Assignment #2

What is a tropic cascade?

A Trophic Cascade is when the impact of a predator on its prey's ecology trickles down one more feeding level to affect the density and/or behavior of the prey's prey

What is the difference between the bottom-up and top-down paradigms for regulating the primary productivity of ecosystems?

A top-down cascade is a trophic cascade where the food chain or food web is disrupted by the removal of a top predator, or a third or fourth level consumer. On the other hand, a bottom-up cascade occurs when a primary producer, or primary consumer is removed, and there is a reduction of population size through the community.

What arguments did Hairston and colleagues put forth in 1960 that challenged the bottom-up paradigm and supported the top-down paradigm?

Hairston and Colleagues came up with the view that consumers play an important role in structuring plant-dominated ecosystems. They argued that the world is/was green because higher Trophic Levels control herbivore abundance. This challenged the bottom up paradigm and supported the top-down paradigm because the top down cascade paradigm states that the food web is distributed by the removal of a top predator, hence exemplifying how crucial predators are to the ecosystem. This theory challenged the bottom up paradigm because this paradigm states that the removal of consumers will negatively affect an ecosystem where as Hairston and colleagues beliefs state that the predator is only necessary to keep an ecoystem in check

Add. Help #3

Hairston, Smith and Slobodkin argued that predators reduce the abundance of herbivores, allowing plants to flourish. This is often referred to as the green world hypothesis.

Add. Help #2

Hairston, Smith and Slobodkin argued that the ecological communities acted as food chains with three trophic levels.

Why is over consumption of producers by primary consumers considered an issue for conservation and management of species?

Over consumption of producers by primary consumers is considered an issue for conservation and management of other species because primary consumers make their own food and transfer energy to/through the different consumers. If there is not enough of them, animals higher up in the Trophic Levels will not get enough food, also meaning they will not get enough energy. And in the scenario that primary consumers do find a way to make primary producers extinct, they will then run out of food and begin to die, leaving the secondary and tertiary consumers to soon perish in numbers as well.

What are the differences between population-level and community-level trophic cascades?

Population-level Trophic Cascades are when the reduction of the number of predators results in overgrazing and local extinction of a dominant plant species, however, a "less pleasing" species replaces the first dominant specie. This keeps the ecosystem intact, despite of the shift. In a Community-level Trophic Cascade, the reduction of the number of predators results in overgrazing of the entire plant community, including the loss of the associated eycosystem services.

Strong 1992 proposed that trophic cascades were likely to be more predominant ecosystems with certain characteristics. What are these characteristics and why are they important?

Strong 1992 believed that Trophic Cascades were more likely to be found in aquatic ecosystems with few predators, that are not protected from the "run-away" consumer effects, to defend the primary producers. These characteristics are important because with weak predators....

What Conservation implications are associated with Trophic Cascades?

Temperate and tropical forests, kelp beds, grasslands, and salt marsh communities, have long been viewed as classic examples of bottom-up regulated systems dominated by relatively unpalatable plants controlled by physical conditions and nutrients. Accordingly, the conservation of these and other plants systems have generally neglected top-down effects in management and conservation efforts for over half of a century. Results from the studies described above call into question the dominance of the bottom-up only paradigm and its wide-scale application to conservation and restoration of plant ecosystems. Managers and ecologists will need to reevaluate their understanding of controls on plant communities and incorporate top-down effects into their conservation plans. Failure to identify and integrate top-down forces may lead to trophic cascades transforming highly diverse and productive plant communities to barren or almost barren flats, with concomitant loss of associated biodiversity and ecosystem function.

What is the minimal number of trophic levels that must be involved in a trophic cascade? Use scientific names to describe each tropic level (e.g., tertiary consumer).

The minimum of trophic levels that must be involved in a Trophic Cascade is 3. It involves the Primary Producer, Primary Consumer, and Secondary Consumer.

Add. Help #1

Trophic cascades occur when predators in a food web suppress the abundance or alter the behavior of their prey, thereby releasing the next lower trophic level from predation (or herbivory if the intermediate trophic level is a herbivore)

Describe 1 of the 4 examples of Trophic Cascades in Ecosystems that are described in the article. Focus on why the particular example you choose to discuss supports the top down paradigm for primary productivity of ecosystems.

Tropical Rainforest