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20 results for “Large Mammalian Herbivores”
Body size modulates the extent of seasonal diet switching by large mammalian herbivores in Yellowstone National Park
<div> <p><span>Large mammalian herbivores vary their diets markedly with changes in resource availability yet the ways that seasonal changes in individual foraging behaviors scale up to reconfigure complex trophic networks are poorly understood. Two years of dietary DNA data enabled us to quantify fine-grained dietary variation within and among populations of five large herbivore species at Yellowstone National Park, revealing remarkably strong and significant correlations between body size and five key indicators of diet seasonality (R<sup>2</sup> = 0.71–0.80). Data from GPS collars implicated seasonal changes in each species' movement- and habitat-use patterns as potential determinants of foraging constraints and specializations that give rise to the strong allometry in diet composition. Bison and elk showed relatively muted seasonal changes compared to smaller species that exhibited stronger switches. Whereas the taxonomic breadth of individual diets contracted for all species in winter, larger species generally consumed a greater functional diversity of plants and thus maintained more unique dietary niches under resource limitations.</span></p> </div>
Functional traits—not nativeness—shape the effects of large mammalian herbivores on plant communities
<p>Large mammalian herbivores (megafauna) have experienced extinctions and declines since prehistory. Introduced megafauna have partly counteracted these losses yet are thought to have unusually negative effects compared to native megafauna. Using a meta-analysis of 3,995 plot-scale plant abundance and diversity responses from 221 studies, we found no evidence that megafauna impacts were shaped by nativeness, 'invasiveness', 'feralness', coevolutionary history, or functional and phylogenetic novelty. Nor was there evidence that introduced megafauna facilitate introduced plants more than native megafauna. Instead, we found strong evidence that functional traits shaped megafauna impacts, with larger-bodied and bulk-feeding megafauna promoting plant diversity. Our work suggests that trait-based ecology provides better insight into interactions between megafauna and plants than concepts of nativeness.</p>
Functional traits—not nativeness—shape the effects of large mammalian herbivores on plant communities
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Body size modulates the extent of seasonal diet switching by large mammalian herbivores in Yellowstone National Park
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Multiple dimensions of dietary diversity in large mammalian herbivores
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The burden of size and growth for the juveniles of large mammalian herbivores: structural and functional constraints in the feeding biology of juveniles relative to adults in red kangaroos, Osphranter rufus
<p>Juvenile mammals in their post weaning developmental stages face many challenges in transitioning to adulthood. Among large grazing species such as ruminant bovids and cervids an overarching challenge is acquiring and processing sufficient nutrients to survive and grow, with a gut that may not yet be fully developed. Marsupial kangaroos of Australia face similar challenges; they also digest vegetation by fermentation in a large foregut. In red kangaroos, Osphranter rufus (= Macropus rufus), the dominant species of Australia's arid interior, females may breed continuously; however, juvenile recruitment to the adult population is irregular and coincident with sporadic rainfall. As compared with adult females the nutritional requirements of juvenile O. rufus are high in relation to their body mass (BM), largely due to the cost of their rapid growth. We examined processes that juveniles have in their morphology, physiology and behaviours to meet their elevated nutritional needs, by comparing recently weaned juveniles of both sexes and adult female O. rufus in their desert habitat. Features studied include relative body sizes, relative dimensions and capacities of principal gut regions, the foregut, small intestine, caecum and large intestine with rectum. Also examined were digesta attributes and rates of digesta excretion. Additionally, the rates of change in skull parameters and dental characteristics to maturity were assessed. Field determinations of diet choice were made for both age classes. In juveniles the content masses of major gut structures were related to body mass (BM), as were those of adult females, i. e. ~BM1.0. In both age classes the digesta mass of the foreguts exceeded 75 % of the total digesta mass. Diets of both juvenile and adult O. rufus largely focused on grasses. Juveniles had higher rates of digesta excretion while foraging than adults. In addition, the foregut contents in juveniles occupies proportionally less of the total gut than in adult females. Together, the higher excretion rate and smaller relative foregut of juveniles suggests that they necessarily focus on forage that can be rapidly digested, such as young, green grasses or herbage. Comparison of the skulls of juveniles and adults revealed how this harvest can occur. Relative to BM juveniles had skulls of larger volume than adults. Additionally, during growth the skull lengthens proportionally faster than increasing. By weaning the dimensions of the incisor bite of juveniles neared those of adult females. The area of wear on premolars/molars increased only slowly relative to the development of incisors, further pointing to juveniles selecting more digestible forage than adults. The intermittent availability of such forage, principally young grasses, appears key to the significant recruitment into the O. rufus population in their arid habitat.</p>
