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.

Paleoecology and the Coarse-Filter Approach to Maintaining Biological Diversity

Abstract: The difficulties of saving millions of species from extinction often cause conservationists to focus on a higher level of biological organization, the community. They do so for two reasons: (1) communities are considered important biological entities in their own right; and (2) conserving representative samples of communities is seen as an efficient way to maintain high levels of species diversity. This approach will work if the chosen communities contain almost all species. Because it potentially saves most but not all species, community conservation is a “coarse-filter” approach to the maintenance of biological diversity, and contrasts with the “fine-filter” approach of saving individual species. Paleoecological information on the distribution of plant taxa in North America, however, indicates that most modern plant communities are less than 8,000 years old and therefore are not highly organized units reflecting long-term co-evolution among species. Rather, they are only transitory assemblages or co-occurrences among plant taxa that have changed in abundance, distribution, and association in response to the large climate changes of the past 20,000 years. During periods when climate changes are large, communities are too ephemeral to be considered important biological entities in their own right. Large climatic changes are also likely to occur during the next century because of increased concentrations of CO2, and we therefore propose that the coarse-filter approach to selecting nature reserves should be more strongly influenced by the distribution of physical environments than by the distribution of modern communities. Ideally, nature reserves should also encompass a broad enough range of environments to allow organisms to adjust their local distribution in response to long-term environmental change and should be connected by regional corridors that would allow species to change their geographic distributions. Resumen: Las dificultades en salvar millones de especies de extincion muchas veces lleva a los conservacionistas a enfocarse a un nivel mas alto de organizacion biologica: la comunidad. Ellos lo hacen por dos razones: 1. las communidades son consideradas entidades biologicas importantes en su derecho, y 2. conservando ejemplos representativos de las communidades se considera manera eficiente de mantener niveles altos de diversidad de especies. Esta aproximacion aproche trabaja si las comunidades escogidas contienen casi todas las especies. Al salvar potencialmente la mayoria, pero no todas las especies, la conservacion de comunidades es solo una aproximacion gruesa para el mantenimiento de la diversidad biologica, y contrasta con la mayor resolucion que representa el de salvar especies individuales. Sin embargo, informacion paleoecologico sobre la distribucion de la taxonomia de plantas en Norte America indica que las comunidades mas modernas de plantas tienen menos de 8,000 anos y por eso no son unidades bien organizadas reflejando coevolucion de largo plazo entre las especies. Mas bien, son ensamblajes transitorios o concurrentes entre la taxonomia de plantas que ban cambiado su abundancia, distribucion y asociacion en respuesta a cambios grandes climaticos de los ultimos 20,000 anos. Durante periodos cuando los cambios de clima son grandes, comunidades son muy efimeras para considerarse entidades biologicos importantes Cambios grandes climaticos tambienson probables durante el proximo siglo por las concentraciones crecientes de CO2, y nosotros, por esta razon proponemos que la aproximucion gruesa de seleccionar reservas de la naturaleza debe ser mas influenciada por la distribucion de ambientes fisicos que por la distribucion de comunidades modernas. Idealmente, las reservas de la naturaleza tambien deben considerar un rango suficientemente amplio de ambientes diferentes para permitir a los organismos a ajustar su distribucion local en respuesta a cambios ambientales de largo plazo. Asi mismo las reservas deben, en lo posible, formar corredores regionales que permitan a las especies cambiar su distribucion geograficas.

A 50,000-year record of climate oscillations from Florida and its temporal correlation with the heinrich events.

Abstract: Oscillations of Pinus (pine) pollen in a 50,000-year sequence from Lake Tulane, Florida, indicate that there were major vegetation shifts during the last glacial cycle. Episodes of abundant Pinus populations indicate a climate that was more wet than intervening phases dominated by Quercus (oak) and Ambrosia-type (ragweed and marsh-elder). The Pinus episodes seem to be temporally correlated with the North Atlantic Heinrich events, which were massive, periodic advances of ice streams from the eastern margin of the Laurentide Ice Sheet. Possible links between the Tulane Pinus and Heinrich events include hemispheric cooling, the influences of Mississippi meltwater on sea-surface temperatures in the Gulf of Mexico, and the effects of North Atlantic thermohaline circulation on currents in the Gulf.

