Patterns of Evolution Objectives: Compare and contrast different patterns of evolution Describe how adaptive radiation occurs Explain the difference between divergent and convergent evolution

Natural Selection Leads to predictable outcomes… Closely related species share many homologous structures yet these structures serve different functions. Vestigial features may have at one time serve a function in ancestors Remote islands are inhabited by unique species that have descended from a founder population isolated from their original species

But how did these species evolve??? There are 4 patterns that the evolutionary process may follow… Adaptive radiation Divergent evolution Convergent evolution Coevolution

Adaptive Radiation A single species evolves into a number of other species. These species are distinct from one another but are closely related. Each species is specialized for a different environment (fills a different niche). Niche: How an organism lives and interacts with its environment.

Darwin’s Finches

Many finches evolved from a single seed eating ground finch. Initially finches arriving to Galapagos would have to compete with each other for food. Finches with different shaped beaks could exploit different food sources. As finches exploited new food sources they most likely exploited new habitats where their food was more plentiful. Their different habitats may have selected for more different traits. In adaptive radiation, an initial species evolves into a variety of new species that differ in varied ways from the original species.

Divergent Evolution A large scale evolution of a group of species into many different species. Ex: Adaptive radiation Leads to two outcomes: Reduces competition between different species New species evolve and exploit different niches as competition within species increase because of limited resources.

New species evolve from a common ancestor. Populations move into different environments Differences accumulate as these populations adapt to the conditions Gene flow may be blocked (reproductive isolation)

Convergent Evolution The evolution of similar traits in distantly related species. Two different species living in similar environments under similar selective pressures will evolve similar traits that allow them to occupy similar niches

Example Two groups of plants Cacti – deserts of S. America Euphorbia – deserts of S. Africa - Both have adaptations to dry conditions and spines. Cacti have spines that evolved from leaves. Euphorbia have spines that evolved from stem tissue. Both serve a protective function.

Co evolution One species evolves in response to evolution of another species. Ex: Some plants have evolved to produce seeds with hard shells . Some mammals that eat seeds have coevolved to have powerful jaws and teeth to chew through these hard shells.

Hawk Moth and Madagascar long-spurred orchid

Plenary What is adaptive radiation? Explain what divergent evolution means. Explain what convergent evolution means. Explain why one species would have to evolve as a result of another species evolving. What pattern of evolution is this? Give an example to illustrate adaptive radiation, divergent evolution, convergent evolution and co evolution.