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17 results for “megaherbivores”
Data from: Exotic megaherbivores as ecosystem engineers in Australian savannas: Do they facilitate predator movement?
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Habitats of Pleistocene megaherbivores reconstructed from the frozen fauna remains
The Late Pleistocene landscape in northern Eurasia and North America was inhabited by a specific megafaunal complex, which largely disappeared during the Pleistocene/Holocene transition. Vegetation changes are considered as one of the factors responsible for these extinctions, but the structure and composition of the Pleistocene vegetation are still poorly known. Here we complement previous studies by comparing the taxonomic composition of the plant remains found in the gastrointestinal tracts of the frozen carcasses of Pleistocene megaherbivores with the species composition of the current Siberian vegetation. We compiled a dataset of palaeobotanical records from frozen individuals of Pleistocene megaherbivores found in northern Siberia and Beringia and dated to the period from more than 50 kyr BP to 9 kyr BP. We also compiled a dataset of vegetation plots from several regions in Siberia. We analysed the similarity in taxonomic composition of plants between these two datasets using a novel method that accounts for variable taxonomic resolution in palaeobotanical data. For most megaherbivore individuals, plant remains in their gastrointestinal tracts corresponded to tundra, forest and mire vegetation, while they showed low similarity to steppe. This pattern was relatively constant over time, showing no remarkable differences between the Last Glacial Maximum and the periods before and afterwards. This suggests that during the Upper Pleistocene, a mosaic of mesic and wet vegetation types such as tundra with patches of forests and mires was common in northern Siberia and Beringia. In contrast, the steppe was rare to absent in the landscape or underused by the megaherbivores as a pasture since they found enough food in the widespread mesic and wet habitats with more productive vegetation.
Data from: The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms
<p><span>The Cretaceous–Paleogene (K-Pg) extinction of the non-avian dinosaurs (66 Ma) led to a 25 million year gap of megaherbivores (>1000 kg) before the evolution of megaherbivorous mammals in the Late Eocene (40 Ma). The botanical consequences of this 'Paleocene megaherbivore gap' (PMHG) remain poorly explored. We hypothesize that the absence of megaherbivores should result in changes in the diversification and trait evolution of associated plant lineages. We used phylogenetic time- and trait-dependent diversification models with palms (Arecaceae) and show that the PMHG was characterized by speciation slowdowns, decreased evolution of armature, and increased evolution of megafaunal (</span>≥<span>4cm) fruits. This suggests that the absence of browsing by megaherbivores during the PMHG may have led to a loss of defence traits, but absence of megaherbivorous seed dispersers did not lead to a loss of megafaunal fruits. Instead, increases in PMHG fruit sizes may be explained by Late Paleocene rising temperatures, rainforest expansion, and the subsequent radiation of seed dispersing birds and mammals. We show that the profound impact of the PMHG on plant diversification can be detected even with the overwriting of adaptations by the subsequent Late Eocene opening-up of megaherbivore-associated ecological opportunities. Our study provides a quantitative, comparative framework to assess </span>diversification and adaptation during one of the most enigmatic periods in angiosperm history.</p>
An underwater Serengeti: Seagrass-mediated effects on intake and cultivation grazing behavior of a marine megaherbivore
<p>Populations of green turtles (<em>Chelonia mydas</em>), a megaherbivore that consumes seagrasses via cultivation grazing, are recovering worldwide. Information on plant-mediated effects on herbivore foraging behavior is critical to understanding plant-herbivore interactions and sustainability of grazing as ecosystems continue to change. In a Caribbean seagrass ecosystem, we use stationary cameras and benthic surveys to evaluate effects of seagrass morphology and leaf nitrogen content on green turtle grazing behavior. Thalassia testudinum leaf morphology has significant effects on forage intake (mg dry mass [DM] min-1) for green turtles, whereas leaf nitrogen content has no effect. Intake increases in grazed areas with shorter leaves and higher leaf biomass concentration (mg DM cm-3), indicating more efficient foraging under these conditions. Bite rate (bites min-1) increases in grazed areas with short leaves, a result of reduced search time. Bite size (mg DM bite-1) increases in grazed areas with short but dense canopies, because a turtle crops more shoots with each bite. Increased foraging efficiency and reduced search time in grazed areas with high biomass concentrations collectively maximize intake. Ingested leaves are shorter than the mean height of all available leaves in grazed areas, indicating herbivore selection for shorter leaves. Our estimate for daily intake is 86.1 g DM d-1 per 33-kg turtle. Our study provides a novel contribution on the effects of plant-level cues on the grazing behavior of a marine megaherbivore, and how cultivation grazing behavior optimizes the green turtle foraging strategy by maximizing foraging efficiency and intake.</p>
Data from: Are crop fields pharmacies for megaherbivores? From ecophysiological studies of elephant (<em>Loxodonta cycotis</em>) crop raiders in Gabon
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Data from: The megaherbivore gap after the non-avian dinosaur extinctions modified trait evolution and diversification of tropical palms
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An underwater Serengeti: Seagrass-mediated effects on intake and cultivation grazing behavior of a marine megaherbivore
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Data from: Seagrass coastal protection services reduced by invasive species expansion and megaherbivore grazing
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Habitats of Pleistocene megaherbivores reconstructed from the frozen fauna remains
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Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species' traits
