Evolution of Species

Species have the ability to interbreed and produce fertile offspring in nature. Speciation is the evolution of a new species. Speciation can occur only when either interbreeding or the production of fertile offspring is somehow prevented. For example, these happy face spiders look different, but since they can interbreed, they are considered the same species: Theridion grallator.

Evolution of Species Physical barriers can prevent interbreeding. * Drought * Shift in river flow * Volcanic eruptions * Sea level changes

Evolution of Species Geographic isolation occurs if a physical barrier separates a population into groups. Geographical isolation prevents interbreeding and gene exchange. Over time, each population would adapt to the local environment through the process of Natural Selection. Eventually, the gene pools of each group would become so different that one could be considered a new species.

Mode of speciation New species formed from... Allopatric geographically isolated populations Peripatric Similar to allopatric, except only a small population isolated at the edge of a larger population (the gene pool of one becomes very small) Parapatric Common in plants, the ranges do not significantly overlap which give them a narrow contact zone (or the range is really large) Sympatric Some reproduce as their ancestors did (on a certain type of fruit) while others choose to reproduce using their current environment (most abundant fruit)

Bison have come close to extinction due to uncontrolled hunting, drought, and disease. There is now very little genetic variation in bison populations. Which of the following is a result of the limited genetic variation in the current bison populations compared to earlier bison populations with more variation? A.Bison in current populations are more resistant to new diseases. B.The survival rate of young bison has increased in current populations. C.Bison in current populations are less able to interbreed with other species. D.The current bison populations are less likely to be able to adapt to environmental changes.

Bison have come close to extinction due to uncontrolled hunting, drought, and disease. There is now very little genetic variation in bison populations. Which of the following is a result of the limited genetic variation in the current bison populations compared to earlier bison populations with more variation? A.Bison in current populations are more resistant to new diseases. B.The survival rate of young bison has increased in current populations. C.Bison in current populations are less able to interbreed with other species. D.The current bison populations are less likely to be able to adapt to environmental changes.