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Algae:

Classification:

• Kingdom - Protista
  Divisions - Euglenophyta, Phaeophyta, Rhodophyta, Chlorophyta
  

Characteristics:
Division Euglenophyta, euglenoids - Free-living (mostly), unicellular algae; motile by a flagellum; photosynthetic (autotrophic) spp.; some saprophytic spp., and some heterotrophic spp. which lack chloroplasts. Typical photosynthetic, free-living spp. is Euglena spp., euglena.

Division Phaeophyta, brown algae - Multicellular (mostly) algae, some unicellular spp.; mostly marine; comprise most of the conspicuous seaweeds of temperate regions; dominate rocky shores throughout the cooler regions of the world; larger brown algae of the order Laminariales are the kelps.

Division Rhodophyta, red algae - Mostly, multicellular algae, some unicellular spp.; mostly marine; largest number of seaweed spp. in marine habitats.

Division Chlorophyta, green algae - Mostly multicellular algae, some unicellular spp.; most diverse of all the algae; mostly aquatic (both freshwater and marine spp.) some terrestrial spp. found in snow, on tree trunks, and in the soil; free-living, colonial, and symbiotic spp. with certain fungal spp. (lichens) and protozoa. Typical free-living, unicellular spp. is Chlamydomonas sp.; typical colonial, unicellular form are members of the genus Volvox.

Fungi:

Classification:

• Kingdom - Fungi
  Divisions - Zygomycota, Ascomycota, and Basidiomycota

Characteristics:
Division Zygomycota, certain black and non-pigmented molds, etc. - Live on decaying plant and animal matter in soil; some are parasites of plants, insects or small soil animals; a few are occasionally pathogens of humans and domestic animals. One of the most common spp. is the black bread mold Rhizopus sp.

Division Ascomycota, pigmented molds, certain bread molds, morels (type of edible "mushroom-like fungus"), etc. - Molds that cause food spoilage; certain plant diseases such as powdery mildews on leaves, chestnut blight, and Dutch elm disease; some spp. are unicellular (e.g. the yeasts such as Saccharomyces cerevisiae, beakers' yeast; brewers' yeast is also in the same genus). Lichens are mutualistic symbiotic associations between ascomycete fungi and certain genera of green Algae or cyanobacteria ("blue-green algae").

Division Basidiomycota, mushrooms, toadstools, puffballs, and the plant pathogens: the rusts and smuts - The most familiar group of fungi distinguished by their production of basidiospores which are produced on the outside of a club-shaped sporangium called a basidium.

Bacteria:

Classification:

• Kingdom - Monera, the prokaryotes
  

Characteristics:
Unicellular, simplest, smallest, and most abundant organisms. Plant pathogens and the photosynthetic cyanobacteria, erroneously referred to frequently as "blue green algae" (why erroneously? ______________) are of the most relevance for this class. Most have cell walls of peptidoglycan (exception are the plant and human pathogenic mycoplasmas which lack cell walls). Anabaena sp. is the scientific name for most of the nitrogen-fixing cyanobacteria. This organism plays important ecological rolls we will discuss during our plant ecology lectures and next semester in Ecology.

Plant Ecology:

ECOLOGICAL TERMINOLOGY AND DEFINITIONS

INTERACTIONS BETWEEN ORGANISMS:
Symbiotic relationships

• Mutualism - interaction in which growth and survival of both individuals are enhanced (e.g. leguminous plants and nitrogen-fixing bacteria).
• Parasitism - interaction in which one individual grows and survives at the expense of a host organism (e.g. microbial plant pathogens, parasitic plants such as mistletoe, and parasitic insects such as aphids).
• Commensalism - interaction in which one individual grows and survives on another organism, but not at the expense of the host (e.g. epiphytic plants which grow on other plants without causing harm to the host plant).

Competition -interactions within communities and populations of organisms for one or more key resources. In plants, competition for light is of primary importance. Competition for other resources such as soil nutrients and water is also of importance.

• Allelopathy - inhibition of plant growth by production of chemicals by one sp. which affects either other members of the same sp. or members of other plant spp. (e.g. Johnson grass, dandelion, and purple sage; purple sage, Salvia leucophylla, produces volatile chemicals which inhibit the establishment of seedlings of many spp. of plants in its vicinity).

Plant-Herbivore and Plant-Pathogen Interactions - defence against herbivory via spines, thorns, or toxic chemicals sequestered within vacuoles. Examples include prickly-pear cactus (Opuntia spp. - spines; certain spp. of euphorbs - thorns, spines, and chemicals; milkweed (family Asclepiadaceae) - production of cardiac glycosides which are toxic to most organisms.

Protection from plant pathogens occurs in some plants by production of phytoalexins - naturally-produced "antibiotics" produced by some plants in response to fungal or bacterial infection. Phytoalexins are lipid-like compounds which are produced in response to the presence of specific carbohydrate molecules (elicitors) that are present on the fungal or bacterial cell walls. The elicitors simulate phytoalexin production following leaf damage initiated by the pathogen.

CYCLING OF NUTRIENTS
Recycling in Ecosystems

• Carbon cycle
• Nitrogen cycle
• Oxygen cycle
• Water cycle

TROPHIC LEVELS ("FEEDING LEVELS")

• Autotrophs (Primary producers)
• Heterotrophs
  • Primary consumers (herbivores)
  • Secondary consumers (carnivores and parasites)
  • Decomposers (fungi, bacteria, and a certain small animals which feed on detritus ("dead" material).

Energy Flow in Ecosystems - flow of energy is, usually, from solar energy captured during photosynthesis and used to make carbohydrates. Flow is not cyclic but rather in somewhat of a linear fashion from primary producers through various trophic levels eventually to decomposers with a large amount of energy lost as heat.

DEVELOPMENT OF COMMUNITIES AND ECOSYSTEMS
Succession - orderly progression of changes in community composition, eventually reaching a "mature" community (climax community) has been established.

• Primary succession - initial establishment and eventual colonization of a given geographic location. Lichens play a major role in this due to the secretion of acids by the fungal component of the mutualistic symbiosis. The acid breaks down rock and facilitates the formation of soil, with in which plants and other organisms can become established.
• Secondary succession (recolonization) - establishment and recolonization of a given geographic location following disturbance or the original, intermediate, or climax community. Usually, grasses are the first to be established, followed by short-generation-time forbs (non-grass monocots and herbaceous dicots) which produce abundant numbers of seeds which are easily dispersed.

BIOMES
See Chapter 32 (Raven, et al., 1986) for full description of specific biomes.

Raven PH, Evert RF, Eichhorn SE (1986) Biology of Plants. Worth, Inc., New York

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