BCOR 12 1nd Edition Lecture 23 Outline of Last Lecture I Major Life History Traits Repeated II Human Population cont III Critical Perspective Questions IV Community Ecology Beginning of Chapter 54 V Intra and Interspecific interactions Outline of Current Lecture I Competitive Exclusion II Ecological Niche and Resource Partitioning III Fundamental Features of Community Structure IV Disturbances Current Lecture Competitive Exclusion Competitive exclusion principle when two populations of two similar species compete for same limited resources food space etc one population will use resources more efficiently and have a reproductive advantage in time an evolutionary advantage o Result the other species will be eliminated over time Ecological Niche and Resource Partitioning Niche sum of a species use of both biotic and abiotic resources in its environment ecological role o Habitat where an organisms lives o Ecological niche organism s profession or job Example many different lizards living in the trees of the tropics all eat insects but they live in different parts of the tree nicke shift Resource partitioning a pattern in which species whose niches overlap may diverge to minimize the overlap Example Lizards diverged to live in all parts of the trees to limit their competition with other lizards and led to speciation Competitive exclusion principle is too simplistic to be seen in the natural world 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 Keystone species a species that exerts strong control on the community structure by the nature of its niche o Example The sea otter in the North Pacific When it was almost completely eliminated by orca whales the sea urchins that sea otters prey on population grew quickly and diminished the kelp forests This led to a decline in animal abundance for the kelp forests were a habitat to many animals Sea otter keystone species of North Pacific The sea otter had a DIRECT NEGATIVE effect on the sea urchins and an INDIRECT POSITIVE effect on the kelp Fundamental Features of Community Structure Fundamental Community Properties I II Species Diversity Tropic Structure Species diversity Species richness number of different species in the community Relative abundance the proportion of each species in the community Can have same species richness in two different communities BUT have different relative abundances of those species Diverse communities are MORE stable and have increased productivity Example Minnesota Experiment set up 168 plots Plots either had 1 2 4 8 or 16 species of grass perennial native grasslands and these plots were replicated o Found 16 species plots were 70 more productive when compared to a 1 species plot Communities with higher diversity are o Better able to withstand or recover from environmental stresses o More resistant to invasive species organisms that become established outside their native range Tropic structure Tropic structure different feeding relationship in an ecosystem o Route of energy flow o Pattern of chemical cycling driven by decomposers Food Chain Primary Producers autotrophs Primary Consumers herbivores Secondary Consumers Carnivores Tertiary Consumers Carnivores Quaternary Consumers Carnivores Disturbances Disturbance an event that changes a community by removing organisms from it or altering resource availability o Influences species diversity and composition Succession the predictable process of recovery after a disturbance natural or unnatural Pioneer species first species to colonize a disturbed area o Bryophytes are most abundant pioneer species due to the fact they don t need soil for they don t have roots and were the first to colonize land Succession following a disturbance species colonize and transform the habitat in a predictable sequence