Allopatric & Sympatric Speciation

Allopatric Speciation

Allopatric speciation is a type of speciation where two (or more) populations are geographically isolated from each other.

Geographical isolation

Populations of a species can split into two or more populations.
This may be caused by environmental changes (e.g. emergence of a river) or random events (e.g. a storm causing a population of birds to be carried to another island).
When two populations are physically separated, they are geographically isolated.

Selection pressures

Populations in different environments will be exposed to different environmental conditions (e.g. climate, food availability).
The different environments will place different selection pressures on the populations.
The different selection pressures will drive natural selection in different directions.

Allele frequencies

The different selection pressures on the populations cause the allele frequencies in the two populations to change.
If the populations continue to be geographically isolated for a long time, eventually the allele frequencies will change so much that if the populations are brought back together they can no longer interbreed.

Speciation

Species are defined as a group of actually or potentially interbreeding individuals.
If two populations that have been geographically isolated can no longer interbreed when they are brought back together, they are considered to be two species.
This is allopatric speciation.

Sympatric Speciation

Sympatric speciation is a type of speciation where two (or more) populations are not geographically isolated from each other and involves reproductive isolation.

Reproductive isolation

Scientists organize reproductive isolation into two groups: prezygotic and postzygotic.
- Recall that a zygote is a fertilized egg: the first cell of the development of an organism that reproduces sexually.
So, a prezygotic barrier blocks reproduction from taking place such as barriers that prevent fertilization when organisms attempt reproduction.
A postzygotic barrier occurs after zygote formation, such as organisms that don’t survive the embryonic stage and those born sterile.

Reproductive isolation mutations

Sympatric speciation could be caused by mutations that influence many different factors:
- Polyploidy - where a cell or organism has an extra set, or sets, of chromosomes. Polyploidy organisms are reproductively isolated from diploid organisms.
- Mutations may influence the flowering times or mating times of individuals.
- Mutations may alter the reproductive organs.
- Mutations may alter mating behaviors.

Prezygotic barriers

Differences in breeding schedules, called temporal isolation, can act as a form of reproductive isolation.
- For example, two species of frogs inhabit the same area, but one reproduces from January to March, whereas the other reproduces from March to May.
In some cases, populations of a species move or are moved to a new habitat and take up residence in a place that no longer overlaps with the other populations of the same species.
- This situation is called habitat isolation.

Prezygotic barriers - 2

Behavioral isolation occurs when a specific behavior prevents reproduction from taking place.
- For example, male fireflies use specific light patterns to attract females. If a male of one species tried to attract the female of another, she would not recognize the light pattern.
Other prezygotic barriers work when differences in their gamete cells (eggs and sperm) prevent fertilization from taking place; this is called a gametic barrier.

Postzygotic barriers

When fertilization takes place and a zygote forms, postzygotic barriers can prevent reproduction.
Hybrid individuals in many cases cannot form normally in the womb and simply do not survive past the embryonic stages.
- This is called hybrid inviability because the hybrid organisms simply are not viable.
In another postzygotic situation, reproduction leads to the birth and growth of a hybrid that is sterile and unable to reproduce offspring of their own.
- This is called hybrid sterility.

Speciation

The biological definition of a species is a group of individuals that can actually or potentially interbreed.
The emergence of a mutation that prevents two (or more) populations from interbreeding is called sympatric speciation.

