hey everybody it's Mr smeads and today we're going to be reviewing unit 2 of the AP environmental science course and exam if you're ready to think like a mountain and write like a scholar let's get started before we go any further with unit 2 today make sure you've got your ultimate review packet study guide printed out and ready to go as we go through this video you want to answer the practice questions make sure that you really understand the concepts that are covered in unit 2. that exam I may is just too tough to go into without practicing the writing style that you need in Apes so make sure you're practicing with the mini frqs at the end of each unit so on we go into unit 2 with a short but sweet look at biodiversity many of these Concepts would be familiar already from your biology classes so if you want to see where we cover specific Concepts make sure to take a look at the video time stamps here that way you can pop down to those sections if you just need A Brief Review now the first Topic in unit 2 is biodiversity and it's one that students think they understand but often don't fully grasp and that's because the basic definition is really simple it's just the diversity of different life forms found in an ecosystem but what we really need to make sure we have down are the three different levels of biodiversity and why biodiversity is so beneficial remember that the three levels of biodiversity are genetic biodiversity ecosystem biodiversity and species biodiversity and these three levels are nested within each other which helps us remember why they're so beneficial genetic diversity is the variance of genes or traits found within individuals of a population so high genetic diversity or a wide range of different traits is beneficial to species because it increases the likelihood that if there's an environmental disturbance or a change in that ecosystem some of the members will have genes or traits that allow them to adapt so if you have a population of sparrows and then there's a drought that causes the seeds they eat to become dry and harder High genetic diversity in that population will increase the likelihood that some of them have bigger beaks that can still crack those harder seeds open species diversity is the diversity of different types of organisms found in an ecosystem now there's a really simple way to measure and there's a more complex way to measure it now the easy way to measure is species richness this is just a count of the total number of different species found in a given ecosystem but a higher species richness doesn't necessarily mean that an ecosystem has more species diversity we also want to consider what's called species evenness this is the distribution or the balance of the population sizes of all the different populations present so if we look at this diagram we can see that even though the two forests have the same species richness Force number one will have a higher species evenness now this higher species evenness is beneficial to the whole ecosystem of forest number one that's because if there were disease that spread among one deciduous tree species in that ecosystem there would still be plenty of conifers or other deciduous species to repopulate that Forest now if the same disease were to strike in force number two that force would have the potential to lose 70 percent of its tree cover if this dominant tree species were susceptible to that disease now that would devastate the forest in a way that Forest number one wouldn't be so just like genetic diversity is beneficial to populations and species diversity is beneficial to ecosystems ecosystem biodiversity is beneficial to entire biomes an ecosystem diversity just refers to the variance in the different ecosystems found in a given area so the tropical rainforest would have a really high ecosystem diversity you're going to find Rivers different types of tree stands Edge habitats where a forest meets an open area whereas a desert biome is going to have a lot lower ecosystem diversity and be able to support less species richness because of that so now that we understand why biodiversity benefits ecosystems let's take a look at how ecosystems benefit humans by making us richer now I know what you're probably thinking wait uh what is going on here the vegan bike riding carbon emission cutting environmental science teacher is talking about exploiting nature for money but remember many of the things that we attach monetary value to ultimately come directly from or are dependent on the natural function of ecosystems now these Financial benefits that we get from ecosystems are called ecosystem services and in Apes we categorize the different type of services into four key categories provisioning services are the easiest to remember and that's because these are things provided directly to us by natural ecosystems examples would include things like wood for furniture or houses that can be harvested and sold for a profit supporting services are processes done by ecosystems that support a valuable Human Action such as agriculture for example insects like bees and moths May pollinate a farmer's crops increasing the amount of produce they can sell now the farmer could still produce some food without those pollinators but not nearly as much so their profits or their yields are supported by those pollinators regulating Services refer to the fact that ecosystems often regulate or stabilize climate or other environmental factors which saves US money from having to pay to clean up unstable conditions