Recolonization of Mount St. Helens Mount St. Helens is an active volcano located
ID: 268050 • Letter: R
Question
Recolonization of Mount St. Helens Mount St. Helens is an active volcano located in the Cascade Range in southern Washington, USA. In the morning of May 18 in 1980, the volcando experienced an earthquake which triggered a massive eruption. The eruption was the deadliest and most destructive volcanic event in the history of the USA with magma and debris from the volcano covering vegetation, roads and building within an area of over 600km2 For ecologists, St. Helens presented a unique opportunity to study animal and plant re-colonization of areas affected by the eruption. Ecologists have studied the population dynamics of snowshoe hares in the area around Mount St. Helens for several decades. Hares did not survive in the area most heavily disturbed by the eruption, but they returned after a few years. The graph below shows how the growth rate (i.e. r= birth rate death rate) varied with population density. What is the carrying capacity K of the snowshoe hare population?Explanation / Answer
Carrying capacity is the maximum number of individuals that can be sustained indefinitely by an area’s resources without significant depletion of those resources. The symbol for carrying capacity K and N= growth rate.
When there are very few individuals in a population, N < K. Hence, the growth rate is close to r, which is the intrinsic rate of growth. The growth rate will decrease as population density increases.
When the population density is equal to carrying capacity, the growth rate will be equal to zero. The population will now reach and equilibrium. When N>K, the growth rate will become negative.
In the graph of snowshoe hares, the growth rate is zero at a population of 100 individuals/km2. Hence, the carrying capacity for this population is 100 individuals/Km2, where the line merges with the x-axis.
Right option is 100 individuals/Km2
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