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Institution

University of Maine

EducationOrono, Maine, United States
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.


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Journal ArticleDOI
TL;DR: In this article, the evolution of the Lake Malawi cichlid population has been discussed in relation to current ideas on allopatric speciation, and the changes in lake level imply longterm changes in climate; these are highly relevant in the field of droughtrisk assessment.
Abstract: Lake Malawi, the third largest lake in Africa, is several million years old. Lake levels have fluctuated to a considerable extent in the late Pleistocene. Although tectonism may have influenced earlier level changes, the more recent changes have been climatically controlled. Major recessions occurred in the period before 25 000 years ago and 10740 $\pm $ 130 years ago, with further large falls between 1150 and 1250 A.D. and within the period 1500-1850. The 1500-1850 lake recession-refilling cycle is documented by using a variety of techniques. Sediment cores show an erosional hiatus stretching across the southern area of Lake Malawi down to water depths of at least 121 m. Diatoms sharply decline in abundance and diversity across this break, with Melosira nyassensis dominating in the post-erosion period. During the low stage, exposed littoral sands were reworked into aeolian dune-fields along windward shorelines. Oral histories reflect a group memory of this low period, which is supported by $^{14}$C dated archaeological finds in beach ridges surrounding the lake. Dating by $^{210}$Pb methods show that lacustrine sedimentation had resumed by about 1860. At this time, early explorers, such as Livingstone, were reporting evidence of rising lake levels. Hydrological modelling shows that the lake-level changes indicated are possible in the timespan available. Various permutations of rainfall and timescale are discussed, e.g. a drop of 110 m over 250 years would require rainfall at 50% of modern values. The changes in lake level imply longterm changes in climate; these are highly relevant in the field of droughtrisk assessment. The species flock of rocky-shore dwelling Lake Malawi cichlids known as `Mbuna' contains about 200 species in Malawi's waters. Mitochondrial DNA differentiation shows that the flock as a whole is of extremely recent origin. Almost every rocky outcrop and island has a unique Mbuna fauna, with endemic colour forms and species. As many of these islands and outcrops were dry land within the last 200-300 years, the establishment of the faunas has taken place within that time. The evolution of distinct forms in such a brief timespan is discussed in relation to current ideas on allopatric speciation. The present diversity of the Malawi cichlid-species flock, and particularly the Mbuna, may be readily explained by the rapidity with which small founder populations can diverge from the parent population, as demonstrated by the present chronological evidence on changes in lake levels and by the Mbuna distribution data. The repeated recessions and refillings of the lake have provided numerous opportunities for the establishment of different founder populations and consequently different selection pressures, leading to further bouts of speciation.

239 citations

Journal ArticleDOI
01 Jun 2005-Geology
TL;DR: The mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance as discussed by the authors, but they offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory.
Abstract: The mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance. We offer definitive evidence on the mode of bubble formation in the form of X-ray computed tomographic images and comparison with theory. Natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids (disks) that grow either by fracturing the sediment or by reopening preexisting fractures. In contrast, bubbles in soft sandy sediment tend to be spherical, suggesting that sand acts fluidly or plastically in response to growth stresses. We also present bubble-rise results from gelatin, a mechanically similar but transparent medium, that suggest that initial rise is also accomplished by fracture. Given that muddy sediments are elastic and yield by fracture, it becomes much easier to explain physically related phenomena such as seafloor pockmark formation, animal burrowing, and gas buildup during methane hydrate melting.

238 citations

Journal ArticleDOI
TL;DR: In this paper, two extreme late Wisconsin reconstructions of the Ross ice drainage system were given, showing little elevation change of the polar plateau coincident with extensive ice-shelf grounding along the inner Ross Embayment.

238 citations

Journal ArticleDOI
TL;DR: Anthropogenic burning in New Zealand highlights the vulnerability of closed-canopy forests to novel disturbance regimes and suggests that similar settings may be less resilient to climate-induced changes in the future.
Abstract: Humans have altered natural patterns of fire for millennia, but the impact of human-set fires is thought to have been slight in wet closed-canopy forests. In the South Island of New Zealand, Polynesians (Māori), who arrived 700–800 calibrated years (cal y) ago, and then Europeans, who settled ∼150 cal y ago, used fire as a tool for forest clearance, but the structure and environmental consequences of these fires are poorly understood. High-resolution charcoal and pollen records from 16 lakes were analyzed to reconstruct the fire and vegetation history of the last 1,000 y. Diatom, chironomid, and element concentration data were examined to identify disturbance-related limnobiotic and biogeochemical changes within burned watersheds. At most sites, several high-severity fire events occurred within the first two centuries of Māori arrival and were often accompanied by a transformation in vegetation, slope stability, and lake chemistry. Proxies of past climate suggest that human activity alone, rather than unusually dry or warm conditions, was responsible for this increased fire activity. The transformation of scrub to grassland by Europeans in the mid-19th century triggered further, sometimes severe, watershed change, through additional fires, erosion, and the introduction of nonnative plant species. Alteration of natural disturbance regimes had lasting impacts, primarily because native forests had little or no previous history of fire and little resilience to the severity of burning. Anthropogenic burning in New Zealand highlights the vulnerability of closed-canopy forests to novel disturbance regimes and suggests that similar settings may be less resilient to climate-induced changes in the future.

237 citations

Journal ArticleDOI
TL;DR: Cultural appropriate childhood and adolescent interventions for reservation-based populations must be developed, tested and evaluated longitudinally to address the relationship between the number of types of exposures to ACEs and risk behaviors and mental health outcomes among reservation- based Native Americans.
Abstract: Adverse childhood experiences (ACEs) are associated with numerous risk behaviors and mental health outcomes among youth. This study examines the relationship between the number of types of exposures to ACEs and risk behaviors and mental health outcomes among reservation-based Native Americans. In 2011, data were collected from Native American (N = 288; 15-24 years of age) tribal members from a remote plains reservation using an anonymous web-based questionnaire. We analyzed the relationship between six ACEs, emotional, physical, and sexual abuse, physical and emotional neglect, witness to intimate partner violence, for those <18 years, and included historical loss associated symptoms, and perceived discrimination for those <19 years; and four risk behavior/mental health outcomes: post-traumatic stress disorder (PTSD) symptoms, depression symptoms, poly-drug use, and suicide attempt. Seventy-eight percent of the sample reported at least one ACE and 40 % reported at least two. The cumulative impact of the ACEs were significant (p < .001) for the four outcomes with each additional ACE increasing the odds of suicide attempt (37 %), poly-drug use (51 %), PTSD symptoms (55 %), and depression symptoms (57 %). To address these findings culturally appropriate childhood and adolescent interventions for reservation-based populations must be developed, tested and evaluated longitudinally.

237 citations


Authors

Showing all 8729 results

NameH-indexPapersCitations
Clifford J. Rosen11165547881
Juan S. Bonifacino10830346554
John D. Aber10720448500
Surendra P. Shah9971032832
Charles T. Driscoll9755437355
Samuel Madden9538846424
Lihua Xiao9349532721
Patrick G. Hatcher9140127519
Pedro J. J. Alvarez8937834837
George R. Pettit8984831759
James R. Wilson89127137470
Steven Girvin8636638963
Peter Marler8117422070
Garry R. Buettner8030429273
Paul Andrew Mayewski8042029356
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Performance
Metrics
No. of papers from the Institution in previous years
YearPapers
202332
2022134
2021834
2020756
2019738
2018725