Factors That Affect The Distribution Of Biomes

These factors include plate tectonics, atmospheric circulation, and tropical convergence zones, to name a few. The movement of the Earth’s plates causes continental distribution, mountain formation, and oceanic breaks. Different biomes are found because of the different latitudes/longitudes, altitudes, and depths respectively. Temperature and moisture at higher elevations differ from that of lower elevations thus creating different distributions for biomes to be found. Atmospheric circulation patterns cause wind patterns that will warm/cool different areas. Around the equator, where the sun hits most directly, the air is warm, and we find tropical rainforests.

Moving towards the poles, the temperature and moisture in the air gradually become much cooler and drier. This change causes the changes in longitudinal distribution and biome variety we see making our way towards the north or south.

The Inter-Tropical Convergence Zone (ITCZ) is a low-pressure belt that circulates the Earth where the trade winds merge near the equator (4) Tropical biomes are dependent on the movement and position of this essential source of rainfall.

In high-pressure biomes closer to the poles, the small amount of rainfall is dependent on the ITCZ. In general, the ITCZ is an important factor that is involved in biome distribution by providing different moisture levels to different areas. The distribution of biomes is caused by many different factors that occur on Earth. All these factors relate back to temperature and moisture in complex ways. It can be said that biome distribution is “simply” due to temperature and moisture, however, the causes are far from simple.

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The repeated glaciation cycles during the Pleistocene caused habitat alteration of many biotas. Some habitats experienced temperature change, downsizing or upsizing, natural land bridges were formed or eradicated, and the biota had to adjust or became extinct. Vertebrates roaming the Earth included sloths, mastodons, and very large birds. The main cause for the huge extinction during the Pleistocene is not fully understood. However, if Earth had not undergone extensive glaciation cycles during this epoch, some of these vertebrates might still roam the planet. Habitats, such as Florida, would still be double the size it is today. A much larger habitat would provide vertebrates with larger places to evolve and thrive. The low sea levels would continue to connect North and South America allowing vertebrates to migrate to and from both continents. Vertebrate diversity would likely be greater if extensive glaciation hadn’t shaped the planet during the Pleistocene and eradicated many habitats.

Besides Darwin and Wallace, one very important contributor to biogeography was German astronomer/meteorologist Alfred Wegener. Wegener devoted his adult life to researching continental drift and proving why the drop-off-of-the-ocean basins line up seamlessly. The theory of plate tectonics proved to be a revolutionary idea which aids in the explanation of species and climate distribution. Another important contributor to biogeography is 18th-19th century explorer, Alexander von Humboldt. His work “laid the foundation for the science of biogeography” Von Humboldt was among the first to consider why certain biota thrives in specific areas. He explained how weather patterns, geology, and biology were all factors to consider. This work in combination with other important biogeography contributors was essential to setting the foundations of biogeography.

Allopatric and sympatric speciation are two ways in which speciation changes or separates species over time. Allopatric speciation is defined as speciation that happens when two populations of the same species become isolated due to geographic barriers over long periods of time. An example of allopatric speciation is the Galapagos finch. The ocean has isolated these finches on separate islands for millions of years. Over time, each island homes finch species with a unique beak to best thrive in that habitat. Conditions that favor allopatric speciation include small population sizes, no gene flow, and reproductive isolation. Gene flow can be stopped by natural barriers or unnatural causes such as human deforestation and construction.

Sympatric speciation is defined as the process through which new species evolve from a single ancestral species while inhabiting the same geographic region. Once sympatric speciation has occurred, species A and species B can no longer produce viable offspring with each other. One member of a species develops a new characteristic that is useful to them. Over time, this characteristic is favored while the original characteristic continues to thrive in the original species. One key condition for this theory is selection against hybrids. If the two evolving species were to produce hybrid offspring, the chances of new characteristics evolving are reduced. Heterozygosity must be selected against. If the necessary conditions are met, species B diverges so much from species A that they are officially a new species. Allopatric speciation is more important than sympatric speciation because it is much more common, and the conditions are frequently met. In the last few hundred years habitat, destruction rates have continued to increase. Many species, like the Culex molestus mosquitoes are an example of allopatric speciation due to habitat barriers. Underground C. molestus in the London Underground Railroad system have developed significant differences, including reproductive biology, to the same species directly above the ground.

The Theory of Plate Tectonics was introduced in the early 1900s. Plate tectonics theory “explains the origin and destruction of Earth’s plates as well as their lateral movement, or drift.” Early scientists set out to discover the reason why the continents line up so well, and why the oceanic floor lines up even better. Alfred Wegener’s theory became the most accepted, long after his death. According to Wegener, the reason that they line up so precisely is that they were all connected at one point in history. The molten core of the Earth produces magma that rises towards the lithosphere, the Earth’s surface. As it drifts sideways, the Earth’s crust is moved apart a rate of about 3cm per year. The spreading of the crust is what causes the continental drift, and collision of the plates creating oceanic basins. Plate movement matters because it is the explanation for many questions, including why species reside where they do.