ENVIR ST 260 1st Edition Lecture 6 Outline of Last Lecture I Student Questions II Exam Information Outline of Current 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 Current Lecture There are still some problems with the iCLicker The professor has our participation down but is having problems listing it on Moodle Community Levels of Study What comes to mind when you think about a community from class Support Mutualism Diversity Multiple Population Interactions 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 Your dorm or residence hall has a community to it Your major or college may have a community feel to it Typically we have ideas of support Communities in the ecological and biological sense are less supportive They re more about interactions and competition Know the separate definitions 3 Part Definition of Community Two or more species Could be as simple as predator prey interaction or pollinators and flowers but it could be as big as food webs or trophic cascades Living in the same place Really important And interacting Interactions can come in all sorts of forms direct indirect positive negative Defining a community in space Transitions and ecotones Space can get a little tricky We draw arbitrary lines some times When dealing with space you see a lot of transitions between communities and ecotones Vertical and horizontal structure There can be different communities going up and across the space Ecotones Zone where two ecosystems meet that share characteristics of both One of clearest examples to think about is the space between a terrestrial ecosystem and an aquatic ecosystem The zone where they meet might have wet lands or flood plains With the ocean there is a high tide to low tide ecotone Another example is in southern Arizona In Tucson there s a desert ecosystem with cacti and shrubby things There are mountain ranges that come up around Tucson and as you climb in elevation you have a huge change in the plant and animal communities You go from barren dessert where things are dry and hot to the mountain top with pine trees and oak trees Within this change in elevation there are a lot of ecotones You transition from desert into shrub land and from shrub land to forest Most of the ecotones and community gradients that you see in the Midwest aren t quite as drastic but you still get ecotones If you think about prairie pot holes the areas with depressions are a little bit moister so there s a different plant community than in the surrounding area Vertical Space From the ground up you get a change in communities There s an herbaceous ground layer then a shrub layer then a mid story tree layer and finally a canopy tree layer As much as it s all in the same space you ll find different birds and insects in different layers You can look at that specific communities and look at differences between those communities Interactions can be Direct and indirect Example In a simple food web there are blue jays that feed on caterpillars so they have a negative effect on the caterpillar population Caterpillars eat plants so they have a negative effect on that population If blue jays eat more caterpillars there s a positive effect on the plants This is indirect interaction Positive negative neutral Species can have negative impacts on each other such as with competition for resources and predator prey relations There are positive impacts too Plants have a positive relationship with pollinators Some interactions are pretty neutral If there are two different species that utilize a shared water resource but they don t utilize it at the same time and it s not limited the impact is neutral Often relates to competition Some of this is because natural communities aren t so much supportive but more aggressive Example with prairie plants Really strong competitive interactions because they can t get away from each other Aboveground competition for light Things that get tall can shade out competitors Belowground competition for water and nutrients In order to get water and nutrients many plants have differences in root structure Some will send down longer roots to try to access deeper pools while some will have fine roots near the top to intersect rainfall Competitive interactions select for certain traits such as root types Clicker Question Plant communities form consistently true or false Answer 70 said false 20 said true Succession When communities start from a blank slate There are two kinds The main difference is the starting point and whether or not there is soil Typically predictable Primary Succession Bare Rock Can be result of volcanoes erupting and creating new rock or glaciers moving and exposing bare rock There s no soil It has to make soil before anything can grow Initially there are lichen and mosses and only once there s a bit of soil grasses can start to grow Secondary Can be result of fire abandoned crop land and windstorms There s typically soil present Example If there s a big fire after some time there will be new trees You have an event that removes all above ground vegetation but there s still soil there and a kind of seed bank First you get grasses and low plants Then you get trees that come in Clicker Question True or false plant communities form consistently Answer 65 say that plant communities form consistently but it s actually a trick question Ecological debate over communities There are predictable patterns but they don t always hold true There s a debate between whether communities are super organisms or are dominated by individual s needs and reactions There s an idea that communities are super organisms and balanced because different species are working together and balance each other with competitive reactions This idea is really challenged throughout the book The individualistic view is that it s more random based on different species and occurrences in the area that continuously alter it The professor doesn t really buy either because there are some predictable patterns She believes it s a mix between the two ideas It could depend on the community or it could depend on random events For example adding a drought to the process of a community rebuilding itself could really change the