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The article presents the author's comments on the research paper "Environmental Imperatives Reconsidered," by Terry L. Jones and his colleagues. The author views that the paper lacks convincing demonstration of how climatic change affected the cultural growth of human population of four different studied region. He views that Jones and colleagues were correct to mention that economic factors depending on local factors influence population dynamic up to some extent.

The article presents the author's views on the research paper "Environmental Imperatives Reconsidered," by Terry L. Jones and associates, which is published within the issue. He criticizes the overstated significance given to environmental flux as a factor responsible for the extinction of the late prehistoric population in western North America. He argues that there is a lack of convincing demonstration in the paper to support the vigorous effect of climatic anomalies on human system.

Premise of research. Pterocarya (Juglandaceae) was widespread in the Cenozoic of the Northern Hemisphere, including western and eastern North America, but presently survives only in the Caucasus Mountains and eastern Asia. We describe two macrofossil fruit occurrences, one from the Miocene of Maryland and one from the Pliocene of Alabama. These augment existing palynological evidence of its survival in eastern North America to the Pliocene. We also explore hypotheses for its demise in what should have been a promising modern-day refugium. Methodology. The morphology of both fossils was observed using a dissecting microscope, and characters of extant and previously described fossil species of Pterocarya , both from the literature and from living specimens, were examined. Measurements of wing size and fruit size were made with imaging software to establish a wing-to-fruit ratio. Pivotal results. The fossils from the Miocene of Maryland can be assigned to Pterocarya section Platyptera , aff. P. rhoifolia , of Japan. The new Pterocarya fruit from the Pliocene of Alabama cannot be assigned to a modern section. It possesses an abnormally large nut and the lowest wing-to-fruit ratio of any living or fossil species. We describe this fruit as P. magnifructa , a new species. Conclusions. Pterocarya was a common constituent of the Miocene flora of the mid-Atlantic coast but became restricted to southeastern North America in the Pliocene, where it was apparently less common. The size and wing-to-fruit ratio of the Pliocene specimen suggest that it may have been evolving toward biotic dispersal, perhaps in response to climate change and/or competition from the radiating diversity of accompanying Carya species. [ABSTRACT FROM AUTHOR]

A hypothesized extraterrestrial impact in North America at -~12,900 calendar years BP (12.9 ka) has been proposed as the cause of Younger Dryas climate changes, terminal Pleistocene mammalian extinctions, and a supposed "termination" of the Clovis archaeological culture. In regard to the latter, however, an examination of archaeological, geochronological, and stratigraphic evidence fails to provide evidence of a demographic collapse of post-Clovis human populations, especially where the Clovis and post-Clovis site records are reasonably well constrained chronologically. Although few Clovis sites contain evidence of an immediate post-Clovis occupation, interpreting that absence as population collapse is problematic because the great majority of Paleoindian sites also lack immediately succeeding occupations. Where multiple occupations do occur, stratigraphic hiatuses between them are readily explained by geomorphic processes. Furthermore, calibrated radiocarbon ages demonstrate continuous occupation across the time of the purported "Younger Dryas event." And, finally, the relatively few sites purported to provide direct evidence of the 12.9-ka impact are not well constrained to that time. Whether or not the proposed extraterrestrial impact occurred is matter for empirical testing in the geological record. Insofar as concerns the archaeological record, an extra- terrestrial impact is an unnecessary solution for an archaeological problem that does not exist. [ABSTRACT FROM AUTHOR]

We examined the physiological rates of 2 freshwater mussel species, Lampsilis cardium and Amblema plicata , as they experienced rising temperatures in a controlled laboratory setting. We chose these species because they have a widespread distribution, are common throughout North America, and vary in thermal tolerance. We varied the density and species composition of mussels in tanks. We measured algal clearance rate, oxygen consumption, biodeposition, and changes in nutrient concentration as mussels were exposed to incrementally-increasing temperatures relevant to regional climate projections. We found that these species have distinct physiological responses to increasing temperatures. The mass-specific physiological rates of L. cardium changed more than those of A. plicata when exposed to rising temperatures. Additionally, our findings suggest that mussel response to rising temperatures may vary as a result of mussel assemblage, density, and species composition. Thus, negative impacts of warming stream temperatures on freshwater mussels have the potential to affect the entire ecosystem. Understanding how freshwater mussel species may respond to climate change will help us better manage mussel communities and aquatic ecosystems. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are highly vulnerable to warming climates. However, macroecological studies of climate-change effects on aquatic biodiversity are rare because of a lack of standardized large-scale surveys, e.g., along large latitudinal gradients. Our goal was to assess the overall richness pattern and projected differences in present and future patterns of the stream insect orders Ephemeroptera (E), Plecoptera (P), Trichoptera (T), and combined EPT along an extensive latitudinal gradient across North America (30 to 70°N). We applied Bioclimatic Envelope Models (BEMs) to project present-day and future climatically suitable areas for EPTs on a spatial resolution of 10 arc-min (20 km × 20 km) across North America. To overcome issues related to spatially biased sampling, we assessed climatically suitable areas (CSAs) for each genus and modeled potential generic richness/grid cell, rather than assessing observed generic richness patterns directly. Projected present-day generic richness was greatest between 40 and 48°N latitude, with peaks at 44, 45, and 47°N for the E, P, and T orders, respectively. Our models projected that CSAs would shift an average 4.2 to 5.2°, 4.4 to 5.3° and 3.4 to 4.1°N latitude by 2080 for E, P, and T genera, respectively. Overall, the present-day projected generic EPT richness is highest in the warm and cool temperate zones and shows a unimodal richness pattern that is projected to shift northward under climate-change conditions. A similar northward shift of richness patterns might also apply to other aquatic insects with relatively narrow thermal sensitivity and terrestrial, winged adults, e.g., freshwater Diptera or many aquatic Coleoptera. This large-scale application of genus-by-genus models gives a first approximation of the likely consequences of climate-change effects on freshwater biota across North America. [ABSTRACT FROM AUTHOR]

The article presents the author's reply to the comments in response to his article "Environmental Imperatives Reconsidered," which was focused on the correlation between environmental factors and cultural development. The author expresses happiness over the successful accomplishment of his objectives behind writing the article. His hypothesis of medieval-drought in western North America emerged successful in evaluating the ecological themes of the region during the pre-historic age.