Biology subjects

Thel, L.

Publications and source records attributed to Thel, L..

11 recordsLinked to original sources

bioRxiv2026

Effect of the environment, predation and life history on reproductive synchrony in Perissodactyla

Synchronising birth timing with the adequate environmental conditions as well as with congeners can affect juvenile survival and at a later stage, recruitment. In the case of endangered species, understanding the factors driving birth phenology is therefore critical to implement effective conservation and reintroduction policies. Currently, 75% of the Perissodactyla species (odd-toed ungulates) are threatened and some even already had to be reintroduced in their natural habitat. Using a comparative analysis framework, we investigated the effect of nine environmental, life history and predation factors on the synchrony of births in 27 populations of wild Perissodactyla across Africa and Asia. We confirmed the positive effect of environmental seasonality and latitude, as well as the negative effect of environmental productivity on birth synchrony, but we found no significant effect of environmental unpredictability. Life history traits had limited effects on birth synchrony in this order: the intensity of daily reproductive effort and pace of life were non-significant, and migratory behaviour had an unexpected positive association with birth synchrony, suggesting that the link between migration and reproduction might be more complex than the relief of environmental constraints initially expected. We found a positive effect of group size on birth synchrony, in line with the swamping hypothesis to reduce predation risk on neonates, but we found no strong support for a positive effect of predation exposure, measured as a qualitative index combining species-specific sensitivity to predation and site-specific predator abundance. Overall, our findings suggest that individuals adjust reproductive cycles in response to local ecological and social conditions, suggesting that conservation efforts such as reintroductions could benefit from taking into account the extent of the differences between the site of origin and the reintroduction site.

ecology↗

bioRxiv2026

The evolution of non-seasonal breeding in primates

Reproductive seasonality offsets the energetic costs of reproduction by synchronizing births with peak resources and is traditionally expected to increase with latitude and environmental seasonality. However, life-history and behavioural strategies may also buffer energetic shortages and reduce dependency on environmental cycles. Here, we propose and test an integrative framework integrating climatic, life-history and behavioural factors using high-resolution measures of reproductive seasonality for 132 wild primate populations from 94 species. As expected, reproductive seasonality declines at lower latitudes, in less seasonal and in less predictable environments, even after controlling for productivity. It also decreases in species that spread reproductive costs by extending developmental periods, or when a higher infant mortality urges females to resume fertility shortly after loss. Unexpectedly, reproductive seasonality increases with environmental productivity and is not reduced by cognitive (foraging innovations), social (allomaternal care), or ecological (dietary breadth) buffering. Broader diets even enhance seasonality. These findings suggest that reproductive seasonality emerges from opportunity more than from constraints in productive environments, where females exploit abundant resources to accelerate their reproductive pace. Together, our results shed light on the diverse selective pressures shaping primate reproductive seasonality, including climate, life-history pace, and infanticide risk, and help to explain why humans reproduce year-round.

evolutionary biology↗

bioRxiv2025

Evolutionary and ecological determinants of the phenology of births in wild large herbivores, a systematic review

1. IntroductionTiming of birth is a major determinant of individuals reproductive success and phenotypic performances, driven by multiple factors. However, there is currently no quantitative assessment of the support received by the drivers of the phenology of births in mammals. 2. Aimsour objective was to identify the drivers tested for their effect on the phenology of births in large herbivores and how much empirical support they received, as well as determine thematic, taxonomic and spatial gaps in the literature. 3. MethodsWe conducted a systematic review focusing on the drivers of the phenology of births in large herbivores. We extracted the outcomes of 124 articles and assessed the reliability of their findings using a general index based on the quality of the data and methods used. 4. Results and DiscussionWe identified a major research gap in Asian and South and Central American species. The effect of population and individual characteristics remained marginally accounted for, even though there was evidence of their importance in the determination of the phenology of births. The two dominant hypotheses (seasonality and predation) received good to moderate empirical support regarding their effect on birth timing and synchrony, respectively. Given the strong geographic and methodological biases, these hypotheses should be considered as most consistently supported in the existing literature rather than definitively established across systems. 5. ConclusionsWe encourage research in these understudied domains, as well as large scale multi-species comparative analyses to fill in these gaps and improve our understanding of reproductive phenology. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=97 SRC="FIGDIR/small/694258v2_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@4f1a9org.highwire.dtl.DTLVardef@95c5a6org.highwire.dtl.DTLVardef@e3324forg.highwire.dtl.DTLVardef@1fc1a6f_HPS_FORMAT_FIGEXP M_FIG C_FIG This semi-systematic review supports the two dominant drivers of birth phenology, the seasonality and predation hypotheses. Even though there is evidence of their importance, the effects of female, offspring and population characteristics remain marginally accounted for. Asian and South and Central American species are currently understudied.

