Presentation on theme: "What are Darwin's finches? When Darwin fist came to the Galapagos islands back in the 1800s he noted that there existed a variety of finches that all."— Presentation transcript:
This process of modification over time to fill a variety of niches is adaptive radiationadaptive radiation
Put another way… It is the emergence of numerous species from a common ancestor introduced into a new environment, presenting a diversity of new opportunities and problems – Campbell, Biology
This happens in instances when there exist unrealized opportunities in a new environment. Over time once rare characteristics are emphasized and beneficial. This s divergent or directional selection depending on the circumstance
Divergent evolution Traits with similar internal structure are called homologous traits When homologous features become used for different purposes - are no longer analogous - the process is called divergent evolution, the splitting of a family tree in different directions. analogous
ADAPTIVE RADIATION – AN EXAMPLE OF DIVERGENT EVOLUTION Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. http://evolution.berkeley.edu/evolibrary/home.php http://www.vanderbilt.edu/AnS/english/Clayton/Galapago_finches.gif
Convergent evolution When unrelated groups have analogous but nonhomologous features (wings in birds and butterflies, fins in squids and seals), the process is called convergent evolution (sometimes parallel evolution) - similar needs produce similar structures, even if they're based on different architecture. Both support the concepts of evolutionary change by selection.
Due to similar selection pressures that are consistent over long periods of time, unrelated organisms (or distantly related ones) acquire similar traits to deal with those similar pressures.
Convergent evolution ANATOMY –HOMOLOGOUS STRUCTURES –ANALOGOUS STRUCTURES Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College. http://evolution.berkeley.edu/evolibrary/home.php
The following is taken from… http://www.pbs.org/wgbh/evolution/library/ 01/6/l_016_01.htmlhttp://www.pbs.org/wgbh/evolution/library/ 01/6/l_016_01.html (and adapted by Mr.R)
Peter and Rosemary Grant, spent part of each year since 1973 in a tent on a tiny, barren volcanic island in the Galapagos.Peter and Rosemary Grant They caught, weighed, measured, and identified hundreds of small birds and record their diets ever year.
In their natural laboratory, the 100-acre island called Daphne Major, the Grants and their assistants watched the struggle for survival among individuals in two species of small birds called Darwin's finches. http://www.math.umd.edu/~wwa/zgalapagos/dadwebsite2/images/692islaseymour.jpg
The struggle is mainly about food -- different types of seeds -- and the availability of that food is dramatically influenced by year-to-year weather changes.
For the finches, body size and the size and shape of their beaks are traits that vary in adapting to environmental niches or changes in those niches. Body and beak variation occurs randomly.traitsniches http://www.rit.edu/~rhrsbi/GalapagosPages/Darwin Finch2.html
Natural selection at its most powerful winnowed certain finches harshly during a severe drought in 1977. That year, the vegetation withered. Seeds of all kinds were scarce. The small, soft ones were quickly exhausted by the birds, leaving mainly large, tough seeds that the finches normally ignore. Under these drastically changing conditions, the struggle to survive favored the larger birds with deep, strong beaks for opening the hard seeds.
The Grants found that the offspring of the birds that survived the 1977 drought tended to be larger, with bigger beaks. So the adaptation to a changed environment led to a larger-beaked finch population in the following generation.
Adaptation can go either way, of course. As the Grants later found, unusually rainy weather in 1984-85 resulted in more small, soft seeds on the menu and fewer of the large, tough ones.
Long Live the KING!!!! Sure enough, the birds best adapted to eat those seeds because of their smaller beaks were the ones that survived and produced the most offspring.