Academic literature on the topic 'Herbivore pressure'
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Journal articles on the topic "Herbivore pressure"
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Bont, Zoe, Marc Pfander, Christelle A. M. Robert, Meret Huber, Erik H. Poelman, Ciska E. Raaijmakers, and Matthias Erb. "Adapted dandelions trade dispersal for germination upon root herbivore attack." Proceedings of the Royal Society B: Biological Sciences 287, no. 1921 (February 26, 2020): 20192930. http://dx.doi.org/10.1098/rspb.2019.2930.
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A plant's offspring may escape unfavourable local conditions through seed dispersal. Whether plants use this strategy to escape insect herbivores is not well understood. Here, we explore how different dandelion ( Taraxacum officinale agg.) populations, including diploid outcrossers and triploid apomicts, modify seed dispersal in response to root herbivore attack by their main root-feeding natural enemy, the larvae of the common cockchafer Melolontha melolontha. In a manipulative field experiment, root herbivore attack increased seed dispersal potential through a reduction in seed weight in populations that evolved under high root herbivore pressure, but not in populations that evolved under low pressure. This increase in dispersal potential was independent of plant cytotype, but associated with a reduction in germination rate, suggesting that adapted dandelions trade dispersal for establishment upon attack by root herbivores. Analysis of vegetative growth parameters suggested that the increased dispersal capacity was not the result of stress flowering. In summary, these results suggest that root herbivory selects for an induced increase in dispersal ability in response to herbivore attack. Induced seed dispersal may be a strategy that allows adapted plants to escape from herbivores.
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Potter, Arjun B., Muhammad Ali Imron, Satyawan Pudyatmoko, and Matthew C. Hutchinson. "Short-term plant-community responses to large mammalian herbivore exclusion in a rewilded Javan savanna." PLOS ONE 16, no. 7 (July 22, 2021): e0255056. http://dx.doi.org/10.1371/journal.pone.0255056.
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Grassy biomes such as savannas are maintained by an interacting suite of ecosystem processes from herbivory to rainfall to 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 a fertile, humid, and semi-managed savanna. We erected large-herbivore exclosures in Alas Purwo National Park, Java, Indonesia where rainfall is high and fire is suppressed to test how herbivores impact plant community development across the growing season. Where large mammalian herbivores were excluded, herbaceous plant communities contained more non-grasses and were less similar; diverging in their composition as the growing season progressed. Effects of herbivore exclusion on plant species richness, evenness, and biomass per quadrat were generally weak. Notably, however, two weedy plant species (one native, Imperata cylindrica and one introduced, Senna cf. tora) appeared to benefit most from herbivore release. Our results suggest that heavy grazing pressure by native large mammalian herbivores controlled the composition of the herbaceous plant community. Moreover, exclusion of large mammalian herbivores led to divergence in the plant species composition of exclosures; compositional dissimilarity between herbivore-exclusion plots was higher than between plots exposed to large mammalian herbivores. Our findings suggest that, at this high-rainfall site, large mammalian herbivores constrained the developmental trajectory of plant communities across the growing season.
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SCHMIDT, GEROLD, and GERHARD ZOTZ. "Herbivory in the epiphyte, Vriesea sanguinolenta Cogn. & Marchal (Bromeliaceae)." Journal of Tropical Ecology 16, no. 6 (November 2000): 829–39. http://dx.doi.org/10.1017/s0266467400001747.
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Although herbivory in ground-rooted flora is well documented, current knowledge of the herbivore pressure on vascular epiphytes remains mostly anecdotal. Here, we present the results of a 3-year study on the herbivory in a population of the epiphytic bromeliad Vriesea sanguinolenta. In different years, 26–61% of all epiphytes showed traces of herbivore attack, while up to 4.4% of the entire leaf area of the epiphyte population was consumed annually. The recorded levels of damage to photosynthetic tissue, mostly caused by the larvae of Napaea eucharilla (Riodinidae, Lepidoptera), indicate that vascular epiphytes may be regularly and sometimes even lethally attacked by insect herbivores. The level of damage is comparable to ground-rooted tropical flora, which certainly does not support the prevalent notion of low and negligible levels of herbivory in vascular epiphytes.
