Trophic Cascade Essay

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Trophic cascades occur in nature when predators in a food web alter the behavior of their prey or suppress their number, thereby indirectly affecting the next lower trophic level. Usually these cascades are driven from the top-down, but may also occur bottom-up. This theory has been shown to be important in understanding the effects of removing a keystone species from a food web. A classic example of a terrestrial trophic cascade is the reintroduction of Gray Wolves to Yellowstone National Park, which reduced the number and behavior of Elk. This in turn released several plant species from predation of Elks and flourished across Yellowstone National Park (Ripple et al, 2011). This example of a trophic cascade is vividly shown and explained in a viral video “How Wolves Change Rivers.” However few trophic cascade have been done with bird predators. Such…show more content…
Hummingbird nests were searched for, individually numbered, and monitored throughout three nesting seasons. They were located in riparian zones centered around six hawk nests identified as being active and six were inactive during the first year of the study. Hummingbird and hawk nests were mapped with a GPS, and their heights above the ground, other nest placement data to calculate spatial relationships. The status of hummingbird nests was checked every 2 to 3 days. Relationships between jay foraging heights, distance to a raptor nest, and activity of the raptor nest were examined with ANCOVA. Jay flocks were replotted every 15 min if they remained within the plot area. The jay-free cone in each plot with an active hawk nest was conservatively defined by the location of the lowest individual jays and closest (to the hawk nest) detected during the study. Locations of all foraging jay flocks associated with an active raptor nest were used to graphically summarize the cone-shaped areas of enemy-free space. (Greeney et al,

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