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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

Conservation of Declining Populations

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

Population Growth

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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Updated: Jul 11, 2026

Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling
20:36

Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling

Published on: July 4, 2007

集団死亡率とその環境的,進化的影響

K J Hsü, Q He, J A McKenzie

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

    クレータ紀・三次紀の絶滅は,海洋の生産性が著しく低下し,大気中の二酸化炭素が増加し,その後の気温上昇を引き起こした. この絶滅は数万年にわたって展開され,彗星の衝突シナリオと一致しています.

    さらに関連する動画

    Resurrection of Dormant Daphnia magna: Protocol and Applications
    07:37

    Resurrection of Dormant Daphnia magna: Protocol and Applications

    Published on: January 19, 2018

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems
    07:41

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

    Published on: July 30, 2019

    関連する実験動画

    Last Updated: Jul 11, 2026

    Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling
    20:36

    Predicting the Effectiveness of Population Replacement Strategy Using Mathematical Modeling

    Published on: July 4, 2007

    Resurrection of Dormant Daphnia magna: Protocol and Applications
    07:37

    Resurrection of Dormant Daphnia magna: Protocol and Applications

    Published on: January 19, 2018

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems
    07:41

    Modeling the Size Spectrum for Macroinvertebrates and Fishes in Stream Ecosystems

    Published on: July 30, 2019

    科学分野:

    • パレオセアノグラフィー
    • バイオストラティグラフィー
    • 地質化学 地質化学

    背景:

    • クレータ紀-三次紀 (K-Pg) の境界線は,重大な大量絶滅の出来事を示しています.
    • 深海掘削プロジェクト (DSDP) サイト524は,この移行の詳細な堆積物の記録を提供します.

    研究 の 目的:

    • K-Pg境界の環境と生物ストラティグラフィックの変化を再構築する.
    • 絶滅期間の海洋大気炭素循環の動態を調査する.
    • 絶滅イベントのタイミングと期間を評価する.

    主な方法:

    • バルク炭酸塩および微量金属組成物の分析. 近い距離の堆積物サンプル.
    • 堆積物核の酸素と炭素の同位体分析.
    • 微生物化石のバイオストラティグラフィック検査.

    主要な成果:

    • 海洋生産性の低下は,K-Pg境界で発生しました.
    • 溶けた二酸化炭素が海洋から大気中に流れ,大気中のCO2濃度が上昇した.
    • 酸素イソトープデータは,5万年以上にわたる温度上昇を明らかにしています.
    • 最下層の三次期の堆積物で見つかった白期の親類化石は,生存および/または再処理を示唆しています.

    結論:

    • K-Pgの絶滅は,大気中のCO2が増加し,温暖化が長期間続いた.
    • ペラジック生物の絶滅は,数万年にわたって起こった.
    • この発見は,彗星の衝突が集団死亡率と環境変化を引き起こしたものと一致しています.