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Ecology is the study of how living things(biotic factors) interact with their non-living environment(abiotic factors). This includes the study of the various ecosystems and biomes. After you have studied these, you take a written test. Last year's (2008) topic was Forests and Deserts; this year (2009) it is Deserts and Grasslands. Next year (2010) it is proposed to be Grasslands and Taiga. For both of the biomes, you should know the main nutrients found there and their cycles, animals and plants found there along with their adaptations, life zones, and other common processes found there.

Forests: This area of ecology is great for the people who participated in Forestry. You will have to know the different parts of the forest, and various kinds of forests and information about them. The main subdivisions that you need to learn for this biome would be taiga/boreal forest, rainforest, and deciduous forests.

Deserts: Presumably you will have to know various water conservation and temperature regulation strategies organism have developed to cope with the extremely arid environment.

Basics of Ecology

Food Web

On many of the Ecology tests, you were given around a dozen organisms and you had to organize them into a food web. For 2009, the theme is grasslands and deserts, so you should have a general idea of the organisms that inhabit both areas, and which organism consumes the other (ex. shrub -> shrew -> snake -> hawk)

Ecology Definitions

Know how to apply all of below to defining variables, analyzing data from graphs and tables, presenting data in graphs and tables, forming hypotheses, and making calculations and predictions

Ecological Roles

Any organism that is capable of producing its own food, usually through photosynthesis
An organism that feeds on other living organisms, for example animals and parasitic plants would be considered consumers.
consumes a producer
consumes a primary consumer
consumes a secondary consumer
an organism that breaks down organic matter into inorganic form, plants often uses this material as fuel
Carrying Capacity
the maximum number of individuals of a given species that a site can support during the most unfavorable time of year, without causing deterioration of the site

Community Interactions

Predator and Prey
one organism eats another organism (frog eats fly)
Two organisms living in direct contact with one another
Two organisms living together in a relationship in which both benefit from the association. (bee pollinates flower)
Two organisms in a relationship in which one benefits and one is harmed (dog has heartworms). Generally the host is not killed
Two organisms in a relationship in which one benefits and the other is killed (house cat eats mouse)
Two organisms in a relationship in which one is unaffected and one is harmed (the black walnut tree secretes juglone which kills the plants living at base of tree, but the lack of competition doesn't help or harm the tree). This is a very rare type of symbiosis.
Two organisms in a relationship in which one benefits and the other is unaffected (shark and remora)
The replacement of one community by another, developing toward a climax
the ecological succession of vegetation that occurs in passing from barren earth or water to a climax community
The development of biotic communities in an area where the natural vegetation has been removed or destroyed but where soil is present

More Terms

Extinction-gone forever
In the context of evolution, certain traits or alleles of a species may be subject to selection. Under selection, individuals with advantageous or "adaptive" traits tend to be more successful than their peers reproductively--meaning they contribute more offspring to the succeeding generation than others do
The differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources
Stabilizing selection is a type of natural selection in which genetic diversity decreases as the population stabilizes on a particular trait
Disruptive selection is a type of natural selection that simultaneously favors individuals at both extremes of the distribution. When disruptive selection operates, individuals at the extremes contribute more offspring than those in the center, producing two peaks in the distribution of a particular trait
In population genetics, directional selection occurs when natural selection favors a single allele and therefore allele frequency continuously shift in one direction.
The process in which breeders choose the variants to be used to produce succeeding generations
Limiting Factors
A factor that limits a population's growth; i.e.resources and shelter
The number and variety of organisms within one region

Ecology Graphs and Charts

Survival Curves
Graph of the probability of survival (y-axis) versus time (x-axis). Some basic life history strategies can be seen from the basic shape of this graph. Type I organisms have lower mortality rate at low ages which gradually increases with age. Type II organisms have mortality rates that stay the same throughout life. Type III organisms have the largest mortality rates at birth. Most survivalship curves are combinations of more than one type of organism. The three general shapes can be seen below.

Survivor curve.jpg

Life Table
an age-specific death schedule. Such a schedule is often converted to a more palatable survivorship schedule. For each age interval there is an predicted life expectancy or survivorship. From a life table, one can produce a survival curve.

