if you're getting ready for a comprehensive Unita test about ecology or the AP Bio exam then you've got a big challenge ahead of you APB Unit 8 consists of difficult Concepts mathematical models a ridiculous amount of vocabulary and it was all delivered to you at an unrelenting Pace but don't worry in this video we're going to cover everything that you need so that you can crush it on the AP Bio exam or on that upcoming Unit 8 test we're going to start with responses to the environment that'll include some case studies related to animal behavior and communication that'll move us on to energy utilization in organisms then energy flow in ecosystems and then matter flow in ecosystems biogeochemical cycles then population growth with its population growth formulas followed by Community ecology where we'll look at topics like competition fundamental Niche versus real Iz Niche keystone species and trophic Cascades that will take us to the topic of biodiversity which will include looking at another mathematical model the Simpson biodiversity index how you can calculate it for various communities and then we'll end with the topic of ecosystem disruption my name is Glenn wenel also known as Mr W and I love teaching b i o l o g y to help you study I've put together a checklist that tells you exactly what you need to study in AP Bio Unit 8 and in fact all of AP biology to download it go to apbio su. checklist topic 8.1 responses to the environment unlike the rest of Unit 8 topic 8.1 is somewhat difficult in terms of providing you with exact guidance about what to study that's because the objectives are very general and the College Board has provided these exclusion statements which tell you that you don't really need to know any specific body of knowledge in order to be able to handle this topic so what we're going to do is we're going to look at a couple of fascinating case studies and illustrative examples that'll give you practice at handling the kinds of data sets and images that the college board or your teacher might be throwing at you on the AP Bio exam or your upcoming test we're going to start by looking at Predator warnings Predator warnings also called a alarm signals are calls or cries emitted by social animals in response to Predator danger these have been extensively studied in the belding's ground squirrel which lives in the Sierra Nevada mountains of California belding's ground squirrel has distinct warning calls for aerial Predators like Hawks and Eagles and for terrestrial threats from Bobcats coyotes and weasels here's warning call type one for an aerial predator and here's warning called type two for a terrestrial [Music] Predator note that these Predator warnings are not unique to the belding's ground squirrel African vervet monkeys which are primates like us have distinct calls for leopards snakes and Eagles Predator warnings are altruistic they're self-sacrificing they involve individual risk to the self to protect others when a squirrel emits a call about an aerial Predator it increases the chance that that Predator will attack the animal that calls out that's of course true for a terrestrial Predator as well and that leads us to the question why would an animal risk its own life to protect others altruism can be explained by kin selection and Inclusive fitness let's define both of these terms kin selection means that the value of a gene is not based on whether it promotes survival in a single individual but also in how it affects survival in the individual's relatives Inclusive fitness means that if an Al promotes sacrificing oneself for the benefit of one's close relatives who also share that alil then that Al might increase in frequency the idea of kin selection and Inclusive fitness was cleverly captured by the British biologist JBS halan a very important evolutionary thinker of the 1900s who famously said I would lay down my life for two brothers or eight cousins what did halane mean well here's me I obviously have 100% of my genes but my siblings have 50% of my genes so if I sacrifice myself and thereby allow my brother and sister to continue living and passing on my genes it's an even trade so it makes sense to sacrifice myself for two siblings I have a 12.5% relationship to each of my cousins and just think about the fact that you have a 25% relationship to your aunt or Uncle so you'd have a 12.5% relationship to their children again it makes sense for me to lay down my life so that eight of my cousins would survive and continue to pass on my genes within our shared gene pool with those Concepts in mind let's take a look at a study by Paul Sherman about Predator warnings in belding's ground squirrels he carried out the study in the 1970s to begin with notice this graph it shows the mean distance that males and females move from their natal burrow that means the burrow where they were born so everybody obviously starts out in the burrow where they were born but then the behavior of males and females is quite different females wander very little over the course of their lifespan these squirrels don't live very long so even when these squirrels are 26 months old which is quite old for a squirrel they're pretty close to the burrow where they were born less than 50 m the males by contrast move quite a bit so by the time they're 2 years old they're up to 28 80 or so met away from the burrow where they were born Sherman's key move was to observe these ground squirrels and then to classify who was calling based on two characteristics the age class whether they were juveniles one-year-olds or adult and then their sex I've labeled the age class but I haven't labeled the sex male or female here's how to read this the left side of this graph shows the distribution of each of these age classes and sexes in the population and again you know the age you know that these are adults but you don't know which one's male and you don't know which one's female and that's true for adults one-year-olds and juveniles the top graph shows the first squirrel to give the alarm call and the second shows all callers regardless of precedent in other words it might have been the first call the second call the third call and these were calls to a predatory mammal so to a ground predator on the right side it shows what Sherman actually observed in terms of who was giving the call and what I'd like you to do is to predict which rows are for males and which rows are for females and I'd like you to inform your prediction by this graph over here and also what you've learned so far about kin selection and Inclusive fitness make a prediction and then I'll show you what the answer is here's what Sherman found females were overwhelmingly more likely to emit alarm calls than males were for example among adult females there were about 30% of the population but adult females emitted over 60% of the first call for a predatory mammal with males represent about 20% of the population but they don't even call 5% of the time so males are way under represented in terms of their taking the risk to call whereas the females are way over represented and that's true of every age class and that's also true of callers in general not just the first call but callers regardless of Precedence so my challenge to you is how would you interpret this think about about it and then you can see my answer Sherman's interpretation is that females are more altruistic than males but why would that be remember that a warning call attracts attention when females admit a call they're drawing attention to themselves and warning their close female relatives their sisters their daughters their female cousins the males don't call because the risk to themselves is not not offset by a benefit to their close relatives so the conclusion is that Predator warnings in buildings ground squirrels are an example of kin selection and Inclusive fitness and what you should take away in addition to this concept is the way that we used claim evidence and reasoning to pull this together especially how you connect this piece of data to this piece of data to thereby conclude what we did about kin selection and Inclusive fitness the altruism that we just discussed in the belding's ground squirrel reaches its peak in a type of animal behavior and social organization that's called you sociality what is you sociality it's a social structure in which some individuals within a colony breed While others are nonreproductive and just to State the obvious humans are highly social but we're not usocial who is usocial bees in bees there's a single queen who lays the eggs she's reproductive there are thousands of workers that take care of the larv they build and clean the nest they forage but they don't reproduce themselves in other words what they do is they work so that the queen can successfully reproduce and there are a couple of dozen of males and the males leave the nest to meate and then they die that's us sociality us sociality is not just found in the bees as we just discussed it's also found in ants and wasps in termites in one species of shrimp and two species of mole rats that's a type of mammal and