1Cell Biology

2Molecular Biology

2.1Water

2.1.1Water & Hydrogen Bonding

2.1.2IB Multiple Choice - Water & Hydrogen Bonding

2.1.3Extended Response - Water

2.2Carbohydrates & Lipids

2.2.1Monosaccharides

2.2.2Disaccharides & Polysaccharides

2.2.3Triglycerides & Phospholipids

2.2.4Cellulose

2.2.5Starch & Glycogen

2.3Proteins

2.3.1Structure & Functions of Proteins

2.4Enzymes

2.4.1Enzymes

2.4.2Factors Affecting Enzyme Activity

2.4.3Enzyme-Controlled Reactions

2.4.4End of Topic Test - Enzymes

2.5Structure of DNA & RNA

2.5.1DNA & RNA

2.6DNA Replication, Transcription & Translation

2.6.1Protein Synthesis

2.6.2Transcription & Translation

2.6.3End of Topic Test - DNA, Genes & Protein Synthesis

2.6.4Exam-Style Question - Protein Synthesis

2.6.5End of Topic Test - Coronavirus Translation

2.6.6IB Multiple Choice - Transcription

2.6.7IB Multiple Choice - Translation

2.7Cell Respiration

2.7.1Overview of Respiration

2.7.2Anaerobic Respiration

2.7.3End of Topic Test - Anaerobic Respiration

2.7.4Respiration Experiments

2.7.5End of Topic Test - Respiration

2.7.6IB Multiple Choice - Respiration

2.8Photosynthesis

2.8.1Overview of Photosynthesis

3Genetics

4Ecology

4.1Species, Communities & Ecosytems

4.1.1Population Dynamics

4.1.2Communities & Measuring Diversity

4.1.3Relationships Between Populations

4.1.4Overview of Ecosystems

4.1.5Nutrient Cycles

4.1.6Fertilisers

4.1.7Eutrophication

4.1.8Chi-Squared Test

4.2Energy Flow

4.2.1Energy

4.2.2Energy Flow

4.2.3Biomass & Food Chains

4.2.4Heterotrophs & Autotrophs

4.3Carbon Cycle

4.3.1Carbon Cycle

4.4Climate Change

4.4.1Carbon Dioxide

4.4.2The Greenhouse Effect

4.4.3Global Warming

4.4.4Maintaining Biodiversity

5Evolution & Biodiversity

5.1Evidence for Evolution

5.1.1Evidence for Evolution - Fossils & DNA

5.1.2Evidence for Evolution - Anatomy & Geography

5.1.3IB Multiple Choice - Evidence for Evolution

5.1.4Extended Response - DNA & Evolution

5.2Natural Selection

5.2.1Introduction

5.2.2Evolutionary Fitness

5.2.3Natural Selection & Variation

5.2.4End of Topic Quiz - Natural Selection

5.2.5IB Multiple Choice - Natural Selection

5.2.6Speciation

5.3Classification of Biodiversity

5.3.1Introduction to Biodiversity

5.3.2Keystone Species

5.3.3Courtship & Ancestry

5.3.4Classification

5.4Cladistics

5.4.1Evolutionary Relationships

5.4.2IB Multiple Choice - Species & Taxonomy

6Human Physiology

6.1Digestion & Absorption

6.1.1Overview of Digestion

6.1.2Digestion in Mammals

6.1.3Absorption

6.1.4End of Topic Test - Substance Exchange & Digestion

6.1.5End of Topic Test - Substance Ex & Digestion

6.2The Blood System

6.2.1The Circulatory System

6.2.2The Heart

6.2.3Blood Vessels

6.2.4Cardiovascular Disease

6.3Defence Against Infectious Disease

6.3.1Immune System

6.3.2The Immune Response

6.3.3Antibodies

6.3.4Primary & Secondary Response

6.3.5Vaccines

6.3.6HIV

6.3.7End of Topic Test - Immune System

6.3.8Exam-Style Question - Immune System

6.3.9End of Topic Test - Immune System

6.4Gas Exchange

6.4.1Lung Structure & Alveoli

6.4.2Ventilation

6.4.3Lung Disease

6.4.4Lung Disease Data

6.5Neurons & Synapses

6.5.1Neuron Structure

6.5.2Transmission of an Impulse

6.5.3Speed of Transmission

6.5.4End of Topic Test - Neurones & Action Potentials

6.5.5Synapses

6.5.6Types of Synapse

6.5.7Medical Application

6.5.8End of Topic Test - Synapses

6.5.9End of Topic Test - Nervous Comm&Coord

6.6Hormones, HomeoStasis & Reproduction

6.6.1Overview of Homeostasis

6.6.2Blood Glucose Concentration

6.6.3Controlling Blood Glucose Concentration

6.6.4End of Topic Test - Blood Glucose

6.6.5Type I & Type II Diabetes

6.6.6Human Reproductive Systems

6.6.7Hormonal Control of the Menstrual Cycle

7AHL: Nucleic Acids

7.1DNA Structure & Replication

7.1.1DNA

7.1.2RNA

7.1.3DNA Replication

7.1.4DNA Replication - Summary

7.1.5IB Multiple Choice - DNA Replication

7.2Transcription & Gene Expression

7.2.1Introduction to Transcription & Protein Synthesis

7.2.2Types of RNA

7.2.3Transcription

7.2.4RNA Processing in Eukaryotes

7.2.5IB Multiple Choice - Transcription

7.3Translation

7.3.1Translation

7.3.2Retroviruses

7.3.3Scientific Practices: Coronavirus

7.3.4IB Multiple Choice - Translation

8AHL: Metabolism, Cell Respiration & Photosynthesis

8.1Metabolism

8.1.1Molecules to Metabolism

8.2Cell Respiration

8.2.1Glycolysis

8.2.2Aerobic Respiration

8.3Photosynthesis

8.3.1Light-Dependent Reaction

8.3.2Light-Independent Reaction

8.3.3End of Topic Test - Photosynthesis Reactions

8.3.4Limiting Factors

8.3.5Photosynthesis Experiments

8.3.6End of Topic Test - Photosynthesis

8.3.7End of Topic Test - Photosynthesis

9AHL: Plant Biology

9.1Transport in the Xylem of Plants

9.1.1Structure

9.1.2Cohesion-Tension Theory

9.1.3Investigating Transpiration Rate

9.2Transport in the Phloem of Plants

9.2.1Structure

9.2.2Translocation

9.3Growth in Plants

9.3.1Plant Tropisms

10AHL: Genetics & Evolution

10.1Meiosis

10.1.1Stages of Meiosis

10.2Inheritance

10.2.1Linked Genes

10.2.2Sex-Linked Genes

10.2.3Non-Nuclear Inheritance

10.2.4Chi-Squared Test

10.2.5End of Topic Quiz - Inheritance

10.2.6IB Multiple Choice - Non-Mendelian Genetics

10.2.7Introduction to Non-Mendelian Inheritance

10.2.8Extended Response - Inheritance

10.2.9Grade 4-5 (Scientific Practices) - Inheritance

10.3Gene Pools & Speciation

10.3.1Populations

10.3.2Mutations, Genetic Drift, & Gene Flow

10.3.3Speciation

10.3.4Rate of Speciation

10.3.5Allopatric & Sympatric Speciation

11AHL: Animal Physiology

11.1Antibody Production & Vaccination

11.1.1Immune System

11.1.2The Immune Response

11.1.3Antibodies

11.1.4Primary & Secondary Response

11.1.5Vaccines

11.2Movement

11.2.1Skeletal Muscle

11.2.2Sliding Filament Theory

11.2.3Contraction

11.3The Kidney & Osmoregulation

11.3.1Kidneys & Osmoregulation

Jump to other topics