Rucete ✏ AP Biology In a Nutshell
20. The Basics of Ecology
This chapter introduces key ecological principles, including how organisms respond to environmental changes, how energy flows through ecosystems, and how these factors shape population size, biodiversity, and evolutionary change.
Organismal Responses to Environmental Change
• Organisms use behavioral or physiological mechanisms to respond to environmental stimuli.
• A stimulus triggers a response. – Example: Change in day length → birds migrate or animals enter torpor.
• Signals facilitate communication among organisms and may be:
– Audible (e.g., bird calls, primate warnings)
– Chemical (e.g., pheromones in insects, skunks, plants)
– Electrical (e.g., sharks locating prey)
– Tactile (e.g., grooming in primates, plants responding to touch)
– Visual (e.g., aposematic coloration in poisonous frogs)
• Communication improves reproduction, social organization, and survival—traits favored by natural selection.
Cooperative Behaviors
• Group behaviors enhance individual and population fitness.
• Examples:
– Starlings: murmurations deter predators and conserve warmth.
– Meerkats: sentinel behavior, grooming, group defense increase survival.
Energy Flow and Thermoregulation
• Endotherms: use metabolic energy to maintain internal temperature (e.g., birds, mammals).
• Ectotherms: rely on environmental heat (e.g., reptiles, fish); regulate temperature behaviorally.
• Metabolic rate: higher in smaller organisms due to greater surface area to volume ratio.
Energy Balance and Ecosystem Impact
• Net gain of energy → growth or storage (e.g., fat reserves).
• Net loss of energy → weight loss, reduced survival, or death.
• Energy limitation affects ecosystem dynamics:
– Reduced sunlight → fewer producers → food web disruption (e.g., coral bleaching).
Trophic Levels and Energy Transfer
• Producers → primary consumers → secondary/tertiary consumers
• Food chains: show linear energy flow; food webs: show interconnections.
• Arrows in food webs point to the consumer (predator).
Autotrophs and Heterotrophs
• Autotrophs: make energy-rich molecules from inorganic sources – Photoautotrophs (e.g., plants) – Chemoautotrophs (e.g., bacteria in thermal vents)
• Heterotrophs: obtain energy from organic compounds – Includes herbivores, carnivores, omnivores
• Decomposers: recycle nutrients by breaking down organic matter (e.g., fungi, bacteria)
• Detritivores: eat waste and dead material (e.g., earthworms, millipedes)
Unique Energy Strategies
• Kleptoplasty: sea slugs incorporate chloroplasts from algae → photosynthesize when food is unavailable.
Energy Loss and Trophic Structure
• Energy is lost at each trophic level (as heat or metabolism).
• Higher trophic levels have fewer organisms and less biomass.
• Bottom-up regulation: decline in producers causes collapse of higher levels.
• Top-down regulation: loss of predators allows overgrazing and plant decline.
Energy and Reproductive Strategies
• Unstable environments (low energy): many offspring, low survival (r-strategy).
• Stable environments (high energy): few offspring, high survival (K-strategy).
In a Nutshell
Ecology connects organismal responses to environmental change with energy flow and ecosystem stability. Communication and cooperation enhance survival, and energy availability shapes population size, biodiversity, and reproductive strategies. Disruptions in energy input or trophic structure can destabilize entire ecosystems.