BIO10& ch.&19&& Populations&&&Communities&&127&Chapter 19 Populations & Communities  Ecology  Population Dynamics  Competition Shapes Communities  Species Interactions/ Relationships  Coevolution/symbiosis  Predation/ animal defenses  mimicry Levels of Ecological Organization Populations Species Communities Ecosystems Biomes BiosphereBIO10& ch.&19&& Populations&&&Communities&&128& Population Growth What is a population? a group of individuals of a species that live together and influence each other’s survival Properties that describe Populations  population size is the number of individuals in the population  population density is the population size that occurs in a given area  population dispersion is the scatter of individuals within the population’s range  Population dispersion o The scatter of individual organisms within the populations range.  Population Growth o its capacity to grow o Biotic potential, r, o rate at which a pop of a given species increases when no limits are placed on its rate of growth o assumes a population grows w/o limits at max rate o No matter how rapidly populations grow, they eventually reach a limit imposed by shortages of important environmental factors o A population ultimately stabilizes at a certain size, called the carrying capacity o K o the max # of individuals that an area can supportBIO10& ch.&19&& Populations&&&Communities&&129&—The sigmoid growth curve is characteristic of most biological populations —The processes of competition and emigration tend to increase as a population approaches its carrying capacity The Influence of Population Density  commercial fisheries  attempt to operate so that they harvest a population near its point of maximal sustainable yield Maximal sustainable yield  The consequences of exponential growth Population Demography  statistical study of populations  measures characteristics of populations and helps predict how population sizes will change in the future  populations grow if # births > deaths and shrink if deaths outnumber births  birth and death rates are dependent on age and sex  Cohort: a group of individuals of same age Characterisitcs of a cohort  fecundity, or birthrate, ( # of offspring produced )  mortality, or deathrate, (# of individuals that die in that period)  the relative number of individual’s in each cohort defines a populations age structureBIO10& ch.&19&& Populations&&&Communities&&130& Sex ratio: proportion of males and females in pop  # of births is usually directly related to the # of females  Age distribution: the proportion of individuals in different age categories  when a pop lives in a constant environment for a few generations, its pop size remains fairly constant = stable population A survivorship curve  expresses the age distribution characteristics of a population  survivorship is defined as the percentage of an original population that survives to a given age there are three types of survivorship curves —type I has highest mortality for the youngest individuals —type II has relatively the same mortality risk for all ages —type III has highest mortality for the oldest individualsBIO10& ch.&19&& Populations&&&Communities&&131&Communities A community is the component of an ecosystem that is living communities named by their most dominant species (usually a plant) Niche and Competition The niche concept  Niche: an organism’s biological role ○ a pattern of living  the sum of all ways an organism uses the resources of its environment, (space, food, etc)  Fundamental niche is the entire niche that an organism may theoretically occupy  Realized niche is the actual niche that the organism is able to occupy because of competition NICHE: all the ways an organism utilizes the resources of its environment  sometimes species are not able to occupy their entire niche because of the presence or absence of other speciesBIO10& ch.&19&& Populations&&&Communities&&132& Competition: 2 organisms attempt to use the same resource when there is not enough of the resource to satisfy both  interspecific competition occurs between individuals of different species  intraspecific competition occurs between individuals of the same species How species evolve to occupy different niches within an ecosystem Species in communities act to avoid competition whenever possible 2 outcomes are possible 1. competitive exclusion (i.e., winner takes all) 2. resource partitioning: divide up resources creates 2 niches persistent competition between two species is rare in natural communities  either one species drives the other to extinction or natural selection reduces the competition between the them Principle of competitive exclusion ecologists say no 2 species with the same niche can coexist when 2 species compete for same resource, the superior competitor will drive its rival away Resource partitioning natural selection favors changes among competitors to reduce the competition between them each species can avoid competition by using different resources than competitors this reduces niche overlapBIO10& ch.&19&& Populations&&&Communities&&133&  Resource partitioning in warblers Resource partitioning can often be seen in similar species that occupy the same geographical area  such species are sympatric  they tend to exhibit greater differences in morphology and behavior then the same two species do when living in different habitats (i.e., when they are allopatric)  the evident differences are called character displacement  facilitate habitat partitioning and reduce competition Resource partitioning among lizards Coevolution and Symbiosis Coevolution: adaptation of a species not only to its physical environment but also to the other organisms that share it examples of coevolution include —plants and animal pollinators —predator-prey interactions —symbiotic relationships Many flowers have coevolved with other species to facilitate pollen transfer.BIO10& ch.&19&& Populations&&&Communities&&134&Species Interaction Coevolution: the long term evolutionary adjustments of species to one another  Symbiosis  Mutualism  Commensalism  Parasitism