so the fact that trees sequester carbon dioxide can save us money because it reduces some of the expensive consequences of climate change this could be things such as droughts which damage Farmers crops or storm damage which could damage your home and finally we have cultural Services which are the recreational or intellectual benefits we get from nature so a tourist going to visit the Grand Canyon is going to pay a park fee and stay at a local hotel which generates Revenue scientists research ecosystems and they might write books or reports that lead to valuable products being created in addition to being able to identify the four categories of ecosystem Services we also want to understand how humans can disrupt ecosystem services so great example would be drilling for and transporting crude oil so when the deep water Horizon oil spill happened in the Gulf Coast of Mexico a ton of ecosystem Services were disrupted fishermen weren't able to catch as many fish and their profits suffered mangrove swamps and salt grasses died which destabilized the coastline and led to more storm damage and the tourism industry was impacted as beaches were covered in oil and tourists were less likely to come visit and on topic 2.3 we'll take a look at the theory of Island biogeography this can sound like a super complex topic but it really just boils down to two Simple Rules so let's say we have two islands of equal size but one is closer to the mainland than the other the closer Island would be likely to have a higher species richness just because there are more species capable of migrating to the island from the mainland the further away from the mainland island is the fewer species that are able to fly or swim there so if we plot distance from the mainland and number of species on a graph we'll see an inverse relationship between the two now if we look at two islands that are the same distance from the mainland the larger Island would be likely to have a higher species richness this is due to the fact that it's going to have a higher ecosystem or habitat diversity with more space there's a greater variety of Landscapes like forests or grasslands or ponds this means that we can have a wider variety of plant and animal species supported in this ecosystem so if we plot Island area and number of species on a graph we'll see a direct relationship between the two as the Island area increases so too does the number of species supported by this island we also need to remember that Island ecosystems are somewhat unique in that they're going to offer a narrow range of food and habitat choices to species this often leads to really specific adaptations where species are adapted to the conditions of these narrow food and habitat choices take the dodo bird for example this large flightless bird species evolved from a member of the pigeon family some 20 million years ago now because it only inhabited the small island of Mauritius it didn't have a lot of competition from other herbivores or pressure from predators this led to an increasing body size and the loss of flight because a small flight worthy body wasn't advantageous anymore without competitors or carnivores to fly away from and the problem for these highly specialized species is that because they're uniquely adapted to these narrow conditions they're often unable to adapt to or compete with invasive species that show up on their Island and this is precisely what happened to the dodo bird when the most invasive species of all time showed up on their Island the humans now without getting too graphic suffice it to say that the dodo bird is not around anymore and the big takeaway here is that islands are going to have a higher percentage of specialist species than the mainland and those specialist species are going to be more vulnerable to invasives because they're so uniquely adapted to the narrow conditions of those islands dodo brain so as good as DW is at cooking Arthur this one doesn't really add up definitely didn't go extinct because they were dumb they just evolved on an island with no natural predators and so they weren't afraid of the humans when they showed up so maybe the real dodo brains were the Dutch Sailors who hunted dodos at a way faster rate than they could repopulate and somehow didn't think that would lead them to Extinction so moving on from islands and dodo brains we'll take a look at a really simple concept called ecological tolerance this just refers to the range of conditions an organism or species can tolerate before death or Serious injury ensues so let's start with an easy example that we're all really familiar with and that's human body temperature most of us are sitting somewhere between a comfortable 97 and 99 degrees Fahrenheit now there are a few outliers with especially high or low body temperatures and this is a great example of genetic diversity but in general humans have an optimal range for body temperature of about 97 degrees to 99 degrees this is the range where bodies function most optimally we're able to survive grow and develop so what happens if an organism moves outside of its optimal range the first thing that happens is it enters What's called the zone of physiological stress so let's return turn to this human body temperature example if your body goes above 99.5 or below 95 degrees you're going to enter a stressed physiological State you're not going to think or move as quickly as you would normally and you're not going to be able to remain here for long without serious consequences if you move even