The Distribution of Earth’s Ecological Systems

41 The Distribution of Earth’sEcological Systems

Chapter 41 The Distribution of Earth’s Ecological Systems • Key Concepts • 41.1 Ecological Systems Vary over Space and Time • 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • 41.3 Biogeography Reflects Physical Geography • 41.4 Biogeography Also Reflects Geological History • 41.5 Human Activities Affect Ecological Systems on a Global Scale

Chapter 41 Opening Question • Can basic ecological principles suggest why removing cattle has not restored grasses to the Borderlands?

Concept 41.1 Ecological Systems Vary over Space and Time • Physical geography—study of the spatial distribution of Earth’s climates and surface features • Biogeography—study of the spatial distributions of species • The explorer/scientists in the 18th and 19th centuries began to realize that the distributions of species and environments are linked.

Concept 41.1 Ecological Systems Vary over Space and Time • Abiotic components of the environment are nonliving. • Biotic components—living organisms • An ecological system—one or more organisms plus the external environment with which they exchange energy and materials.

Concept 41.1 Ecological Systems Vary over Space and Time • “Ecology” was coined by Ernst Haeckel in 1866; he helped establish it as a formal science. • He also emphasized ecology’s relevance to Darwin’s theory of evolution by natural selection.

Concept 41.1 Ecological Systems Vary over Space and Time • A system is defined by the interacting parts it contains. • Ecological systems can include any part of the biological hierarchy from the individual to the biosphere. • Each level brings in new interacting parts at progressively larger spatial scales.

Concept 41.1 Ecological Systems Vary over Space and Time • At the smallest scale is the individual organism and its immediate environment. • Individuals remove materials and energy from the environment, convert them into forms that can be used by other organisms, and, by their presence and activities, modify the environment.

Concept 41.1 Ecological Systems Vary over Space and Time • Population—group of individuals of the same species that live, interact, and reproduce in a particular geographic area • Community—assemblage of interacting populations of different species in one area • Landscapes include multiple communities. • Biosphere—all the organisms and environments of the planet

Concept 41.1 Ecological Systems Vary over Space and Time • Ecologists replace the term “ecological system” with ecosystem when they are explicitly including the abiotic components of the environment; • And in particular when considering communities and their environmental context.

Concept 41.1 Ecological Systems Vary over Space and Time • Generally, large ecological systems tend to be more complex because they have more interacting parts, and larger spatial scale. • But small systems can also be complex: • The human gut is densely populated with hundreds of microbial species. These cells far outnumber the trillion or so human cells in the body.

Concept 41.1 Ecological Systems Vary over Space and Time • The mammalian gut environment provides stable conditions and ample nutrients. • Gut microbes metabolize foods, including some the host cannot digest, and excrete waste products that provide nutrition to the host or to other microbes. • Microbial species interact with one another and with host cells by forming biofilms that coat the gut lining.

Concept 41.1 Ecological Systems Vary over Space and Time • Biotic and abiotic components of ecosystems are distributed unevenly in space, and ecosystems can change over time. • The human gut illustrates this variation—each person has a unique gut community. • But patterns do exist: gut communities of genetically related people are more similar that those of unrelated people.

Concept 41.1 Ecological Systems Vary over Space and Time • Gut communities in lean people and obese people vary in the ratio of two bacterial phyla. • When obese people lose weight, their gut community becomes more similar to that of a lean person. • Bacteria in the phylum Firmicutes are good at breaking down indigestible polysaccharides and extracting more energy from food than Bacteroidetes.

Figure 41.1 Genetics and Diet Affect the Composition of the Gut Microbial Community

Concept 41.1 Ecological Systems Vary over Space and Time • In experiments with mice, it has been shown that the gut community contributes to obesity, along with diet and genetic factors.

Figure 41.2 The Microbial Communities of Genetically Obese Mice Contribute to Their Obesity (Part 1)

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Earth’s environments vary greatly from place to place and also through time. • On long time scales, the coming and going of oceans, ice ages, and other geologic events shape environments. • On short time scales, physical conditions depend largely on solar energy input, which drives the circulation of the atmosphere and the oceans.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Weather is the state of atmospheric conditions in a particular place at a particular time. • Climate is the average conditions and patterns of variation over longer periods. • Climate is what you expect; weather is what you get. • Adaptations to climate prepare organisms for expected weather patterns.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Earth receives uneven inputs of solar radiation due to its spherical shape and the tilt of its axis as it orbits the sun. • It is colder at the poles because there is less solar input: the sun’s rays are spread over a larger area and pass through more atmosphere. • High latitudes experience more seasonality—greater fluctuation over the course of a year.

Figure 41.3 Solar Energy Input Varies with Latitude

Figure 41.4 The Tilt of Earth’s Axis of Rotation Causes the Seasons

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Solar energy inputs are always greatest in the tropics and decrease poleward. • This latitudinal gradient drives global circulation patterns in the atmosphere.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Hadley cells: • The tropical air is warmed, rises, and then cools adiabatically (an expanding gas cools). • The rising warm air is replaced by surface air flowing in from the north and south. • The cooling air sinks at 30°N and 30°S.

