Change Is the Only Certainty
The geosphere is in an almost constant state of change, punctuated by catastrophic events that completely wipe out or shift habitats.
Nearly 250 million years ago, there was a mass extinction that that wiped out 90% of all life on earth. What could have caused such extinction, and how do extinctions like this affect evolution? Read this page to gets some clues.
One of the strongest theories on the cause of the Permian-Triassic extinction is that earth's climate changed dramatically, making life impossible for 90% of all species on earth. However, the remaining 10% evolved and adapted to the new climate. While this is a dramatic example of geologic change, there are many other ways in which a changing geosphere created opportunities for new species to evolve. How do you think geologic processes and climate change affect evolution? Click on the images below to find out more.
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Short Term Plate Tectonics: The earth’s plates drift atop the hot mantle, diverging in volcanically active spreading centers, and converging to create mountains, earthquakes, and explosive volcanoes. All of these events can wipe out, separate, or isolate species, creating new ecosystems.
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Long Term Plate Tectonics: Continents have moved around the planet to various locations over geologic time as the plates have moved. In fact, 225 million years ago, all of the plates were locked together in one large landmass called Pangaea. Over time, the continents broke apart, and they continue to drift to this day. This caused dramatic changes in climate and geology on each continent, providing opportunities for the evolution of new species.
Short Term Plate Tectonics: The earth’s plates drift atop the hot mantle, diverging in volcanically active spreading centers, and converging to create mountains, earthquakes, and explosive volcanoes. All of these events can wipe out, separate, or isolate species, creating new ecosystems.
Long Term Plate Tectonics: Continents have moved around the planet to various locations over geologic time as the plates have moved. In fact, 225 million years ago, all of the plates were locked together in one large landmass called Pangaea. Over time, the continents broke apart, and they continue to drift to this day. This caused dramatic changes in climate and geology on each continent, providing opportunities for the evolution of new species.
Speciation
How do you think a shift in continents and a split in a continent might affect species on earth? How do catastrophic geologic events like tsunamis, earthquakes, and volcanic eruptions affect evolution?
Lemurs are endemic to Madagascar and are geographically isolated from the rest of the world.
New species evolve after these types of changes through natural selection in a process called speciation. Speciation occurs when different groups of a population are geographically or reproductively isolated from one another over long periods of time.
We can demonstrate speciation in a simple laboratory with fruit flies.
In this experiment, fruit flies, Drosophila pseudoobscura, were separated into two different groups. One was fed starch-based food and the other sugar-based food. This separation was continued through several generations, and as a result, the populations diverged. When the groups were again mixed, scientists found that the flies only mated with their adapted population.
Extinction
Did you know that all species eventually become extinct? By looking at the fossil record, scientists can estimate that there is a background extinction rate of 1-5 species per million per year.
This background extinction results from changing conditions on earth providing opportunities for the evolution of new species. The balance between the evolution of new species and extinction of existing species is what creates earth's biodiversity.
In contrast, mass extinctions significantly affect the number of species on earth at a given time. Click on the images below to learn more about mass extinctions throughout earth's history.
Answer
In preindustrial society the background extinction rate was only 0.1-1 species per million per year. The current rate is 100 species per million per year! This loss of biodiversity is something we desperately need to address.
Ecosystem Roles
You've seen how ecosystems on earth change over time and how that affects biodiversity through the evolution of new species. Let's narrow our focus to look closely at the role of species in stable ecosystems now. Take a look at each of the classified ads in the image from the Understanding Evolution website.
Did you notice how each one of these organisms has a role to play in this ecosystem? Each organism depends on a certain type of group of resources and requires specific conditions to thrive. What do you think would happen if there were a large number of organisms that all required the same resources and conditions? There might be too much competition between them for every single one to survive. In a stable ecosystem, each organism inhabits an ecological niche. A niche is a distinct role that that organism plays in its community.
Answer
These small fish are called remoras. They eat leftovers dropped by the larger fish they attach to. The larger organism does not gain or lose anything from the presence of the remora, but the remora gets easy access to plentiful food by hitching a ride on a larger fish. This is one example of resource partitioning-- where two species depend on different resources within the same ecosystem.
Generalists and Specialists
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A: Specialist species with narrow niche B: Generalist species with broad niche C: Niche overlap D: Niche breadth E: Niche seperation |
Consider the image above. The y axis is the number of individuals (i.e., panda and raccoon) and the x axis is the distribution of resources used by the species. Notice that one of the two species has a much broader niche that incorporates more resources, while the other can only survive on a limited set of resources.
Answer
The specialist species, the one with a narrow niche, would be prone to extinction during changing environmental conditions due to its limited resource requirements, while the generalist species, the one with the broad niche, could weather changes better because it can live in a variety of habitats and eat a variety of foods.
Reflection: Specialist and Generalist
Can you think of some examples of generalist and specialist species? In a discussion post, identify at least two specialists and two generalists along with an explanation of why each one can be categorized as such.
Record your answers in your science journal.