Detailed explanation would be appreciated. 2. What type of interspecific interac

Question

Detailed explanation would be appreciated.

2. What type of interspecific interaction would you hypothesize could account for the difference between the number of fir seedlings in the aspen stage and in the meadow stage
in Figure A? What type of interspecific interaction might explain the difference between the number of aspen suckers in the mixed and the fir stages?

We learned in Concept 17.3 that successional patterns are often the result of complex species interactions. Such inter- actions are exemplified in a study investigating the patterns of succession in mountain forests in Utah dominated by quaking aspen (Populus tremuloides) and subalpine fir (Abies lasiocarpa) (Calder and St. Clair 2012).* In some cases, aspen can form stable and self-sustaining populations, but more commonly these trees occur in mixed stands with firs. Observations show that aspen initiate the earliest stage of secondary suc- cession in open meadows created by fire or deforestation, using root suckers (underground shoots that produce clonal plants; see Figure 9.5) to colonize open meadows. Over time, mixed aspen-fir stands are formed as the shade-tolerant firs become established and increase in abundance while aspen decline. The stands are eventually dominated by firs, which are more susceptible to fire than pure stands ofaspen, thus increasing the chance of starting the successional cycle anew. Figure A Aspen suckers Fir seedlings 1.4 1.2 1.0 2 0.8 0.6 0.4 0.2 Meadow As Mixed aspen-fir Fir Successional stage Figure B 80 Aspen>0.5 m from fir Aspen 0.5 m from aspen Fir

Explanation / Answer

1. From the graph A it can be seen that in the meadow stage the population of both Aspen sucker and Fir seedling is very low, while at the aspen stage the density has drastically increased for both the population.It shows that there is a mutualism in the species which enhance or motivate the growth of each other. Since the Aspen were the first to undergo succession, they appear first in meadow stage, but later in the mutualism relation with each other both the species grew significantly.

2. In figure B it is shown that the Aspen that are less distant from the FIR grow very significantly at a higher rate in FIR stage as compared to the mixed aspen Fir stage. It means there is commensalism where one species is benefitted while the other remains unaffected. Since the FIR are more prone to fire or deforestation therefore helps to protect the aspen sucker. In this way it can be said that the aspen that are more closer to the fir will be protected and increased in the density will be seen.

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