Use the Following Information to Answer the Question

question 64

Multiple Choice

Use the following information to answer the question.
Canadian and Swiss researchers wanted to know if the diversity of arbuscular mycorrhizal fungi (AMF) was important to the productivity of grasslands (M.G.A. van der Heijden, J. N. Klironomos, M. Ursic, P. Moutoglis, R. Streitwolf-Engel, T. Boler, A. Wiemken, and I. R. Sanders. 1998. Mycorrhizal fungal diversity determines plant biodiversity, ecosystem variability, and productivity. Nature 396:69-72) . Specifically, they wanted to know if it mattered which specific AMF species were present, or just that some type of AMF was present. They grew various plants in combination with one of four AMF species (A, B, C, and D) , no AMF species (O) , or all four AMF species together (A + B + C + D) ; and they measured plant growth under each set of conditions. All plant species were grown in each plot, so they always competed with each other with the only difference being which AMF species were present.
On the graphs, the x-axis labels indicate the number and identity of AMF species (bar 0 = no fungi; bars A - D = individual AMF species; bar A + B + C + D = all AMF species together) . The y-axis indicates the amount (grams) of plant biomass for the species shown in italics above each graph. Graph e is the total biomass (grams) of all 11 plant species combined; graph f is the biomass of Bromus erectus plants only, separated from the total.

What is the most likely explanation for the observation that total biomass (graph e) does not vary with AMF diversity?

• A) Plant growth is unaffected by fungal diversity.
• B) Most of the plants in this system do not form mycorrhizal associations
• C) Bromus erectus is the dominant plant species.
• D) Lotus corniculatus is a rare species.

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Definitions:

Founder Effect

A genetic phenomenon that occurs when a new population is established by a very small number of individuals, leading to a reduction in genetic variation.

Genetic Flow

The transfer of genetic material between populations of the same species or between different species, leading to changes in genetic makeup.

Genetic Drift

A mechanism of evolution involving random fluctuations in the frequency of alleles within a population, which can cause genetic variation to decrease over time.

Bottleneck

A sudden decrease in a population size caused by adverse environmental factors; may result in genetic drift; also called genetic bottleneck or population bottleneck.