ECOL 182R 1st Edition Lecture 24 Outline of Last Lecture I Chili peppers II Biomass A Consequences B Exceptions III Species diversity vs richness IV Diversity gradients A Hypotheses Outline of Current Lecture I Island diversity A Island biogeography theory II Community as a unit A Superorganisms B Individualistic III Patterns in time A Succession B Predictability Current Lecture Island diversity ecologists like studying diversity patterns on islands Because it s easy to count everything Known pattern worth exploring more species on larger islands Ex Reptiles amphibians on West Indies islands the bigger islands have more Same with plants in the Galapagos Islands Island Biogeography Theory tries to explain this pattern Biogeography study of species distributions in space A good assumption is that dispersal to islands from mainland occurs constantly Time 0 on the species graph is when nothing is on the island The plateau on the species graph is all species that can get to the island The number of species on any day is a balance between immigration new species arriving that day extinction species disappearing that day These two things determine the plateau Island size effect on smaller islands there s higher extinction and lower number of species at equilibrium Is the community a functional unit Species occur together interact so do they act like a single organism They might occur in space because 1 They interact closely True for some species pairs Called the superorganism concept of the community Functions as one big organism 2 They have similar needs tolerances Called the individualistic concept of the community Like students in the same Bio class Which is correct The two concepts make different predictions as to how many species will be distributed The individualistic is supported if species distributed independently In nature we see more of the individualistic concept One of the most famous examples are the trees as you move along the highway near Mt lemmon Patterns in time communities change over time not only in space Succession orderly predictable sequence of species that colonize and then die out in a given habitat over time It happens because environment changes in a predictable way over time That s also why it s predictable Primary succession begins with NO organisms present Very few organisms can colonize in this situation they re called pioneer species Lichens are very important pioneer species because they break down rock decay and increase presence of available nutrients So then you get a buildup of organic material which allows other species to colonize At the end it turns into a climax community which is a stabled group of species reached at the end of succession The adults are only replaced by young of the same species Secondary succession begins with well developed soil some seeds some plants It s pretty much the same minus the pioneer species What s predictable about this Early species must arrive fast grow fast Late species must tolerate shade competition etc Each species modify their own environments in predictable ways Facilitation is the process by which early successional species change the environment so it is more suitable for altar species Ex Glacier Bay pioneer species add nitrogen to soil When willows die they acidify the soil It is NOT to be generous it s an inevitable process it makes things worse for early species Once the facilitators are present later species competitively exclude the early species Inhibition is when earlier species inhibit invasions until they die only then can later species get in Important in late succession
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