Types of Isolation
Two species of snakes live in the same forest. One spends almost all of its time in trees, while the other lives mostly on the forest floor. They rarely meet to mate. What type of reproductive barrier is this?
habitat isolation
Most of the time species are in a state of _________, meaning they are not changing very much.
equilibrium
Two closely related species of frogs live in the same pond. One species breeds in early spring, and the other breeds in late summer. Even if they are physically capable of mating, they never encounter each other during breeding season. What type of reproductive barrier is this?
prezygotic
A river slowly forms in the middle of a forest, splitting a population of squirrels into two groups on opposite sides. Over thousands of years, the two groups evolve different traits and can no longer interbreed. Is this an example of allopatric or sympatric speciation? Explain your reasoning.
allopatric-geographic barrier
In a population of peafowl, males with larger, more colorful tail feathers attract more mates than males with smaller tails. Over many generations, these traits become more common in the population. What process explains how these traits spread even though they don’t necessarily help survival?
sexual selection
Two species of oak trees release pollen at different times of the year. Even though their ranges overlap, cross-pollination never happens. What type of reproductive barrier is this?
temporal isolation
Fossil records showing a species changing slightly from one generation to the next over a long period of time support this evolutionary model.
gradualism
A cross between two closely related plant species produces hybrid flowers that bloom and attract pollinators normally, but the hybrids never produce viable seeds. Should this barrier be classified as prezygotic or postzygotic?
postzygotic
At what point do you know that a geographic barrier has lead to speciation?
The two species are no longer capable of reproducing and producing fertile offspring.
This type of evolution explains why marsupial sugar gliders in Australia and flying squirrels in North America both evolved skin flaps for gliding, even though they are not closely related.
convergent evolution
Male crickets of two closely related species produce different chirping patterns at night. Females only respond to the chirp of their own species, so even though the crickets live in the same field, they never mate with the other species. What type of reproductive barrier is this?
behavioral isolation
A species of lizard shows almost no change in fossils for millions of years, but after a sudden climate shift, several new lizard species appear in a relatively short time. What pattern of speciation does this demonstrate?
punctuated equilibrium
Why is a mule, the offspring of a horse and a donkey, not considered a separate species even though it has characteristics of both parents?
hybrid infertility
In a lake, a population of fish begins to feed on different types of food—some stay near the surface eating insects, while others feed on the bottom eating small crustaceans. Over many generations, the two groups develop different traits and can no longer interbreed. Is this an example of allopatric or sympatric speciation? Explain your reasoning.
sympatric-no geographic barrier
AFTER a geographic barrier forms, what two evolutionary forces lead to two populations accumulating different allele frequencies.
natural selection, genetic drift.
Two species of flowers grow side by side. The shape of their reproductive organs is different, so the pollen from one cannot reach the stigma of the other even when pollinators visit both. What type of reproductive barrier is this?
mechanical isolation
Compare and contrast gradualism to punctuated equilibrium and give an example of each pattern.
Answers will vary.
A population of wheat plants suddenly produces some offspring with double the normal number of chromosomes. These new plants can successfully mate with each other but cannot produce viable offspring with the original population. Explain why these plants could form a new species and why they cannot reproduce with the parent population.
This is polyploidy. The new plants have extra sets of chromosomes, which makes them genetically incompatible with the parent population. Because they cannot produce viable offspring with the original plants, they are reproductively isolated, allowing a new species to form.
Allopatric occurs most often when populations are _____ and _______.
small and isolated
This type of evolution explains how a single squirrel population was split by the Grand Canyon and eventually became two different species due to geographic isolation.
divergent evolution.
Sea urchins of two species release sperm and eggs into the same tide pool. Fertilization rarely occurs because the sperm of one species cannot recognize the eggs of the other. What type of reproductive barrier is this?
gametic isolation
Create a visual that shows the difference between a fossil record that depicts punctuated equilibrium and one that demonstrates gradualism.
Punctuated Equilibrium: no change-no change-no change-tiny change-no change- BOOOOOM LOTS OF CHANGE- no change- tiny change
gradualism: minor change, minor change, minor change, minor change, minor change, minor change, minor change, minor change, minor change
Give an example of postzygotic isolaiton that is not hybrid infertility.
A developing embryo being aborted at some stage of embryological development
A large population of insects inhabits an island with a continuous forest. Over time, some individuals begin exploiting a rare, fast-growing shrub in sunny clearings, while others remain on the common understory plants in shaded areas. The two groups develop differences in mating calls, activity patterns, and timing of egg-laying. Although the groups sometimes cross paths in transitional areas, almost no mating occurs. Are these populations undergoing allopatric or sympatric speciation? Explain your reasoning.
Sympatric, no physical barrier.
Two types of painted turtles are found in a lake in Ontario. One population, the western painted turtle, spends most of its time near the rocky, fast-moving parts of the lake hunting insects. The other population, the eastern painted turtle, stays mostly in calm, vegetated areas of the lake feeding on plants and small fish. Explain what type of isolation this is and how it would lead to speciation over time.
This is habitat isolation. The two turtle populations live in different parts of the lake and rarely encounter each other to mate. Over time, reduced gene flow could lead to genetic differences accumulating, eventually resulting in speciation.