Tri-Trophic Paradoxes

In a study conducted on the west coast of Vancouver Island by Markel & Shurn (2015), they observed a classic tri-trophic cascade involving sea otters, sea urchins, and kelp. Their findings displayed a clear relationship between the presence of sea otters, with the abundance of sea urchins, and the resulting kelp forest depth and surface area. In the areas where sea otters were absent, sea urchins were found to be overabundant and the kelp forests were small and shallow. However, at locations with sea otters present, sea urchins were rare and the kelp forests extended 3.7 times deeper than they had at locations with an absence of sea otters. Markel & Shurn also found the kelp forest surface area to be on average 18.8 times larger with a presence
The species being affected by the loss of an apex predator, and the way in which they are affected, is not always fixed. In a study conducted by Pujoni et al. (2016), they observed the effect of adding an intermediate predator to a classic tri-trophic system. The original three-level chain under observation was: planktivorous fish- caldocera (water flea)- algae. They noticed that the addition of a predator reversed the correlation between the apex predator (planktivorous fish) and the lowest trophic level (algae). Pujoni’s experimental four-level trophic model is as follows: planktivorous fish-Chaoborus (glassworm)-cladocera- algae. Where the original tri-trophic results would have expected the decline in fish density to lead to a decline in algae density, the results of Pujoni’s four-level study displayed that a decrease in planktivorous fish density would lead to an increase in algae. The loss of planktivorous fish released Chaoboridae from predation, therefore leading to a decrease in the cladocera population, hence leading to higher algae density. This particular study gives insight into the complexity and flexibility within ecosystems- especially when it comes to the disseminating effects of apex
The scientific community is increasing its studies dedicated to understanding the causes and effects of trophic cascades, due in part by human actions that are immensely decreasing the populations of apex predators worldwide. Since the mid-1900’s, numerous studies by well-known ecologists have displayed the effects of apex predators on smaller animal species, as well as plant communities. While there is sufficient evidence on the effects of apex predator removal on small ecosystem levels, the question remains as to the impact that will occur at a global scale. Due to obvious limitations on large-scale experiments, scientists are unsure just how profound the repercussions of apex predator decline may be for future