Current theory predicts that plains zebra (Equus quagga) populations should be resource-limited. Long-term, detailed work in the Hwange ecosystem (Zimbabwe) on zebras and all their major predators provides empirical data to test this on a population that has been at a low density for at least 2 decades and is largely naturally regulated. Information on body condition is used as an indicator of resource use, and offtakes by the three major predators are estimated from a synthesis of data on densities and diets. This information leads to rejection of the expectations for resource limitation. Zebras provide a significant part of the diets of all the main predators and are important (11%) for the most abundant of these, spotted hyaenas (Crocuta crocuta). Using conservative values, we calculate that the three main predators, hyaenas, lions (Panthera leo), and leopards (Panthera pardus), kill some 17.5% of the zebra population. Given that this estimated offtake is of the same order of magnitude as maximum population growth (22.3% per year), we conclude that this population is likely to be limited by predation. Further work is needed to better understand the mechanisms by which the greater susceptibility of juveniles to predation in ungulates contributes to population limitation.

BackgroundNetwork theory is largely applied in real-world systems to assess landscape connectivity using empirical or theoretical networks. Empirical networks are usually built from discontinuous individual movement trajectories without knowing the effect of relocation frequency on the assessment of landscape connectivity while theoretical networks generally rely on simple movement rules. We investigated the combined effects of relocation sampling frequency and landscape fragmentation on the assessment of landscape connectivity using simulated trajectories and empirical high-resolution (1 Hz) trajectories of Alpine ibex (Capra ibex). We also quantified the capacity of commonly used theoretical networks to accurately predict landscape connectivity from multiple movement processes.MethodsWe simulated forager trajectories from continuous correlated biased random walks in simulated landscapes with three levels of landscape fragmentation. High-resolution ibex trajectories were reconstructed using GPS-enabled multi-sensor biologging data and the dead-reckoning technique. For both simulated and empirical trajectories, we generated spatial networks from regularly resampled trajectories and assessed changes in their topology and information loss depending on the resampling frequency and landscape fragmentation. We finally built commonly used theoretical networks in the same landscapes and compared their predictions to actual connectivity.ResultsWe demonstrated that an accurate assessment of landscape connectivity can be severely hampered (e.g., up to 66% of undetected visited patches and 29% of spurious links) when the relocation frequency is too coarse compared to the temporal dynamics of animal movement. However, the level of landscape fragmentation and underlying movement processes can both mitigate the effect of relocation sampling frequency. We also showed that network topologies emerging from different movement behaviours and a wide range of landscape fragmentation were complex, and that commonly used theoretical networks accurately predicted only 30-50% of landscape connectivity in such environments.ConclusionsVery high-resolution trajectories were generally necessary to accurately identify complex network topologies and avoid the generation of spurious information on landscape connectivity. New technologies providing such high-resolution datasets over long periods should thus grow in the movement ecology sphere. In addition, commonly used theoretical models should be applied with caution to the study of landscape connectivity in real-world systems as they did not perform well as predictive tools.

Six years after the expedition "Our Planet Reviewed - French Guiana 2015" in the Mitaraka massif, we present a synthesis of the taxonomic and faunistic results obtained from the analysis of the 108 published articles and the 10 600 observations that were databased and disseminated. In this relatively short period of time, 218 new species for French Guiana including 127 species new to science, and also four genera new to science have been published based on the expedition material. These are primarily insects, notably Coleoptera (98), Diptera (60), Lepidoptera (16) and Orthoptera (17). For the 2015 to 2020 period, approximately 13% of the descriptions of new animal species in French Guiana use material from the expedition. The 3100 species identified in Mitaraka represent nearly 15% of the 21 042 animal species known from French Guiana. The observation data from the expedition that are open access via the Global Biodiversity Information Facility (GBIF) portal render the Mitaraka massif the area with the greatest documented and disclosed entomological richness on the Guiana Shield. Feedback has enabled us to draw up some recommendations for inventories aimed at taxonomic discovery: assign a person per taxonomic group to mobilize, coordinate, and motivate the taxonomic experts involved; deploy a variety of collecting strategies, from interception and attractive traps to active search; invest heavily in the sample processing phase; get a journal editor engaged to dedicate issues to thematic publications on the survey; and disclose the survey data through GBIF data sets and/or datapapers.