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Moreira, Xoaquín, Luis Abdala-Roberts, Hans Henrik Bruun, Felisa Covelo, Pieter De Frenne, Andrea Galmán, Álvaro Gaytán, et al. "Latitudinal variation in seed predation correlates with latitudinal variation in seed defensive and nutritional traits in a widespread oak species." Annals of Botany 125, no. 6 (December 20, 2019): 881–90. http://dx.doi.org/10.1093/aob/mcz207.
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Abstract Background and Aims Classic theory on geographical gradients in plant–herbivore interactions assumes that herbivore pressure and plant defences increase towards warmer and more stable climates found at lower latitudes. However, the generality of these expectations has been recently called into question by conflicting empirical evidence. One possible explanation for this ambiguity is that most studies have reported on patterns of either herbivory or plant defences whereas few have measured both, thus preventing a full understanding of the implications of observed patterns for plant–herbivore interactions. In addition, studies have typically not measured climatic factors affecting plant–herbivore interactions, despite their expected influence on plant and herbivore traits. Methods Here we tested for latitudinal variation in insect seed predation and seed traits putatively associated with insect attack across 36 Quercus robur populations distributed along a 20° latitudinal gradient. We then further investigated the associations between climatic factors, seed traits and seed predation to test for climate-based mechanisms of latitudinal variation in seed predation. Key Results We found strong but contrasting latitudinal clines in seed predation and seed traits, whereby seed predation increased whereas seed phenolics and phosphorus decreased towards lower latitudes. We also found a strong direct association between temperature and seed predation, with the latter increasing towards warmer climates. In addition, temperature was negatively associated with seed traits, with populations at warmer sites having lower levels of total phenolics and phosphorus. In turn, these negative associations between temperature and seed traits led to a positive indirect association between temperature and seed predation. Conclusions These results help unravel how plant–herbivore interactions play out along latitudinal gradients and expose the role of climate in driving these outcomes through its dual effects on plant defences and herbivores. Accordingly, this emphasizes the need to account for abiotic variation while testing concurrently for latitudinal variation in plant traits and herbivore pressure.
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Frederickson, Megan E., and Deborah M. Gordon. "The devil to pay: a cost of mutualism with Myrmelachista schumanni ants in ‘devil's gardens’ is increased herbivory on Duroia hirsuta trees." Proceedings of the Royal Society B: Biological Sciences 274, no. 1613 (February 13, 2007): 1117–23. http://dx.doi.org/10.1098/rspb.2006.0415.
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‘Devil's gardens’ are nearly pure stands of the myrmecophyte, Duroia hirsuta , that occur in Amazonian rainforests. Devil's gardens are created by Myrmelachista schumanni ants, which nest in D. hirsuta trees and kill other plants using formic acid as an herbicide. Here, we show that this ant–plant mutualism has an associated cost; by making devil's gardens, M. schumanni increases herbivory on D. hirsuta. We measured standing leaf herbivory on D. hirsuta trees and found that they sustain higher herbivory inside than outside devil's gardens. We also measured the rate of herbivory on nursery-grown D. hirsuta saplings planted inside and outside devil's gardens in ant-exclusion and control treatments. We found that when we excluded ants, herbivory on D. hirsuta was higher inside than outside devil's gardens. These results suggest that devil's gardens are a concentrated resource for herbivores. Myrmelachista schumanni workers defend D. hirsuta against herbivores, but do not fully counterbalance the high herbivore pressure in devil's gardens. We suggest that high herbivory may limit the spread of devil's gardens, possibly explaining why devil's gardens do not overrun Amazonian rainforests.
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Guignard, Maïté S., Michael J. Crawley, Dasha Kovalenko, Richard A. Nichols, Mark Trimmer, Andrew R. Leitch, and Ilia J. Leitch. "Interactions between plant genome size, nutrients and herbivory by rabbits, molluscs and insects on a temperate grassland." Proceedings of the Royal Society B: Biological Sciences 286, no. 1899 (March 20, 2019): 20182619. http://dx.doi.org/10.1098/rspb.2018.2619.