again what are we saying we're saying that in a termite Mound there are a couple of reproductive individuals and everybody else is non reproductive working for their benefit and that's true in a colony of naked mole rats as well there are individuals who get to reproduce and everybody else serves them and serves their reproductive interests you sociality can be partly explained in animals like bees and ants through the phenomenon of Happo diploidy and that's a kind of sex determination that we discussed back in unit five I'll review it now and I'll connect it to you sociality the idea of haplodiploidy is that females are deployed in the same way as you are deployed with two sets of chromosomes here we see the chromosomal situation of the diploid Queen and it's very simplified bees have 32 chromosomes as their diploid number I'm showing only six here the diploid Queen creates gametes by iosis in the same way that humans and mammals do and as she does she passes on 50% of her genes to her daughters the daughters are the non reproducing females in males things are quite different males are haid they have only half the chromosomes in every cell of their body that the females do a haid male drone who's reproductive creates gtes by mitosis not by meiosis and what that means is that he's passing on one 100% of his genes how do you get to be a male males develop from unfertilized eggs that are laid by the queen and the drones as I just said pass on 100% of their genes to their daughters so how does HAO diploid connect to you sociality the the sisters are 75% related to each other what do I mean by that well they inherit 50% of their mother's chromosomes and 100% of their father's chromosomes so on average they're 75% related to one another that means that they're more related to one another to their fellow sisters than they would be to their own offspring that means that genetically it makes more sense in terms of the inclusion of their genes in the gene pool for workers to help their Queen create more sisters than it would be for the females to reproduce themselves because their own daughters would be 50% related to them so that is a genetic explanation for the altruism of the female workers within a beehive and just to emphasize something you sociality can exist without haplodiploidy termites are not haplodiploidy and they are usocial and that's true of the naked mole rat as well and again this is an important concept it's important for you to know about as an AP biology student but the most important thing for you to be able to do is to look at a diagram like this and you use that as the basis for formulating a claim with some evidence and some reasoning about the connection between us sociality and Hao diploidy topic 8.1 is full of fascinating case studies we're going to stop presenting them here right now but what I want to encourage you to do is to go up to learn biology.com where you can learn about amazing things like why some voles a small type of rodent are monogamous While others are promiscuous you can learn about how ants learn how to make their way back to the nest after finding food in a straight line not an easy thing for them to do how Turtles can go out to seea forage there for years and then how they make their way back to their nest how and why animal school and how honeybees with their relatively small brains can Comm communicate to one another through their dances about the location of food sources it's unbelievable stuff in and of its own right but the most important thing is that by looking at these case studies you'll get to be very good at looking at data sets illustrative examples visual representations that will be the kinds of things that you need to do on the AP Bio exam or your upcoming test on Unit 8 your success in AP biology starts here are you struggling struggling with AP Bio with learn biology.com students get the skills and confidence to be a top student and earn fours and fivs on the AP Bio exam guaranteed go to learn biology.com to find out how you can master your biology course and crush the AP Bio [Music] exam topic 8.2 part one metabolism and individual energy use let's start by answering the question what is metabolism metabolism is the sum total of the chemical processes that take place within an organism here we're showing a cell but it could be the inputs the processes and the outputs for an entire organism what is metabolic rate it's the amount of energy that an organism expends during a given amount of time basil metabolic rate is the amount of energy consumed by an organism at rest at a comfortable temperature they don't have to be sleeping as these lions are but it's resting metabolism how is metabolic rate measured to answer this we have to hearken back to unit 3 and think about the formula for cellular respiration shown over here you can measure the input oxygen that could be happening here in this woman at rest who is hooked up to a kind of metabolism measuring machine you can measure carbon dioxide production this machine also might be measuring the amount of carbon dioxide she's emitting in a respirometer which is typically used in a lab back and unit three you're measuring consumption of oxygen and you can also measure the production of heat that leads us to a discussion of two major metabolic strategies that involved with being an ectotherm and that involved with being an endotherm endotherms are limited to mammals birds and a few other species endotherms generate their body heat internally metabolically as a result of heat that's generated through cellular respiration their body temperature is regulated around a set point so for example here we see an endotherm a wolf and despite the environmental temperature it's internal temperature is going to stay the same ectotherms are different their body temperature conforms to the environmental temperature so when it's 20° out the snake's body temperature will be about 20° that's true as it gets colder and that's true as it gets warmer what are the advantages of being an endotherm you can be active regardless of the environmental temperature and that gives you flexibility throughout the seasons and whether it's day or night and it explains why the predominant animals in the coldest environments are endotherms mammals like polar bears and birds like penguins those are the animals that can survive on snow and ice so what are the advantages of being an ectotherm the energy requirements of ectotherms are much less ectotherms need about one tenth the food per gram of tissue than endotherms do as an example at 400 lb this American alligator needs the caloric equivalent of only a few slices of bread to meet its energy needs you as a mammal need the entire loaf to meet your energy needs that's how endotherms and ectotherms compare what's the relationship between temperature and metabolic rate in ectotherms metabolic rate increases with temperature as the temperature goes up the metabolic rate goes up in an ectothermic organism like a snake in an endothermic organism a mammal or a bird the relationship is more complex to begin with at cold temperatures the metabolic rate needs to be high why because a lot of energy needs to be consumed to create heat so that the animal can maintain its metabolic rate at that high constant set point as temperatures become more moderate the metabolic rate Falls and it can fall to the basil metabolic rate and as temperatures get high then the metabolism Rises as cooling mechanisms are deployed and those require some energy as well metabolism and size in endotherm as endothermic animals get bigger their rate of energy use their basil metabolic rate increases no surprise but an elephant consumes a lot more energy than a mouse does and if you scale your axes your x- axis and your y AIS as is shown here that increase in energy use scales in a linear way if you look at energy use from a slightly different angle there's a fascinating relationship between size and metabolic rate that relates to the relative metabolic rate the relative metabolic rate is the metabolic rate per unit of body mass and it decreases as size increases so the smaller the mammal the more energy each gram of tissue requires in other words each gram of tissue in a shrew is burning much much more energy per the same unit of time than a gram of tissue in an elephant let's look at some specific examples here's an African elephant weighs in at 6 million gram it consumes 70,000 calories a day its energy usage per gram is 0.011 now let's look at the other end of the scale a tiny shrew which weighs only 1.8 G it needs 144 calories a day and that's 80 calories per day per gram of tissue that difference in relative metabolic rate has vast consequences in the physiology of an organism we look again at the Shrew 1.8 gram weighing less than a dime its heart rate is 1,200 beats per minute it has 800 respirations 800 breaths per minute it starves to death if deprived of food in Just 4 hours and it has to eat 200% of its body weight every day an elephant by contrast its heartbeat is only 30 beats per minute it takes about four or five breaths per minute