Biology subjects

Valeix, M.

Publications and source records attributed to Valeix, M..

5 recordsLinked to original sources

bioRxiv2025

Are all waterholes equal from a lion's view? Exploring the role of prey abundance and catchability in waterhole visitation patterns in a savannah ecosystem

Prey abundance and catchability shape the spatial ecology of predators. Predators can select habitats where prey are more abundant to maximize encounter rate with prey or habitats where prey are more catchable to maximize prey capture. These hypotheses are commonly referred to as prey-abundance and prey-catchability hypotheses. Although these hypotheses are often tested at the landscape scale, little is known about how between-patch variations in prey abundance and catchability determine the space use of predators. In many savannah ecosystems, large herbivores aggregate around waterholes, which become hotspots of prey and their selection by predators is classically interpreted as supporting the prey-abundance hypothesis. Here, we investigated whether between-waterhole variations in prey abundance and catchability influence the frequency and duration of lion visits to waterholes, testing the prey-abundance and prey-catchability hypotheses at the resource-patch scale. We combined datasets on (1) lion movements recorded from GPS collars deployed on 20 adult males and 16 adult females between 2002 and 2015, (2) prey abundance evaluated from long-term, regular monitoring of waterholes and (3) prey catchability evaluated from remote-sensing satellite imagery of vegetation cover around waterholes in Hwange National Park (Zimbabwe). Lions did not use all waterholes in their territory equally: there was a high variability in the frequency and duration of visits. Surprisingly, between-waterhole variations in prey abundance and catchability only slightly explained these variations in frequency - and even less in duration - of lion visits to waterholes. Yet, the frequency of lion visits to waterholes decreased with the number of waterholes within their territory, and male lions more frequently visited the waterholes surrounded by more open habitats. We discuss the limits of our work, but also the ecological mechanisms that may explain these findings. First, lions and their prey are involved in a shell-game that leads them to adopt unpredictable movement strategies. Second, lions have only access to a limited number of waterholes amongst which to distribute their hunting effort. Lastly, lions visit waterholes not only to hunt but also to interact with social mates and competitors. This work challenges the implicit assumption that all waterholes are the same from a lions view and calls for further studies investigating the drivers of the variability in lion visits at the resource-patch scale.

ecology↗

bioRxiv2024

Do mixed-species groups travel as one? An investigation on large African herbivores using animal-borne video collars

Although prey foraging in mixed-species groups benefit from a reduced risk of predation, whether heterospecific groupmates move together in the landscape, and more generally to what extent mixed-species groups remain cohesive over time and space remains unknown. Here, we used GPS collars with video cameras to investigate the movements of plains zebras (Equus quagga) in mixed-species groups. Blue wildebeest (Connochaetes taurinus), impalas (Aepyceros melampus) and giraffes (Giraffa camelopardalis) commonly form mixed-species groups with zebras in savanna ecosystems. We found that zebras adjust their movement decisions solely to the presence of giraffes, being more likely to move in zebra-giraffe herds, and this was correlated to a higher cohesion of such groups. Additionally, zebras moving with giraffes spent longer time grazing, suggesting that zebras follow giraffes to forage in their proximity. Our results provide new insights on animal movements in mixed-species groups, contributing to a better consideration of mutualism in movement ecology.

ecology↗

bioRxiv2023

Abundance of mega-carcasses does not profoundly affect trends in the population dynamics of a facultative scavenger predator and its prey

The interplay between facultative scavenging and predation has gained interest in the last decade. The prevalence of scavenging induced by the availability of large carcasses may modify predator density or behaviour, potentially affecting prey. In contrast to behavioural mechanisms through which scavenging affects predation, the demographic effects of facultative scavenging on predator and prey populations remain poorly studied. We used the semi-natural experimental opportunity in Hwange National Park, Zimbabwe, where contrasted management measures (culling and artificial supply of water) have led to fluctuations in elephant carrion abundance, to identify the consequences of facultative scavenging on the population dynamics of a large mammalian carnivore, the spotted hyaena (Crocuta crocuta), and its prey. Using a 50-year dataset and Multivariate Autoregressive State Space models, we estimated hyaena and prey densities over four periods contrasted in elephant carrion availability due to management practices. Models that allow hyaena and their prey populations growth rate to vary depending on these four periods contributed significantly to explain variations in their density, which is consistent with an effect of management measures on the population dynamics of hyaena and its prey. Although our results support a predominant role of bottom-up mechanisms, whereby hyaena density is driven by herbivore density, itself driven by resources availability, some subtle patterns of densities could be interpreted as consequences of changes in predation pressure following changes in scavenging opportunities. We discuss why signals of prey and predator population dynamics decoupling are less likely to be observed in systems with a high diversity of prey, such as African savannas, and why inputs of mega-carcasses as pulsed resources hardly impacted top-down relationships in the long run. This study represents a first investigation of the long-term effects of carrion pulses, whose frequency may increase with climate changes, on the classical predator-prey coupling for large mammals.

ecology↗

bioRxiv2023

Time-varying habitat selection analysis: a model and applications for studying diel, seasonal and post-release changes

Resource selection functions are commonly employed to evaluate animals habitat selection, e.g. the disproportionate use of habitats relative to their availability. While environmental conditions or animal motivations may vary over time, sometimes in an unknown manner, studying changes in habitat selection usually requires a priori time discretization. This limits our ability to precisely answer the question when is an animals habitat selection changing?. Here, we present a straightforward and flexible alternative approach based on fitting dynamic logistic models to used/available data. First, using simulated dataset, we demonstrate that dynamic logistic models performed well to recover temporal variations in habitat selection. We then show real-world applications for studying diel, seasonal, and post-release changes in habitat selection of blue wildebeest (Connochaetes taurinus). Finally, we provide the relevant R scripts to facilitate the adoption of the method by ecologists. Dynamic logistic models allow to study temporal changes in habitat selection in a framework consistent with resource selection functions, but without the need to discretize time, which can be a difficult task when little is known about the process studied, or may obscure inter-individual variability in timing of change. These models should undoubtedly find their place in the movement ecology toolbox.

ecology↗

bioRxiv2017

Zebra diel migrations reduce encounter risk with lions over selection for safe habitats

Diel migrations (DMs) undertaken by prey to avoid visual predators during the day have been demonstrated in many taxa in aquatic ecosystems. We reveal that zebras in Hwange National Park (Zimbabwe) employ a similar anti-predator strategy. Zebras forage near waterholes during the day but move away from them at sunset. We demonstrate that this DM, occurring over a few km, dramatically reduces their night-time risk of encountering lions, which generally remain close to waterholes. By contrast, zebra changes in night-time selection for vegetation types marginally reduced their risk of encountering lions. This may arise from a trade-off between encounter risk and vulnerability across vegetation types, with zebras favouring low vulnerability once DM has reduced encounter risk. In summary, here we (1) quantify the effect of a predator-induced DM in a terrestrial system on the likelihood of encountering a predator, (2) distinguish the effects of the DM from those related to day/night changes in selection for vegetation types. We discuss how revealing how prey partition their risk between predator encounter risk and habitat-driven vulnerability is likely critical to understand the emergence of anti-predator behavioural strategies.

ecology↗