ecology↗

bioRxiv2025

Absence of reactive temporal response of baboons to the occurrence of predators

Predators exert strong selective pressure on prey species, shaping their behavioral adaptations. Prey species use proactive responses, such as site selection and the adjustment of daily activity patterns to anticipate and avoid predation exposure. In contrast, reactive responses, including fleeing, referential signaling and retaliation, occur after encountering a predator to mitigate the immediate predation risk. The presence of a predator in an area can also generate longer-term responses, such as reactive avoidance, defined here as the temporary avoidance of the area following the passage of a predator. Such a long-term reactive response remains understudied in primates. To investigate reactive avoidance, we analyzed an extensive camera trap data set of 3,042 detections (defined here as a motion-triggered event of three pictures per trigger during the day and one picture at night) of both chacma (Papio ursinus) and olive (Papio anubis) baboons, including 6,958 detections of their main predators, lions (Panthera leo), leopards (Panthera pardus) and spotted hyenas (Crocuta crocuta), in four savanna sites (Madikwe Game Reserve, Tswalu Kalahari Private Wildlife Reserve and the Associated Private Nature Reserves, South Africa; Serengeti National Park, Tanzania). We examined whether baboons display species-specific reactive avoidance towards predators up to 72 hours after the detection of a predator using randomization tests. We found no significant decrease in baboon presence (defined as the number of baboon detections) 0 to 24 hours, 24 to 48 hours and 48 to 72 hours after the detection of any predator species. These results suggest that baboons may not display reactive avoidance and rely on alternative predator-avoidance strategies, such as proactive avoidance or aggressive retaliation, to mitigate predation risk.

animal behavior and cognition↗

bioRxiv2024

The effect of an increasing elephant population on the allometry of trees

African elephants (Loxodonta africana), in conjunction with the community of browser species, exert substantial top-down control over the woody vegetation in savannas by utilising large amounts of plant biomass, as well as through non-consumptive effects. However, how much browsers affect the pattern of proportional growth between different tree components remains understudied. Using vegetation data collected in 2000-2001 and 2019 for more than 3,500 trees inside and outside Madikwe Game Reserve, South Africa, we determined the long-term effects of an increasing elephant population, in conjunction with the community of meso-browsers, on structural relationships in 13 tree species. The number of trees utilised by elephants increased between 2000 and 2019, but individuals were not more intensively utilised. After almost two decades of use by elephants, we observed a reduction in the logged initial growth rate of the structural relationship between tree height and stem diameter, without modification of the asymptotic change in growth rate. Despite species-specific variability, tree height was overall reduced for a given stem diameter. Canopy area, as well as its structural relationship with stem diameter remained mostly stable. We suggest that elephants are responsible for hedging by reducing tree height. Together with impala (Aepyceros melampus), the dominant species in this meso-browser community, they could stimulate regrowth by browsing the canopy of the vegetation maintained in the browsing trap. Our study emphasises the necessity of long-term, species-specific studies to improve our understanding of how the browser community, and elephant in particular, affect structural relationships in trees.

ecology↗

bioRxiv2024

Sex-specific mate choice and mate change based on MHC-IIB dissimilarity in a genetically monogamous seabird

