The Biodiversity Crisis - Biology LibreTexts
rules” that govern the rates of immigration and extinction of assumed identical . relative species abundance, species-area relationships, and phylogeny than current . broke away from the conventional neo-Darwinian view of ecological. Quantitative models of the species-area-distance relation, based on equilibria between immigration and extinction rates, have been tested against data for birds . To formulate a simple mechanistic model using neutral theory that links extinction debt with the species–area relationship (SAR).
These researchers hypothesized that this iridium spike was caused by an asteroid impact that resulted in the K—Pg mass extinction. In the photo, the iridium layer is the light band.
Which of the following statements most likely represents their findings? An abundance of fern spores from several species was found below the K—Pg boundary, but none was found above. An abundance of fern spores from several species was found above the K—Pg boundary, but none was found below. An abundance of fern spores was found both above and below the K—Pg boundary, but only one species was found below the boundary, and many species were found above the boundary.
Many species of fern spores were found both above and below the boundary, but the total number of spores was greater below the boundary. Link to Learning Explore this interactive website about mass extinctions.
The Pleistocene Extinction The Pleistocene Extinction is one of the lesser extinctions, and a recent one. It is well known that the North American, and to some degree Eurasian, megafauna, or large animals, disappeared toward the end of the last glaciation period.
The extinction appears to have happened in a relatively restricted time period of 10,—12, years ago. In North America, the losses were quite dramatic and included the woolly mammoths last dated about 4, years ago in an isolated populationmastodon, giant beavers, giant ground sloths, saber-toothed cats, and the North American camel, just to name a few. The possibility that the rapid extinction of these large animals was caused by over-hunting was first suggested in the s.
Research into this hypothesis continues today.Ecology:Biodiversity Short Tricks-biology bytes-Ncert Biology for NEET-AIIMS-JIPMER-class 12
It seems likely that over-hunting caused many pre-written history extinctions in many regions of the world. In general, the timing of the Pleistocene extinctions correlated with the arrival of humans and not with climate-change events, which is the main competing hypothesis for these extinctions.
The extinctions began in Australia about 40, to 50, years ago, just after the arrival of humans in the area: In North America, the extinctions of almost all of the large mammals occurred 10,—12, years ago. All that are left are the smaller mammals such as bears, elk, moose, and cougars. Finally, on many remote oceanic islands, the extinctions of many species occurred coincident with human arrivals. Not all of the islands had large animals, but when there were large animals, they were lost.
Madagascar was colonized about 2, years ago and the large mammals that lived there became extinct. Eurasia and Africa do not show this pattern, but they also did not experience a recent arrival of humans. Humans arrived in Eurasia hundreds of thousands of years ago after the origin of the species in Africa.
This topic remains an area of active research and hypothesizing. It seems clear that even if climate played a role, in most cases human hunting precipitated the extinctions. Present-Time Extinctions The sixth, or Holocene, mass extinction appears to have begun earlier than previously believed and has mostly to do with the activities of Homo sapiens.
Species–area relationship - Wikipedia
Since the beginning of the Holocene period, there are numerous recent extinctions of individual species that are recorded in human writings. Most of these are coincident with the expansion of the European colonies since the s. One of the earlier and popularly known examples is the dodo bird. The dodo bird lived in the forests of Mauritius, an island in the Indian Ocean.
The dodo bird became extinct around It was hunted for its meat by sailors and was easy prey because the dodo, which did not evolve with humans, would approach people without fear. Introduced pigs, rats, and dogs brought to the island by European ships also killed dodo young and eggs. Steller's sea cow became extinct in ; it was related to the manatee and probably once lived along the northwest coast of North America. Steller's sea cow was first discovered by Europeans in and was hunted for meat and oil.
The last sea cow was killed in All covariates were mean centred and standardized to facilitate the interpretation and comparison of these models [ 17 ].
An approximate measure of habitat breadth for mammalian species was found by counting the number of Global Land Cover Characteristics GLCC habitat cover classes across all the We then calculated the Kendall's correlation between family species richness and both the number of habitats and number of major habitats.
In order to explore the effects of area on the temporal patterns of recent diversification within mammals, we identified two sets of monophyletic clades from the mammal supertree [ 1819 ], excluding monotypic clades. One set had crown ages younger than 20 Myr cladesthe other had crown ages younger than 10 Myr clades and was nested inside the older set.
We recorded each clade's species richness, stem-group age and present-day area either the total area of all TDWG level 4 provinces or of all biotic regions finest scale in which the component species occurred. We then fitted a suite of six models of diversification rate across each set [ 2021 ]. We also fitted five simplifications of this model by fixing sets of parameters at zero: We optimized parameter estimates for the free variables in each model by maximizing the sum of log likelihoods of the observed species richness n across clades given clade age and the model estimates following [ 21 — 23 ].
As the two methods to define regions gave qualitatively similar results, we report only the TDWG analysis here see the electronic supplementary material for biotic region results. A verbal model for clade diversification in space Diversity-dependent models of diversification have two main features: The precise shape of diversity-dependent diversification has been debated [ 2627 ], but the exact shape of the diversification trajectory should not change the broad-scale implications of the existence of diversity-dependent diversification.
A variety of processes could generate diversity-dependent diversification. Therefore larger islands, at equilibrium, would have a greater number of species. On the other hand, if we have two islands equal in size and habitat diversity but at different distances from the source, then extinction rates would be expected to be the same, but immigration rates would be higher for the nearer island, and at equilibrium the near island would have more species.
The species-area relationship can be approximated by a power function of the form: The constants C and z are fitted from the data on island area and number of species, and so are specific to a data set. Browne and Peck used long-horned beetles Cerambycidae: Coleoptera to investigate the species-area relationship in the Florida Keys and mainland.
Their data are plotted below, using the log10 of the area and species number. The two data points furthest to the right represent, from left to right, South Florida the area south of Lake Okeechobee and the entire state of Florida.