Nothing lasts forever. Species, too, become extinct. The ...

Nothing lasts forever. Species, too, become extinct. The ...

Fig. 14.8a Horseshoe crab" fossil from the Ordovician Age. This 450-million-year-old fossil is no different from specimens living today. Chapter 13 Extinctions Nothing lasts forever. Species, too, become extinct. The paleontologist G. G. Simpson estimated; since the Cambrian 544 million years ago, more

than 99% are extinct today. Evolution: speciation vs extinction Had the dinosaurs not become extinct, mammals may never have experienced the opportunity to radiate SurvivorsLingula A marine organism (brachiopod) occupying vertical burrows in sand and mud has survived morphologically unchanged since the Silurian.

SurvivorsHorseshoe crabs The horseshoe crab, an inhabitant of marine shores, has lived morphologically unchanged since the Ordovician. A horseshoe crab in ventral (underside) view is shown. Species come and go Some taxonomic groups are carried out as part of

large, wide-spread catastrophic or mass extinctions. In uniform or background extinctions, members of taxonomic groups are lost gradually over long time periods without abrupt loss of large numbers. Most of the 99% of species now extinct were lost not suddenly, but slowly, Fig. 24.24 Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Macroevolution is an evolutionary event the origin of species and higher-level taxa.

FIGURE 6.5 Morphological Series Why species become extinct Horses arose in North America during the Eocene and spread eventually to Asia, Africa, and South America. As the most recent glacial ice sheet went into retreat 15, 000 years ago, horses became extinct in North and South America,

but survived in Europe and Asia, and in Africa as zebras. Change in habitat, and unfavorable horse perished Four hundred years ago, the Spanish invaded North America, bringing with them again. Coevolution Dodo bird (extinct)

The koala lives in Australia and feeds exclusively on the leaves of eucalyptus trees whose toxic oils are harmful to other herbivores. Koala

Co-evolution extinction of the island dodo bird in the sevente enth century endangered the Calvaria tree. The koala, an Australian marsupial, feeds exclu sively upon the leaves of eucalyptus trees, who se toxic oils are harmful to other herbivores. Th e koalas digestive system neutralizes these toxi ns.

Eucalyptus alba Eucalyptus albens Eucalyptus amygdalina Eucalyptus aromaphloia Eucalyptus baileyana Eucalyptus balladoniensis Eucalyptus bicostata Eucalyptus botryoides Eucalyptus brachyandra Eucalyptus brassiana

Eucalyptus brevistylis Eucalyptus brockwayi Eucalyptus camaldulensis (Murray red gum) Eucalyptus ceracea Eucalyptus cloeziana (Queensland messmate) Eucalyptus coccifera Eucalyptus cordata Eucalyptus cornuta Eucalyptus corticosa Eucalyptus crebra

Eucalyptus croajingolensis Eucalyptus curtisii Eucalyptus dalrympleana Eucalyptus deglupta Eucalyptus delegatensis Eucalyptus delicata Eucalyptus diversicolor Eucalyptus diversifolia Eucalyptus dives Eucalyptus dolichocarpa

Eucalyptus dundasii Eucalyptus dunnii Eucalyptus elata Eucalyptus erythrocorys (illyarie) Eucalyptus erythrophloia Eucalyptus eudesmoides Eucalyptus falcata Eucalyptus gamophylla Eucalyptus glaucina Eucalyptus globulus (blue gum)

Eucalyptus globulus subsp. bicostata Eucalyptus globulus subsp. globulus Eucalyptus gongylocarpa

Eucalyptus globulus subsp. globulus Eucalyptus gongylocarpa Eucalyptus grandis Eucalyptus grandis x Eucalyptus nitens

Eucalyptus grandis x Eucalyptus urophylla Eucalyptus guilfoylei Eucalyptus gunnii (cider tree) Eucalyptus haemastoma (scribbly gum) Eucalyptus hallii Eucalyptus houseana Eucalyptus jacksonii Eucalyptus lansdowneana Eucalyptus latisinensis Eucalyptus leucophloia

Eucalyptus leucoxylon (white ironbark) Eucalyptus lockyeri Eucalyptus lucasii Eucalyptus maidenii Eucalyptus marginata Eucalyptus megacarpa Eucalyptus melliodora Eucalyptus michaeliana Eucalyptus microcorys (tallowwood) Eucalyptus microtheca Eucalyptus morrisbyi