Among species reproducing sexually, mating strategies represent a major component of individual fitness. The major histocompatibility complex (MHC) is an extremely diverse set of genes responsible for immunological recognition and defence against pathogens. Although dissimilarity between mates at the major histocompatibility complex has been proposed to drive mate choice through increased offspring pathogen resistance, evidence is mixed. In addition, explorations of the role of the major histocompatibility complex in other mating strategies, such as divorce, are rare. We investigated whether dissimilarity at the major histocompatibility complex class IIB is associated with mate choice and divorce probability in the genetically monogamous black-legged kittiwake (Rissa tridactyla). We found that first-time male breeders, as well as divorced males, were paired with females more dissimilar at the major histocompatibility complex class IIB than expected under random mating. We did not find evidence for mate choice based on major histocompatibility complex class IIB dissimilarity when considering females. In addition, in the studied population, divorce probability was very low compared with other populations and did not significantly vary with the dissimilarity of the pair at the major histocompatibility complex class IIB. Our results pave the way to a better understanding of the complex role of major histocompatibility complex dissimilarity in mating decisions of species displaying mutual choice and biparental care.

animal behavior and cognition↗

bioRxiv2024

Climate and predation drive variation of diel activity patterns in chacma baboons (Papio ursinus) across southern Africa

Understanding how animals adjust daily activity to environmental gradients reveals key drivers of behavioral plasticity. While diel activity is theorized to reflect trade-offs among thermoregulation, energy balance, and predation risk, few studies test these interactions at broad spatial scales within species. We investigated this in chacma baboons (Papio ursinus) using over a million camera-trap detections across 29 sites in six biomes (2016-2022) in South Africa and Zimbabwe. Activity declined by about 3% with latitude, consistent with lower resource predictability and increased with thermal stress, while sleep and wake times were similar across sites. Baboons avoided midday heat but increased dawn and night activity under predator pressure. These findings show how abiotic and biotic pressures shape diel schedules and highlight temporal flexibility as an adaptive strategy for generalist mammals in a changing world.

animal behavior and cognition↗

bioRxiv2023

Too disturbed or too hot: summer temperatures more than hikers disturbance affect circadian activity of females in northern chamois

Recreational activities often result in a spatial and/or temporal activity shift in wildlife. With the concurrent development of outdoor activities and increase in temperatures due to climate change, mountain species face increasing pressures in terms of managing their activity pattern to limit both risk exposure and thermal discomfort. Using more than 15 years of long-term GPS and activity sensor data, we investigated how female northern chamois, Rupicapra rupicapra rupicapra, adjust their summer circadian activity to spatiotemporal variation in both temperatures and hikers presence. Chamois behaviour was more affected by high temperatures than by hikers presence. During the hottest days, they shifted their activity peak earlier in the morning, were more active at night, less active during daytime and had longer morning and evening peaks compared to the coldest days. Global activity was only slightly different during the hottest than the coldest days. Conversely, hikers disturbance had weak effects on activity levels and on the timing of activity peaks. This is especially true for temporal disturbance (weekdays versus weekends and public holidays), possibly because most weekdays in summer fell during school holidays. During the hottest conditions, the morning activity peak was shorter and the evening peak longer in females living in the most exposed areas compared to females living in the least exposed areas. One possible explanation for the overall low effect of hikers disturbance may be that behavioural changes buffering animals from high temperatures and hikers presence (e.g. moving away from trails) allow them to just marginally modify their activity pattern. In the context of ongoing socioenvironmental changes, it is critical to conserve habitats providing thermal refuges against summer heat and protection from disturbance to mitigate potential detrimental consequences.

animal behavior and cognition↗

bioRxiv2021

Does timing of birth affect juvenile and mare survival in wild plains zebra?