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Angiosperm genome sizes (GS) vary ca 2400-fold. Recent research has shown that GS influences plant abundance, and plant competition. There are also tantalizing reports that herbivores may select plants as food dependent on their GS. To test the hypothesis that GS plays a role in shaping plant communities under herbivore pressure, we exploit a grassland experiment that has experimentally excluded herbivores and applied nutrient over 8 years. Using phylogenetically informed statistical models and path analyses, we show that under rabbit grazing, plant species with small GS generated the most biomass. By contrast, on mollusc and insect-grazed plots, it was the plant species with larger GS that increased in biomass. GS was also shown to influence plant community properties (e.g. competitive strategy, total biomass) although the impact varied between different herbivore guilds (i.e. rabbits versus invertebrates) and nutrient inputs. Overall, we demonstrate that GS plays a role in influencing plant–herbivore interactions, and suggest potential reasons for this response, which include the impact of GS on a plant's response to different herbivore guilds, and on a plant's nutrient quality. The inclusion of GS in ecological models has the potential to expand our understanding of plant productivity and community ecology under nutrient and herbivore stress.
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Miranda, María, Ignacio Cristóbal, Leticia Díaz, Marisa Sicilia, Eduarda Molina-Alcaide, Jordi Bartolomé, Yolanda Fierro, and Jorge Cassinello. "Ecological effects of game management: does supplemental feeding affect herbivory pressure on native vegetation?" Wildlife Research 42, no. 4 (2015): 353. http://dx.doi.org/10.1071/wr15025.
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Context Supplemental feeding of large mammalian herbivores is a common management tool mainly aimed at promoting healthy populations and at increasing productivity and trophy sizes. Such management measure may indirectly affect herbivore effects on plant communities through altered foraging patterns. The quantification of the ecological effects of large herbivore management is important for designing holistic management and conservation programs. Aims Here we aimed at quantifying the ecological effects of supplemental feeding of Iberian red deer, Cervus elaphus hispanicus, on the composition of and on the browsing effects on Mediterranean woody plant community. Methods An experiment was set up in a hunting rangeland located in central Spain, where female deer were kept in enclosures with either exclusive access to natural forages or with additional ad libitum access to a nutritionally rich concentrate. The experiment also included a control area where deer were absent. Key results We observed significant differences in browsing impacts among the supplemented, non-supplemented and control areas, and such effect varied for the different plant species. Plant species which nutritional content complemented that of fodder were more highly consumed, for instance, Erica spp., which digestible fibre content is higher and N content lower than that of provided fodder. The presence of deer and the concentrate supplied, instead, did not influence the relative abundances of shrub species. Conclusions Artificial supplemental feeding provided to ungulates led to increased browsing on plant species which nutritional composition complemented that of the supplement provided. Implications So as to alleviate herbivory impact on all shrubs, we suggest that composition of supplemental feeding should adjust both to the natural forage availability and quality and to ungulate requirements across seasons.
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Barbosa, BC, R. Fagundes, LF Silva, JFV Tofoli, AM Santos, BYP Imai, GG Gomes, MM Hermidorff, and SP Ribeiro. "Evidences that human disturbance simplify the ant fauna associated a Stachytarpheta glabra Cham. (Verbenaceae) compromising the benefits of ant-plant mutualism." Brazilian Journal of Biology 75, no. 1 (March 2015): 58–68. http://dx.doi.org/10.1590/1519-6984.07213.
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Interaction among species, like ants and plants through extrafloral nectaries (EFNs), are important components of ecological communities’ evolution. However, the effect of human disturbance on such specific interactions and its ecological consequences is poorly understood. This study evaluated the outcomes of mutualism between ants and the EFN-bearing plant Stachytarpheta glabra under anthropogenic disturbance. We compared the arthropod fauna composition between two groups of twenty plant individuals, one in an area disturbed by human activities and one in a preserved area. We also check the plant investment in herbivory defense and the consequential leaf damage by herbivore. Our results indicate that such disturbances cause simplification of the associated fauna and lack of proper ant mutualist. This led to four times more herbivory on plants of disturbed areas, despite the equal amount of EFN and ant visitors and low abundance of herbivores. The high pressure of herbivory may difficult the re-establishment of S. glabra, an important pioneer species in ferruginous fields, therefore it may affect resilience of this fragile ecological community.
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Milchunas, D. G. "Plant community dynamics in shortgrass steppe with grazing relaxation and imposition by large and small herbivores." Israel Journal of Ecology and Evolution 57, no. 1-2 (May 6, 2011): 23–41. http://dx.doi.org/10.1560/ijee.57.1-2.23.