Eucalyptus muelleriana (yellow stringybark) Eucalyptus nitens Eucalyptus nitida Eucalyptus obliqua (messmate stringybark) Eucalyptus obtusiflora Eucalyptus occidentalis Eucalyptus optima Eucalyptus ovata Eucalyptus pachyphylla Eucalyptus pauciflora

Eucalyptus pellita Eucalyptus perriniana Eucalyptus petiolaris Eucalyptus pilularis Eucalyptus piperita Eucalyptus platyphylla Eucalyptus polyanthemos Eucalyptus populnea Eucalyptus preissiana (bell-fruited mallee) Eucalyptus pseudoglobulus

Eucalyptus pulchella Eucalyptus radiata

Eucalyptus regnans Eucalyptus risdonii Eucalyptus robertsonii Eucalyptus rodwayi Eucalyptus rubida Eucalyptus rubiginosa Eucalyptus saligna Eucalyptus salmonophloia Eucalyptus scoparia

Eucalyptus sieberi Eucalyptus spathulata Eucalyptus staeri Eucalyptus stoatei Eucalyptus tenuipes Eucalyptus tenuiramis Eucalyptus tereticornis Eucalyptus tetragona (white-leaved marlock Eucalyptus tetrodonta Eucalyptus tindaliae

Eucalyptus torquata Eucalyptus umbra Eucalyptus urophylla Eucalyptus vernicosa Eucalyptus viminalis Eucalyptus wandoo Eucalyptus wetarensis Eucalyptus willisii

Eucalyptus willisii subsp Eucalyptus willisii subsp Eucalyptus woodwardii Species Area relationships The larger an island, the more species of plants and animals the island supports. Conversely, the

smaller the area, the fewer the species. Species area relationship One factor contributing to new species appearance on this island is the immigration rate of new species arriving on the island from the mainland. A second factor, acting in opposition to immigrati on rate, is the extinction rate. We would likely find fewer total number of species t han the number present on the mainland.

A basic model of island equilibrium. Immigration an d extinction act in opposite ways, tending to add or eliminate species, respectively. FIG. 13.3 Immigration and Extinction on Islands (a) Immigration curve. As colonists fill the island, the rate of arrival of new species drops. (b) Extin ction curve. As colonists fill up the island, the rat e at which species disappear increases. (After M

acArthur and Wilson 1967.) FIGURE 13.4 Species Equilibrium Where immigration and extinction curves cross, an equilibrium number of species is reached. In this example, there are 10 species on the nearby mainland, making it possible for up to 10 species to be on the island. However, in this example the equilibrium sustainable by the island is 6. The equilibrium number depends upon the actual ecological hospitality and resource

richness of the particular island. But the general principle will be the same. Islands will reach an equilibrium number of species that is below that of the larger mainland nearby. (Roderick and Gillespie, 1998) Suppose we change the location of our island relative to the mainland. What happens to the

equilibrium Because it is the same island; so the extinction curve remains unchanged. However, the immigration curve adjusts. Located farther from the mainland, the chance that new species will reach the distant island decreases overall. Distance affects the immigration rate. Now suppose that we keep the island in the same location relative to the mainland but

change the area of the island. What happens now? If we make the island larger, the immigration rate increases because the island is a larger target, the extinction rate, declines overall because a larger island has more space and resources. The reverse occurs if we make our island smaller, and extinctions would follow. Distance and Area Effects on Species Equilibrium

(a) Distance effect. If our island (from figure 13.4) were moved farther from the mainland, the equilibrium would shift to the left, settling at 2, and some species would become extinct on the island. (b) Area effect. A large island reaches a higher equilibrium than a small island. It often produces many fragmented and isolated groups out of the original, single population. Because isolated groups are smaller,

Island Insights From the standpoint of a species, alpine mountaintops, separated bodies of water, or an isolated tree can be islands. What we have modeled on proper islands is also applicable to a variety of other situations in nature, where small parcels of habitat stand apart from large enclaves of resources elsewhere. Reducing area reduces the number of species

supported, and extinctions follow. Red Queen Leigh Van Valen expected extinctions to be abr upt, the result of some sudden, unfavorable cha nge in the environment. What he found instead was that most groups of species became extinct gradually, at a constant rate characteristic of their taxonomic group.

