Biology subjects

Tankink, J. A.

Publications and source records attributed to Tankink, J. A..

4 recordsLinked to original sources

bioRxiv2026

Collateral effects of lethal management operations: biologging reveals multiscale responses in non-target vervet monkeys

Lethal wildlife management operations are typically evaluated through their direct effects on target species, yet their disturbance footprint may extend to non-target animals sharing the same landscape. We opportunistically used a large-scale helicopter-assisted culling event targeting ungulates at Mawana Game Reserve, South Africa, as a natural experiment to examine how such an operation affected the behaviour and space use of non-target vervet monkeys (Chlorocebus pygerythrus). Using GPS and tri-axial accelerometry from 21 collared individuals across seven habituated social groups, we quantified behavioural and spatial responses around the culling event, including changes in activity budgets, circadian activity patterns, short-term walking and running responses, daily space use, and habitat composition. Vervets showed fear-consistent responses that differed among behaviours, social groups, and temporal scales. Foraging declined at the population level, with the strongest reduction occurring in the morning, when helicopter and shooting activity were the most intense. Inactivity increased during culling and remained elevated afterwards, suggesting both disturbance-related change and seasonal background effects, while social behaviour showed a transient increase consistent with a possible social-buffering response. Walking and running showed little consistent change in daily averages across the culling period, but finer-scale analyses revealed short-lived deviations concentrated in specific groups and time windows. Spatially, groups remained within existing ranges but showed divergent responses, from contraction and increased use of dense vegetation to greater movement in more open areas, highlighting how population-level inference can obscure context-dependent responses when heterogeneity among groups, individuals, or habitats is not explicitly considered. Together, our findings show that lethal management can generate multiscale, context-dependent responses in non-target wildlife, and that overlooking these effects may lead to systematic underestimation of their ecological consequences.

ecology↗

bioRxiv2026

Mothers letting go: postnatal maternal investment shapes sex-specific social development in wild vervet monkeys

Sex differences in behaviour and life-history trajectories are widespread across species, yet the mechanisms through which mothers shape these differences remain poorly understood. Classic theories emphasize sex-biased allocation at birth or differential energetic investment, but how maternal effects might operate instead through postnatal investment remains understudied. Using long-term demographic and behavioural data from female-philopatric vervet monkeys (Chlorocebus pygerythrus), we examined how maternal age and dominance rank influence offspring sex ratios at birth, survival to adulthood, maternal investment, and offspring social integration in both sons and daughters. Maternal age, but not rank, influenced offspring sex ratios, with older females producing more daughters. Maternal rank was positively associated with daughters survival and social engagement, with estimated effects consistently stronger in daughters than in sons. While both sexes were highly vulnerable to maternal loss, post-hoc trends suggested a potentially steeper effect on sons. Sons received more maternal proximity (under some maternal conditions) and maternal grooming, whereas daughters seemed to gain earlier and greater engagement with other group members and appeared to derive indirect advantages from maternal rank through social exposure. Together, these findings indicate that maternal investment in this species differs in form rather than in magnitude, primarily through postnatal developmental pathways rather than biased allocation at birth. By demonstrating how maternal age and social status shape divergent early-life trajectories, our study highlights the role of early social environments in generating sex-specific life histories. HighlightsO_LISex differences in life-history trajectories can arise through postnatal social development, not only sex allocation at birth; C_LIO_LIIn wild female-philopatric vervets, maternal age (not rank) predicts offspring sex ratios, with older females producing more daughters; C_LIO_LIMaternal rank shows stronger associations with daughters survival and social engagement, while sons were potentially more dependent on maternal presence; C_LIO_LIMaternal investment differs in form rather than magnitude, consistent with role-specific developmental preparation. C_LI

evolutionary biology↗

bioRxiv2025

Leadership under risk: male vervet monkey's roles in group progression across high-risk terrain

The evolution of cooperative behaviour among unrelated individuals is still incompletely understood. One example is the reported service provisioning by males in primate societies, which is difficult to explain by traditional reciprocity-based models. In this study, we investigated group progressions and sex roles in wild vervet monkeys (Chlorocebus pygerythrus) to test two hypotheses for the observed male bias in cooperative and protective behaviours: paternal care versus reputation-based partner choice. Over more than two years, we recorded the order and timing of individual progressions in five neighbouring groups of vervet monkeys across two terrain types differing in risk (rivers and roads). Males, particularly dominant males, were more likely to lead than females or juveniles, and their probability of leading increased in high-risk terrain. When leading, males often crossed alone, thereby assuming higher predation risk, whereas when not leading, males usually crossed within subgroups. Dominant males who had no offspring yet were most likely to lead during risky progressions. Males who did not lead did not preferentially cross with infants based on their paternal status, refuting the paternal care hypothesis. Instead, male leadership in risky contexts appears to represent a cooperative service. While some of these findings are consistent with the reputation-based partner choice model, we found no clear evidence that such services translated into direct mating advantages. Overall, our results highlight the role of dominance and reproductive status in shaping male service provisioning and underscore its potential adaptable function in primate social organisation.

evolutionary biology↗

bioRxiv2025

Making friends in an asymmetric game: the establishment of male-female grooming exchanges in vervet monkeys

An important challenge for individuals of group-living species is to build cooperative relationships with new partners. One famous strategy for doing so is "raise-the-stakes", proposing low initial investments that increase if the partner matches these investments in a series of exchanges. Contrarily, the "all-in" strategy predicts high initial investment that may be maintained, but downregulated if not fully matched. We tested these predictions on grooming exchanges between wild male-female vervet monkeys, a species with regular male dispersal. Contrary to model predictions, we found uneven initial investment between novel partners that reached near reciprocity after approximately six months. To identify which sex altered investment, we examined grooming durations and frequencies of novel and established partners. Females showed consistently high initial investment and gradually reduced grooming over the first six months. Males did not alter grooming duration but had higher grooming frequency after a year of residency. Eventually, grooming exchanges nearly evened out. Female behaviour aligns more closely with the "all-in" strategy, which suggests competition among female groups over dispersing males. Male behaviour partly fits the "raise-the-stakes" hypothesis. The study highlights the complexity of real-life cooperation, emphasizing the need to explicitly incorporate life history parameters to understand cooperative strategies.

evolutionary biology↗