Speciation (4) Flashcards
(33 cards)
What is speciation?
Speciation is the evolutionary formation of new species that are genetically distinct from the older, parental species.
What is speciation due to?
Speciation is most often due to one species dividing into two or more species, which is called cladogenesis.
What is extinction?
Extinction is the permanent loss of all members of a species.
What are well-known examples of extinct species?
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.
What happens after mass extinction occurs?
After a mass extinction speciation occurs more easily as there is less competition.
What causes speciation?
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
What are the two major types of speciation? (2)
- 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
When does Geographic (allopatric) speciation occur?
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.
How do populations become geographically isolated? (2)
• 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.
How does geographical speciation occur?
If a population of a single species: (5)
- 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.
What is sympatric speciation?
Sympatric speciation is when a new species arises in the same area as the ancestral species without any geographic isolation.
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.
polyploidy
hybridisation
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.
evolution
geological
How did the ancestral finch group find their way to the islands?
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.
How did the different species arise? (3)
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.
What are the stages in the speciation process? (2)
- Division of habitat
2. Division of food resources by trophic (feeding) specialisation
What does the division of habitat entail?
A single finch ancestral species divided into two lineages each occupying different habitats – the ground and tree finches.
What does Division of food resources by trophic (feeding) specialisation entail? (2)
• 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.
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)
- 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
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.
tectonic
geological
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.
speciation
cichlids
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.
laterally
cylindrical
elongated
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)
- 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.
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)
- 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.
