8.2 Energy Flow Through Ecosystems

• Endotherms

  Organisms that use thermal energy generated by metabolism to maintain homeostatic body temperature
• Ectotherms

  Organisms that lack efficient internal mechanisms to regulate and maintain body temperature, and rely on behaviors to regulate temperature
• Metabolic rate per unit body mass

  Inversely related to the size of multicellular organisms
• Generally, the smaller the organism, the higher the metabolic rate
• Net gain in energy

  Results in energy storage or growth for an organism
• Net loss of energy

  Results in loss of mass and ultimately the death of an organism
• Changes in energy availability

  Can result in changes in population size and disruption to an ecosystem
• Changes in energy resources such as sunlight can affect the number and size of the trophic levels
• Trophic level

  The position an organism occupies in the food chain
• Food chains show the direction of nutrients and energy transferred from one organism to another
• Food webs consist of many interconnected food chains
• The transfer of energy between trophic levels is inefficient, typically around 10% efficient
• This energy inefficiency limits the length of food chains and the size of populations
• Autotrophs

  Organisms that capture energy from physical or chemical sources in the environment, including photosynthetic and chemosynthetic organisms
• Heterotrophs

  Organisms that capture energy present in carbon compounds produced by other organisms, and metabolize carbohydrates, lipids and proteins as sources of energy
• Seasonal reproduction in animals and plants occurs at different times of year, triggered by factors like critical photoperiod