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Comparative analysis of the functional and morphological characteristics of the central nervous system of extant vertebrates can shed light on the evolutionary forces that have shaped different vertebrate brains, which, although sharing similar elements and a basic plan, have had to cope with extremely diverse environments. We chose the Didelphis opossum as an experimental model because of its putative resemblance to cretaceous mammals. This marsupial can be quite accurate in performing activities that rely on visual skills. The existence of an oculomotor system that stabilizes the image on the opossum's retina is of primary importance, compensating for movements of the head and providing this species with a framework to stabilize the retinal image while foraging for food. We review evidence for how the nucleus of the optic tract, a key structure involved in this function, is organized to provide an appropriate blending of form and function to bring about this basic behavior.
We performed a meta-analysis on the basis of 69 past studies that have assessed a limit to the world population. The estimates of this limit range from 0.5 billion to 1 × 1021 billion people. A meta-analysis allows us to see what overall picture emerges when different methods, limiting factors, levels of aggregation, and data are taken into account. Limiting factors for the world population include water availability, energy, carbon, forest products, nonrenewable resources, heat removal, photosynthetic capacity, and the availability of land for food production. Methods employed in the population studies include spatial extrapolation, modeling of multiple regions, temporal extrapolation, actual supply of a resource, hypothetical modeling, and dynamic systems modeling. Many studies rely on important assumptions about the level of technology, the energy intake per person, and the available arable land. The meta-analysis employs both descriptive statistics and regression analysis. We used the findings of these analyses to propose a number of meta-estimates of limits to world population. When taking all studies into account, the best point estimate is 7.7 billion people; the lower and upper bounds, given current technology, are 0.65 billion and 98 billion people, respectively. We offer a range of other conditional estimates as well. An important conclusion of this study is that recent predictions of stabilized world population levels for 2050 exceed several of our meta-estimates of a world population limit.
Great Plains streams are highly endangered and can serve as model systems for studying disturbance ecology and related issues of resistance and resilience in temperate freshwaters. These streams exist in a precarious balance between flood and drying. In general, microbial activity recovers in days to weeks after drying or flooding, and invertebrate and fish species are quick to follow. In lower forested reaches, floods may be more intense but drying less common. Upstream reaches of prairie streams are characterized by frequent drying, little canopy cover, and limited leaf input. Life history and adaptations alter the ways in which stream organisms respond to these linear patterns. Human modification has altered these patterns, leading to large-scale loss of native grassland streams. The future for Great Plains streams is bleak, given the land-use changes and water-use patterns in the region and the large areas required to preserve intact, ecologically functional watersheds.
Biotic resources are under all kinds of old and new threats. Ecosystem transformation in many areas of high biodiversity has not diminished, in spite of national and international meetings, agreements, and discussions. The main reasons to protect these resources are that little information is available on those we know exist and that the great majority of resources are yet to be discovered. One argument used to convince the general public and governments of the need to preserve biological resources is that there are many potential uses of unknown plants, animals, or micro organisms: New medicines, foods, chemicals, and genes are there to be discovered. Unfortunately, this argument has been overused and, as a result, has created unrealistic expectations of great riches and spurred stringent legal measures to restrict biodiversity research. The limits placed on bio diversity research and on access to biological resources are becoming a major obstacle to scientific discovery. Major projects have been suspended following unjustified criticisms. In this article, I discuss possible explanations for this problem and present some possible solutions.
Species respond to habitat at different spatial scales, yet many studies have considered this response only at relatively small scales. We developed a technique and accompanying software (Focus) that use a focal patch approach to select multiple sets of spatially independent sites. For each independent set, regressions are conducted between the habitat variable and counts of species abundance at different scales to determine the spatial scale at which species respond most strongly to an environmental or habitat variable of interest. We applied the technique to determine the spatial scales at which 12 different species of cerambycid beetles respond to forest cover. The beetles responded at different scales, from 20 to 2000 meters. We expect this technique and the accompanying software to be useful for a wide range of studies, including the analysis of existing data sets to answer questions related to the large-scale response of organisms to their environment.
Scientific rejection is a frequent part of the publication process that is rarely explicitly discussed. Peer review is an essential and well-established part of the scientific method. But to what degree is manuscript rejection indicative of scientific inadequacy? Here we quantify the extent to which a sample of scientists with successful publication careers in our discipline, ecology, have experienced manuscript rejection. We show that publication success and manuscript rejection are definitely not exclusive. Notably, we find that the ecologists with the highest number of publications also suffered the largest proportion of manuscript rejections. Rejection is not easy even for the most successfully publishing ecologists; however, manuscript rejection does not seem to have deterred our respondents or to have hampered their career advancement. We hope that our results will encourage ecologists (and particularly research students) to continue submitting their studies for publication.
Understanding environmental complexity and other dimensions of ecological systems necessitates a holistic approach that can be achieved only by identifying, retrieving, and synthesizing diverse data from distributed sources; by collaborating with other scientists from a broad range of dis ciplines; and by investigating many different systems. Knowledge Network for Biocomplexity (KNB) is developing new software tools to advance ecological understanding through discovery, access, retrieval, and management of distributed and heterogeneous ecological and environmental data. To address the need for cultural change in ecologists and other environmental scientists and to promote collaborative and synthetic approaches, KNB and the National Center for Ecological Analysis and Synthesis are training a cadre of young investigators in techniques for the management and analysis of ecological data, with emphasis on multiscale integration and synthesis.
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