Biodiversity in Ecosystems
Ecologists measure biodiversity, a general term for the variety present in the biosphere, by taking into account both the number of species and their commonness.
Extinction is a natural process of macroevolution that occurs at the rate of about one out of 1 million species becoming extinct per year.
Genetic diversity or variation is the raw material for adaptation in a species. A species’ future potential for adaptation depends on the genetic diversity held in the genomes of the individuals
Ecosystem diversity, is defined as the number of different ecosystems on the planet or in a given geographic area.
Biodiversity hotspots are geographical areas that contain high numbers of endemic species.
The Five Mass Extinctions
The Ordovician-Silurian extinction event is the first recorded mass extinction and the second largest, about 85 percent of marine species (few species lived outside the oceans) became extinct.
The late Devonian extinction may have occurred over a relatively long period of time. It appears to have affected marine species and not the plants or animals inhabiting terrestrial habitats.
The end-Permian extinction was the largest in the history of life. Estimates are that 96 percent of all marine species and 70 percent of all terrestrial species were lost.
The causes of the Triassic-Jurassic extinction event are not clear and hypotheses of climate change, asteroid impact, and volcanic eruptions have been argued.
During the end-Cretaceous extinction event the dinosaurs, the dominant vertebrate group for millions of years, disappeared from the planet, every land animal that weighed more then 25 kg became extinct.
The Pleistocene Extinction is one of the lesser extinctions, and a recent one.
The Holocene, mass extinction appears to have begun earlier than previously believed and has mostly to do with the activities of Homo sapiens. There are numerous recent extinctions of individual species that are recorded in human writings.
Estimates of Extinction Rates
The background extinction rate is estimated to be about one per million species per year (E/MSY).
One contemporary extinction rate estimate uses the extinctions in the written record since the year 1500.
Log in to save your progress and obtain a certificate in Alison’s free Ecology Studies - Conservation Biology and Biodiversity online course
Sign up to save your progress and obtain a certificate in Alison’s free Ecology Studies - Conservation Biology and Biodiversity online course
Please enter you email address and we will mail you a link to reset your password.