Ecosystems are diverse environments where living organisms interact with their surroundings. From lush rainforests to vast oceans, Earth's ecosystems showcase a remarkable variety of life. Understanding these systems is crucial for grasping how energy flows through nature.

Food chains and webs illustrate the complex relationships between organisms in ecosystems. Energy transfer between trophic levels, from producers to top predators, reveals the intricate balance of life. This knowledge helps us appreciate the delicate interconnections within our planet's ecosystems.

Types of Ecosystems and Energy Flow

Types of Earth's ecosystems

• Terrestrial ecosystems consist of land-based habitats
  • Forest ecosystems are characterized by dense tree cover (Amazon rainforest, temperate deciduous forests, boreal forests)
    • Tropical rainforests have high biodiversity, warm temperatures, and abundant rainfall year-round
    • Temperate forests experience distinct seasonal changes and moderate climates (oak and maple forests)
    • Boreal forests (taiga) are found in cold climates with coniferous trees adapted to harsh conditions (spruce and fir forests)
  • Grassland ecosystems have grasses as the dominant vegetation with few or no trees
    • Savannas are tropical grasslands with scattered trees and large herbivores (African savannas, llanos)
    • Prairies are temperate grasslands with tall grasses and deep, fertile soils (Great Plains)
    • Steppes are semi-arid grasslands with short grasses and continental climates (Eurasian steppes, Patagonian steppe)
  • Desert ecosystems receive very little precipitation and host adapted plants and animals
    • Hot deserts experience high daytime temperatures and cold nights (Sahara, Sonoran Desert)
    • Cold deserts have cool average temperatures and experience frost and snow (Gobi Desert, Antarctic Desert)
  • Tundra ecosystems are found in cold climates with low-growing vegetation and permafrost
    • Arctic tundra is located in the Northern Hemisphere with long, cold winters and short summers
    • Alpine tundra occurs at high elevations above the tree line in mountainous regions
• Aquatic ecosystems are water-based habitats
  • Freshwater ecosystems have low salt concentrations
    • Rivers and streams are flowing water ecosystems that transport water from sources to lakes or oceans
    • Lakes and ponds are standing water ecosystems that vary in size, depth, and nutrient levels
    • Wetlands are transitional areas between land and water, such as marshes, swamps, and bogs
  • Marine ecosystems have high salt concentrations and cover a vast portion of the Earth's surface
    • Coastal ecosystems are found in shallow, nutrient-rich waters near land
      • Estuaries are partially enclosed areas where freshwater rivers meet the ocean (Chesapeake Bay)
      • Coral reefs are underwater structures built by coral polyps in warm, clear waters (Great Barrier Reef)
    • Open ocean ecosystems are vast areas of deep water divided into zones based on depth and light penetration
      • Pelagic zone is the open water column where many fish and marine mammals live
      • Benthic zone is the ocean floor, home to a diverse array of organisms adapted to dark, high-pressure conditions

Ecosystem Components and Interactions

• Ecosystems are composed of both living (biotic) and non-living (abiotic) components
  • Biotic factors include all living organisms within an ecosystem (plants, animals, microorganisms)
  • Abiotic factors include physical and chemical elements of the environment (temperature, water, soil, light)
• Energy flow through ecosystems involves the transfer of energy from one organism to another
• Nutrient cycling is the process by which essential elements and compounds are circulated through the ecosystem
• Each species occupies a specific ecological niche, which is its unique role and position within the ecosystem
• The carrying capacity of an ecosystem is the maximum population size that can be sustained by available resources

Food chains vs food webs

• Food chains depict a linear sequence of energy transfer from producers to consumers
  • Each level in the food chain represents a trophic level
    • Producers (autotrophs) make up the first trophic level and convert solar energy into chemical energy through photosynthesis (plants, algae)
    • Primary consumers (herbivores) occupy the second trophic level and feed on producers (rabbits, zooplankton)
    • Secondary consumers (carnivores) occupy the third trophic level and feed on primary consumers (hawks, small fish)
    • Tertiary consumers (top predators) occupy the fourth trophic level and feed on secondary consumers (lions, sharks)
  • Decomposers break down dead organisms and return nutrients to the ecosystem (bacteria, fungi)
• Food webs represent a complex network of interconnected food chains within an ecosystem
  • Depict multiple feeding relationships and energy pathways, providing a more realistic representation of energy flow compared to food chains
  • Offer stability and resilience to ecosystems
    • If one species is removed, alternative energy pathways can maintain ecosystem function, preventing collapse

Energy transfer in food webs

• Primary producers convert solar energy into chemical energy through photosynthesis
  • Photosynthesis: $6CO_2 + 6H_2O + \text{solar energy} \rightarrow C_6H_{12}O_6 + 6O_2$
• Consumers obtain energy by consuming other organisms
  • Herbivores feed on producers, transferring energy to the second trophic level (caterpillars eating leaves)
  • Carnivores feed on herbivores or other carnivores, transferring energy to higher trophic levels (birds eating insects, lions eating zebras)
• Decomposers break down dead organisms and release nutrients back into the ecosystem
  • Bacteria and fungi are the main decomposers in ecosystems (mushrooms, soil bacteria)
• Energy is lost at each trophic level due to:
  1. Incomplete consumption of prey (leftovers)
  2. Energy used for metabolic processes like respiration (energy for survival)
  3. Energy lost as heat (through movement and digestion)

Impact of energy transfer efficiency

• Trophic efficiency is the percentage of energy transferred from one trophic level to the next
  • Typically, only about 10% of energy is transferred between trophic levels
  • $\text{Trophic efficiency} = \frac{\text{Energy transferred to next level}}{\text{Total energy in current level}} \times 100%$
• Energy pyramids visually represent energy flow and trophic efficiency in ecosystems
  • Producers form the broad base of the pyramid, representing the highest amount of available energy
  • Each successive trophic level has less available energy and supports fewer organisms, creating a narrowing pyramid shape
• Low trophic efficiency has consequences for ecosystem structure and function
  • Limits the number of trophic levels in an ecosystem (usually 4-5 levels maximum)
  • Ecosystems with lower trophic efficiencies support fewer top predators (less energy reaches the top)
  • Biomass decreases with each successive trophic level (less energy to support growth and reproduction)
• Factors influencing trophic efficiency include:
  • Type of ecosystem (terrestrial ecosystems tend to have lower efficiency than aquatic ecosystems)
  • Metabolic rates of organisms (higher metabolic rates lead to more energy loss)
  • Ecological strategies (r-selected species have higher reproduction rates and lower efficiency compared to K-selected species)