further from the optimal range so above 106 degrees or below 86 degrees you're going to leave the zone of physiological stress and enter what we call the zone of intolerance which quickly leads to death now this is a great time to review why genetic diversity is so important there's a general range of tolerance that all the members of a given species share such as this optimal range for human body temperature but there's also some variation between individuals and that's due to genetic diversity so some individuals may have a wider range of tolerance or a wider optimal range than others and this is how genetic diversity can act as sort of a buffer against environmental disturbance so if the environmental conditions of a population change such as the temperature or the pH of their environment some of the members are going to have a wider range of tolerance due to genetic diversity they can survive the environmental change and pass on these tolerant genes to their offspring which allows a new population to evolve that is now adapted to this new condition speaking of environmental disturbances we need to take a minute to review the non-human or natural events that can disturb ecosystems now before you start thinking I'm letting humans off the hook for disturbing the environment with five whole units dedicated to the different ways that we impact the environment so don't worry but for natural events that cause ecosystem disruptions there's three main levels of frequency we need to understand first we have periodic events these are things like rainy Seasons or dry seasons that happen with some regularity then we have episodic events these occur less regularly but they're still occurring with some regularity especially when the environmental conditions are right great examples of these events would be hurricanes and forest fires they don't happen super regularly but they are more likely to occur when the environmental conditions are right and finally we have random events which as their name implies occur with no Rhyme or Reason whatsoever these are things like an asteroid striking Earth or volcano erupting however ecosystems can also will be disrupted by slow gradual changes in Earth's climate over time the reason Earth's climate change is naturally over time is because the orbit that the Earth takes around the Sun changes naturally over time the first way that the Earth's orbit around the sun changes is called eccentricity this refers to the shape of the orbital path that the Earth takes around the Sun sometimes this shape brings the earth a bit closer to the Sun in its orbit and sometimes a bit further away the second is called axial precession where how much the Earth wobbles on its axis and the third is the change in Earth's obliquity or tilt we call these variations in Earth's orbit malankovic Cycles since each of these Cycles happens with a regular frequency they produce regular changes in Earth's climate as a result notice on the x-axis of these graphs that we're talking about cycles that unfold over tens of thousands of years so they produce really gradual climate change not the type of change we're seeing right now which is easily observable in one human lifetime what scientists have learned from lining up the timing of these malakovich Cycles with ice core temperature data is that these Cycles impact the temperature versus climate by bringing closer or further away from the Sun or tilting the Northern Hemisphere closer or further away from the Sun now don't worry about understanding the intricacies of the malakovich Cycles you don't need to go this in depth in Apes what you do need to know is that earth's climate changes naturally over time over the course of tens of thousands of years as Earth's orbit brings Earth either closer or further away from the Sun or tilts the Northern Hemisphere closer or further away from the Sun the other thing we need to remember about Earth's natural gradual cycling of climate change is that it causes a change in sea level as we can see here there's a really clear link when we look at the last 400 000 years worth of data on global temperature and sea level during periods where earth's climate is warmer sea level rises due to both the melting of glacial and polar ice sheets and also the thermal expansion of water molecules in the ocean now in the context of ecosystems let's think about what this rise in sea level and change in temperature can mean low-lying Coastal ecosystems like estuaries may be completely flooded and may disappear during periods of high sea level shallow ocean waters that provide tons of sunlight to Coral Reef ecosystems may become deeper and light may not penetrate to the bottom which completely changes those ecosystems these are the types of ecosystem disturbances we need to think about when we're talking about this slow gradual cycle of natural climate change now you may be thinking poor manatees or Coral or other species that are impacted by natural ecosystem disturbance but don't forget that ecosystems and organisms can adapt in fact every species on Earth is the result of adaptation on the part of some ancestor species forced to change based on natural ecosystem disturbances and environmental upheaval so the next time you catch a dub in Call of Duty or fortnite don't forget to thank homo habulous for those opposable thumbs in all seriousness though let's take a closer look at how this trait of opposable thumbs may have Arisen in ancestors of Homo habilis first we need to think back to the genetic diversity concept