it can go many days without food and it eats about 4% of its body weight every day why are relative metabolic rates so different for large animals and small animals why is the metabolic engine of a mouse or a shrew revving at such a higher speed than that of a huge animal like an elephant it has to do a lot with surface area to volume ratios that's a lot of the explanation smaller animals they'd be over here they have a much larger surface area to volume ratio than do larger animals remember that volume is a cubic function whereas surface area is a square function so as an animal increases in size its volume increases much faster than its surface area and you can look back to my video about that in unit 2 if you need more instruction about that as a result smaller animals lose heat through their surface much more easily than large animals do to replace that heat smaller animals need to perform more cellular respiration increasing their relative metabolic rate topic 8.2 part two energy flow through ecosystems what is an ecosystem it's a community the living populations in an area plus the abiotic non- living parts of the environment those abiotic Parts include the air the soil the water and the energy that's flowing through that ecosystem two essential concepts related to ecosystems are food chains and food webs a food chain is the passage of energy and matter from one organism to the next within an ecosystem on the left we see a terrestrial food chain where a plant is getting eaten by insects which is getting eaten by other insects which passes to a frog Etc on the right side we see something equivalent for an aquatic food chain on the right side we have a food web and a food web shows all the interconnected food chains in an ecosystem and the arrows flow from the organism that gets eaten to the organism that eats it and if these arrows look like they're flowing in the wrong direction they're not the small birds eat the fish and that passes energy and matter from the fish to the small birds and the same thing happens with mollusks and small birds and so on and so forth what are trophic levels describe the trophic levels found in most ecosystems a trophic level is an organism's position in a food chain or a food web you've seen this word root tro before in terms like hetero trro and autoro which we worked with in unit 3 produc producers autot troes create energetic compounds almost always through photosynthesis the one notable exception are those ecosystems that are based on geothermal energy way under the sea near hydrothermal vents primary consumers or herbivores eat the producers secondary consumers or carnivores eat the primary consumers tertiary consumers eat secondary consumers and the level goes up to fourth level and fifth level consumers when organisms at any level die their remains are broken down by decomposers really important but not shown in this diagram of a food chain describe the pyramid of energy and explain the 10% rule the pyramid of energy shows the amount of harvestable chemical energy at each trophic level so this is saying that at the producers you could Harvest 10,000 kilo calories worth of chemical energy at the primary consum consumer level there's only 1,000 kilo calories and that relationship stands true for the other trophic levels as well each trophic level has 10% of the chemical potential energy of the level beneath it we'll see why in the next slide what are the reasons for the 10% rule the first reason has to do with physics energy is lost to heat during any energy transformation that's the second law of Thermodynamics so when primary consumers are eating producers that's an energy transformation some of that energy is simply lost as heat the other reasons that we're going to discuss are more biological so any organism is using the fuel that it takes in as part of its metabolism that doesn't go to growth and therefore it's not available for the next trophic level there are limits to harvest deficiency in other words these caterpillars over here they're not going to eat every single bit of the leaves that they're eating and they're certainly not going to eat the stems or the roots so they're not harvesting everything and then in terms of what they do Harvest they don't assimilate everything a lot of the food that any organism eats goes through it and passes out as feces just note that the 10% rule is an average it's a rule of thumb that explains how energy is transferred from one trophic level to the next within ecosystems the pyramid of energy is only one way to represent what's happening in ecosystems there are other ecological pyramids as well one is the Pyramid of biomass and what that shows is how much living mass is passed from one trophic level to the next and that's usually Mass with water removed it's the dry weight of all of The Producers compared to the dry weight of all of the consumers some pyramids of biomass are indeed like pyramids but there are others like this one that's been famously studied in the English Channel that are not and if that seems counterintuitive the basic idea is that the producers grow at an enormous rate and they're consumed by the consumer so if you measure at any one moment the standing biomass of The Producers can be less than that of the consumers there's also a pyramid of numbers and some of those are pyramidal but if you think about a pyramid of numbers for a tree you'll have one tree that's being the source of food for thousands or millions of herbivores that are in turn being consumed by carnivore so the Pyramid of numbers not always pyramidal either a biogeochemical cycle is yet another way to represent what's going on in an ecosystem a biogeochemical cycle shows the movement of elements or compounds between the biotic living and the abiotic non-living parts of an ecosystem and the components include reservoirs that's locations where elements or compounds accumulate often in chemically different forms so for example one reservoir for the carbon cycle is carbon dioxide in the atmosphere another Reservoir would be all of the carbon that's found in plants fluxes or flows are ways in which these compounds or elements move from one reservoir to another so photosynthesis is a flux by which carbon dioxide in the atmosphere comes into plants consumption is a kind of flux by which the carbon that's trapped in Plants moves to animals if there's one biogeochemical cycle to be familiar with in your AP bio class that would be the carbon cycle and here's how it works the carbon cycle could start anywhere but let's start with carbon dioxide in the atmosphere that carbon dioxide gets pulled into plants through the process of photosynthesis and think back to the Calvin cycle back in unit 3 those plants themselves respire and that returns carbon dioxide to the atmosphere plants can also be consumed by animals animals respire and that returns carbon dioxide to the atmosphere when plants die when animals die their carbon moves to decomposers the decomposer ERS do cellular respiration on those remains of plants and animals and respiration returns carbon dioxide to the atmosphere sometimes when plants die and to a much smaller degree when animals die too they become fossilized into fossil fuels things like coal and oil those get extracted through oil drilling and coal mining and then those power the machines of our civilization and so that becomes another major flux called combustion that of course is having impacts on our climate but that's more of a topic for an environmental science class than it is for AP biology topics 8.3 to 8.4 population growth what are the four factors that directly change population size if you had driven into my home City Berkeley California a couple of years ago you would have seen this sign listing the population at 11 12,580 it's now a little bit bigger what could cause that to increase or decrease there's only four factors those are births which increase the population deaths which decrease it immigration which increases population size and immigration which decreases it for AP Biology one of the most important Concepts to understand is exponential growth and its limits exponential growth is a pattern of population increase in which the population size doubles at a consistent rate over regular time intervals resulting in Rapid and accelerating increase why because the growth of the population is proportional to the amount already present in this growth curve over here the rate isn't changing it's continuing to be at 140% but when there are 1,000 individuals the number of individuals added over a period of time is going to be much higher than it was when there were 200 individuals the basic idea is that an exponential growth the bigger the population the bigger the increase exponential growth is based on a mathematical model and that's something you need to understand for AP Bio then you don't need to memorize it there's a formula sheet the formula is Delta n over delta T = R * n and in this formula n represents the population size T equals time R is the rate of increase so in plain English the change in population over time equals the