Fossil vertebrates from Antigua, Lesser Antilles: Evidence for late Holocene human-caused extinctions in the West Indies

Changes in parrot diversity after human arrival to the Caribbean

Humans did not arrive on most of the world's islands until relatively recently, making islands favorable places for disentangling the timing and magnitude of natural and anthropogenic impacts on species diversity and distributions. Here, we focus on Amazona parrots in the Caribbean, which have close relationships with humans (e.g., as pets as well as sources of meat and colorful feathers). Caribbean parrots also have substantial fossil and archaeological records that span the Holocene. We leverage this exemplary record to showcase how combining ancient and modern DNA, along with radiometric dating, can shed light on diversification and extinction dynamics and answer long-standing questions about the magnitude of human impacts in the region. Our results reveal a striking loss of parrot diversity, much of which took place during human occupation of the islands. The most widespread species, the Cuban Parrot, exhibits interisland divergences throughout the Pleistocene. Within this radiation, we identified an extinct, genetically distinct lineage that survived on the Turks and Caicos until Indigenous human settlement of the islands. We also found that the narrowly distributed Hispaniolan Parrot had a natural range that once included The Bahamas; it thus became "endemic" to Hispaniola during the late Holocene. The Hispaniolan Parrot also likely was introduced by Indigenous people to Grand Turk and Montserrat, two islands where it is now also extirpated. Our research demonstrates that genetic information spanning paleontological, archaeological, and modern contexts is essential to understand the role of humans in altering the diversity and distribution of biota.

Archaeological occurrences of terrestrial herpetofauna in the insular Caribbean: cultural and biological significance

Although the importance of the archaeological record for addressing questions of biodiversity is gaining ground, its relevance for describing past faunal communities is still under-exploited, particularly for the most under-documented areas and species. Among the most poorly documented taxa are reptiles and amphibians, which are rarely studied in detail in the archaeological record, even in tropical areas where most of these species occur today. Here I evaluate the archaeological and paleontological significance of reptiles and amphibians from the Indigenous archaeological record of the insular Caribbean. Quantitative (bone counts) and qualitative (taxonomic identification) analyses allow researchers to discuss the role of herpetofauna in the subsistence strategies of Indigenous populations as well as their interest for assessing past insular biodiversity. This overview sheds light on both the poor representation of herpetofaunal taxa in Caribbean archaeological deposits and trends in the potential exploitation of reptiles and amphibians by Indigenous populations. In terms of paleoecology, the presented results reveal strong regional differences in the quality and density of data as well as the inadequacy of available archaeofaunal data for addressing questions of past biodiversity.

Large-scale reptile extinctions following European colonization of the Guadeloupe Islands

Large-scale extinction is one of the defining challenges of our time, as human processes fundamentally and irreversibly reshape global ecosystems. While the extinction of large animals with popular appeal garners widespread public and research interest, the importance of smaller, less "charismatic" species to ecosystem health is increasingly recognized. Benefitting from systematically collected fossil and archaeological archives, we examined snake and lizard extinctions in the Guadeloupe Islands of the Caribbean. Study of 43,000 bone remains across six islands revealed a massive extinction of 50 to 70% of Guadeloupe's snakes and lizards following European colonization. In contrast, earlier Indigenous populations coexisted with snakes and lizards for thousands of years without affecting their diversity. Study of archaeological remains provides insights into the causes of snake and lizard extinctions and shows that failure to consider fossil-derived data probably contributes to substantial underestimation of human impacts to global biodiversity.

Ancient DNA and high-resolution chronometry reveal a long-term human role in the historical diversity and biogeography of the Bahamian hutia

Quaternary paleontological and archaeological evidence often is crucial for uncovering the historical mechanisms shaping modern diversity and distributions. We take an interdisciplinary approach using multiple lines of evidence to understand how past human activity has shaped long-term animal diversity in an island system. Islands afford unique opportunities for such studies given their robust fossil and archaeological records. Herein, we examine the only non-volant terrestrial mammal endemic to the Bahamian Archipelago, the hutia Geocapromys ingrahami. This capromyine rodent once inhabited many islands but is now restricted to several small cays. Radiocarbon dated fossils indicate that hutias were present on the Great Bahama Bank islands before humans arrived at AD ~800-1000; all dates from other islands post-date human arrival. Using ancient DNA from a subset of these fossils, along with modern representatives of Bahamian hutia and related taxa, we develop a fossil-calibrated phylogeny. We found little genetic divergence among individuals from within either the northern or southern Bahamas but discovered a relatively deep North-South divergence (~750 ka). This result, combined with radiocarbon dating and archaeological evidence, reveals a pre-human biogeographic divergence, and an unexpected human role in shaping Bahamian hutia diversity and biogeography across islands.

