4,898 research outputs found
The Rodent assemblages from the late Aragonian and the Vallesian (middle to late Miocene) of the Vallès-Penedès basin (Catalonia, Spain)
Consultable des del TDXTítol obtingut de la portada digitalitzadaLa conca del Vallès-Penedès es una àrea clau per a l'estudi de les successions de mamífers del Miocè europeu, donat que el seu abundant registre cobreix gairebé la totalitat d'aquest període. Recentment, degut a les obres d'ampliació de l'Abocador de Can Mata (ACM), al terme municipal de Els Hostalets de Pierola (l'Anoia, Barcelona), el nombre de jaciments coneguts de micro- i macromamífers s'ha duplicat. L'estudi de les faunes de micromamífers de la sèrie estratigràfica de l'ACM ha permès aportar importants dades bioestratigràfiques per a la definició de les biozones MN 7 i MN 8, actualment basades en localitats aïllades de França i Alemanya. També es proposa una correlació bioestratigràfica amb altres conques ibèriques com Calataiud-Terol. Pel que fa als rosegadors de la sèrie de l'ACM, es descriu una nova espècie de castòrid: Chalicomys n. sp. Aquesta espècie ja presenta un mode de locomoció aquàtica molt similar al del castor actual. Durant les obres d'ampliació de l'ACM es localitzà un nou jaciment, Barranc de Can Vila 1 (BCV1), que, a més d'una abundant mostra de micro- i macrofauna, ha lliurat un esquelet remarcablement complet d'una nova espècie de gran antropomorf: Pierolapithecus catalaunicus. L'estudi dels rosegadors de BCV1 ha permès situar cronològicament aquesta localitat a la part baixa de la MN 7+8, entre els 12,5 i els 12 Ma. En conseqüència aquesta localitat representa el registre més antic dels grans antropomorfs a la Península Ibèrica. L'estudi tafonòmic de les restes recuperades a BCV1 revela que diferents agents tafonòmics estigueren involucrats en la gènesi de l'acumulació. Es reconeix la depredació com el principal agent d'acumulació en el cas de l'individu de primat. Per contra l'acumulació de la majoria de la resta de fòssils no sembla estar associada a l'acció de depredadors i/o carronyaires. La fauna de micromamífers de BCV1 ens indica la presència d'un ambient forestal subtropical i humit en oposició a l'ambient clarament més sec i obert imperant a les conques de l'interior d'Espanya. Aquest fet podria explicar l'absència d'antropomorfs a aquestes àrees durant el Miocè. Seguidament es compara la composició i estructura de la taxocenosi de rosegadors de l'Aragonià terminal i del Vallesià de la conca del Vallès-Penedès amb la dues conques ibèriques (Calataiud-Terol i Duero). Els resultats dels anàlisis estadístics multivariants mostren que les paleocomunitats de rosegadors de la conca del Vallès-Penedès són marcadament diferents de les de les conques de l'interior d'Espanya durant la major part de l'interval de temps considerat. L'ambient al Vallès-Penedès sembla que fou més humit i boscós, assimilant-se a l'existent a zones més septentrionals. Al límit entre el Vallesià Inferior i el Superior (vers fa 9,7 milions d'anys) les paleocomunitats de rosegadors canvien bruscament a totes les conques. Aquest període és testimoni d'un canvi vers a associacions menys diverses i dominades per un o uns pocs gèneres. La diferenciació biogeogràfica existent a la Península Ibèrica es manté i fins hi tot incrementa durant el Vallesià Superior. Aquest canvi abrupte es coneix com la Crisi Vallesiana i també afectà a les comunitats de macromamífers, implicant en ambdós casos l'extinció de formes pròpies del Miocè Mitjà adaptades a ambients càlids i boscosos i resultant en un descens en la diversitat. Mitjançant diferents tècniques es mostra que aquest esdeveniment d'extinció no es va estendre a altres àrees d'Europa, on la diversitat es va mantenir estable o fins hi tot va incrementar.The Vallès-Penedès Basin is a crucial area for the study of the mammal succession of the European Miocene, since its abundant record covers nearly the totality of this period. Recently, thanks to the extension works of a rubbish dump, the so-called «Abocador de Can Mata» (ACM) at Els Hostalets de Pierola (l'Anoia, Barcelona), the number of known micro- and macromammal sites has doubled. The study of the micromammal faunas of the stratigraphic series of the ACM has added important data for the definition of the biozones MN 7 and MN 8, which now are based in isolated sites from France and Germany. We have also proposed biostratigraphic correlation for the Late Aragonian of the Vallès-Penedès Basin to other Iberian basins such as Calatayud-Teruel. Concerning the rodents of the ACM series, a new species of castorid is described: Chalicomys n. sp. This species already shows a mode of aquatic locomotion very similar to that of the extant beaver. A new site which has yielded an