Speciation

Little side note The Energy Economy An important concept in biology is the Energy Economy Economics – the study of interactions via scarce goods and services The energy economy is the interactions in biology where energy is the scarce good. This is a helpful concept in explaining a lot of behaviours and adaptations made by living organisms.

The energy economy Flowering plants reproduce with pollen. They attract pollinators using nectar – a sugar compound. Nectar is a large investment in energy for the plant to make However, it is an effective trade off for the plant as pollinators complete reproduction efficiently. Without them, plants would need to produce massive amounts of pollen and rely on the wind to spread it for them. This is a much greater energy investment than the nectar.

The energy economy The Giant Panda is a species that struggles to survive. It gets its energy almost exclusively from bamboo – a grass Grasses are hard to digest, especially for a panda. Pandas have the digestive system of a carnivore. Pandas have difficulty extracting energy from a food they eat that is not adapted to their body. Pandas therefore have difficulty adapting to their environments as they are highly specialize and invest most of their time in gaining energy.

The energy economy This is important in biology as it shows us the interaction of species is largely related to energy The end goal of gaining energy is often to reproduce. If you have ‘good investments’ with the energy you have or have novel ways of getting/maintaining your energy you will likely have a better chance to reproduce and pass on your genetics ‘Poor investments’ can lead an individual (or sometimes a population or species) to struggle

Speciation Speciation is the process of a species changing over time into a new species. A species is a group of individuals that can interbreed to produce fertile offspring

Barriers to breeding There are often barriers that prevent different species from reproducing each other. These fit into 2 different categories: Prezygotic Mechanism Barriers that prevent a zygote from being formed Zygote - first cell of an organism formed when sperm and egg combine Postzygotic Mechanisms Barriers that take place after a zygote is formed.

Prezygotic Mechanisms There are many ways that organisms can prevent a zygote from being formed. They can all be fit into five main categories: Habitat Isolation When a geographic barrier separates species from each other Temporal Isolation When species mate at different times or seasons Behaviour Isolation When species have a behaviours that cause they to be sexually attracted to different species.

Prezygotic Mechanisms Mechanical Isolation Physical features make it impossible for two different species to reproduce. Gametic Isolation Gametes (sex cells) can get transferred but they cannot combine.

Postzygotic barriers Postzygotic isolation is the methods of preventing a viable or fertile offspring Much rarer as they are large energy investments Hybrid Unviability The fertilized egg does not survive beyond embryonic stages Hybrid Sterility The interspecies hybrid survives but it is sterile Hybrid Breakdown The initial hybrid survives and is fertile. Their offspring do not survive

Speciation When species are made, it typically happens for a couple of reason (not interbreeding) Species can arise in order to fit an ecological niche Species can arise after reproductive isolation

Speciation Anagenesis – is the process of one species changed into a different species. Anagenesis appears to be much more rare Human evolution from Austrolapithecus aferensis is often looked at being anagensis The peppered moth also demonstrates anagensis

Speciation Cladogenesis – when a species evolves by division – two or more species are developed from a single species There MUST be some barrier to prevent reproduction between a single population for cladogenesis to occur Otherwise they could just keep interbreeding and there would be no divergence This is usually caused by geographic isolation

Allopatric Speciation Allopatric Speciation is thought to be the major mechanism of cladogenesis Allopatric speciation occurs when a geographic barrier occurs and the same species are unable to reproduce together. It may also occur when a small population of a species relocate or are forced to a new location.

Sympatric Speciation Sympatric speciation occurs when a new species is formed without geographic isolation. Major genetic changes (such as a major mutation) can lead to a viable offspring that can no longer reproduce. Sometimes the genetic changes can allow the new organisms to occupy a new niche but within the same habitat

How fast is speciation? This is a long debated question in biology Darwin suggested that it actually occurs both quickly and slowly There are currently two major ideas behind the rate of change: Gradualism Punctuated Equilibrium

Gradualism Gradualism is the idea that species are slowly changing over time. This gradual pace of change takes many, many generations and causes speciation over time.

Punctuated Equilibrium Punctuated equilibrium is the idea that species spend long periods of geological time relatively unchanged. Major events, such as sudden climate changes, forced migration, etc. cause species to feel large evolutionary pressures suddenly. This forces speciation to happen quickly (in terms of geological time).

Filling a niche Many people think of living things as adapting and evolving to ‘get better’ Life is often viewed as a hierarchy However, evolution is not about ‘getting better’ AKA, closer to human Speciation creates species that occupy available niches and find effective ways to fit into the energy economy.

Filling a niche If a niche is available for a living thing, it is beneficial to adapt to fit into it. This allows you less competition and greater benefit in the energy economy For example – after dinosaurs went extinct, many niches were left unoccupied Animals that could adapt to a new niche had an advantage Mammals were capable of surviving the extinction event and became able to adapt to the unoccupied niches