Biology by Bradford
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The subtopic in the middle and five tasks round it: label a diagram, complete two tables and fill 11 gaps. Every box rests on a learning objective of the topic in the AP Biology course and exam description. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
| Barrier | How it keeps species apart |
|---|---|
| isolation | species live in different places and rarely meet |
| Temporal isolation | they breed at different times of day or year |
| isolation | courtship signals are not recognized |
| Gametic isolation | sperm and egg do not fuse |
| Hybrid sterility | a hybrid, such as a mule, survives but is sterile |
Species also disappear. Extinction can follow a change in climate, a new competitor or predator, or the loss of . Mass extinctions have been followed by adaptive radiations, as the survivors move into niches that were left empty.
| Model | Pattern of change |
|---|---|
| species change slowly and steadily | |
| long periods of little change, then short bursts, often after the environment changes | |
| Adaptive radiation | one ancestor gives many species quickly, filling many niches, as with Darwin's finches |
By the biological species concept, a species is a group of populations that can in nature and produce fertile offspring, and which are reproductively isolated from other groups. In speciation, populations are separated by a geographic barrier, so gene flow stops and mutation, drift and selection make them different. In sympatric speciation, new species arise without a barrier: in plants, a polyploid can be reproductively isolated in a single generation.
| Barrier | How it keeps species apart |
|---|---|
| Habitat isolation | species live in different places and rarely meet |
| Temporal isolation | they breed at different times of day or year |
| Behavioral isolation | courtship signals are not recognized |
| Gametic isolation | sperm and egg do not fuse |
| Hybrid sterility | a hybrid, such as a mule, survives but is sterile |
By the biological species concept, a species is a group of populations that can interbreed in nature and produce fertile offspring, and which are reproductively isolated from other groups. In allopatric speciation, populations are separated by a geographic barrier, so gene flow stops and mutation, drift and selection make them different. In sympatric speciation, new species arise without a barrier: in plants, a polyploid can be reproductively isolated in a single generation.
| Model | Pattern of change |
|---|---|
| Gradualism | species change slowly and steadily |
| Punctuated equilibrium | long periods of little change, then short bursts, often after the environment changes |
| Adaptive radiation | one ancestor gives many species quickly, filling many niches, as with Darwin's finches |
Species also disappear. Extinction can follow a change in climate, a new competitor or predator, or the loss of habitat. Mass extinctions have been followed by adaptive radiations, as the survivors move into niches that were left empty.