Final PDF to printer CHAPTER 17 Ecosystems and Biogeochemical Cycles THE BIOSPHERE IS THE REALM OF LIFE. Biogeography explores the biosphere and the Earth systems that support organisms. Adequate water, energy, and nutrients are necessary to sustain life, and their availability is controlled by cli- mate and other aspects of physical geography. This chapter examines how organisms interact with each other and with their physical environment — ecology. The provisions and constraints of the physical environment along with the entire community of interacting organisms (plants, animals, and others) in an area is an ecosystem. Biogeographers study eco- systems from a broad perspective that considers spatial and temporal variations of physical and chemical processes in the biosphere and how the biosphere impacts Earth’s systems, from local to global scales. Costa Rica provides a wonderful example of ecology, ecosys- tems, and biogeography. Earlier in this textbook, we explored the region’s weather and climatic patterns, always an excellent place to start when considering the biogeography of a region. The large perspective view here (⊲) is a satellite image draped over the topography of the land. Land, Water, and Atmosphere 17.00.a2 The backbone of the country is a line of volcanoes, such as Volcán Arenal (⊳), which has nearly continuous low-level eruptions of molten lava and ash. The volcanoes are formed by plate-tectonic activity (specifically subduc- tion) along the west coast. The eruptions of Arenal are sufficiently continuous that the volcano has become a major site for ecotourism. The volcano interacts with the moist air in this tropical place, so it is often partially obscured by clouds and volcanic steam. How do interactions between the land and atmosphere affect life, including humans? 17.00.a1 17.00.a3 Eruptions of lava and ash flow down the mountain and bury anything on the surface (⊳). The initially barren lava flows are colonized by certain types of plants and animals that can establish themselves on such “new land,” and these are known as a pioneer commu- 17.00.a5 17.00.a6 nity. Once the pioneer community is Abundant tropical moisture sustains Tropical rains, combined with locally established, an entire succession of a dense growth of tropical rain forest, impermeable tropical soils, result in other types of life can colonize the and the rain forest releases some of plentiful runoff in streams. These area. Over time, weathering begins to 17.00.a4 this moisture during transpiration. In corridors of running water attract form soils (⊳), which in this volcanic addition, plants remove carbon many animals, forming a small terrain are mostly Andisols, and the dioxide (CO2) from the air to produce streambed ecosystem within the new land begins to blend into the carbon-rich wood, leaves, roots, and larger tropical ecosystem. landscape. other material. What are the main components of How do life and land interact chemi- How does carbon move from one an ecosystem, and what role does cally through the interface of soil? part of the environment to another? water play in a healthy ecosystem? rey42432_ch17_534-563.indd 534 11/16/16 03:07 PM Final PDF to printer Ecosystems and Biogeochemical Cycles 535 TOPICS IN THIS CHAPTER 1 7.1 How Is the Ecosystem Approach Useful 1 7. 9 What Is the Role of Nitrogen in Ecosystems? 552 in Understanding the Biosphere? 536 1 7.1 0 What Is the Role of Phosphorus in Ecosystems? 554 1 7. 2 What Types of Organisms Inhabit Ecosystems? 538 1 7.1 1 What Is the Role of Sulfur in the Environment? 556 1 7. 3 What Interactions Occur in Ecosystems? 540 1 7.1 2 How Does a Lack of Oxygen Harm Ecosystems? 558 1 7. 4 How Can Biodiversity Be Assessed? 542 1 7.1 3 CONNECTIONS: How Do Invasive Species 1 7. 5 How Does Energy Flow Through Ecosystems? 544 Impact U.S. Gulf Coast Ecosystems? 560 1 7. 6 How Do We Describe Ecosystem Productivity? 546 1 7.1 4 INVESTIGATION: What Factors Influence 1 7.7 How Do Ecosystems React to Disturbance? 548 the Desert Ecosystems of Namibia in Southern Africa? 562 1 7. 8 What Is the Role of Carbon in Ecosystems? 550 Life 17.00.a8 17.00.a7 Various forms of life thrive in the tropical and mountain habitats, including coatimundi (⊳), a mammal in the raccoon family, and colorful and interest- ing tropical birds, such as a toucan (⊲). The lush vegetation hosts other classes 17.00.a9 of animals, for example reptiles, including this eyelash snake, a venomous pit viper (⊲). How do different types of animals interact, and what happens to their populations if they compete with one another or depend on one another? 