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Semiarid rangelands often respond slowly to rest/relaxation of grazing pressure by large herbivores, and the effects of grazing are most often inferred from this direction of study because the imposition of grazing onto previous ungrazed/lightly grazed areas occurred prior to the age of scientific studies. These rangelands host a diversity of small and large herbivores, but grazing studies most often concern effects of the large generalists. Here, the effects of herbivore body size on plant species richness and dominant species, and imposition and relaxation of grazing by large herbivores were studied by opening half of exclosures established in 1939 and building new exclosures to large herbivores, and to small-plus-large herbivores. Plant richness using sensitive species-area sampling was studied in a dry and a wet year, about 62 years after initiating the long-term experiment and about 6-10 years after initiating the altered designs. Convergence of the newly opened to large herbivore grazing treatment to the long-term grazed treatment occurred within 10 years, but convergence of the newly excluded to large herbivore treatment to the long-term excluded treatment had only partly occurred. This indicated that recovery from grazing is slow relative to imposition of grazing by large herbivores, but effects of the additional exclusion of small-plus-large herbivores occurred relatively rapidly. These results were mirrored by trajectories of convergence of the dominant species, and this is discussed with respect to implications for state-and-transition models. Short-term exclusion of small-plus-large herbivores resulted in greater richness than even long-term exclusion of only large herbivores, even though quantities consumed by small herbivores are much less than by large. Grazing effects on plant richness were large in the wet year, but the very dry year suppressed richness on all treatments. When sampling effort and area are the same, the numbers and attributes of species unique to a treatment are indicators of rareness of the richness and traits selected for by the treatment. More unique species were sampled in the small-plus-large herbivore exclosures when comparing body size, and the long-term large herbivore exclosures when comparing time of exclosure. Unique species encountered during sampling the ungrazed treatments were generally forbs, exotic and/or weedy invasive species, and often tall, annual species.
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Buckley, James, Foteini G. Pashalidou, Martin C. Fischer, Alex Widmer, Mark C. Mescher, and Consuelo M. De Moraes. "Divergence in Glucosinolate Profiles between High- and Low-Elevation Populations of Arabidopsis halleri Correspond to Variation in Field Herbivory and Herbivore Behavioral Preferences." International Journal of Molecular Sciences 20, no. 1 (January 5, 2019): 174. http://dx.doi.org/10.3390/ijms20010174.
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Variation in local herbivore pressure along elevation gradients is predicted to drive variation in plant defense traits. Yet, the extent of intraspecific variation in defense investment along elevation gradients, and its effects on both herbivore preference and performance, remain relatively unexplored. Using populations of Arabidopsis halleri (Brassicaceae) occurring at different elevations in the Alps, we tested for associations between elevation, herbivore damage in the field, and constitutive chemical defense traits (glucosinolates) assayed under common-garden conditions. Additionally, we examined the feeding preferences and performance of a specialist herbivore, the butterfly Pieris brassicae, on plants from different elevations in the Alps. Although we found no effect of elevation on the overall levels of constitutive glucosinolates in leaves, relative amounts of indole glucosinolates increased significantly with elevation and were negatively correlated with herbivore damage in the field. In oviposition preference assays, P. brassicae females laid fewer eggs on plants from high-elevation populations, although larval performance was similar on populations from different elevations. Taken together, these results support the prediction that species distributed along elevation gradients exhibit genetic variation in chemical defenses, which can have consequences for interactions with herbivores in the field.
Dissertations / Theses on the topic "Herbivore pressure"
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Parsons, Malcolm. "Herbivore pressure of reindeer, rodents and invertebrates in the Fennoscandian tundra: a comparison of three methods." Thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-125917.
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Estimating herbivore density is an important part of understanding their impact on vegetation. Many studies have been carried out on the impact of reindeer and other herbivores on arctic and sub-arctic vegetation, but they are difficult to compare as they typically use different methods to estimate herbivore activities. The aim of this study was to compare three methods that were based on the recent International Tundra Experiment herbivory protocol to measure the activities of three herbivore groups: reindeer, rodents and invertebrates. The robustness of the methods themselves was then evaluated. Fieldwork was carried out at 12 sites in the Fennoscandian mountain area, with controls inside reindeer exclosures. The results showed that the methods were the most robust when measuring reindeer activities. The reindeer measurements were also well correlated with a reindeer-density estimate calculated from official reindeer population data. This study recommends considering the use of photographs to increase the time-efficiency of pellet-counts. The rodent activity estimates were good, but the patterns inside exclosures differed to the patterns outside exclosures. The results for invertebrates were deemed to be less reliable as the measurements for one method were not recorded at an appropriate scale. In conclusion, the findings of this study will help improve the comparability of future studies on the impact of reindeer herbivory and other herbivores, and gives suggestions for more accurate ways of measuring herbivore pressure in arctic and sub-arctic vegetation.
