The main difference between allopatric sympatric and parapatric speciation is that allopatric speciation occurs when a population becomes geographically isolated from other populations of the same species. In contrast, sympatric speciation occurs when a new species forms from a population within the same geographic area as the parent species, without geographic isolation, and parapatric speciation is a mode of speciation that occurs when two populations have partial geographic overlap, where their ranges border each other.
Speciation refers to the formation of new species. Allopatric, sympatric, and parapatric speciation are three different modes of speciation. These modes differ in terms of the geographical distribution and reproductive isolation of populations.
Key Areas Covered
1. What is Allopatric Speciation
– Definition, Characteristics, Gene Flow
2. What is Sympatric Speciation
– Definition, Characteristics, Gene Flow
3. What is Parapatric Speciation
– Definition, Characteristics, Gene Flow
4. Similarities Between Allopatric Sympatric and Parapatric Speciation
– Outline of Common Features
5. Difference Between Allopatric Sympatric and Parapatric Speciation
– Comparison of Key Differences
Key Terms
Allopatric Speciation, Sympatric Speciation, Parapatric Speciation
What is Allopatric Speciation
Allopatric speciation is a process that drives the formation of new species by geographically isolating populations. In fact, geographic isolation is the fundamental aspect of allopatric speciation. When a population becomes physically separated from other populations of the same species, it loses the ability to exchange genes through interbreeding. This isolation can occur through various mechanisms, such as the emergence of mountains, rivers, or other physical barriers that create distinct habitats. Additionally, colonization events, like migrating to remote islands or establishing populations in new territories, can result in geographic isolation. Once isolation occurs, populations are exposed to different environmental conditions and selective pressures. These varying circumstances influence the genetic makeup of each population and promote independent evolutionary trajectories.
Genetic drift, mutations, and natural selection act upon each isolated population accumulating genetic differences over time. The accumulation of genetic differences is a critical step in allopatric speciation. As populations adapt to their distinct environments, genetic changes can occur, resulting in unique traits and characteristics. These genetic differences may arise through point mutations, chromosomal rearrangements, or the introduction of novel genetic material through hybridization events with related species. Natural selection then acts upon these genetic variations, favoring individuals with traits that enhance survival and reproduction in their specific habitats.
Figure 1: Allopatric Speciation
Reproductive isolation is a key consequence of genetic divergence in allopatric speciation. As isolated populations accumulate genetic differences, barriers to reproduction may arise. These barriers can be prezygotic, meaning they prevent mating or fertilization, or postzygotic, meaning they reduce the fitness of hybrid offspring. Prezygotic barriers can manifest in various forms, such as differences in mating behaviors, mating preferences, or physical incompatibilities. Postzygotic barriers can include reduced hybrid viability or fertility, which limits the successful production of viable offspring between populations.
Examples of Allopatric Speciation
Numerous examples of allopatric speciation exist across different taxa. One well-known example is the divergence of Darwin’s finches in the Galapagos Islands. These finches exhibit remarkable diversity in beak morphology, which corresponds to their specific ecological niches. It is believed that a single ancestral species colonized the islands, and subsequent geographic isolation and adaptation to different food sources led to the evolution of distinct finch species with unique beak shapes.
What is Sympatric Speciation
Sympatric speciation is a process of species formation that occurs within the same geographic area without physical isolation. Sympatric speciation challenges the conventional notion that geographic isolation is a prerequisite for speciation. Instead, this mode of speciation involves the emergence of reproductive barriers that prevent interbreeding between different groups within the same population. These reproductive barriers can result from various mechanisms, including changes in mating behaviors, mate preferences, or genetic incompatibilities.
Figure 2: Sympatric Speciation
One of the critical factors driving sympatric speciation is ecological specialization. Within a shared habitat, populations may exploit different ecological niches or resources, leading to divergent selection pressures. This can result in the evolution of distinct phenotypic traits and adaptations, which may contribute to reproductive isolation. For example, in a lake ecosystem, some fish populations might adapt to feeding at different depths or on different food sources, reducing the likelihood of interbreeding between them. Another mechanism contributing to sympatric speciation is disruptive selection. Disruptive selection occurs when extreme phenotypic traits are favored over intermediate forms, splitting the population into distinct groups. This process can result from various factors, such as resource competition or divergent ecological pressures. Over time, individuals with extreme traits have higher fitness, leading to developing reproductive barriers and forming new species.
