It has been observed that the number of phonemes in languages in use today tends to decrease with increasing distance from Africa. A previous formal model has recently reproduced the observed cline, ...but under two strong assumptions. Here we tackle the question of whether an alternative explanation for the worldwide phonemic cline is possible, by using alternative assumptions. The answer is affirmative. We show this by formalizing a proposal, following Atkinson, that this pattern may be due to a repeated bottleneck effect and phonemic loss. In our simulations, low-density populations lose phonemes during the Out-of-Africa dispersal of modern humans. Our results reproduce the observed global cline for the number of phonemes. In addition, we also detect a cline of phonemic diversity and reproduce it using our simulation model. We suggest how future work could determine whether the previous model or the new one (or even a combination of them) is valid. Simulations also show that the clines can still be present even 300 kyr after the Out-of-Africa dispersal, which is contrary to some previous claims which were not supported by numerical simulations.
It has been proposed that a serial founder effect could have caused the present observed pattern of global phonemic diversity. Here we present a model that simulates the human range expansion out of ...Africa and the subsequent spatial linguistic dynamics until today. It does not assume copying errors, Darwinian competition, reduced contrastive possibilities or any other specific linguistic mechanism. We show that the decrease of linguistic diversity with distance (from the presumed origin of the expansion) arises under three assumptions, previously introduced by other authors: (i) an accumulation rate for phonemes; (ii) small phonemic inventories for the languages spoken before the out-of-Africa dispersal; (iii) an increase in the phonemic accumulation rate with the number of speakers per unit area. Numerical simulations show that the predictions of the model agree with the observed decrease of linguistic diversity with increasing distance from the most likely origin of the out-of-Africa dispersal. Thus, the proposal that a serial founder effect could have caused the present observed pattern of global phonemic diversity is viable, if three strong assumptions are satisfied.
The transition from hunter-gathering to agriculture (Neolithic) spread gradually across Europe from the Southeast. A reduction in cultural diversity of crop farming practices has been previously ...observed by comparing pre-LBK Neolithic sites in Greece and the Balkans (dated about 8500 yr BP) to LBK Neolithic sites in Central Europe (dated about 7000 yr BP). The decrease in crop diversity is statistically significant even when considering only the species less likely to have been subject to smaller productivity due to climatic factors (reductions in growing season, temperature, daylight, etc.). This reduction in cultural diversity has not been explained previously. In this paper we show that spatial drift, which occurred on the front of the advancing wave of pioneer settlements, can explain the observed loss of diversity during the LBK range expansion. Our results suggest that spatial dimensions can have a relevant effect also in other case studies in which cultural drift is important.
► Drift can explain the decrease of cultural diversity in the LBK culture in Neolithic Europe, provided that the role of space is adequately taken into account. ► The loss in LBK crop diversity may be a product of spatial drift. ► When spatial dimensions are taken into account, drift has a drastically more significant effect than previously recognized.
We use two coupled equations to analyze the space/time dynamics of two interacting languages. First, we introduce a cohabitation model, which is more appropriate for human populations than classical ...(noncohabitation) models. Second, using numerical simulations, we find the front speed of a new language spreading into a region in which another language was previously used. Third, for a special case, we derive an analytical formula that makes it possible to check the validity of our numerical simulations. Finally, as an example, we find that the observed front speed for the spread of the English language into Wales in the period 1961 through 1981 is consistent with the model predictions. We also find that the effects of linguistic parameters are much more important than the effects of parameters related to population dispersal and reproduction. If the initial population densities of both languages are similar, they have no effect on the front speed. We outline the potential of the new model to analyze relationships between language replacement and genetic replacement.
