Ecosystems Nutrient Cycles AP Biology Trophic Relationships A

Ecosystems & Nutrient Cycles AP Biology

Trophic Relationships

A Review of Trophic Levels • Primary Producers = Autotrophs create their own energy (converted through photosynthesis or chemical methods) • Primary Consumers = Herbivores, Heterotrophs (can’t make own energy) • Secondary & Tertiary Consumers = Heterotrophs, Carnivores • Detritivores/Decomposers = get nutrients from nonliving organic material (detritus)

Ecosystem Energetics • Gross Primary Productivity (GPP) = Total amount of light energy converted to chemical energy in a fixed time (by photosynthesis) • Net Primary Productivity (NPP) = Amount of chemical energy actually available to pass on to consumers (accounts for energy lost through cellular respiration) = GPP – cellular respiration

How will changes in climate and the atmospheric environment affect primary productivity?

• Net Primary Productivity varies between ecosystems because of the climate and other atmospheric conditions (linked to nutrients available)

Secondary Productivity • the rate at which consumers convert the chemical energy of the food they eat into their own biomass - Biomass = mass of living tissue (dry weight) - Limited by Net Primary Production

Transfer of energy between trophic levels • A considerable amount of energy is lost between trophic levels – Energy used up in respiration – Energy released in feces • Usually, about an average of 10% is transferred between levels

Biomass pyramids • Most pyramids narrow rapidly because energy transfer across levels is so poor – Cannot support large number of organisms at higher levels

• Why would one pyramid be upside down? • Because producers are consumed too quickly to ever develop a large population size

Green World Hypothesis • Why don’t all the herbivores eat all the green plants? • Herbivore populations are kept in check by – Plant defenses against herbivory – Limited nutrients supplied by plants – Unfavorable environmental conditions/changes – Competition within the species – Other interactions like predation, parasites, disease.

Nutrient Cycles • Chemical nutrients are limited in ecosystems must be recycled both globally and locally • Ex. Carbon, Nitrogen, Water, Phosphorus

Carbon Cycle • Key Processes: – Cellular Respiration – Photosynthesis

Nitrogen Cycle • Nitrogen is used to build nucleic acids & proteins • cycle converts N 2 gas into forms plants can use • Key Processes: • Nitrification: Through a series of conversions by specialized bacteria, N 2 is converted into nitrates • Assimilation: Plants take in nitrates

Phosphorus Cycle • Phosphorus is used in nucleic acids and certain lipids. • Key Processes: – Weathering and Erosion – Sedimentation & Rock Formation – Decomposition