What is Ecology?

Ecology - the study of how organisms interact with one another and with their physical and chemical environments - mainly seeks to understand interactions among organisms, populations, communities, ecosystems, and the ecosphere.

An organism is any form of life. A species is a group of organisms that resemble one another in appearance, behavior, chemistry and genes, and if they can breed and produce live, fertile offspring ·under normal conditions. About 1.4 million species have been identified and named, but there are estimates of about 5 million to 100 million species that exist on earth (mostly insects and microorganisms).

A population is all members of the same species occupying a given area at the same time. Individuals do not look orbehave exactly alike due to genetic diversity -slight variation in genetic makeup. Populations are dynamic; they change in size, age distribution, density and genetic composition due to changes in the environment.

The place where a population typically lives is its habitat. The populations Of all species in a particular place make up a community.

An ecosystem is a community of different species interacting with one another and with their nonliving environment of matter and energy. The size of an ecosystem is defrned by the system that is studied. Natural ecosystems tend to merge with the next in an ecotone, a region containing a mixture of species from adjacent region.

Climate - long term weather - basically determines what type of life will thrive in a given area. Biomes are large regions (forests, deserts, grasslands) characterized by climatic conditions and inhabited by certain types of life. Each biome consists of many ecosystems whose communities have adapted to environmental differences within the biome.

Marine and freshwater regions are divided into aquatic life zones, each containing many ecosystems. (marine; estuaries, coastlines, coral reefs, coastal marshes, mangrove swamps, continental shelves and deep ocean) (freshwater; lakes and streams).

What is Biodiversity, and why Is It So Important?

Biodiversity is the vanety of life forms that can best survive the various conditions currently found on earth. Biodiversity includes:


  • genetic diversity - genetic variability among individuals in one species.
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  • species diversity - variety of species in different habitats.
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  • ecological diversity- variety of biological communities that interact.
  • "Biocapital" provides a rich variety of genes, species and ecosystems that give us food, wood, fibers, energy, raw materials, industrial chemicals and medicines, and pours billions of dollars into the world economy.

    Biodiversity also provides recycling and purification systems and natural pest control. Every species contains stored genetic information that could provide adaptations for future environmental changes.

    Human cultural diversity is the variety of human cultures that provides social and technological "solutions" that have enabled us to adapt.

    What Types of Organisms Are Found on Earth?

    Eukaryotic (all organisms except bacteria) cells have a nucleus and membrane-bounded internal structures (organelles). Prokaryotic (bacteria) cells do not have a distinct nucleus or internal parts enclosed by membranes.

    Earth's organisms can be divided into five kingdoms: monera, protists, fungi, plants, and animals.

    Monera - (bacteria and cyanobacteria) single-celled, microscopic, prokaryotic; decomposers that break down dead organisms into simpler compounds (nutrients).

    Protista - single-celled eukaryotic (diatoms, dinoflagellates, amoebas, slime molds, protozoa, yellow-green algae); some protists use calcium to make protective shells that turn into limestone over millions of years.

    Fungi -many-celled eukaryotic (mushrooms, molds, mildews, yeasts); many are decomposers, others kill plants (most bacteria, fungi and protists are microorganisms- need a microscope to see).

    Plantae- many-celled eukaryotic (red, brown and green algae, mosses, ferns, conifers and flowering):

  • Evergreen plants - keep some leaves or needles all year; can carryout photosynthesis year-round (ferns, pines, spruces sequoias).
  • Deciduous plants - shed leaves to survive drought and cold (oak, maple).
  • Succulent plants - no leaves (adaptation to dry climate); store water in fleshy stems and branches, trap dew on hairs (cacti).
  • Epiphytes (air plants)- grow on branches rather than soils (orchids).
  • Annuals have life cycle of one year (corn, marigolds) and perennials can live for more than two years (roses, ivy, grapes, elms).

    Water and nutrients are transported through vascular tissue in most land plants. Some water transpires (evaporates) through pores in leaves.

    Animalia - many-celled eukaryotic.


