Hey everybody, it's Mr. Smedes, and today we'll be covering topic 2.5, which is natural disruptions to ecosystems. Our objective for the day is to be able to explain how natural disruptions, both short-term and long-term, impact ecosystems and habitats, and then we'll practice the skill of describing trends and data at the end of today's video. So a natural disturbance is just a natural event that disrupts the structure and or the function of an ecosystem. So it's going to interrupt energy and matter cycling through the ecosystem.
It may displace organisms. It may totally reshape or even destroy the ecosystem or the habitat. So some examples would be tornadoes, hurricanes, fires, asteroid impacts. So like the asteroid that killed the dinosaurs, that would be an example of a natural disturbance.
It's important to point out that natural disturbances can be even greater than human disturbances. So we disturb ecosystems by clear-cutting, by farming, but natural disturbances can be even greater than some of these disturbances we cause. So like I mentioned earlier, the asteroid that struck Earth about 65 million years ago and wiped out the dinosaurs along with several other species, this is an example of a natural disturbance that is very destructive and far more impactful than many human disturbances.
So another important thing we need to know is that natural disturbances can appear on three different time scales. So they can be periodic, episodic, or random. So a periodic event is one that occurs with some regular frequency.
It's somewhat predictable. And a great example is the wet and the rainy seasons that are followed then by dry seasons. So in an ecosystem such as the savannah in Africa, these happen pretty regularly.
And so we would call them periodic. Next we have episodic events. Episodic events are ones that occur somewhat frequently but not with a really regular interval.
We can't necessarily predict exactly when they're going to happen. There may be times of the year where they're more likely. So hurricanes are a great example, droughts and fires. We expect more fires to happen in California during the summer than in the winter and so we have some idea of when they might occur, the conditions that would contribute to them, but we can't predict them with absolute certainty.
Then finally we have random events and they're just like what they sound. We understand why they happen but we don't necessarily know when they happen. There aren't times of the year where they're more or less likely per se and so things like earthquakes or an asteroid striking earth would be great examples of random events.
Now we'll talk about natural climate change. So over long periods of time earth's climate has varied quite a bit for numerous reasons that are natural or non-human reasons. So one example is that there are slight changes in Earth's orbit and its tilt as it goes around the Sun. And that's going to cause many periods of ice ages and many periods that are warmer.
And these occur with somewhat regular frequency. So we can take a look at these images here. And what we can see is as the Earth is orbiting the Sun, there's going to be some slight changes.
So every 100,000 to 400,000 years, we'll see this shift in eccentricity where the Earth... will move slightly closer to the sun in its orbit or slightly further away. There's also some variation in the Earth's tilt, which would tilt us slightly closer or slightly further away from the sun, depending on what hemisphere we're in. And so these changes result in somewhat regular shifts in temperature on Earth. So if we look now at temperature over the past 800 years, in the red, we'll see that temperature rises and falls.
We have periods where it's cooler, where there are small ice ages. We have periods where it's warmer. And also, there's variation in carbon dioxide levels in the atmosphere that are naturally occurring. So these could be due to the oceans warming, which then gives off carbon dioxide.
It could be due to periods of increased plant growth, which would take in some carbon dioxide. And so there are several natural patterns that occur over time that result in climate change. We will talk a lot in this course about human driven climate change, which is a very big concern. I don't want to undermine the importance of human.
cause climate change, but we do have to understand that there are natural factors that also contribute to climate change over time. For some perspective, we can look at these carbon dioxide levels over the past 800,000 years, and we can see that although they have varied naturally, what we are seeing currently far exceeds any level of natural carbon dioxide change that we have seen in human history. And so this is why scientists are rightfully concerned about this. So again, We have to understand why there are natural changes in climate, but I do not say that at all to undermine the importance of human-driven climate change currently. That will be our last unit of the year.
It's one of our most important, and so that will be something we focus on a lot in this course. Another natural change that has happened on Earth over the years is sea level rise. So sea level has varied significantly over geologic time, and that happens primarily due to Earth's changing in temperature over time. So if we look at this graph here, what we'll see is that periods of increased carbon dioxide will lead to warmer periods, and warmer periods lead to melting of polar ice caps.
