HarknessEcosystems

Wilson P's Question: //Why is a rainforest considered to have one of the highest NPP's when areas like savannahs are able to support animals of such large weights, like elephants, giraffes, zebras, etc? Rainforests typically have one large/heavier animal, such as a jaguar.//

Ms. Tuttle's Best Answer:
 * Rainforests are productive year-round, while Savannahs typically have a season of growth and a season without growth. So over the course of a year, rainforests may produce more total energy simply because their growing season is longer
 * The pyramid of biomass asks us to consider total mass of each consumption level. Elephants, being herbivores, are primary consumers. They are able to convert 10% of the savannah mass directly into their own body mass, which the pyramid of biomass illustrates. This mass allocation decreases higher up the pyramid; lions can only convert 1% of the savannah biomass into body mass, as they first have to transfer through the lower two trophic levels. The __total weight__ of all primary consumers cannot exceed 10% of the savannah biomass weight. It seems like there needs to be a lot of savannah biomass to be able to support this, and there is, but it is in a huge area. It also seems like elephants are huge, but there aren't a lot of them.
 * In the rainforest the pyramid of biomass still holds true. However, there are a lot more small individuals that in total would still equal 10% of the mass of the production level. Given the same square area, a rainforest can be a lot more productive than a grassland. 10 sq. m of rainforest may be able to support an elephant-weight of insects, but 10 sq. m of savannah could not support one elephant for one full meal. So the truth is that savannahs have a lot more area to sustain heavy organisms, and there are also less of those heavy organisms than we think. There could be 1000 insects in that 10 sq. m area, whereas there may only be 1000 elephants total in one whole country in Africa.
 * NPP also deals with the amount left over after a plant provides its own life processes. As Rainforest NPP > Savannah NPP, this simply means a rainforest plant and a savannah plant that do perform the same amount of photosynthesis will have different Net outcomes. The rainforest plant may need to __expend less energy__ for its own life than a savannah plant. Savannah plants live in a harsher environment; less rain (it rains in a rainforest everyday- and as we'll discuss later, this relates to the plants transpirating and creating their own raincloud every day), more nutrients, and less wind to stand up against. So the NPP of a rainforest is higher, but that may also be because it is easier to be a plant in a rainforest.