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Transcript
Reading Goals Community Structure Symbiosis Succession Chapter 15 Read for vocabulary 375-377 Confidence Interval Box on 387 Summary 393-394 Chapter 17 Read for vocabulary 419-425 427-429 Box 430 432-434 Summary 438 Chapter 21 Chapter 16 Read for vocabulary 398-411 Summary 415-416 Read for vocabulary 512-518 519-522 525-529 530-533 Summary 533 Created with MindGenius Business 2005® 2005® Community Structure Created with MindGenius Business 2005® 2005® Community Structure Characteristics of Communities Vertical Structure Physical Structure •Vertical layers •Horizontal (patchiness) •dispersion Biological Structure •Guilds •Dominants •Complexity •diversity Horizontal Structure Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® 1 Community Structure Community Structure Canopy Mid- Canopy Understory Organic Layer Created with MindGenius Business 2005® 2005® Community Structure Created with MindGenius Business 2005® 2005® Community Structure Diversity and Stability How would structure look in a Kelp Forest? Desert ? Does diversity of a system affect its stability? How would structure look PNW Stream ? What do we mean by diversity? Stability Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® 2 Community Structure Diversity and Stability Community Structure Two groups of Theories concerning Stability and Diversity in Communities Does diversity of a system affect its stability? Equilibrium Persistence – ability to survive disturbance Non- Equilibrium Resilience – ability to rebound following a disturbance Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Community Structure Equilibrium Community Structure Non-Equilibrium Diversity is determined by the number of available niches • • Traditional view Number of species does not fluctuate markedly from an equilibrium determined by •Predation •Competition • Disturbances are dampened out • New species can invade only after similar species leave Created with MindGenius Business 2005® 2005® • • Species diversity is dynamic Community structure determined by disturbance • prevents dominance • increases horizontal structure • can increase or decrease diversity Created with MindGenius Business 2005® 2005® 3 Community Structure Response to Disturbance Community Structure Response to Disturbance Non-Equilibrium models ‘K’ Equilibrium models Pop Size Pop Size ‘r’ ‘r’ Co-existence ‘K’ Time after disturbance •Fast growth •Early maturation •High fecundity •Small size •Good colonizers Time after disturbance •slow growth •late maturation •low fecundity •large size •Good competitors Diversity maintained by frequent disturbance Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Community Structure Community Structure Intermediate Disturbance Hypothesis Pop Size Examples low biodiversity is highest when disturbance is neither too rare nor too frequent. •Coral reefs and hurricanes •Tropical forests and tree gaps •Boulders in intertidal areas •Prairie dogs in grasslands high Frequency of disturbance or size of disturbance or frequency of population reduction Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® 4 Community Structure Community Structure A keystone predator is an animal that is important for maintaining species richness (number of species) in a community. Keystone predators feed on different species that normally would compete with each other. Competitive exclusion of a species does not occur because the densities of competitors are kept reduced by a common predator. Dynamic Equilibrium Model • community structure is maintained by controlling competitive interactions between species (e.g., keystone species) Page 423 in Text A good example of a keystone predator is Piaster, a sea star, that reduces the populations of a mussel, Mytilus. If Piaster is experimentally removed from the community, the species richness of the community decreased from 15 to 8 species. Created with MindGenius Business 2005® 2005® Community Structure Created with MindGenius Business 2005® 2005® Community Structure Some Terms Species Richness (S) – number of species in an area (number of ind. / area) Diversity Values – used to •Establish trends •Make comparisons •Produce conservation policies Species Diversity – number of species in a community or region OR Differences between biomes • Tropical rainforest – 50-100 spp. per ha • grasslands, savannas, deciduous forests 15-60 spp. per ha • Tiaga, redwood forests, dry deserts, open ocean 7-20 spp. per ha Is there more . . . . Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® 5 Community Structure Community Structure Problems with Species Richness Values – • • No. spp. will increase with sample size May not provide useful information about ecology of a community (e.g., abundance or physical structure may have more significance than richness). Therefore, ecologists tend to use Diversity Indices rather than just Species Richness (S) when talking about Diversity Many diversity Indices Incorporate both richness (S) and evenness (relative abundance) Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Community Structure In the graph below, species richness and the Shannon diversity index (symbol H, see below for its calculation) are provided for each community. You can see that the diversity index H is lower for the communities at the left, indicating their lower diversity. Community Structure Also, other types of Diversity besides Species Diversity …. Scale S= Species Richness Gamma Diversity Alpha Diversity (regional) (local) Beta Diversity (species turnover) http://images.google.com/imgres?imgurl=http://www.worldagroforestry.org/sites/rsu/resources/biodiversity/anal ysistypes/Divers2.gif&imgrefurl=http://www.worldagroforestry.org/sites/rsu/resources/biodiversity/analysistypes /diversityindices.asp&h=275&w=478&sz=6&tbnid=HbjImINhNF0J:&tbnh=72&tbnw=126&hl=en&start=17&prev =/images%3Fq%3Ddiversity%2Bevenness%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG Created with MindGenius Business 2005® 2005® Increasing scale Created with MindGenius Business 2005® 2005® 6 Community Structure Community Structure Conserving ‘ Diversity’ • Tend to focus on species – even only rare species Alpha – diversity of small areas of relatively homogenous habitat; No. spp. per unit area. Used to describe community structure. Beta – change in species composition over relatively small distances; often used between distinct adjacent habitats. Used to describe species turnover. Gamma – diversity of similar habitat separated by wide geographic distances; regional diversity. Used to address the relative roles that history and ecology have played in organizing assemblages of species. • Current efforts starting to shift to conserving complete ecosystems • There are an estimated 10-30 million species described in the world; only 1.7 million described! • Extinction rates are increasing • natural rate 2-25 spp. / yr • present rate 10,000 spp. / yr. Causes of Extinction? Why worry about conserving ? Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Symbiosis Symbiosis – intimate association between individuals of two different species living together Symbiosis Created with MindGenius Business 2005® 2005® Species 1 Species 2 Parasitism + - Commensalism + No effect Mutualism + + Created with MindGenius Business 2005® 2005® 7 Symbiosis Symbiosis Types of Mutualism Mutualism Defensive – food or shelter in return for defense Trophic exchange of nutrients and energy Facultative – partners can live singly Obligate – partners cannot exist singly Dispersive – food in return for moving propagules or pollen Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Symbiosis Symbiosis Lichen – fungus and cyanobacteria or green algae Soybean & Rhizobium Species 1 Species 2 Parasitism + - Parasitism + - Commensalism + No effect Commensalism + No effect Mutualism + + Mutualism + + Created with MindGenius Business 2005® 2005® Species 1 Species 2 Created with MindGenius Business 2005® 2005® 8 Symbiosis Symbiosis Cocklebur & Animals Lichen on a Tree Species 1 Species 2 Species 1 Species 2 Parasitism + - Parasitism + - Commensalism + No effect Commensalism + No effect Mutualism + + Mutualism + + Created with MindGenius Business 2005® 2005® Created with MindGenius Business 2005® 2005® Symbiosis Symbiosis Remora and Shark Ants and Acacia Species 1 Species 2 Parasitism + - Parasitism + - Commensalism + No effect Commensalism + No effect Mutualism + + Mutualism + + Created with MindGenius Business 2005® 2005® Species 1 Species 2 Created with MindGenius Business 2005® 2005® 9 Symbiosis Sawfly (Pontania sp.) larva inside a gall. Note the external parasitoid larva (translucent white) attached to the dorsal surface of the sawfly larva. http://images.google.com/imgres?imgurl=http://tiee.ecoe d.net/vol/v3/experiments/sawfly/img/sawfly(parasite)%25 5BHR%255D.jpg&imgrefurl=http://tiee.ecoed.net/vol/v3/ experiments/sawfly/downloads.html&h=1061&w=721&sz =107&tbnid=IwoeejTl0bMJ:&tbnh=150&tbnw=101&hl=e n&start=9&prev=/images%3Fq%3Dparasite%26svnum %3D10%26hl%3Den%26lr%3D Species 1 Species 2 Parasitism + - Commensalism + No effect Mutualism + + Created with MindGenius Business 2005® 2005® 10