rate of population growth times the population size in biological systems when does exponential growth occur it occurs when a population has ideal resources and nothing is slowing down its rate of growth this can be the arrival of an invasive species the early phase of a bacterial infection the early phase of an epidemic or pandemic so it's always always ultimately limited because nature is finite but during this phase when the population has ideal growing conditions exponential growth can occur that's what occurred early during the Corona virus pandemic this shows one country Brazil 2020 and you can see this exponential growth curve as the virus entered the Brazilian population and spread from Individual to individual exponential growth exponential growth is related to the idea of biotic potential and that is the maximum rate at which a population can expand and you can see it represented by the letter r submax that represents biotic potential exponential growth can continue forever and ultimately it's limited by the environment's carrying capacity that's represented by the letter K it's this dotted red line over here and it's the maximum number of individuals that a particular environment can support it's caused by limiting factors factors that limit population growth as a population approaches its carrying capacity there's increased environmental resistance the environment starts pushing back against exponential growth as density dependent limiting factors slow and then stop a population's growth density dependent limiting factors are exactly what they sound like these are factors that increase in intensity as a population approaches K as the population grows its density the number of individuals in a particular area is going to go up that's when these density dependent limiting factors kick in they include competition between the individuals in the population for resources parasitism parasites that are parasitizing the individuals in the population and it gets easy for those parasites to spread from one individual to the next as the population increases it gets easier for predators to pick off members of the population as the population increases and it becomes more stressful for the individuals in that population and that tends to lower their rate of increase to incorporate the effect of limiting factors and carrying capacity in our understanding of population growth we need a more sophisticated model that's the logistic growth model and it's represented by this formula over here it shows how a population's growth rate decreases as the population's number approaches its carrying capacity or K and it's represented by the formula Delta n over delta T equals the growth rate time n multiplied by this expression k- n / k n is the population size T is time R is the rate of increase and K is the carrying capacity let's plug some numbers into this logistic growth formula and see how it actually works in this example k equals 1,000 that's our carrying capacity over here but let's say that our population is 10 if n is 10 if that's our population size then Kus n / K is 1,000 that's K minus n that's our population divided by the carrying capacity 1,000 that's 990 divided by 1,000 that's 99 growth looks exponential because whatever our rate of growth would have been from multiplying it times .99 will be in our exponential growth phase but if we increase the population to 900 then look what this does to this expression k- n / K it's now 1, -900 / 1,00 K - n over k that's 10 so whatever our rate of growth would have been over here we now we're going to multiply it by 10 and that's going to cause growth to quickly level off as we get to K as population is equal to the carrying capacity then population growth stops all together those density dependent limiting factors that are part of the logistic growth model that characterize carrying capacity can be extrinsic or intrinsic extrinsic factors come from outside the growing population and it includes things like predation parasitism competition intrinsic factors come from within the physiology of the growing population and it's usually about stress caused by increased crowding and competition between individuals in the growing population and that lowers the birth rate limiting factors can also be density independent and these are factors that are unrelated to a population size they're not related to the population's increasing density so examples are things like hurricanes floods earthquakes human-caused environmental disasters like an oil spill a toxic chemical release all of those have nothing to do with the population but for example there is a population of birds that was living within these trees well its population is going to be vastly reduced by the damage that's caused by this storm but that had nothing to do with whether there were a lot of individuals or just a few individuals it's outside the population's density its density independent so to check your understanding take a look at this graph which shows the results of a student experiment where they're growing duckweed in a cup this graph is from learn biology.com it's part of an frq or a multiple choice question this is what duckweed looks like and the question is in this graph I'd like you to identify carrying capacity I'd like you to identify the exponential growth phase and I'd like you to identify where you see density independent regulations so pause the video do that and then see my answer carrying capacity is over here at B you can see that there was an exponential growth phase and then it levels off that's got to be carrying capacity the exponential growth phase is over here at a when you have the J curve of growth and density independent regulation would be at letter C how do you know because here's the population it's growing just as it is over here but then at this point something abruptly stops population growth that didn't have to do with the density the density dependent regulation kicks in over here so that had to be independent of density density independent regulation what happens as a population reaches or surpasses its carrying capacity I'm going to show two scenarios there are probably more one is oscillation you have a cyclical overshoot of the carrying capacity and Decline and that's caused by a reduction of resources and then recovery so here's a population that's grown Beyond its environments carrying capacity that caused somewhat of a degradation of resources and that reduces for example the food supply so the population Falls a little bit when it falls the car in capacity recovers and then the population Rises slightly overshoots and then Falls and that goes on and on that is different from what's shown on the right which shows a catastrophic overshoot the line in blue represents the population of deer the line in green represents the shrubs that the deer used to forage and to supply themselves with food well in this case there's a catastrophic overshoot of the carrying capacity and that causes essentially a environmental collapse and the population of shrubs crashes and the populations of deer crashes and there's no subsequent recovery we have serious environmental degradation another population growth pattern to know about for your AP bio class is about Predator prey population Cycles here's an incredible data set that shows the population of lynxes a cat that's a predator in North America and hairs both of these animals live in Canada both have great data sets because their pelts were collected by trading companies that were active in Canada in the 1800s into the 1900s so we see this kind of oscillation what's going on it's partly explained by density dependent regulation of the hair population by lynxes the lynxes are the predators the hair is the prey as the population of hairs goes up that provides more food for the lynxes their population goes up they eat more of the hairs the hair population declines and then the lynx population declines but when the lynx population declines there's less predation on the hairs so their population increases but that's only a partial explanation what's also going on is that there's cyclical oscillation of the hair population by food availability so they're herbivores they're praying on plants that are available in this area and they're competing with one another so cyclical oscillation of the Hera population by food availability and interspecific competition which in turn affects the lynx population everything is complex that's what makes biology so fantastic I want to acknowledge how difficult and complex some of these Concepts can be and I want to encourage you to go to learn-y. and with a free trial you can do the tutorials and you can use our unit reviews and it's going to really help you to get on top of this material setting you up for Success on your unit test or the AP Bio exam topic 8.5 Community ecology part one symbiosis what is symbiosis symbiosis is an interaction when two species live together in close proximity and one species might be harmed by that interaction the other might gain or both species might benefit or one of the two species