Ecological Consequences of a Millennium of Introduced Dogs on Madagascar

Sean W Hixon,Brooke E Crowley,Simon Haberle,Kristina G Douglass,Douglas J Kennett,Laurie Eccles,Laurie R Godfrey,Atholl Anderson,Henry T Wright,Lucien Marie Aimé Rakotozafy,Geoffrey Clark

doi:10.3389/fevo.2021.689559

Abstract

Introduced predators currently threaten endemic animals on Madagascar through predation, facilitation of human-led hunts, competition, and disease transmission, but the antiquity and past consequences of these introductions are poorly known. We use directly radiocarbon dated bones of introduced dogs (Canis familiaris) to test whether dogs could have aided human-led hunts of the island’s extinct megafauna. We compare carbon and nitrogen isotope data from the bone collagen of dogs and endemic “fosa” (Cryptoproctaspp.) in central and southwestern Madagascar to test for competition between introduced and endemic predators. The distinct isotopic niches of dogs and fosa suggest that any past antagonistic relationship between these predators did not follow from predation or competition for shared prey. Radiocarbon dates confirm that dogs have been present on Madagascar for over a millennium and suggest that they at least briefly co-occurred with the island’s extinct megafauna, which included giant lemurs, elephant birds, and pygmy hippopotamuses. Today, dogs share a mutualism with pastoralists who also occasionally hunt endemic vertebrates, and similar behavior is reflected in deposits at several Malagasy paleontological sites that contain dog and livestock bones along with butchered bones of extinct megafauna and extant lemurs. Dogs on Madagascar have had a wide range of diets during the past millennium, but relatively high stable carbon isotope values suggest few individuals relied primarily on forest bushmeat. Our newly generated data suggest that dogs were part of a suite of animal introductions beginning over a millennium ago that coincided with widespread landscape transformation and megafaunal extinction.

Highlights

Madagascar is a biodiversity hotspot that has repeatedly faced a variety of biological invasions over the past millennium (Middleton, 1999; Kolby, 2014; Hixon et al, submitted)
We focus on the arid SW, because each ecoregion has its own chronology of species introductions and extinctions, and most existing 14C datasets come from this ecoregion (Crowley, 2010; Douglass et al, 2019)
We focus on comparing dog and Cryptoprocta spp. data with those from extinct giant lemurs, because (1) there is widespread evidence that at least Cryptoprocta spp. and humans preyed on these animals (Meador et al, 2019; Godfrey et al, submitted), and (2) these taxa have robust 14C chronologies that suggest they disappeared at approximately the same time as other megafauna such as pygmy hippos and giant tortoises (Crowley, 2010; Hixon et al, submitted)

Summary

Introduction

Madagascar is a biodiversity hotspot that has repeatedly faced a variety of biological invasions over the past millennium (Middleton, 1999; Kolby, 2014; Hixon et al, submitted). Changes in human land use (i.e., the spread of pastoralism and commensal species) generally coincide with past environmental transformations (Stephens et al, 2019) that contribute to biotic homogenization (McKinney, 1997; McKinney and Lockwood, 1999). As part of this transformation, introduced predators can disrupt island ecosystems by facilitating human hunting, creating novel predation pressure, and competing with other predators (e.g., competition between dingoes and red foxes in Australia; Cupples et al, 2011), yet we know very little about the antiquity of introduced predators on Madagascar

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Results

Conclusion