The rise of hyperabundant native generalists threatens both humans and nature

Human disturbance and aridity influence biomass harvesting by leaf-cutting ants with impacts on nutrient dynamics in a Caatinga dry forest

Human activities have converted mature forests into mosaics of successional vegetation and chronically disturbed habitats, altering the patterns of population distribution, foraging ecology and thus, the flow of matter and nutrients through ecosystems. Although the effects of human disturbance are mostly harmful, hyperabundant native generalist species can emerge and increase their populations under disturbance, such as leaf-cutting ants (LCA), prominent herbivores that are considered ecosystem engineers. Here, we examined the population response of two LCA species of the Caatinga dry forest (Acromyrmex balzani and A. rugosus) to increasing levels of chronic anthropogenic disturbance and aridity, and assessed the foraging activity, biomass and nutrients harvested by their colonies. We found that colony densities increased at more disturbed habitats, varying considerably from 0 to 81 nests/ha, but aridity had no effect. The two species exhibited markedly different foraging activities (44.66 ± 28.76 and 294.6 ± 260.53 ants foraging daily), with the foraging rate increasing in more arid conditions for a species with smaller nests, but with no response to disturbance. Biomass consumption varied distinctly between species, ranging from 0 to 4.81 g (7.24 kg ha.year-1, in A. balzani) and from 5.6 to 74 g (174.39 kg ha.year-1, in A. rugosus). Furthermore, there was no effect of disturbance and aridity on the biomass harvesting of individual colonies. However, there was a considerable increase in the biomass harvested by the populations of colonies in the plots (i.e. accounting for colony densities). Moreover, the species A. balzani foraged upon more nutrient-rich material at more disturbed and arid habitats, with plant material containing higher concentrations of N, Ca, S, Sr, Fe and Mn, as well as a lower C:N ratio in these areas. Our results suggest that Acromyrmex species (1) can achieve larger populations in more disturbed habitats, though not directly associated with aridity, (2) operate as a key herbivore able to fit harvesting/diet through the entire environmental gradient and forage complementarily (monocot vs. dicot) and (3) reallocate expressive amount of forest biomass, resulting in temporary nutrient sinks with potential impacts on Caatinga resilience.

Habitat Suitability Assessment of Key Wildlife in Hainan Tropical Rainforest Based on ESDM

Hainan tropical rainforest is the largest contiguous tropical rainforest in China, but it has experienced increasing disturbances from anthropogenic activities in recent decades due to economic and social development. However, the current status of wildlife habitats within the rainforest remains insufficiently studied, lacking systematic and scientific assessments necessary to guide effective biodiversity conservation strategies. This study focuses on Jianfengling area of Hainan tropical rainforest, using wildlife infrared camera monitoring data and habitat environmental factor data collected through multi-source monitoring in 2020-2021. By applying the Ensemble Species Distribution Model (ESDM), we assessed the spatial distribution of habitat suitability and its influencing factors for seven representative wildlife species, as well as the overall spatial distribution of multi-species habitat suitability. The results indicate that wildlife habitat suitability in Jianfengling study area exhibits a spatial pattern of high suitability in the central regions and low suitability in surrounding areas. Anthropogenic activities and DEM were identified as the most significant factors influencing habitat selection, with most species favoring mid and high altitude areas (500-1000 m) where human activities are less prevalent. This study provides scientific support for tropical rainforest management authorities to optimize resource allocation, develop dynamic monitoring strategies, and implement effective conservation measures.

Defaunation impacts on the carbon balance of tropical forests

The urgent need to mitigate and adapt to climate change necessitates a comprehensive understanding of carbon cycling dynamics. Traditionally, global carbon cycle models have focused on vegetation, but recent research suggests that animals can play a significant role in carbon dynamics under some circumstances, potentially enhancing the effectiveness of nature-based solutions to mitigate climate change. However, links between animals, plants, and carbon remain unclear. We explored the complex interactions between defaunation and ecosystem carbon in Earth's most biodiverse and carbon-rich biome, tropical rainforests. Defaunation can change patterns of seed dispersal, granivory, and herbivory in ways that alter tree species composition and, therefore, forest carbon above- and belowground. Most studies we reviewed show that defaunation reduces carbon storage 0-26% in the Neo- and Afrotropics, primarily via population declines in large-seeded, animal-dispersed trees. However, Asian forests are not predicted to experience changes because their high-carbon trees are wind dispersed. Extrapolating these local effects to entire ecosystems implies losses of ∼1.6 Pg CO2 equivalent across the Brazilian Atlantic Forest and 4-9.2 Pg across the Amazon over 100 years and of ∼14.7-26.3 Pg across the Congo basin over 250 years. In addition to being hard to quantify with precision, the effects of defaunation on ecosystem carbon are highly context dependent; outcomes varied based on the balance between antagonist and mutualist species interactions, abiotic conditions, human pressure, and numerous other factors. A combination of experiments, large-scale comparative studies, and mechanistic models could help disentangle the effects of defaunation from other anthropogenic forces in the face of the incredible complexity of tropical forest systems. Overall, our synthesis emphasizes the importance of-and inconsistent results when-integrating animal dynamics into carbon cycle models, which is crucial for developing climate change mitigation strategies and effective policies.

Rewilding herbivores: too much or little of a good thing?

Large herbivores are important components of rewilding. However, populations can grow fast: we predict that, where top-down control is insufficient, herbivores could undermine long-term rewilding goals. To avoid this, nature-mimicking interventions are required to achieve the right amount of herbivory, in the right place, at the right time through the rewilding process.

