ECO - Biodiversity and Ecosystems [LESSON]

Biodiversity and Ecosystems

Ecosystems include both the biotic and abiotic parts of the environment working together and influencing each other. Remember from Lesson 2 that energy in ecosystems is a one-way flow. Here, we contrast this with matter which is recycled in the ecosystem.

Biogeochemical Cycles

Unlike the one-way flow of energy, matter is recycled within and between ecosystems. Elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another through cycles that connect living things to the Earth.  Biogeochemical cycles connect living things to the earth.   In our unit on organic chemistry and macromolecules, we discussed that the four chemicals that make up 95% of living things are carbon, hydrogen, oxygen, and nitrogen. These elements are constantly being cycled through living and non-living organic matter.

Scientists create models to represent natural interactions in the environment which make it easier to study and understand the 'big picture' without having to physically measure an entire ecosystem. Diagrams of the nutrient cycles could be considered models of the actual cycles as they occur in nature. The use of models also allows scientists to make predictions about how a particular event might affect an ecosystem without having to expose the real ecosystem to that event.   Review the interactivity and the movies below to refresh your understanding of the various biogeochemical cycles.

The Water Cycle:   the movement of water between different reservoirs on the earth, underground, and in the atmosphere. Water cycle shows steps in water cycle: groundwater discharge, runoff, transpiration, condensation, & precipitation

  1. Biological importance: The availability of water determines the diversity of organisms in an ecosystem as it is particularly important for primary productivity and cellular function.
  2. Availability: Liquid water is most abundant on earth, but water is also found as a gas and a solid.
  3. Reservoirs: The majority of water is found in the ocean (97%), some in the ice caps and glaciers (2%), and the remaining in lakes, rivers, and groundwater.
  4. Process: The water cycle is driven by solar energy as water is evaporated from the earth, transpires from plants, condenses in the atmosphere, and falls down to the earth as precipitation.

 

 

The Carbon Cycle: the framework for cycling organic molecules through living things. 

Carboncycle

  • Biological importance: Photosynthesis and cellular respiration form the basis of the carbon cycle. Carbon is found in all of the major macromolecules necessary for all living systems.
  • Availability: Photosynthetic organisms use atmospheric carbon dioxide to convert carbon to organic forms. Other organisms use the autotrophs as a source of carbon and energy.
  • Reservoirs: Carbon stores include limestone, fossil fuels, the ocean, soils, the sediment of aquatic systems, plant and animal biomass, and the atmosphere.
  • Process: The carbon cycle is indirectly driven by the sun as photosynthesis is fundamental to the fixation of carbon. Both autotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration. Carbon is returned to the environment through decomposers and cellular respiration. This cycle also includes the transformation of carbon through volcanic eruptions and combustion.

The Nitrogen Cycle: the cycling of nitrogen in organic and inorganic forms for effective biosynthesis of macromolecules.

Image shows nitrogen cycle and the importance of bacteria in the processes of nitrogen fixation & denitrification

  • Biological importance: Nitrogen is required for the synthesis of amino acids, proteins, and nucleic acids.
  • Availability: Bacteria and plants can use inorganic NH4 + and NO3 as well as organic forms found in amino acids. Bacteria can also use NO2 -; animals can only use organic forms.
  • Reservoirs: Most nitrogen is found in the atmosphere (80%) as N2, and most living things cannot use it. Other forms of nitrogen are found in the soil, water reservoirs, and in living organisms.
  • Process: Nitrogen is introduced to the ecosystem after nitrogen fixation, the conversion of nitrogen gas to ammonia. Through the processes of assimilation, ammonification, denitrification, and nitrification, nitrogen cycles in various forms are suitable for use in various organisms.

 

The Phosphorus Cycle: a series of long term and short term cycling of phosphorus throughout the environment.

Phosphorus cycle as set of long & short term cycles. Phosphate is eventually released from the soil & dissolved in water

  • Biological importance: Phosphorus is required in nucleic acids, phospholipids, and ATP.
  • Availability: Inorganic phosphate, PO4 3, is absorbed by plants and used to create various organic molecules.
  • Reservoirs: Marine sedimentary rocks are the largest stores of phosphorus, but phosphorus is also found in soils, oceans, and organisms.
  • Process: Weathering of rock adds phosphorus to the soil and water, where it is absorbed by producers and incorporated into biological molecules. Phosphate is returned through the soil or water from the excretion or decomposition of organisms.

 

 

 

 

Ecological Succession

Over time, as environmental conditions change, organisms and communities also change. Eventually, new communities replace current communities, and the ecosystem changes. A series of predictable changes in an ecosystem is called succession. Two types of succession are primary succession and secondary succession.

diagram

Secondary Succession is the re-population of an area after its destruction due to natural or man-made causes. One example of secondary succession might occur after a forest fire changes an ecosystem. Grasses and other small organisms are first to appear, forming a low layer of vegetation. This changes the burned area, allowing shrubs and small trees to become established. The shrubs and small tree species change the environment, and eventually, larger tree species will become established. As plants become established, small animals, then larger ones return and re-populate the area.   This continues until the ecosystem returns to its former condition. This mature ecosystem is referred to as a climax community.

Primary Succession occurs where there has never before been an ecosystem; for example, a volcano erupts spreading lava; over time the lava weathers and soil formation begins. Spores are blown into the area that develop into a specialized fungi called a lichen. Lichens are capable of photosynthesis and enzymatically breaking down rock or other dead organic matter. Eventually, enough soil forms to hold windblown seeds and moisture so that grasses and weeds can grow. From this point, changes continue similar to secondary succession. Review the activity below and compare the influence of nutrients, topsoil, temperature, and rainfall on the rates of primary and secondary succession.

Review the Ecological Succession video below to compare the influence of nutrients, topsoil, temperature, and rainfall on the rates of primary and secondary succession.

Biodiversity

Biodiversity is the measure of the number and frequency of various species in an ecosystem. Likewise, habitat is the physical location of a population or community of organisms. As humans, it is our responsibility to recognize how our behaviors have impacted various environments and determine actions to save the species and environments of this planet. Biodiversity is evident at three main levels, genetic diversity, species diversity, and ecosystem diversity. Genetic diversity includes genetic variation within a population as well as genetic variation between populations. If a population of species becomes extinct, then genetic diversity within that species will decrease and may lead to microevolution. Species diversity is the variation in species within ecosystems. Awareness of species diversity has increased as the U.S. Endangered Species Act defined both threatened and endangered species to prevent extinction. Species extinction may be local or global, depending on the sustainability of a species within the environment. Ecosystem diversity is the variety of ecosystems within the biosphere. Very often, the extinction of dominant or keystone species may put an ecosystem at risk for extinction. Keeping species and genetic diversity in a healthy balance is critically important for the success of the biosphere and for us as humans. Wild populations of plants provide genetic resources that can be used to improve crop qualities and many species of plants have proven essential to the medical field. Therefore, as scientists, we must examine the threats to biodiversity and encourage behaviors that will maintain a healthy biosphere.

MATH: Simpson’s Diversity Index

Simpson’s Diversity Index is a measure of biodiversity. Here is the equation:

This image shows the Simpson’s Diversity Index equation from the AP Biology equation sheet.

Watch the following Simpson's Index of Diversity video to learn more about how to use this equation.

Simpson's Index of Diversity [Video]. (n. d.). Khan Academy. https://www.khanacademy.org/science/ap-biology/ecology-ap/community-ecology/v/simpsons-index-of-diversity Links to an external site.

Now, practice using the Simpson's Diversity Index equation with the practice problems below.

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