摘要: Scatter-hoarding rodents play important roles in plant regeneration and species coexistence in many forest ecosystems. Cache pilferage, the behavior of rodents seeking or relocating seeds cached by other individuals, is ubiquitous during the scatter-hoarding process. The effects of canopy openness on cache pilferage have received considerable attention, most of which have focused on the comparison between full canopy cover and completely open areas, such as forest gaps. However, little attention has been given to whether the subtle variation in forest canopy openness affects cache pilferage, although subtle variation in light environments exists in many forests, especially tropical and subtropical forests, where the overall canopy is large and the forest window is relatively small. Here, we directly tested these questions by simulating 400 artificial caches, each containing one seed from four selected tree species, in a subtropical forest in southwestern China. The overall canopy openness of the forest was relatively small (with a mean value of 11.1%), but subtle spatial variation still existed (ranging from 5.7% to 19.5%). Overall, caches with lower canopy openness were more likely to be pilfered and removed faster, although not all species showed the same pattern. Our study highlights that subtle variation in forest canopy openness, even in a closed primary forest, has significant effects on cache pilferage by rodents, which may influence the following seed germination and forest regeneration processes. Additionally, seedling species composition may further be altered because the canopy effects on cache pilferage are species-specific. Our study highlights that subtle variation in forest canopy openness, even in a closed primary forest, has significant effects on cache pilferage by rodents. Caches with lower canopy openness were more likely to be pilfered and removed faster, which may influence the following seed germination and forest regeneration processes. Seedling species composition may further be altered because the canopy effects on cache pilferage are species-specific. image

摘要: Emitting alarm calls may be costly, but few studies have asked whether calling increases a caller's risk of predation and survival. Since observing animals calling and being killed is relatively rare, we capitalized on over 24,000 h of observations of marmot colonies and asked whether variation in the rate that yellow-bellied marmots (Marmota flaviventer) alarm called was associated with the probability of summer mortality, a proxy for predation. Using a generalized mixed model that controlled for factors that influenced the likelihood of survival, we found that marmots who called at higher rates were substantially more likely to die over the summer. Because virtually all summer mortality is due to predation, these results suggest that calling is indeed costly for marmots. Additionally, the results from a Cox survival analysis showed that marmots that called more lived significantly shorter lives. Prior studies have shown that marmots reduce the risk by emitting calls only when close to their burrows, but this newly quantified survival cost suggests a constraint on eliminating risks. Quantifying the cost of alarm calling using a similar approach in other systems will help us better understand its true costs, which is an essential value for theoretical models of calling and social behavior.

摘要: Eyespots have been shown to perform an anti-predator function by intimidating predators. However, whether predators are deterred by the eyespots' mimicking eyes of higher-order predators, or by the conspicuousness of the spots, is still being debated. The anti-predator mechanism of eyespots, which involves the predator's visual perception and cognition, urges to be examined. To explore the eye mimicry hypothesis and conspicuous signal hypothesis, we designed prey with deceptive eyespots eliciting 2-dimensional (2D) or 3-dimensional (3D) visual illusions for domestic chicks (as predators). For 2D visual illusion, we provided prey with occluded eyespots for chicks. Chicks can complete the occluded eyespots into a full 2D concentric circle by the amodal completion mechanism, that is, one of visual illusion. For 3D visual illusion, we created the crescent-shaped sparkles on the eyespots to simulate a visually 3D eye. Our result indicated that (1) 2D: chicks hesitated more when facing preys with occluded eyespots than facing preys with broken eyespots and (2) 3D: compared to prey with no-sparkle eyespots, chicks spent more time approaching prey with sparkle eyespots and were more likely to approach them tangentially. Thus, the visual illusion perceived by chicks would impact the anti-predation effectiveness of eyespots. Eyespots that more closely resemble the real eyes, especially those with 3-dimensionality, provided more effective protection. Our study supported the eye mimicry hypothesis from the perspective of visual illusion.

摘要: Sleeping site selection is essential for understanding primate behavioral ecology and survival. Identifying where species sleep helps determine priority areas and critical resources for targeted conservation efforts. However, observing sleeping sites at night is challenging, especially for species sensitive to human disturbance. Thermal infrared imaging (TIR) with drones is increasingly used for detecting and counting primates, yet it has not been utilized to investigate ecological strategies. This study investigates the sleeping site selection of the Critically Endangered black-shanked douc langur (Pygathrix nigripes) in Cat Tien National Park, Vietnam. Our aim is to assess the feasibility of using a TIR drone to test sleeping site selection strategies in non-nesting primates, specifically examining hypotheses related to predation avoidance and food proximity. Between January and April 2023, we conducted 120 drone flights along 22 transects (similar to 1-km long) and identified 114 sleeping sites via thermal imaging. We established 116 forest structure plots along 29 transects in non-selected sites and 65 plots within douc langur sleeping sites. Our observations reveal that douc langurs selected tall and large trees that may provide protection against predators. Additionally, they selected sleeping sites with increased access to food, such as Afzelia xylocarpa, which serves as a preferred food source during the dry season. These results highlight the effective use of TIR drones for studying douc langur sleeping site selection with minimal disturbance. Besides offering valuable insights into habitat selection and behavioral ecology for conservation, TIR drones hold great promise for the noninvasive and long-term monitoring of large-bodied arboreal species.

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