that we reviewed in the beginning of this video because of genetic diversity there's a range of traits even thumb muscle arrangement in all members of a population so some early members of the homo habulous species randomly developed an new thumb muscle Arrangement roughly 2 million years ago this thumb muscle Arrangement allowed for a tighter more nuanced grip that ultimately led to the ability to manipulate and create stone tools now the prevailing scientific consensus is that this new thumb muscle Arrangement enabled homo habulous to create and wield more efficient stone tools for cracking open animal bones this gained them access to the energy-rich marrow inside and gave them a huge energetical advantage over similar primates that didn't have this same access to bone marrow now because of this big energetical Advantage the opposable thumbs brought members that had this adaptation survived longer due to access to more marrow and passed on those traits to more offspring an adaptation is just a genetic mutation like a new thumb muscle Arrangement that gives an organism a higher likelihood of surviving and reproducing as we wrap up our review of adaptations here the important thing to remember is that organisms are either able to adapt to environmental disturbances or they're unable to adapt to environmental disturbances and then they go extinct some of the environmental changes that early hominids adapted to were moving out of dense forests and into grasslands in these new grassland conditions it became advantageous to be able to stand up so we see Homo erectus with the ability to stand upright look around and Survey the environment it was also advantageous to be able to wield more efficient tools to break open animal bones to get more energy all of these are great examples of adaptations that allowed species like Homo habilis to adapt to new environmental conditions survive and pass those traits onto Offspring and speaking of surviving look at you surviving all the way to the end of the unit 2 review as we wrap up our review of ecosystems we'll review ecological succession and keystone species first of all we have to remember that there are two types of ecological succession that's primary succession and secondary succession in primary succession pioneer species like moss and lichen start to colonize a bare rock ecosystem when the wind transports their seeds or their spores there now they're able to grow on bare rock because they can secrete acids which release the nutrients and minerals they need from The Rock through a process called chemical weathering this chemical weathering process combined with a death and regrowth of the Moss and lichen slowly lead to the formation of shallow rocky soil this in turn allows other pioneer species like grass wildflowers and shrubs to colonize the area eventually the continual death and regrowth of these early successional plants adds more and more organic matter and depth to the soil this then enables intermediate successional species like shade intolerant fast-growing trees to come and colonize the area over time slower growing shade tolerant species of trees like Oak and Maple grow up and replace the intermediate successional trees and trucks we call this community that has progressed through these stages of succession in climax community these ecosystems typically have large amounts of biomass and support a high species richness secondary succession follows a really similar progression of changes with one key difference there's already soil present instead of moss and lichen being blown in by the wind and colonizing bare rock you have pioneer species like grass and wildflowers being blown in by the wind and they're colonizing Disturbed soil you see secondary succession tends to take place after a disturbance that clears out the existing vegetation this could be a forest fire a glacial Retreat or even humans abandoning an agricultural field the pioneer species in secondary succession are still fast growing and Sun tolerant and typically they have their seeds dissers by either the wind or by animals and finally we'll review keystone species now remember a keystone species is more than just an important species every species has some level of function in its ecosystem but a keystone species is one that's so vital to its ecosystem function that if it's removed the entire ecosystem can collapse so if we were to lose a keystone species like wolves from a forest ecosystem the deer and Alchemy overpopulate this would lead to over grazing of the vegetation of that ecosystem and this could be so intense that other organisms would lose those trees and food and habitat resources this could even lead to the reshaping of the landscape as the tree's roots would no longer be there to hold the soil intact and the banks of rivers might erode without those plants stabilizing the soil along the banks other keystone species examples include ecosystem Engineers like beavers and man groceries these species shaped landscape so dramatically that they create habitats That Couldn't exist without them the mangrove swamp would be impossible without those stilt-like roots of the mangrove tree and the Beaver Pond would be impossible without the Beaver Dam and that is unit two in the books hopefully you feel like the vocabulary richest of your mind has increased maybe you even have some fast growing mid-successional Apes ideas taking root in the soil of your brain thanks for watching today ape Scholars as always think like a mountain and write like a scholar