7 research outputs found
Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget
Globally, large-bodied wild mammals are in peril. Because “megamammals” have a disproportionate influence on vegetation, trophic interactions, and ecosystem function, declining populations are of considerable conservation concern. However, this is not new; trophic downgrading occurred in the past, including the African rinderpest epizootic of the 1890s, the massive Great Plains bison kill-off in the 1860s, and the terminal Pleistocene extinction of megafauna. Examining the consequences of these earlier events yields insights into contemporary ecosystem function. Here, we focus on changes inmethane emissions, produced as a byproduct of enteric fermentation by herbivores. Although methane is ∼200 times less abundant than carbon dioxide in the atmosphere, the greater efficiency of methane in trapping radiation leads to a significant role in radiative forcing of climate. Using global datasets of late Quaternary mammals, domestic livestock, and human population from the United Nations as well as literature sources, we develop a series of allometric regressions relating mammal body mass to population density and CH4 production, which allows estimation of methane production by wild and domestic herbivores for each historic or ancient time period. We find the extirpation ofmegaherbivores reduced global enteric emissions between 2.2–69.6 Tg CH4 y−1 during the various time periods, representing a decrease of 0.8–34.8% of the overall inputs to tropospheric input. Our analyses suggest that large-bodied mammals have a greater influence on methane emissions than previously appreciated and, further, that changes in the source pool from herbivores can influence global biogeochemical cycles and, potentially, climate
Discovery of the Yellow-Bellied Marmot (Marmota flaviventris) in the Jemez Mountains, New Mexico: Examining Competing Hypotheses for Range Extension
Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget
Globally, large-bodied wild mammals are in peril. Because “megamammals” have a disproportionate influence on vegetation, trophic interactions, and ecosystem function, declining populations are of considerable conservation concern. However, this is not new; trophic downgrading occurred in the past, including the African rinderpest epizootic of the 1890s, the massive Great Plains bison kill-off in the 1860s, and the terminal Pleistocene extinction of megafauna. Examining the consequences of these earlier events yields insights into contemporary ecosystem function. Here, we focus on changes inmethane emissions, produced as a byproduct of enteric fermentation by herbivores. Although methane is ∼200 times less abundant than carbon dioxide in the atmosphere, the greater efficiency of methane in trapping radiation leads to a significant role in radiative forcing of climate. Using global datasets of late Quaternary mammals, domestic livestock, and human population from the United Nations as well as literature sources, we develop a series of allometric regressions relating mammal body mass to population density and CH4 production, which allows estimation of methane production by wild and domestic herbivores for each historic or ancient time period. We find the extirpation ofmegaherbivores reduced global enteric emissions between 2.2–69.6 Tg CH4 y−1 during the various time periods, representing a decrease of 0.8–34.8% of the overall inputs to tropospheric input. Our analyses suggest that large-bodied mammals have a greater influence on methane emissions than previously appreciated and, further, that changes in the source pool from herbivores can influence global biogeochemical cycles and, potentially, climate
Exploring the influence of ancient and historic megaherbivore extirpations on the global methane budget
The challenge of drug resistance in cancer treatment: a current overview
It is generally accepted that recent advances in anticancer agents have contributed significantly to the improvement of both the disease-free survival and quality of life in cancer patients. However, in many instances, a favorable initial response to treatment changes afterwards, thereby leading to cancer relapse and recurrence. This phenomenon of acquired resistance to therapy, it is a major problem for totally efficient anticancer therapy. The failure to obtain an initial response reflects a form of intrinsic resistance. Specific cell membrane transporter proteins are implicated in intrinsic drug resistance by altering drug transport and pumping drugs out of the tumor cells. Moreover, the gradual acquisition of specific genetic and epigenetic abnormalities in cancer cells could contribute greatly to acquired drug resistance. A critical issue in the clinical setting, is that the problem of drug resistance appears to have a negative effect on also the new molecularly-targeted anticancer drugs. Several ongoing efforts are being made by the medical community aimed to the identification of such resistance mechanisms and the development of novel drugs that could overcome them. In this review, the major drug resistance mechanisms and strategies to overcome them are critically discussed, and also possible future directions are suggested