Speciation (4)

Question 1

What is speciation?

Answer 1

Speciation is the evolutionary formation of new species that are genetically distinct from the older, parental species.

Question 2

What is speciation due to?

Answer 2

Speciation is most often due to one species dividing into two or more species, which is called cladogenesis.

Question 3

What is extinction?

Answer 3

Extinction is the permanent loss of all members of a species.

Question 4

What are well-known examples of extinct species?

Answer 4

Well-known examples of extinct species are the dinosaurs, dodo and sabre-toothed tigers. Most of the extinctions are thought to have resulted from environmental changes.

Question 5

What happens after mass extinction occurs?

Answer 5

After a mass extinction speciation occurs more easily as there is less competition.

Question 6

What causes speciation?

Answer 6

Each population contains genotypic variations. These variations are important as they increase a species’ chance of adapting and thus surviving under different conditions. Variation can eventually lead to speciation

Question 7

What are the two major types of speciation? (2)

Answer 7

• geographic (allopatric) speciation, which is due to part of the population becoming isolated.
• sympatric speciation, which occurs in a population that occupy the same geographical area

Question 8

When does Geographic (allopatric) speciation occur?

Answer 8

Geographic speciation occurs when a new species is formed as a result of the whole or part of a population becoming geographically isolated from the ancestral species. It is the most common form of speciation in animals, but not in plants.

Question 9

How do populations become geographically isolated? (2)

Answer 9

• In the past, isolation could have been due to geological events such as erosion, earth quakes, volcanoes and continental drift.
• Today, geographic speciation could start when:
− a lake dries, forming two separate smaller bodies of water.
− a few seeds stuck on a bird’s feather fall onto a newly formed island.
− sea currents wash a few lizards or insects onto an island with no such organisms.

Question 10

How does geographical speciation occur?

If a population of a single species: (5)

Answer 10

• Becomes separated by a geographical barrier (river, sea, mountain, lake) then the population splits into two populations. See A and B.
• There is now no gene flow between the populations.
• Since each population may be exposed to different environmental conditions(environmental pressures/selective forces) natural selection occurs independently in each of the two populations.
• The individuals of the two populations become very different from each other genotypically and phenotypically.
• Even if the populations were to mix again they will not be able to reproduce with each other.

Question 11

What is sympatric speciation?

Answer 11

Sympatric speciation is when a new species arises in the same area as the ancestral species without any geographic isolation.

Question 12

Plants frequently develop new species by a combination of ____ and _____, creating an individual that is instantly different and cannot interbreed with the parental species even though they are living in the same area, ie they are sympatric. Sympatric speciation is very important in plant speciation.

Answer 12

polyploidy

hybridisation

Question 13

Being volcanic the Galapagos Islands emerged from the sea relatively recently. Initially they obviously had no land organisms. Therefore all _____ of the islands’ unique animals and plants has occurred within the past 3 to 4 million years, a short period in _____ terms.

Answer 13

evolution

geological

Question 14

How did the ancestral finch group find their way to the islands?

Answer 14

A recent suggestion is that an ancestral group, driven by strong winds, from the nearest mainland about 1 000 kilometres away landed on one of the islands. This group would give rise to all 14 Galapagos finch species found on the islands. All these finch species are sparrow-sized and similar in appearance but they differ in beak structure and feeding habits.

Question 15

How did the different species arise? (3)

Answer 15

After arrival on an island the finches remained permanently isolated from their point of origin, the South American mainland and were free to evolve because there was:
• an absence of pre-existing predators.
• no competition from other land birds as there were none there.
• a variety of empty ecological niches, each with its own type of food.

Question 16

What are the stages in the speciation process? (2)

Answer 16

1. Division of habitat

2. Division of food resources by trophic (feeding) specialisation

Question 17

What does the division of habitat entail?

Answer 17

A single finch ancestral species divided into two lineages each occupying different habitats – the ground and tree finches.

Question 18

What does Division of food resources by trophic (feeding) specialisation entail? (2)

Answer 18

• As the finch population grew and there were periods of food scarcity competition for food resources increased.
• With the large variety of feeding niches open, the early finch species developed feeding specialisations to get food from different sources. This resulted in them evolving into the variety of finch species we know today. The size and shape of the beaks clearly reflect their specialisations, for example:
− grasping beaks, e.g. the tree finch, which eats buds, fruit and insects.
− crushing beaks, e.g. the vegetarian finch, which eats seeds, and the ground finch, which eats ticks and blood of sea birds.
− probing beaks, e.g. the cactus finch, which probes cactus fruit for seeds, and the woodpecker finch, which uses small twigs and cactus spines to poke into crevices in dead branches for insect larvae.

