Secondary Production

Secondary production refers to the production of biomass in consumers Production efficiency = (Net Secondary Production) / (Assimilation of primary production) Energy lost from waste is not considered assimilated

Animals are inefficient Energy is lost in the form of cellular respiration for all animals, but efficiency differs from organism to organism. Insects ~ 40% efficiency Fish ~ 10% efficiency Mammals/Birds ~ 3% efficiency

Trophic efficiency Efficiency can be measured by trophic levels as the percent of production transferred to the next trophic level Production can never increase, only decrease As a rule, only about 10% of energy transfers from one trophic level to the next. Pyramid of production

Biomass pyramids show the amount of biomass at each trophic level and are usually similar to pyramids of production Rarely a short turnover rate (standing crop mass / production) can result in a system with higher primary consumer biomass than primary producer biomass.

Pyramid of numbers Because top predators tend to be large, and the top trophic levels already are constrained to small biomass numbers there are very few predators in most populations compared to primary consumers.

Why is the world green? One question that has been surprisingly difficult to answer is “Why is the world green?” Put another way, “Why are herbivores unable to deplete primary producer biomass?”

Green World Hypothesis Predators, parasites, and disease keep herbivore populations from overwhelming primary producers Other factors that may explain this observation: Plants have defenses against herbivores It is not energy, but nutrients that limit growth Abiotic factors like season limit consumers

Cycling

Nutrient Cycling