Week 11 Notes
Week 11 Notes Bio209WeekOneNotes
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Date Created: 11/21/15
Week 11 BIOS 209 Notes Population Ecology in the real world populations cannot grow forever eventually various factors limit population growth Limited population growth populations do not grow inde nitely e g like Reindeer on an island off Alaska Exponential population growth assumes unlimited resources when resources start to become limited pop growth slows Carrying Capacity K of the population s environment Logistic Growth S shaped population growth logistic growth occurs when a resource in the environment is limited REMEMBER Logistic model starts with exponential model but adds an expression that reduces per capita rate of increase r as N approached K which in the example is 1500 logistic assumes that resources are NOT limitless rather that growth slows down as approaches K In which is per capita growth rate constant exponential growth dependent on N and the environment Logistic growth K depends on which resource is MOST limiting What limits populations populations do not grow inde nitely a limiting factor may be 1 density independent often true of severe weather event e g tsunami cold winter 2 density dependent often true of competition contagious diseases toxic waste in logistic growth model r is density dependent birth or death rates depend on the population s size In drought plants with eXposed roots often die densityindependent mortality when a population gets large more nutrients in sand get used up and reproduction declines densitydependent birth rate eg Dune Fescue a costal grass in the UK often grows alongside golf courses Factors that in uence populations competition with other organisms infraspecific or interspecific gt predation mortality disease parasites morality or reduced reproduction THESE EFFECTS OF THESE FACTORS MAY CHANGE OVER TIME Life Histories patterns of reproduction survival in a species Producing Offspring 1 Semelparity one sensational birth eg century plant owers grows for 1030 years owers once then dies eg Salmon 2 Iteroparity repeated throughout lifetime e g eastern cottontail breeds 34 times a year Species can sometime be described as r or K selected 1 rselected rapid reproduction large number of small offspring little parental care in animals 2 Kselected fewer offspring wellprovisioned or cared for increase competitive ability Why does variation in life history traits exists 1 organisms energy for life functions is finite 2 Thus energy used for one function may not be available for other functions there are tradeoffs in maintaining body growing and producing offspring gt Human population growth has been exponential Current human population 7 3 billion b 020 births per individual per year In 008 deaths per individual per year rbm 020008 012 per individual per year if r stayed constant doubling time would be 58 years Serious questions that have to be asked can world food production continue to increase is there enough fresh water are resources many of which are being used more rapidly today going to run out Population Projections Recently there has been a Decrease in population growth rate So population size is not growing as fast but it is still growing Reproductive Decisions and r US family size has decreased in past century this is typical when shift from agricultural in industrial economy b decrease is usually associated with a decrease in m Via improvements in education nutrition and medical care growth is affected not only by family size but also by age structure more young people father growth So what do we do if we don t want to run out of resources smaller family size greater delay of reproduction Another option population size matters relative to K which may be limited by water food habitable space nonrenewable resources buildup of wastes we could increase K if resources used per person went down Ecological Footprint area if resources used per person gt many people could lower theirs and still have a high quality of life 1 Community all the different species in ONE place Many different types of interactions e g competition symbiosis mutualism predation parasitism herbivory 2 Competition when gt 2 organisms use same resource and the resource is limited in short supply there are TWO ways to compete l Fights territoriality or Via chemicals 2 Use resource 1st before competitor before competitor negative effect on both organisms fitness Competition with whom I Interspecific different species 2 infraspecific same species population growth models considered just 1 species but competition is one factor that can lead to logistic growth Niche all the biotic and abiotic resources an organism uses in its environment EX What it eats Where it seeks shelter abiotic factors it can Withstand temp rain time of day and year it is active or reproduces Niche Overlap determines the strength of competition between species Fundamental Niche the range of conditions a species has the potential to live Realized Niche the portion of those conditions that is actually occupied Bamacles babe jointed legs and are closely related to pillbugs and shrimp Phylum Arthropoda Class Crustacea Competitive Exclusion is a short term outcome of competition Longterm evolutionary outcomes of interspecific competition 1 Selection may favor use of resource for Which there is less competition niche shifts resource partitioning 2 expect such selection to be STRONGER in sympatry than in allopatry if it is shift in trait e g in beak depth is called character displacement 3 Predation Parasitism and Herbivory predation prey is killed and consumed Parasitism obtain resources from host but don t always kill it Herbivory plant is consumed partly or entirely Ecological time effects in short term e g changes in population size for both prey and predators gt reduced fitness and thus population size or parasite s host gt reduced seed production in plants that suffer herbivory Effects In Evolutionary Times 1 adaptation including coevolution eg the newt s skin contains an unusual toxin not usually seen in newts for most predators lethal or paralysis because toxin backs sodium channels in cell membrane s lipid bilayer often allows newt to escape but some garter snakes are tolerate to the toxin they have few amino acid differences in their sodium channel proteins Other adaptations against predators Aposematic coloration in frogs increases fitness because predators associative learning is quicker if signal is strong cryptic coloration Batesian Mimicry it is BS eg y and bee Mullerian Mimicry it is mutual e g Cuckoo bee Yellow jacket Cryptic coloration can work for predators too Mutualism both species tness is increased by the interaction EX ants get shelter in the thorns and food Acacia tree gets protection both get bene ts widespread mutualism includes pollination and seed dispersal speech richness number of species in a community relative abundance some species are numerous some are rare species diversity gt Higher diversity communities tend to be more stable they are also less affected by disturbances like drought less likely to be invaded by a nonnative species Tropic Structure feeding relationships Food Chains about 10 transfer energy as from 1 trophic level to the one above thus usually lt 5 trophic levels Food web diagram of feeding trophic relationships in a community Control of Community Structure TopDown controls go from HIGHER to LOWER trophic levels BottomUp controls goes from LOWER to HIGHER trophic levels remember that both differ communities are not always at equilibrium stays the same ecological succession Secondary Succession Where solid and some species remain after a disturbance EX forest fire gt Also ecological succession in our mouth Pathogens can play important in ecological communities Zoonotic Pathogens When spread from animals to humans
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