Comparative Effects on Plants of Caribou/Reindeer, Moose and White-tailed Deer Herbivory

We reviewed the literature reporting negative or positive effects on vegetation of herbivory by caribou/reindeer, moose, and white-tailed deer in light of the hypothesis of exploitation ecosystems (EEH), which predicts that most of the negative impacts will occur in areas where wolves were extirpated. We were able to list 197 plant taxa negatively affected by the three cervid species, as opposed to 24 that benefited from their herbivory. The plant taxa negatively affected by caribou/reindeer (19), moose (37), and white-tailed deer (141) comprised 5%, 9%, and 11% of vascular plants present in their respective ranges. Each cervid affected mostly species eaten during the growing season: lichens and woody species for caribou/reindeer, woody species and aquatics for moose, and herbs and woody species for white-tailed deer. White-tailed deer were the only deer reported to feed on threatened or endangered plants. Studies related to damage caused by caribou/reindeer were scarce and often concerned lichens. Most reports for moose and white-tailed deer came from areas where wolves were absent or rare. Among the three cervids, white-tailed deer might damage the most vegetation because of its smaller size and preference for herbs.À la lumière de l'hypothèse de l'exploitation des écosystèmes (EEH), nous avons examiné les publications qui mentionnent les effets négatifs ou positifs, sur la végétation, du broutement du caribou/renne, de l'orignal et du cerf de Virginie. Cette hypothèse prédit que les impacts négatifs se concentrent dans des endroits où le loup a été éliminé. Nous avons pu énumérer 197 taxons végétaux affectés négativement par les trois cervidés, contre 24 qui profitaient du broutement. Le nombre de taxons végétaux affectés négativement par le broutement du caribou/renne (19), de l'orignal (37) et du cerf de Virginie (141) représentait respectivement 5, 9 et 11 p. cent des plantes vasculaires situées dans les aires de répartition spécifiques des animaux. Chaque cervidé affectait surtout les espèces consommées durant la saison de croissance végétale: lichens et plantes ligneuses pour le caribou/renne, plantes ligneuses et aquatiques pour l'orignal, et plantes herbacées et ligneuses pour le cerf de Virginie. Selon les rapports, ce dernier était le seul cerf qui broutait des plantes menacées ou en voie de disparition. Les études rapportant des dommages causés par le caribou/renne étaient rares et traitaient souvent des lichens. La plupart des rapports sur l'orignal et le cerf de Virginie couvraient des zones où le loup était rare ou absent. Des trois cervidés, celui qui causerait le plus de dommages à la végétation est le cerf de Virginie, en raison de sa taille plus petite et de sa préférence pour les plantes herbacées

Summer Diet of Two White-tailed Deer, Odocoileus virginianus, Populations Living at Low and High Density in Southern Québec

We investigated summer diets of two White-tailed Deer (Odocoileus virginianus) populations through rumen content analyses. Samples from 93 deer were collected in a low density, LD (1 deer/km2) and a high density, HD (14 deer/km2) area of southern Québec during the growing seasons of 1997 and 1998. Availability of preferred forage in forests was greater in LD than in HD, whereas agriculture covered a larger proportion of the area in HD than LD. Rumen composition differed between the two populations. Deer from HD consumed less forbs and leaves of shrubs and trees than did LD deer, whereas they consumed more fruits, grasses and farm crops. The rarity in HD rumens of food items common in LD, as well as in many parts of the White-tailed Deer range (i.e., Lilliacae), indicated that deer could not compensate for the rarity of preferred forest forage by increasing foraging time and had to feed on cultivated crops. Rumen contents of LD deer had a higher level of cell solubles and lignin, which reflected their greater reliance on quality forage growing in forests. Feeding habits and forage quality can explain why deer body size decreased in HD between the 1970s and 1990s whereas LD deer remained large.Nous avons examiné le régime alimentaire estival de deux populations de cerf de Virginie (Odocoileus virginianus) par l’analyse du contenu des rumens. Des échantillons ont été prélevés sur 93 cerfs provenant d’un secteur à faible densité de cerfs, LD, (1 cerf/km2) et d’un secteur à haute densité, HD, (14 cerfs/km2) du sud du Québec durant la saison de croissance des végétaux de 1997 et 1998. La disponibilité des aliments forestiers préférés des cerfs était plus grande dans LD que dans HD alors que la proportion du territoire agricole était supérieure dans HD. La composition des rumens des cerfs de chacune des régions différait. Les cerfs de HD ont consommé de moins grandes proportions de plantes herbacées et de feuilles d’arbustes et d’arbres que ceux du secteur LD, mais de plus grandes proportions de fruits, de graminées et de plantes agricoles. La rareté dans les rumens du secteur HD d’aliments communs dans ceux du secteur LD et dans plusieurs autres régions de l’aire de répartition du cerf (e.g., Lilliacae), indique que les cerfs du secteur HD ne pouvaient compenser pour la rareté de leurs aliments préférés par un accroissement de la durée de la quête alimentaire, et qu’ils devaient consommer des plantes agricoles. Les cerfs de LD ont mangé des aliments contenant plus de solubles cellulaires et de lignine que ceux de HD, ce qui reflète une consommation de plantes forestières de bonne qualité. Le régime alimentaire et la qualité de la nourriture peuvent expliquer pourquoi la taille des cerfs de HD a diminué entre les années 1970 et 1990 alors que celle des cerfs de LD est demeurée grande