FIGURE 13.6 Phylogeny of a Group FIGURE 13.7 Evolutionary protists deer Survivorship Curves ferns

horses (a) Protists: foraminifera. (b) Mammals: artiodactyladeer, elk, and related sp ecies. (c) Pteridophyta: ferns and related species. (d) Mammals: perissodactyl ahorses and related species. M.Y.: millions of years passed. (After Van Vale n 1973.)

Red Queen Hypothesis.--The "Red Queen" hypothesis is us ed to describe two similar ideas, which are both based on co evolution. The original idea is that coevolution could lead to situations f or which the probability of extinction is relatively constant ov er millions of years (Van Valen 1973). The gist of the idea is that, in tightly coevolved interactions, evolutionary change by one species (e.g., a prey or host) co uld lead to extinction of other species (e.g. a predator or par asite.

Van Valen named the idea "the Red Queen hypothesis," bec ause, under this view, species had to "run" (evolve) in order t o stay in the same place (extant). 3000 200

Assessment of Uniform Extinctions Among species of plants, mammals, insects, and marine invertebrates, the typical survival time of a species varies--marine invertebrates are the most resilient, with an average species survival time of around 30 million years, and mammal species generally are the least durable, averaging about 2 or 3 million years per species.

Mass Extinctions Select, at random, ten samples of genera fro m a large data set of fossils, then plot the ma ximum and minimum numbers becoming extinct over available intervals of time. Five common extinction peaks are noted-late in or at the end of the Ordovician, Devonian, Per mian, Triassic, and Creatceous. FIGURE 13.8 Extinction EpisodesRandom Sample

Of more than 19,000 genera, 10 samples of 1,000 genera were chosen at random and the percentage becoming extinct was plotted. Major peaks of mass extinction are indicated. Family in Tetr apods

Based largely upon families of marine vertebrates and invertebrates. The total extinction rate can be determined from the fossil record calculated as the number of families becoming extinct per million-year interval. Mass extinctions case studies The first occurred at the end of Ordovician, with

85% of marine species becoming extinct within about 10 million years. The late-Devonian extinction, which lasted less than 3 million years and took an estimated 83% of marine species. At the end of the Permian, and saw a loss of 53% of marine invertebrate families. At the end of the Triassic, lasted 4 million years, and took many land vertebrates, but up to

80% of all marine species. At the end of the Cretaceous, taking all the dinosaurs, many large marine reptiles, small foraminifera, and many other marine species, over a period of about 1 million years. Several categories of extinction causes have been proposed: plate tectonics , ice ages, and cosmic collisions.

Collision zones Continents and extinctions Mingling of species The isthmus of Panama-the first land connection between the two continents in more than 60 million years. Today, almost half of the medium to large

mammalian species in South America originated in North America; and about onequarter of those in North America originated in South America. vs competition On each of the separated continents, organisms were accommodated to each other. But with the s udden, on a geologic time scale, appearance of n

ew competitors arriving across the land bridge, th e co-evolutionary dynamics were suddeningly cha nged. There were new competitors, and little ti me to adapt. Prediction: We would predict that at moments in Earth history when isolated continents made first contact, mass extinctions should occur. Test cases

1. At the end of the Permian, plate tectonics had b rought all the major continents of the world togeth er into a supercontinent called Pangaea. 2. At the end of the Cretaceous-the continents wer e actually moving apart, separating them. Trophic stability The more stable the trophic resources, the mor e species; conversely, the more unstable the tro phic resources, the fewer the species.

When continents come together, trophic resou rces are unstable, leading to low numbers of spe cies When the same landmass is broken up into separ ate continents, trophic resources are more stable and more species. The reason is that when a large continent breaks up into separate, smaller continents, the surroundi ng ocean has more influence in moderating the co

ntinental climate. Predictions: When plate tectonics bring continents together i nto one supercontinent, mass extinctions shoul d occur. Fragments into separate continents, mass extin ctions should be absent. Test cases 1. the end of the Permian

2. the end of the Cretaceous fragmenting into the smaller and more recognizable continents Changes in sea level Sea-level changes may result from the influence of plate tectonic activity.

