On the extinction (and survival) of Caribbean mammals

A new meta-analysis clarifies Caribbean extinction timing across the past 15,000 years -- and illuminates the consequences for conservation today .

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Downed power lines, flooded streets, wind-swept palm trees -- a view from the Caribbean in the aftermath of Hurricanes Irma and Maria yields images of sheer devastation. These disastrous events remind us that tropical islands aren’t always serene beaches and striking sunsets, but they instead exist in the context of a rapidly changing world. Their small size and isolation from the mainland can make them and their inhabitants - both human and animal - exceedingly vulnerable to the forces of disturbance.

Digging deeper, the fossil record tells us that the Caribbean has been a dynamic site of natural and human change for thousands of years. Lessons from this not-so-distant past may help us understand the role of islands as biodiversity reservoirs as we move into an increasingly turbulent future. 

The islands of the Caribbean provide the world’s largest laboratory of extinction. Although current estimates place Madagascar as the greatest single concentration of threatened mammals today, more mammals went extinct in the Caribbean over the last 20,000 years than anywhere else on Earth. Extinction has so dramatically transformed these islands that an entire lost world of monkeys, ground sloths, large and small rodents, and insectivores is today unknown to most – even the people who live there (Figure 1). Thanks to more than a century’s worth of paleontological collections, both the stunning richness and diverse features of these mammals are better understood today than ever before. These collections show the swift demise of many species, in turn inspiring an enduring question: why did species as different from each other as the Cuban vampire bat or the massive 150-kilogram Megalocnus ground sloth vanish in the geological equivalent of the blink of an eye? Answering this question requires first determining when these mammals went extinct.

Figure 1. The lost world of Caribbean mammal diversity -- a forest in Dominican Republic circa 10,000 years ago, before the arrival of humans and after the Younger Dryas’ climatic changes (left, illustration by D. Rini). Monkeys and ground sloths are absent from Dominican forests today, with native solenodons and hutias becoming increasingly rare in the face of subsistence agriculture and charcoal production (right, photo of Las Mercedes by A. Mychajliw).

Solving the puzzle of mammal extinctions requires putting all the pieces of the board: dates observed for both humans and now-extinct species. Radiocarbon dates are the currency of extinction studies, allowing us to line up the last appearance date (LAD) of mammals and first appearance date (FAD) of people with other causes of extinction, such as natural changes in the environment, or the arrival of non-native species. But studies focused on human culture and actions, and work on the demise of this fauna, make up a vast literature scattered across dozens of journals and books. We assembled the most comprehensive radiocarbon dataset of Caribbean mammals to date, with dates representing 57 extinction/extirpation events for native species (Cooke et al 2017). Because the Caribbean fossil record has traditionally been understudied, fewer than half of all species have one direct or indirect radiocarbon date available. To accommodate this uncertainty, we created models of the temporal overlap between people and mammals, and controlled for the different ways the dates were compiled, as well as the specific islands where the remains were found. This meta-analysis allowed us to evaluate whether humans could have interacted with Caribbean mammals and therefore lead to their disappearance.

Figure 2. The ground sloth Parocnus serus, a prehistoric victim: artist reconstruction (left, by D. Rini) and a Holocene fossil skull from the Dominican Republic (right, scale bar 1 cm, by S. Cooke). The extinction of the Caribbean’s only ‘true’ megafauna (an animal weighing >44 kg) occurred in the Mid Holocene, following human arrival - though no direct archaeological evidence of sloth-human interactions has been found so far.

Such approaches aligning radiocarbon dates have been widely used in the study of Quaternary extinctions, and are a critical line of evidence in the debate over whether humans or the end of the glaciation led to the extinction of the North American Pleistocene megafauna, including mammoths, dire wolves, giant ground sloths, and saber-tooth cats. The Caribbean record is distinctive, however, because most of its native mammal lineages persisted into the Holocene – thereby surpassing the deglaciation of the Pleistocene-Holocene transition and, in many cases, Younger Dryas (11,000 years ago). On the other hand, people arrived in the Caribbean more than 5,000 years later than they did in South America, settling in the earliest sites on Cuba and Hispaniola ~7-6,000 years ago. Our meta-analysis revealed an early pulse of LADs on the larger islands at about 5,000 years ago, consistent with overlap and extinction following the arrival of ‘Archaic’ humans in the Caribbean. Similar to continental extinctions in the Pleistocene, these losses were size-biased and targeted the endemic genera of ground sloths found in Cuba, Hispaniola, and Puerto Rico (Figure 2). This meta-analysis result is secured by direct radiocarbon dates from Cuban and Hispaniolan ground sloth bones by Steadman et al. (2005) and MacPhee et al. (2007). The first Caribbean people likely came from Central or South America, and supplemental evidence of lithic objects and charcoal patterns suggest that hunting and landscape change may have dealt the blows that wiped out Caribbean sloths.

Figure 3. A historic victim: reconstruction of Nesophontes (left, by D. Rini), an insectivore closely related to extant Solenodon (right, by R. Kennerly, IUCN Small Mammal Specialist Group). Nesophontes is abundant in the fossil record, and was formerly widespread across the islands of Cuba, Hispaniola, Puerto Rico, and the Caymans. Today, solenodons are found only on Cuba and Hispaniola, and face critical conservation challenges. The Cuban solenodon is Endangered, and populations of Hispaniolan solenodons are highly fragmented, with the Haitian subspecies restricted to a small area in the western Tiburon peninsula.

