157 research outputs found
Spatial memory shapes density dependence in population dynamics
Most population dynamics studies assume that individuals use space
uniformly, and thus mix well spatially. In numerous species, however, individuals
do not move randomly, but use spatial memory to visit renewable
resource patches repeatedly. To understand the extent to which memorybased
foraging movement may affect density-dependent population
dynamics through its impact on competition, we developed a spatially explicit,
individual-based movement model where reproduction and death are
functions of foraging efficiency. We compared the dynamics of populations
of with- and without-memory individuals. We showed that memory-based
movement leads to a higher population size at equilibrium, to a higher
depletion of the environment, to a marked discrepancy between the global
(i.e. measured at the population level) and local (i.e. measured at the individual
level) intensities of competition, and to a nonlinear density dependence.
These results call for a deeper investigation of the impact of individual
movement strategies and cognitive abilities on population dynamics
Total and tropospheric ozone changes: observations and numerical modelling
A survey has been made of total and tropospheric ozone dynamics in the context of its impacts on climate, human health and ecosystems. Observation data on total ozone content (TOZ) in the atmosphere and relevant numerical modelling results have been discussed as well as similar information for tropospheric ozone, whose formation and changes are being determined by quite different causes. A
necessity has been emphasized to get more adequate global observational data on TOZ and tropospheric ozone (this is especially important in the latter case, because information on tropospheric ozone is far from being complete). Unsolved problems relevant to both total and tropospheric ozone have been briefly considered
Climate effects on prey vulnerability modify expectations of predator responses to short- and long-term climate fluctuations
Climate changes affect the distribution and abundance of organisms, often via changes
in species interactions. Most animals experience predation, and a number of models
have investigated how climate fluctuations can influence predatorâprey dynamics by
affecting prey abundance through changes in resource availability. However, field studies
have shown that prey vulnerability is a key feature determining the outcome of predatorâ
prey interactions, which also varies with climatic conditions, via changes in prey body
condition or in habitat characteristics (e.g. vegetation cover). In this theoretical work, we
explore, with large mammals of African savannas in mind, how the interplay between
climate-induced changes in prey abundance and climate-induced changes in prey
vulnerability affects the immediate and long-term responses of predator populations. We
account for prey body condition and habitat effects on prey vulnerability to predation.
We show that predictions on how predator abundance responds to climate fluctuations
differ depending on how climate influences prey vulnerability (habitat characteristics vs.
prey body condition). We discuss how species traits influence the relative importance of
the different sources of vulnerability. For example, our results suggest that populations
of cursorial predators (such as spotted hyaenas) are expected to fare better than
populations of ambush predators (such as African lions) in African ecosystems that
will be characterised by an aridification. This study highlights the importance of
understanding, and accounting for, the vulnerability factors associated to a given
predatorâprey pair, and improves our comprehension of predatorâprey relationships in a
changing climate.We thank C. Wilmers for providing the code of the published
model that serves as the basis of ours. In addition, this work
benefited from the computing cluster platform of the Centre
dâEcologie Fonctionnelle et Evolutive and from Biosphere, the
IFB cloud for life sciences. We thank Bruno Spataro and
Stéphane Delmotte from the LBBE computing services for
their help in using computing facilities. Finally, we thank two
reviewers for their fruitful comments on a previous draft of
this manuscript.This work was partly funded by the Agence Nationale
de la Recherche (project Landthirst ANR-16-CE02-0001-
01 and FUTURE-PRED ANR-18-CE02-0005-01) and was
further supported by a grant from the âMinistĂšre français de
lâEnseignement supĂ©rieur, de la Recherche et de lâInnovationâ
through the âEcole Doctorale E2M2â of âUniversitĂ© Claude
Bernard Lyon 1â.The Agence Nationale de la Recherche and a grant from the âMinistĂšre français de lâEnseignement supĂ©rieur, de la Recherche et de lâInnovationâ through the âEcole Doctorale E2M2â of âUniversitĂ© Claude Bernard Lyon 1â.https://www.frontiersin.org/journals/ecology-and-evolution#am2022Mammal Research InstituteZoology and Entomolog
Changes in feeding behavior and patch use by herbivores in response to the introduction of a new predator
Top-order carnivores are naturally returning, or are being reintroduced, in a number of places where they have previously been extirpated. To explore how prey species adjust their antipredator behavior in response to these predators, we measured giving-up densities (GUDs) in experimental feeding patches and time spent vigilant for greater kudu (Tragelaphus strepsiceros), sable antelope (Hippotragus niger), and warthogs (Phacochoerus africanus) before and after an introduction of wild dogs (Lycaon pictus). Before the introduction, the only predators in the system were cheetahs (Acinonyx jubatus). After the release, none of the prey species changed their microhabitat preference, in that they all preferred open grasslands to mixed tree and bush-clumps and bush-clumps. However, kudu and sable fed more intensively (i.e., achieved lower GUDs) and had lower vigilance in open grasslands, while reducing their feeding effort (i.e., higher GUDs) and increasing their vigilance near denser vegetation. When the wild dogs denned in the study site, potentially increasing contact with the prey species, the time kudu spent vigilant and their GUDs increased significantly across all patches, and continued to increase over time. In contrast, sable and warthogs stopped feeding from the experimental patches altogether during this period. The change in feeding intensity and vigilance levels by kudu likely reflected an additive antipredator response to both cheetahs and wild dogs, whereas sable and warthogs only responded to the increased risk from the wild dogs. Our results indicate that the addition of wild dogs influenced the foraging-safety trade-off for the 3 prey species, but that the antipredator behaviors utilized by these species to mitigate predation risk varied within the newly established 2-predator system.The National Research Foundation (grant number 77582 to AMS), UKZN, GreenMatter, and the Tswalu Foundation.http://jmammal.oxfordjournals.org2019-04-03hj2018Mammal 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 dwolfâ€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 (ÎŒQ) and patch size (ÎłQ) resulting in three level of patchiness: 1) low (ÎŒQ = -1.5, ÎłQ = 2), 2) intermediate (ÎŒQ = -0.5, ÎłQ = 2) and 3) high (ÎŒQ = 1, ÎłQ = 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 0â1 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 2005â2016.