If the ocean basins deepen, sea level along the continental edges drops; if the ocean basins be come more shallow, sea level rises. Glacial activity, A drop in sea level has three consequences First, shallow marine habitat is lost. Second, a drop in sea level indirectly leads to more severe terrestrial climates of the interior

continent. Third, the groundwater table drops, indirectly leading to dry, even drought, conditions within the interior of the continent. Drop 100-200 meters Predictions:

Mass extinctions should correlate with a drop in sea level. Conversely, a rise in sea level should not coincide with mass extinctions. 1. at the end of the Permian, the sea level dropped significantly 2. sea level also dropped at the end of the Cretaceous, by some estimates by as much as 150 to 200 meters. Ice ages we are currently, right now, in an ice ag

e. One of at least three , during the Phanerozoic. An ice age is made up of cycles wherein there is a glacial phase (climate cools, ice sheets form and s pread) and an interglacial phase (climate temporari ly warms, ice sheets retreat). A wobbling of the earth on its axis plate tectonics that might move continents into positions where they intercept and disrupt the flow

of warm tropical waters to polar regions. Reflects more sunlight back into space, and the climate cooling deepens. Deep ice cores taken from old galciers in Greenlan d and Antarctica give an almost annual record of cl imate conditions over the last 252,000 years. Polle n and oxygen isotopes captured in each annual cy cle of the corer bear witness to the annual flora an d temperatures,

oxygen comes in several varieties, called isotopes: oxygen-18(O18) and oxygen-16 (O16); The ratio goe s up or down with the temperature. Each layers isotope ratios can be used to calculat e the successive climate temperatures, The current ice age began about 30 to 40 million years ago, We are currently enjoying an interglacial phase that began only about 12,000 years ago,

lasted about 100,000 years and was preceded by an interglacial period lasting 20,000 years, and so on back through vacillating cycles over the 30 to 40 million years of the current ice age. Prediction: glacial phases accompanied by a drop in average t emperatures, and deterioration of climate, During interglacial phases, climate recovers and w arms, and galciers retreat. Such dramatic environ

mental changes Ice ages should correlate with mass extinctions. Test Cases Only the end of the Ordovician is roughly correlate d with an ice age. Asteroid collision with the Earth This figure depicts events on the young planet Earth when, still hot from its cosmic birth, it endured a pummeling by rocky

debris 4 billion years ago. This bombardment waned but did not cease entirely. A similar strike by cosmic debris (asteroid or comet) is thought by some scientists to have caused the extinction of dinosaurs 65 million years ago. Until recently, convincing evidence supported the proposal that earthly extinctions occurred on a regular schedule, about every 26 million years.

Iridium spikes, big jumps in iridium concentration, were documented in rocky formations at the very end of the Cretaceous. Mineral formed under high heat and pressure An impact crater at this same time horizon and about 100 miles (150km) The object that produced it is estimated to have been almost 6 miles (10km) wide. Cosmic collision

At the end of the Cretaceous, an asteroid or comet struck the Earth in the location of present day Yucatan Peninsula in Mexico. Although such a collision certainly occurred, it is debated whether or not this collision was directly responsible for the dinosaur extinctions. Critique of Collision Theory First of all, it is too fast. The scenario of extinctions is

completed within years, Second, dinosaur numbers were already dwindling several million years before the asteroid impact occurred. Third, the catastrophe was too selective. Amphibians showed no; nor turtles or crocodiles or mammals, Others have suggested that prolonged volcanism might be the cause. Adapting to changes As environment changes, the population at

A experiences a decline (bell-shaped curve) through time and becomes extinct. At B, the original population declines to extinction, but before then a lineage diverges via speciation to survive. Applied island biogeography Principles of island biogeography applied to the management of nature reserves helps make decisions about survival of organisms living in the reserve. In each

comparison, design A is superior to B. Origin and extinction The rise and fall of various groups of anim als are shown relative to the geologic time scale. The Permo-Triassic and Cretaceous extinctions are evident. Extinction of dinosaurs After their demise at the end of the

Cretaceous, dinosaurs were replaced as dominant land vertebrates by birds and mammals. [The geologic dates given here are now revised, but provide a relative picture of groups.] After the dinosaurs Extinction of the dinosaurs left may ecological niches empty. In part, the subsequent flourishing of mammals and

birds represents an adaptive radiation into many of these vacated life styles.

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