Large mammalian herbivores affect arthropod food webs via changes in vegetation characteristics and microclimate
<ol> <li>Large mammalian herbivores are vital components of terrestrial ecosystems, influencing the plants they feed on, but also serving as ecosystem engineers that impact the occurrence and survival of many other organisms. Arthropods are the most abundant and diverse animal group on earth, filling all trophic levels in food webs and facilitating essential ecosystem services. However, the impacts of large herbivores on arthropod communities and the mechanisms via which these impacts are mediated are not fully understood. </li> <li>Here, we experimentally separated the mechanistic pathways whereby large herbivores affect arthropod food webs using a 24-year manipulative multi-site field experiment in the Netherlands. We analyzed the abundance, biomass, and community composition of arthropods in the plant canopy and on the soil surface, both in grazed sites or sites where large herbivores were excluded.</li> <li>We found that the presence of large herbivores resulted in considerable differences in vegetation properties and microclimate which influenced the abundance and biomass of arthropods to varying trophic levels. Large herbivore grazing enhanced the overall abundance and biomass of arthropod herbivores, pollinators, omnivores, and soil-dwelling predators, but reduced that of detritivores, scavengers, parasitoids, and canopy predators. Structural equation models revealed that different trophic groups are affected by grazing via different pathways. Specially, large herbivores facilitated herbivores via increasing plant quality and enhanced ground-dwelling predators via increasing plant diversity. In contrast, plant-dwelling predators were suppressed via decreased plant quantity, and parasitoids were mainly affected by changes in microclimate conditions. </li> <li> <em>Synthesis</em>. Our results show that large mammalian herbivores play a significant role in shaping grassland arthropod food webs and that these impacts were independently mediated by multiple aspects of vegetation properties, i.e., physical structure, plant diversity, standing crop biomass, and leaf nutrient content. Arthropods of different trophic groups responded differently to the large herbivores, and these functional group-specific responses in turn may have strong cascading effects on numerous ecosystem services.</li> </ol>
The burden of size and growth for the juveniles of large mammalian herbivores: structural and functional constraints in the feeding biology of juveniles relative to adults in red kangaroos, Osphranter rufus
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Large mammalian herbivores affect arthropod food webs via changes in vegetation characteristics and microclimate
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Large mammalian herbivores contribute to conspecific negative density dependence in a temperate forest
<p>1. The Janzen-Connell Hypothesis (JCH) predicts that density-responsive and host-specific natural enemies limit the population sizes of abundant species. Importantly, these interactions help to maintain local community diversity through time. While ample evidence exists for the demographic predictions of the JCH, it remains unclear which natural enemies drive these dynamics across different plant communities.</p> <p>2. While large mammalian herbivores are often assumed to lack the specialized diet needed to drive Janzen-Connell effects, they do show a degree of host-preference that could drive density-dependent plant demography. However, the potential role of large mammalian herbivores in Janzen-Connell interactions has only rarely been investigated.</p> <p>3. Using 204 seedling transects (1 x 10 m) at 51 sites across a 900-hectare forested reserve in southwestern Pennsylvania (USA), we examined the role that large mammals play in driving conspecific negative density dependence (CNDD) in temperate tree seedlings. Individual fences were erected around half of the transects (N=102) to exclude large mammals, and were paired with adjacent unfenced transects. Within transects, a total of ~15,000 individual seedlings were monitored over three growing seasons.</p> <p>4. Demographic neighborhood models were constructed to examine the influence of neighborhood composition and density on seedling survival and growth. An interaction term between conspecific neighbor density and fencing treatment was included to test the hypothesis that large herbivores cause CNDD.</p> <p>5. We found that seedling survival was influenced by both conspecific neighbor density and fencing. CNDD was strongest when large mammals were allowed access to seedlings, and these results were driven by two abundant taxa (Prunus serotina and Fraxinus spp). Despite evidence that large mammals mediate CNDD, we found no effect of fencing on rarified species richness or evenness in seedling transects during the study.</p> <p>6. Synthesis: Debate regarding the role of large herbivores in fostering the diversity and stability of forest communities continues. Our results indicate that large mammalian herbivores can cause CNDD in some temperate tree species, but whether they help to promote community diversity over time remains unclear. Further research is needed to assess the role of large mammalian herbivores in driving conspecific negative density dependence in plant communities.</p>
