PS 43-86 - Sources and sinks in an urban turtle metapopulation

Background/Question/Methods

Metapopulation theory applies to habitats that occur in discrete patches, can be recolonized, and contain local breeding populations that are at risk of extirpation. Long-term studies of turtle populations that live in ponds or wetlands often fit this model, with turtles moving among ponds and recolonizing ponds or wetlands after drying events. However, few studies have examined turtle metapopulation dynamics in urban environments. Urban areas may present challenges to movement and recolonization that are generally not encountered in more natural habitats.

We have been studying turtle populations in nine ponds on the campus of Missouri Western State University (MWSU) in St. Joseph, MO, since 2008. Using baited hoop nets, we captured turtles in all ponds, measured them and gave them unique, permanent marks. Over this period three ponds have either dried naturally or were drained. Our goal for this portion of the long-term study was to focus on the three campus ponds that have dried at least once since 2008, and to determine how these ponds have been recolonized by turtles originally marked in these ponds as well as other ponds. Specifically, we wanted to determine which ponds served as sources and which were sinks.

Results/Conclusions

With over 700 captures of three species (Chelydra serpentina, Chrysemys picta bellii, and Trachemys scripta elegans), we documented that 18% of turtles moved between ponds over distances of 115-875 m. In the three ponds that dried, 27 turtles were marked before pond drying with seven (26%) returning to the same pond. Twenty-six turtles originally marked in other campus ponds moved into these three ponds after they refilled. Pond 4, which has the largest population of turtles and never dries, was a source population for other ponds. Pond 5 seemed to be a sink, drying in seven of the last 13 years, with 49% of the turtles never returning. Eight of the nine turtles that colonized this pond after drying events were from Pond 4. However, summary data can mask the difficulties, complexity and time scale of these movement patterns. For example, it took one snapping turtle 12 years to return to a pond. Turtles move in and out of permanent ponds as well as ponds that dried, often crossing roads and maneuvering around parking lots and buildings. The results of this long-term study are important in the context of documenting metapopulation dynamics of aquatic species in an urban environment.