Environmental Systems & Societies 1.3 Energy & Equilibria Environmental Systems & Societies

Significant Ideas The laws of thermodynamics govern the flow of energy in a system and the ability to do work. Systems can exist in alternative stable states or as equilibria between which there are tipping points. Destabilizing positive feedback mechanisms will drive systems toward these tipping points, whereas stabilizing negative feedback mechanisms will resist such changes.

Knowledge & Understanding The 1st law of thermodynamics is the principle of conservation of energy: energy in an isolated system can be transformed but cannot be created or destroyed. The principle of conservation of energy can be modeled by the energy transformations along food chains and energy production systems. The second law of thermodynamics states that the entropy of a system increases over time. Entropy is the measure of the amount of disorder in a system. An increase in entropy arising from energy transformations reduces the energy available to do work. The second law of thermodynamics explains the inefficiency and decrease in available energy along a food chain and energy generation systems. An open system, an ecosystem, will normally exist in a stable equilibrium, either a steady-state or one developing over time (eg., succession), and maintained by stabilizing negative feedback loops.

Knowledge & Understanding Negative feedback loops (stabilizing) occur when the output of a process inhibits or reverses the operation of the same process in such a way to reduce change or deviation from the norm. Positive feedback loops (destabilizing) will tend to amplify changes and drive the system toward a tipping point where a new equilibrium (new norm) is established. The resilience of a system, ecological or social, refers to its tendency to avoid such tipping points and maintain stability. Diversity and size of storages within systems can contribute to their resilience and affect the speed of response to change (time lags). Humans can affect the resilience of systems through reducing these storages and diversity. The delays involved in feedback loops make it difficult to predict tipping points and add to the complexity of modeling systems.

Energy in Systems Energy in Systems are Subject to the Laws of Thermodynamics 1st Law of Thermodynamics (Principle of Conservation of Energy: Energy is neither created nor destroyed but converted from one form to another. The total energy in the universe (isolated system) remains constant.

Energy in Systems The Second Law of Thermodynamics: The entropy of an isolated system not in equilibrium will tend to increase over time. Entropy is the measure of disorder of a system (refers to the spreading/dispersal of energy).

Entropy (more energy = less order) Over time, all differences in energy in the universe will be evened out and nothing can change.

Energy = work + heat (heat is low-quality, wasted energy) Heat dissipates, without order, to the environment. Heat has high-entropy. Although heat can warm the environment, it can not power any processes. Energy conversions are never 100% efficient. For example, <50% of solar radiation reaches the Earth’s surface, plants convert only 1-2% to sugars. Assimilation by consumers is about 10%. There will always be a reduction in the amount of energy passed to the next trophic (feeding) level. Life is a battle against entropy and, without constant replenishment of energy, life would cease to exist.

What is the efficiency of a light bulb? Efficiency = (work or useful energy produced/energy consumed) x 100 Based on the above information, what is the efficiency of a standard filament light bulb (left) vs. a modern, energy-saving bulb?

Complexity and Stability The less complex and diverse an ecosystem is, the less stability and resiliency those systems have. For example: Monocultures → A monoculture is a farming system in which there is only one major crop. (ex. Potato famine, Ireland, 1845-1848).

Equilibrium Equilibrium is the tendency of a system to return to its original state following a disturbance; at equilibrium, a state of balance exists among the components of that system. Types of Equilibria Steady-state (dynamic) Equilibrium Static or Stable Equilibrium Unstable Equilibrium Stable Equilibrium Open systems tend to exist in a state of balance or stable equilibrium. Open systems (ecosystems) tend to avoid sudden changes. Ecosystems fluctuate (within limits).

Steady-State (Dynamic Equilibrium) Characteristic of open systems (ecosystems). Continuous inputs and outputs of energy and matter → The system as a whole remains in a balanced state. NEGATIVE FEEDBACK The process by which any deviations or fluctuations from an equilibrium are neutralized or counteracted. The system returns to its previous state after small fluctuations in the short-term.