  • Invertebrates have no backbones (sponges, jellies, worms, arthropods, mollusks and echinoderms).
  • · Vertebrates are animals with backbones (fishes, amphibians, reptiles, birds, and mammals).
  • What Are the Major Living Components of Ecosystems?

    The ecosphere is divides into two parts: biotic (living) and abiotic (nonliving). Living organisms are classified as either producers or consumers.

    Producers (or autotrophs) make their own food. On land green plants are producers and in aquatic ecosystems producers are phytoplankton.

    Most producers use sunlight to make complex compounds (glucose) by photosynthesis. Green plants trap solar energy in pigments called chlorophyll. Photosynthesis (a very complex reaction) can be summarized as follows:

    6CO2 + 6H2O + solar energy -----> C6H12O6 (glucose) + 6O2

    A few specialized bacteria can synthesize food without sunlight in a process known as chemosynthesis.

    Consumers (or heterotrophs) get their organic nutrients from feeding on producers or other consumers.

    · Herbivores (plant eaters) are called primary consumers because they feed directly on producers.

    · Carnivores (meat eaters) are called secondary consumers because they feed on primary consumers.

  • · Tertiary (higher-level) feed only on other carnivores.
  • · Omnivores eat both plants and animals (pigs, rats, cockroaches, humans).
  • Scavengers feed on dead organisms.

    Detritivores live off detritus - parts of dead organisms and wastes of living organisms.

    Decomposers are consumers that recycle organic matter by breaking down dead organic matter (detritus) to get nutrients. Something that is biodegradable can be broken down by decomposers.

    Both producers and consumers use chemical energy stored in glucose to fuel their life processes through a process of aerobic respiration. The net effect of this complex reactions:

    C6H12O6 + 602 -----> 6CO2 + 6H2O + energy (ATP)

    Some decomposers get energy from glucose in the absence of oxygen in a process called anaerobic respiration or fermentation. The end products are compounds like methane gas, ethyl alcohol, acetic acid hydrogen sulfide and lactic acid.

    The survival of an individual organism depends on the flow of matter and energy through its body. In an ecosystem, matter recycling and one-way energy flow are the important factors for survival. Each type of organism plays a role in this flow.

    What Are the Major Nonliving Components or the Ecosystem?

    The physical factors that influence living organisms are sunlight and shade, average temperature and temperature range, average precipitation and its timing, wind, latitude, altitude, frequency of fire, nature of soil, water currents and amount of suspended solid material in aquatic-ecosystems.

    The chemical factors affecting ecosystems are water, air in the soil, plant nutrients dissolved in soil and water, level of toxic substances, salinity and levels of dissolved oxygen in aquatic systems.

    How Much Change in Abiotic Factors Can Populations Tolerate?

    Each population has a range of tolerance to variations in its physical and chemical environment. The largest number ofindividuals in a population will be in fhe optimum level or range, While a few can survive above or below that range (possibly in stress), but no individuals can survive outside of the range of tolerance.

    The law of tolerance: the existence, abundance, and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemial factors fall within the range tolerated by that species. Tolerance limits are the minimum and maximum limits for physical conditions beyond which no members of a species can survive.

    Acclimation is adapting to a change that is gradual, but it does have its limits.

    As change occurs, a species comes closer to its absolute limit, and the next small change can trigger a threshold effect as the tolerance limit is exceeded. It may seem that environmental problems arise suddenly, when in fact they have been growing slowly.

    Limiting Factors: Too Much or Too Little Can Be Deadly

    The limiting factor principle: too much or too little of any abiotic factor can limit or prevent growth of a population, even if all other factors are of or near the optimum range of tolerance. Some limiting factors for land are temperature, water, light, soil nutrients and shelter; for aquatic systems they are salinity (dissolved salts), temperature, sunlight, nutrients and dissolved oxygen content (in a given volume at a particular temperature and pressure). The ultimate limiting factor for any individual is their genes (bean stalks are never going to be as tall as oak trees). The limiting factor for a population can change.