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Videos de Conceptos Relacionados

Threats to Biodiversity01:50

Threats to Biodiversity

There have been five major extinction events throughout geological history, resulting in the elimination of biodiversity, followed by a rebound of species that adapted to the new conditions. In the current geological epoch, the Holocene, there is a sixth extinction event in progress. This mass extinction has been attributed to human activities and is thus provisionally called the Anthropocene. In 2019 the human population reached 7.7 billion people and is projected to comprise 10 billion by...
Conservation of Declining Populations02:07

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Conservation of declining population focuses on ways of detecting, diagnosing, and halting a population decline. The approach uses methods to prevent populations from going extinct.
Population Growth00:57

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Population size is dynamic, increasing with birth rates and immigration, and decreasing with death rates and emigration. In ideal conditions with unlimited resources, populations can increase exponentially, which plots as a J-shaped growth rate curve of population size against time. This type of curve is characteristic of newly-introduced invasive species, or populations that have suffered catastrophic declines and are rebounding.However, realistic environmental conditions limit the number of...
Genetic Drift03:33

Genetic Drift

Natural selection—probably the most well-known evolutionary mechanism—increases the prevalence of traits that enhance survival and reproduction. However, evolution does not merely propagate favorable traits, nor does it always benefit populations.Life is not fair. A deer grazing contentedly in a field can have her meal cut tragically short by a bolt of lightning. If the doomed doe is one of only three in the population, 1/3 of the population’s gene pool is lost. Random events like this can...
Limits to Natural Selection01:38

Limits to Natural Selection

Organisms that are well-adapted to their environment are more likely to survive and reproduce. However, natural selection does not lead to perfectly adapted organisms. Several factors constrain natural selection.For one, natural selection can only act upon existing genetic variation. Hypothetically, redtusks may enhance elephant survival by deterring ivory-seeking poachers. However, if there are no gene variants—or alleles—for redtusks, natural selection cannot increase the prevalence of...
Conservation of Small Populations02:04

Conservation of Small Populations

Small population sizes put a species at extreme risk of extinction due to a lack of variation, and a consequent decrease in adaptability. This weakens the chances of survival under pressures such as climate change, competition from other species, or new diseases. Large populations are more likely to survive pressures such as these, as such populations are more likely to harbor individuals that have genetic variants that are adaptive under new stresses. Small populations are much less likely to...

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Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling
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Published on: July 4, 2007

La mortalidad masiva y sus consecuencias ambientales y evolutivas.

K J Hsü, Q He, J A McKenzie

    Science (New York, N.Y.)
    |April 16, 1982
    PubMed
    Resumen

    El evento de extinción del Cretácico-Terciario causó una disminución significativa en la productividad del océano, lo que condujo a un aumento del dióxido de carbono atmosférico y un subsiguiente aumento de la temperatura. Esta extinción se desarrolló durante decenas de miles de años, en consonancia con un escenario de impacto cometario.

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    Área de la Ciencia:

    • La paleoceanografía es la paleoceanografía.
    • La bioestratigrafía es una estratigrafía biológica.
    • La geoquímica es la geoquímica.

    Sus antecedentes:

    • El límite Cretácico-Terciario (K-Pg) marca un evento significativo de extinción masiva.
    • Proyecto de perforación de aguas profundas (DSDP) Sitio 524 ofrece un registro sedimentario detallado de esta transición.

    Objetivo del estudio:

    • Para reconstruir los cambios ambientales y biostratigráficos en el límite K-Pg.
    • Para investigar la dinámica del ciclo del carbono océano-atmósfera durante la extinción.
    • Para evaluar el momento y la duración del evento de extinción.

    Principales métodos:

    • Análisis de composiciones masivas de carbonato y metales traza en muestras de sedimentos muy espaciadas.
    • Análisis isotópicos de oxígeno y carbono de núcleos de sedimentos.
    • El examen biostratigráfico de los microfósiles.

    Principales resultados:

    • Se produjo una reducción en la productividad oceánica en el límite K-Pg.
    • El dióxido de carbono disuelto se transfiere de los océanos a la atmósfera, aumentando los niveles de CO2 atmosférico.
    • Los datos de isótopos de oxígeno revelan un posterior aumento de la temperatura durante 50.000 años.
    • Los fósiles de afinidad con el Cretácico encontrados en los sedimentos terciarios más bajos sugieren supervivencia y/o reelaboración.

    Conclusiones:

    • El evento de extinción de K-Pg condujo a un período prolongado de CO2 atmosférico elevado y calentamiento.
    • La extinción de los organismos pelágicos ocurrió durante decenas de miles de años.
    • Los hallazgos son consistentes con un impacto cometario que desencadena la mortalidad masiva y los cambios ambientales.