Primary production can determine the outcome of management actions on ecosystem properties, thereby defining sustainable management. Yet human agencies commonly overlook spatio-temporal variations in productivity by recommending fixed resource extraction thresholds. We studied the influence of forest productivity on habitat disturbance levels that boreal caribou - a threatened, late-seral ungulate under top-down control - should be able to withstand. Based on 10 years of boreal caribou monitoring, we found that adult survival and recruitment to populations decreased with landscape disturbance, but increased with forest productivity. This benefit of productivity reflected the net outcome of an increase in resources for apparent competitors and predators of caribou, and a more rapid return to the safety of mature conifer forests. We estimated 3-fold differences in forest harvesting levels that caribou populations could withstand due to variations in forest productivity. The adjustment of ecosystem provisioning services to local forest productivity should provide strong conservation and socio-economic advantages.

Indicator species are widely used biodiversity surrogates that allow the assessment of biodiversity without the expensive and time-consuming construction of species inventories. The selection of indicator species often relies on species co-occurrence patterns, which may be altered by anthropogenic disturbance such as forest harvesting, imposing a unique challenge to their application in managed forest. Here, we studied boreal bird communities in natural forests originating from wildfire and managed forests originating from clearcutting. We aimed to (1) compare species co-occurrence patterns in natural and clearcut forest stands, (2) select indicator species based on species co-occurrence patterns to predict avian diversity, and (3) evaluate the predictive performance of indicator species under both natural and clearcutting disturbance regimes using the same training data set and an independent testing data set. We found that species co-occurrence patterns differ substantially between natural and clearcut stands, suggesting that forest harvesting alters species-environment relationships and/or interspecific interactions. Consequently, we selected different sets of species as indicators of avian diversity based on data from natural or clearcut stands. However, according to internal and external evaluation, selecting indicator species using data from both natural and clearcut stands produced surrogates that predicted avian diversity accurately and precisely in both types of forests. Our results suggest that, despite forest harvesting altering species co-occurrence patterns, a comprehensive understanding of species co-occurrence patterns across natural and managed forests can be used to develop robust biodiversity surrogates. Our study shows that small sets of indicator species can represent the biodiversity of a wide range of species in ecosystems undergoing anthropogenic disturbance, which has important implications for the application of biodiversity surrogates for conservation. (C) 2017 Elsevier B.V. All rights reserved.

When prey are time limited in their access to food, any trade-off involving time should ultimately affect their intake rate. In many herbivores, males and females experience different ecological pressures affecting their survival and reproduction because of differences in morphology, physiology and energy/nutrient requirements. If males and females have different vigilance strategies that affect their intake rates differently, they will suffer different foraging costs. This is particularly relevant in sexually monomorphic herbivores, where the two sexes have similar basal energy/nutrient requirements and risk of predation. We investigated how gender, reproductive status, age, group size, predation risk, and food biomass affected vigilance, intake rate, and their trade-off in a monomorphic species, the plains zebra (Equus quagga). Males were more vigilant than females, and lactating females were less vigilant than other females; the levels of vigilance were low (ca. 10 % of feeding time). The effects on time spent feeding, bite rates and intake rates were small and statistically not significant. Reproductive status did not affect the strength of the relationship between vigilance and intake rate, but intake rates increased with group size and, for adult females, were higher in tall grass. While gender and reproductive status were major drivers of vigilance, and group size and food biomass of the rate of food intake, males and females adjust their bite rates and food intake with vigilance in similar ways. Our results support the hypothesis that in monomorphic animals, males and females seem to make similar trade-offs (i.e. adjustments) between vigilance and intake rate.

