Ecological Eyes
The Basics:
Energy enters an ecosystem from the outside, flows through, and leaves. For sun-powered systems, if this energy flow were to be interrupted for more than a few hours at night, the ecosystem would cease to exist. In terrestrial systems, water enters the ecosystem from the outside, flows through, and leaves.
Many critical nutrients (e.g. phosphorus, potassium, sulfur) cycle within the ecosystem; little is being delivered from the outside. Nitrogen, carbon and oxygen are supplied from the atmosphere.
Nothing is discarded (there is no waste) in an ecosystem. Over time many ecosystems will evolve strategies for retaining energy and nutrients for longer periods of time, leading to greater biodiversity.
All ecosystems have a carrying capacity for any one species—a limit to the population it can support with being degraded. This is the case because all individual species are part of a larger system, with a multiplicity of species are necessary to enable an ecosystem to function—to capture energy and cycle nutrients. For example it is estimated that the ratio of plant life to animal life on land is approximately 1000: 1 by weight. Plants, with their capture/storage of energy and infusion of oxygen into the atmosphere, are the dominant precursor to animal life.
The ecosystem services provided by biological diversity include: Primary production of food; decomposition and nutrient retention and cycling; energy transfer from sunlight through a succession of life forms; oxygen and CO2 production; carbon sequestration/climate modification; building soil; and ecosystem stability.
Try looking through ecological eyes at your own local environment:
1. ‘Everything is connected to everything else’ on earth. Identify some of the interconnections in the ecosystem that you are in.
Comment: It is somewhat axiomatic in ecology that ‘everything is connected to everything else.’ One basic example is the oxygen/carbon dioxide balance in the atmosphere; plants breathe in CO2 and give off oxygen as a waste product; animals breathe in oxygen and give off CO2. Oxygen is such a reactive element that if it were not constantly pumped into the atmosphere by plants its current abundance of 20% of the atmosphere would diminish to 1% in less than a year. Critical nutrients (elements) such as phosphorus and nitrogen are made available to the larger biosphere by neither plants nor animals, but rather by bacteria and fungi.
2. Where does the energy for the ecosystem come from? What are the variables in energy supply, and how do plants and animals respond to these variables? How does energy leave the system?
Comment: Most of the available energy on earth comes from sunlight. Plants have to compete for it—that is one reason they have grown taller over evolutionary history. In the Methow, different plants grow on different aspects because the amount of solar gain (and evaporation) varies greatly between north and south-facing slopes. Other variables include day length through the year, the angle of the sun, cloud cover and latitude. The energy balance for the system has to be fairly precise, or it would either heat up and cook or freeze solid.
3. Where does the water for the ecosystem come from? What are the variables in water supply, and how do plants respond to these variables?
Comment: Obviously water comes from the sky, but plants are very responsive to how it moves across the land, with different species on north and south slopes and in the draws. The shapes of conifer and broadleaf trees and their leaves/needles, the strategies of evergreen verses deciduous leaves, and the strategies of annual, perennial and woody plants are all varied responses to how moisture is delivered and how long it is available.
4. Where do the nutrients critical to life (carbon, oxygen, nitrogen, phosphorus, potassium) come from in this ecosystem, and how are they retained (cycled) within the ecosystem?
Comment: The atmosphere is composed of 80% nitrogen, but it is bound up as a molecule (N2) and is unavailable to plants and animals in this form. Only certain species of bacteria can split the molecule and make nitrogen available to the larger life community. Carbon is critical to the structure of living cells; most of it is supplied by the carbon dioxide in the atmosphere, which only resides there in parts per million (currently about 390 ppm; it is estimated that life captures about 100 billion tons of carbon per year from the atmosphere). Phosphorus and potassium are present in rock and soil, but they are water soluble and will be lost to ecosystems unless retained in living cells.
5. What are the main primary producers (the photosynthesizers) in the ecosystem? Who are the primary, secondary, and tertiary consumers? Who are the decomposers? In other words, who lives here, and what are the relationships?
Comment: Primary consumers are those that eat plant material, secondary consumers are carnivores that eat primary consumers, tertiary consumers are the top predators and eat everybody else. The earth only receives one billionth of the energy the sun gives off, and plants only capture about 1% of that solar flux. Primary consumers are only able to utilize 10% of the energy stored in the plant tissues they ingest, and secondary and tertiary consumers only capture 10% of the energy in the animal tissue that they consume. It is for this reason that the ratio of plant life to animal life on the plant is in the neighborhood of 1000:1.
No comments yet.