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Boalt, Elin. "Ecology and evolution of tolerance in two cruciferous species." Doctoral thesis, Stockholm : Department of Botany, Stockholm University, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8139.
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Ferreira, Camilo Moitinho. "Padrões espaciais e temporais na predação do coral construtor Montastrea Cavernosa e de algas calcarias incrustantes por budiões (Pisces: Labridae: Scarinae e Sparisomatinae) no Banco dos Abrolhos, BA." Universidade Estadual da Paraíba, 2012. http://tede.bc.uepb.edu.br/tede/jspui/handle/tede/1708.
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The benefits of herbivory by parrotfishes in reef systems have been relatively well studied. However, in recent years some studies have put these benefits in check. Although they feed preferentially on algae may also consume the parrotfish and coral encrusting coralline algae (ACIs), thus compromising the growth and reproduction of corals and facilitating the colonization of open spaces by non-builders. The study presented here aims to describe the spatial and temporal dynamics in density and biomass of parrotfish in the Abrolhos Bank and its relation to predation of coral Montastrea carvenosa and ACIs. The parrotfish and the two functional groups (scrapers and excavators) showed distinct spatial patterns. There was no temporal variation in the density and biomass of parrotfish. This same pattern was observed for coverage area and relative preyed on M. cavernosa and ACIs. Encrusting coralline algae covered by epilithic algae (ACICS) were the only organisms that are influenced by density and biomass of scrapers excavators. It registered a strong positive influence of biomass Sc. trispinosus in coverage without encrusting coralline algae coverage epilithic algae (ACISs) and M. cavernosa. The absence of temporal variation in the area preyed on M. cavernosa may be due to (1) low intensity of predation to detect temporal patterns clear, (2) low density and biomass of the top predator of coral, Sp.amplum, and (3) low preference for this coral parrotfish. In addition, predation on ACICS is probably beneficial for the reef system, since this substrate is competition areas between epilithic IACs and algae. Our results indicate that the parrotfish play beneficial effect on corals, stressing the need for conservation of this threatened group of overfishing.
Os benefícios proporcionados pela herbivoria dos budiões em sistemas recifais têm sido relativamente bem estudados. Entretanto, nos últimos anos, alguns estudos colocaram tais benefícios em cheque. Apesar de se alimentarem preferencialmente de algas os budiões podem também consumir corais e algas calcárias incrustantes (ACIs), comprometendo assim o crescimento e reprodução dos corais e facilitando a colonização dos espaços abertos por organismos não construtores. O estudo apresentado aqui visa descrever a dinâmica espacial e temporal na densidade e biomassa de budiões no Banco dos Abrolhos e sua relação com a predação do coral Montastrea carvenosa e ACIs. Os budiões e os dois grupos funcionais (raspadores e escavadores) apresentaram padrões espaciais distintos. Não houve variação temporal na densidade e biomassa de budiões. Esse mesmo padrão foi observado para cobertura relativa e área relativa predada de M. cavernosa e ACIs. Algas calcárias incrustantes recobertas por algas epilíticas (ACICs) foram os únicos organismos que sofreram influência da densidade de raspadores e biomassa de escavadores. Foi registrada uma forte influência positiva da biomassa de Sc. trispinosus na cobertura de algas calcárias incrustantes sem cobertura de algas epilíticas (ACISs) e de M. cavernosa. A ausência de variação temporal na área relativa predada de M. cavernosa pode ter ocorrido por (1) baixa intensidade de predação para detecção de padrões temporais nítidos; (2) baixa densidade e biomassa do principal predador desse coral, Sp.amplum; e (3) baixa preferência dos budiões por este coral. Além disso, a predação em ACICs provavelmente é benéfica para o sistema recifal, pois este substrato representa áreas de competição entre ACIs e algas epilíticas. Os resultados aqui obtidos indicam que os budiões desempenham efeito benéfico sobre os corais, salientando a necessidade de conservação deste grupo ameaçado de sobrepesca.
