Chapters 17 and 18 Notes
Chapters 17 and 18 Notes 301
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This 0 page Class Notes was uploaded by Morgan Deal on Monday November 16, 2015. The Class Notes belongs to 301 at University of South Carolina taught by Dr. April South in Summer 2015. Since its upload, it has received 27 views. For similar materials see Ecology and Evolution in Biology at University of South Carolina.
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Date Created: 11/16/15
CHAPTER 17 Mutualism Types Mutualism positive interaction between 2 species 0 1 species gets bene ts that only the other can provide to it 0 Common in nature 0 Affects populations species communities and ecosystems Categorizing o Generalists 1 species interacts with many others 0 Specialists 1 species interacts with 1 or a few other closely related species 0 Obligate mutualists 2 species give each other tness bene ts and cannot survive without each other 0 Facultative mutualists 2 species bene t each other but mutualism isn t necessary for survival Plant Mutualisms Fungi mutualistic relationships between over 6K species of mycorrhizae and 200K species of plants 0 Mycorrhizal fungi surrounds roots and helps plants obtain water and nutrients plants contribute oxygen and glucose Endomycorrhizal fungi threads penetrate root cell wall and membrane and reach into soil 0 Arbuscular mycorrhizal fungi most common type of endomycorrhizal fungi Ectomycorrhizal fungi only have relationships with trees and shrubs Bacteria o Rhizobium bacteria converts unusable nitrogen into forms that plants can use ammonia bacteria get a home and products of photosynthesis Animal Mutualisms Protozoans termites and gut protozoa o Protozoa get food wood and a home 0 Termites get food from protozoan wastes Bacteria humans and gut bacteria 0 Animals alpheid shrimp and goby sh 0 Shrimp cannot see very well so goby sh warns them of predators 0 Shrimp allow gobies to share its burrow Humans humans follow honeyguide birds for honey in exchange for exposed bee larvae Defense 0 Plants 0 Acacias and ants ants nest in trees and protect the tree from herbivores and competitors 0 Endophytic fungi live in plant tissue fungi produce chemicals that repel herbivores and increase drought resistance in exchange for products of photosynthesis 0 Animals 0 Wrasse and larger sh wrasse consume ectoparasites attached to larger sh 0 Oxpeckers and grazing animals Pollination and Seed Dispersal 0 Flowers plants have evolved reward mechanisms for pollinators o Pollennectar pollinators consume and get covered by pollen which is then dispersed 0 Some mutualisms are very speci c bats and desert cacti cacti owers only open at night for the bats Dispersal many animals eat seeds which pass through their digestive system unharmed Seed numbers bird species collect thousands of seeds for food but do not consume all of them unconsumed seeds are dispersed and can grow Ending Mutualistic Relationships 0 Positive interactions can turn to herbivory predation or parasitism if the relationship stops bene tting the other individual 0 Increase individual tness Cheating 1 partner stops bene tting from the relationship 0 1 receives a bene t but does not provide one 0 Natural selection favors cheating AND mechanisms of defense against it Effects Beyond Mutualists Species distributions disruptions of mutualistic relationships 0 May decrease abundance and distribution Ecosystem functions loss of dispersers decrease plant abundancedispersal Conservation CHAPTER 18 Community Structure Communities and Boundaries Community species living together in an area Zonation distribution of species due to parameters 0 Species composition changes across landscapes o Tolerance ranges 0 Competitive ability Categorizing Communities Terrestrial 0 Dominant organisms 0 Physical conditions affecting distribution of species Aquatic systems 0 Dominant organisms 0 Physical characteristics Ecologists study subset of species in an area rather than every species there Ecotones Ecotone boundary created by sharp changes over short distances accompanied by change in species composition 0 Some species move between communities 0 Most species live in 1 community but spread into ecotone Supports large number of species Linetransect survey distinguish ecotones Interdependence v Independence lnterdependent community species depend on each other to exist 0 Independent community species don t depend on each other for survival 0 Determining which is occurring 0 Linetransect surveys not de nitive 0 Remove species thought to be interdependent o Interdependence found more in harsh environments Patterns of Species Abundance Species richness number of species in a community 0 Relative abundance proportion of individuals in a community represented by each species 0 Most species have intermediate abundance Lognormal distribution log scale on xaxis normal distribution Rankabundance curves plots relative abundance of each species in community in rank order from most to least abundant Species evenness compares relative abundance of each species in community 0 0 slope even Effects of Resources on Diversity 0 Species richness can be affected by amount of available resources 0 Relationship between productivity and species richness 0 Wide range of patterns u shape negative hump shaped positive none 0 Experiments have manipulated productivity addingremoving resources 0 Added fertility typically causes decrease in species richness of producers 0 Park grass experiment species richness decreased with added fertilizer Decrease in number of species when nutrients increased 0 Unclear why may cause dominant plants to take over Effect of Habitat Diversity 0 Communities with higher habitat diversity should have increased diversity of species 0 More potential niches Keystone Species Substantially affects community structure removal can cause collapse of community 0 Ecosystem engineers affect community by in uencing habitat structure Effect of Disturbances on Diversity 0 Intermediate disturbance hypothesis more species present in a community with intermediate disturbances 0 Competitive species become dominant with too few disturbances Food Webs Food chain linear representation of feeding patterns 0 Food web complex and realistic representation of feeding patterns 0 Trophic level level in food chainweb 0 Primary consumer eat producers 0 Secondary consumer eats primary consumers o Tertiary consumer eats secondary consumers Omnivore consumes organisms at several trophic levels 0 Guild group of species feeding on several similar things Direct v Indirect Effects 0 Direct effect sometimes affects other species in the community 0 2 species only 0 Direct effect of 1 species can set off chain of events that affects other species 0 Indirect effect can occur between communities 0 Intermediate species involved 0 Densitymediated indirect effect caused by changes in density of intermediate species 0 Traitmediated indirect effect caused by trait changes of intermediate species Trophic cascade indirect effects initiated by a predator TopDown and BottomUp Effects Bottomup control activity of producers controls abundance of trophic groups Topdown control abundance of trophic groups is determined by predators