1. Chapter 25
Ecology
Ecology: Is the study of relationships of organisms (microorganisms, plants and animals) to one another and their environment.

2. Regional Ecological Issues:
1. Acid rain:
How acid rain is formed? Burned fuels release sulfur and nitrogen in the air which are then converted by moisture into nitric acid and sulfur dioxide.
Effects of acid rain: it kills many useful living organisms such as mycchorizal fungi and increase the concentration of toxic elements. Also reduces plant root’s ability to absorb nutrients.

3. 2. Water contamination: toxic industrial waste (dumping in rivers), spraying pesticides and contaminating ground water.
3. Wetlands (swamps, marshes, river margins, lagoons and floodplains): are not wasteland as have been mistakenly considered.
4. Hazardous waste such as oil spills, industrial waste and radioactive waste.

4. Global Ecological Issues:
Plants, animals and microorganisms live together and interact with the surrounding environment in various ways:
1. Populations: Groups of individuals of the same species. Biologists estimate population size by
-i- counting total number of individuals, or
-ii- by estimating the number of individuals per unit volume (density), or
-iii- by estimating the total biomass (total mass of the individuals present) if the individuals have different sizes or unevenly distributed.

5. 2. Communities: Are populations of one to many species of organisms living together in the same location (the biotic community). Example, the lichen and moss flora living together on a rock is a community. Ecotypes are individuals adapted to specific communities within their overall distribution.

6. 3. Ecosystems: Are the interactions of all the living organisms, in communities, with one another and with their physical environment in a given area.

7. The distribution of a plant species in an ecosystem is controlled by:
-i- Environmental factors or abiotic factors (temperature, precipitation, soil type). Examples:
- Mediterranean climates as in parts of California (wet winters and dry summers) favour spring annuals that complete their life cycle before end of summer and evergreen shrubs that can tolerate long periods of drought.
- Areas with heavy winters snowfall favor forests.
- Desert, arid areas favor xerophytes that are adapted for this climate (modified leaves as spines, thick wax layer on stems, CAM photosynthesis).
- Aquatic (Lakes, ponds , oceans, seas) environments favor hydrophytes (air vacuoles).
-ii- Biotic factor (other living organisms) such as competition for light, water and mineral nutrients, and grazing by animals.

8. Ecosystems sustain themselves by
- photosynthetic activity
- energy flow through food chains
- recycling of nutrients.

9. Energy flow in an ecosystem: In an ecosystem energy flows in the following order from one level to the other:
1. Producers; organisms capable of performing photosynthesis i.e. capture light energy to convert carbon dioxide and water to energy-rich molecules (e.g. Plants and algae).
2. Primary consumers; animals that feed on producers (e.g. cows, caterpillars and humans).
3. Secondary consumers; animals that feed on primary consumers (e.g. tigers and humans).
4. Decomposers; such as bacteria and fungi breakdown dead organic material from dead producers, and dead bodies of primary and secondary consumers to very simple forms that can be re-assimilated by the live primary producers.

10. In an ecosystem, producers and consumers interact to form food chains or interlocking food webs.

12. - Energy flows in an ecosystem in a pyramid form with more energy at the bottom of the pyramid than at the top. At each level in the pyramid of energy, only 10% of the energy flows from one level to the upper level and the rest is lost in the form of heat (respiration). Thus at the top of the pyramid, a very small fraction of the original energy of the sun light is captured by the secondary consumers. In long food chains there is more loss of energy. In short food chains there is less loss of energy between levels.

14. - A vegetarian diet makes more use of solar energy than diets containing meats.
- There is a sharp reduction of the number of individuals and the total mass at each level of a food chain (e.g. ocean ecosystem).
- The food chains are cyclical in nature (Balance of Nature).

15. Forms of interactions between plants, herbivores, and other organisms:
1. Secretion of chemical substances: Examples
-i- Roots of black walnut trees produce a substance that wilts tomatoes and potatoes and inhibits apple trees from growth.
-ii- Some plants secrete phytoalexins, an inhibitor for the growth of disease-causing fungi and bacteria.
-iii- Some bacteria excrete inhibitory substances that limit plant growth.

16. 2. Parasitism: Example, the snapdragons lack chlorophyll and thus rely on their flowering plant host for obtaining energy and food.

17. 3. Mutualism (exchange benefits): Example;
- Mycorrhizal fungi are associated with the roots of some woody plants where they obtain energy from the plants. In return they increase the surface area of the roots and thus help the plants absorb more nutrients.
- Association of ants with the thorny plant, Acacia. Ants live in their hollow thorns obtaining sugars from their nectaries and in return attack any insect, animal or even plant that come in contact with Acacia.
- Some plants use structural defence means as spines or chemical means such as secreting certain compounds that protect them from extinction due to heavy attack by primary consumers.