might be unaffected on learn D biology we have a couple of interactive exercises that you can use to learn about all the different kinds of symbiosis that you need to know about for AP Biology one thing that I want to emphasize now is that there's a symbol system that's used to describe their relationship a kind of shorthand and a plus sign is used for the species that gains a minus sign is used for the species that loses and a zero is used if there's no effect so for example in competition it's a minus minus interaction in mutualism it's a plus plus interaction with that in mind we'll now go through the various types of symbiosis that you need to know competition is a kind of symbiosis where two species require for the same resource and they're competing for that resource it's a minus minus interaction here we have the example of two Predators a leopard and a lion and they're competing for the same prey here we have the interaction between two trees that live in the forest of the North American Northwest and the Douglas furry and the coast Redwood compete for resources such as light water space and soil nutrients mutualism is an interaction where both species benefit from the interaction it's a plus plus a winwin interaction and here we have two examples one is between clownfish and anemones the clownfish lives amidst the tentacles of the anemon and evolution has led to a situation where the anemon doesn't sting the clownfish so the clown fish gets safety that's its win what does the anemone get well the clown fish is a Messy eater so food falls out of its mouth into the tentacles of the anemon where they're digested and when the clownfish defecates the feces are also used by the anemone for food a winwin relationship not all of these symbiosis that are mutualistic involve anemones but I couldn't resist sharing this other one this involves the giant green anemon that lives off the coast in the inter tidal zone of the Northwestern part of the United States and this anemon which is in the same clay as jellyfish s stinging tentacles just as we saw over here kind of a predator it Harbors symbiotic algae that live within its tissues well those algae get a safe place to live and they produce food that the anemone can digest so it's a wind for the anemone and it's a wind for the allergy that the anemone Harbors predation is a relationship where animal species one kills and eats animal species 2 it's obviously a plus for the predator and a minus relationship for the prey it's a win lose interaction here we have a leopard killing a bushbuck and here we have a king fisher killing a tan Poole that's predation in herbivory an animal species eats a plant and that's a plus for the animal and it's a minus for the plant it's a wind lose interaction here we have deer grazing on a tree and here we have a softfly caterpillar eating a leaf commensalism is a relationship where species one benefits and species 2 is unaffected so it's a plus slz relationship win no effect in this example over here we have a cattle Egret that likes to perch on top of the cattle the Egret gets a nice place to perch and the cattle is pretty much unaffected on the right we have moss growing on a tree trunk the Moss gets a nice place to live and grow and the tree is pretty much unaffected parasitism is a long-term relationship in which species one the parasite lives in or on species 2 which is the host and the host is harmed by that interaction so it's a plus minus win lose interaction here are two examples one involves viruses viruses are obligate intracellular parasites in order to reproduce themselves they need to infect cells and those can be your cells the cells of animals the cells of plants the cells of bacteria the cells of protus so the virus is the parasite and you or another organism or another cell is the host here's another parasite this one is giardia that's a single cell UK carot that infects people when they take in contaminated water food Etc the Giardia reproduces inside our intestinal tracts it causes diarrhea other kinds of intestinal upset and then it leaves via the feces to contaminate other food water and spread to another person brood parasitism is a relationship in which bird species one lays its eggs in the nests of bird species 2 species 2 feed needs and nurtures species one at the cost of its own young that's obviously a win lose plus minus relationship and here we see this little Reed warbler that's feeding this cuckoo that has parasitized its nest parasitoidism is yet another variation on parasitism it's mostly limited to insects and it's where species one lays its eggs in or on the eggs or larv of species species 2 individuals in species 2 are eventually killed and that can take quite some time this is a plus minus relationship a win lose relationship and here we have parasitoid wasp cocoons and a lime butterfly caterpillar and the part of the story that you're not seeing is that a wasp came over to the caterpillar injected in its eggs the eggs developed inside the caterpillar and then emerged through these holes over here and then the larv formed cocoons around themselves when the cocoons have fully developed little wasp will emerge and they'll go ahead and they'll parasitize other caterpillars just in case you're thinking that this parasitism Niche is unique and unusual it's not there are more parasitic species than any other kind of animal Niche hi Mr W from learn Das biology where we believe that interaction and feedback is what leads to deep substantial learning we're so sure of that that we provide a money back guarantee that comes with your subscription topic 8.5 Community ecology part two competition and co-evolution before we get into competition and co-evolution I want to define a term that I used in the last section and I've used throughout the series the term is ecological need you can also say Niche and it's how an animal makes a living here we have a bunch of dinosaurs and other Mesozoic reptiles this one is an apex predator and a scavenger this flying reptile over here was an aerial predator and a scavenger this the Triceratops was a large herbivore here's an omnivorous forager this one's an omnivore this one's an herbivore or an omnivore this one a small predator and here's an herbivore also an armored Grazer those are various dinosaur niches plants have niches as well so an oak is a sun tolerant tree a rododendron is a shade tolerant shrub a mangrove is a salt tolerant tree or shrub a cactus is a desert adapted plant a water lily is an air requiring aquatic plant that lives on the surface of lakes or ponds and Ivy is a climbing vine there are other plant niches as well but this should give you the idea an important idea related to competition is gauss's competitive exclusion principle this principle states that two competing species can't coexist in the same ecological niche gaus did experiments with various species of paramia so here are two species of paramia IA one of which lives on the bottom of lakes and ponds that's their natural habitat and the other is a Surface forager so it swims up higher and you can see that by the position they would take in a test tube when these two species were combined in the same test tube they were able to coexist just fine why because their ecological niches their ways of making a living were different but when Gaal took two species that had the same ecological niche both of them were surface foragers and when you combined them in the same test tube what he found was that species a outcompeted species B which became extinct what do we see we see two species in the same ecological niche can't coexist that's gauss's competitive exclusion principle over long periods of time competition can be a powerful evolutionary Force One possibility is that species become extinct the other possibility is that the competing species evolve through natural selection to do something that's called a resource partitioning that's exploiting different parts of the resource that they were competing for the way that that happens is through specialization there's selection for different kinds of traits and that results in character displacement that simply means differences so that each species will dominate its sub Niche more effectively here we have the example of a variety of shore birds and you can see the character displacement the different length of the legs the different shape of the beaks and what that does is that it enables each bird to exploit a different part of the resource so that the avocets aren't really competing with the ducts because they're foraging in this part of the shoreline habitat whereas the Ducks are foraging over here and the oyster catchers are actually on the sand and the plovers are higher up on the sand so again character displacements are the differences and what they wind up with is species that can effectively exploit the resource that they were formerly competing for to make this clear I want to offer an economic analogy character displacement and resource partitioning in the coffee Niche so here we have three companies that live in my part of the world and they've all