Data from: Mechanisms and implications of a type IV functional response for short-term intake rate of dry matter in large mammalian herbivores
1. The functional response (i.e. the relationship between consumers' intake rate and resource density) is central in plant-herbivore interactions. Its shape and the biological processes leading to it have significant implications for both foraging theory and ecology of grazing systems. 2. A type IV functional response (i.e. dome-shaped relationship) of short-term intake rate of dry matter (intake while grazing) has rarely been reported for large herbivores and the conditions that can lead to it are poorly understood. 3. We report a type IV functional response observed in heifers grazing monocultures of Cynodon sp. and Avena strigosa. The mechanisms and consequences of this type of functional response for grazed system dynamics are discussed. 4. Intake rate was higher at intermediate than at short or tall sward heights in both grass species. The type IV functional response resulted from changes in bite mass instead of a longer time needed to encounter and process bites. Thus, the decrease of intake rate of dry matter in tall swards is not explained by a shift from process 3 (potential bites are concentrated and apparent) to process 2 (potential bites are apparent but dispersed, Spalinger & Hobbs 1992). Bite mass was smaller in tall than in intermediate swards due to a reduction of bite volume possibly caused by the greater proportion of stem and sheath acting as a physical barrier to bite formation. 5. It is generally accepted that potential bites are abundant and apparent in most grassland and meadow systems, as they were in the present experiments. Therefore, a type IV response of intake rate not directly related to digestive constraints may determine the dynamics of intake and defoliation under a much larger set of conditions than previously thought. These results have implications for foraging theory and stability of grazing systems. For example, if animals prefer patches of intermediate stature that yield the highest intake rate, grazing should lead to the widely observed bimodal distribution of plant mass per unit area, even when tall patches are not of significantly lower digestive quality than the pasture average.
Data from: Indirect effects of a large mammalian herbivore on small mammal populations: context-dependent variation across habitat types, mammal species and seasons
Multiple consumer species frequently co-occur in the same landscape and, through effects on surrounding environments, can interact in direct and indirect ways. These interactions can vary in occurrence and importance, and focusing on this variation is critical for understanding the dynamics of interactions among consumers. Large mammalian herbivores are important engineers of ecosystems worldwide, have substantial impacts on vegetation and can indirectly affect small-mammal populations. However, the degree to which such indirect effects vary within the same system has received minimal attention. We used a 16-year-old exclosure experiment, stratified across a heterogeneous landscape, to evaluate the importance of context-dependent interactions between tule elk (Cervus canadensis nannodes) and small mammals [deer mice (Peromyscus maniculatus), meadow voles (Microtus californicus) and harvest mice (Reithrodontymys megalotis)] in a coastal grassland in California. Effects of elk on voles varied among habitats and seasons: in open grasslands, elk reduced vole numbers during fall 2013 but not summer 2014; in Lupinus-dominated grasslands, elk reduced vole numbers during summer 2014 but not fall 2013; and in Baccharis-dominated grasslands, elk had no effect on vole numbers in either season. Effects of elk on the two mice species also varied among habitats and seasons, but often in different ways from voles and each other. In fall 2013, elk decreased mice abundances in Lupinus-dominated grasslands, but not in Baccharis-dominated or open grasslands. In summer 2014, elk decreased the abundance of harvest mice consistently across habitat types. In contrast, elk increased deer-mice numbers in open grasslands but not other habitats. Within the same heterogenous study system, the influence of elk on small mammals was strongly context dependent, varying among habitats, mammal species and seasons. We hypothesize that such variability is common in nature, and that failure to consider it may yield inaccurate findings and limit our understanding of interactions among co-occurring consumers.
