Sum of fears among intraguild predators drives the survival of green sea turtle ( Chelonia mydas ) eggs

Abstract

Ecologists have long theorized that apex predators stabilize trophic systems by exerting a net protective effect on the basal resource of a food web. Although experimental and observational studies have borne this out, it is not always clear what behavioural mechanisms among the trophically connected species are responsible for this stability. Fear of intraguild predation is commonly identified as one such mechanism in models and mesocosm studies, but empirical evidence in natural systems remains limited, as the complexity of many trophic systems renders detailed behavioural studies of species interactions challenging. Here, we combine long-term field observations of a trophic system in nature with experimental behavioural studies of how all the species in this system interact, in both pairs and groups. The results demonstrate how an abundant, sessile and palatable prey item (sea turtle eggs, Chelonia mydas ) survives when faced by three potential predators that all readily eat eggs: an apex predator (the stink ratsnake, Elaphe carinata ) and two mesopredators (the brown rat, Rattus norvegicus , and kukri snake, Oligodon formosanus ). Our results detail how fear of intraguild predation, conspecific cannibalism, habitat structure and territorial behaviour among these species interact in a complex fashion that results in high egg survival.

Loss of sea turtle eggs drives the collapse of an insular reptile community

“…Although these findings represent compelling evidence for the loss of sea turtle eggs causing a shift in snake predatory behavior that subsequently drove steep declines in populations of lizards, the data are correlational, and a variety of other factors could also result in the patterns we documented. This region is susceptible to increasing human development ( 24 ), more frequent and intense storms driven by climate change ( 25 ), rising sea levels ( 26 ), and invasive species such as rats ( 27 ), and more intensive monitoring or more empirical studies would be needed to definitively demonstrate a causal relationship between kukri snake egg predation and lizard population declines. Nevertheless, the fact that populations of these lizards that occur in nearby areas that lack large kukri snake populations were stable across this same time frame ( Fig.…”

“…Most sea turtle conservation studies use predator exclusion to reduce predation pressure from invasive species such as foxes, dogs, or rats ( 20 ), but there is currently no evidence of invasive species consuming sea turtle eggs on Orchid Island ( 27 ). We suggest that not excluding kukri snakes from the nesting beach, while also implementing long-term population monitoring for all species, could provide more balance between conserving sea turtles and protecting the local reptile community.…”

“…The impact of kukri snakes on sea turtle populations is likely to be minimal. Kukri snakes territorially exclude each other from sea turtle nests, and a single snake can consume only a small number of the dozens of eggs present in a nest before they hatch ( 27 ). In addition, sea turtles exhibit classic “type III” survivorship, with extremely high mortality of eggs and hatchlings, and past studies have shown that conservation efforts targeting adults are more effective than those protecting eggs ( 39 ).…”