<p>The extinction of 80% of megaherbivore (>1,000 kg) species towards the end of the Pleistocene altered vegetation structure, fire dynamics, and nutrient cycling worldwide. Ecologists have proposed (re)introducing megaherbivores or their ecological analogues to restore lost ecosystem functions and reinforce extant but declining megaherbivore populations. However, the effects of megaherbivores on smaller herbivores are poorly understood.</p> <p>We used long-term exclusion experiments and multispecies hierarchical models fitted to dung counts to test 1) the effect of megaherbivore (elephant and giraffe) presence-absence on the occurrence (dung presence) and use intensity (dung-pile density) of mesoherbivores (2–1,000 kg), and 2) the extent to which the responses of each mesoherbivore species was predictable based on their traits (diet and shoulder height) and phylogenetic relatedness.</p> <p>Megaherbivores increased the predicted occurrence and use intensity of zebras but reduced the occurrence and use intensity of several other mesoherbivore species. The negative effect of megaherbivores on mesoherbivore occurrence was stronger for shorter species, regardless of diet or relatedness.</p> <p>Megaherbivores substantially reduced the expected total use intensity (i.e., cumulative dung density of all species) of mesoherbivores, but only minimally reduced the expected species richness (i.e., cumulative predicted occurrence probabilities of all species) of mesoherbivores (by <1 species).</p> <p>Simulated extirpation of megaherbivores altered use intensity by mesoherbivores, which should be considered during (re)introductions of megaherbivores or their ecological proxies. Species' traits (in this case shoulder height) may be more reliable predictors of mesoherbivores' responses to megaherbivores than phylogenetic relatedness, and may be useful for predicting responses of data-limited species.</p>
Contrasting selection pressure on body and weapon size in a polygynous megaherbivore
<p>Sexual size dimorphism (SSD) is a common morphological trait in ungulates, with polygyny considered the leading driver of larger male body mass and weapon size. However, not all polygynous species exhibit SSD, while molecular evidence has revealed a more complex relationship between paternity and mating system than originally predicted. SSD is, therefore, likely to be shaped by a range of social, ecological and physiological factors. We present the first definitive analysis of SSD in the common hippopotamus (Hippopotamus amphibius ) using a unique morphological dataset collected from 2994 aged individuals. The results confirm that hippos exhibit SSD, but the mean body mass differed by only 5% between the sexes, which is rather limited compared with many other polygynous ungulates. However, jaw and canine mass are significantly greater in males than females (44% and 81% heavier, respectively), highlighting the considerable selection pressure for acquiring larger weapons. A predominantly aquatic lifestyle coupled with the physiological limitations of their foregut fermenting morphology likely restricts body size differences between the sexes. Indeed, hippos appear to be a rare example among ungulates whereby sexual selection favours increased weapon size over body mass, underlining the important role that species-specific ecology and physiology have in shaping SSD.</p>
Data from: The functional and palaeoecological implications of tooth morphology and wear for the megaherbivorous dinosaurs from the Dinosaur Park Formation (upper Campanian) of Alberta, Canada
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Experimental evidence that effects of megaherbivores on mesoherbivore space use are influenced by species’ traits
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Megaherbivores suppress precipitation-driven plant irruptions in a tropical savanna
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Contrasting selection pressure on body and weapon size in a polygynous megaherbivore
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All data for: Megaherbivore impacts on ecosystem and Earth system functioning: The current state of the science
<p>Megaherbivores (adult body mass >1000 kg) are suggested to disproportionately shape ecosystem and Earth system functioning. We systematically reviewed the empirical basis for this general thesis and for the more specific hypotheses that (i) megaherbivores have disproportionately larger effects on Earth system functioning than their smaller counterparts, (ii) this is true for all extant megaherbivore species and (iii) their effects vary along environmental gradients. We furthermore explored possible biases in our understanding of megaherbivore impacts. We found that there are too few studies to quantitatively evaluate the general thesis or any of the hypotheses for all but the African savanna elephant. Following this finding, we performed a qualitative vote counting analysis. Our synthesis of this analysis suggests that megaherbivores can elicit strong impacts on e.g. vegetation structure, and biodiversity and all the elephant species promote seed dispersal. We were however unable to evaluate whether these effects are disproportionate to smaller large herbivores. Although environmental conditions can mediate megaherbivore impact, few studies quantified the effect of rainfall or soil fertility on megaherbivore impacts, precluding prediction of megaherbivore effects on the Earth system, particularly under future climates. Moreover, our review highlights major taxonomic, thematic and geographic biases in our understanding of megaherbivore effects. Most of the studies focused on African savanna elephant impacts on vegetation structure and biodiversity, with other megaherbivores and Earth system functions comparatively neglected. Studies were also biased towards semi-arid and relatively fertile systems, with the arid, high-rainfall and/or nutrient-poor parts of the megaherbivores' distribution ranges largely unrepresented. Our findings highlight that the empirical basis of our understanding of the ecological effects of extant megaherbivores is still limited for all species, except African savanna elephant, and that our current understanding is biased towards certain environmental and geographic areas. We further outline a detailed, urgently needed avenue for future research.</p>
All data for: Megaherbivore impacts on ecosystem and Earth system functioning: The current state of the science
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International Brain Laboratory public data
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OpenNeuro
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