Lecture 18 indirect effects

Question 1

Direct vs indirect effects

Answer 1

Direct: predators directly effect prey populations by consuming individuals

Indirect; and example of an indirect effect is exploitive competition. Where red squirrels and red crossbills negatively effect each other’s populations by competing for the same resource (pinecones in this case)

Question 2

Types of indirect effects 2

Answer 2

Indirect effects can be either:

Density mediated: where the predator reduces prey numbers

Trait mediated : where the predator effects the preys phenotype to reduce its risk of predation

Question 3

Yellowstone wolves

Answer 3

There were very little willow trees in Yellowstone with the absence of wolves. When the wolves were once again a part of the ecosystem they lowered the elk population(direct) as well as altering their behaviour as the elk had took spend more time avoiding predation and less on foraging (indirect). This lead to a sharp increase in the Willow tree population

Question 4

How the lemming population effects the boreal region

Answer 4

Lemmings live i the bottom of the snow pack in the\ subnivian zone. With the arctic getting warmer subnivian zone has a lower density depth and quality. When the snow melts, lemmings are exposed earlier leading to a decline in their population. This causes multiple populations of species to be effected as the predators who rely on lemmings will either have to find a new food source (indirectly effecting the new food) or starve (directly effecting predators)

Question 5

The green world hypothesis

Answer 5

By controlling herbivores, predators allow plant species to thrive

Question 6

Roles of foxes in the arctic food web (2)

Answer 6

*predation pressure on birds and rodents

*redistribute nutrients as ecosystem engineers which helps the lemming population, increasing plant productivity and diversity and therefore effecting other consumers