Data from: Indirect effects of a large mammalian herbivore on small mammal populations: context-dependent variation across habitat types, mammal species and seasons
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Data from: Mechanisms and implications of a type IV functional response for short-term intake rate of dry matter in large mammalian herbivores
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Large mammalian herbivores contribute to conspecific negative density dependence in a temperate forest
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Short-term plant-community responses to large mammalian herbivore exclusion in a rewilded Javan savanna
<p>Grassy biomes such as savannas are maintained by a suite of ecosystem processes from herbivory to rainfall and fire. Many studies have examined the impacts of large mammalian herbivores on herbaceous plant communities but few of these studies have been conducted in humid, fertile savannas. We present the findings of a short-term experiment that investigated the effects of herbivory in one such savanna. We erected large-herbivore exclosures in Alas Purwo National Park, Java where rainfall is high and fire is suppressed to test how herbivores impact plant community development during and in response to the wet season. When large mammalian herbivores were excluded, herbaceous plant communities in Alas Purwo were less grassy and less similar; diverging in their composition as the growing season progressed. Notably, weedy plant species (Imperata cylindrica and Senna cf. tora) appeared to benefit most from herbivore release. Our results suggest that heavy grazing pressure by native large herbivores controlled the composition of the herbaceous layer and prevented strong light competitors from becoming dominant. At the end of the growing season, herbivore exclusion plots showed higher beta diversity than plots exposed to herbivores. Our findings suggest that, at our high-rainfall site, large mammalian herbivores constrain the developmental trajectory of plant communities through the growing season.</p>
Revealing cryptic interactions between large mammalian herbivores and plant-dwelling arthropods via DNA metabarcoding
<p><span>In the past decade, it has become clear that omnivory, feeding on more than one trophic level, is important in natural and agricultural systems. Large mammalian herbivores (LMH) frequently encounter plant-dwelling arthropods (PDA) on their food plants. Yet, ingestion of PDA by LMH is only rarely addressed and the extent of this direct trophic interaction, especially at the PDA community level, remains unknown. Using a DNA metabarcoding analysis on feces of free-ranging cattle from a replicated field experiment of heavily and moderately grazed paddocks, we reveal that feeding cattle (incidentally) ingest an entire food-chain of PDA including herbivores, predators and parasites. Overall, 25 families of insects and 4 families of arachnids were ingested, a pattern that varied over the season, but not with grazing intensity. We identified the functional groups of PDA vulnerable to ingestion, such as sessile species and immature life stages. Most of the fecal samples (76%) contained sequences belonging to PDA, indicating that direct interactions are frequent. This study highlights the complex trophic connections between LMH and PDA. It may even be appropriate to consider LMH as omnivorous enemies of PDA. </span></p>
Short-term plant-community responses to large mammalian herbivore exclusion in a rewilded Javan savanna
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Revealing cryptic interactions between large mammalian herbivores and plant-dwelling arthropods via DNA metabarcoding
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Data for "Loss of grazing by large mammalian herbivores can destabilize the soil carbon pool"
<p>Data on soil-carbon and soil-nitrogen. </p> <p>D. G. T. Naidu, S. Roy, S. Bagchi, Loss of grazing by large mammalian herbivores can destabilize the soil carbon pool. <em>Proceedings of the National Academy of Sciences</em> <strong>in press</strong> (2022).</p> <p> </p>
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