In large herbivores, the timing of births often coincides with the seasonal peak of food resources availability, likely to improve juvenile survival and reduce reproduction costs. Some species however, breed year-round, even in seasonal environments. Demographic processes, such as to what extent being born during the lean season reduces survival of juveniles and reproductive females, remain understudied in large mammals inhabiting tropical ecosystems. We investigated survival rates in plains zebras (Equus quagga) in Hwange National Park (Zimbabwe), a highly seasonal savanna ecosystem. We used capture-recapture models to analyse long-term demographic data (2008-2019). We investigated the effect of seasonality as a categorical (wet versus dry season) and continuous (duration of the dry season) variable on survival. We found little variability in early juvenile survival ({varphi} = 0.458 {+/-} 0.044 SE, < 6 m.o.), whereas late juvenile and yearling survival was higher and decreased with increasing length of the dry season (from 0.850 {+/-} 0.095 SE to 0.480 {+/-} 0.120 SE). Female survival was high (> 0.703 {+/-} 0.057 SE and up to 0.995 {+/-} 0.006 SE) but decreased with increasing exposure to the dry season in non-reproductive females. The probability of females becoming reproductive in the following year was not affected by the length of the dry season (0.423 and 0.420 for reproductive and non-reproductive females respectively). Our results highlight the importance of individual quality in reproductive performance, as reproductive females seem to buffer the effect of environmental variability on their own survival and that of their foal.

ecology↗

bioRxiv2021

How to describe and measure phenology? An investigation on the diversity of metrics using phenology of births in large herbivores

Proposed in 1849 by Charles Morren to depict periodical phenomena governed by seasons, the term "phenology" has spread in many fields of biology. With the wide adoption of the concept of phenology flourished a large number of metrics with different meaning and interpretation. Here, we first a priori classified 52 previously published metrics used to characterise the phenology of births in large herbivores according to four biological characteristics of interest: timing, synchrony, rhythmicity and regularity of births. We then applied each metric retrieved on simulation data, considering normal and non-normal distributions of births, and varying distributions of births in time. We then evaluated the ability of each metric to capture the variation of the four phenology characteristics via a sensitivity analysis. Finally, we scored each metric according to eight criteria we considered important to describe phenology correctly. The high correlation we found among the many metrics we retrieved suggests that such diversity of metrics is unnecessary. We further show that the best metrics are not the most commonly used, and that simpler is often better. Circular statistics with the mean vector orientation and mean vector length seems, respectively, particularly suitable to describe the timing and synchrony of births in a wide range of phenology patterns. Tests designed to compare statistical distributions, like Mood and Kolmogorov-Smirnov tests, allow a first and easy quantification of rhythmicity and regularity of birth phenology respectively. By identifying the most relevant metrics our study should facilitate comparative studies of phenology of births or of any other life-history event. For instance, comparative studies of the phenology of mating or migration dates are particularly important in the context of climate change.

ecology↗

bioRxiv2020

Can citizen science analysis of camera trap data be used to study reproduction? Lessons from Snapshot Serengeti program

Ecologists increasingly rely on camera-trap data to estimate biological parameters such as population abundance. Because of the huge amount of data, the assistance of non-scientists is often sought after, but an assessment of the data quality is necessary. We tested whether volunteers data from one of the largest citizen science projects - Snapshot Serengeti - could be used to study breeding phenology. We tested whether the presence of juveniles (less than one or 12 months old) of species in the Serengeti: topi, kongoni, Grants gazelle, could be reliably detected by the "naive" volunteers vs. trained observers. We expected a positive correlation between the proportion of volunteers identifying juveniles and their effective presence within photographs, assessed by the trained observers. The agreement between the trained observers was good (Fleiss {kappa} > 0.61 for juveniles of less than one and 12 month(s) old), suggesting that morphological criteria can be used to determine age. The relationship between the proportion of volunteers detecting juveniles less than a month old and their actual presence plateaued at 0.45 for Grants gazelle, reached 0.70 for topi and 0.56 for kongoni. The same relationships were much stronger for juveniles younger than 12 months, reaching 1 for topi and kongoni. The absence of individuals < one month and the presence of juveniles < 12 months could be reliably assumed, respectively, when no volunteer and when all volunteers reported a presence of a young. In contrast, the presence of very young individuals and the absence of juveniles appeared more difficult to ascertain from volunteers classification, given how the classification task was presented to them. Volunteers classification allows a moderately accurate but quick sorting of photograph with/without juveniles. We discuss the limitations of using citizen science camera-traps data to study breeding phenology, and the options to improve the detection of juveniles.

ecology↗