17.2 Energy Flow in Ecosystems

Energy flow in ecosystems is all about how organisms get and use energy. It starts with producers like plants making food from sunlight, then moves up through consumers eating each other. Each step loses some energy, shaping how ecosystems work.

Food chains show this energy flow simply, while food webs show it more realistically. Energy pyramids and biomass help us see how much energy and living stuff is at each level. This helps explain why there are fewer top predators than plants in nature.

Food Chains and Food Webs

Trophic Relationships in Ecosystems

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• Food chains depict the linear flow of energy from producers to consumers in an ecosystem
  • Consist of producers (plants) at the base, followed by primary consumers (herbivores), secondary consumers (carnivores), and tertiary consumers (top predators)
  • Energy is transferred from one trophic level to the next, with some energy lost as heat at each level (approximately 10% of energy is transferred)
• Food webs illustrate the complex network of feeding relationships within an ecosystem
  • Include multiple interconnected food chains
  • Demonstrate how species can occupy multiple trophic levels and have various food sources (omnivores consume both plants and animals)
• Trophic levels represent the position of an organism in the food chain or web
  • Producers (autotrophs) make up the first trophic level, converting sunlight into chemical energy through photosynthesis (plants, algae, cyanobacteria)
  • Consumers (heterotrophs) occupy higher trophic levels, obtaining energy by consuming other organisms
    • Primary consumers (herbivores) feed on producers (rabbits, caterpillars, zooplankton)
    • Secondary consumers (carnivores) eat primary consumers (birds, spiders, small fish)
    • Tertiary consumers (top predators) consume secondary consumers (hawks, wolves, sharks)
  • Decomposers break down dead organisms and waste products, releasing nutrients back into the ecosystem (bacteria, fungi)

Ecological Roles of Organisms

• Producers, also known as autotrophs, are organisms that convert inorganic compounds into organic compounds using energy from the sun (photosynthesis) or chemical reactions (chemosynthesis)
  • Photosynthetic producers include plants, algae, and cyanobacteria
  • Chemosynthetic producers, such as certain bacteria, use chemical energy to produce organic compounds in extreme environments (deep-sea hydrothermal vents)
• Consumers, or heterotrophs, obtain energy and nutrients by feeding on other organisms
  • Primary consumers (herbivores) feed exclusively on producers (plants)
  • Secondary consumers (carnivores) eat primary consumers
  • Tertiary consumers (top predators) consume secondary consumers
  • Omnivores feed on both producers and consumers (humans, bears, crows)
• Decomposers, including bacteria and fungi, break down dead organisms and waste products
  • Recycle nutrients back into the ecosystem, making them available for producers
  • Play a crucial role in maintaining the flow of energy and matter within ecosystems

Energy Flow and Biomass

Energy Pyramids and Trophic Levels

• Energy pyramids represent the flow of energy through trophic levels in an ecosystem
  • The base of the pyramid represents producers, with each successive level representing consumers
  • The width of each level indicates the amount of energy available at that trophic level
  • Energy is lost as heat at each trophic transfer (approximately 10% efficiency), resulting in a narrowing of the pyramid
• Biomass refers to the total mass of living organisms in a given area or ecosystem
  • Biomass pyramids depict the amount of biomass at each trophic level
  • Producers typically have the highest biomass, followed by primary consumers, secondary consumers, and tertiary consumers
  • Biomass pyramids can be inverted in some aquatic ecosystems where producers (phytoplankton) have a rapid turnover rate and support a larger biomass of consumers

Ecological Efficiency and Energy Transfer

• Ecological efficiency is the percentage of energy transferred from one trophic level to the next
  • Typically, about 10% of the energy is transferred, while 90% is lost as heat, used for metabolic processes, or undigested
  • This low efficiency limits the number of trophic levels in an ecosystem (usually 4-5)
  • Ecosystems with higher ecological efficiencies can support more trophic levels and a greater abundance of organisms
• Energy transfer between trophic levels is inefficient due to several factors
  • Heat loss during metabolic processes
  • Undigested material in waste products
  • Energy used for growth, reproduction, and other life functions
  • Incomplete consumption of organisms by predators

Bioaccumulation

Accumulation of Toxins in Food Chains

• Bioaccumulation is the gradual buildup of toxic substances, such as heavy metals or persistent organic pollutants, in an organism's tissues over time
  • Occurs when the rate of intake exceeds the rate of excretion or metabolic breakdown
  • Toxins are often stored in fatty tissues and can persist for long periods
• Bioaccumulation can be amplified through food chains, a process called biomagnification
  • Toxins are transferred from producers to consumers, with concentrations increasing at each trophic level
  • Top predators, such as birds of prey or large fish, tend to have the highest levels of accumulated toxins
• Bioaccumulation and biomagnification can have detrimental effects on organisms and ecosystems
  • High levels of toxins can cause health problems, reduced fertility, and increased mortality rates
  • Persistent organic pollutants (POPs) and heavy metals (mercury, lead) are common bioaccumulative substances
  • DDT, a pesticide, is a well-known example of a POP that bioaccumulated in birds of prey, causing eggshell thinning and population declines