Biodiversity (Ch 4) Lecture notes Importance Biodiversity is a part of natural capital and is a renewable resource. Having a variety of organisms provides us with more ecosystems services ex: trees soaking up carbon dioxide, a diverse forest absorbing water to prevent flooding, a variety of pollinators for different crops (bees, moths etc). Biodiversity promotes resilience both within a species (genetic diversity will give more chances of survival in the face of a catastrophe) and within a biological community. As the quote from Ishmael says, when there are many species in an ecosystem and conditions change, high diversity means there are more possible species that could have characteristics that would help them cope with the environmental changes. Whereas in an ecosystem with very few species it is much less likely that the right combinations of genes exists to allow species to survive environmental changes. Additionally, the diversity of living things on earth provide a lot of things that humans use such as medicines, foods, lumber etc. How is Biodiversity created? Speciation is when two species evolve from one. Allopatric speciation is when two populations of one species become physically separated (geographic isolation) and eventually evolve into separate species. In the example of the squirrels, sea level rises which separates two groups of the same species. Overtime, they evolve separately and become reproductively isolated even when they are back in contact with each other. This indicates that they are separate species. There are other methods of speciation, but this is the main mode of species creation. Another process affects the number & types of species on earth-­‐ it is extinction Extinction Extinction balances out speciation and is a natural and ongoing process in the biosphere. The natural rate of extinction (without human interference) is called the background extinction rate. It is equal to approximately 1-­‐5 species per million on earth per year. Certain types of species called Endemic species are particularly vulnerable to extinction because they are only found in one location on earth. If they die out there, there are none anywhere else. -­‐ ei one island or chain of islands Examples: Dodo birds on Mauritius (island in Indian Ocean), Catalina Island Fox (only found on Channel Islands in Southern California) Mass extinction are situations where extinction has exceeded the background rate due to some massive change or disruption of the earth system. There have been 5 in the past. Extinction of dinosaurs 65 mya due to meteorite impact is an example of a mass extinction. Another, between the Permian and Triassic Periods (250 mya), caused as many as 95% of species to go extinct. Many scientists say that we are in the midst of a 6th, anthropogenic mass extinction right now. Mass extinctions do provide an opportunity for evolution to take a new direction and for speciation to take off. Components of Biodiversity Biodiversity is a balance between speciation and extinction. Which side is winning? Currently speciation is winning out-­‐ we have millions of species on the planet now because overall speciation has kept ahead of extinction. When we get down to the details of biodiversity, there are actually 4 types. Species diversity is the number of different species in a particular ecosystem. Genetic diversity is the variety of genes that exist within one species. Both species diversity and genetic diversity help promote resilience within ecosystems and populations. For example if you have a high genetic diversity of pine trees in a forest, that population has more of a chance of withstanding a tree fungus than if all the trees were genetically the same. One concern with having food crops that are all genetically similar is that they do not have enough different genes to be able to have some resistance to pests. There is also a diversity of different ecosystems, or biomes, on earth (Ecosystem diversity). These are particularly important to humans since they provide so many different resources for us. Finally, there is functional diversity, which is made up of all the different services that those different ecosystems provide, like coral reefs protecting coastlines from erosion and forests purifying air. Species Diversity Right now we are most concerned with species diversity. We can measure species diversity in a couple of ways. We can talk about species richness (the number of species in a community), which is the most common way. It is also useful to look at the number of individuals in each species (or how evenly distributed are individuals between species). This is called species evenness. When ecosystems have one species with many more individuals, we say that particular species shows dominance. The aspen forest in the photo shows low richness and the aspens are dominant. Diversity indicies help biologists quantify biodiversity for comparison purposes. It is a difficult thing to do. There are a couple of diversity indices that are used including the Shannon index and the Simpson index. The Shannon Index (H’) ranges from 0-­‐4.6, with higher values indicating higher diversity. Biologists use the Shannon Index value to compute the Shannon’s equitability value (EH)which is a measure of the evenness of the community. EH values can range from 0 to 1. A value of 1 indicates high evenness whereas a value of 0 indicates that every individual is the same species (low evenness). Ecosystems with high species richness have a large number of different species, but tend to have a low number of individuals of each species. Some examples are tropical rainforests, coral reefs, ocean bottom, large tropical lakes. What else do these ecosystems have in common? They all have high NPP. These ecosystems appear to have a higher productivity due to different species using different portions of available resources. They also appear to have higher levels of stability over time due to more complex food webs give it the ability to withstand environmental stress Species Roles in Ecosystems One of the reasons why having high levels of species diversity is important because of all of the roles in an ecosystem that different species can fill. There are a number of ways to describe these roles. When we describe a species’ role in an ecosystem we are looking at its niche. A species’ niche is its “pattern of living” includes its habitat, resource use/ needs, space required, temperature range it can tolerate, among other things. There are two ways that we can describe a species’ niche. Generalist species have a broad niche (wide range of tolerable conditions). Examples are raccoons and cockroaches. Specialist species have a narrow niche (very narrow range of conditions it can tolerate). An example is the Giant Panda Classification of Niches There are a number of ways that we can further classify niches to describe the important role that different species play in ecosystems. Native species are those that evolved in a particular place. There are also nonnative (invasive) species, indicator species, keystone species and foundation species. Nonnative species can be introduced deliberately or accidentally. Although some species introductions can be very detrimental to ecosystems, most species introductions are beneficial. For example, most food crops grown in the US are nonnative and provide many benefits for humans. Indicator species are species that are particularly sensitive to environmental changes. They act as the “canary in the coal mine” for their ecosystem. (Coal miners used to use canaries to detect toxic fumes in coal mines, because the canaries would respond to the fumes before the miners). These species give scientists a way to know that something is harming an ecosystem before the enter ecosystem begins to show damage. Birds, trout species, butterflies, and amphibians are all examples of possible indicator species. Keystone species play a critical role in an ecosystem and help to maintain balance in the ecosystem. They could be pollinators or top predators that help to regulate the populations of other species. Examples are sea otters which help to manage the sea urchin populations in kelp forest ecosystems. Sharks eat dead and dying fish in the ocean helping to recycle those nutrients. The American alligator eats other predators in its ecosystem helping to keep their populations in check. A special type of keystone species is a foundation species. These species perform a critical role in their ecosystem by physically changing their habitat. A beaver is an example. They build dams in rivers that create deep pools where other species can live. Elephants are also foundation species. They uproot trees on the grasslands where they live. This makes more room for grass species as they remove the trees. Without this service the grassland would turn into a forest, eliminating habitats for many organisms Tropic Cascades When a keystone species (particularly a top predator) is removed from an ecosystem, a domino effect can occur. Often the removal of the predator upsets the populations of lower trophic levels and sets the ecosystem out of balance. It is as if the effect of the disturbance is rippling through the trophic levels one by one. Ultimately, a trophic cascade can eventually change the abiotic features of an ecosystem as well. An example of this occurred in Yellowstone National Park when wolves were reintroduced.