Rewilding in Southeast Asia: Singapore as a case study

Abstract

Re‐establishing extirpated wildlife—or “rewilding”—is touted as a way to restore biodiversity and ecosystem processes, but we lack real‐world examples of this process, particularly in Southeast Asia. Here, we use a decade of aggregated camera trap data, N‐mixture occupancy models, and input from local wildlife experts to describe the unassisted recolonization of two native large herbivores in Singapore. Sambar deer (Rusa unicolor) escaped from captivity (in private or public zoos) in the 1970s and contemporary camera trap data show they have only colonized nearby forest fragments and their abundance remains low. Wild pigs (Sus scrofa), in contrast, naturally recolonized by swimming from Malaysia in the 1990s and have rapidly expanded their range and abundance across Singapore. While wild pigs have not recolonized all viable green spaces yet, their trajectory indicates they soon will. We also note that a third ungulate, the muntjac deer (Muntiacus muntjak), was captured in camera trapping in 2014 and 2015 but was never recorded afterward despite increased sampling effort, and thus we do not focus on their presumably unsuccessful recolonization. The divergent rewilding trajectories between sambar deer and wild pigs suggest different conservation outcomes and management requirements. Sambar deer may restore lost plant–animal interactions such as herbivory and seed dispersal without requiring significant management. Wild pigs, in contrast, have reached high numbers rapidly and may require active management to avoid hyperabundance and negative ecological impacts in regions, such as Singapore that lack both hunting and large predators.

The rise of hyperabundant native generalists threatens both humans and nature

“…Hyperabundant species can impact humans and local fauna and flora in a multitude of negative ways, requiring extensive control measures (Taylor et al ., 2016; Wilson & Edwards, 2019; Moore et al ., 2022). There are significant efforts to manage hyperabundant pig and macaque populations in Malaysia, Singapore and Indonesia (Luskin et al ., 2014; Lamperty et al ., 2023). Population control through cage trapping, culling, hunting and sterilisation may be effective when adequate resources are available (Priston & McLennan, 2013; Luskin et al ., 2014; Croft et al ., 2020).…”

Sunda pangolins show inconsistent responses to disturbances across multiple scales

“…We evaluated Sunda pangolin distribution, occupancy, and habitat associations using occurrence records available in the peer‐reviewed literature and online databases. To disentangle the effects of habitat versus poaching in shaping Sunda pangolin habitat associations, we compare landscapes with poaching to those in Singapore, where strict regulations and enforcement have nearly eliminated all forms of hunting (Lamperty et al, 2023). Other Southeast Asia countries have documented problems with hunting (Harrison et al, 2016) including cases of Sunda pangolin poaching in Myanmar (Nijman et al, 2016), Thailand (Kitamura et al, 2010), Lao (Nooren & Claridge, 2001), Vietnam (Newton et al, 2008; Nuwer & Bell, 2014; MacMillan & Nguyen, 2014), Cambodia (Gray et al, 2017), Malaysia (Jayasilan, 2018; Mohd‐Azlan et al, 2018), and Indonesia (Semiadi et al, 2009; Shepherd, 2009).…”

Recolonizing native wildlife facilitates exotic plant invasion into Singapore's rain forests

“…Their recolonization has been facilitated by forest restoration efforts in Singapore aiming to restore its degraded biodiversity and ecosystems, which have provided increasing secondary forest cover and thus suitable habitats for pigs (Lamperty et al, 2023;Shono et al, 2006). Singapore's pigs have slowly spread across most parts of the island and have reached high densities in some early recolonized forests (Khoo et al, 2021;Lamperty et al, 2023). Pig densities are expected to rise given the hunting ban, lack of predators, and food subsidies from crops and urban areas, and their accumulated soil and vegetation disturbances can become deleterious to the local forest ecology (Amir et al, 2022;Luskin et al, 2019Luskin et al, , 2021Moore et al, 2023).…”

“…Pigs are native to Singapore but were extirpated in the 1950s on mainland Singapore and only persisted in small numbers on offshore islands including Pulau Ubin and Pulau Tekong (Corlett, 1992; Yong et al, 2010). However, they have recolonized without human assistance (i.e., not directly reintroduced by humans) in the early 2000s from nearby Peninsular Malaysia (Lamperty et al, 2023). Their recolonization has been facilitated by forest restoration efforts in Singapore aiming to restore its degraded biodiversity and ecosystems, which have provided increasing secondary forest cover and thus suitable habitats for pigs (Lamperty et al, 2023; Shono et al, 2006).…”

“…However, they have recolonized without human assistance (i.e., not directly reintroduced by humans) in the early 2000s from nearby Peninsular Malaysia (Lamperty et al, 2023). Their recolonization has been facilitated by forest restoration efforts in Singapore aiming to restore its degraded biodiversity and ecosystems, which have provided increasing secondary forest cover and thus suitable habitats for pigs (Lamperty et al, 2023; Shono et al, 2006). Singapore's pigs have slowly spread across most parts of the island and have reached high densities in some early recolonized forests (Khoo et al, 2021; Lamperty et al, 2023).…”