In vitro evaluation of oral contraceptives on long-tailed macaque (Macaca fascicularis) primary ovarian cells

Hormonal contraception has been advocated as an alternative population control method for the long-tailed macaque population, which has increased exponentially due to anthropogenic changes and incidental food subsidies from human food waste. Risks of increased zoonosis and conflict are imminent if the population growth of long-tailed macaques is unchecked. However, there's a gap in the literature about the effect of hormonal contraceptives on long-tailed macaque reproductive tissues cell line. The present study aims to investigate the effect of oral contraceptives (Nordette, Noriday, and Ella) on long-tailed macaque ovarian cells. We determine the cell viability and cytotoxicity as well as the morphological changes of the drugs on long-tailed macaque ovarian cells using the MTT assay, Acridine orange/propidium iodide double staining method, morphological examination, and the 4, 6-diamidino-2-phenylindole (DAPI) staining method. For the MTT assay, The drugs were dissolved in culture media before use to have a concentration ranging from 0.5 μg/mL, 2.5 μg/mL, 0.125 μg/mL, 0.0625 μg/mL, and 0.0315 μg/mL to have three replicates for each treatment. In contrast, the concentration of 0.0315 μg/mL was used for the morphological and histopathological analysis. The result of the study indicates that human oral contraceptives (Nordette, Noriday, and Ella) inhibit the growth of long-tailed macaque ovarian cells and induce apoptosis in a concentration- and time-dependent manner (at a concentration of 0.0315 μg/mL and an IC50 lower than 10 μg/mL), With a statistically significant value of ****P < 0.001 for each drug compared to the negative control. The result of the present study contributes toward addressing the gap in the literature on the effect of oral contraceptives in long-tailed macaque ovarian cells. Hence, we conclude that human oral contraceptives (Nordette, Noriday, and Ella) are safe and effective in long-tailed macaque ovarian cells as such could be used to develop non-invasive oral contraceptives for controlling the population of long-tailed macaques as an alternative population control method.

A model for the noninvasive, habitat-inclusive estimation of upper limit abundance for synanthropes, exemplified by M. fascicularis

Accurately estimating population sizes for free-ranging animals through noninvasive methods, such as camera trap images, remains particularly limited by small datasets. To overcome this, we developed a flexible model for estimating upper limit populations and exemplified it by studying a group-living synanthrope, the long-tailed macaque (Macaca fascicularis). Habitat preference maps, based on environmental and GPS data, were generated with a maximum entropy model and combined with data obtained from camera traps, line transect distance sampling, and direct sightings to produce an expected number of individuals. The mapping between habitat preference and number of individuals was optimized through a tunable parameter ρ (inquisitiveness) that accounts for repeated observations of individuals. Benchmarking against published data highlights the high accuracy of the model. Overall, this approach combines citizen science with scientific observations and reveals the long-tailed macaque populations to be (up to 80%) smaller than expected. The model's flexibility makes it suitable for many species, providing a scalable, noninvasive tool for wildlife conservation.

Potential Food Inclination of Crab-Eating Macaques in Laboratory Environments: Enhancing Positive Reinforcement Training and Health Optimization

Positive reinforcement and training for health optimization are pivotal for successful studies with monkeys. Potential food inclination is important for studies on crab-eating macaques in laboratory environments, but evaluations remain scarce. We explored crab-eating macaques' potential food inclination to establish a reward system for future behavioral assessments. Twelve male and three female monkeys underwent a food inclination assessment in which they were offered four food categories-fruits, vegetables, proteins, and nuts. The monkeys exhibited a higher inclination for plant-based foods, particularly fruits and vegetables, over animal-based proteins like chicken and tuna (p < 0.0001), with a notable inclination for nuts (eaten/provided = 100%). Additionally, the consistency of potential food inclination after repeated offerings was investigated, revealing a time-dependent increase in inclination for protein items. Food consumption ratios correlated positively with caloric intake (r = 0.59, p = 0.02), implying that individuals with a regular high caloric intake and increased body weight are more likely to accept food during positive reinforcement training. Our findings suggest fruits, vegetables, protein-rich foods, and nuts can help with health optimization. However, animal-based protein-rich foods initially had a low preference, which may increase over time. Our study can provide guidelines for positive reinforcement training and health optimization.

Is the long-tailed macaque at risk of extinction?

We review the evidence that long-tailed macaques are at risk of extinction and find that papers supporting this argument present no data supporting a hypothesized decline in abundance. These papers contain numerous misrepresentations of the published literature. Long-tailed macaques thrive in human-altered habitats, are listed by the International Union for the Conservation of Nature as an invasive species of concern, and have shown the ability to increase by 7%-10% per year from low numbers, making the probability of extinction very low.

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

Some animal species shift their activity towards increased nocturnality in disturbed habitats to avoid predominantly diurnal humans. This may alter diel overlap among species, a precondition to most predation and competition interactions that structure food webs. Here, using camera trap data from 10 tropical forest landscapes, we find that hyperdiverse Southeast Asian wildlife communities shift their peak activity from early mornings in intact habitats towards dawn and dusk in disturbed habitats (increased crepuscularity). Our results indicate that anthropogenic disturbances drive opposing behavioural adaptations based on rarity, size and feeding guild, with more nocturnality among the 59 rarer specialists' species, more diurnality for medium-sized generalists, and less diurnality for larger hunted species. Species turnover also played a role in underpinning community- and guild-level responses, with disturbances associated with markedly more detections of diurnal generalists and their medium-sized diurnal predators. However, overlap among predator-prey or competitor guilds does not vary with disturbance, suggesting that net species interactions may be conserved.