ENVIR ST 260 1st Edition Lecture 7Outline of Last Lecture I. Communitya. Definitionb. Space: Ecotones and Vertical Spacec. InteractionsII. Successiona. Primaryb. SecondaryIII. Ecological DebateIV. Determination of formation of communitiesV. Species in communitiesa. Dominantb. KeystoneOutline of Current Lecture I. Species: Dominant versus KeystoneII. Regulation: Top Down versus Bottom UpIII. Succession and StabilityIV. HousekeepingCurrent Lecture Clicker Question: Longleaf pine are a dominant species because They maintain the fires critical to the ecosystem They have the most biomass The shade the other trees to remain dominant The answers were pretty equally split among the class. Sea otters are a keystone species because Sea otters are a predator Sea otters maintain the food web and greater ecosystem Both It was typically between B and C.Dominant versus keystone speciesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Dominant species have the most biomass (may maintain critical structure/function) American Chestnut Example. American chestnut was the dominant tree species on the East Coast. Their nuts are very nutritious and a lot of critters ate them, but then chestnut blight was introduced and wiped out pretty much all of the American chestnut. Some people really feared that you’d see an ecosystem collapse because so many animals were dependent on chestnuts, but that didn’t happen. The system changed, but other trees increased where American Chestnut populations grew and animals kind of shifted their food source. This was a dominant species, but it was not a keystone species because the ecosystem didn’t greatly change.  Keystone species have large impacts (when removed system collapses) They’re called keystone species because when they’re removed the whole system will collapse inon itself A lot of times it deals with predators maintain an ecosystem, such as sea stars Indiana Jones Video Clip Example Either one thing can be replaced by another or it cannot. When Indiana Jones tried to steal the idol, he swapped it with something else, but the swap didn’t work because the idol couldnot be replaced. The professor equates this to communities. You think of the role a single species can play and whether or not you can make a swap.  Example: Wolves decline, Coyotes increase The top predators were wolves. A lot of people hunted wolves consequently coyotes kind of moved up to take the place of wolves in the ecosystem, but the swap wasn’t really equivalent. Coyotes in the northeast have started to interbreed with wills and are doing things that aren’t typical of coyote behavior. But they’re still not an equivalent switch. Earlier Coyotes were really restricted, but now they’re all over Wolves are considered keystone because they’re the top predator and the coyotes don’t regulate the system in the same way. A dominant species might be able to be switched out with minimal effect but with coyotes, they’re not doing as good of a job as wolves were and there’s consequently overpopulation of deer and lime disease Clicker Question: How many species can you remove before an ecosystem is negatively impacted? The removal of even a single species has a negative impact The impacts are proportional to the species present – There is a large impact of removing a single species in “small” systems 42 The impacts are proportional to the role of the species – Removing a top predator has a greater impact than removing low statured plants Most of the people said D. There isn’t really a right answer. A lot of it comes down to the ecosystems that you’re dealing with and the perception of people involved. Regulation Top down or bottom up? Take the example of the typical triangle diagram with producers at the bottom, then herbivores as primary consumers, then primary carnivores as secondary consumers and then secondary carnivores as tertiary consumers. The factors that influence population can influence not justone population but a whole community. It can work from the top down or bottom up, because energy and relationships flow through the diagram. Regulated from bottom up flows from autotrophs to consumers. From the top down there are cascades that influence down to autotrophs and plants.  Clicker: The trophic cascade of bottom-up impacts are equivalent to those regulated form the top-down? True  False Most people said B. She agrees with that.  Regulation continued All examples based on the following chain: Nutrients <-> Plants <-> Herbivores <-> Carnivores Bottom up Example with aquatic ecosystems: If you add some nutrients to that system, you’ll probably see a positive effect on all the species. The autotroph population would increase causing the herbivores to increase and so on. The positive effects are there, but it’s not something where if you keep adding and pumping nutrients they populations would continue to increase. It’s really quickly limited to how fast populations grow; sometimes negative effects mayeven occur. Top down regulation with removal of apex predator:. The herbivore population will grow, and then the plants will really suffer because the herbivores are eating too many plants (which eventually limit the herbivores in turn). These negative effects are a bit stronger, so you’re more likely to see them cascade through bottom down pathway. Succession and Stability All about successional pathways and ecosystem stability. With succession, there’s typically disturbance.  Do disturbances “reset” or “maintain”? Communities have this succession build in in a way. You’re removing a later successional community, so you can go back to an earlier point.  Disturbances are kind of a maintaining force. You may land on a cycle.Housekeeping In the next few weeks: Need to re-update schedule Discussion this week is focused on book chapters  (Chapters 6 and 12 get a bit deeper into the ideas of how communities are structured which give a lot of examples, so if you haven’t read them you’ll need to) Essays back in discussion – grades posted on Moodle Remember that if you’ve got questions about the grading or any of her comments, email herto set up a time to talk and give her a sense of what