evolved through competition slight differences Starbucks it's the mainstream everyday coughing experience with sugary specialty drinks and snacks seasonal offerings that's different from pets which appeals to Coffee purist really high quality beans dark roast more robust coffee taste and that's different again from Phil's Coffee which specializes in pour overs each cup brewed fresh to order customers are encouraged to customize their drinks so again we have three competing companies each is partitioning the resource for different parts of the um economic market for different customers and they've done that by evolving different characteristics if you can apply that to animals and plants you'll understand these Concepts well resource partitioning can lead to what are called Ecom morphs and those are species that are morphologically adapted adapted through their form to specific niches so in the Caribbean islands you have lizards that have adapted to different parts of the forest canopy you have these very large lizards that are called Crown Giants smaller ones called trunk Crown ones that live on the trunk ones that live on the ground and ones that live in the grass well that's resource partitioning that is all about character displacement but what's really cool is that through convergent evolution ecomorphs from different regions different islands in this case can develop similar traits so you have crown giant lizards that can be found on Cuba Jamaica the island of Hispanola and Puerto Rico but they're not closely related to one another they evolve these traits independently through convergent evolution and that's true of the trunk Crown lizards the ones that live in the trunk the trunk ground and the grass Bush and this relates to a really cool case study from the Howard Hughes Medical Institute that most AP biology students experience and now you'll understand it better here's a really interesting data set that could show up on the AP Bio exam or in your course related to beak depth in the Galapagos finches here are three of the Galapagos Finch species that live on the galopagos islands which are off the coast of Ecuador the character that's been Quantified here is the beak depth the distance between here and here in the beak different size beaks are adaptations for exploiting different types of food here is what's going on on islands where these birds live together they're all inhabiting the same island note that there 's no overlap in terms of the beak depth that's true of Island set a and Island set B an island set C that involves floriana and San christobal one of the bird species G magaris is absent but note that there's no overlap between bird species G fanosa and the other bird species G foris but on these really small Islands quatro Hermanos over here here and dhne moror over here only one bird species is present and with only one bird species note the overlap in beak depth what I'd like you to do is try and explain that so pause the video and see if you can come up with an explanation on island set A and B over here there are three species that are coexisting and competition between those three is leading to Niche partitioning and adapt to different types of food is leading to character displacement so there's no overlap in the beak depth we have the much larger beaks over here the mediumsized and the smaller size over here an island set c one of the species G magaris is missing but because there's still competition between these two species G fenosa and G foris there is character displacement and there's no beak depth overlap on the smallest Islands DNE there's only one species and without competition with no competition between different species character displacement decreases the beak depths overlap so here we have a kind of natural historical validation of these ideas related to character displacement and resource partitioning another concept related competition is the difference between a fundamental Niche and a realized Niche a fundamental Niche is the range of resources that a species could exploit in the absence of competition a realized Niche is the range of resources that a species actually does exploit in the competitive context in which it lives an interesting natural history study was done in the intertitle zone involving two species of barnacles that's a kind of crustation that lives on the rocks of the intertial Zone here's species a which lives closer to the high tide line here's species B which lives closer to the low tide line if species B is removed which you can do by scraping these Barnacles off the rock notice how species a expands into the low tide zone where species B was living but if species a is removed species B pretty much stays where it is so your task is for species A and B to compare their fundamental and realized niches pause the video do that and then go on for species a the fundamental Niche is much wider than its realized Niche how do we know that because when species B is removed species a is capable of colonizing this Zone over here that's much closer to the low tide zone species B by comparison has a fundamental Niche that's pretty much the same as its realized Niche and how do we know that because when species a is removed species B is incapable of expanding into this Zone over here closer to the to the high tide line species B can out compete species a but it can't live in the area where species a is predominant that's the difference between a fundamental Niche and a realized Niche let's end this discussion of symbiosis by talking about evolutionary arms races these are positive feedback loops where adaptations in one species lead to counter adaptations in the second species and they're associated with predation parasitism and herbivory they result in extreme adaptations related to speed sensing camouflage defensive and offensive Weaponry that can be physical Weaponry or chemical Weaponry why is a cheetah capable of running 60 M an hour well it's because the cheetah speed has selected its prey for Speed and as the prey have evolved to become faster that's caused a counter adaptation in the Cheetahs which has caused them to become faster this obviously doesn't go on forever because there are physical and physiological limits but when you see an amazing adaptation it probably stems from an evolutionary arms race why is this insect so incredibly well camouflaged because there's some predator on the end which has incredible visual accuity why is this crocodile or alligator so incredibly well camou PL in the water where it's swimming because on the other end there's a prey organism which has acute hearing and acute vision and so the alligator has evolved counter adaptations and so it goes in the amazing pageant of life that we call b i o l o g y topic 8.5 Community ecology part three keystone species and Tropic Cascades what are Keystone own species these are species whose action in a biological community structures the entire Community they're frequently but not always Predators who keep a particular herbivore in check and their effect is to increase the overall biodiversity of a biological community using the example of sea stars in The intertitle Zone explain how keystone species promote biodiversity sea stars are predators and they pre on a variety of other animals in the intertial zone here's the inter tidal Zone The Zone between the low tide and the high tide and here are some of the many animals that sea stars pre on including importantly muscles when sea stars are removed from the intertial Zone biodiversity can plummet that's because by praying on the muscles ceas Stars create ecological space physical space for other invertebrates to live in this community and that keeps biodiversity high so this is what this community looks like when sea stars are present when sea stars are experimentally removed which happened in a famous experiment by Robert Payne in the 1960s where he took sea stars and threw them into the ocean away from the intertitle Zone where they were praying on muscles the muscles overgrew the entire intertial Zone and that caused species diversity to fall all the other species that were previously living in that zone couldn't live there anymore so that's the effect of the removal of a keystone species upon the diversity of a biological community another example of a trophic Cascade relates to the reintroduction of wolves into Yellowstone National Park that reintroduction happened in the 1990s previous to that wolves had become locally extinct in the Yellowstone ecosystem mostly due to over hunting when wolves were reintroduced they started to Prey Upon elk the elk in the Wolves absence had reduced the numbers of Aspen and Willows particularly along Riverbanks so the Aspen and Willows were able to regrow that provided habitat for beavers to used the Willows and Aspens to create beaver dams that created great aquatic habitat and that led to an increase in organisms like amphibians fish and song birds the Wolves were also competitors with the coyotes so their reintroduction led to a decrease in coyote numbers and that led to flourishing of some coyote