Figure 41.5 Tropical Solar Energy Input Sets the Atmosphere in Motion

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Hadley cell circulation produces latitudinal precipitation patterns: • Rising warm tropical air releases lots of moisture as rainfall. The sinking air at 30°N and 30°S is dry—most of the great deserts are at these latitudes.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Some of the descending air in the Hadley cells flows towards the poles, overriding cold, dense polar air that is flowing equatorward. • The interaction of these warm and cold air masses generates winter storms that sweep from west to east through the middle latitudes. • Earth’s rotation adds an east–west component to the north–south movement of the air masses—the Coriolis effect.

Figure 41.6 Global Atmospheric Circulation and Prevailing Winds

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • These atmospheric circulation patterns affect climate patterns by transferring heat energy from the hot tropics to the cold poles. • Without this transfer, the poles would sink toward absolute zero in winter, and the equator would reach fantastically high temperatures throughout the year.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Prevailing surface winds drive the major ocean surface currents, which carry materials, organisms, and heat with them. • Example: In the northern tropics, the trade winds drag water to the west; when it reaches a continent, it is deflected northward until the westerlies drive the water back to the east. The result is a clockwise gyre.

Figure 41.7 Ocean Surface Currents

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • As they move poleward, tropical surface waters transfer heat from low to high latitudes, adding to the heat transfer by atmospheric circulation. • The Gulf Stream and North Atlantic Drift bring warm water towards northern Europe, warming the air there. The same latitudes in Canada are much colder.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Deep ocean currents are driven by water density differences. • Colder, saltier water is more dense and sinks to form deep currents. • Deep currents regain the surface in areas of upwelling, completing a vertical ocean circulation.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Oceans and large lakes moderate terrestrial climates because water has a high heat capacity: • Temperature of water changes slowly as it exchanges heat with the air. • Water temperatures fluctuate less than land temperatures, and the air over land close to oceans or lakes also shows less seasonal and daily temperature fluctuation.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Topography (variation in elevation) also affects the physical environment. • As you go up a mountain, air temperature drops by about 1°C for each 220 m of elevation because rising air expands and cools adiabatically. • When prevailing winds bump into mountain ranges, the air rises, cools, and releases moisture. The now-dry air descends on the leeward side, creating a rain shadow.

Figure 41.8 A Rain Shadow

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Topography also influences aquatic environments: • Flow velocity depends on slope. • Water depth determines gradients of many abiotic factors, including temperature, pressure, light penetration, and water movement.

Concept 41.2 Solar Energy Input and Topography Shape Earth’s Physical Environments • Climate diagram—superimposed graphs of average monthly temperature and precipitation over a year. • The axes are scaled so that it is easy to see the growing season: • When temperatures are above freezing and the precipitation line is above the temperature line

Figure 41.9 Climate Diagrams Summarize Climate in an Ecologically Relevant Way

Concept 41.3 Biogeography Reflects Physical Geography • An organism’s physiology, morphology, and behavior affect how well it can tolerate a particular physical environment. • Thus, the physical environment greatly influences what species can live there. • We expect species that occur in similar environments to have evolved similar phenotypic adaptations.

Concept 41.3 Biogeography Reflects Physical Geography • Early scientist–explorers began to understand how the distribution of Earth’s physical environments shapes the distribution of organisms. • Their observations revealed a convergence in characteristics of vegetation found in similar climates around the world.

Concept 41.3 Biogeography Reflects Physical Geography • Biome—a distinct physical environment inhabited by ecologically similar organisms with similar adaptations. • Species in the same biome in geographically separate regions display convergent evolution of morphological, physiological, or behavioral traits.

Concept 41.3 Biogeography Reflects Physical Geography • Terrestrial biomes are distinguished by their characteristic vegetation. • Distribution of terrestrial biomes is broadly determined by annual patterns of temperature and precipitation. • These factors vary along both latitudinal and elevational gradients.

Figure 41.10 Terrestrial Biomes Reflect Average Annual Temperature and Precipitation

Figure 41.11 Global Terrestrial Biomes

Concept 41.3 Biogeography Reflects Physical Geography • Other factors, especially soil characteristics, interact with climate to influence vegetation. • Example: Southwestern Australia has Mediterranean climate with hot, dry summers and cool, moist winters. The vegetation is woodland/shrubland, with no succulent plants. • The soils are nutrient-poor, and there are frequent fires. Succulents are easily killed by fires.

Concept 41.3 Biogeography Reflects Physical Geography • Grasslands normally occur where there is not enough precipitation to support forests, but is more plentiful than is typical of deserts. • But some grasslands occur in unexpected places, demonstrating that biome boundaries are not perfectly predicted by temperature and precipitation—other factors also affect the vegetation.

Figure 41.12 Similar Vegetation Types, Different Conditions

The Distribution of Earth’s Ecological Systems