PBIO 100 Lecture Notes

I. Important terms

• A. Ecology is a very complex field of study involving the effects of the environment on living organisms, the effects of living organisms on the environment, and the effects that living organisms have on one another.

• B. Plant ecology is the study of the interaction among plants, and between plants and their environment.
  • 1. Understanding these relationships is important for those who grow crops, provide lumber, raise cattle, protect endangered species or threatened ecosystems, and for any concerned citizen. How life functions is one of the most fundamental questions for humans throughout history.
    • a. involves energy flow from the sun through organisms
      b. involves cycling of matter
      c. involves species diversity and their interactions
       

  C. Population- all the members of a single species that live together

  • 1. For example, an ecologist might investigate a population of ponderosa pine trees (Pinus ponderosa) by examining both its physiology and its habitat (the location where the population is found).

II. Plant community

A plant community consists of different populations of plants living together in the same geographic area.

• A. Plant communities are usually defined by the dominant species, such as the white pine forest community. The dominant species are the most influential species in the community.

  B. They control the structure, and to some degree, the species composition of the community through their effects on the physical and chemical factors in the community including:

  • 1. light (provide shade)
    2. wind (wind screen)
    3. humidity (higher than in open areas)
    4. availability of water and nutrients in the soils
     

  C. Within each plant community may be a variety of plant forms, such as trees, shrubs, and a plant ground cover.

  • 1. a tree is a woody plant that generally has a single stem (trunk)
    2. a relatively small woody plant typically with several stems arising near the ground is called a shrub
    3. the ground cover may consist grasses or forbs. A forb is any small herbaceous (no wood) plant that is not a grass. Some or all of the ground may not be covered by plants. There may be bare ground or sand. In some forest communities, the ground may be covered by litter, a layer of slightly decomposed organic matter

III. Ecosystems

Ecosystem- a community with all its living organisms (biotic) and its nonliving environment (abiotic).

• A. A plant community exists in a particular habitat created by all the biotic and abiotic factors. Every plant species has a range of environmental conditions that it can tolerate. Some plant species can live only in dry soil and others in wet, some in bright light and others in shade, some in hot climates and others in cold. The plants that live within a community are able to tolerate the various environmental factors that make up that community's habitat.

  B. Biotic - There are many more organisms that live in a community besides the plants. The community supports a variety of animals including mammals, birds, reptiles, amphibians, and insects.

  • 1. organisms interact and form a food chain
    • a. the organisms that obtain their energy from the sun through the process of photosynthesis are called primary producers
      • i. these producers may include plants , algae,
        cyanobacteria (photosynthesizing bacteria)

      b. animals that eat the primary producers are called herbivores or 1st order consumers
      c. animals that eat the 1st order consumers are called carnivores or 2nd order consumers, and so on

    2. dead material in the community is decomposed by fungi (such as mushrooms) and soil bacteria

  C. Abiotic

  • 1. climate - Temperate climates with generally moderate temperatures and significant rainfall, such as that found in the eastern United States, permit extensive plant growth.
    • a. there are climates that are wetter, as in the temperate or tropical rain forests where plant abundance and species diversity are greater, and climates that are drier, as in the deserts where plant abundance is lower
      b. plants within a community respond to the seasons of the year; in winter, deciduous trees have dropped their leaves and are dormant. Some plants bloom in the spring, whereas others bloom in summer or fall

    2. light - The availability of affects plant composition in the communities; plants requiring strong sunlight cannot grow in the dark understory of the summer forest; other plants are uniquely adapted to the shade.
    3. soil - the depth and type of soil dictates what kinds of plants may grow; the soil provides support, inorganic nutrients, water, and suitable gases for the root systems.

    • a. the plants contribute to the composition of the soil through litter; meaning the old leaves and stems that have dropped from the trees and accumulated on the ground surface; these decompose through the action of bacteria and fungi to produce the organic material in the soil
      b. example: the litter in pine forests is slightly acidic, so the soils in these communities are acidic
      c. the degree of soil moisture also affects the distribution of plants; constantly wet soil supports aquatic or marsh plant communities; succulent plants often dominate areas where the soil is always dry
      d. matter - living organisms are composed of matter or inorganic substances made of atoms.

    4. All inorganic substances essential for life tend to move in cycles from the physical environment to organisms, then back to the environment.

    • a. these cycles are called biogeochemical cycles
      b. examples of such cycles- water cycle, carbon cycle, nitrogen cycle

IV. Biosphere

• A. Biosphere- all of the communities on Earth (i.e., all of Earth's living organisms)

• B. Ecosphere- interactions among Earth's biosphere, atmosphere, water, and land

Other Sites of Interest:

Biogeography in Geography 121, Okanagan University College
Ecosystems
Energy flow and productivity
Biogeochemical cycling as an environmental problem

Last revised: September 1, 1998 - Browning