prey including foxes rodents and antelopes the main thing for you as an AP biology student is to be able to interpret a diagram like this and to know the basic idea which is that the reintroduction of a keystone species increases biodiversity through at trophic Cascade effect to clear up a possible source of confusion note that the top predator is not always the keystone species this emerged from a famous study by James SS in the waters of Alaska in the 1990s and what SDS discovered is that when orcas changed their prey preference from Seals to Otter then otter were no longer able to control the population of urchins urchins overgrazed the kelp and that led to an overall decline in the kelp forest ecosystem you can see this in this data set and this kind of data set is something that could definitely appear on the AP Bio exam or on your teachers next test and what this shows is that a reduction in otter by orcas these numbers show the various islands where SDS studied this decline led to an increase in the biomass of sea urchins here it is in late 1980s here it is just before 1997 that led to more intense grazing by sea urchins upon kelp this is a measure of their grazing intensity and that led to kelp forest decline which you can see in the overall decrease in kelp forest density again what's important it's your ability to interpret these data sets and connect it to the idea of a trophic Cascade finally it's important to note that not all keystone species are top predators for example beavers are what are called ecosystem engineers and their dams create habitats for dozens of other species increasing biodivers University are you asking yourself how am I going to get a four or a five on the AP Bio exam it's a good question because it's a hard test but we have a plan for your success go to learn biology.com sign up for a free trial and complete our interactive tutorials and interactive AP Bio exam reviews we guarantee you a four or a five on the AP Bio exam see you on learn biology.com topic 8.5 Community ecology art for ecological succession what is ecological succession it's how a community under goes predictable changes following a disturbance such as a fire flood Landslide or volcanic eruption each array of species in each stage so these are the different stages of succession creates conditions that subsequently allow different plant and animal communities to thrive so as the community ages the plant and anim Community here is going to be different over time and it culminates in a climax community that will endure in relative equilibrium until a disturbance restarts the process succession is classified as being either primary or secondary primary succession starts from bare rock and it follows in events such as a rock slide a volcanic eruption Glacier Retreat and the most important thing is that primary succession requires creation of soil which is the basis of plant communities here's a picture of my wife and myself in Maui and we're standing in a volcanic crater and you can see that there was a lava flow and plants are starting to come in that's primary succession on the right we have secondary succession the soil is still intact and it follows a fire a flood a clearing of Forest Etc because the soils already present the process can occur much more quickly how does ecological succession unfold it begins with pioneer species those are shown over here at stage two and those are organisms like lyans and algae that can live on bare rock which was over here in stage one this is obviously a primary succession scenario and that begins the accumulation of biomass and the creation of soil after we have those pioneer species we have Sun tolerant mosses and herbs they're shown over here in stage three and they create soil you can see the soil starting to develop over here that sets the stage for sun tolerant grasses and ferns that are over here at stage four that's followed by the um introduction of small shrubs and then trees over here here at stage five and those trees create a shady underst story that's simply the area below the canopy of the trees and that creates a niche for sun tolerant shrubs in other words plants that really can't survive in full sun but are well adapt to live in partial Sun finally what we have is a self-perpetuating climax community and again that can endure until a disturbance resets the clock some of those communities like the Redwood forest of the Pacific Northwest of California those can endure for tens of thousands of years what are the key trends associated with ecological succession note first of all that here we have sucession not on a terrestrial ecosystem but in an aquatic ecosystem we have what's called Pond succession because successional processes occur there as well and the process runs sequentially a through F overall as the process unfolds abiotic conditions nonliving conditions are replaced by biotic conditions soil mass increases you can see the creation of soil as this Pond begins to fill in over here overall biodiversity increases in other words there are more species over time the number of interspecific interactions increases as there are more spe species and the community over time becomes more stable and more resilient topic 8.6 biodiversity what is biodiversity what are its components biodiversity is the variety and variability of life within an area and it has several components that includes ecosystem diversity so if you think about an ecosystem like the one in Yellowstone National Park there are mountains there are meadows there are aquatic ecosystems so a variety of ecosystems in one area you can also talk about species diversity the number of different species within an ecosystem or you can talk about genetic diversity so if you're looking at that species how much genetic variability is there among the individuals that comprise that species an important idea related to biodiversity in AP Bio is that biodiversity increases resilience what's resilience it's the ability of a system to respond to change and to bounce back from difficulties here's an example here's a field of corn with one species and in fact in today's world this might be a genetically engineered Field of Corn where there's really only one individual that's cloned over and over again so we have low genetic diversity and low species diversity combined into one if there were some kind of fungal pathogen that were to enter the system or an insect herbivore that were to figure out how to uh eat this corn in the face of pesticides and herbicides and all the other things that we do to protect fields of corn well this field would be extremely susceptible to damage in a grassland like this with many different species if there were a fungal pathogen that impacted one species there are many other species that are in this same system am I saying that we shouldn't be converting grasslands into fields of corn no of course we need corn for food and for other products but as we develop our planet we need to do that with an eye towards maintaining biodiversity ecosystem species and genetic at as high a level as possible because that promotes resilience we just made a connection between biodiversity and ecosystem resilience that's a benefit of biodiversity but there are several more one is that biodiversity is intrinsically beneficial that means it's a good thing in and of itself and to prove that just go out into nature and you can experience the joy of the diversity of different ecosystems the diversity of all the different species within those ecosystems and the variability of the organisms within the ecosystem so that is the intrinsic benefit of biodiversity in addition biodiversity provides many present and potential benefits to humanity one example is the Pacific U which is a shrub that lives in the forest and what was discovered years ago is that the U contains a compound that has anti-cancer properties and that's been developed into an important anti-cancer drug that's treating millions of people who knows what other compounds like that exist within the incredible biodiversity that exists in the rainforests or in coral reefs so on and so forth so we need to maintain biodiversity to gain those benefits if all those species become extinct those direct benefits won't be things that we'll be able to get and finally there are ecosystem Services those are things that biodiversity provides to us for free that might otherwise have huge huge economic costs the oxygen in the atmosphere where's that from it's from photosynthesis provided for free by the producers of planet Earth the oceans when they're intact and healthy can absorb carbon dioxide that can mitigate climate change that is an important ecosystem service the bats that fly around eating insects that keeps insects under control another ecosystem service and there are thousands just like that the economic benefit of ecosystems that are intact and healthy is incalculable and that's the benefit of biodiversity within the AP Bio curriculum diversity comes up in two places in unit 7 we looked a lot at the importance of variability within species and if you want to review