Triploblastic relationships with emphasis on the acoelomates and the position of Gnathostomulida, Cycliophora, Plathelminthes, and Chaetognatha: a combined approach of 18S rDNA sequences and morphology.

Abstract: Triploblastic relationships were examined in the light of molecular and morphological evidence. Representatives for all triploblastic "phyla" (except Loricifera) were represented by both sources of phylogenetic data. The 18S ribosomal (rDNA) sequence data for 145 terminal taxa and 276 morphological characters coded for 36 supraspecific taxa were combined in a total evidence regime to determine the most consistent picture of triploblastic relationships for these data. Only triploblastic taxa are used to avoid rooting with distant outgroups, which seems to happen be? cause of the extreme distance tl tat separates diploblastic from triploblastic taxa according to the 18S rDNA data. Multiple phylogenetic analyses performed with variable analysis parameters yield largely inconsistent results for certain groups such as Chaetognatha, Acoela, and Nemertodermatida. A normalized incongruence length metric is used to assay the relative merit of the multiple analy? ses. The combined analysis having the least character incongruence yields the following scheme of relationships of four main clades: (1) Deuterostomia (((Echinodermata + Enteropneusta) (Cephalo? chordata (Urochordata + Vertebrata)))); (2) Ecdysozoa ((((Priapulida + Kinorhyncha) (Nematoda + Nematomorpha)) ((Onychophora + Tardigrada) Arthropoda))); (3) Trochozoa (((Phoronida + Bra? chiopoda) (Entoprocta (Nemertea (Sipuncula (Mollusca (Pogonophora (Echiura + Annelida)))))))); and (4) Platyzoa (((Gnathostomulida (Cycliophora + Syndermata)) (Gastrotricha + Plathelminthes))). Chaetognatha, Nemertodermatida, and Bryozoa cannot be assigned to any one of these four groups. For the first time, a data analysis recognizes a clade of acoelomates, the Platyzoa (sensu Cavalier-Smith, Biol. Rev. 73:203-266, 1998). Other relationships that corroborate some morphological analyses are the existence of a clade that groups Gnathostomulida + Syndermata (= Gnathifera), which is ex? panded to include the enigmatic phylum Cycliophora, as sister group to Syndermata. (Ecdysozoa; Metazoa; morphology; phylogeny; Platyzoa; 18S rRNA; Triploblastica.)

The pace of modern life II: from rates of contemporary microevolution to pattern and process.

Abstract: We compiled a database of microevolution on contemporary time scales in nature (47 source articles; 30 animal species), comprising 2649 evolutionary rates in darwins (proportional change per million years) and 2151 evolutionary rates in haldanes (standard deviations per generation). Here we demonstrate how quantitative rate measures can provide general insights into patterns and processes of evolution. The frequency distribution of evolutionary rates was approximately log-normal, with many slow rates and few fast rates. Net selection intensities estimated from haldanes were on average lower than selection intensities commonly measured directly in natural populations. This difference suggests that natural selection could easily accomplish observed microevolution but that the intensities of selection typically measured in nature are rarely maintained for long (otherwise observed evolutionary rates would be higher). Traits closely associated with fitness (life history traits) appear to evolve at least as fast as traits less closely tied to fitness (morphology). The magnitude of evolutionary difference increased with the length of the time interval, particularly when maximum rates from a given study were considered. This pattern suggests a general underlying tendency toward increasing evolutionary diversification with time. However, evolutionary rates also tended to decrease with time, perhaps because longer time intervals average increasingly disparate rates over time, or because evolution slows when populations approach new optima or as genetic variation is depleted. In combination, our results suggest that macroevolutionary transitions may ultimately arise through microevolution occasionally ‘writ large’ but are perhaps temporally characterized by microevolution ‘writ in fits and starts’.