any person or thing lives or is developed; the sum-total of influences which modify and determine the development of life or character."
The earth has four components that make up the environment.
- Atmosphere - the air and weather
- Hydrosphere - water (oceans, seas, rivers, lakes etc.)
- Lithosphere - rock and dirt
- Biosphere - everything alive
The various physical factors that can affect the biosphere involve these components. Specifically, temperature, moisture( atmosphere, hydrosphere), elevation, aspect, geology (lithosphere), and organism interactions (biosphere) are major influences on living things, to name just a few. Click here to see a diagram showing how temperature and moisture differences lead to completely different ecosystems.
Make sure to check out the NASA Earth Observatory page; lots of cool images, including ozone depletion and UV radiation hot spots!
Ecosystems refer to a community of organisms (biota) and the physical factors that affect them (abiota). Therefore, ecosystems can be defined as biota + abiota. Ecosystems are usually classified by their plant communities, as the physical factors constrain what can grow, and in turn what animals can live there.
This portion of the lab focuses on three different ecosystems:
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Desert Ecosystem >10 inches of rain each year |
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Woodland Ecosystem ~25-60 inches of rain each year |
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Aquatic Ecosystem Sometimes show seasonal changes |
Up until this point the focus has been on communities and populations that exist mainly above ground. This rest of this lab emphasizes the communities that live in the soil and how they affect life on earth. It is the type of soil in a specific area that determines what will grow and be successful. In return the types of plants that grow in an area influence the make up of the soil, sometimes positively, other times negatively. Soils are vastly different from the world above, but the basic components (water, oxygen, space, nutrients, and food), ecological processes, and species interactions (prey-predator, carnivore-herbivore, etc.) are still present and essential. All of these components help to make the soil a life growing source for vegetation.
Soil Communities
There are many different species that play an active part in the soil world. For example bacteria, protozoa and fungi break down organics from above the surface into usable nutrients for plants. Burrowing worms break down soil particles and concentrate soil nutrients by ingesting the soil, allowing it to digest and then passing it out as castings. These processed nutrients are much easier for plants to utilize.
There are several factors that determine the organism density in a soil type – the amount of organic matter, soil structure and vegetation. This can be observed by studying the invertebrates found in different types of soils.
To compare several different communities, a diversity index is used:
Simpson’s index (D)
Where:
i = “community” number
“species” numbers = total # of communities or species
= summation starting from “i” community and going to “s” community
P(i) = # of individuals of “community” i
total # of individuals counted
In this lab, four different soil communities were studied: desert, field, grassland, and woodland.
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Desert Soil Community
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Field Soil Community
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Grassland Soil Community
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Woodland Soil Community
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Review Questions
- Define Biogeography.
- Define Ecotone.
- Would you expect to see more plant species within an Ecotone or in the middle
of a specific vegetation zone.
- What are the 6 major vegetation zones discussed in lab?
- Biomes have been characterized along gradients of which of the following
factors:
1. Latitude
2. Longitude
3. Altitude
4. Temperature
5. Moisture
- T/F West exposure in the Sandia mountains allows for
expansion of vegetation zones to higher elevations.
- Name 2 resources that are necessary for soil communities to survive.
- What is the equation for the Simpson's diversity index?
- Be able to calculate the Simpson's index and interpret the results.
- What does a value of D actually mean?
- Name the components of the environment.
- Define the difference between the environment and an ecosystem.
- Describe some strategies that desert animals use to survive in the desert
climate.