hey everybody it's mr smeads and today we'll be covering topic 2.3 which is the theory of island biogeography our objective for the day is to one be able to describe what island biogeography is but also explain the role that it plays in evolution we'll also be practicing the skill at the end of today's video of describing an environmental concept or process so island biogeography is the study of ecological relationships and community structure on islands now it's important to point out these can be actual islands so land that you'd find in the middle of water or they can be more figurative islands meaning a natural habitat that's surrounded by an urban environment or a developed human environment so if we take a look here at central park in new york city this is a great example of a habitat island now again it's not an actual body of land in the middle of water but it functions like an island because it's completely surrounded by uninhabitable space for most of the species that live in central park so there are two main observations or ideas that go into island biogeography the first is that larger islands will support more total species they'll have a higher species richness this is because when an island is larger it has more ecosystem diversity and when it has more ecosystem diversity it means there's more food and habitat sources that can support a wider variety of species it also means that there are more niches or more ecological roles available for species and so again a wider variety of species can survive on that island distance to the mainland is another big factor so the closer an island is to the mainland the higher the species richness or the more species we'd expect to find in the island this is because it's easier for colonizers to actually get to the island now colonizers are organisms that move from the mainland and take up residence on the island so they live there and establish a new population there it's also easier for new organisms from the mainland to migrate to that colony and that brings in different genes so it will add to genetic diversity and genetic diversity will increase the species resilience on the island and support their establishment there so again a island that is closer to the mainland is going to have more species richness than an island for their way we have a graphic here to help us visualize this so at the top we have a large island and a small island that are equal distances away from the mainland and then we have a graph showing us that the large island is going to have more total species represented and again that's due to the diversity of habitats and food resources there then in the lower half of the diagram we have two islands that are the same size but now one island is much closer to the mainland than the other so we would also expect that island to have higher species richness or more total species again due to that ease of colonization it's much easier for organisms to spread from the mainland to the closer island because they don't have to swim or fly as far to get there now we'll focus in a little bit more on this idea that larger islands support more species and we'll discuss the different reasons for this so the first one is that larger islands have higher ecosystem diversity so if we take a look at this diagram here we can see that as an island grows in size it has all of these different almost micro habitats that have different food resources and different habitat resources so that can support a wider variety of different species that may have different needs so one species may be well suited to this arid zone where it's dryer and there are cacti and other things available there versus a species that's more adapted to the pompa zone which is higher and has more lush vegetation so again the larger an island the more diversity of ecosystems the more diversity of ecosystems the more diversity of food sources and we'll see an example of this with the galapagos finch evolution that we'll talk about at the end of today's video larger space also equals larger population size so as populations grow in size they have more members they get more genetically diverse and therefore they're going to be more resistant to disturbance so if there's a hurricane on this island or there's a drought larger populations that are enabled by those larger islands make those species less likely to go regionally extinct or to disappear from that island so we have a lower rate of extinction of species on an island that's larger so that preserves those species and keeps that species richness higher and then finally we want to remember that we would call this a positive correlation or positive relationship between island size and species richness so if we look at this graph we can see that as we go out on the x-axis so as we increase the island size in square kilometers we're also increasing the number of species found there or the species richness and this is a very linear relationship so again as we increase the size of an island we increase the number of species that are found there and we call that a positive correlation it's really important to be able to describe trends and data and so we want to have that vocabulary a positive relationship now we'll focus in a bit more on how the distance to the mainland impacts species richness so remember the closer an island is to the mainland the higher the species richness this is because it's easier for species to colonize an island from the mainland so to colonize again means for a population to move from the mainland to a new island ecosystem or habitat that they have not occupied before and so oftentimes if we're talking about an actual island in terms of a body of water in the ocean or in water the species have to actually swim or fly there and so the closer that distance is or the shorter that distance is the easier it is for a wider variety of species to get there there's also going to be more continual migration which brings increased genetic diversity and it adds larger population sizes and remember the more genetically diverse a population is and the larger our population is the more likely it is to stay established on that island and not go extinct when there's a slight disturbance on the island so if we take a look at this diagram we have island a b and c we can see that island a will have three different species found on it but as we get further from the mainland island b no longer has one of those species found on island a now it could be that species just isn't able to swim or fly that far so we've decreased the species richness down to two and when we get all the way out to island c which is now the furthest from the mainland we have only one species that's able to swim or fly that far and so this helps us understand how getting further from the mainland decreases species richness again it's all related to the ability of different species to actually migrate out to these further islands so the way we would describe this is an inverse relationship so that means that as the distance from the island to the mainland increases the species richness decreases so again we call it an inverse relationship because as one variable goes up the other goes down so if we look at a graph here we can see that these two islands which are equal in size are different in their distance to the mainland so that further island out is going to have a lower species richness and if we look at the direction of the arrow in the graph we can see here again as we're getting larger in distance from the mainland we're going down in the number of species supported so we call that an inverse relationship and finally we'll discuss how evolution on islands is shaped by these theories of island biogeography so because islands have limited space and resources it creates a unique condition for evolution to take place there's more pressure for species to adopt to narrower or more specific conditions and that's because you don't have huge expanses of continuous habitat like these organisms had access to on the mainland so let's take a look at the diagram here the galapagos islands provide a great example to understand how these conditions influence evolution and so the finches that colonize the galapagos demonstrate this idea really well if we look at the galapagos islands here we can see there's all these different little micro climates or micro habitats and so those lead to very different conditions and therefore very different food resources so something occurs here called adaptive radiation this is a single species that rapidly evolves into several new species to use different resources in this case use different food resources to reduce competition now this isn't something that the birds consciously do it's just that evolution favors when the species radiates out to use different food sources to reduce competition so we have different beaks evolving to fit all of these different food resources that are available on the island if we look at this diagram we can see that we have a common ancestor that came from the mainland it moves out to one of these galapagos islands and then very quickly we have a number of different unique species that evolve from the common ancestor to fit all these different food resources so we have birds that are going to be eating the cactus flowers we have birds that will be eating seeds birds that will be eating insects and birds that will be eating plant buds so by utilizing all of these different food resources they don't compete directly and the island can support far more birds than if they all ate cactus flowers or if they all ate seeds or if they all relied on whatever the main food source was on the mainland so again what this is going to do is result in really rapidly the evolution of several distinct species that are slightly different from one another in a specific characteristic in a specific trait and in this example it's bird beak size so again we can look at the common ancestor we can see the beak that it had and then we can see how the selective pressure of this micro habitat that exists all over the island with different food sources being present in different areas results in the evolution of different bird beaks so again we have the arid zone where cacti are more prevalent so that's going to drive the evolution of some birds that can eat those cactus flowers then we have the transition zone that might feature more seeds that fall off these plants and so the birds might adapt to eat those so again by evolving all of these different bird beaks to fit all these different food resources we call it adaptive radiation and it ultimately supports more total organisms on the island than if they all stayed as one species and directly competed against one another our practice frq for topic 2.3 will involve the skill of describing the environmental concept or process so i want you to first describe the process of organisms colonizing an island habitat and then i want you to describe how the island's distance from the mainland influences the number of species that will ultimately colonize that island 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 write like a scholar