The monitoring of species’ geographic range is necessary to implement impactful conservation strategies. Understandably it is difficult to obtain detailed data on spatial locations of individuals and populations over their entire range. Moreover to study range dynamics, distributional data from different time periods is required. By integrating museum specimen collection records and citizen-science observations into a GIS platform, the capability of researchers to effectively analyze patterns of range characteristics as they change over time should be greatly enhanced. To test this, I used museum and citizen-science databases to observe the range dynamics of a species suspected to have experienced a significant range contraction in recent decades, the Texas horned lizard (Phrynosoma cornutum). I integrated the long-term spatial data from Vertnet.org and iNaturalist.org into ArcMap 10.6 and segregated observations into discrete time periods. For each time period, I generated a minimum convex polygon (MCP) to enclose all observations and then regarded the MCPs as proxies for the P. cornutum range during each time span. I calculated several metrics to characterize the size and location of the range in each time period and to test for (using ANOVA) any directionality component to the contraction. These metrics included mean distance from the historic center to the range edge and to observations which included observations internal to the edge.
Results/Conclusions
From the historic to the current time period, MCP area declined 10%; the eastern quadrant’s area declined by 35%. The eastern quadrant was the only quadrant to experience a steady decline in mean edge distance and mean observation distance from the historic to the current time period. Although mean distance between historic center and observations differed among time periods for the other quadrants (all ANOVAs were statistically significant, P < 0.001), the change was not consistent over time. For mean distance to the range edge, only the eastern and southern quadrants had significant differences (P < 0.001) among time periods. The southern quadrant was characterized by low sample sizes and erratic patterns of change among time periods. Range edge in the northern and western quadrants remained stable over time. The use of citizen-science and museum records provides a level of data collection necessary for monitoring broad-scale range dynamics. MCPs and derived metrics provide a straightforward approach for monitoring range dynamics, though they may be prone to overestimate range size and may not be informative for irregularly-shaped distributions or for rare species.