Question

Northwestern Alaska is home to a variety of species. Some of these species and their interactions with one another are described here. Beavers (Castor canadensis, pictured on the left) eat willow shrubs; they also use willow as a source of material for building dams. Damming of waterways causes water to pool, which creates habitats that salmon use as spawning locations. Moose eat the same willow shrubs that beavers use to build their dams. The ptarmigan (pictured on the right) is a bird that relies on willow shrubs as protective cover; ptarmigan also eat parts of the willow shrubs. Finally, wolves prey on a variety of organisms in the community, including beaver, moose, and ptarmigen; in areas where wolves and beavers coexist, beavers can make up as much as 30% of a wolf’s diet. For wolves, one of the most common causes of death is starvation.

1. Use all the information provided to draw a community interaction model that represents the direct interaction between following species in northwest Alaska: beaver, willow shrub, salmon, moose, ptarmigan, wolf. Remember to illustrate the species in boxes and to mark direct interactions with +/-/0, based on their effects on relative fitness.

2. In northwestern Alaska, the beaver population has recently expanded its range and now occupies habitats where beavers were not found before. Use the community interaction model you created to make predictions about how an increase in the size of the beaver population will impact (either directly or indirectly) other species within the community.

a) The willow population is likely to  increase  decrease  not be affected Explain:

b) The ptarmingen population is likely to  increase  decrease  not be affected Explain:

c) The salmon population is likely to  increase  decrease  not be affected Explain:

Answer 1

1.Community interaction is shown in below:

2. a. The willow shrub population is likely to decrease

As beaver population feeds on willow population, increase in beaver population would result in more consumption of willow shrubs and hence the population of willow shrubs will decrease.

b. The ptarmingen population is likely to decrease

As both beaver population and ptarmingen population feed on same willow shrub, increase in beaver population cause a decline in food supply for ptarmingen population and this indirectly affect ptarmingen population.

c. The salmon population is likely to increase

As increase in Beaver population will result in more damming and the salmon will get more place for spawning and thus their population will increase.