Pavel Tománek’s research while affiliated with Czech University of Life Sciences Prague and other places

Members of the Neotropical primate genus Chiropotes eat large volumes of immature seeds. However, such items are often low in available proteins, and digestion of seeds is further inhibited by tannins. This suggests that overall plant‐derived protein intake is relatively low. We examined the presence of insect larvae in partially eaten fruits, compared with intact fruit on trees, and examined fecal pellets for the presence of larvae. We found that red‐nosed cuxiú ( Chiropotes albinasus ) individuals may supplement their limited seed‐derived protein intake by ingesting seed‐inhabiting insects. Comparison of fruits partially eaten for their seeds with those sampled directly from trees showed that fruits with insect‐containing seeds were positively selected in 20 of the 41 C. albinasus diet items tested, suggesting that fruits with infested seeds are actively selected by foraging animals. We found no differences in accessibility to seeds, that is, no differences in husk penetrability between fruits with infested and uninfested seeds excluding the likelihood that insect‐infestation results in easier access to the seeds in such fruits. Additionally, none of the C. albinasus fecal samples showed any evidence of living pupae or larvae, indicating that infesting larvae are digested. Our findings raise the possibility that these seed‐predating primates might provide net benefits to the plant species they feed on, since they feed from many species of plants and their actions may reduce the populations of seed‐infesting insects. Abstract in Portuguese is available with online material.

Various species of animals maximise energy gained through foraging by minimising excessive energy spent on nonessential activities. Avoiding predation is key for maximising an individual's lifespan, as well as that of its kin; however, anti-predation behaviours can be energetically costly. We investigated the relationship between the potential threat levels by predators, pseudo-predators, and non-predators, and the subsequent energetic cost of behavioural reactions to these threats, in the white-bellied spider monkey (Ateles belzebuth), golden-backed uacari (Cacajao ouakary), and red-nosed cuxiú (Chiropotes albinasus). We analyzed a total of 270 interactions across three independent field studies of the three primate species. Our results revealed significant differences in the behavioural response to predators and non-predators for both C. ouakary and C. albinasus, but not for A. belzebuth. In terms of risk-categorized behaviours, response to predators differed from response to non-predators (being much more intense and energy intensive), while there was no difference in response to predators versus pseudo-predators. Thus, response to potential predators represents an integral part of the time-management and defence strategies of two of the three studied species, and should be integrated into future studies of primate responses to varying levels of predation threat.

Optimal foraging theory predicts that animals will seek simultaneously to minimize food processing time and maximize energetic gain. To test this hypothesis, we evaluated whether a specialist seed‐predator primate forages optimally when choosing among variable‐sized thick‐husked fruits. Our objects of study were the golden‐backed uacari (Cacajao ouakary, Pitheciidae) and single‐seeded pods of the macucu tree (Aldina latifolia, Fabaceae). We predict that golden‐backed uacari will consume fruits of the size class that requires the least time to obtain, handle, and ingest. We used scan sampling, ad libitum to record feeding observations, and measured fruits, their penetrability, and the size of taxidermized C. ouakary hands. To test whether uacaris selected for optimal characteristics, we compared 8 metrics from 75 eaten and 105 uneaten seeds/fruits collected. Uacaris selected fruits of medium size and weight disproportionately to their abundance. Processing large fruits took six times longer than did medium‐sized fruits, but seeds were only four times as large, that is, for energetic yield per unit time, thus choosing medium‐sized pods was optimal. Disproportionate selection by C. ouakary of fruits of medium size and mass in relation to their abundance suggests active sub‐sampling of the available weight–size continuum. This selectivity probably maximizes trade‐offs between the energy derived from a seed, and time and energy expended in processing fruit to access this, so following optimal foraging theory predictions. The greater time spent processing large pods is attributed to difficulties manipulating objects five to seven times the size of the animal's palm and one‐sixth its own body weight.

Predation risk is important in influencing animal behaviour. We investigated how the choice of nocturnal sleeping and diurnal resting sites by two species of primates was influenced by the most likely forms of attack (diurnal raptors and nocturnal felids). We recorded vertical and horizontal patterns of occupancy for 47 sleeping and 31 resting sites, as well as the presence of lianas or vines on trees. We compared the heights of trees used as resting or sleeping sites by the monkeys with those of 200 forest trees that the monkeys did not use. Trees used as nocturnal sleeping sites were taller than those used as diurnal resting sites, and taller than trees that the monkeys did not use. However, while trees used as diurnal resting sites were not significantly taller than non-used trees, diurnal resting sites were located on branches closer to the ground, closer to the main trunk of the tree and in trees with more lianas/vines than nocturnal sleeping sites. The differences in site location can be explained by the type of predator most likely to attack at a particular time: raptors in the day and felids at night.