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Basic Energetics & Theory behind Human Responses. The basic laws of thermodynamics define energy-budgets—and therefore determine the essential nature of our life-support systems. Human beings intercept energy flows in very creative ways so that we can support a whole lot of ourselves.
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Basic Energetics & Theory behind Human Responses • The basic laws of thermodynamics define energy-budgets—and therefore determine the essential nature of our life-support systems. • Human beings intercept energy flows in very creative ways so that we can support a whole lot of ourselves.
Remember, we agreed that all biologically important energy comes from the sun (so, as an intro to today’s class, I repeat my silly fusion-diagram). Here is a summary of how solar power originates.
Ecologists are especially concerned with two results of solar processes: FUEL: Solar energy powers photosynthesis, by which process green plants turn light-energy into chemical-energy and thereby feed virtually all LIFE. WARMTH: Solar energy mixes and moves air and water to drive weather and climate, the subject of the next several lectures.
Now we need to think about the fate of this solar energy captured by plants—and about how people use it. Any analysis of solar power & photosynthesis will lead us into a consideration of food-webs.
Starting as solar power, energy moves through an ecosystem: This model is essential to understanding why people eat the sorts of things they do!
“Plants” are the primary producers in virtually all systems. (The world runs on solar power and photosynthesis.) Though not exactly plants, green algae can be particularly important photosynthesizers. Rainforests are great energy-fixers. Grasslands are highly productive terrestrial photosynthetic systems. In evaluating photosynthetic production, think about the % of solar energy fixed in a system (it’s typically 0%-3%) and about the % of fixed energy available for production (making more plant-stuff as opposed to doing plant housekeeping such as respiration; production is typically c. 30% to 60% of fixed energy). Contrast a rainforest (fixes c. 3.5%; uses c. 50-80% of that for maintenance) with a sugarcane field (fixes about 1.8%; uses c. 40-50% of that for maintenance).
Detritivores gain energy by eating parts of plants and animals that die, as well as by consuming energy-rich metabolic by-products such as urea and uric acid. In terrestrial systems animals such as springtails break down rotting plants. This copepod represents the especial importance of detrital levels in aquatic ecosystems. Often ignored in textbooks—and henceforth ignored in this course– detritivores usually process most of the energy photosynthetically fixed and produced into “stuff.” Detritivores often also serve as bases of higher “food chains.” Bacteria are probably the most important living components in all detrital systems.
Insects dominate primary consumption in almost all terrestrial habitats. Primary consumers: animals that eat plants Rodents are the most important mammalian primary consumers; many are specialized seed-eaters. People often introduce primary consumers into the system; many are cellulose-processors. In aquatic habitats most primary consumers are very small. But some are big too. In evaluating energy-flow through primary consumers, one should think about how much of plant-production they can/do eat. And two other considerations may be even more critical. (1) Of plant-energy consumed, how much is absorbed into an animal’s system (as opposed to passing through into energy-rich feces)? (2) Of the energy actually absorbed, what proportion is burned for maintenance activities (respiration) and what proportion is available for producing more animal-tissue (including babies)? Factor # 2 depends in large part on the animal’s thermoregulatory strategy.
Secondary consumers: animals that eat animals At least numerically, insects are the most important secondary consumers. Our state bird is a noble secondary/tertiary consumer. Currently, the most impressive secondary consumers are mammals. Relatively little animal matter passes into the detritivore system (contrast with plants). Large, endothermic, secondary consumers are very rare. Yet they may structure ecosystems in ways still poorly understood. Also, the presence of these animals may be an important indicator of overall ecosystem health. Most of our favorite pan fish are secondary (or even tertiary) consumers. But why don’t people raise secondary consumers for food?
Ecologists are especially concerned with two results of solar processes: FUEL: In last class I tried to explain how solar energy powers photosynthesis, by which process green plants (etc.) feed all animal life. Today we talk briefly about agricultural intercepts of the system. Next we’ll consider WARMTH: Solar energy mixes and moves air & water to drive weather and climate, the subject of the next several lectures.
The Six Commandments of Theoretical Agriculture • Thou shalt steal land from a natural ecosystem. • Thou shalt replace the natural flora with plants that will serve thee by: • Fitting with thy nutrition-theory (see below) • Fixing lots of sunlight • Expending their fixed energy on production (as opposed to maintenance) • Concentrating their production in edible tissues (as opposed to lignin / cellulose) • Thou shalt input tremendous amounts of energy to supply thy plants with: • Protection from predators (e.g., insects) and competitors (e.g., weeds) • Stuff whose lack would otherwise limit production (irrigation, fertilizer) • Thou shalt develop an adequate theory of nutrition: • That supplies sufficient calories • That supplies an appropriate mix of amino acids (“protein complementarity”) • Thou shalt exchange stuff of which thou hast a surplus for stuff that thou lacketh: • By developing animal husbandry • By trading with other communities • Thou shalt develop ways to perpetuate (and improve?) the system: • By conserving soil resources • By improving thy captive organisms (through cultivar-substitution and artificial selection) • By stealing more land from a natural ecosystem (or from thy weaker neighbors)
Theoretical Ag, Part 1: Selecting the plants that will serve you • They do you no good unless they fix sunlight, but For photosynthetic capture, no ag system tops a rainforest. But a rainforest spends its energy in maintenance while you must produce stuff. So, first, choose plants that produce. For production of stuff, few ag systems can top a wildgrass prairie. But you can’t digest the green grass. So, choose plants that concentrate their production in edible tissue. Think (solar capture)*(production/maintenance)*(edible tissue) • From hundreds of thousands of wild plants • Maybe 100 important domestications maybe 20 critical • These fall into four categories: • Grasses!!!!!!!!!!!!!!!!!!!!!!!!!!!!! • Legumes!!!!!! • Starchy staples!!! • Others! I shall spend much of the semester discussing some favorite agricultural choices from among these groups.
