A function for the Portal data set

1. If surveys.csv, species.csv, and plots.csv are not available in your workspace download them, and load them into R using read.csv().
2. Combine the surveys and species tables into a single data frame.
3. Write a function that:
   • Takes three arguments - a data frame (the combined table created before), a genus name, and a species name,
   • Uses functions from the dplyr package to produce a data frame with two columns: year and count, where count is the number of individuals (i.e., the number of rows) for the species indicated by genus and species in that year,
   • Returns the resulting data frame. Note that this data frame is a time series by year.
4. Use your function to get the data frame of time series by year for the genus Dipodomys and the species merriami and then make a graph of this time series using ggplot that has year on the x axis, count on the y axis, and displays the data as points.
5. Use your function to get the data frame time series by year for the genus Chaetodipus and species penicillatus and then make a graph of this time-series using ggplot that has year on the x axis, count on the y axis, and displays the data as blue points (with size = 1) connected by blue lines (with size = 2). Change the x axis label to Year and the y axis label to Number of Individuals.