Darwin’s Observations • Species have high reproductive rates but selection pressures act to create a struggle for existence • There is variation in offspring, some better adapted than other. • Those best adapted will survive longer and therefore have an increased chance of passing on their favourable characteristics • Fittest will survive • It is from Darwins observations that his theory of Natural Selection was devised.
Gene Pools • Gene Pool: all the genes in the population Factors which affect the gene pool Immigration Emmigration Natural Selection Mutations
Genetic Drift Genetic Drift: Allele frequency’s change over time (drift) Founder Effect: A small number of individuals colonise a new area. Bottleneck Effect: Where the population is reduced due to a catastrophic effect.
Fitness • Fitness is the measure of how well suited an organism is to its environment.
The Species Concept • A species is a group of individuals which can interbreed to produce fertile offspring. Speciation is the process by which one or more new species are formed. There are different types of speciation Allopatric: Occurs when species become geographically isolated. Sympatric: Occurs through ecologically isolating mechanisms. Eg polyploidy Pg 247 Biozone
Allopatric Speciation Mainland Robin Chatham Island Robin Pg 251 Biozone
Instantaneous speciation • Eg Polyploidy in wheat 40 Chromosomes 20 Chromosomes
Reproductive Isolating Mechanisms These lead to speciation These can be Prezygotic: before fertilisation Postzygotic: after fertilisation
Prezygotic Barriers • Temporal- different breeding times • Behavioural- different courtship patterns • Structural- different reproductive structures • Gamete Incompatability- gametes cant fuse, may have wrong enzymes etc.
Postzygotic Barriers • Hybrid Invariability: even if fertilisation occurs the chromosome numbers may not match up and the zygote may not develop • Hybrid sterility: They may reach maturity but be sterile eg Mules have 63 Chromosomes • Hybrid disadvantage: Hybrids may be less likely to survive. (not to be confused with hybrid vigour)
Deme • A local interbreeding population of a species.
Niche Differentiation • Where species have very recently evolved from an existing species they will still have very similar adaptations and will strongly compete. This is where Gauses principle applies.
Character Displacement • Where the ranges of these 2 species overlap the visible differences between the 2 species may become more pronounced. This is called Character displacement. • Mate recognition? • Where the 2 species are geographically separated they often remain very similar.
A Cline A cline is a gradient of phenotypic character along a geographic variable such as latitude or altitude. A A B C C D D E
Examples • Salamanders on the east coast of USA
NZ Example- Ranunculus insignis • Lobing in the leaf increases as we travel further south
NZ Example-Tomtits • North Island tomtits have shorter tails and wings than south Island tom tits. This gradually happens as you travel down the country.
Ring Species • A special type of cline where the demes(local populations) are arranged in a circle across the species range and the demes at the ends, although adjacent may be unable to interbreed. • Pg 246 Biozone D E C F B G A
Types of evolution • Divergent Evolution: Isolation of a population leads to reproductive barriers, eventually a new species forms.
Types of evolution • Adaptive Radiation: Evolutionary diversification of related species into different environments or ways of life.
Types of evolution • Convergent evolution: The independent evolution of similar features in unrelated species. Eg Dolphins and sharks Pg 259- 260 Biozone
Analogous Structures • Same function and external appearance, but quite different origins.
Parallel evolution • Some biologists argue that this is just convergent evolution. • It is the development of similarities in separate but related evolutionary lineages.
Gradualism and Punctuated Equilibrum • Pg 263 Biozone
Co- Evolution • 2 species evolve together to form a mutually beneficial relationship. They may become dependant on one another for survival. • Pg 261-2 Biozone
Major periods of extinction • Pg 271 Biozone • Permian 225mya 90%marine org • Cretaceous 65mya dinosaurs • Megafaunal 10,000ya mammals-hunt • The 6th extinction present reef/ rainforest