hi everybody its mr. Smith's and today we'll be talking about topic three point four which is carrying capacity carry capacity is a relatively simple concept but we'll look at some more complex examples of how it can be determined by different resources or even predator-prey relationships so one way to think about carrying capacity is kind of like the maximum occupancy limit for a restaurant or a building if you look around a restaurant they often have a maximum occupancy limit posted somewhere the building and it's based on how many customers they can see and serve at one time so the limiting resource in the restaurant is usually space or seats or could be waitstaff how many servers they have at one time populations in an ecosystem are the same way each ecosystem has a carrying capacity for given species and it's based on resource availability things like food water habitat needs such as nesting sites these are the main factors that determine carrying capacity and natural ecosystems we called these limiting factors since they limit how many individuals can survive in a given population caring capacity is different for each species though so while this yellow line in the graph could be the carrying capacity for deer in an ecosystem the carrying capacity for wolves would likely be a lot lower since they have different habitat and food needs you'll also notice that populations usually don't exist perfectly at the carrying capacity but instead fluctuate around it and we'll talk about why that is later on in the video let's take a look at our objectives for the day so we need to be able to describe what carrying capacity is and to describe the impact it has on ecosystems in order to do that we need to know that when populations go over their carrying capacity which is called the overshoot there's a die-off that follows usually because they've depleted a resource such as food we also need to know that sometimes the die-off is catastrophic meaning that it isn't just a little dip back below the carrying capacity but a major major decline in population size this can happen if resources are severely depleted or if the population becomes really dense allowing a severe disease outbreak could even lead to famine which again is going to lead to a massive massive die-off and a decline in population size our suggested science practice for the day is data analysis and specifically explaining what the data illustrates about an environmental issue so remember that every population has a carrying capacity and it's based on the resource needs of that species and the availability of those resources in a given ecosystem we call these resources limiting resources and they're most often food water or space such as habitat or hunting areas it's important to remember though that we don't usually see a population maintain a perfect carrying capacity like this theoretical graph in Figure one usually populations experience overshoot where there are briefly more organisms than the ecosystem can support and then a die-off of some of these organisms starve or eaten by a predator or fail to find the habitats they need in order to survive an example of overshooting die-off is the population cycle that large mammals like deer will sometimes follow since deer mate in the fall and then give birth in the spring there's a sudden and dramatic increase in the deer population each spring as the new fawns are added to the ecosystem there are too many new fawns for the vegetation to support and so many deer struggle to find food resources and die-off which brings the population back below its carrying capacity here we have an example of a more intense die-off that resulted in a population crash so reindeer are large herbivores who need to eat a lot of vegetation in order to survive and in the winter when vegetation is scarce lichen are a very valuable food source for them because they still grow during the cold winter months in 1910 a small herd of 25 reindeer were introduced to st. Paul Island at first there's plenty of vegetation and the population grew gradually from about 1910 to 1930 but then as the population got larger it started to grow exponentially so growth is very rapid from 1930 to 1937 and what we can't tell exactly from this graph what the carrying capacity is it's safe to assume that the reindeer seriously overshot their carrying capacity what this led to was the reindeer heavily over grazing that important winter food source of lichen since the lichen take time to regrow and some scientists estimate that the density of the reindeer population at its peak population size in 1938 was three times what is usually their maximum density there was a severe population crash down to only eight individuals in 1950 however reindeer have proved to be more of a generalist species than previously thought when they exhausted the supply of lichen which has historically been their most important winter food source the reindeer of st. Paul Island adapted to eat and dig up grasses during the winter this allowed them to survive and has allowed their population to gradually recover to a size of about 400 today we can also see a carrying capacity that is limited less by food or water availability and more by predation so the hair is the main prey of the Lynx and we can see that their population sizes can influence you influence each other in a very predictable pattern so it's a fairly repetitive cycle it doesn't really matter where we start in the cycle but we'll start in number 1 on the graph and in step 1 here the hare population starts to increase dramatically with such a small Lynx population so without their predator to keep them in check they grow very rapidly then in step 2 we see the Lynx population grow very rapidly because there's such an abundance of hair which is their main food source however in step 3 here the Lynx population has grown so rapidly that they start eating the hair faster than the hair can reproduce leading to a crash in the hare population then as lucas step 4 here the Lynx population is going to crash as well following that huge decline in their main food source so the carrying capacity for Lynx has decreased dramatically because the limiting resource of food has decreased dramatically and as you can guess here in step number five we're going to start the whole thing over again so the hare population is going to start growing in the absence of their main predator and the whole cycle starts again so if we were to try to establish a carrying capacity here for each based on the graph we might draw the line for the hair around 60,000 and we might draw the carrying capacity for Lynx at around 30,000 since these seem to be the values for each that they sort of fluctuate above and below our science guild for today is explaining what data illustrate about an environmental issue and the practice of our key will be to explain the impact that this canine virus had on the moose population alright everybody thanks for tuning in today don't forget to like this video if it was helpful subscribe for future apes video updates and check out other notes over here to the side and as always think like a mountain right like a scholar