Lecture Outline - Chapter 34

34.1. Aquatic Communities (p. 674)

1. Aquatic communities are classified into: freshwater (inland) communities and marine (saltwater or oceanic) communities.
2. Plankton are free-drifting microscopic organisms, including:
   • a. Phytoplankton made of plantlike algae photosynthesizers.
   • b. Zooplankton animals that feed on phytoplankton.
3. Lakes and Ponds
   • a. Lakes are larger than ponds; are stratified in summer and winter. (Fig. 34.1)
     • i. Epilimnion is upper surface layer, warm in summer.
     • ii. Hypolimnion is cold lower layer.
     • iii. Abrupt drop in temperature occurs at middle thermocline.
     • iv. Layering prevents mixing between lower hypolimnion rich in nutrients and upper epilimnion with oxygen absorbed from surface.
     • v. Epilimnion warms in spring and cools in fall, causing temporary mixing; phytoplankton become more abundant due to more nutrients.
   • b. Life zones of lakes and ponds.
     • i. Littoral zone is closest to shore.
     • ii. Limnetic zone is sunlit body of lake.
     • iii. Profundal zone is dark below level of sunlight penetration. (Fig. 34.2)
     • iv. Benthic zone is at soil-water interface; benthos are animals that live on bottom.
4. Rivers and Streams
   • a. Rapidly flowing, bubbling streams have insects and fish adapted to oxygen-laden water.
   • b. Slow moving streams have aquatic life more similar to lake and pond life.
5. Coastal Communities
   • a. Estuaries are bays where rivers empty into the sea.
   • b. Erosion brings down nutrients and tides wash in salt water; forms nutrient trap.
   • c. Estuaries have high production for organisms that can tolerate changing salinity.
   • d. Called "nurseries of the sea" because many young marine fish develop in this protected environment.
6. Seashores (p. 676)
   • a. Rocky shorelines offer anchorage for sessile organisms. (Fig. 34.4)
     • i. Seaweeds are main photosynthesizers and use holdfasts to anchor.
     • ii. Barnacles glue themselves to stone.
     • iii. Oysters and mussels attach themselves by byssus threads.
     • iv. Limpets and periwinkles either hide in crevices or fasten flat to rocks.
   • b. Sandy beaches and shores are shifting strata.
     • i. Permanent residents therefore burrow underground.
     • ii. Worms live permanently in tubes.
     • iii. Amphipods and ghost crabs burrow above high tide and feed at night.
7. Coral Reefs (Fig. 34.5)
   • a. Areas of biological abundance in shallow, warm tropical waters.
   • b. Stony corals have calcium carbonate exoskeleton and may include algae.
   • c. Most form colonies; may associate with zooxanthellae dinoflagellates.
   • d. Reef is densely populated with animal life.
   • e. Great Barrier Reef of Australia suffers from heavy predation by crown-of-thorns sea star, perhaps because humans have harvested its predator, the giant triton.
8. Oceans (p. 678)
   • a. Cover about three-quarters of planet's surface.
   • b. Ocean organisms are placed in either pelagic (open water) or benthic (ocean floor) categories. (Fig. 34.6)
   • c. Pelagic division is divided into neritic and three levels of pelagic provinces.
     • i. Neritic province has greater concentration of organisms because sunlight penetrates; nutrients are found here.
     • ii. Epipelagic zone is brightly lit, has much photosynthetic phytoplankton, that support zooplankton that are food for fish, squid, dolphins, and whales.
     • iii. Mesopelagic zone is semi-dark and contains carnivores; adapted organisms tend to be translucent, red colored, or luminescent; for example: shrimps, squids, lantern and hatchet fishes.
     • iv. Bathypelagic zone is completely dark and largest in size; it has strange-looking fish.
   • d. Benthic division includes organisms on continental shelf (sublittoral), continental slope (bathyal), and the abyssal plain. (Fig. 34.6)
     • i. Sublittoral zone harbors seaweed that becomes sparse where deeper; most dependent on slow rain of plankton and detritus from sunlit water above.
     • ii. Bathyal zone continues with thinning of sublittoral organisms.
     • iii. Abyssal zone is mainly animals at soil-water interface of dark abyssal plain; in spite of high pressure, darkness and coldness, many invertebrates thrive here among sea urchins and tubeworms. (Fig. 34.7)
     • iv. Thermal vents along oceanic ridges form unique community.
       -Molten magma heats seawater to 350^oC, reacting with sulfate to form hydrogen sulfide (H₂S).
       -Chemosynthetic bacteria obtain energy from oxidizing hydrogen sulfide.
       -Resulting food chain supports community of tubeworms and clams.

