Question

the introduction of the emerald ash borer, an invasive beetle, into north american forests: the beetle exclusively feeds on and kills ash trees.
year ash tree population (per hectare) red oak population (per hectare) bird species diversity (shannon index)
2005 125 85 1.85
2010 10 120 1.50
2015 1 145 1.12
2020 0 155 1.05
the table above shows population data for a forest ecosystem from 2005 to 2020, following the arrival of the emerald ash borer. ash trees were a primary food source for many native insects, and their seeds were a key food source for small mammals. a student makes the claim that the introduction of the emerald ash borer has caused the forest to shift to a less stable ecosystem. which of the following pieces of evidence provides the most effective reasoning for this claim?
a the red oak population increased, which proves that the ecosystem is resilient and will not change significantly.
b the decline of the ash tree population directly caused a decrease in overall bird species diversity, disrupting the ecosystems complex food web interactions.
c the emerald ash borer population eventually crashed once all the ash trees were gone, which shows the ecosystem is self - regulating.
d the invasive species changed the species composition of the forest, which is the only factor required for an ecosystem to be considered unstable.

Explanation:

A stable ecosystem has balanced food - web interactions and high species diversity. The decline of ash trees, a key species, led to a decrease in bird species diversity, disrupting the food - web. Option A suggests resilience, not instability. Option C shows self - regulation, not instability. Option D is incorrect as species composition change alone is not the only factor for instability.

Answer:

B. The decline of the ash tree population directly caused a decrease in overall bird species diversity, disrupting the ecosystem's complex food web interactions.