Theoretical agriculture, Part 2:Working for the plants that work for you • If you select plants that are ideal for serving your needs, then they will automatically be pitifully inadequate for serving their own needs. • If your plants are to make lots of stuff, you may need to supply things that they lack. • In many agrisystems, supplying water will be a critical problem. • Nutrients will probably also be (or become) an important concern. • If you maintain an ecosystem suitable for high-production plants that serve you, then you automatically maintain an ecosystem suitable for their high-production competitors. • Weeds almost always become a serious problem. • This is particularly true in tropical and warm-temperate agrisystems. • If you maintain a lot of identical plants in the same place, then you automatically provide a tempting target for predators. • In most systems insects and soil-nematodes become the main problems. • Pests are usually most serious in areas where winters are mild or nonexistent.
Theoretical agriculture, Part 3:Developing a nutritional strategy • The vast majority of the world’s people will need to rely on some “eat plants” strategy. • Rule #1 is “Get sufficient calories!” • Rule #2 is “Balance your amino acids the best you can!” • Rule #3 is “Eat as much variety as you can.” The media are full of complex nutritional advice, but ag-theorists can simplify to 3 short rules.
Theoretical agriculture, Part 4:Exchanging your surplus for things you lack • Here are the three main points: • Historically, plant-ag systems that fail to produce a surplus of anything– well, they soon improve or cease to exist. • Thus many plant-ag systems produce a surplus of at lease one product. But many don’t produce enough variety to support a balanced nutritional strategy. So, people have to do some trading. • There are two common ways to swap off your surplus. • Most commonly, agricultural peoples give surplus land or food to animals. • One scheme is to run cellulose, which you couldn’t digest anyhow, through a fermenter (preferably a foregut fermenter). • Another scheme is to feed a non-picky potential competitor (probably pigs) on scraps, etc. • Ag folks also trade with other cultures.
Theoretical agriculture, Part 5Preserving the system:The Striving that Ceaseth not • Every ag system is potentially sustainable and potentially self-destructive. • As we’ve seen, traditional “slash-and-burn” can continue indefinitely, but only at very low density! • Because by definition they export into other systems, capitalistic ag systems are in particular danger. This is especially true in a global economy. • The exportation of wheat from the American southwest is the exportation of limited water resources. • Traditional Southern cotton was doomed by competition, low price, and soil degradation. • American beef-ranching is profitable only because corn, oil, and antibiotics are very cheap. • Perhaps sustainability should be the main concern of ag researchers.
Now let’s start considering the abiotic context in which ag is practiced. I.e., let’s think climate. Uh, obviously some initial simplification would help. So we’ll build a climate model.
Like all other scientists, human ecologists synthesize their knowledge and insights by use of models. • Often they may not use exactly that term. • Many models seek to present an easily apprehended theoretical picture of how the world works. • Scientists must never confuse their limited, human-created models of the world with the world itself. • Across the next few slides, think about the simplistic model of climatethat we’ll be presenting: • In what ways is the model scientific? • On what deeper physics-models and chemistry-models is it based? • On what parts of the earth does it work best? On what parts does it work (much) less well? • What major, important variables are omitted from the simplistic model? What would be gained and what would be lost by their inclusion? • What are some less important omitted variables? • If you strung 1000 variables together, in what ways would the model change?
Climate-model, Factor 1:Insolation-intensity is largely a function of latitude.
Try a few well-known cities: CITY LATITUDE % __________________________________________ Quito, Singapore, Manaus 0o 100 Darwin, Managua 12o, 10 98 Calcutta, Veracruz 22o, 20o 93 Jacksonville, Cairo 30o 86 Spartanburg 35o 82 Denver, Washington, D.C. 40o 77 Boston 50o 65 Barrow, Alaska 73o 23' 32
Thus we’ve seen that equatorial regions are often quite warm.They can also be very, very wet. • Here’s the deal: • Warm air over warm equatorial seas becomes saturated with moisture. • The warm air rises, and as it does so, it cools. • Water molecules & micro-droplets in the cooling air slow their random motion. • When some collide, they co-adhere and therefore increase in size. • When the droplets become so heavy that they cannot be supported by random molecular movement in air, they fall. • Convective rain occurs when warm, moist air rises, cools, and gets the water squeezed out of it. (See next slide.)
The connection between heat-input and rain: Next slide: seasonality
But, of course, solar heat-input (& therefore temperature and rainfall) also varies by season:
If you put this climate-stuff together, you ought to be able to figure out when convective rains are mostly likely to fall where. That’s where we’ll start on Tuesday. I hope this makes you think about the geographical location of major habitat-types.