abundant sample of micro- and macrofauna, Barranc de Can Vila 1 (BCV1), was discovered during the extension works of the ACM. This site has also provided a remarkably complete skeleton of a new species of great ape: Pierolapithecus catalaunicus. The study of the rodents of BCV1 allows us to chronologically place this site in the lower part of MN 7+8, that is between 12.5 and 12 Ma. Accordingly this locality represents the oldest record of great apes in the Iberian Peninsula. The taphonomical study of the remains recovered at BCV1 reveals that different taphonomical agents were involved in the origin of the accumulation. Predation is recognized as the main accumulation agent in the case of the primate individual. In contrast, the accumulation of the rest of the fossils does not seem related to the action of predators and/or scavengers. The micromammal fauna from BCV1 indicates the presence of a humid subtropical forest environment as opposed to the clearly dryer an more open environment dominant in inner Spanish basins. This fact may account for the absence of great apes in those areas during the Miocene. Straight after that the composition and structure of rodent taxocenosis from the latest Aragonian and the Vallesian of the Vallès-Penedès Basin is compared with those of two Iberian basins (Calatayud-Teruel and Duero). The results of the multivariate statistic analyses show that the rodent paleocommunities of the Vallès-Penedès are markedly different from those of the inner Spanish basins during most of the considered time span. The environment in the Vallès-Penedès Basin appears to have been more humid and forested, being similar to that occurring at higher latitudes. At the Early/Late Vallesian boundary (at 9.7 Ma) an abrupt change in the rodent paleocommunities of all the basins is recorded. This period witnesses a shift towards lower-diversity faunas dominated by one or a few genera. The biogeographic differentiation existing in the Iberian Peninsula is retained and even increases during the Late Vallesian. This abrupt change is known as the Vallesian Crisis and also affected the macromammal communities, implying in both cases the extinction of forms of characteristic of the Middle Miocene and adapted to warm forest environments. That ultimately resulted in a decrease of diversity. By the means of different techniques we show that this extinction event did not affected other areas of Europe, where diversity remained stable or even increased
Classical planar algebraic curves realizable by quadratic polynomial differential systems
In this paper we show planar quadratic polynomial differentialsystems exhibiting as solutions some famous planar invariant algebraic curves. Also we put particular attention to the Darboux integrability of these differential systems.The author is partially supported by a MINECO grant number MTM2014-53703-P and an AGAUR grant number 2014SGR1204.
†The author is partially supported by a FEDER-MINECO grant MTM2016-77278-P, a MINECO grant MTM2013-40998-P, and an AGAUR grant number 2014SGR-56
A Tale of Two Trusts: A Case Study of the Consolidation of Two Community Land Trust Affordable Housing Organizations in Vermont
Between early 2010 and May 2011 the Windham Housing Trust conducted a feasibility analysis to study the possibility of merging with or acquiring the Rockingham Area Community Land Trust, a similar community land trust organization providing affordable housing in an adjacent county.
This study analyzed the one year feasibility study and merger negotiation process between the two organizations, and explored the complex set of relationships between financial partners, communities, residents, and funding stakeholders. The methodology for this work included reviewing current literature about nonprofit mergers and acquisitions, funder involvement, and community impact of consolidating services. In addition the author interviewed five key stakeholders in this merger, reviewed internal and financial documents, and drew on participant observation as a manager with the Windham & Windsor Housing Trust.
The study reveals that more can be learned about the future of the community land trust model of affordable housing in Vermont than the just the technical aspects of the merger. The merger highlights many of the challenges of long term stewardship of an expanding portfolio of affordable housing around the state and extracts key lessons-learned from the merger which may be useful to any small, rural nonprofit interested in merging, but is most likely to be valuable to funding and advocacy organizations who are seeking to maintain networks of providers in their service area in the face of increasing community need
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