Question

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Name: 18. In the northern Pacific Ocean sea otters feed on sea urchins and on starfish. sea urchins Teed on kelp and starfish feed on mussels. Beginning in the 1700s, sea otters were hunted for theirfur and driven nearly to extinction in some areas, resulting in trophic cascades in their communities. When the fur trade ended, sea otter numbers increased and their communities began to recover. One would expect that this recovery would result in an increase in numbers and a decrease in numbers of a) kelp and mussels; sea urchins and starfish b) sea urchins and kelp; starfish and mussels c) sea urchins and starfish; kelp and mussels d) starfish and mussels; sea urchins and kelp e) sea urchins and mussels; starfish and kelp 19. A new community is forming in a region devastated by a multi-year drought. Rain has recently returned to the area; in some cases, the rain has been severe enough to cause flooding and rapid runoff. Seeds of many plant species enter from the surrounding region and begin to grow. However, periodic storms erode the soil, and many species have difficulty becoming established. Based on this series of events, which factor is likely the most important in determining membership in the new community? a) Species supply b) Environmental conditions c) Species interactions d) Invasions by outside species e) Herbivores eating the seeds 20. Which of the following statements about succession is false? a) Facilitation plays an important role in succession. b) Inhibition plays an important role in succession c) Primary succession begins from a bare substratum. d) Food webs increase in complexity during succession. e) As succession progresses, competitively superior K-strategy plants are replaced by competitively inferior r-strategy plants. 21. When Mount St. Helens erupted, three relatively distinct zones of destruction resulted: (1) the Pumice Plain, which was essentially sterilized and had no remaining life; (2) the Blowdown Zone on the mountain slopes, where downed trees and vegetation were covered with mud and ash; and (3) farther down, forests that remained standing but were also covered with mud and ash. Based on these levels of destruction, what would the rate of recovery be for these zones? a) All would recover quickly, at relatively equal rates. b) None would recover; the heat, mud, and ash would prevent regrowth. c) Pumice Plain would recover fastest, followed by Blowdown Zone, then the lower forests. d) Lower forests would recover fastest, followed by Blowdown Zone, then Pumice Plain. e) Blowdown Zone and lower forests would recover relatively quickly; the Pumice Plain would never recover.

Answer 1

18. a) kelp and mussels; sea urchins and star fish

As the population of sea otters increases, they feed on sea urchins and starfish which eventually results in decrease of kelp and mussels population.

19. b) Environmental condition

This is because, it is due to rain and strom the species of the region get washed off

20. e) K strategy plants are replaced by R strategy plants

K strategy plants are slow growing and less in population at the begining but have better longivity. On the other hand, the R strategy plants are fast growing with less life span. Thus, in the event of time, the R strategy plants are replaced by K strategy plants.

21. d) Lower forests would recover faster, followed by Blowdown zone, then Pumice Plain

Though there is complete sterilization of species from Pumice Plain, due to primary succession, there is a chance of recovery of vegetation.