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Nielson, Patrice Alexa. "Variable Palatability of Quaking Aspen for Large Ungulate Herbivores." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2589.
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Aspen is a key resource in the Rocky Mountain Region for wildlife forage and habitat, lumber products, scenery, and plays important roles in fire ecology and hydrological processes. There is evidence of aspen decline over much of the Intermountain West for approximately 100 years. In Dixie and Fishlake National Forests, UT, aspen distribution has decreased by nearly half. Causes of this decline are not well understood, although wildlife browsing by ungulates has been implicated as playing a major role. The objective of this research was to examine what soil or plant factors might be involved in wildlife browse choice in aspen. Twenty-two pairs of moderately and intensively browsed sites were studied to identify factors related to browse preferences over two field seasons. In the summer of 2008, sites were sampled in June, July, and August, and in the summer of 2009 sites were sampled in August only. Soils were analyzed for pH, EC, total nitrogen and carbon, and mineral nutrients. Leaf tissue samples were analyzed for defense chemical (tannin and phenolic glycoside) concentrations, mineral nutrients (via acid digestion), acid-detergent fiber, water content, carbon:nitrogen ratio, and non-structural carbohydrate (sugar) concentration. No significant difference in phenolic glycoside concentrations between moderately and intensively browsed sites was found. Tannins were highest in sites with intensive levels of browsing. Iron was significantly higher and zinc lower in intensively than moderately browsed sites. Leaf moisture was also significantly lower in intensively browsed sites. In the absence of differences in phenolic glycosides, ungulates may be selecting browse sites based on iron requirements. Seasonal changes in the studied factors could be identified in 2008. Over the course of the summer, we found significant decreases in nitrogen, phosphorus, potassium, sulfur, zinc, iron, copper, phenolic glycosides, and moisture concentration. Seasonal increases in calcium, sodium, tannins, sugars, acid-detergent fiber, and carbon:nitrogen ratios were observed. The need for large ungulates to obtain specific nutrients may indicate that aspen is in higher demand as a forage at different times of the year, particularly in areas with forages low in these nutrients. Our data suggest that aspen high in iron may be at risk since other factors explaining browsing choice were not significantly different in our study. This information can help identify clones that are at risk and direct resources where and when they are needed most.
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Boulanger, Vincent. "Pression d'herbivorie et dynamique des communautés végétales : Influence à court et moyen termes des populations de cervidés sur la diversité des communautés végétales en forêt." Phd thesis, Nancy 1, 2010. http://tel.archives-ouvertes.fr/tel-00518080.
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Les cervidés, animaux mobiles et herbivores, peuvent influencer les distributions, assemblages et dynamiques d'espèces végétales. L'objectif de cette thèse est d'évaluer le rôle joué par les cervidés sur la composition, stratification et dynamique de la végétation forestière. Le ré-échantillonnage de relevés couplant composition et abroutissement de la flore, implantés en 1976 en Forêt d'Arc-en-Barrois (52) a permis d'identifier (i) des espèces ligneuses préférées (Cornus sp., Rosa arvensis ) ou au contraire évitées par les cervidés qui sélectionnent les espèces arbustives et à bois dense et (ii) le niveau trophique et la pression d'abroutissement comme gradients structurant la végétation et déterminant les dynamiques des espèces et des communautés. Nous analysons plus précisément le rôle des cervidés dans la progression spectaculaire de Cynoglossum germanicum, espèce rare, épizoochore et toxique.A partir d'un réseau national d'enclos/exclos suivis sur 10 ans, nous montrons que les cervidés limitent la croissance des arbustes et des espèces compétitrices, ce qui profite à la richesse spécifique de la strate herbacée. La valeur écologique et patrimoniale des espèces en progression est discutée. A l'aide de données de chasse, nous tentons d'isoler les rôles des différentes espèces d'ongulés dans ces dynamiques.Ces résultats exposent la complexité et la diversité des effets des cervidés sur la végétation forestière. Enfin, ce travail met l'accent sur la nécessité des suivis temporels intégrant toutes les composantes de l'écosystème forestier pour mieux appréhender les changements en cours.
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Granberg, Tynan. "Variation of Treeline Mountain Birch Establishment Under Herbivory Pressure." Thesis, 2012. http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11774.