1. Earth's surface can be divided into various zones containing one or more biomes: taiga, grasslands, deserts, etc. (Fig. 34.8)
2. Climate (mainly temperature and rainfall) determine location of biomes.
3. Solar energy-direct on equator and dispersed at poles-is ultimate cause of air and ocean currents that distribute heat.
4. Amount of rainfall determined by distance from equator, mountain ranges, and ocean and wind currents.
5. Deserts
   • a. Found where annual rainfall is less than 25 cm (10 in). (Fig. 34.9)
   • b. Days are hot, nights are cold because of lack of cloud cover.
   • c. Vegetation may be lacking but usually some succulents such as leafless cacti whose stems store water and carry on photosynthesis, can survive.
   • d. Some shrubs can store water and shed leaves during dry period.
   • e. Insects thrive during any rain and adjust their life cycle.
   • f. Lizards, snakes, some birds, rodents, and predatory mammals are most characteristic vertebrates.
6. Tundra (Fig. 34.10) (p. 682)
   • a. Tundra encircles the earth just south of polar seas in Northern Hemisphere.
   • b. Alpine tundra is similar community above timberline on mountain ranges.
   • c. Arctic tundra is cold and dark much of year; receives only 20 cm of rain a year.
   • d. This rainfall is less than some deserts but is frozen; ice melt provides plentiful melted water in summer.
   • e. Only topmost layer thaws during summer; permafrost beneath is always frozen.
   • f. Sedges, shortgrasses, lichens, and mosses grow in the summer.
   • g. Few animals, like the rat-like lemmings, stay the year round; in summer, numerous insects, birds, caribou, reindeer, and wolves migrate in.
7. Grasslands
   • a. Grasslands occur where rainfall is greater than 25 cm but insufficient to support trees.
   • b. Extensive root systems allow rapid recovery from drought and fire that damages trees.
   • c. Organic matter builds up in rich grassland soils; provides most productive agricultural land.
   • d. Savanna is unique African tropical grassland. (Fig. 34.11)
     • i. Flat-topped acacia is one of few small trees that can survive.
     • ii. Savannas support greatest variety and number of large herbivores; in turn, this supports large population of carnivores.
     • iii. Termites use remaining plant litter to grow fungal gardens; build immense nests.
   • e. Prairie is temperate grassland.
     • i. Found in midwestern portion of United States; much converted to farmland.
     • ii. Tall prairie grass gives way to short-grass prairie.
     • iii. Grazers (bison, pronghorn antelope) were very common.
     • iv. Small mammals (mice, prairie dogs, rabbits), hawks, snakes, coyotes are present; many are adapted to living in burrows.
8. Scrubland
   • a. Found in California, parts of South Africa, western Australia, and central Chile.
   • b. Most of rain falls in winter; summers are very dry.
   • c. Dense scrubland called chaparral; shrubs have small, thick evergreen leaves coated with waxy material, thick underground stems survive dry summers and frequent fires.
9. Coniferous Forests (p. 685)
   • a. Needlelike leaves withstand load of heavy snow; needles and bark has thick covering.
   • b. Taiga is coniferous forest biome that extends across northern Eurasia and North America, near mountaintops, and downward along northern California coast.
   • c. Understory of plants is lacking; fungi, mosses, and lichens grow on or below layer of needles; dense canopy of needles shuts out most sunlight.
   • d. Includes some of tallest trees, including coastal redwoods.
10. Temperate Forests (Fig. 34.13)
    • a. Found south of taiga in eastern North America, eastern Asia, and much of Europe.
    • b. Well-defined growing season of between 140 and 300 days with 75-150 cm of rainfall a year.
    • c. Deciduous trees (oak, hemlock, maple) lose their broad leaves in fall.
    • d. Enough light penetrates canopy for a well-developed understory layer of shrubs, herbaceous plants, and ground cover.
    • e. Animal life is plentiful with birds, rodents, bobcats, foxes, and wolves.
11. Tropical Forests (p. 686)
    • a. Tropical rain forests occur near the equator in South America, Africa, and Indo-Malayan region.
    • b. Always warm (between 20^oC and 25^oC) with plentiful rainfall (minimum of 190 cm per year).
    • c. Richest of biomes in both number of species and total biomass.
    • d. Tropical rain forest has complex structure with many levels of life. (Fig. 34.14)
    • e. Understory is dense in open areas where it produces a thick jungle.
    • f. Lianas, or woody vines, encircle tree as it grows; help strengthen the trunk.
    • g. Some animals live only in the trees.
    • h. Abundant insects, birds, amphibians, and reptiles are well represented.
    • i. Monkeys, jaguars, and leopards are large mammals present.
    • j. Epiphytes are plants that grow on tall trees but do not parasitize them.
    • k. Some tropical forests have a dry season and develop an understory.

1. If you travel from equator to North Pole, you encounter the sequence: tropical rain forest, temperate deciduous forest, taiga and tundra.
2. Biomes change with latitude because latitude determines temperature.
3. As altitude increases (with decreasing temperature and rainfall) there is same sequence of biomes as above.
4. Productivity
   • a. The organic energy produced by a community is its primary productivity. (Fig. 34.15)
   • b. Productivity goes up with greater sunlight, rainfall, nutrients, and length of growing season.
   • c. The more productive a community, the more life can be supported per unit area.
   • d. An open ocean is not much more productive than a desert.