So when polar ice caps melt due to the warmer temperature, that water flows into the ocean and so we can see these peaks of sea level rise are coinciding with carbon dioxide peaks that are warming the atmosphere and therefore the ocean and there's a little bit of a positive feedback loop because when the ocean warms it can't hold as much carbon dioxide so it gives off more to the atmosphere which warms a little bit more and so we get these periods again where carbon dioxide peaks warms the atmosphere and therefore the ocean and the ocean then leads to melting of polar ice caps as well as the warmer atmosphere and there's something called thermal expansion so the ocean level actually rises a little bit when it's warmer due to the water molecules actually spreading out so these two factors contribute to sea level rise that occurs naturally over time now we'll talk about the implications for habitats with environmental change so these major environmental disturbances are going to cause widespread habitat destruction or alteration, sometimes even habitat loss. A great example that we should be really comfortable explaining in this course is sea level rise. So as sea level rise happens, we actually lose coastal estuaries as they go underwater.
They no longer function as these sort of brackish, part salt, part freshwater areas that have some exposed land right next to water. They get completely flooded and that changes the way these habitats function. It removes this habitat for species that require the land, and it changes the depth of water, which changes some of the characteristics of the plant community.
So let's look at some diagrams to help us understand. If we take a look at this diagram here, what we'll see is that now we have a sea level here that then allows for the existence of these salt marshes and these mangroves, a really important estuary habitat. Remember that a lot of shellfish are going to breed here.
A lot of birds are going to find their homes here. But as sea level rises, we lose the amount of this estuary habitat because it can't exist in these deeper waters. So it has to shift into the shore and we actually lose some of that habitat.
So many of these species would have to migrate or they would die as a result of this change. And we can see another example of what this looks like when we look at the change in depth. So here we have sea level rise and we can see that these aquatic plants that used to be close enough to the surface to get enough sunlight. are now receiving decreased amounts of sunlight due to how far they are underwater.
And certain species cannot even survive these conditions where there's so much water over them that they're not receiving adequate sunlight. And so we have a change in this community here. These species that used to thrive in shallow waters can no longer thrive in shallow waters.
These mangroves and this edge forest ecosystem are going to become flooded. And so the organisms that relied on those terrestrial aspects of that ecosystem can no longer rely on that. So really important to understand that sea level rise changes estuary habitats by increasing the depth of the water and the saltiness or the salinity of the water and then it's going to actually flood inland habitats right along the coast which completely removes those habitats for species that need to land. And finally we'll talk about migration. So natural disturbances to environments can cause species to migrate and sometimes these can be unpredictable and repetitive patterns such as wildebeest migrating to follow the rainy season across the Serengeti Plains here.
So they're essentially going to follow rainfall patterns so that they can get access to the water that that rain brings and the plant growth for their food source. But it may be less predictable and less regular. So another example is ocean species migrating further north as the ocean warms and opens up new ranges that used to be too cold for those species or cold tolerant ocean species that have to migrate even further north as equatorial waters and lower latitude waters closer to the equator become too warm for them. And then finally we have bird migration patterns which have had to shift earlier in the year to accommodate the changes in insect hatching that have occurred due to climate change.
Let's look at this graph here to help us understand. So previously around 1980 or so we can see that the caterpillar hatching date coincided perfectly with the peak food demand needs for the bird hatchlings. So we have the parents laying their eggs on a date that results in the hatching happening slightly before the caterpillar hatching. Again, so that there is the peak demand for food for their hatchlings coinciding with the peak caterpillar hatching.
However, as we look at today, due to climate change, there's now a mismatch in this timing. So caterpillar hatching has shifted forward due to it becoming warmer earlier in the spring. So the previous date of laying and date of hatching for birds now coincides with a peak hatchling food demand. occurring at the tail end of caterpillar hatching. That's a problem.
So what that means is that birds have had to shift their migratory patterns earlier in the year so that their breeding, their egg laying, and their hatching can also occur earlier in the year to be back in sync with caterpillar hatching. So again, another example of how environmental change, in this case climate change, alters migration habits of organisms. Our practice FRQ for topic 2.5 today will involve the skill of describing trends or patterns in data. So we have a map here of the U.S. and we have the change in first leaf date for the honeysuckle plant.
So we can see is in dark orange. This is going to be eight days earlier than previously. And in dark blue, this is going to be eight days later than previously.
So what I want you to do is look at this map and describe the relationship between latitude or distance from the equator and the change in first leaf date that's depicted. in this graph. Then I want you to explain why you think this relationship exists. All right everybody, thanks for tuning in today.
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