In natural ecosystems, ungulate densities show strong temporal variations. The ecological processes driving these fluctuations are complex: food limitation and predation are both important and can interact. Survival rates are central to this debate, but data are sparse for tropical ecosystems. Here, we estimate age- and sex-specific survival rates for plains zebra in Hwange National Park, a nutrient-poor savanna with a high predator–prey ratio. We estimated survival from a detailed Capture-Mark-Recapture (CMR) monitoring based on 248 individual life histories, for the first time in an African grazer. We controlled for variations in detection probabilities among adult females, which resulted from their social structure. As expected, annual survival was low during the first year (0.441); increased in yearlings (0.560) and peaked at 0.795 and 0.847 in adult males and females respectively. The survival of adult females was lower during the dry season, which probably resulted from higher predation due to predictable movements of zebras to waterholes. Survival at all ages was low compared to ungulates without predators. The demographic model we constructed showed a declining trend (λ = 0.94), which was consistent with the data from road counts (\(\hat{\lambda }\) = 0.92). Life Table Response Experiment (LTRE) analyses using the Serengeti and Kruger populations as references showed that the main cause of this declining trend in the Hwange population was low survival in yearling and adult females; low foal survival also contributed. In this ecosystem, predation is likely to be the main ecological process causing low survival, and therefore a decline in the zebra population.

Predators influence prey populations not only through predation itself, but also indirectly through prompting changes in prey behaviour. The behavioural adjustments of prey to predation risk may carry nutritional costs, but this has seldom been studied in the wild in large mammals. Here, we studied the effects of an ambush predator, the African lion (Panthera leo), on the diet quality of plains zebras (Equus quagga) in Hwange National Park, Zimbabwe. We combined information on movements of both prey and predators, using GPS data, and measurements of faecal crude protein, an index of diet quality in the prey. Zebras which had been in close proximity to lions had a lower quality diet, showing that adjustments in behaviour when lions are within short distance carry nutritional costs. The ultimate fitness cost will depend on the frequency of predator-prey encounters and on whether bottom-up or top-down forces are more important in the prey population. Our finding is the first attempt to our knowledge to assess nutritionally mediated risk effects in a large mammalian prey species under the threat of an ambush predator, and brings support to the hypothesis that the behavioural effects of predation induce important risk effects on prey populations.

Animals are assumed to play a key role in ecosystem functioning through their effects on seed set, seed consumption, seed dispersal, and maintenance of plant communities. However, there are no studies investigating the consequences of animal scarcity on seed set, seed consumption and seed dispersal at large geographical scales. We exploited the unprecedented scarcity of pollinating bumblebees and butterflies in the vicinity of Chernobyl, Ukraine, linked to the effects of radiation on pollinator abundance, to test for effects of pollinator abundance on the ecosystem. There were considerably fewer pollinating insects in areas with high levels of radiation. Fruit trees and bushes (apple Malus domestica, pear Pyrus communis, rowan Sorbus aucuparia, wild rose Rosa rugosa, twistingwood Viburnum lantana, and European cranberry bush Viburnum opulus) that are all pollinated by insects produced fewer fruit in highly radioactively contaminated areas, partly linked to the local reduction in abundance of pollinators. This was the case even when controlling for the fact that fruit trees were generally smaller in more contaminated areas. Fruit-eating birds like thrushes and warblers that are known seed dispersers were less numerous in areas with lower fruit abundance, even after controlling for the effects of radiation, providing a direct link between radiation, pollinator abundance, fruit abundance and abundance of frugivores. Given that the Chernobyl disaster happened 25 years ago, one would predict reduced local recruitment of fruit trees if fruit set has been persistently depressed during that period; indeed, local recruitment was negatively related to the level of radiation and positively to the local level of fruit set. The patterns at the level of trees were replicated at the level of villages across the study site. This study provides the first large-scale study of the effects of a suppressed pollinator community on ecosystem functioning.

