Modes of Evolution Speciation Extinction Macroevolution Major transformations

Modes of Evolution

Speciation, Extinction, & Macroevolution Major transformations in anatomy, phylogeny, ecology. And behavior, which usually take place in larger clades are known as macroevolutionary patterns. The emergence of new species through speciation, and their disappearance through extinction, is a simple macroevolutionary pattern.

What patterns describe the sequential nature of groups in the fossil record? The emergence, growth, and extinction of larger clades, such as dinosaurs, mammals, or flowering plants, are examples of macroevolutionary patterns that describe the sequential nature of groups in the fossil record. Fossil record provides evidence about the nature and rate of evolutionary change in species and larger clades.

Macroevolution and Cladistics Fossils are classified using the same cladistic techniques used to classify living species. In some cases, fossils are placed in clades that contain only extinct organisms. In other cases, fossils are classified into clades that include living organisms. Cladograms illustrate hypotheses about how closely related organisms are by proposing relationships among living species, extinct species, and common ancestors they share.

Speciation, Extinction, & Macroevolution Dinosauria Ornithischia Crocodiles Ornithischians Saurischia Sauropods T. rex Aves Archaeopteryx Modern birds **Note that hypothesizing that an extinct species is related to a living species is not the same thing as claiming that the extinct organism is a direct ancestor of that living species.

Patterns of Extinction Species are always becoming extinct as they adapt, or fail to adapt, to competition and changing environments. Paleontologists describe this kind of “business as usual” extinction as background extinction. During background extinction, there is likely a period of “stasis” for many species. Rates of background extinction vary over time. But every now and then, something really different happens—a mass extinction during which many species become extinct over a relatively short time period.

Mass Extinction A mass extinction isn’t just a small increase in background extinction. Entire ecosystems vanish, and entire food webs collapse. Species become extinct because their environment breaks down and the ordinary process of natural selection can’t compensate quickly enough.

Patterns of Extinction

Rate of Evolution: Gradualism Darwin suggested that evolution proceeded slowly and steadily, an idea called gradualism. These species are said to have been in a state of equilibrium, or stasis. This means that their structures do not change much even though they continue to evolve genetically.

Rates of Evolution: Punctuated Equilibrium Fossil record that show a pattern during which equilibrium is interrupted by brief periods of geologically rapid change. This pattern is called punctuated equilibrium. Some biologists suggest that most new species are produced during periods of relatively rapid change. *Disclaimer- “rapid” can refer to thousands even millions of years.

Macroevolutionary Patterns: Adaptive Radiation Evolutionary biologists look for patterns. Two important patterns of macroevolution are adaptive radiation & convergent evolution. Artiodactyls Cetaceans Perissodactyls Tubulidentates Hyracoids Sirenians Proboscideans adaptive means “having a capacity for or tendency toward adaptation, ” & radiation means “the action of spreading around as if from a center. ”

Macroevolutionary Patterns: Convergent Evolution Unrelated organisms in similar environments may evolve adaptations to similar niches The production of similar characteristics in unrelated organisms is known as convergent evolution.

Coevolution Two or more species are so closely connected ecologically that they evolve together Many flowering plants, for example, can reproduce only if their flowers attract a specific pollinator species. Pollinators, in turn, may depend on the flowers of certain plants for pollen or nectar. The process by which two species evolve in response to changes in each other over time is called coevolution

Coevolution The relationship between coevolving organisms often becomes so specific that neither organism can survive without the other. Evolutionary change in one organism is usually followed by a change in the other organism. Darwin described an orchid whose nectar was at the bottom of a tube nearly 40 centimeters long. He predicted the existence of an insect with a feeding structure long enough to reach that nectar. Darwin never found it. But about 40 years later, researchers discovered a moth with a 40 -centimeter-long feeding tube, exactly as Darwin predicted.