The rise of hyperabundant native generalists threatens both humans and nature

Abstract

In many disturbed terrestrial landscapes, a subset of native generalist vertebrates thrives. The population trends of these disturbance‐tolerant species may be driven by multiple factors, including habitat preferences, foraging opportunities (including crop raiding or human refuse), lower mortality when their predators are persecuted (the ‘human shield’ effect) and reduced competition due to declines of disturbance‐sensitive species. A pronounced elevation in the abundance of disturbance‐tolerant wildlife can drive numerous cascading impacts on food webs, biodiversity, vegetation structure and people in coupled human–natural systems. There is also concern for increased risk of zoonotic disease transfer to humans and domestic animals from wildlife species with high pathogen loads as their abundance and proximity to humans increases. Here we use field data from 58 landscapes to document a supra‐regional phenomenon of the hyperabundance and community dominance of Southeast Asian wild pigs and macaques. These two groups were chosen as prime candidates capable of reaching hyperabundance as they are edge adapted, with gregarious social structure, omnivorous diets, rapid reproduction and high tolerance to human proximity. Compared to intact interior forests, population densities in degraded forests were 148% and 87% higher for wild boar and macaques, respectively. In landscapes with >60% oil palm coverage, wild boar and pig‐tailed macaque estimated abundances were 337% and 447% higher than landscapes with <1% oil palm coverage, respectively, suggesting marked demographic benefits accrued by crop raiding on calorie‐rich food subsidies. There was extreme community dominance in forest landscapes with >20% oil palm cover where two pig and two macaque species accounted for >80% of independent camera trap detections, leaving <20% for the other 85 mammal species >1 kg considered. Establishing the population trends of pigs and macaques is imperative since they are linked to cascading impacts on the fauna and flora of local forest ecosystems, disease and human health, and economics (i.e., crop losses). The severity of potential negative cascading effects may motivate control efforts to achieve ecosystem integrity, human health and conservation objectives. Our review concludes that the rise of native generalists can be mediated by specific types of degradation, which influences the ecology and conservation of natural areas, creating both positive and detrimental impacts on intact ecosystems and human society.

Effects of human disturbances on wildlife behaviour and consequences for predator-prey overlap in Southeast Asia

“…Namely, disturbance increases the likelihood of nocturnal detections in rarer specialists’ species and the likelihood of diurnal detections in medium-sized but not large generalist omnivores (behavioural adaptations) and an increase in the absolute number of detections of generalists and their medium-sized predators (species turnover). The large differences in responses of specialists versus generalists aligns well with recent work on tropical forest mammal occupancy and abundance 20 , 38 , 39 . Differences in the magnitude of guild- and species-level shifts may arise, in part, from differential hunting pressure across taxa and locations.…”

A multi‐scale synthesis of mousedeer habitat associations in Southeast Asia reveals declining abundance but few extirpations in fragments and edges

“…Mousedeer's relatively high persistence compared to larger herbivores (Amir, Moore, et al, 2022;Amir, Sovie, & Luskin, 2022;Carr et al, 2023) may be due to their small home range of 0.056 km 2 , with reports from forest patches as small as 0.138 km 2 in oil palm-dominated landscapes in northern Sumatra (Luskin, Albert, & Tobler, 2017) and long-term persistence on the 10 km 2 island of Pulau Ubin in Singapore (Chua et al, 2009). Mousedeer persistence but declines in small patches and edges differentiates them from some small omnivorous or frugivorous monkeys and civets whose abundance has increased in the same degraded forests (Dehaudt et al, 2022;Honda et al, 2023;Moore et al, 2023). Such omnivores are often reported to benefit from foraging opportunities in agriculture, which has not been reported for mousedeer.…”

“…We tested our second hypothesis using mousedeer counts from published camera trapping studies and analysed this with generalized linear mixed models (glmms). Third, since predators and larger hunted herbivores are often the first to decline in forest edges and fragments (Amir, Moore, et al, 2022;Decoeur et al, 2023;Dehaudt et al, 2022;Dunn et al, 2022;Hendry et al, 2023;Honda et al, 2023;Moore et al, 2023;Nursamsi et al,. 2023), and because mousedeer have been reported from small forest patches, we hypothesized that release from predation and competition would produce a positive association with degraded forests (logged forest, forest edges and forest fragments).…”

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

“…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).…”