University of Maine

About: University of Maine is a education organization based out in Orono, Maine, United States. It is known for research contribution in the topics: Population & Ice sheet. The organization has 8637 authors who have published 16932 publications receiving 590124 citations. The organization is also known as: University of Maine at Orono.

Evolutionary responses to climate change.

Abstract: In their paper Malcolm et al. (2006) use climate-war-ming scenarios to estimate up to 43% loss of specieswithin biodiversity hotspots. This prediction is based ona climate-envelope approach that assumes the distribu-tion, and hence extinction, probability of every speciesis predicted by climate alone. We agree that global cli-mate change will have substantial effects on biodiversityand will cause extinctions (Crowley & North 1990; Hoff-man et al. 2003). Nevertheless, the climate-envelope ap-proach presents a distorted estimate of extinction prob-abilities. Most notably, the approach does not considerevolution and therefore implicitly assumes that speciescannot evolve in response to changing climate.Current empirical evidence suggests that evolution isresponsive to climate variation and occurs at rates thatmake it relevant for consideration of current and pro-jected responses to climate change. For a wide varietyof taxa, thermal performance varies within species’ geo-graphic ranges, suggesting both genetic variation in criti-cal traits and localized evolution in response to climatevariation (Conover & Schultz 1995; Gilchrist et al. 2004).Many examples of contemporary evolution in responseto climate change exist. In less than 40 years, populationsof the frog

Is density an indicator of breeding success

Abstract: -A new method of measuring reproductive success was used to test Van Horne's (1983) contention that reliance on population density as a measure of habitat quality can produce misleading results. None of the three emberizine sparrows in this study showed a clear correlation between high territory density and high reproductive success. Grasshopper Sparrows (Ammodramus savannarum) were most successful in medium-density plots, and did poorly when territory density was low. Savannah Sparrows (Passerculus sandwichensis) were significantly more successful at low density, and were least successful at high density. Vesper Sparrows (Pooecetes gramineus) were the only species whose reproductive success was unaffected by territory density and, thus, for which density would have been a reasonable measure of habitat quality. These results lend support to Van Horne's thesis that the singular use of density may be a poor indicator of habitat quality and that additional factors should be considered. Received 5 March 1991, accepted 10 February 1992. POPULATION DENSITY frequently is used as an indicator of a habitat's quality, because a greater number of individuals within a given area is generally thought to reflect larger amounts of the necessary resources to sustain a species (Van Horne 1983). By extension, it often is assumed that concentration of resources allowing a high population density also will be reflected in greater reproductive success, or other indices of fitness. Because density is easier to measure than fitness, Flood et al. (1977) and others who model habitat relationships have used density to make inferences about habitat quality, although not necessarily with a high degree of predictive success (Lancia et al. 1982, Bart et al. 1984, Maurer 1986). Van Horne (1983) questioned the singular reliance on density as an indicator of habitat quality and suggested that inferences about which habitats support individuals with the highest fitness often may be false. She suggested that, from a populationviability and management perspective, it is preferable to define habitat quality as a product of density and reproductive success. To test the hypothesis that density is a reasonable index of nesting habitat quality for three grassland sparrows, we examined the relationship between 3Present address: Conservation Department, Massachusetts Audubon Society, Lincoln, Massachusetts 01773, USA. 4Present address: Department of Natural Resources, Field of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 14853, USA. breeding densities and reproductive success for each species. METHODS The study site was located on a sandplain grassland in Kennebunk, York County, Maine (43024'N, 70?59'W). We studied three emberizine sparrows: Vesper Sparrow (Pooecetes gramineus); Savannah Sparrow (Passerculus sandwichensis); Grasshopper Sparrow (Ammodramus savannarum). Vickery et al. (1992) provided additional information on site and methods. The site was managed for commercial blueberry production with one-half of the area mowed and burned on a biennial rotation. This management created profound year-to-year changes in the vegetation structure with a concomitant influence on habitat quality. These habitat manipulations allowed us to measure the avian response to these year-to-year changes in each plot. To examine the relationship between territory density and reproductive success, territories were "spot mapped" (International Bird Census Committee 1970) using eight replicate censuses on eight plots (8-24 ha) for three years (1984-1986). For each species, plots were assigned to a class depending on territory density: low, '2.5 territories per 10 ha; medium, >2.5 to <3.5 territories per 10 ha; high, 23.5 territories per 10 ha. There were at least four plots for each density category. The reproductive-index rank (Vickery et al. 1992) for each territory was assigned to the appropriate density category. We then used the KruskalWallis test (Conover 1980:229) to determine if there were differences in the reproductive-index rankings within each density classification. We measured percent cover for nine vegetation features for high-success and low-success Grasshopper, Savannah and Vesper sparrows, and also measured the same parameters on the unoccupied habitat in each plot. To evaluate whether Savannah Sparrows

Greater drought intensity and frequency before AD 1200 in the Northern Great Plains, USA

Abstract: EXTREME large-scale droughts in North America, such as the 'Dust Bowl' of the 1930s, have been infrequent events within the documented history of the past few hundred years, yet this record may not be representative of long-term patterns of natural variation of drought intensity and frequency. In the Great Plains region of central North America, historical droughts have persisted longer than in any other part of the United States1, but no detailed records of drought patterns in this region have hitherto been obtained that extend beyond the past 500 years. Here we present a reconstruction of drought intensity and frequency over the past 2,300 years in the Northern Great Plains, based on lake salinity fluctuations inferred from fossil diatom assemblages. This record, of sub-decadal resolution, suggests that extreme droughts of greater intensity than that of the 1930s were more frequent before AD 1200. This high frequency of extreme droughts persisted for centuries, and was most pronounced during AD 200–370, AD 700–850 and AD 1000–1200. We suggest that before AD 1200, the atmospheric circulation anomalies that produce drought today were more frequent and persistent.