Journal Article•
Stability and instability
TL;DR: In this article, the state of the atmosphere can be a key to getting a smooth, uneventful ride on a ride in a car. But it is not always easy.
Abstract: Subtitle: Studying the state of the atmosphere can be key to getting a smooth, uneventful ride.
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TL;DR: In this article, a combination of multivariate analyses was used to determine how community structure, life forms and individual species responded to the accumulated effects of long-term fire and grazing by native bison in upland, slope and lowland soils.
Abstract: Questions
How do fire and grazing by bison affect the composition and structure of tallgrass prairie plant communities and their temporal stability? Are these responses modulated by topographic location?
Location
Konza Prairie Biological Station, Kansas, USA.
Methods
Plant community composition was monitored in permanent plots in native grassland sites receiving different long-term prescribed burning and bison grazing regimes across a topographic gradient (lowlands, slopes, uplands) following 20 yr of variable burning treatments and 13 yr of grazing by bison. A combination of multivariate analyses was used to determine how community structure, life forms and individual species responded to the accumulated effects of long-term fire and grazing by native bison in upland, slope and lowland soils.
Results
Species diversity was maximized in sites that were infrequently burned and grazed by bison with the strongest response on infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites. In general, grass cover was highest in infrequently burned ungrazed sites and lowest on frequently burned grazed sites, while forb richness was highest in infrequently burned and grazed sites. Community response to fire and grazing differed across the topographic gradient. In general, frequent burning favoured C4 grasses, which reduced the abundance of C3 forbs, especially in lowland sites. Responses of dominant grasses and forbs to fire and grazing varied depending on topographic position. Community stability was positively correlated with species richness.
Conclusions
Overall, we found that fire and grazing are the main determinants of plant community composition and structure in this grassland system, but that topography mediates these effects. A combination of bison grazing and periodic fire is necessary to maximize diversity and community stability across this native grassland landscape.
152 citations
Cites background from "Stability and instability"
...Doi: 10.1111/j.1654-1103.2011.01369.x© 2011 International Association for Vegetation Science 571 Species diversity, grazing and fire frequency are all reported to increase grassland community stability (Anderson & Brown 1986; Tilman 1999; Collins & Smith 2006)....
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TL;DR: In this paper, a suite of N -body simulations that follow the formation and accretion history of the terrestrial planets using a new parallel treecode that was developed is presented. But the authors do not consider the effect of gas in laminar disks.
146 citations
Cites background from "Stability and instability"
...…of planets, increases nearly logarithmically with time (from∼ 20 at 3 Myr to∼ 60 at 800 Myr), and this is probably because the stable time scale of a planetary system exponentially increases with the normalized separation (Chambers et al., 1996; Ito and Tanikawa, 1999; Yoshinaga et al., 1999)....
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...Str ictly speaking, the orbital separation normalized by the mutual Hill radius, and averaged over pair s of planets, increases nearly logarithmically with time (from∼ 20 at 3 Myr to∼ 60 at 800 Myr), and this is probably because the stable time scale of a planetary system exponentially in creases with the normalized separation (Chambers et al., 1996; Ito and Tanikawa, 1999; Yoshina ga et al., 1999)....
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TL;DR: The probability of conception is linked to the stochastic variation in seasonal quality and the phenology of parturition is related to the predictable seasonality of primary productivity, indicating elephants integrate information on known current and expected future conditions when reproducing.
Abstract: The phenology of reproduction is often correlated with resource availability and is hypothesized to be shaped by selective forces in order to maximize lifetime reproductive success. African elephants have the distinctive life history traits of a 22 month gestation and extended offspring investment, necessitating a long-term strategy of energy acquisition and reproductive expenditure to ensure successful offspring recruitment. We investigated the relationship between the reproductive phenology of a wild elephant population and resource availability using remotely sensed Normalized differential vegetation index (NDVI) data as a measure of time-specific primary productivity and hence forage quality. The initiation of female elephants’ 3 /yr reproductive bout was dependent on conditions during the season of conception but timed so parturition occurred during the most likely periods of high primary productivity 22 months later. Thus, the probability of conception is linked to the stochastic variation in seasonal quality and the phenology of parturition is related to the predictable seasonality of primary productivity, indicating elephants integrate information on known current and expected future conditions when reproducing. Juvenile mortality was not correlated with ecological variability, hence female fecundity rather than calf mortality appears to drive demographic processes in the study population.
122 citations
TL;DR: This review reports on major advances in the field of nonequilibrium dynamics and thermodynamics for bridging the knowledge gap in describing how biology works, from small molecular motors to aging, through the lens of a physicist.
Abstract: Life is characterized by a myriad of complex dynamic processes allowing organisms to grow, reproduce, and evolve. Physical approaches for describing systems out of thermodynamic equilibrium have been increasingly applied to living systems, which often exhibit phenomena not found in those traditionally studied in physics. Spectacular advances in experimentation during the last decade or two, for example, in microscopy, single-cell dynamics, in the reconstruction of subcellular and multicellular systems outside of living organisms, and in high throughput data acquisition, have yielded an unprecedented wealth of data on cell dynamics, genetic regulation, and organismal development. These data have motivated the development and refinement of concepts and tools to dissect the physical mechanisms underlying biological processes. Notably, landscape and flux theory as well as active hydrodynamic gel theory have proven useful in this endeavor. Together with concepts and tools developed in other areas of nonequilibrium physics, significant progress has been made in unraveling the principles underlying efficient energy transport in photosynthesis, cellular regulatory networks, cellular movements and organization, embryonic development and cancer, neural network dynamics, population dynamics and ecology, as well as aging, immune responses, and evolution. Here recent advances in nonequilibrium physics are reviewd and their application to biological systems is surveyed. Many of these results are expected to be important cornerstones as the field continues to build our understanding of life.
99 citations
Cites background from "Stability and instability"
...The existence of two additional states is thus surprising which contrasts the conventional wisdom of only two existing states (Little and Michalowski, 2010; Ptashne, 2004a)....
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TL;DR: In this paper, Tarr et al. analyzed the benefits and pitfalls of the utilization of substantial subnational constitutional discretion and the likely consequences of this mode of reform for the Spanish model of federalism.
Abstract: This article analyzes the constitutional change in federations that is driven by the bottom-up reform of subnational units’ constitutional arrangements as an alternative to the reforms of the federal constitution. Looking at the case of Catalonia’s recent reform of its statute of autonomy, it discusses and evaluates some of the benefits and pitfalls of the utilization of substantial subnational constitutional discretion and the likely consequences of this mode of reform for the Spanish model of federalism and others. This is done through the study of the initiation of the Catalan reform process, its content and scope, and through the investigation of the political and institutional factors that account for its occurrence and final outcomes. Federal systems transform themselves in order to adapt to external conditions and to evolving internal power relations through implicit or explicit constitutional change or through a combination of both (Voigt 1999; Benz 2008). This constitutional change in federations and its different manifestations and propensity across countries has been mostly approached by focusing on federal constitutions at the national level. More recently, however, increasing attention is being paid to change occurring at the subnational level’s constitutional arrangements and its impact on the overall rules and evolution of the federation (Williams and Tarr 2004). Component units in federations may have subnational constitutions or autonomy charters, which are usually more easily reformed than national constitutions and differ in the degree to which they confer to some or all of the subnational actors different degrees of discretion or ‘‘subnational constitutional space’’ (Tarr 2007) for changing their own governing arrangements and, indirectly, the federal constitution. Depending on several political factors, subnational governments in different federations may decide to use this constitutional space allotted to them differently,
83 citations