The description and number of undiscovered mammal species

Abstract

Global species counts are a key measure of biodiversity and associated metrics of conservation. It is both scientifically and practically important to know how many species exist, how many undescribed species remain, and where they are found. We modify a model for the number of undescribed species using species description data and incorporating taxonomic information. We assume a Poisson distribution for the number of species described in an interval and use maximum likelihood to estimate parameter values of an unknown intensity function. To test the model's performance, we performed a simulation study comparing our method to a previous model under conditions qualitatively similar to those related to mammal species description over the last two centuries. Because our model more accurately estimates the total number of species, we predict that 5% of mammals remain undescribed. We applied our model to determine the biogeographic realms which hold these undescribed species.

Keywords: biodiversity; conservation; taxonomic effort; total number of species; unknown species.

Figure 1

Map of Biogeographic Realms. Cooler (blue) colors represent regions with fewer undiscovered species, and warmer (red) colors represent regions with more undiscovered species

Figure 2

Taxonomic efficiency. Investigating the fit of the modeled efficiency function (red line) to the calculated efficiency for mammals (black dots). The points which do not follow the modeled efficiency function from 1890 to 1915 result from the ratio of species to taxonomists in those years. As seen in Figure 4, the number of species exceeds the number of taxonomists in a different pattern than expected

Figure 3

Boxplots of simulation results, with the middle line showing the median. Simulated boxes are the number of species simulated to have been described. Gaussian boxes refer to the estimated total number of species using the Joppa et al. method. Poisson boxes refer to the estimated total number of species using our method. a–d refer to scenarios 1‐4, respectively. Dashed lines refer to the actual total number of species

Figure 4

Simulation study results. Panel (a) shows the model bias and total number of species averages from simulated data. Dashed line shows true value. Error bars show 95% confidence interval of the average distance from the true number of species. Panel (b) shows statistical coverages (percent of estimates including the true value) from simulated data

Figure 5

Mammal species discovered per 5‐year interval on a log scale. The dashed blue lines represent the confidence interval around the estimated number of species in each 5‐year interval (S _iest)