title: Best function for modelling diminishing returns
body: <p>I am visiting a bird sanctuary that has many different species of birds. Some species are more numerous while other species are less numerous. I came back to the sanctuary 9 times and after every visit I am calculating the total number of species I observed. Unsurprisingly, there is a diminishing return in my visits, since I observe the most numerous species on my every visit, but it does not increase the count of observed species. What is the best function in R to predict how many birds I will observe on my 20th visit? </p>
  
  <p>Here is the data.frame </p>
  
  <pre><code>d &lt;- structure(list(visit = 1:9, 
                      totalNumSpeciesObserved = c(200.903, 296.329, 370.018, 431.59, 485.14, 533.233, 576.595, 616.536, 654)), 
                      class = "data.frame", row.names = c(NA, 9L))
  </code></pre>
  
  <p>I expect to see a model that fits data well and behaves in a "log-like" fashion, predicting diminishing returns</p>