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Alpine and arctic treelines have been viewed as sensitive indicators of global climate change. While many treelines have advanced under warmer climate regimes in recent decades, the response has not been uniform. Some of this variability may be attributable to the impacts of herbivores. This study investigates the interacting effects of herbivory, climate, and understory vegetation on mountain birch establishment at treeline in the Scandes Mountains of northern Sweden. An extensive dendrochronological database was created to determine periods of establishment, which were then regressed against reindeer (Rangifer tarandus, L.) population data and historical climate data. Vegetation classifications were also created and analyzed to determine if establishment patterns vary by understory vegetation type. I have tested the hypothesis that tree establishment varies within the treeline ecotone and that high reindeer stocking levels negatively impact establishment.
Weakly positive responses to herbivory were observed in patterns of tree establishment at treeline. This indicates that reindeer may modestly promote treeline advance at low densities, contradicting some previous research, but many of the results were not statistically significant. The climate variables found to have significant relationships with establishment were inconsistent across herding districts and aggregation levels. No connections between vegetation assemblages and establishment or between vegetation assemblages and reindeer use were observed.
Book chapters on the topic "Herbivore pressure"
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Parker, John D., John L. Devaney, and Nathan P. Lemoine. "Biotic resistance to plant invasions." In Plant invasions: the role of biotic interactions, 177–91. Wallingford: CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0177.
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Abstract Biotic resistance to plant invasions takes many forms: consumption by native herbivores, competition with native plants and infection by native pathogens. But how often does biotic resistance prevent the damaging monocultures that typify the most problematic plant invaders, and how often is biotic resistance overwhelmed by the direct and indirect impacts of human activities? This chapter attempts to answer these questions, drawing on the long history of research into biotic resistance. We first briefly describe the major forms of biotic resistance to exotic plant invasions as an antecedent to other, more detailed chapters on competition, herbivory and pathogens. We then describe a new neutral model where variance in disturbance promotes invasions over the short term, but over longer timescales only propagule pressure drives invasions. These findings are a cautionary tale; pending increases in global trade and travel, particularly to the tropics, may provide the prerequisite disturbance and propagule pressure needed to ultimately stoke further invasions. Finally, we highlight case studies where invasions have been mitigated by restoration of biotic resistance from native herbivores and competitors. These studies provide strong empirical support that conservation of native biodiversity can be a nature-based solution to some invasions, although it remains to be seen if climate change will alter these effects over longer timescales.
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Traveset, Anna, and David M. Richardson. "Plant invasions: the role of biotic interactions - an overview." In Plant invasions: the role of biotic interactions, 1–25. Wallingford: CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0001.
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Abstract Diverse biotic interactions between non-native plant species and other species from all taxonomic groups are crucial mediators of the dynamics of plant invasions. This chapter reviews the key hypotheses in invasion ecology that invoke biotic interactions to explain aspects of plant invasion dynamics. We examine the historical context of these hypotheses and assess the evidence for accepting or rejecting their predictions. Most hypotheses invoke antagonistic interactions, mainly competition, predation, herbivory interactions and the role of pathogens. Only in the last two decades have positive (facilitative/mutualistic) interactions been explicitly included in invasion biology theory (as in ecological theory in general). Much information has accumulated in testing hypotheses relating to biotic resistance and Enemy Release Theory, although many of the emerging generalizations are still contentious. There is growing consensus that other drivers of plant invasion success, such as propagule pressure and disturbance, mediate the outcome of biotic interactions, thereby complicating our ability to make predictions, but these have rarely been assessed in both native and adventive ranges of non-native invasive species. It is also widely acknowledged that biogeographic comparisons, more than common garden experiments, are needed to shed light on many of the contradictory results. Contrasting findings have also emerged in exploring the roles of positive interactions. Despite strong evidence that such interactions are crucial in many communities, more work is needed to elucidate the factors that influence the relative importance of positive and negative interactions in different ecosystems. Different types of evidence in support of invasional meltdown have emerged for diverse habitats and across spatial scales. In light of increasing evidence that biotic indirect effects are crucial determinants of the structure, dynamics and evolution of ecological communities, both direct and indirect interactions involving native and non-native species must be considered to determine how they shape plant invasion patterns and the ecological impacts of non-native species on recipient communities. Research that examines both biotic interactions and the factors that mediate their strength and alter interaction outcomes is needed to improve our ability to predict the effects of novel interactions between native and non-native species, and to envisage how existing invaded communities will respond to changing environmental conditions. Many opportunities exist for manipulating biotic interactions as part of integrated control strategies to reduce the extent, density and impacts of non-native plant invasions. These include the introduction of species from the native range of the non-native plant for biological control, diverse manipulations of plant - herbivore interactions and many types of interaction to enhance biotic resistance and steer vegetation recovery following non-native plant control.
