Biomes and Aquatic Ecosystems
| 44.1 Biomes
1. Biomes are major types of terrestrial ecosystems. The equivalent in water is an aquatic ecosystem. Each biome or aquatic ecosystem has a characteristic group of species. Biomes occupy large geographic areas.
2. Temperature and rainfall define the major climatic regions. Uneven heating due to the angle of solar rays hitting Earth’s curved surface generates wind and moisture patterns.
3. The tropical rain forest is hot and wet, with diverse life. Competition for light leads to vertical stratification. Nutrients cycle rapidly.
4. Tropical dry forest borders tropical rain forest, with rich soil and distinct dry and wet seasons.
5. Tropical savannas have alternating dry and wet seasons, and are dominated by grasses, with sparse shrubs and woody vegetation and migrating herds of herbivores.
6. Deserts have less than 8 inches (20 centimeters) of rainfall a year. Desert plants are well-adapted for obtaining and storing water, with rapid life cycles, deep roots, or succulent tissues. Animals minimize water loss with tough integuments, and they are active at night. Some desert organisms are adapted to living in high salt conditions.
7. Temperate grasslands receive less water than deciduous forests and more water than deserts. The more moisture, the taller the grasses.
8. Temperate deciduous forests require a growing season of at least 4 months, are vertically stratified, and have less diverse life than tropical rain forests. Tree shapes maximize sun exposure. Decomposers form soil from leaf litter. Temperate coniferous forests have poor soil and a cold climate. Periodic fires occur in these areas.
9. The taiga is a very cold northern coniferous forest. Adaptations of conifers include needle shapes, year-round leaf retention, and conical tree shape.
10. The tundra has very cold and long winters. A layer of frozen soil called permafrost lies beneath the surface. During the spring and summer, meltwater forms rivers and pools. Lichens are common in the treeless tundra, and animals include caribou, reindeer, lemmings, and snowy owls. |
44.2 Freshwater Ecosystems
11. Freshwater ecosystems include standing water (lakes and ponds) and running water (rivers and streams).
12. The littoral zone of a lake is the shallow area where light reaches the bottom; the limnetic zone is the lit upper layer of open water; the profundal zone is the dark deeper layer. The lake bottom is the benthic zone. In the littoral zone, most producers are rooted plants. In the limnetic zone, phytoplankton predominate. Nutrients fall from the upper layers and support life in the profundal and benthic zones.
13. Deep lakes in the temperate zone rely on fall turnover and spring turnover to mix oxygen and nutrients. Young, deep, oligotrophic lakes are clear blue, with few nutrients to support algae. Nutrients gradually accumulate, and algae tint the water green. The lake becomes a productive, or eutrophic, lake.
14. In rivers, organisms are adapted to local current conditions. Near the headwaters the channel is narrow and the current is swift. As the river accumulates water and sediments, the current slows and the channel widens.
44.3 Marine Ecosystems
15. In estuaries rivers empty into oceans. Life here is adapted to fluctuating salinity.
16. Mangrove swamps have changing salinity, and are defined by characteristic salt-tolerant plant species.
17. Residents of the intertidal zone are adapted to stay in place as the tide ebbs and flows.
18. Coral reefs support many thousands of species in and around 400 or so types of coral.
19. The region of ocean near the shore is the neritic zone. Open water is the oceanic zone and includes the benthic zone (the bottom), and the pelagic zone (open water above the ocean floor). The most productive areas are in the neritic zones where upwelling occurs