Ecological Consequences of a Millennium of Introduced Dogs on Madagascar

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” (Cryptoprocta spp.) 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.

Zonal Indian Ocean Variability Drives Millennial‐Scale Precipitation Changes in Northern Madagascar

“…Exceptions include a speleothem record from Tsimanampesotse in Madagascar's arid southwest (Scroxton et al., 2019), diatom records from Lake Tritrivakely (Gasse & Van Campo, 1998) and Lake Maudit (Teixeira et al., 2021), and a runoff record northwest of the island (Ma et al., 2021). There are also radiocarbon‐dated pre‐Holocene subfossils, some of which have been analyzed for δ 13 C and δ 15 N to reconstruct diet and habitat moisture (Crowley, 2010; Crowley et al., 2021; Godfrey et al., 2016; Hixon et al., 2021; Samonds et al., 2019), though they are also spatially limited.…”

Dogs occupying grassy habitat near protected areas in eastern Madagascar rely on foods from forests

“…However, dogs are also known to prey on introduced animals that can flourish in relatively open habitat (e.g., rodents and chickens), and dogs rely heavily on plant and animal scraps in human‐derived food waste (Kshirsagar et al, 2020; Valenta et al, 2016). Additionally, ancient dog bone collagen (primarily from SW Madagascar) tends to be enriched in 13 C relative to ancient fosa collagen (Hixon, Douglass, Godfrey, et al, 2021), which suggests that dogs introduced during the past millennium tended to consume fewer forest‐derived foods than fosa. It is unclear whether dogs living near Madagascar's remaining forests today rely primarily on foods from forest‐dwelling taxa or on taxa in open habitat.…”

“…Additionally, ancient dog bone collagen (primarily from SW Madagascar) tends to be enriched in 13 C relative to ancient fosa collagen (Hixon, Douglass, Godfrey, et al, 2021), which suggests that dogs introduced during the past millennium tended to consume fewer forest-derived foods than fosa. It is unclear whether dogs living near Madagascar's remaining forests today rely primarily on foods from forest-dwelling taxa or on taxa in open habitat.…”

“…No other canids inhabited the island prior to the introduction of domesticated dogs. Radiocarbon dated dog bone recovered from archaeological and paleontological deposits across Madagascar spans the past millennium (Hixon, Douglass, Godfrey, et al, 2021), which left potential for dogs to aid human‐led hunts of now‐extinct megafauna (Burney et al, 2020). Today, dogs kill endemic rodents such as the Malagasy giant jumping rat ( Hypogeomys antimena ; Sommer & Hommen, 2000), occasionally stalk lemurs (Brockman et al, 2008), and help people procure forest bushmeat (including lemurs and tenrecs; Decary, 1939; Garcia & Goodman, 2003; Gardner & Davies, 2014).…”

The Contribution of Kurī (Polynesian Dog) to the Ecological Impacts of the Human Settlement of Aotearoa New Zealand

“…Much archaeological and palaeoecological research has focused on the direct impacts of humans (i.e., hunting, environmental modification; Anderson, 1989;Holdaway et al, 2014;Perry et al, 2014;Nogue et al, 2021) and predation by kiore -the latter based on modern ecological (Rayner et al, 2007;Ismar et al, 2014) and palaeoecological (Wilmshurst and Higham, 2004;Wilmshurst et al, 2008) studies. In contrast, the potential impacts of kurī in particular on the pre-European contact ecosystem have largely been overlooked as they are difficult to assess, despite the potential of dogs to be a major novel predator in recently colonised ecosystems (e.g., Koungoulos and Fillios, 2020;Hixon et al, 2021). Fleming (1962) stated "the simplest explanation is to attribute all late Holocene extinction to the profound ecological changes brought about by man with fire, rats and dogs," while Anderson (1981Anderson ( , 1989 suggested kurī probably contributed to the extinction of moa.…”