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Putman, R. J. "The Pressure of Grazing and its Impact Upon the Vegetation." In Grazing in Temperate Ecosystems Large Herbivores and the Ecology of the New Forest, 134–64. Dordrecht: Springer Netherlands, 1986. http://dx.doi.org/10.1007/978-94-011-6081-0_7.
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Hart, Richard H., and Justin D. Derner. "Cattle Grazing on the Shortgrass Steppe." In Ecology of the Shortgrass Steppe. Oxford University Press, 2008. http://dx.doi.org/10.1093/oso/9780195135824.003.0021.
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Cattle are the primary grazers on the shortgrass steppe. For example, during the late 1990s, 21 shortgrass counties in Colorado reported about 2.36 million cattle compared with 283,000 sheep (National Agricultural Statistics Service, USDA, 1997a), 60,000 pronghorn antelope, and a few thousand bison (Hart, 1994). Assuming one bison or five to six sheep or pronghorn consume as much forage as one bovine (Heady and Child, 1994), cattle provide about 97% of the large-herbivore grazing pressure in this region. The ratio of cattle to other grazers is even greater in the remainder of the shortgrass steppe. In 1997, the three panhandle counties of Oklahoma reported 387,000 cattle and only 1300 sheep, whereas the 38 panhandle counties of Texas reported 4.24 million cattle and 14,000 sheep (National Agricultural Statistics Service, USDA, 1997b,c). How ever, only a bout half the cattle in the panhandle counties of Texas and Oklahoma graze on rangeland the remainer are in feedlots. Rangeland research on the shortgrass steppe (Table 17.1 describes the parameters of the major research stations in the shortgrass steppe) has included a long history of both basic ecology and grazing management. The responses of rangeland plant communities to herbivory are addressed by Milchunas et al. (chapter 16, this volume) and to disturbance are discussed by Peters et al. (chapter 6, this volume). Here we focus on research pertaining to three management practices important to cattle ranching on shortgrass steppe: stocking rates, grazing systems, and extending the grazing season via complementary pastures and use of pastures dominated by Atriplex canescens [Pursh] Nutt (fourwing saltbush). Stocking rate, de. ned as the number of animals per unit area for a speci. ed time period, is the primary and most easily controlled variable in the management of cattle grazing. Cattle weight gain responses to stocking rate or grazing pressure (animal days per unit of forage produced) have been quanti. ed in several grazing studies on the shortgrass steppe (Bement, 1969, 1974; Hart and Ashby, 1998; Klipple and Costello, 1960). Average daily gains per animal are better estimated as a function of grazing pressure, rather than stocking rate, as forage production is highly variable in this semiarid environment (Lauenroth and Sala, 1992; Milchunas et al., 1994).
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Parker, John D., John L. Devaney, and Nathan P. Lemoine. "Biotic resistance to plant invasions." In Plant invasions: the role of biotic interactions, 177–91. CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0009.
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Biotic resistance to plant invasions takes many forms: consumption by native herbivores, competition with native plants and infection by native pathogens. But how often does biotic resistance prevent the damaging monocultures that typify the most problematic plant invaders, and how often is biotic resistance overwhelmed by the direct and indirect impacts of human activities? This chapter attempts to answer these questions, drawing on the long history of research into biotic resistance. We first briefly describe the major forms of biotic resistance to exotic plant invasions as an antecedent to other, more detailed chapters on competition, herbivory and pathogens. We then describe a new neutral model where variance in disturbance promotes invasions over the short term, but over longer timescales only propagule pressure drives invasions. These findings are a cautionary tale; pending increases in global trade and travel, particularly to the tropics, may provide the prerequisite disturbance and propagule pressure needed to ultimately stoke further invasions. Finally, we highlight case studies where invasions have been mitigated by restoration of biotic resistance from native herbivores and competitors. These studies provide strong empirical support that conservation of native biodiversity can be a nature-based solution to some invasions, although it remains to be seen if climate change will alter these effects over longer timescales.