Mammalian reproductive rates vary among individuals for physiological and environmental reasons. This study aims to determine reproductive rates from an individually monitored population of wild Plains zebras Equus quagga, and to assess the sources of variability in inter-birth intervals. The animals were monitored, where possible, every six months from 2004 to 2011. Thirty nine intervals corresponding to 65 births in 26 mares were identified, using direct observations and faecal steroid monitoring. Mean foaling rate of the population is 0.74 foal/year, and comparable with the literature. There was no significant effect of mother's age, nor of the season of previous birih on the length of inter-birth intervals. Inter-birth interval was significantly longer when the first foal was a male. This finding indicates that additional costs of having a son may delay future reproduction and thus reduce the total number of offspring a mare can have during her lifetime. Individually-based data provide critical information on the determinants of reproductive rates, and are therefore a key to understanding the causes of variations in life-history traits. (c) 2011 Elsevier Masson SAS. All rights reserved.

La predation peut avoir des effets tres importants a la fois sur l’ecologie ainsi que sur l’evolution des communautes biologiques. Elle peut notamment etre une force selective favorisant des predateurs plus efficaces et des proies moins vulnerables. De plus, des etudes montrent que les predateurs agissent sur les proies, non seulement directement en les tuant, mais qu’ils peuvent egalement influencer le comportement des proies et induire des reponses physiologiques ou morphologiques. Pourtant, aujourd’hui, encore peu de choses sont connues sur comment les predateurs peuvent influencer les populations de proies, notamment chez les grands herbivores. Les etudes les plus detaillees sur les grands herbivores sont en effet situees dans l’hemisphere Nord, souvent dans des endroits ou ces herbivores n’ont plus de predateurs. Lors de cette these j’ai etudie une population de grands herbivores et l’impact de la predation sur celle-ci : la population de zebres des plaines (Equus quagga) dans le parc national de Hwange au Zimbabwe et son interaction avec les lions. J’ai etudie la dynamique de populations des zebres dans la zone d’etude, mais j’ai egalement travaille sur le zebre au niveau individuel, en tentant de mieux comprendre quels etaient les comportements anti-predateurs utilises par les zebres, ainsi que leurs couts potentiels, tout en m’interessant aux differences entre individus. Cette population de zebres est fortement impactee par la predation, de maniere a la fois directe et indirecte, et les comportements anti-predateurs mis en place par les zebres sont couteux.

Regulative endocrine mechanisms influence the reproductive behaviour and success of mammals, but they have been studied predominantly in domestic and captive animals. The study aims at describing the pattern of faecal 20-oxopregnane and oestrogen concentrations during pregnancy in wild plains zebra Equus quagga chapmani. Data were collected during wet and dry seasons 2007-2009. Enzyme Immunoassays were used to determine 20-oxopregnane and oestrogen concentrations in faecal samples (n=74) collected from individual mares (n=32) whose dates of foaling were known through long-term monitoring. Hormonal profiles were described with a General Additive Model (GAM: Hormone ∼ Days to Foaling). Faecal 20-oxopregnanes have a complex cycle during pregnancy (GAM, n=70, R(2)=0.616, p<0.001). From -250 days to foaling, faecal 20-oxopregnane concentrations were above the baseline levels found in non-pregnant mares, peaking in the last 50 days. Faecal oestrogen levels showed a clear peak in mid-pregnancy (GAM, n=62, R(2)=0.539, p<0.001). The sex of the foetus and season had no detectable effect on hormone concentrations during pregnancy. High levels (>200 ng/g DW) of faecal 20-oxopregnanes associated with high (>160 ng/g DW) faecal oestrogen levels indicate mid-pregnancy in c.90% of cases (16/17). High faecal 20-oxopregnanes (>200 ng/g DW) and low faecal oestrogen levels (<160 ng/g DW) indicate late pregnancy, again in c.90% of cases. Two faecal samples would allow the stage of pregnancy to be determined with confidence.