This prehistoric extinction is only half the story, however. Many monkeys, rodents, and insectivores were able to coexist alongside multiple human cultures over thousands of years in the Caribbean, despite increasing population sizes, land clearing for horticulture and agriculture, and the introduction of several South American mammal species. Excavations of the very recent past, coupled with recordings in historic chronicles, document the loss of much of the Caribbean’s mammal diversity in the past 500 years. Raptor roosts and other deposits record the co-occurrence of Caribbean mammals and Old World rodents within the same temporal level (Turvey 2009). Unlike the previous extinction wave, this historic extinction selected for small-bodied species, including the shrew-like Nesophontes (Figure 3). This pattern of small mammal extinction has been rarely documented, as most studies of endangerment today find a positive correlation between body size and threat. The introduction of non-native carnivores such as cats and mongooses, coupled with the competitive activities of Old World rats and mice, could have been enough to wipe out everything smaller than a kilogram – leaving a few “Goldilocks” survivors to remain.

Figure 4. Ongoing monitoring efforts are critical to the survival of remaining species, such as bat surveys by author LM Dávalos (left). Some bats in Cuba and Jamaica persist in only one cave and the collapse of a single cave can lead to extinction. The loss of native pollinators, such as the Cuban flower bat (Phyllonycteris poeyi, right, by C. Mancina), could significantly disrupt ecosystem services for small-scale farmers.

The transformation of the Caribbean over the past several thousand years has effectively removed native species and replaced them with Old World mammals. With the arrival of widely divergent lineages including mammalian carnivores as well as ungulates such as cows, goats, and sheep, these replacements are different in both identity and ecological function. Today, out of more than 130 Caribbean mammal species, only 13 terrestrial mammals and 60 bats remain. Although there is no evidence of bats used as food, humans may have also contributed to bat extinctions through habitat alteration in the past (Figure 4; Soto-Centeno et al 2015). Protected areas in the Caribbean are now in place for some cases, and active landscape management by local communities and conservation groups, such as Grupo Jaragua, will be vital to future persistence.

Our review of the fossil record has provided context for understanding the conservation value of these “last survivors”, and what evolutionary diversity we stand to lose should ongoing management efforts fail.

If you are interested in supporting Caribbean conservation/science following Hurricanes Irma and Maria, consider participating in Zooniverse’s “Caribbean Storms 2017” mapping initiative or contributing to a cause of your choice, such as Ciencia Puerto Rico.

Featured Article:

Cooke* SB, Dávalos* LM, Mychajliw* AM, Turvey* ST, Upham* NS. 2017. Anthropogenic Extinction Dominates Holocene Declines of West Indian Mammals. Annual Review of Ecology, Evolution, and Systematics. 48. doi.org/10.1146/annurev-ecolsys-110316-022754

    *equal author contributions

References & Further Reading:

  • Barnosky et al. 2016. Merging paleobiology with conservation biology to guide the future of terrestrial ecosystems. Science. 355. DOI: 10.1126/science.aah4787.
  • Brace S, Barnes I, Powell A, Pearson R, Woolaver LG, Thomas MG, Turvey ST. 2012. Population history of the Hispaniolan hutia Plagiodontia aedium (Rodentia: Capromyidae): testing the model of ancient differentiation on a geotectonically complex Caribbean island. Molecular Ecology, 21: 2239-2253. doi: 10.1111/j.1365-294X.2012.05514.x
  • Cooke SB, Rosenberger AL, Turvey S. 2011. An extinct monkey from Haiti and the origins of the Greater Antillean primates. 108: 2699-2705. doi: 10.1073/pnas.1009161108
  • Mann CC. 2006. 1491: New Revelations of the Americas Before Columbus. Knopf Publishing.
  • Newsom LA, Wing ES. 2004. On Land and Sea. The University of Alabama Press.
  • Turvey, ST. 2009. Holocene Extinction. Oxford University Press.
  • Turvey ST, Fernández-Secades C, Nuñez-Miño JM, Hart T, Martinez P, Brocca JL, Young RP. 2014. Is local ecological knowledge a useful conservation tool for small mammals in a Caribbean multicultural landscape? Biological Conservation, 169: 189-197. https://doi.org/10.1016/j.biocon.2013.11.018
  • Soto-Centeno JA, Steadman DW. 2015. Fossils reject climate change as the cause of extinction of Caribbean bats. Scientific Reports. 5: 7971. doi:10.1038/srep07971
  • Steadman DW, Martin PS, MacPhee RDE, Jull AJT, McDonald HG, Woods CA, Iturralde-Vinent M, Hodgins GWL. 2005. Asynchronous extinction of late Quaternary sloths on continents and islands. PNAS, 102: 11763-11768. http://www.pnas.org/content/102/33/11763.full
  • Valente, L., R. Etienne, L.M. Dávalos. 2017. Recent extinctions disturb path to equilibrium diversity in the Caribbean. Nature Ecology and Evolution 1:0026. DOI:10.1038/s41559-016-002.

Alexis Mychajliw

Postdoctoral Researcher, La Brea Tar Pits, Natural History Museum of Los Angeles