We then separated the day in four periods: Night: 22:00â02:00, Dawn: 03:00â06:00, Day: 07:00â15:00 and Dusk: 16:00â21:00.
https://doi.org/10.1371/journal.pone.0272538.s008http://www.plosone.orgdm2022Mammal Research InstituteZoology and Entomolog
Partial migration links local surface-water management to large-scale elephant conservation in the world's largest transfrontier conservation area
Successful conservation of large mammals requires vast areas to maintain viable populations. This often requires to embrace large-scale approaches that extend beyond the borders of formally protected areas. However, the quality of the scientific knowledge about animal movement across large conservation areas vary, and could limit the effectiveness of conservation efforts. Here we used GPS tracking to conduct the first study of large-scale movements of African elephants (Loxodonta africana) in Hwange NP (Zimbabwe), which is an unfenced park part of the Kavango-Zambezi Transfrontier Conservation Area, the world's largest terrestrial conservation area. We show that some, but not all, elephants migrate seasonally, with wet- to dry-season movements linked to the provision of water in Hwange NP. The distance between the most distant locations of individual elephants reaches 260 km. In this partial migration system influenced by management practices, over 20% of the elephants have wet-season ranges established in Botswana, outside of protected areas in private or communal wildlife management areas. Our results call for the urgent drafting of a regional action plan, involving all stakeholders identified by our study and their neighbours, to predict and react to what would happen if water provision in Hwange NP was to suddenly change because of management practices or extreme climate change. Beyond this critical conservation issue for the world's largest elephant meta-population, our results also highlight the relevance of large-scale conservation areas combined with integrative planning involving national wildlife management institutions and the private and communal sector.Jeff Neu, the Wilderness Wildlife Trust, the grants FEAR (ANR-08-BLAN-0022), SAVARID (ANR-11-CEPS-003), LANDTHIRST (ANR-16-CE02-0001-01) of the French âAgence Nationale de la Rechercheâ and the Zone Atelier program of the CNRS.http://www.elsevier.com/locate/biocon2018-11-30hj2017Mammal Research InstituteZoology and Entomolog
InterâGroup Social Behavior, Contact Patterns and Risk for Pathogen Transmission in Cape Buffalo Populations
In social species, the transmission and maintenance of infectious diseases depends on the contact patterns between individuals within groups and on the interactions between groups. In southern Africa, the Cape buffalo (Syncerus caffer caffer) is a vector for many pathogens that can infect sympatric livestock. Although intra-group contact patterns of Cape buffalo have been relatively well described, how groups interact with each other and risks for pathogen transmission remain poorly understood. We identified and compared spatial behavior and contact patterns between neighboring groups of Cape buffalo under contrasting environments: within the seasonally flooded environment of the Okavango Delta in Botswana and the semi-arid environment of northern Kruger National Park in South Africa. We used telemetry data collected between 2007 and 2015 from 10 distinct groups. We estimated seasonal overlap and proximity between home ranges of pairwise neighboring groups, and we quantified seasonal contact patterns between these groups. We defined contact patterns within variable spatiotemporal windows compatible with the transmission of diseases carried by the Cape buffalo: bovine tuberculosis, brucellosis, and Rift Valley fever (mosquito-borne transmission). We examined the effects of habitat and distance to water on contact location. In both study populations, neighboring buffalo groups were highly spatially segregated in the dry and rainy seasons. Inter-group contact patterns were characterized by very few direct and short-term indirect (within 0â2 days) contacts, lasting on average 1âhour and 2âhours, respectively. Contact patterns were generally consistent across populations and seasons, suggesting species-specific behavior. In the drier study site, the probability of indirect and vector-borne contacts generally decreased during the dry season with increasing distance to water. In the seasonally flooded area, only the probability of vector-borne contact decreased with increasing distance to water. Our results highlight the importance of dry season water availability in influencing the dynamics of indirectly transmitted Cape buffalo pathogens but only in areas with low water availability. The results from this study have important implications for future modeling of pathogen dynamics in a single host, and the ecology and management of Cape buffalo at the landscape level
Behavioral responses of terrestrial mammals to COVID-19 lockdowns
COVID-19 lockdowns in early 2020 reduced human mobility, providing an opportunity to disentangle its effects on animals from those of landscape modifications. Using GPS data, we compared movements and road avoidance of 2300 terrestrial mammals (43 species) during the lockdowns to the same period in 2019. Individual responses were variable with no change in average movements or road avoidance behavior, likely due to variable lockdown conditions. However, under strict lockdowns 10-day 95th percentile displacements increased by 73%, suggesting increased landscape permeability. Animals' 1-hour 95th percentile displacements declined by 12% and animals were 36% closer to roads in areas of high human footprint, indicating reduced avoidance during lockdowns. Overall, lockdowns rapidly altered some spatial behaviors, highlighting variable but substantial impacts of human mobility on wildlife worldwide.acceptedVersio
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