Population Growth

Population growth deals with how the size of a population changes over time. Intrinsic rate of growth (r-max) is the rate of growth under ideal conditions.

  • Exponential growth occurs when the growth rate remains the same while the population grows. It creates a J shaped curve (shown in red below).
  • Logistic growth occurs when the growth rate decreases as the population grows due to density-dependent factors (factors increasing mortality rate as population grows such as predation rates, competition, and disease). This creates an S-shaped curve (shown in blue below). It is the most common type of population growth.

Population growth.jpg

Life History Strategies

Age of Reproduction
the average age in an organism when it becomes capable of reproduction ( For example, population A might have many more members than population However, all the members of A might be post-reproductive, whereas population B might consist of mostly prereproductive and reproductive age individuals. Population A might be in danger of extinction)
r-selected organisms
put most of their energy into rapid growth and reproduction. This is common of organisms that occupy unpredictable environments, e.g. weeds are usually annuals with rapid growth and early reproduction. They produce large number of seeds containing few stored nutrients
K-selected organisms
put most of their energy into growth. They are common in stable environments near carrying capacity, e.g. long lived trees such as redwoods take many years of growth to reach reproductive age
Seed Dispersal
the method by which a plant scatters its offspring away from the parent plant to reduce competition. Methods include: wind, insects, animals, tension, and water
Some seeds are carried to a new place by the wind. These seeds are very light. The seeds of the orchid are almost as fine as dust. Many have hairy growths which act like little parachutes and carry the seeds far away from the parent plant.
Fruits which float such as those of the water lily and the coconut palm are carried by water. Coconuts can travel for thousands of kilometers across seas and oceans. The original coconut palms on South Sea islands grew from fruits which were carried there from the mainland by ocean currents.
The animal eats the fruit but only the juicy part is digested. The stones and pips pass through the animal's digestive system and are excreted to form new plants. This can be far away from the parent plant.
Some plants have pods that explode when ripe and shoot out the seeds. Lupins, gorse and broom scatter their seeds in this way. Pea and bean plants also keep their seeds in a pod. When the seeds are ripe and the pod has dried, the pod bursts open and the peas and beans are scattered.
To survive fire some plants have adaptive traits that allow them to reproduce or regenerate. An adaptive trait is a behavior, physical feature or some other characteristic that helps a plant or animal survive and make the most of its habitat. When fire occurs, animals have the ability to fly, run away or burrow deep into the ground. Plants cannot do this and so have adapted other ways of surviving. The way a plant stores its seeds and disperses them is an example of a fire adaptive strategy. The intensity of the fire ( it is important the fire reaches the right temperature) is crucial to the seeds dispersal. Also important is how often the fires occur.

Human Impact on Ecosystems

Global Warming

Greenhouse Effect:

Possible Causes: Problems arise when the atmospheric concentration of greenhouse gases increases. Since the the industrial revolution, atmospheric concentrations of carbon dioxide have increased nearly 30%, methane concentrations have more than doubled, and nitrous oxide concentrations have risen by about 15%. These increases have enhanced the heat--lived in the atmosphere and vary regionally. Scientists generally believe that the combustion of fossil fuels and other human activities are the primary reason for the increased concentration of carbon dioxide. Plant respiration and the decomposition of organic matter release more than 10 times the CO2 released by human activities; but these releases have generally been in balance during the centuries leading up to the industrial revolution with carbon dioxide absorbed by terrestrial vegetation and the oceans. Fossil fuels burned to run cars and trucks, heat homes and businesses, and power factories are responsible for about 98% of U.S. carbon dioxide emissions, 24% of methane emissions, and 18% of nitrous oxide emissions. Increased agriculture, deforestation, landfills, industrial production, and mining also contribute a significant share of emissions. In 1997, the United States emitted about one-fifth of total global greenhouse gases.