Issue Title: Reservoir Limnology and Water Quality The change in the stratification pattern in Boadella Reservoir (Catalonia, Spain) due to the switch in water withdrawal was investigated for a ...6-month period in the year 2000. A numerical one-dimensional model (DLM) was used to predict the thermal structure of the reservoir during the period of maximum water demand. The model was found to satisfactorily predict the basic trends of the thermal stratification of the water column of the reservoir. We used this model to investigate various possible water withdrawal scenarios. When thermal stratification has been completely developed, the location of the main thermocline coincides with the depth of the outlet, in the various withdrawal scenarios considered. The possible effect of the switch between outlets on the water quality of the reservoir is discussed.PUBLICATION ABSTRACT
An additive semi-analytic model of water clarity for the forward problem of calculating apparent optical properties (AOPs) of diffuse attenuation and Secchi depth from the inherent optical properties ...(IOPs) due to suspended matter in oligotrophic waters is presented. The model is general in form, taking into account algal concentration, suspended inorganic sediment concentration, particle size distribution, and dissolved organic matter to predict Secchi depth and diffuse attenuation. The model's application to ultra-oligotrophic Lake Tahoe, California-Nevada, USA is described. The function of the clarity model is to quantify the relative effect of phytoplankton or phytoplankton-derived organic materials, other particles such as suspended mineral sediment, and dissolved organic matter on the lake's clarity. It is concluded that suspended inorganic sediments and phytoplanktonic algae both contribute significantly to the reduction in clarity, and that suspended particulate matter, rather than dissolved organic matter, are the dominant causes of clarity loss.
Warming of Lake Tahoe Coats, Robert; Perez-Losada, Joaquim; Schladow, Geoffrey ...
Climatic change,
05/2006, Volume:
76, Issue:
1-2
Journal Article
Peer reviewed
We investigated the effects of climate variability on the thermal structure of Lake Tahoe, California-Nevada, 1970-2002, and with principal components analysis and step-wise multiple regression, ...related the volume-weighed average lake temperature to trends in climate. We then used a 1-dimensional hydrodynamic model to show that the observed trends in the climatic forcing variables can reasonably explain the observed changes in the lake. Between 1970 and 2002, the volume-weighted mean temperature of the lake increased at an average rate of 0.015 composite function (small circle)C yr-¹. Trends in the climatic drivers include 1) upward trends in maximum and minimum daily air temperature at Tahoe City; and 2) a slight upward trend in downward long-wave radiation. Changes in the thermal structure of the lake include 1) a long-term warming trend, with the highest rates near the surface and at 400 m; 2) an increase in the resistance of the lake to mixing and stratification, as measured by the Schmidt Stability and Birge Work; 3) a trend toward decreasing depth of the October thermocline. The long-term changes in the thermal structure of Lake Tahoe may interact with and exacerbate the well-documented trends in the lake's clarity and primary productivity.
We extend a previous model of the Neolithic transition in Europe J. Fort and V. Méndez, Phys. Rev. Lett. 82, 867 (1999) by taking two effects into account: (i) we do not use the diffusion ...approximation (which corresponds to second-order Taylor expansions), and (ii) we take proper care of the fact that parents do not migrate away from their children (we refer to this as a time-order effect, in the sense that it implies that children grow up with their parents, before they become adults and can survive and migrate). We also derive a time-ordered, second-order equation, which we call the sequential reaction-diffusion equation, and use it to show that effect (ii) is the most important one, and that both of them should in general be taken into account to derive accurate results. As an example, we consider the Neolithic transition: the model predictions agree with the observed front speed, and the corrections relative to previous models are important (up to 70%).
High vertical wave-number modes clearly dominate the internal wave field during the stratification period in Boadella reservoir in northeast Spain. In this period, the extraction of hypolimnetic ...water, due to summer irrigation, brought the surface level down by 6 m in one month and the epilimnetic water progressively occupied the whole water column. The temperature profile, with the exception of a few meters at the surface layer, presented an almost constant temperature gradient of about 0.7°C/m. The period of the main vertical mode is 24 h with an amplitude of around 1 m. Thermistor chain records and meteorological data allow us to deduce that this mode is, at least, a third vertical mode forced by the wind, which normally has a typical periodicity of 24 h. However, when the wind changes direction from south to north, the circulation cells developed due to this forced nonstationary oscillation are destroyed. When this occurs, the Bulk Richardson number is Rib∼1. Similar vertical structures as a response to wind forcing should be expected in similar systems, although this has not been reported in the literature.
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