hi guys welcome to our second episode of the ESS series where we're going to be looking at topic 2 so ecosystems and ecology and this is always start really applying the more theoretical frameworks that we went over last week to something more practical so two ecosystems so in this topic we look at the components that make up an ecosystem how they interact and kind of the laws that govern their interactions so let's get started topic 2 is quite a large chunk of the SS syllabus with a lot of interesting concepts that they go over wheat because I want to keep this video short and sweet we won't be going over all of them but I do want to give you an overall kind of run-through on what they tell you about in this topic so as I said we introduce ecosystems and the kind of key concepts that underlie it and we begin by distinguishing between the abiotic and biotic factors that are at play we also go over limiting factors so those factors that limit the number of a population and we split those into density-dependent and then s'ti independent factors we then also go over some concepts such as carrying capacity and population growth curves which are actually important not just in ecosystems but in human population so shout out to topic eight that we're going to get to and we will we won't go over this together but the IB do like to get you to consider photosynthesis and respiration so the processes on how we acquire our food and break the food down to get our energy and how plants make their food as systems themselves so I wasn't lying when I said that in topic one they like applying the systems approach to a range of different things and then they also tell you about biomes so similar ecosystems that share climatic conditions so then let's distinguish between abiotic and biotic factors that influence an ecosystem I think that's the first and thing to do and abiotic factors are the nonliving factors that influence an ecosystem so temperature sunlight pH so essentially environmental factors that will influence how many organisms are in a population how they're interacting etcetera biotic factors are the living factors that affect a population and they this one is really interesting because they consider the interactions between different organisms as factors themselves so we have things like predation herbivory parasitism that we will go over together in just a moment so yeah you can see how these two kind of categories or factors are very different but both crucial to how an ecosystem would function so let's go over the interactions then predation is when one organism hunts and kills another herbivory is when an organism eats a autotroph or producer and parasitism is a specialized type of predation we're a small parasite usually it's smaller than the host the organism that it kind of leeches off of and instead of killing it it realizes that it's more advantageous to just slowly draw its near nutrients and draw nourishment from its food then to kill it so it just lives on the hosts body for a long period of time slowly weakening it we also have disease which is when caused by pathogen or microorganisms and basically a disorder and we've got two types of competitions so interspecific competition and intraspecific competition inter being between species and intra being within the same species organisms of the same population let's say and one attraction that I find particularly interesting is mutualism which is when two organisms of the same whoa different species are working in symbiosis to basically both benefits so it's not necessarily cooperation where they're helping each other but they just both notice this task or this behavior is helping both of them so here we've got oxpeckers and rhinos and what's happening is the oxpeckers are eating parasites that we just learned about half of the Rhinos bodies so ox crackers get food and the Rhinos get less parasites on their body so they're both just benefiting from this interaction which is quite interesting um okay so now for some definitions I know that a lot of students hate the definitions in topic 2 but I think there's one pneumonic that at least helps me conceptualize them a little bit so the five main definitions in this section are species population community habitat and niche now a species is a group of organisms who can interbreed and produce fertile offspring meaning that their offspring can also interbreed a population is a group of organisms of the same species living in the same area at the same time and interacting a community is a group of different populations living in the same area that's a different at the same time so basically different species right because a population is from a species habitat is an area where a species normally lives and a niche which is probably the most the broadest and most interesting definition here is an organisms role in its environment so it basically describes everything the organism does what it eats when it's active what it mainly competes with so it's a very interesting kind of description of an organism and the way that I remember the difference between species population community and ecosystem especially are that they basically grow in level of complexity so you start with species which is kind of simplest and then a population is a group of organisms from the same species a community is a group of populations and then an ecosystem which is the broadest definition of all is the mix of the biotic and abiotic factors in an so essentially a community and be a biotic factors and so I just remember that if you use the Newmont the mnemonic species and you write it out like this you can see that each subsequent letter describes an increase in complexity of the definition I hope that makes sense all right so let's move on then to limiting factors and a limiting factor is one which limits the distribution so where they are and the number of a particular population or species and typically what happens is a population or the rate the rate of population growth will slow as the population approaches its carrying capacity and here we reach reading portion definition not just in topic 2 but actually throughout all of the SS which is that it is the maximum number of organisms which an environment can sustainably support and the reason I say sustainably is because if you look at this graph below you can have slight overshoots and die backs around a carrying capacity but you can see that overall because of negative feedback mechanisms if you remember topic one you stay around this equilibrium and that is the definition of carrying capacity another distinction I want to make in terms of limiting factors now is between density dependent and density independent factors and what that means is that certain factors will affect some populations ones with more organisms more than ones with less organisms and these are factors like competition predation and disease which basically the more organisms you have in an area are more likely to be abundant so disease is more likely to spread if you have more organisms in an area it's more likely to be targeted by kind of predators and it's more likely to be competition because resources or are lacking extremes of weather and natural disasters are on the other hand our factors that will affect small and larger populations equally because they won't there they don't you don't increase the likelihood of having either of them with a larger population so that is an important interesting distinction to make and that brings us to population growth curves we've got the J curve on the left here and the S curve on the right and they basically describe two different generalized population responses to a particular set of conditions a J population growth curve shows exponential growth so the kind of ideal growth where you have no limiting factors plentiful resources and the population can just grow exponentially the S curve shows logistic growth which is kind of well more typically happens especially with K strategists that we described which is when in the beginning you have an exponential growth rate but as the resources become more limiting and you have more competition more predation that the population size kind of levels off at the carrying capacity which if you remember from a couple of slides ago is the maximum number of organisms that an environment can sustainably support so these are the two population growth curves you have to know and that brings us to just briefly mention energy flow in ecosystems so if you remember from our first episode we described the two laws of thermodynamics and this is again when we really apply it to the more practical level so three definitions for you a food chain is a sequence of organisms each of which is the source of food for the next so the first diagram here just trees deer lion a trophic level being in the position that each of these organisms occupy in the food chain in the sequence a food web is basically interrelated food chains and it more accurately portrays kind of the complexity of real ecosystems because if you imagine if each organism only had one potential source of food that wouldn't be very kind of efficient because if that source of food were to be unavailable for whatever reason then we wouldn't fare very well so I also to tell you guys about three of the RINO's important players in the cycling of energy and matter in an ecosystem and those are producers consumers and decomposers and they each have a unique crucial role in the functioning of ecosystems so let's describe them a little bit for juicers or autotrophs as is their scientific name are the ones that have the ability to fix carbon or converge the carbon in the atmosphere into an organic form that consumers we can eat so they kind of provide full for all food for all subsequent trophic levels consumers or heterotrophs are ones that don't have this ability so in order to acquire their food need to eat other organisms decomposers also cannot fix carbon but what they can do is break down dead organic matter and without them the all the nutrients all of that energy would just kind of be lost to in that form so they are really important in this keeping the energy matter cycling would you remember from topic one is what makes up a open system and succession and zonation is the final thing I want to tell you guys about just because it's such a big kind of source of confusion sorry I appreciate it's a bit of a junk for all I've been talking about so far but I just want you guys to be aware that succession describes how an ecosystem changes over time as you can see in the image below after following a forest fire you can see that how the community reestablishes itself over time and zonation is a very different kind of process because it describes how an ecosystem changes over a distance so over the kind of increasing height in the shore as you can see in the image on the right you can see how the communities again change as you as you throughout zonation so be aware that those two are two very different processes but that a lot of students get confused and that concludes our topic two episodes so if you guys want to go ahead and click on topic 3 I'll tell you a little bit about biodiversity