Effects of Climate Change: Mean surface temperatures have increased 0.5--8 inches over the past century. Worldwide precipitation over land has increased by about one percent. The frequency of extreme rainfall events has increased throughout much of the United States. Increasing concentrations of greenhouse gases are likely to accelerate the rate of climate change. Scientists expect that the average global surface temperature could rise 1----

Invasive Species

A species that has moved into an area and reproduced so aggressively that it has replaced some of the original species. For example if we introduced one species to a new environment the already adapted species to that area would be forced out. This practice can be produced by lost of habitat.

Acid Rain

Acid rain is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry. Wet deposition refers to acidic rain, fog, and snow. As this acidic water flows over and through the ground, it affects a variety of plants and animals. The strength of the effects depend on many factors, including how acidic the water is, the chemistry and buffering capacity of the soils involved, and the types of fish, trees, and other living things that rely on the water. Dry deposition refers to acidic gases and particles. About half of the acidity in the atmosphere falls back to earth through dry deposition. The wind blows these acidic particles and gases onto buildings, cars, homes, and trees. Dry deposited gases and particles can also be washed from trees and other surfaces by rainstorms. When that happens, the runoff water adds those acids to the acid rain, making the combination more acidic than the falling rain alone. Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles.

Scientists discovered, and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the US, About 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal. Acid rain occurs when these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of most of these reactions. The result is a mild solution of sulfuric acid and nitric acid.


The wearing away of land or soil by the action of wind, water, or ice. Soil erosion is a natural process. It becomes a problem when human activity causes it to occur much faster than under natural conditions.

Causes of Soil Erosion

Wind and water are the main agents of soil erosion. The amount of soil they can carry away is influenced by two related factors:

  • speed - the faster either moves, the more soil it can erode;
  • plant cover - plants protect the soil and in their absence wind and water can do much more damage.
The Importance of Plants

Plants provide protective cover on the land and prevent soil erosion for the following reasons:

  • plants slow down water as it flows over the land (runoff) and this allows much of the rain to soak into the ground;
  • plant roots hold the soil in position and prevent it from being washed away;
  • plants break the impact of a raindrop before it hits the soil, thus reducing its ability to erode;
  • plants in wetlands and on the banks of rivers are of particular importance as they slow down the flow of the water and their roots bind the soil, thus preventing erosion.

The loss of protective vegetation through deforestation, over-grazing, ploughing, and fire makes soil vulnerable to being swept away by wind and water. In addition, over-cultivation and compaction cause the soil to lose its structure and cohesion and it becomes more easily eroded. Erosion will remove the top-soil first. Once this nutrient-rich layer of soil is gone, few plants will grow in the soil again. Without soil and plants the land becomes desert-like and unable to support life - this process is called desertification. It is very difficult and often impossible to restore desertified land.

Preventing Soil Erosion

Preventing soil erosion requires political, economic and technical changes. Political and economic changes need to address the distribution of land in South Africa as well as the possibility of incentives to encourage farmers to manage their land sustainably. Aspects of technical changes include:

  • the use of contour ploughing and wind breaks;
  • leaving unploughed grass strips between ploughed land;
  • making sure that there are always plants growing on the soil, and that the soil is rich in humus (decaying plant and animal remains). This organic matter is the "glue" that binds the soil particles together and plays an important part in preventing erosion; ->* avoiding overgrazing and the over-use of crop lands;
  • allowing indigenous plants to grow along the river banks instead of ploughing and planting crops right up to the water's edge;
  • encouraging biological diversity by planting several different types of plants together;
  • conservation of wetlands.

Ecology Glossary

A basic glossary of ecology terms.

  • Abiotic- Non living (Water, wind, rocks)
  • Acid precipitation - Includes acid rain, acid fog, acid snow, and any other form of precipitation that is more acidic that normal (i.e., less that pH 5.6).

