49.1 Levels of Ecological Study

• At the organismal level, researchers explore morphological, physiological, and behavioral adaptations-heritable traits that increase the fitness of an individual in a particular environment relative to individuals lacking the trait.

• A population is a group of individuals of the same species that lives in the same area at the same time.

• A biological community consists of populations of different species that interact with each other within a particular area.

• An ecosystem consists of all the organisms in a particular region along with nonliving components.

• These physical and chemical, or abiotic (non-living), components include air, water, and the nonliving parts of soil.

• Biologists define the biosphere as a thin zone surrounding the Earth where all life exists-the sum of all terrestrial and aquatic ecosystems.

  • It extends from about 5 km below the land surface and 10 km down in the deepest trenches of the sea to over 10 km up into the atmosphere.

  • It represents only 0.002 percent of Earth’s diameter-thinner by comparison than the peel on an apple and most of life occupies a much smaller zone within the biosphere.

• Conservation biology is the effort to study, preserve, and restore threatened genetic diversity in populations, species diversity in communities, and ecosystem function.

49.2 What Determines the Distribution and Abundance of Organisms?

• The range of conditions that a species can tolerate and the range of resources it can use is referred to in ecology as its ecological niche.

  • A niche is a product of many abiotic and biotic factors, both present and past.

• No one species can survive the full array of environmental conditions present on Earth due to fitness trade-offs, the evolutionary compromise that must be made between traits that cannot be optimized simultaneously.

• These resources can include not only abiotic factors such as sunlight but also biotic (“living”) factors related to other organisms, such as access to pollinators or protection from herbivores.

• Wallace founded the study of biogeography-the study of how organisms are distributed geographically and through geologic time.

• But if an exotic species-one that is not native-is introduced into a new area, spreads rapidly, and competes successfully with native species, it is said to be an invasive species.

49.3 Climate Patterns

• Weather consists of the specific short-term atmospheric conditions of temperature, precipitation, sunlight, and wind.

• It turns out that a major cycle in global air circulation called a Hadley cell, is responsible for making the Amazon River basin wet and the Sahara dry.

• The spinning of the Earth on its axis causes a Coriolis effect, the tendency for moving air or water to be deflected from a straight path, instead swerving in a clockwise pattern in the Northern Hemisphere and in a counterclockwise pattern in the Southern Hemisphere.

• Elevation, the height of land above sea level, is an important factor on its own because temperature decreases as a function of altitude-it’s colder in the mountains than in the lowlands, even in the tropics.

• Areas that receive this dry air are said to be in a rain shadow.

• Water has an extremely high specific heat, meaning that it has a large capacity for storing heat energy.

• Massive ocean currents flow in cycles, or gyres, that move in a clockwise direction in the Northern Hemisphere and in a counterclockwise direction in the Southern Hemisphere, due to the Coriolis effect.

49.4 Types of Terrestrial Biomes

• Broad-leaved evergreen forests, deserts, grasslands, and tundra are biomes: regions characterized by distinct abiotic characteristics and dominant types of vegetation.

• Biologists are particularly concerned with how temperature and moisture influence net primary productivity (NPP).

  • NPP is defined as the total amount of biomass generated by the fixation of carbon per year minus the amount that is oxidized during cellular respiration, where biomass refers to the total mass of organisms, of primary producers in this case.

  • NPP is often estimated by measuring aboveground biomass the total mass of living plants, excluding roots.

• The resulting patchwork of fragments of natural biomes and anthromes has inspired a branch of study called landscape ecology, which measures the structure of these patchwork landscapes and their ecological processes, such as the flow of nutrients through watersheds.

49.5 Types of Aquatic Biomes

• The proportion of solutes dissolved in water determines its salinity, generally measured as the number of grams of solute per kilogram of water-a unitless number described as parts per thousand.

• The intertidal zone consists of rocky shoreline, sandy beach, or mud flat that is exposed to the air at low tide but submerged at high tide.

• The neritic zone extends from 1e intertidal zone to dep lS of about 200 m.

  • Its outermost edge is defined by the end of the continental shelf-the gently sloping, submerged portion of a continental plate.

• The oceanic zone is the “ open ocean" -the deepwater region beyond the continental shelf.

• The bottom of the ocean at all depths is the benthic zone.

• The intertidal and sunlit regions of the neritic, oceanic, and benthic zones make up the aphotic zone.

• Areas that do not receive sunlight are in an aphotic zone.

• The littoral zone consists of the waters along the shore that are shallow enough for plants to take root.

• The limnetic zone is offshore and comprises water that receives enough light to support photosynthesis but that is too deep for plants to take root.

• The turbidity, or cloudiness, of water, is an important determinant of light.

  • Turbidity is sometimes caused by natural processes such as the erosion of river sediments by floodwaters and the erosion of coastal sediments by wave action.

  • Turbidity is also caused by many human activities, such as runoff from agricultural fields and algae bloom caused by nutrient pollution.

• A gradient in temperature such as is called a thermocline, or thermal stratification.