(ii) Describe TWO possible reasons why the plant chosen in (i) may have been
more successful. (2 points) Two different species of plants were grown in the
same medium. Nutrient requirements may have been different between the
two species. For example, the amount and ratios of minerals contained in the
potting soil may have met the metabolic requirements of the radish plants
more than the wheat seedlings. Water and light availability (either too much
or too little) may also have affected the outcome. Differences in growth
patterns (radish may sprout earlier than wheat) may have existed. In this case,
the radish seedlings may have sprouted earlier and established a population
that was taking up a fixed amount of nutrients at a faster rate or had
established a canopy that decreased the light available for the wheat
seedlings. Simultaneous to the interspecific competition was intraspecific
competition. Not only were radish seedlings in competition with wheat
seedlings, but they were also in competition with other radish seedlings for
limited nutrients.
(iii) Discuss the results obtained from the class for Part II in terms of two
biological laws or principles. (2 points) In Part II, plant density was held
constant in a substitutive or replacement experimental design in which the
total density of both species was kept constant while the relative densities
were varied (1, 10, and 20). This approach allows for the investigation of the
effects of interspecific competition from the effects of increasing overall
plant density on growth or production of a species. However, it requires first
quantifying the background effect of intraspecific competition on the growth
of each species individually. Such an experiment has three possible outcomes.
First, one species prospers at the expense of the other (competitive
exclusion). Second, one species outperforms the other but only when in
higher proportion (coexistence). Third, the two species have no measurable
effect on each other (no competition). The latter would be the null hypothesis