  • Aerobic - Living or occurring only in the presence of oxygen
  • Ammonification - the process by which decomposers change nitrogen in detritus to ammonium (NH4+)
  • Anaerobic, adj.: 1: Lacking or seriously depleted of oxygen
  • Assimilation - the process by which plants absorb nitrate or ammonium through root hairs to be used within the plant

  • Carrying Capacity - the maximum number of organisms that an environment can support

-sustaining community in an advanced stage of ecological succession; usually has a diverse array of species and ecological niches; captures and uses energy and cycles critical chemicals more efficiently than simpler, immature communities

  • Clumped Distribution - the most common type of population distribution where many members of the population live close together
  • Cohort - a group of individuals born around the same time

-off fragments and wastes of living organisms by breaking down the complex organic molecules in those materials into simpler inorganic compounds and then absorbing the soluble nutrients

  • Denitrification - the reduction of nitrates back into nitrogen gas (N2), completing the nitrogen cycle. This process is performed by bacterial species such as Pseudomonas and Clostridium in anaerobic conditions.

-fed cropland, or irrigated cropland to desertlike land, with a drop of agricultural productivity of 10% or more

-off fragments and wastes of living organisms

-off fragments and wastes of living organisms

  • Extant - a species that is still alive and reproducing
  • Extinct - a species that is no longer living on earth

  • Gene pool - the sum total of all the genes that exist among all the individuals of a species

-76 cm) is enough to support the growth of grass and small plants but not enough to support large stands of trees

  • Gross primary productivity - the rate at which an ecosystem's producers capture and store a given amount of chemical energy as biomass in a given length of time

-eating organism

  • Heterotroph - organism that cannot synthesize the organic nutrients it needs and gets its organic nutrients by feeding off of the tissues of producers or of other consumers
  • Indicator Species - a species that gives an early warning that an ecosystem is in a state of flux, often times fish and amphibians or apex predators

  • J-

  • K-

  • Muellerian Mimicry - resemblance of two equally unpalatable species in order to increase the concentration of individuals with the warning appearance to increase its efficiency
  • Muskeg - an acidic soil type common in Arctic and boreal areas, more-or-less synonymous with bogland

  • Nitrification - the process of oxidizing ammonia to create nitrite (NO2-)then oxidizing the nitrite to create nitrate (NO3-)

  • Nitrogen fixation - the process of chemically converting nitrogen gas (N 2 ) from the air into compounds, such as nitrates (NO 3 ), nitrites (NO 2 ), or ammonia (NH 3 ), that can be used by plants in building amino acids and other nitrogen-containing organic molecules.
  • Nutrient - any food or element an organism must take in to live, grow, or reproduce

  • Phosphorus Cycle - involves the uptake of phosphorus by organisms. Phosphorus in the environment is mainly found in rocks, and natural weathering processes can make it available to biological systems. Phosphorus is an essential nutrient for plants and animals in the form of ions PO43- and HPO42- . It is a part of DNA-molecules and RNA-molecules, molecules that store energy (ATP and ADP) and of fats of cell membranes.

  • r--lived offspring in a short period
  • Rhizobia - soil bacteria that fix nitrogen after becoming established inside root nodules of legumes

  • Second law of thermodynamics, - in any conversion of heat energy to useful work, some of the initial energy input is always degraded to lower quality, more dispersed, less useful energy

  • S--shaped curve when a rapidly growing population exceeds the carrying capacity of its environment and ceases to grow

  • Synergy - is the term used to describe a situation where the final outcome of a system is greater than the sum of its parts.
  • Taiga - the largest land biome. Characterized by conifer forests and cold temperatures. Boreal forest is usually used to refer to the more southerly part of the biome.

source of energy that enters the ecosystem

  • Uniform Distribution - a rare type of population distribution where the population is evenly spread out

Sample Questions

Runoff graph.jpg

The graph above relates nitrate concentration in runoff water near a forest to time. In this experiment, forest A experienced deforestation completed in 1925. Forest B experienced little to no deforestation.

1.Explain the cause for the different concentrations of nitrate in the two ecosystems.

2.What is a possible cause for the increase of nitrate concentration in the runoff water in ecosystem B?


1. Why are similar warblers in the above diagram able to coexist in the same ecosystem?

2. This strategy that allows them to live together is known as __________.


  • Earth and Environmental Systems podcast show notes, look for episodes 29, 33-38

2007 Resources




2009 Resources

Deserts: (Introductory desert material) (good study guide!)

Grasslands: Ecology Glossary