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A PRELIMINARY REPORT ON THE SEED DISPERSAL OF SCLEROCACTUS BREVIHAMATUS SPP. TOBUSCHII: AN ENDEMIC CACTUS
Author(s): M’Kayla G. Motley and Bonnie B. Amos
The Tobusch fishhook cactus (Sclerocactus brevihamatus spp. tobuschii) (TFC) is a small dome-shaped cactus found in Ash Juniper-Liveoak associations in nine counties in the Edwards Plateau, Texas. It is the earliest flowering member of its community with bright yellow-yellowish green flowers formed as early as January and continuing to April with fruits ripening early May to mid June. In 1979 US Fish and Wildlife Service listed TFC as endangered. Much is known about the taxon’s breeding system and pollination; however, little is known about its seed dispersal. Therefore, our objectives were to: define fruit/seed attractants and identify fruit visitors and their behavior for TFC populations at Kerr Wildlife Management Area in Kerr County, TX. Time-lapse cameras were used to obtain approximately 40,000 images and videos of TFC fruit development and visitation. The only fruit visitors observed, in images, videos or field observations, were two species of ants, the fire ant (Solenopsis invicta or a hybrid S. invicta X S. geminata) and a smaller ant, Forelius pruinosus. Neither visited the plants until the fruits opened but then swarmed the fruits (N=10) feeding on the juicy pulp and also harvesting pulp from the fruit. However, neither harvested seeds. Data analyses show that fruit visitation is short-lived with 1.5 to 3 days from first observation of ants to collapse and subsequent drying of the fruit. Seeds remain in the fruit and fall onto and around the plant. These observations differ from those of Emmett (1995) who reported the ant Forelius maccooki (=F. foetida) transported as much as 85% of TFC seeds back to the ant mound at three different sites. Studies in 2018 are planned to obtain additional visitor data, conduct exclusion experiments, and monitor sugar content in fruits. |
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