Shedding Light on Disappearing Turtle Populations

Turtles are an ancient group of animals that have remained relatively unchanged over a long evolutionary history that spans more than 200 million years. A recent review by Lovich et al. (2018) highlights the current global plight of turtles. Some 61% of the world’s turtle species are either threatened or already extinct, making turtles one of the most endangered groups of vertebrates on the planet. 

Turtles have experienced population declines and extinctions from many of the all too familiar factors that are assaulting wildlife populations across the globe. Habitat loss, degradation, and fragmentation are generally the primary drivers of species loss, but turtles are also threatened by other factors, including exploitation by humans (both for consumption and for the pet trade), climate change, and disease. Turtles are popular in the pet trade and as a source of food, and there are many recent examples of the illegal wildlife trade occurring here in the southeastern United States. 

The challenges of a modern world are placing significant strains on turtles’ ability to adapt to rapidly changing environments that are characteristic of the 21st century. In their review, Lovich et al. (2018) point out that turtle biomass (the total mass of organism in a given area) often rivals the biomass of other vertebrate groups. High biomass (and abundance in certain ecosystems) means that turtles can impact overall ecosystem function and provide services that other groups cannot. For example, turtles can be important drivers of nutrient cycling by being consumers (herbivores, carnivores, and omnivores), being prey items for other species, providing nutrients to nutrient-poor environments through egg deposition (e.g., sea turtles nesting on beaches), and storing minerals and nutrients in their shells and bones. 

An often underappreciated benefit that turtles provide is seed dispersal and improved germination rates, particularly on islands where large tortoises are often the dominant herbivores. In fact, the loss of tortoise populations has even been linked to the declines of native tree species (Iverson 1987). Without turtle populations, these and other ecosystem services would not exist.

The Gopher Tortoise (Gopherus polyphemus) is an excellent example of how a single turtle species can have a large impact on the ecosystems that they inhabit. Because of their propensity to dig burrows, Gopher Tortoises are classified as a keystone species and an ecosystem engineer. Gopher Tortoise burrows alter soil chemistry, water and gas diffusion, and increase plant diversity surrounding the burrow aprons. These burrow aprons (the area where a tortoise deposits sand from its burrow) create microhabitats that would not otherwise exist. 

Furthermore, well over 300 species have been documented using Gopher Tortoise burrows for some or all of their life histories. Many species form obligate relationships with the Gopher Tortoise, meaning that they are completely dependent on tortoises and the burrows that they create. By conserving Gopher Tortoise populations and improving habitat for this declining species, conservation efforts are benefiting numerous other species that would generally be overlooked for species-specific conservation initiatives.

As a group, turtles are in the midst of a global decline, and many of the species that we take for granted today will likely push closer to extinction in the coming years. As Lovich et al. (2018) point out, turtles are long-lived species and gauging turtle declines can often be difficult. Adult turtles may be observed for many years even if no successfully reproduction is occurring. 

Perilously small turtle populations have become the norm for many species, and their ecological roles are already diminished. For a group of reptiles that are more accepted and well-liked than either snakes, lizards, or crocodilians, it is a critical time for broad conservation efforts to ensure that this charismatic and ancient group of animals persists for many millennia to come.

Literature Cited

Iverson, J. B. 1987. Tortoises, not dodos, and the tambalacoque tree. Journal of Herpetology 21: 229–230.

Lovich, J. E., J. R. Ennen, M. Agha, and J. W. Gibbons. 2018. Where have all the turtles gone, and why does it matter? Bioscience 68:771–781.