Question 19

A reminder: the central feature of Darwin’s theory is that species change if there are environmental changes. Here the ‘changes in environment’ were: (2)

Answer 19

• the variety of empty ecological niches each with its own type of food provided opportunities for change (adaptation).
• competition in times of food shortage that provided the selective pressure or need for change

Question 20

Lake Malawi is a long narrow lake formed by the East African Rift where the African _____ plate is splitting in two. This makes the lake relatively young in ____ terms, about one million years old. Initially it was a swampy area and not suitable for supporting fish life but later developed into a lake.

Answer 20

tectonic

geological

Question 21

Lake Malawi is one of the Great Lakes of Africa, the others being Lakes Victoria and Tanganyika. As they are isolated from each other and the rest of the world, they are ideal places to study speciation as geographical separation (isolation) is considered to promote _____. The enormous diversity of ____ in these lakes (about 1 300 scientifically described species) has become important in the study of speciation during evolution.

Answer 21

speciation

cichlids

Question 22

In Lake Malawi, sometime between 570 000 ya and 1 mya a single ancestral group arrived and diversified extremely quickly, eventually giving rise to as many as 600 cichlid fish species. They have a wide diversity of body shapes, ranging from strongly ____ compressed species through to species that are _____ and highly ______. They range in length from about 2.5 centimetres to 1 metre.

Answer 22

laterally
cylindrical
elongated

Question 23

The evolution of the different cichlids is a good example of sympatric speciation. One possible reason for this extraordinary diversification is that the ancestral group remained permanently isolated and was free to evolve easily because: (3)

Answer 23

• the lakes provided a variety of empty ecological niches, each with its own type of food.
• with no other fish there was no competition.
• there was an absence of pre-existing predators.

Question 24

The cichlid fishes of Lake Malawi and the other lakes have undergone one of the most rapid adaptive radiations or cladogenesis of any known vertebrate group. Because diversification has been so recent, and rapid, scientists are able to study: (3)

Answer 24

• very early stages of diversification
• the process of speciation
• patterns in the speciation processes. Such studies have suggested a three-stage pattern, each with its own selective forces. These patterns may apply generally to the evolutionary origins of many other vertebrate species.

Question 25

What are the stages in the speciation process? (3)

Answer 25

1. Division of habitat
2. Division of food resources
3. Division by sexual selection

Question 26

A single cichlid ancestral species diverged into two major _______ each occupying different habitats, the sandy bottoms and patches of rocky outcrops – the sand and rock-dwellers. As there was enough food for the early cichlids there was little _______ competition.

Answer 26

lineages

interspecific

Question 27

How do cichlids split up food resources? (4)

Answer 27

• The ancestral cichlid species probably had a varied diet, eating whatever was available. • As the cichlid populations grew, competition for the food resources increased.
• In the newly formed lake there was, however, a large variety of unoccupied feeding niches.
• Therefore fish with adaptations for getting food from different resources, e.g. algae, plankton, insects, other fish and snails became the next basis of selection.

Question 28

It is generally considered that trophic (feeding) ______ is at the heart of the enormous cichlid _____, with each species showing great specialisation for a distinct, fairly narrow food niche.

Answer 28

specialisation

diversification

Question 29

What enabled the cichlid fish to adapt to such narrow food niches?

Answer 29

The cichlids have a unique and strange characteristic; they have two pairs of jaws – the usual outer jaws as well as a second pair (pharyngeal jaws) that are invisible and lie within the throat area. The outer, highly specialised jaw collects the food while the inner jaw chews it.

Question 30

What did jaw adaptations allow cichlids to do?

Answer 30

It has been proposed that the jaw adaptations were the ‘key-innovation’that set off their explosive radiations. The jaw adaptations allowed cichlids to take advantage of every possible food resource and evolve into a great variety of feeding specialists

Question 31

What did the radiation of cichlids lead to?

Answer 31

The radiation of cichlid into diverse species was initially due to adaptation to habitat and then adaptation to different food resources. Subsequent diversification was due to sexual selection

Question 32

What does the diction by sexual selection entail? (2)

Answer 32

• This last stage includes numerous reproductive strategies (methods), all based on behaviours and colours that communicate reproductively important information. These have significantly contributed to the extraordinary variety of cichlid species.
• Sexual selection leads to the evolution of male traits for the attraction of females and of female preferences for these traits.

Question 33

What do sexual selection strategies include? (2)

Answer 33

− complex mating behaviours, for example:

 elaborate male courtship displays, whereby male cichlid build intricate nests, known as bowers, which females inspect in order to decide which males they should best mate.

 females being polyandrous, i.e. having multiple male partners.

−differentiation of male breeding colouration. In this way, the females select not only the best male, but also a male of her same species. Many closely related species differ mainly in male colour pattern