17.00.a10 The rain forest is home to other small creatures, like this “poison- dart frog” (⊲), an amphibian, and The rain forest earns its name from the thick vegetation (the four countless types of insects, including photographs below) that forms a canopy and shades lower levels of ants that recycle vegetation and the ecosystem. Vines and other plants climb or drape on the trees, other materials that have fallen on trying to stay off the ground and gain better access to the light. Plants the ground (photograph on the grow brightly colored flowers to better attract insects that, in turn, bottom right). The number of pollinate the plants, a symbiotic relationship that helps the plants and species in an ecosystem is one the insects. measure of biodiversity. 17.00.a11 What does it mean for a relationship to be called symbiotic, and what What do we mean by biodiversity, other types of relationships exist between living organisms? and what can decrease biodiversity? 17.00.a14 17.00.a13 17.00.a12 17.00.a15 17.0 rey42432_ch17_534-563.indd 535 11/16/16 03:07 PM Final PDF to printer 536 17.1 How Is the Ecosystem Approach Useful in Understanding the Biosphere? IN AN ECOSYSTEM, organisms interact with individuals of the same species and with other types of organisms. The ecosystem is supported by various types of energy, matter, and processes, some that involve living organisms and others that involve nonliving components, like rocks, soil, and water. What Is Ecology? Ecology is the study of how organisms and populations of organisms interact with one another and the nonliving components of their environment. These interactions occur from the local to regional scale — the ecosystem. The intricate array of interactions within an ecosystem evolves in a way that promotes increasing efficiency in energy exchanges and nutrient cycling, because efficiency promotes survival. Ecologists study ecosystems, and biogeographers use ecological principles to explain the distribution of life — the realm of biogeography. Photographs below explore the Galápagos Islands (west of South America), one of the world’s truly unique and fragile ecosystems. 17.01.a1 17.01.a2 17.01.a3 Individual — Most living organisms exist as Population — Although many individuals spend Community — Not only do organisms interact individuals that can function somewhat significant time as solitary creatures, they are with others of their kind, but individuals from independently, at least for a while, such as this always part of a population of individuals of the different species interact, as part of a marine iguana, a type of lizard (reptile) that same species. The population can go up or community. Here, an ocean-dwelling seal started on land but forages in shallow waters. down as the ecosystem changes. sniffs a marine iguana. 17.01.a4 17.01.a5 17.01.a6 Biotic Components — Living plants and animals, Abiotic Components — Components of an Energy — All ecosystems require a source of along with materials such as digestive wastes, ecosystem not directly produced by living energy, in most cases ultimately derived from discarded plant parts, and decaying remains of organisms are abiotic components. These include the Sun. Insolation warms water and air, drives creatures, are the biotic components of an the air, rocks, soils, and water that provide a ocean currents, wind, and weather, and ecosystem. home for the plants and other organisms. provides energy for plant photosynthesis. 17.01.a7 17.01.a8 Habitat — Some species Ecological Niches — The live on land, such as this unique position of a species different species of iguana, in the ecosystem, especially whereas others live in the its role relative to the other water or air. The physical species, is called its environment in which a ecological niche. How species lives, such as a would you characterize the rocky coast where it finds ecological niche of these its particular mix of food Galápagos fur seals? sources, is its habitat. rey42432_ch17_534-563.indd 536 11/16/16 03:07 PM Final PDF to printer Ecosystems and Biogeochemical Cycles 537 What Are the Structures and Functions of Ecosystems? All ecosystems consist of the storage and flow of matter and energy, and various interactions between an organism and other organisms. The components of an ecosystem can be categorized into structures and functions. Ecosystems also have a variety of spaces for a wide array of organisms to exist, both supporting and being supported by the ecosystem. Ecosystem Structures 3. The biotic components include the 1. Ecosystem structures consist of the cow, the trees, the low bushes and biotic, abiotic, and energy components grass, and the roots of the plants. of the ecosystem. In most cases, these Other biotic components that are less are the tangible, observable aspects of visible, but certain to be present, an environment. Observe the ecosys- include insects, birds, burrowing tem structures shown in this diagram. animals, bacteria in the soil, fish, algae, and other organisms in the water. 2. In the site depicted here, the most obvious abiotic components are the 4.