Anthropogenic Extinction Dominates Holocene Declines of West Indian Mammals

The extensive postglacial mammal losses in the West Indies provide an opportunity to evaluate extinction dynamics, but limited data have hindered our ability to test hypotheses. Here, we analyze the tempo and dynamics of extinction using a novel data set of faunal last-appearance dates and human first-appearance dates, demonstrating widespread overlap between humans and now-extinct native mammals. Humans arrived in four waves (Lithic, Archaic, Ceramic, and European), each associated with increased environmental impact. Large-bodied mammals and several bats were extinct by the Archaic, following protracted extinction dynamics perhaps reflecting habitat loss. Most small-bodied rodents and lipotyphlan insectivores survived the Ceramic, but extensive landscape transformation and the introduction of invasive mammals following European colonization caused further extinctions, leaving a threatened remnant fauna. Both large- and small-bodied nonvolant mammals disappeared, reflecting complex relationships between body size, ecology, and anthropogenic change. Extinct bats were generally larger species, paralleling declines from natural catastrophes.

A THEORY OF FAUNAL BUILDUP FOR COMPETITION COMMUNITIES

Invasion-structured communities have more species than do coevolution-structured communities assembled using the same resource distribution. Species in invasion-structured communities are tightly packed, occupying the upper portion of the resource axis; species in coevolution-structured communities are more widely spaced, and most are located in the lower portion of the resource axis. As a consequence, coevolution-structured communities tend to be more stable than comparable invasion-structured communities, but more open to invasion. Both invasion-structured and coevolution-structured communities have niche separations that are significantly different than would be expected if species were assorted at random. Two-species communities formed by the invasion-only algorithm under asymmetric competition had the majority of their niche separations in the range 0-0.5. All other communities had niche separations that were greater than expected. The most common separations were in the range 1.0-3.5. Thus, while not a common feature of many communities, nicheseparation patterns similar to those described by Hutchinson (1959) appear as an "ensemble" property of many communities. The faunal-buildup graphs formed by the coevolutionary algorithm differ from those formed by the invasion-only algorithm, showing community cycling whenever asymmetric competition is present. Through this cycling behavior the coevolutionary faunal-buildup algorithm provides both a theoretical basis for Wilson's (1959) taxon cycle and a hypothesis explaining the distribution of Anolis lizards in the Lesser Antilles.

BODY SIZE OF INSULAR LIZARDS: A PATTERN OF HOLOCENE DWARFISM

Until recently there have been scant historical data available to test and supplement studies on the evolution of body size within insular lizards. However, there is now an accumulating fossil record from islands which shows that numerous species have declined in average maximum body size since the beginning of the Holocene, regardless of phylogenetic afffinities, habits, or even size of the species itself. Coincident with decline in body size, human colonization of islands has permanently altered insular environments, with the consequence that native flora and fauna have been depleted. Indeed, the fossil record documents high extinction rates among insular vertebrates during the past few thousand years. It follows that resource deterioration may have led to the reduction of lizard body size, as expressed genotypically in selection for corresponding smaller dimensions, and phenotypically through arrested growth and development leading to compression of the age-class structure. The effect of human settlement on small islands has been underestimated, and although the consequences do not render completely in vain the attempts to understand ecological processes on them, they are of sufficient magnitude to stress caution in any assessment of a modern insular biota.

