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Environmental science is an interdisciplinary field, meaning it pulls knowledge from many different scientific areas to understand the environment. It's not just about trees and animals; it's also about chemistry, physics, economics, sociology, and even politics. The goal is to figure out how the natural world works, how humans interact with it, and how we can solve environmental problems.

• Energy Flow:
  • Initiated by autotrophs (producers) through photosynthesis (primary production).
  • Gross Primary Production (GPP): Total energy fixed by autotrophs per unit area per unit time.
  • Net Primary Production (NPP): Energy remaining after respiration (R_auto) for growth and reproduction.
    • $NPP = GPP - R_{auto}$ (Units: biomass/area/time, e.g., kg C m⁻² yr⁻¹ or kJ m⁻² yr⁻¹)
  • Secondary Production: Energy assimilated by heterotrophs. Net Secondary Production (NSP) is energy assimilated minus respiration (R_hetero) and egestion.
    • $NSP = A - R_{hetero}$ (where A = Assimilated energy)
  • Ecological Efficiency ($\eta_{TL}$): The efficiency with which energy is transferred from one trophic level ($TL_n$) to the next ($TL_{n+1}$). Typically 5-20%, often approximated at 10%.
    • $\eta_{TL} = (Energy_{TL_{n+1}} / Energy_{TL_n}) \times 100\%$