Identification of functional microRNAs released through asymmetrical processing of HIV-1 TAR element†

The interaction between human immunodeficiency virus type 1 (HIV-1) and RNA silencing pathways is complex and multifaceted. Essential for efficient viral transcription and supporting Tat-mediated transactivation of viral gene expression, the trans-activation responsive (TAR) element is a structured RNA located at the 5′ end of all transcripts derived from HIV-1. Here, we report that this element is a source of microRNAs (miRNAs) in cultured HIV-1-infected cell lines and in HIV-1-infected human CD4+ T lymphocytes. Using primer extension and ribonuclease (RNase) protection assays, we delineated both strands of the TAR miRNA duplex deriving from a model HIV-1 transcript, namely miR-TAR-5p and miR-TAR-3p. In vitro RNase assays indicate that the lack of a free 3′ extremity at the base of TAR may contribute to its low processing reactivity in vivo. Both miR-TAR-5p and miR-TAR-3p down-regulated TAR miRNA sensor activity in a process that required an integral miRNA-guided RNA silencing machinery. miR-TAR-3p exerted superior gene downregulatory effects, probably due to its preferential release from HIV-1 TAR RNA by the RNase III Dicer. Our study suggests that the TAR element of HIV-1 transcripts releases functionally competent miRNAs upon asymmetrical processing by Dicer, thereby providing novel insights into viral miRNA biogenesis

Old forest structural development drives complexity of nest webs in a naturally disturbed boreal mixedwood forest landscape

Structural complexity generated by forest development processes and tree species compositional changes provide key habitat features for vertebrate communities that rely upon tree size and decay processes for foraging, denning or nesting. Complexity of forest structure in old stands could not only be key for harboring increased taxonomic species diversity but also greater functional diversity through more complexity in networks of tree cavity dependent species. Using a nest web approach that hierarchically links cavity-bearing trees with cavity formation agents (natural decay processes and avian excavators) and cavity users (non-excavator species), we compared network characteristics of nest webs along a time since fire gradient in a naturally disturbed boreal mixedwood forest landscape in eastern North America. Since 2003, twelve 24 to 40 ha plots ranging from 61 to more than 245 years after fire were surveyed at the Lake Duparquet Research and Teaching Forest in Abitibi, Quebec, Canada to detect active nesting, and denning cavities. We found that network complexity both in terms of number of vertebrate species and number of interactions among species, increased along the age gradient and was significantly higher in the older stands than predicted by chance. Whereas cavity-nesting communities in old forests used a higher diversity of tree species over a wide range of decay stages, trembling aspen remained a key cavity-bearing tree throughout the age gradient. Woodpeckers were the main cavity formation agents whereas less than 1% of cavities originated from natural decay. The structural development of older forests is thus a driver for functional diversity in cavity-using vertebrate communities through higher interaction richness in nest webs, among cavity-bearing trees, excavators and non-excavating users. The pivotal contribution of the entire gradient of old forest cover types to the overall complexity of nest webs in the boreal mixedwood zone is also a key for the resilience of the cavity-using vertebrate community to natural disturbances. We discuss how such resilience may be compromised by even-aged industrial timber harvesting with short rotations that shifts the age structure of boreal landscapes toward regenerating and young pole forests whereas old forest cover types become below their historical range of variability

Lignin biomarkers as tracers of mercury sources in lakes water column

This study presents the role of specific terrigenous organic compounds as important vectors of mercury (Hg) transported from watersheds to lakes of the Canadian boreal forest. In order to differentiate the autochthonous from the allochthonous organic matter (OM), lignin derived biomarker signatures [Lambda, S/V, C/V, P/(V ? S), 3,5-Bd/V and (Ad/Al)v] were used. Since lignin is exclusively produced by terrigenous plants, this approach can give a non equivocal picture of the watershed inputs to the lakes. Moreover, it allows a characterization of the source of OM and its state of degradation. The water column of six lakes from the Canadian Shield was sampled monthly between June and September 2005. Lake total dissolved Hg concentrations and Lambda were positively correlated, meaning that Hg and ligneous inputs are linked (dissolved OM r2 = 0.62, p\0.0001; particulate OM r2 = 0.76, p\0.0001). Ratios of P/(V ? S) and 3,5-Bd/V from both dissolved OM and particulate OM of the water column suggest an inverse relationship between the progressive state of pedogenesis and maturation of the OM in soil before entering the lake, and the Hg concentrations in the water column. No relation was found between Hg levels in the lakes and the watershed flora composition—angiosperm versus gymnosperm or woody versus non-woody compounds. This study has significant implications for watershed management of ecosystems since limiting fresh terrestrial OM inputs should reduce Hg inputs to the aquatic systems. This is particularly the case for largescale land-use impacts, such as deforestation, agriculture and urbanization, associated to large quantities of soil OM being transferred to aquatic systems

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference