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NATURE ALL AROUND US

THE UNIVERSITY OF CHICAGO PRESS

Contents

Introduction: What Is Ecology?..........................11 Apple at My Core......................................52 Arboreal Aqueducts....................................103 Lawn Lions............................................164 Praise for Lazy Gardeners.............................215 The Evolution of Food.................................256 Hey, Taxi!............................................317 Social Life...........................................368 Bathroom Drama........................................419 Winter Warmth.........................................4610 The Secret Life of Ponds.............................5311 A Life of Extremes...................................5812 Prowling Predator....................................6513 Pigeontown...........................................7014 Animal Intelligentsia................................7615 Squirrelly Neighbors.................................8216 From the Chimney Tops................................8717 Long Lifelines.......................................9218 Canary in the City...................................9919 Wing Beats...........................................10420 Enough Already!......................................10921 Darwin's Sweet Tooth?................................11522 A Breath of Fresh Air................................12023 Successful Little Birds..............................12424 Opportunistic Gulls..................................12925 Urban Roots..........................................134Conclusion..............................................139Glossary................................................141

Chapter One

Our human notion of garbage as old, unusable, or unwanted material does not exist in nature. Instead, living organisms pass the essential materials for life to others in a relay race with no end. Death is not final; it's just a transitory state for what ecologists call organic matter. Let's observe the reincarnation of something you might consider garbage—an apple core discarded in your backyard. Although the word organic is often used these days to refer to healthier food choices, in biology and chemistry it means something quite different. In fact, organic simply means material that is living, or once was. Much of our kitchen waste slowly disintegrates into its organic components: molecules containing carbon and hydrogen (see the boxed definitions at the end of this chapter). The rest of our household waste is made up of inorganic molecules composed of other elements such as nitrogen, phosphorus, or iron. Many of these products of disintegration become nutrients essential for the growth of primary producers, which in most ecosystems are more simply called plants. Primary producers are at the base of all food chains because by using nutrients, sunlight, and water they produce new life that other organisms depend on.

In decomposition, complex waste material (like the core of an apple) is converted into simpler forms that are returned to the food chain. Many hardworking organisms—perhaps not surprisingly called decomposers—carry it out. Without decomposers, every plant or animal that has died since the beginning of life on Earth would accumulate around us, leaving no room for new life. In addition to filling the planet with waste, each death would sequester more of the nutrients surviving organisms need for growth, eventually leading to the extinction of all life as they are used up.

Organic matter starts decomposing as soon as the living organism stops protecting itself from decomposer attacks, usually on the death of the organism or one of its parts. When an apple is picked the tree can no longer protect it, and decomposition starts (we keep fruit in the refrigerator to slow down the decomposers). Let's see what happens to the apple core you throw on your backyard compost heap.

PHASE 1: DECOMPOSITION

The first organisms to attack the apple core are the macroscopic decomposers. These include invertebrates (animals without spinal cords), such as millipedes, fly larvae (maggots), and earthworms, that cut the core into smaller bits. Then smaller organisms, like protozoans and tiny worms called nematodes, take over breaking apart the garbage as these bigger decomposers leave.

Decomposing organisms feed on waste such as apple cores to fuel their metabolism—the same reason we eat. Metabolism produces carbon dioxide (CO₂) through cellular respiration. In this way these initial decomposers produce both CO₂ (a gas) and solid waste products. This solid excrement is rapidly colonized by microscopic decomposers such as bacteria and fungi that complete the work of deconstruction, creating humus, soil high in nutrients and therefore useful for plant growth.

The decomposers haven't yet finished with your apple core. Some proteins, sugars, cellulose, and lignin remain in the humus. These large, complex molecules bind up the nutrients the primary producers need. Once again the bacteria and fungi work to break these molecules into their simpler constituent molecules and elements. An important example of this conversion from complex to simple molecules is the decomposition of proteins found in dead plants and animals. Proteins are very large molecules made up of amino acids rich in nitrogen (N). Within the humus, nitrogen is still unusable for plants, since it is caught up in proteins. Decomposers convert these into smaller molecules: urea, ammonia (NH₄⁺), and nitrites (NO₂), and finally the form plants most prefer, the nitrates (NO₃). Even though N is the most abundant molecule in the air we breathe (78 percent), plants can take up only the forms found in the soil, so microscopic decomposers are essential in degrading proteins into forms of nitrogen that plants can use to make more proteins.

At this point your apple core has completely disintegrated, transformed into its basic constituents of CO₂ and inorganic nutrients like nitrogen. Now it's ready for the next step.

PHASE 2: RECONSTRUCTION

The element at the base of all life on Earth is carbon (C). In plants we find it principally as cellulose and lignin, the major components of wood, pulp, and bark. Carbon is found mostly in animals' tissues, including fat.

All living organisms need carbon for growth, maintenance, and reproduction. Plants take C directly from the air and convert it to other molecules (using light energy) through photosynthesis. Animals take in C by eating organic matter like plants or other animals, then convert it into energy by cellular respiration (the same process the decomposers use to keep growing).

This is the final step in the reincarnation of the apple core, now converted into minuscule molecules of CO₂ and nutrients so that plants in the garden can take it up. If you feed your growing vegetables with compost, parts of the apple will become part of your body when you eat those magnificent home-grown tomatoes and cucumbers.

The number of atoms on Earth has remained more or less the same since the planet was formed. Because they are constantly recycled, some of the atoms in your body may have once belonged to Jurassic dinosaurs, while others might have spent time in the body of Plato or Mozart. Then again, maybe your atoms were part of their forgotten neighbors,...