LU 3 Species Diversity II

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SPECIES CONCEPT & SPECIATION

Biological Species Concept = A species is a population/group of populations where the members have potential to interbreed to produce fertile offsprings, but cannot produce fertile offsprings with other species.

Speciation = Process by which a new species originates & involves the creation of a new population of organisms that are novel enough to be classified in their own group.

Anagenesis = (terus BERTUKAR ! dush !) Accumulation of heritable traits in a population which transform that population into a new species.

Cladogenesis = Branching evolution, new species arises as a branch from the evolutionary tree but the original species STILL exists. This process is the source of biological diversity.

Isolation of members of a species needs to happen for a new species to form. This will create a separate population.

Prezygotic barriers = prevents egg fertilisation if different species try to mate.

Habitat isolation = 2 species, live in the same area, but occupy different habitat. So they rarely meet/encounter each other.

Behavioural isolation = Has different signals or calls. Signals that attract mates are often unique to a species. (Diff species of fireflies - different pattern)

Temporal isolation = Breed at different times of the day/ during diff seasons.

Mechanical isolation = Closely related species try to mate but they are anatomically incompatible.

Gametic isolation = gametes has to recognise each other. (Usually chemical signals between sperm and egg allows sperm to "recognise" the correct egg)

Postzygotic Barriers = prevents a hybrid zygote from developing into fertile adult.

Reduced hybrid viability = abort development of hybrid at some embryonic stage

Reduced hybrid fertility = Meiosis doesn't produce fertile gametes in vigorous hybrids.

Hybrid breakdown = Fertile hybrids in the first generation but the following generation won't produce fertile offspring.

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Alternative Species Concept

Ecological species concept = Species are defined by their use of their environmental resources / their ecological niche. / by their food source.

Morphological Species Concept = Factors such as body shape, size etc are considered.

Paleontological Species Concept = Species in fossil record, characterised according to a unique set of structural features.

Phylogenetic Species Concept = Species are sets of organisms with their own unique genetic histories. This idea, based of molecular analyses = DNA sequences.

Modes of Speciation

Allopatric speciation - speciation takes place in populations with geographically separate ranges. The population are separated and the gene flow will be interrupted. Hence creating a new species.

Sympatric speciation - Speciation that takes place in populations that are geographically overlapping. Chromosomal changes and nonrandom mating reduces gene flow. Both can reduce gene flow between organisms & cause populations to evolve to new species.