ENVIR ST 260 1st Edition Lecture 7 Outline of Last Lecture I Community a Definition b Space Ecotones and Vertical Space c Interactions II Succession a Primary b Secondary III Ecological Debate IV Determination of formation of communities V Species in communities a Dominant b Keystone Outline of Current Lecture I Species Dominant versus Keystone II Regulation Top Down versus Bottom Up III Succession and Stability IV Housekeeping Current 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 species These 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 in on 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 could not 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 just one 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 topdown 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 may even 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 her to set up a time to talk and give her a sense of what your questions or concerns are it helps her to manage all the spinning plates We ll see her comments and if you have the green light begin to get content Start gathering CONTENT to use in STS workshop photos graphics text She s getting STS set up We ll be in a computer lab where she ll set us up with a program to create this