that you can go back to my unit 7 video in Unit 8 what we focus on is mostly species diversity here are three communities Community a community B and Community C and what we're going to do is we're going to compare their diversity and we're going to do that based on two components the first is species richness the number of species in an area and the second is species evenness how evenly distributed the members of a species are so what we're going to do is we're going to rank these three plant communities from most diverse to least diverse and to do that we're going to do some counting and Analysis if you look at Community a it has three species one two and three and in terms of the number of individuals in each one they're very evenly distributed there are four individuals of species one four of species 2 and four of species 3 Community B has four species 1 2 3 and four and they're evenly distributed there are three individuals of each species in community C there are also four species but they're not evenly distributed there are nine individuals of species 1 and there's one individual each of species 2 3 and four as we'll see in a moment we're ultimately going to use some math to determine which of these community is the most diverse but we're going to start a little bit more intuitively Community B is the most diverse why because it's tied with Community C for the highest species richness both communities have four species and it's tied with a for highest species evenness in both A and B the species are completely evenly distributed but how would we compare Community a three species evenly distributed with Community C that has four species but they're not evenly distributed to properly compare the diversity of different communities we're going to need to use a formula that formula is the Simpson diversity index let me tell you what it is what all the symbols represent and then we'll use it to figure out the diversity of community a little n represents the total number of individuals of each species Big N represents a total number of individuals of the entire community and this symbol means the sum of so here's the diversity index let's compute it so for species one there are four individuals 1 2 3 4 so we're going to plug four in over here then we have to figure out n the total number of individuals in the entire community and that is 1 2 3 4 5 6 7 8 9 10 11 12 that's the total number of individuals in the entire community so small n ided by Big N for species 1 is 33 4 ID 12 is33 then we take that value and we Square It 33 sared is 0.111 for this community it happens to be the same for all three species so species 2 also has four individuals out of a total 12 in the entire community so the values are the same again n/ n² is11 and that's true for species 3 as well you add those all together and that comes to 0.333 you subtract that from 1 1 minus 333 and the value is 0.67 that's your diversity index for community and a let's repeat the same steps for communities B and C for Community B There are four species and let's count how many members there are of species one there's one 2 3 so small n equals 3 the total number of individuals again is 12 3 / 12 is25 the values are the same for species 2 3 and four there are three individuals for each of those species out of a total number of 12 individuals in the community so .25 is n small n ided large n and then we're going to square it 0.25 squared is 0.063 the values the same for each species in this community we add that up 0.063 plus 0.063 Etc we add that up and what we get as our sum is 0.250 1 minus 0.250 is 75 so we see that the diversity of community B is indeed higher than that of community a and that's because the species richness is higher even though the evenness of both is the same they're completely even our question was about comparing the diversity of community C with Community a so let's run the numbers for Community C like the other two communities it has a total of 12 individuals of which nine belong to species one so we're going to do little n / big n n / 12 we get 75 then we're going to square that and we get .56 6 3 so that's what this value is for species 1 now let's do the same for species 2 3 and four because it's the same number for each of them there's one individual 1 / 12 is 0.08 that's little n ided by Big N we square that and we get 0.7 and that's the same for species 3 and four so we're going to add up all those values because of this expression over here and when we do that we get 0.583 we know that we have to subtract the sum from one so 1 -. 583 is 0.42 so we see that Community C even though it has four species has a lower diversity than Community a and that's because it had very low species evenness so we can see how by analyzing each of these communities using the Simpson diversity index that Community B has the highest diversity 0.75 and again think about why that is it has high species richness and high species evenness the next community in terms of diversity is community a which also had high evenness but its richness was a little bit below that of community B and community C even though it had a higher species richness than Community a its evenness was so low that its diversity index round up being lower than Community a that's how you use the Simpson diversity index to determine the diversity of various communities topic 8.7 ecosystem disruption humans are causing biodiversity losses around the planet in unit 7 we talked about the five Great mass extinctions there's a sixth great mass extinction that's happening right now and humans are unfortunately the cause of it what we're doing is we're sending many species to the brink down the extinction Vortex By changes that are creating small isolated populations those populations are subject to genetic drift and inbreeding they lose lose genetic diversity they become less fit less adaptable that lowers their reproduction rate that increases their mortality rate that leads to smaller populations and so the cycle goes this is a positive feedback loop or a vicious cycle that's occurring around the planet right now we're going to talk about five things that humans are doing that are causing these biodiversity losses that are generating this six Extinction the first thing is habitat alteration and destruction there is nothing wrong with cities fields or golf courses but every time we build a city a field or a golf course we destroy the habitat of the animals and plants that live there that's happening at a huge scale around planet Earth where a huge amount of the planet's surface has now been in some way modified for human ends that's one of the causes of species Extinction another thing that humans have done is we've overexploited resources and that can be through over harvesting or over hunting in the case of the Tasmanian wolf and the passenger pigeon these animals were hunted to Extinction in the case of the American Bison to the brink of Extinction another major cause of biodiversity disruption has been habitat fragmentation and that's taking a large contiguous area and cutting it up by roads or by development into smaller areas what does that do it creates isolated disconnected populations that experience population bottlenecks and lose their adaptability and it also creates situations where there's too much Edge habitat Edge habitat is exactly what it sounds like it's the habitat on the edge of an area and when you fragment an area you create a lot of edge relative to the amount of habitat in the interior and those Edge habitats are Disturbed areas that have different conditions from the interior conditions and that makes it harder for the species that are trapped in the fragments to survive another cause of ecosystem disruption is the introduction of invasive species invasive species have the following characteristics they're highly adaptable they tend to be generalists in terms of their niches they can figure out many ways to survive they're good at dispersing them themselves they have high reproduction rates their effects include preying or parasitizing local species in the new area where they arrive and out competing local species and disrupting food chains and food webs again invasive species another main cause of habitat disruption a final cause of ecosystem disruption is deforestation obviously when you cut a forest you disrupt those ecosystems and forests particularly tropical rainforests are some of the most diverse habitats ecosystems on the planet I'm Mr W from learn biology.com where we believe that interaction and feedback is what leads to deep substantial learning we're so sure of that that we provide a money back guarantee that comes with your subscription that brings this review of apbi Unit 8 to a close and you've got two moves to enure your success on the AP bio test or on that test that's coming up in AP Bio Unit 8 the first is subscribe to learn biology.com this is a website that was created for you so that you could get the practice to crush that next test or crush the AP Bio exam also please watch this next video which will help you in your efforts to review good luck