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.The ‘Ministère Français de l'Enseignement Supérieur, de la Recherche et de l'Innovation' through the ‘Ecole Doctorale E2M2' of the ‘Université Claude Bernard Lyon 1'.http://www.oikosjournal.orghj2023Mammal Research InstituteZoology and Entomolog

Multi-mode movement decisions across widely ranging behavioral processes

Movement of organisms plays a fundamental role in the evolution and diversity of life. Animals typically move at an irregular pace over time and space, alternating among movement states. Understanding movement decisions and developing mechanistic models of animal distribution dynamics can thus be contingent to adequate discrimination of behavioral phases. Existing methods to disentangle movement states typically require a follow-up analysis to identify state-dependent drivers of animal movement, which overlooks statistical uncertainty that comes with the state delineation process. Here, we developed populationlevel, multi-state step selection functions (HMM-SSF) that can identify simultaneously the different behavioral bouts and the specific underlying behavior-habitat relationship. Using simulated data and relocation data from mule deer (Odocoileus hemionus), plains bison (Bison bison bison) and plains zebra (Equus quagga), we illustrated the HMM-SSF robustness, versatility, and predictive ability for animals involved in distinct behavioral processes: foraging, migrating and avoiding a nearby predator. Individuals displayed different habitat selection pattern during the encamped and the travelling phase. Some landscape attributes switched from being selected to avoided, depending on the movement phase. We further showed that HMM-SSF can detect multi-modes of movement triggered by predators, with prey switching to the travelling phase when predators are in close vicinity. HMM-SSFs thus can be used to gain a mechanistic understanding of how animals use their environment in relation to the complex interplay between their needs to move, their knowledge of the environment and navigation capacity, their motion capacity and the external factors related to landscape heterogeneity.DATA AVAILABILITY STATEMENT : The data are available at: https://osf.io/v5pnc/SUPPLEMENTARY MATERIAL : S1 Appendix. Calculation of average travelled distance using coefficient estimates associated to step length. https://doi.org/10.1371/journal.pone.0272538.s001S1 Table. Values and definition [from c] of model parameters used to simulate multi-state correlated random walks in three scenarios of landscape patchiness. https://doi.org/10.1371/journal.pone.0272538.s002S2 Table. Coefficient estimates along with their 95% confidence interval (95% CI) of the mixed-effects generalized linear model with binomial distribution (HMM-SSF + GLMM) and the multi-state correlated random walk model (HMM-CRW) to predict probability of switching from encamped to travelling mode, in 500 simulated foragers moving among resource patches and avoiding a predator. In resource patch is a dummy variable indicating whether the forager is within a resource patch (i.e., patch quality >0), equals the actual distance of the predator from the forager (dPredator) when dPredator ≤ 0.8 km and 0.8 km, otherwise. log(dPredator) is the natural logarithm of dPredator. https://doi.org/10.1371/journal.pone.0272538.s003S3 Table. Coefficient estimates along with their 95% confidence interval (95% CI) of mixed-effects generalized linear models with binomial distribution to predict probability of switching from encamped to travelling mode of movement, in plains bison during summer in Prince Albert National Park (SK, Canada). Each table represents estimates for a specific threshold probability (Pthreshold) used to categorized transition and non-transition from the conditional probabilities of being in encamped or travelling state, obtained from the fit of the HMM-SSF to plains bison trajectories. was set to the actual distance between bison and wolf (dwolf) when dwolf≤dthreshold and dthreshold, otherwise. https://doi.org/10.1371/journal.pone.0272538.s004S1 Fig. Simulated heterogeneous landscape used in the multi-state biased correlated random walk simulations, from gaussian random field with an exponential covariance function with variance = 1, nugget = 0 and a set of patch concentration (μQ) and patch size (γQ) resulting in three level of patchiness: 1) low (μQ = -1.5, γQ = 2), 2) intermediate (μQ = -0.5, γQ = 2) and 3) high (μQ = 1, γQ = 10). https://doi.org/10.1371/journal.pone.0272538.s005S2 Fig. Distribution of distance to the closest waterhole according to the mode of movement estimated from the HMM-SSF for 18 zebras in Hwange National Park during the dry hot season. The conditional probabilities of being in each state, obtained from the fit of the HMM-SFF, were dichotomized to 0–1 based on a 0.5 threshold to determine the state of the individual at each step on its trajectory. https://doi.org/10.1371/journal.pone.0272538.s006S3 Fig. Log-likelihood profile from mixed-effects generalized linear model with binomial distribution to predict probability of switching from encamped to travelling mode of movement, according to a gradient of threshold distance, dthreshold. https://doi.org/10.1371/journal.pone.0272538.s007S4 Fig. Total number of switches from encamped to travelling mode of movement according to day time, estimated using conditional probabilities of being in each state, obtained from the fit of the HMM-SFF to plains bison trajectories followed during the summers 2005–2016. We then separated the day in four periods: Night: 22:00–02:00, Dawn: 03:00–06:00, Day: 07:00–15:00 and Dusk: 16:00–21:00. https://doi.org/10.1371/journal.pone.0272538.s008http://www.plosone.orgdm2022Mammal Research InstituteZoology and Entomolog

Body size and digestive system shape resource selection by ungulates : a cross-taxa test of the forage maturation hypothesis

