Deciphering the isotopic niches of now-extinct Hispaniolan rodents

ABSTRACT

Hispaniola once had a large and diverse endemic rodent community. Today, a single species, Plagiodontia aedium, survives alongside invasive murids. Ecological adaptations and resource competition among species have not been previously studied. Here, we undertake the first investigation of the foraging ecology of the endemic taxa using estimated body mass and carbon and oxygen isotope values in incisor enamel. Our sample includes nine endemic taxa, eight of which are extinct, from two Holocene cave assemblages in southern Haiti. We also measured isotopic signatures for the invasive genus Rattus to explore potential niche overlap and competition between introduced and endemic fauna. We expected to detect isotopic evidence for niche partitioning among phylogenetically related rodents with similar morphological adaptations. We find clear differences in body mass and isotope values among rodent taxa. The combination of carbon and oxygen isotopes suggests that some taxa lived in the forest understory, whereas others likely frequented the canopy or open habitats. We may also be able to distinguish dietary preferences (e.g., folivory, frugivory, and potentially trophic omnivory). Small individuals attributed to an undescribed species of Isolobodon are isotopically distinct from their congeners, I. montanus and I. portoricensis, and appear to have relied to a modest degree on C₄ foods. Rattus had a broad generalist niche, which coincided with several endemics, including extant P. aedium. Although preliminary, these data shed light on how a closely related community of island rodents partitions resources and provide context for understanding the ecological role that invasive species may play in extinction processes and future conservation efforts.

ALTERNATE-LANGUAGE SUMMARY IN HAITIAN CREOLE

Depi lontan, te gen anpil ak on divès kantite wonjè ki te abite sou zile Ispanyola an. Jodi a se yon sèl espès, Plagiodontia aedium, k’ap siviv ansanm ak on tip de wonjè mirid ki anvayisan. Pèsòn poko etidye adaptasyon ekolojik ak konpetisyon pou resous ant espès yo. Nan dokiman sa-a, nou antreprann premye ankèt sou ekoloji jan wonjè ki te abite sou zile an te konn chèche manje, nou sèvi avèk mas kò a ke nou estime epi avèk kabòn ak valè oksijèn ki nan emay dan yo. Echantiyon nou an gen ladan nèf tip de wonjè ki te konn abite sou zile an, wit nan yo pa egziste ankò, echantiyon sa yo sòti nan kav Olosè nan sid Ayiti. Nou menm mezire siyati izotopik varyete Rattus ki anvayisan pou nou eksplore si gen sipèpozisyon nan nich yo avèk konpetisyon ant nouvo ak bèt ki te la deja. Nou te panse ke nou t’ap detekte prèv izotopik sou pataj nich ant wonjè ki sòti nan menm ras filojenetik e ki gen menm adaptasyon mòfolojik. Nou jwenn diferans ki klè nan mas kò ak valè isotop oksijèn nan diferan gwoup wonjè yo. Konbinezon nan izotòp kabòn ak oksijèn yo sijere ke gen kèk gwoup ki te viv anba forè yo pandan ke gen lòt ki te viv nan mitan plant forè yo oswa nan louvri. Nou anmezi pou nou distenge preferans dyetetik (tankou si yo te manje fèy, fwi, ak sa ki ka manje tout bagay). Kelke endividyèl ki atribye nan yon espès Isolobodon ki pa defini te izotopikman diferan ke lòt nan menm gwoup biyolojik yo, I. montanus ak I. portoricensis, epi yo parèt yo te konte sou yon degre modès manje C₄. Rattus te gen yon kategori jeneralis, ki koresponn ak plizyè wonjè ki te abite sou zile an tankou P. aedium. Pandan ke yo preliminè, done sa yo montre kijan kominote wonjè zile yo te pataje resous yo epi sa ba nou kontèks pou nou konprann wòl nan ekolojik ke espès anvayisan ka jwe nan pwosesis ekstèsyon ak efò konsèvasyon nan lavni.

ACKNOWLEDGMENTS

We thank J. Bloch and R. Hulbert of the Florida Museum of Natural History for granting us permission to destructively sample material. I. Castro and J. Curtis assisted with sample preparation and analysis. We thank M. Boyer for translating the abstract into Haitian Creole. Comments from two anonymous reviewers greatly improved a previous version of the manuscript. Analyses were funded with Faculty Startup money to B.E.C. and S.B.C. Both authors contributed equally to the manuscript.