Question

In an Australian grassland, dingoes and feral dogs regulate the population of red fox. Because dingoes and feral dogs killed sheep, Australian authorities began to remove dingoes and feral dogs. As a result you will expect population of the red fox to...…... (increase or decrease).

In this case, dingoes and feral dogs are ……...(mesopredators or top predators) and red fox is...…….. (mesopredators or top predators).

It turned out red fox also killed sheep and caused the decrease in sheep populations and the extinction of other herbivores in the community. Such scenario can be explained by...……. (two words) hypothesis, which often leads to ………. (positive or negative), ……….. (top-down or bottom-up) effects on prey species and community structure.

Answer 1

In an Australian grassland, dingoes and feral dogs regulate the population of red fox. Because dingoes and feral dogs killed sheep, Australian authorities began to remove dingoes and feral dogs. As a result you will expect population of the red fox to increase.

(Dingoes and feral dogs regulate the population of red fox directly by actually chasing foxes and killing them, and indirectly by instilling fear in them which leads to foxes actively avoiding areas where dingoes are present. This is an example where reducing predators from the food web lead to increase in prey population.)

In this case, dingoes and feral dogs are top predators and red fox is mesopredator.

(A mesopredator is a predator in the middle level or trophic of the food web whereas, a top predator is a predator at the highest level.)

It turned out red fox also killed sheep and caused the decrease in sheep populations and the extinction of other herbivores in the community. Such scenario can be explained by keystone species hypothesis, which often leads to negative top-down effects on prey species and community structure.

(Key stone hypothesis: An ecosystem may experience a serious change if an important or keystone species is removed, even if the species was a small part of the ecosystem with respect to its productivity or biomass. In other words, it is a non-abundant species that has an outsized impact on the ecosystem as a whole.

This is an example of a negative top down effect because reduction in top predator population adversely affected the diversity of the ecosystem.)