52. Ecosystems
Introduction to Ecosystems
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Top down control cascades are seen in ecosystems where a predator high on the food web is going to control prey populations. Now, what we can see is a trophic cascade where the predator is going to lower the abundance of prey, and then reduce the next trophic level from predation, or in this case that we're going to take a look at herbivory. You see, the wolf population in Yellowstone used to keep the elk population in check. But due to overhunting of wolves for very terrible political reasons, the wolf population of Yellowstone was diminished to nothing. They were hunted to extinction, and then the elk population exploded. And this actually led to, you know, a lot of herbivory and it greatly reduced the vegetation in the area. So this was an example of a trophic cascade because those wolves were actually protecting the vegetation indirectly by controlling the elk population. Now primary production is something we look at in ecosystems, and this is the synthesis of organic compounds from inorganic carbon dioxide. Usually, we're gonna see this in the form of photosynthesis, and you can see the reaction here, in the Calvin cycle that will perform this carbon fixation. And we're gonna be looking at different measures of production. There is gross primary productivity, which is the amount of energy generated by primary producers in an area over time. So, here, we can see our gross primary productivity, it's just all the energy generated. Now, a useful, measure to look at is the net primary productivity. So some of that energy that is generated by the plants is gonna be used by the plants own respiration. So they're gonna be returning that, carbon to c o two. Now what you're left with after you take the gross primary productivity and remove what the plants use for respiration is the net primary productivity. So that's the gross primary production minus the energy consumed by the primary producer's own respiration. And you can think of this as the total amount of new biomass added by primary producers. Now, net ecosystem productivity looks at the total accumulation of new biomass after the respiration of all organisms. So here you can see the net ecosystem, productivity takes that net primary productivity, minus everything that gets diverted to the heterotroph's respiration. So everything we're left with, all that biomass left over, is the net ecosystem productivity. Now with that, let's go ahead and flip the page.
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