What is Parapatric Speciation
Parapatric speciation is a form of speciation that occurs when two populations of a species evolve into distinct species while sharing a common border or range. Unlike allopatric speciation, where geographic barriers completely isolate populations, parapatric speciation involves adjacent populations with limited gene flow among them.
Figure 3: Parapatric Speciation
In parapatric speciation, the populations occupy slightly different habitats or ecological niches along the gradient of their range. This can result in divergent natural selection pressures acting on each population, leading to the accumulation of genetic differences and the development of unique traits. Over time, reproductive barriers may evolve between the populations, reducing gene flow and promoting further genetic divergence.
Parapatric speciation is often associated with species that exhibit clinal variation, where gradual changes in traits or allele frequencies occur along a geographic gradient.
Similarities Between Allopatric Sympatric and Parapatric Speciation
- The primary similarity between these modes is that they all involve forming new species.
- In all three modes, genetic divergence plays a crucial role.
- Reproductive isolation is a common outcome in all three modes of speciation.
Difference Between Allopatric Sympatric and Parapatric Speciation
Definition
Allopatric speciation is a mode of speciation that occurs when a population of organisms becomes geographically isolated from other populations of the same species. At the same time, sympatric speciation is a mode of speciation in which new species emerge from a single ancestral species within the same geographic area without the presence of physical barriers or geographic isolation. On the other hand, parapatric speciation is a mode of speciation that occurs when populations of a species diverge and form new species while maintaining limited contact along a geographical gradient.
Geographic Arrangement
In allopatric speciation, populations are geographically isolated from one another by physical barriers such as mountains, rivers, or oceans. The isolation restricts gene flow between populations. Meanwhile, sympatric speciation occurs when new species arise within the same geographic area without geographic isolation. The populations share the same habitat or overlapping ranges. Parapatric speciation, on the other hand, involves adjacent populations that share a contact zone along a geographic gradient. The populations are not entirely isolated but have limited gene flow and exhibit some degree of genetic and ecological divergence.
Gene Flow
Gene flow between allopatric populations is restricted due to physical barriers, resulting in limited or no gene exchange. Sympatric populations may have ongoing gene flow as they occupy the same geographic area. However, there may be reproductive barriers or ecological factors that limit interbreeding and promote genetic divergence. Parapatric populations have partial geographic overlap and limited gene flow. There may be some gene exchange within the contact zone, but as distance increases along the geographic gradient, gene flow becomes more restricted.
Reproductive Isolation
Allopatric populations experience reproductive isolation due to geographic barriers. Over time, genetic and behavioral differences may accumulate, leading to reproductive barriers that prevent interbreeding upon secondary contact. Sympatric speciation involves the development of reproductive barriers within the same geographic area. Factors such as ecological differentiation, disruptive selection, or polyploidy can contribute to reproductive isolation. Parapatric populations may have some level of reproductive isolation due to genetic and ecological differences. Reproductive barriers can arise along the geographic gradient, limiting gene flow and promoting divergence.
Conclusion
Allopatric speciation occurs when a population becomes geographically isolated from other populations of the same species. In contrast, sympatric speciation occurs when a new species forms from a population within the same geographic area as the parent species without geographic isolation. Meanwhile, parapatric speciation is a mode of speciation that occurs when two populations have partial geographic overlap, where their ranges border each other. This is the main difference between allopatric sympatric and parapatric speciation.
Reference:
1. “Allopatric Speciation.” Biology Online.
2. “Sympatric Speciation.” Wikipedia. Wikipedia Foundation.
Image Courtesy:
1. “Allopatric speciation caused by topography” By Andrew Z. Colvin – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Sympatric Speciation Schematic” By Andrew Z. Colvin – Own work (CC BY-SA 4.0) via Commons Wikimedia
3. “Parapatric Speciation Schematic” By Andrew Z. Colvin – Own work (CC BY-SA 4.0) via Commons Wikimedia
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