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44 results for “Mammalian herbivores”
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: Experimental defaunation of terrestrial mammalian herbivores alters tropical rain forest understory diversity
It has been suggested that tropical defaunation may unleash community-wide cascading effects, leading to reductions in plant diversity. However, experimental evidence establishing cause–effect relationships thereof is poor. Through a 5 year exclosure experiment, we tested the hypothesis that mammalian defaunation affects tree seedling/sapling community dynamics leading to reductions in understorey plant diversity. We established plot triplets (n = 25) representing three defaunation contexts: terrestrial-mammal exclosure (TE), medium/large mammal exclosure (PE) and open access controls (C). Seedlings/saplings 30–100 cm tall were marked and identified within each of these plots and re-censused three times to record survival and recruitment. In the periods 2010–2011 and 2011–2013, survival was greater in PE than in C plots and recruitment was higher in TE plots than in C plots. Overall, seedling density increased by 61% in TE plots and 23% in PE plots, whereas it decreased by 5% in C plots. Common species highly consumed by mammals (e.g. Brosimum alicastrum and Ampelocera hottlei) increased in their abundance in TE plots. Rarefaction curves showed that species diversity decreased in TE plots from 2008 to 2013, whereas it remained similar for C plots. Given the prevalence of tropical defaunation, we posit this is an anthropogenic effect threatening the maintenance of tropical forest diversity.
Data from: Cascading effects of mammalian herbivores on ground-dwelling arthropods: variable responses across arthropod groups, habitats and years
1. Large mammalian herbivores are well known to shape the structure and function of ecosystems worldwide and these effects can in turn cascade through systems to indirectly influence other animal species. A wealth of studies have explored the effects of large mammals on arthropods, but to date they have reported such widely varying results that generalizations have been elusive. Three factors are likely drivers of this variability: the widely varying life-history characteristics of different arthropod groups, the highly variable landscapes that mammalian herbivores commonly inhabit, and temporal variation in environmental conditions. 2. Here, we use an 18-year-old exclosure experiment stratified across three distinct coastal prairie habitats in northern California to address the effects of a reintroduced mammalian herbivore, tule elk (Cervus canadensis nannodes) on the composition, richness, and abundance of ground-dwelling arthropods over two years with very different precipitation regimes. 3. We found that elk shifted the composition of arthropod communities, increasing the abundance of ants, beetles, spiders and mites, decreasing the abundance of woodlice and bristletails in some but not all habitats types, and having no effect on the abundance of bugs, crickets and springtails. Elk also increased richness and changed the composition of ant-genera and beetle morpho-species. Interestingly, the effects of elk on arthropod composition, richness and abundance varied little between years, despite very different precipitation levels, biomass accumulation, and thatch height. 4. Elk reduced shrub cover, aboveground herbaceous biomass, and thatch height and increased soil compaction, and these changes predicted the abundance and richness of arthropods, although taxonomic groups varied in their responses, presumably due to differences in environmental requirements. 5. Synthesis. Our research highlights the importance of using long-term experiments to assess the cascading effects of large herbivores on the composition of ground-dwelling arthropod communities and to identify the mechanisms that indirectly shape arthropod responses to herbivores among variable habitats and years in order to develop a greater understanding of the variable responses of arthropods to large mammalian herbivores.
Raw data from: Differentiating siliceous particulate matter in the diets of mammalian herbivores
<p class="MsoNormal"><span>1. Silica is crucial to terrestrial plant life and geochemical cycling on Earth. It is also implicated in the evolution of mammalian teeth, but there is debate over which type of siliceous particle has exerted the strongest selective pressure on tooth morphology.</span></p> <p class="MsoNormal"><span>2. </span><span>Debate revolves around the amorphous silica bodies (phytoliths) in plants and forms of siliceous grit––i.e., crystalline quartz (sand, soil, dust)––on plant surfaces. The problem is that conventional measures of silica often quantify both particle types simultaneously.</span></p> <p class="MsoNormal"><span>3. </span><span>Here we describe a protocol that relies on heavy-liquid flotation to separate and quantify siliceous particulate matter in the diets of herbivores. The method is reproducible and well-suited to detecting species- or population-level differences in silica ingestion. In addition, we detected meaningful variation within the digestive tracts of cows, an outcome that supports the premise of ruminal fluid 'washing' of siliceous grit.</span></p> <p class="MsoNormal"><span>4. </span><span>We used bootstrap resampling to estimate the sample sizes needed to compare species, populations, or individuals in space and time. We found that a minimum sample of 12 individuals is necessary if the species is a browser or as many as 55 if the species is a grazer, which are more variable. But a sample size of 20 is adequate for detecting statistical differences. We conclude by suggesting that our protocol for differentiating and quantifying silica holds promise for testing competing hypotheses on the evolution of dental traits.</span></p>
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: Experimental defaunation of terrestrial mammalian herbivores alters tropical rain forest understory diversity
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Data from: Ambient temperature influences tolerance to plant secondary compounds in a mammalian herbivore
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Data from: Cascading effects of mammalian herbivores on ground-dwelling arthropods: variable responses across arthropod groups, habitats and years
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Data from: Effects of mammalian herbivores and termites on performance of native and exotic plantation tree seedlings
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Data from: Food quality and quantity is more important in explaining foraging of an intermediate-sized mammalian herbivore than predation risk or competition
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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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Raw data from: Differentiating siliceous particulate matter in the diets of mammalian herbivores
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Data from: Nutrient availability controls the impact of mammalian herbivores on soil carbon and nitrogen pools in grasslands
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Data from: Mammalian herbivores affect leafhoppers associated with specific plant functional types at different timescales
1. Theory predicts that mammalian herbivores affect the quantity and quality of plants on which they preferentially feed in the short term. In the longer term, they can promote either preferred or less preferred plants, depending on whether preferred plants are adapted or sensitive to grazing. Less clear are the short- and long-term responses of herbivorous insects to mammalian herbivory, and how these responses depend on the specific plants or plant functional types on which the insects feed. 2. We progressively excluded large, medium, and small mammals for five growing seasons in two subalpine vegetation types with long-term differences in mammalian grazing intensity. Short-grass vegetation has a history of intensive grazing, while tall-grass vegetation has been grazed less intensively. We tested whether mammals altered the abundance and body size of leafhoppers specialized on specific plant functional types (grasses, sedges, forbs, or legumes/forbs), distinguishing between short-term (exclosures) and long-term (vegetation types) differences in mammalian grazing pressure. Furthermore, we assessed whether leafhoppers' responses were explained by changes in biomass or quality of the plant functional types on which they feed. 3. In the short term, mammal exclosures increased the abundance of grass- and forb-feeding leafhoppers via increases in the biomass of grasses and forbs, regardless of vegetation type. Both grasses and forbs are preferred food plants of mammals. In the long term, the biomass of sedges, which are less preferred by mammals, increased in the less intensively grazed tall-grass vegetation. This resulted in a higher abundance of sedge-feeding leafhoppers. The small size of these sedge feeders lowered the average leafhopper body size in the tall-grass vegetation. Plant nutritional quality did not explain any effects of exclusions or vegetation types. 4. Our results demonstrate that both short- and long-term effects of mammalian herbivores on the biomass of specific plant functional types caused concurrent changes in the abundance of specialized herbivorous insects, which scaled up to community-wide shifts in insect body size, a key life-history trait. A plant-functional-type approach can thus help to predict how overabundance or extinction of mammalian herbivores impacts on other components of the food web at various timescales.
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>
Data from: Mammalian herbivores affect leafhoppers associated with specific plant functional types at different timescales
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