Question

You can estimate quantitative data (fairly precisely) from a graph. The first step is to obtain a conversion factor by measuring along an axis that has a scale. In this case, 25 million years (my; from 60 to 35 million years ago (mya) on the x-axis) is represented by a distance of 7.0 cm. This yields a conversion factor (a ratio) of 25 my/7.0 cm = 3.6 my/cm. To estimate the time period represented by a horizontal bar on this graph, measure the length of that bar in centimeters and multiply that measurement by the conversion factor, 3.6 my/cm. For example, a bar that measures 1.1 cm on the graph represents a persistence time of 1.1 cm * 3.6 my/cm = 4 million years.

Short answer

Snails are molluscans and possess both planktonic and non-planktonic larvae. These larvae show a broad distribution and are studied by many researchers to examine the mode of dispersal. The larvae of snails are isolated from each other. Fossil records are reviewed to explore more about the distribution of larvae.

Step-by-step solution

Snails

Snails are molluscans and possess both planktonic and non-planktonic larvae. These larvae show a broad distribution and are studied by many researchers to examine the mode of dispersal. The larvae of snails are isolated from each other. Fossil records are reviewed to explore more about the distribution of larvae.

Persistence time of the species

The number of planktonic larvae was 13, and the number of non-planktonic larvae was 29. For calculating the persistence time of species, the length of the bar is multiplied with the conversion factor of 3.6 my/cm. The formula which represents the calculation is

\({\bf{Persistent}}{\rm{ }}{\bf{time}}{\rm{ }}{\bf{of}}{\rm{ }}{\bf{the}}{\rm{ }}{\bf{species}} = {\bf{length}}{\rm{ }}{\bf{of}}{\rm{ }}{\bf{the}}{\rm{ }}{\bf{bar}}{\rm{ }} \times {\rm{ }}{\bf{conversion}}{\rm{ }}{\bf{factor}}{\rm{ }}\left( {{\bf{3}}.{\bf{6}}{\rm{ }}{\bf{my}}/{\bf{cm}}} \right)\)

Result of time period representation

The persistent time obtained by measuring the length of the bar and multiplying it with the conversion factor indicates the position of species in the graph that is left to the right. In other words,it suggests the resistance time of the species moving from left to right in the graph.

Therefore, the average bar length of the planktonic larva is 1.29 cm/bar, and the average length of non-planktonic species is 0.47 cm/bar.