Examples of Steady-State Equilibrium 1. Body Temperature Maintenance: 2. A Mature, Climax Ecosystem: No long-term changes. Inputs (light, water, nutrients , gases) and outputs (gases, heat, salts) balance each other. Climax Communities look much the same for long- periods of time.

Static Equilibrium (no change over time) This cannot occur in living systems as live involves a constant exchange of energy and matter with the environment. Examples Include: The oxygen content of our atmosphere (21% for the past 2 billion years). A pile of rocks, building or stone wall. They don’t change their positions for long-periods of time.

Unstable and stable equilibrium Systems can also be stable or unstable. Most systems display stability by default. In stable equilibrium, the system tends to return to the same equilibrium after a disturbance. In an unstable equilibrium, the systems returns to a NEW equilibrium after a disturbance. (ex. Climate Change)

Feedback Loops Feedback loops can be ► 1. Positive: Deviation AWAY from the norm toward a tipping point. Change a system to a NEW state. Destabilizing as they INCREASE change. 2. Negative: Return a system to its original state. Homeostatic (maintenance of a stable environment). Stabilizing as they reduce change/deviations from norm.

Feedback loops explained

. . . . Negative Feedback Examples Predator-Prey Interactions & The Lotka-Volterra Model: Climate Change: Rising Global Temperatures ► Melting Ice Caps ► More water available for evaporation ► More clouds ► More solar radiation reflected by clouds ► Falling Global Temperatures.

Positive feedback Examples Freezing to Death: Your body temperature falls below 37 degrees. Shivering/metabolic rate increase but are insufficient. Metabolic rate falls and continues to fall as enzymes fail to work. You become lethargic/sleepy. Body cools even further. You die of hypothermia. Your body is discovered in the summer. Climate Change (again): Rising global temperatures ►Melting Polar Ice Caps ►Dark soil exposed/melting of permafrost/methane released ►More solar radiation absorbed ►Drop in Albedo (reflecting ability of a surface).

Resilience of systems Resilience of a system is its ability to return to its initial state following a disturbance. Good Resilience: Eucalypt forests of Australia Bad Resilience: Antibiotic-resistant, pathogenic bacteria.

Factors affecting ecosystem resilience The more diverse/complex an ecosystem, the more resilient it tends to be (more interactions between species). The greater the species biodiversity of an ecosystem, the greater the likelihood there is a species that can replace another if it dies (to maintain equilibrium). The greater the genetic diversity within a species, the greater resilience. A monoculture of wheat or rice can be wiped out by disease if none of the plants have genetic resistance. Species that can shift geographic ranges are more resilient. The climate affects resilience. In the Arctic, regeneration/growth of plants is slow (low temps slow down photosynthesis/cell respiration). In tropical rain forests, growth rates are fast (light, temp, water are not limiting factors). The faster the rate at which a species can reproduce means recovery is faster. r-strategists (fast reproductive rate) can recolonize the system better than K-strategists (slow reproducers). Humans can remove or mitigate threats to the system (pollution, invasive species) – resulting in faster recovery.

Tipping points Small (or large) changes in a system can tip the equilibrium beyond a threshold (tipping) point. Best approach is precautionary. An ecological tipping point is reached when an ecosystem experiences a shift to a new state in which there are significant changes to its biodiversity and/or services: Tipping points involve positive feedback. Positive feedback is self-perpetuating (ex. Deforestation). There is a threshold beyond which a fast shift of ecological states occurs. The threshold point cannot be precisely predicted. The changes are long-lasting. The changes are hard to reverse. There is a significant lag-time between the pressures driving change and the appearance of impacts, creating problems with motivation and ecological management.

The precautionary principle

Examples of tipping points 1. Lake Eutrophication: 2. Extinction of a Keystone Species: Removal of elephants from a savannah ecosystem can result in irreversible damage to that system. 3. Coral Reef Death: If ocean acidity levels increase, the reef coral dies and cannot regenerate.