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Biology Reading Notes.doc

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University of Toronto St. George
James Thomson

Biology Reading NotesChapter 10 Distribution and Spatial Structure of Populations1 Introduction Habitat fragmentation is damaging to many species small isolated subpopulations die out due to lack of genetic diversity Fragmentation reduces habitat quality smaller habitatcloser any particular point is to the edge serious consequences involving brownheaded crowbird Population individuals of a species within a given area but since habitats are often patchy subpopulations formThe extent or distribution of a population is the geographic area occupied by a population during is whole lifePopulation structure encompasses many attributes including spatial structure involves density and spacing of individuals 2 Populations are limited to ecologically suitable habitats Natural world varies so there are not uniform habitats extending across large areas Leads to concept of fundamental niche of species range of physical conditions over which species can persist However other factors such as predators pathogens and competitors can limit distribution of species to a smaller realized niche Angert and Douges study of different species of monkeyflowers in different elevational distributions low elevation monkeyflowers survived better at lower elevations and viceversa for high elevation onesDispersal limitationabsence of a population from suitable habitats because of barriers to dispersal These barriers can be overcome through humans carrying plants and animals with themMigration adds to the geographical distribution of species3 Environmental niche modeling predicts the distribution of species Ecological niche modeling uses known occurrences of a species in a geographical space to form an ecological envelope which can then be projected back onto geography to predict the native range of a species as well as its possible invaded range prediction 4 The dispersion of individuals reflects habitat heterogeneity and social interactions Dispersion describes spacing of individuals with respect to one another two typesclumped and spaced Clumped distributions may result form social predisposition to form groups clustered resources or tendencies of progeny to remain close to parentsSpace distributions may result from direct interactions between individuals and competition 5 The spatial structure of populations parallels environmental variations Species inhabit patches of suitable habitat and neglect unsuitable ones population is denser in suitable habitats But the density may be so high in suitable habitats that it the previously unfavorable habitats become equally as good candidates for inhabitation because of more resources availableideal free distribution each patch has same value for individual fitness regardless of intrinsic patch qualityIdeal free distribution is rarely realized in nature because of dominance of competitive species in good patchesIndividuals tend to disperse from high density to low density patches This is what can maintain marginal populations in lowdensity patches However this dispersion keeps populations on periphery to evolve greater tolerance of local conditionsdispersal hinders range expansion rather than promotes it 6 Three types of models describe the spatial structure of populations Metapopulation models describe set of subpopulations occupying patches of particular habitat type between which individuals move occasionallyIntervening habitat is known as the habitat matrix Sourcesink models add differences in quality of suitable habitat patches Source populations are located in high quality patches in which production of individuals exceed the death rate Thus individuals from source populations immigrate to sink populationspoor quality patches in which too few offspring are produced to maintain population without immigrationLandscape models add quality of habitat matrix as well into the picture This tells how likely it is for a species to move between subpopulations 7 Dispersal is essential to the integration of populations Dispersal links subpopulations together and makes the whole population function and evolve as single structure Lifetime dispersal distance of a species indicates how far individuals move on average from their birthplace to where they reproduce Neighborhood sizelifetime dispersal area times population density Species with small different densities and lifetime dispersal areas can have similar neighborhood sizesEx songsbirds high lifetime dispersal low density vs snails low lifetime dispersal high densityHaddads experiment with central patch connected to one peripheral patch and three other completely isolated patches Measure dispersal of species butterfly insectborne pollen and birddispersed fruits and seedsdiscovered that connected peripheral patch received more traffic from central patch than did isolated peripheral patches 8 Macroecology addresses patterns of range size and population density Geographic range and population density in the center of a distribution is positively correlatedPopulation density decreases with increasing organism size Population density decreases with body mass at the same rate that food consumption increasesEnergy equivalence rule populations tend to consume about the same amount of food per unit of area and thus have similar effects on population and ecosystem processes regardless of the size of individuals Chapter 16 Competition1 Introduction British Botanist AG Tansleys experiment with G slyvestre and G saxatile Three main results the presenceabsence of a species could be determined by competition with other species conditions of environment affect outcome of competition present ecological segregation of species may be result of past competitionInterspecific competition between different species and in intraspecific competition between individuals within a species competition More crowded the population more intense the competition Intraspecific comp regulates population growth in density dependent mannerIn interspecific comp species that can survive at lower resource levels outcompete the other However competition will depress population of both species to below their normal carrying capacities 2 Consumers compete for resources Resource any substance or factor that is both consumed by an organism and supports increased population growth rates as its availability in the environment increase Types of resources include space for sessile animals food refuges and other safe sites Usually competition between closely related species is more intense Darwins hypothesis but complex web of interactions leads to high rates of competition between nonrelated species also Ex birds and lizards eating similar food Renewable and nonrenewable resources
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