Question

Describe the use of the symbols + and - when characterizing a trophic cascade.

Answer 1

Answer:

Explanation:

Trophic cascade, an ecological phenomenon triggered by the addition or removal of top predators and involving reciprocal changes in the relative populations of predator and prey through a food chain, which often results in dramatic changes in ecosystem structure and nutrient cycling.

In a three-level food chain, an increase (or decrease) in carnivores causes a decrease (or increase) in herbivores and an increase (or decrease) in primary producers such as plants and phytoplankton. For example, in eastern North America the removal of wolves (Canis lupus) has been associated with an increase in white-tailed deer (Odocoileus virginianus) and a decline in plants eaten by the deer. American zoologist Robert Paine coined the term trophic cascade in 1980 to describe reciprocal changes in food webs caused by experimental manipulations of top predators. In the 1980s others used the term to describe changes in aquatic ecosystems arising from factors such as sudden increases in predatory fish populations from stocking or dramatic declines in predatory fishes caused by overfishing.

Effects On Aquatic And Terrestrial Ecosystems

During the 1980s and ’90s a series of experiments demonstrated trophic cascades by adding or removing top carnivores, such as bass (Micropterus) and yellow perch (Perca flavescens), to or from freshwater lakes. Those experiments showed that trophic cascades controlled biomass and production of phytoplankton, recycling rates of nutrients, the ratio of nitrogen to phosphorus available to phytoplankton, activity of bacteria, and sedimentation rates. Because trophic cascades affected the rates of primary production and respiration by the lake as a whole, they affected rates of exchange of carbon dioxide and oxygen between the lake and the atmosphere.

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Research in a wide variety of terrestrial and aquatic environments has shown that trophic cascades control species composition, biomass, and production of herbivores and plants. For example, overfishing of cod (Gadus morhua) and other commercially exploited fishes such as haddock (Melanogrammus) and hake (Urophycis, Raniceps, and Phycis) in the North Atlantic Ocean led to an increase in small pelagic (open ocean) fish consumed by cod, snow crab (Chionoecetes opilio), and shrimp. As a result, populations of large-bodied herbivorous zooplankton, which are consumed by small pelagic fishes, decreased, which in turn led to an increase in the phytoplankton. Restoration of wolves to the Bow Valley of Alberta, Canada, decreased the population of elk (Cervus elaphus) and increased the growth of aspen (Populus) and willow (Salix). In another example, the commercial harvesting of sea otters (Enhydra lutris) for the fur trade off the west coast of North America triggered an increase in sea urchins and a decline in kelp forests, because of kelp consumption by the urchins, in nearby marine environments.

Answer 2

Answer:

+ and - represents top down cascade and bottom up cascade respectively.

Explanation:

• The ecological phenomena known as "trophic cascade," which involves reciprocal changes in the relative populations of predators and prey down a food chain, is what causes the most frequent dramatic changes in ecosystem structure and nutrient cycling.
• The species composition, biomass, and output of herbivores and plants are regulated by trophic cascades, according to research conducted in a wide range of terrestrial and aquatic habitats.
• Large-bodied herbivorous zooplankton populations, which are eaten by small pelagic fish, dropped as a result, which in turn caused a rise in phytoplankton.
• Historically, it was believed that physical or chemical variables, such as solar radiation, climate, and nutrient availability, regulated plant growth and the cycling of nutrients. Producer communities and their metabolic rates are regulated by trophic cascades in addition to physical and chemical factors.
• The populations of the species at the lower trophic levels (the base of the pyramid) are governed top-down by those at the top. This strategy is also known as an ecosystem's predator-controlled food chain.
• The presence or absence of the producers in the ecosystem determines the bottom-up control. Changes in their population will have an impact on the environment as a whole as well as the population of every species in the food chain. The resource-controlled (or food-limited) food web of an ecosystem is another name for this strategy.

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