Fossils reject climate change as the cause of extinction of Caribbean bats

We combined novel radiocarbon dates of bat fossils with time-scaled ecological niche models (ENM) to study bat extinctions in the Caribbean. Radiocarbon-dated fossils show that late Quaternary losses of bat populations took place during the late Holocene (<4 ka) rather than late Pleistocene (>10 ka). All bat radiocarbon dates from Abaco (Bahamas) that represent extirpated populations are younger than 4 ka. We include data on six bat species, three of which are Caribbean endemics, and include nectarivores as well as insectivores. Climate-based ENMs from the Last Glacial Maximum to the present reflect overall stability in distributions, with suitable climatic habitat being present over time. In the absence of radiocarbon dates, bat extinctions had been presumed to take place during the last glacial-interglacial transition (ca. 10 ka). Now we see that extirpation of bats on these tropical islands is more complex than previously thought and primarily postdates the major climate changes that took place during the late Pleistocene-Holocene transition.

Morphology and genetics reveal an intriguing pattern of differentiation at a very small geographic scale in a bird species, the forest thrush Turdus lherminieri

Mobile organisms are expected to show population differentiation only over fairly large geographical distances. However, there is growing evidence of discrepancy between dispersal potential and realized gene flow. Here we report an intriguing pattern of differentiation at a very small spatial scale in the forest thrush (Turdus lherminieri), a bird species endemic to the Lesser Antilles. Analysis of 331 individuals from 17 sampling sites distributed over three islands revealed a clear morphological and genetic differentiation between these islands isolated by 40-50 km. More surprisingly, we found that the phenotypic divergence between the two geographic zones of the island of Guadeloupe was associated with a very strong genetic differentiation (Fst from 0.073-0.153), making this pattern a remarkable case in birds given the very small spatial scale considered. Molecular data (mitochondrial control region sequences and microsatellite genotypes) suggest that this strong differentiation could have occurred in situ, although alternative hypotheses cannot be fully discarded. This study suggests that the ongoing habitat fragmentation, especially in tropical forests, may have a deeper impact than previously thought on avian populations.

Bird remains from an archaeological site on Henderson Island, South Pacific: Man-caused extinctions on an "uninhabited" island

Long thought never to have been inhabited and to be in a pristine ecological state, Henderson Island (southeast Pacific) is now known to have been colonized and then abandoned by Polynesians. Bones from an archaeological site on the island associated with (14)C dates of approximately 800 and approximately 500 years B.P. include specimens of 12 species of birds, of which 3, a storm-petrel and two pigeons (Nesofregetta fuliginosa, Ducula cf. aurorae or D. pacifica, and Ducula cf. galeata), no longer occur on Henderson, and two others (Puffinus nativitatis and Sula sula) still visit but are not known to breed. The vanished species were presumably exterminated by Polynesians and the biota of Henderson Island can thus no longer be regarded as being in an unaltered state. The prehistoric abandonment of various small, unarable islands by Polynesians may have been due to the depletion of seabirds and pigeons, the only readily available food source. The species of pigeons identified from Henderson are known historically only from distant archipelagos and have never before been found sympatrically. Distributional patterns resulting from man-caused extinctions may give rise to erroneous interpretations of the relationships and evolutionary history of insular organisms. Certain endangered species, such as Ducula galeata, might effectively be preserved by reintroduction to abandoned islands that they occupied before human intervention.

Radiocarbon dates on bones of extinct birds from Hawaii

Bones from a stratified sedimentary deposit in the Puu Naio Cave site on Maui, Hawaiian Islands, reveal the late Holocene extinction of 19 species of birds. The age of the sediment and associated fauna was determined by direct radiocarbon dating (tandem particle accelerator-mass spectrometer; TAMS) of amino acids extracted from bones weighing as little as 450 mg. The 14C dates indicate that sediment has been accumulating in the lava tube for at least the last 7750 years, a suitable time frame for testing the hypothesis that Holocene extinction on islands began after human colonization. Despite growing evidence that a worldwide wave of extinctions coincided with human colonization of oceanic islands, little radiometric data have been available to date the extinction of most small fossil vertebrates on islands. The TAMS technique of dating purified collagen from the bones of small vertebrates could lead to vastly improved chronologies of extinction for oceanic islands where catastrophic mid- to late-Holocene extinction is expected or known to have occurred. Chronologies derived from nonarcheological sites that show continuous sedimentation, such as the Puu Naio Cave deposit, may also yield key evidence on the timing of earliest human settlement of Oceania.