Gopher tortoise burrow fly by Amanda Hipps.
Gopher tortoise commensal species are wildlife species which benefit from tortoise burrows. Tortoise burrows provide shelter with a relatively constant temperature year-round and offer protection from fire and extreme weather. More than 350 species benefit from gopher tortoise burrows. Over 300 of these are invertebrates including moths, beetles, crickets, flies, snails, isopods, centipedes, millipedes, spiders, ticks, wasps, and ants.
Behavior
Little gopher tortoise scarab beetle by Amanda Hipps
Invertebrate commensals are characterized by how they interact with gopher tortoises and their burrows. Some commensal species -- termed 'obligate' --fully depend on the tortoise and burrow for survival. Others, called 'facultative', only occasionally make use of the burrows as a convenience.
Some invertebrate species have a mutualistic relationship with tortoises, meaning both gopher tortoises and invertebrate commensals benefit from their interactions. Mutualist commensal species provide pest fly and dung removal services near or within the burrow. Pest flies and dung that are not removed can have negative impacts on the gopher tortoise. The gopher tortoise burrow fly, the gopher tortoise acrolophus moth and the gopher tortoise copris beetle are a few examples of obligate commensal species that feed on tortoise dung, reducing tortoise parasites. The gopher tortoise robber fly and gopher tortoise hister beetle feed on pest flies and fly larvae.
Though not a burrow commensal, at least one invertebrate depends on dead gopher tortoises. The larvae of the gopher tortoise shell moth live exclusively on decomposing tortoise shells and feed on the shell’s keratin.
Invertebrate commensals, like the camel or gopher cricket and tortoise burrow fly, can also act as a food source for vertebrate burrow commensal species including the gopher frog.
Habitat
Invertebrate commensal species are found in the same habitats as gopher tortoises, including upland natural communities like sandhill and scrub. However, the distribution of gopher tortoise invertebrate commensals varies across Florida. Some obligate commensals do not occur in all known gopher tortoise-occupied areas. For more information about obligate commensals, including current species distribution maps, visit the FWC’s gopher tortoise obligate invertebrate commensal page.
Threats
Gopher tortoise copris beetle by Amanda Hipps.
Healthy and widespread gopher tortoise populations are necessary for obligate invertebrate commensal populations to exist. Even smaller gopher tortoise populations are important in providing stepping-stones for some obligate commensal invertebrate populations. The loss of gopher tortoise burrows and suitable upland habitat threatens commensal populations alongside gopher tortoises themselves. The primary threats to gopher tortoises in Florida are habitat destruction, fragmentation and degradation from incompatible land use. Gopher tortoise populations are also threatened by a lack of prescribed fire and/or suppression of natural fires. Fire suppression can lead to an overgrowth of tree cover, which reduces sunlight needed to grow the plants tortoises feed on.
Conservation and Management
Gopher tortoise robber fly by Jonathan Mays.
The biodiversity of commensal species in Florida is connected directly with the conservation of the gopher tortoise. The Gopher Tortoise Management Plan highlights actions geared towards maintaining the gopher tortoise’s function as a keystone species and actions that aid the conservation and management of invertebrate commensal species.
Current knowledge about invertebrate gopher tortoise commensals is limited. More information about the biology, distribution, status and behaviors of obligate invertebrate commensals is needed to conserve and manage these species.
References
Almquist D. 2016. Filling in the Data Gaps for Obligate Invertebrate Commensals of the Gopher Tortoise. Florida Fish and Wildlife Conservation Commission. Final Report: Project 14040.