18. The Nitrogen Cycle:
- Most of the nitrogen in the atmosphere is inert.
- Ammonia produced by the effect of decomposers (decay bacteria and fungi) of dead organisms is fixed by nitrogen fixing bacteria, either free in soil or in association with roots of legumes, to nitrite then nitrate (a form useful for plants).
- Small amount of nitrogen is returned to soil from the atmosphere by the action of light on industrial pollutants and by fixation by flashes of lightning.
- Large amounts of nitrogen are lost from our soils by harvesting crops, fires, erosion of topsoil followed by water leaching it out.
- Denitrifying bacteria in poorly aerated (flooded) soil uses nitrate instead of oxygen for their respiration and converts it to inert nitrogen adding to the depletion of soils from useful nitrate.

20. The Carbon Cycle:
Cardon dioxide (0.03% of atmosphere) needed for photosynthesis is replaced by : Decay bacteria and fungi (90%), small amounts by burning of fossil fuels, from fires and volcanic activities.

23. Succession
Is the appearance of living organisms on an exposed piece of land (or water) due to volcanic, earthquake or landslide activity. First species change the environment by time so that it becomes more favourable for a second type of species and so on. Such sequence of events leading to the gradual change of the environment by living organisms is known as succession

24. Two types of succession:
1. Primary succession: Is the succession that occurs in an area that has not been covered with soil or vegetation before i.e. involves the formation of soil, for the first time in a given area. Types:
(a) Xerosere (terrestial)
(b) Hydrosere (water)

25. (a) Xerosphere (terrestial): Lava or bare rocks cool down and crack while cooling. The following sequence occurs
Lichens ----->Larger lichens > Soil accumulates
> mosses establish > ferns and seed plant
-----> soil builds up large plants grow until an equilibrium in vegetation with other organisms is reached and this is known as climax vegetation. For example in the USA the climax vegetation of the North Eastern deciduous forests is trees of oaks, maples, hickories; of the South Western desert is cacti; of the Pacific Northwest is large coniferous trees. In the Midwest, grasses and other herbaceous plants form the climax vegetation.

26. (b) Hydrosphere (water):
- Succession in wet habitats. Occurs in lakes and ponds that were left behind by retreating glaciers.
- Succession starts by algae followed by floating plants (e.g. duckweeds) on the margins followed by rooted aquatic plants.
- Gradually the exposed water diminishes and grasses start establishing followed by shrubby plants then coniferous trees that cover the entire pond or lake site.
- In stream-fed lakes, the streams feed the lakes with organic material enriching the lake for a rapid succession. This rapid enrichment is known as eutrophication.

27. 2. Secondary succession: It follows when an area has been disturbed by fires, floods and landslides. It is faster than primary succession. Grasses establish first followed by trees and shrubs.

28. Fire Ecology: -Some trees such as the giant redwood and ponderosa pines often survive fires. Fire scars can be seen on their annual growth rings.
-Fires are useful to grasslands because they convert dead organic material to mineral-rich ash that provides nutrients to the ecosystem.
-After a fire some useful soil bacteria (the blue-green algae which are capable of fixing nitrogen from air) actually were found to increase in numbers while disease-causing fungi decrease in numbers.
-Grasses are better adapted to fires than woody plants. Why?
Therefore fires can determine the type and composition of forests.
-Seeds of some tree species do not germinate until exposed to fire.

29. Effects of Humans on the Ecosystem:
Humans have caused some damage to their ecosystem (i.e. to both the earth and its surrounding atmosphere). Examples of such effects are: The greenhouse effect (carbon dioxide, methane); acid rain; depletion of the ozone layer; contamination of water; and loss of biodiversity.

30. 1. The Greenhouse effect: is the accumulation in the atmosphere of gases that permit sun's radiation to reach the earth's surface but prevent the heat from escaping back to the space. This leads to a raise in the earth's temperature. Two gases cause this effect:
(i) Carbon dioxide from burning fossil fuels and de-forestation increased by 25% in the atmosphere since In the last 25 years the temperature of the earth's surface increased by 0.4oC.
(ii) Methane produced by anaerobic bacteria in swamps or wet lands and by the wood-digesting organisms within the guts of termites.

31. 2. Acid rain: Burning of fossil fuels releases sulfur and nitrogen which react with sunlight to produce nitric acid and sulfur dioxide that in turn react with rain to produce acid rain of pH less than 5.5. Acid rain causes the soil to be acidic killing some useful microorganisms and reducing the ability of roots to absorb nutrients.

32. 3. Ozone depletion: Is a layer of special oxygen (O3) that is found in the upper layers of the atmosphere and acts as a shield to filter the sun radiation from the damaging short wave, ultraviolet rays that can cause serious damage to living organisms (skin cancer to humans). Methane gas, chlorofluorocarbons (both are byproducts of the refrigeration industry) and the bromine-based compounds called halons (found in portable fire extinguishers) are broken down by sunlight and their products destroy the ozone layer.

33. 4. Contamination of water: caused by dumping of toxic waste, runoff over polluted land, pesticides and fertilizers are major sources for contaminating our waters.

34. 5. Loss of biodiversity: The destruction or even fragmentation of natural habitats of some animals and plants due to human activities led to severe reduction in numbers of individual of some species (endangered species).