Known numbers of seeds from two species ( and
) of annual plants are mixed together in different proportions and planted in five small plots of soil in the spring. The plants grow, flower, and produce seeds. It is found that the percentage of seeds of species
and species
in the harvest is usually different from the proportion that was planted, although the total number of seeds produced is the same as the number of seeds planted. The data are plotted on the graph below.
What do the data indicate about the ecological relationship between species and species
?
Select an Answer
and
are mutualistic for low percentages of
seeds.
and
are mutualistic for high percentages of
seeds.
and
compete when both
and
seeds are present.
competes successfully against
at all percentages of
and
seeds.
is a parasite of
when
is rare.
View Correct Answer
The graph shows that the survival of either of the two species depends on the relative abundance of each species at the time of seed planting. In a mutualistic relationship both species benefit, but the data do not show that this is true at either low or high percentages of species X, ruling out choices (A) and (B). Species Y does not compete successfully against species X in all mixtures, ruling out choice (D). There is no evidence for parasitism, ruling out choice (E). Competition occurs in all seed mixtures and species X is a stronger competitor in most of the seed mixtures.