The forage maturation hypothesis (FMH) states that energy intake for ungulates is maximised when forage biomass is at intermediate levels. Nevertheless, metabolic allometry and different digestive systems suggest that resource selection should vary across ungulate species. By combining GPS relocations with remotely sensed data on forage characteristics and surface water, we quantified the effect of body size and digestive system in determining movements of 30 populations of hindgut fermenters (equids) and ruminants across biomes. Selection for intermediate forage biomass was negatively related to body size, regardless of digestive system. Selection for proximity to surface water was stronger for equids relative to ruminants, regardless of body size. To be more generalisable, we suggest that the FMH explicitly incorporate contingencies in body size and digestive system, with small-bodied ruminants selecting more strongly for potential energy intake, and hindgut fermenters selecting more strongly for surface water.DATA AVAILABILITY STATEMENT : The dataset used in our analyses is available via Dryad repository (https://doi.org/10.5061/dryad.jsxksn09f) following a year-long embargo from publication of the manuscript. The coordinates associated with mountain zebra data are not provided in an effort to protect critically endangered black rhino (Diceros bicornis) locations. Interested researchers can contact the data owner (Minnesota Zoo) directly for inquiries.https://wileyonlinelibrary.com/journal/elehj2022Mammal Research InstituteZoology and Entomolog

Sous le ciel africain (des fluctuations climatiques à la régulation des populations, le rôle de l'eau de surface dans la dynamique spatio-temporelle d'une populations d'éléphants)

Les fluctuations climatiques et les variations associées de la disponibilité des ressources alimentaires sont des facteurs majeurs de la régulation des populations de grands mammifères herbivores. En milieu tropical l eau de surface est une ressource contraignant la distribution des individus, mais son rôle dans la régulation des populations a été peu étudié. Ce travail apporte une contribution à travers l étude de l effet des fluctuations climatiques sur la variabilité des ressources et sur la dynamique spatiale et temporelle de la population d éléphants d Afrique du parc national de Hwange, Zimbabwe. Après une phase de croissance suite à l arrêt en 1986 d abattages massifs de régulation, la population a fluctué de manière densité dépendante en interaction avec le climat. Si la zone d alimentation des individus est contrainte par la distance à l eau, l effet des fluctuations climatiques sur la disponibilité des ressources alimentaires de la population se fait principalement à travers une variation de la disponibilité en eau de surface. Lors d années sèches le nombre de points d eau actifs en saison sèche décroît, le nombre d éléphants à ces points d eau augmente, et les éléphants se distribuent alors de manière moins agrégée, suggérant un coût associé aux concentrations d éléphants aux points d eau. Sur le long terme la population n a augmenté qu aux points d eau les moins occupés. Les possibles mécanismes de compétition intraspécifique, et leurs applications aux autres grands herbivores, sont discutés.PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Multi-mode movement decisions across widely ranging behavioral processes

International audienceMovement of organisms plays a fundamental role in the evolution and diversity of life. Animals typically move at an irregular pace over time and space, alternating among movement states. Understanding movement decisions and developing mechanistic models of animal distribution dynamics can thus be contingent to adequate discrimination of behavioral phases. Existing methods to disentangle movement states typically require a follow-up analysis to identify state-dependent drivers of animal movement, which overlooks statistical uncertainty that comes with the state delineation process. Here, we developed population-level, multi-state step selection functions (HMM-SSF) that can identify simultaneously the different behavioral bouts and the specific underlying behavior-habitat relationship. Using simulated data and relocation data from mule deer ( Odocoileus hemionus ), plains bison ( Bison bison bison ) and plains zebra ( Equus quagga ), we illustrated the HMM-SSF robustness, versatility, and predictive ability for animals involved in distinct behavioral processes: foraging, migrating and avoiding a nearby predator. Individuals displayed different habitat selection pattern during the encamped and the travelling phase. Some landscape attributes switched from being selected to avoided, depending on the movement phase. We further showed that HMM-SSF can detect multi-modes of movement triggered by predators, with prey switching to the travelling phase when predators are in close vicinity. HMM-SSFs thus can be used to gain a mechanistic understanding of how animals use their environment in relation to the complex interplay between their needs to move, their knowledge of the environment and navigation capacity, their motion capacity and the external factors related to landscape heterogeneity

Cueing on distant conditions before migrating does not prevent false starts : a case study with African elephants

Migratory animals often use environmental cues to time their seasonal migrations. Local conditions may, however, differ from distant ones, and current conditions may poorly predict future conditions. This may be particularly true for early wet season conditions in tropical systems, as storms and associated rainfall events are generally not predictable at the scale of weeks or days and are heterogeneously distributed even at the scale of a few kilometres. How migratory animals cope with such challenges, and the consequences they may have, remain poorly known. We used time-to-event models based on GPS data from 19 African elephant herds from Hwange National Park (Zimbabwe) to study the effect of local and distant rainfall events on the elephants’ decision to initiate their wet season migration. Elephants relied more on distant rainfall events occurring along the future migration route than on local events when initiating their migration. Such ability to use distant cues does not, however, ensure an immediate migration success. In over 30% of the cases, the elephants came back to their dry season range, sometimes after having travelled > 80% of the expected migration distance. This happened particularly when there was little additional rain falling during the migration. All elephants successfully migrated later in the season. Our study improves the understanding of the migratory ecology of elephants. More broadly, it raises questions about the reliability of rainfall as a migratory cue in tropical systems, and shed light on one of its potential consequences, the poorly quantified phenomenon of migration false starts.Jeff Neu, the Wilderness Wildlife Trust, and the French ‘Agence Nationale de la Recherche’ through grants FEAR (ANR-08-BLAN-0022), SAVARD (ANR-11-CEPS-003), LANDTHIRST (ANR-16-CE02-0001-01). Work in Hwange National Park is generally supported by the ‘Zone Atelier’ program of the CNRS.https://link.springer.com/journal/4422023-03-13hj2023Mammal Research InstituteZoology and Entomolog