Intertidal systems have been models for the study of the roles of competition, predation, and disturbance in determining community structure. These systems exhibit considerable regional variability in percentage cover and in the strength of interspecific interactions, which may be due largely to effects of varying larval supply. In Oregon and Washington, experimental studies of space allocation among sessile invertebrates have emphasized the role of benthic processes such as competition and predation. In contrast, studies in central California have emphasized the importance of larval supply. In this article, we identify a gradient in percentage cover in the middle and upper intertidal zone that is consistent with an oceanographically based explanation for these differences: percentage cover of mussels and barnacles is much higher in Oregon, where nearshore circulation promotes high recruitment, than in California, where strong offshore currents inhibit recruitment. A mathematical model incorporating larval transport and interspecific competition for space offers an explanation for the one violation of the hypothesis-higher percentage cover of Chthamalus spp. in California. The findings illustrate that attempts to synthesize regional differences in community structure and dynamics can benefit from considering both the benthic adult and pelagic larval environments.

Middle Paleolithic lithic and faunal assemblages throughout Eurasia reflect short-term Neanderthal occupations, which suggest high group mobility. However, the timing of these short-term occupations, a key factor to assess group mobility and territorial range, remains unresolved. Anthropogenic combustion structures are prominent in the Middle Paleolithic record and conceal information on the timing and intensity and natural setting of their associated human occupations. This paper examines a concentration of eleven combustion structures from unit Xb of El Salt, a Middle Paleolithic site in Spain through a geoarchaeological approach, in search of temporal, human impact and paleoenvironmental indicators to assess the timing, intensity and natural setting of the associated human occupations. The study was conducted using micromorphology, lipid biomarker analysis and compound specific isotope analysis. Results show in situ hearths built on different diachronic topsoils rich in herbivore excrements and angiosperm plant residues with rare anthropogenic remains. These data are suggestive of low impact, short-term human occupations separated by relatively long periods of time, with possible indicators of seasonality. Results also show an absence of conifer biomarkers in the mentioned topsoils and presence of conifer charcoal among the fuel residues (ash), indicating that fire wood was brought to the site from elsewhere. A microscopic and molecular approach in the study of combustion structures allows us to narrow down the timescale of archaeological analysis and contributes valuable information towards an understanding of Neanderthal group mobility and settlement patterns.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

SUMMARYThe parents chosen to continue 10 independent selection lines of Sc/zizophyllurn commune over eight successive generations of selection, along with unselected controls, have been retrospectively examined for their response to growth at 15°, 20°, 25°, 30° and 35°C. The regression of rate of growth on temperature was essentially linear over the range 15° to 30°C for all lines irs all generations as was also the regression of rate of growth on various biological assessments of the environments over the whole temperature range. Either regression, therefore, provided linear regression coefficients which adequately accounted for the relative sensitivities of the lines to temperature in each generation of selection. These measures of environmental sensitivity confirmed our earlier report that selection for high mean performance in a good environment or for low mean performance in a poor environment leads to selections that are more sensitive to environmental variation than selections for high mean performance in a poor environment or for low mean performance in a good environment. These differences in sensitivity emerge as correlated responses during selection and the magnitude of these correlated responses is higher in the good environment than in the poor environment irrespective of the direction of selection.The environmental sensitivity of selection lines can be modified in either direction as required by either selecting for sensitivity simultaneously with the selection for mean performance or by selecting for mean performance in an above or below average environment. The quality of environments in which artificial selection is usually carried out is likely to have led to high selections with maximum environmental sensitivity and low selections with minimum sensitivity.

No abstract