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The Big Picture
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The Big Picture… The trophic cascade hypothesis states that a rise in piscivore (fish-eating) biomass brings decrease in planktivore biomass (plankton-eating fish), increased herbivore biomass, and decreased phytoplankton biomass. So in simpler terms, an increase in fish biomass causes a decrease in food organisms of the fish, which cascades down to regulate lower trophic levels by different consumption demands. Below are three graphs demonstrating the trophic cascade model from 1985, when the model was first proposed. (data and graphs from Carpenter, Kitchell, and Hodgson 1985) When fish eating fish are introduced to an area and plankton eating fish, the rate of primary production is significantly altered by increasing the rate of consuming algae production. The amount of nutrients available and the structure of the food web function together to produce biomass at each trophic level. In explaining the food web of a typical lake, it can be very complex with hundreds of organisms contributing all depending on the size of the particular lake. The most important step in a food web is the role the primary producers have. At each trophic level, the amount of energy decreases so it is essential for primary producers, which are mainly plants, to support the large fish at the top of the food web. The food web below is the structure for a typical lake. FOOD WEB OF TYPICAL LAKE (Water on the Web) The plants and algae may die or be eaten by primary consumers such as zooplankton. These include larval fish eating the zooplankton all in the second trophic level. In the third trophic level, secondary consumers such as small fish eat the primary consumers. In the fourth trophic level, larger fish, ospreys and people are tertiary consumers and eat the smaller fish. So the primary producers all the way back to the beginning of the food web spread their energy and nutrients throughout the rest of the web. In answering the resource manager’s question, the trophic cascade hypothesis for controlling productivity in lakes can apply to managing algal blooms in eutrophic lakes. If upon her studies, she finds that it is not just the excessive amounts of nutrient inputs that are causing these algal blooms, then other factors are a key here. The trophic cascade hypothesis is all about the management of top predators that bring out changes in the primary producers of a lake. So for example, say a large predacious fish, a piscivore, eats all the minnows from a small lake and eliminates them from the food chain. Resulting will be a reduction of planktivores, or minnows. With the minnows, “missing in action” are gone, zooplankton which is the minnow’s primary food source will now dominate the lake. Since zooplankton can now feed off the algae as their primary food source, algae biomass, the primary production is reduced. The results will be improvements of water quality and no major problems with algal blooms.
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Paper Information
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Title: The Big Picture
Words: 2360
Rating: None
Pages: 9.4
submitted by: molly24hath
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