Dynamic Biological Processes Influence Population Density Dispersion and Demographics Population group of individuals of a single species living in the same general area Rely on same resources Influenced by similar environmental factors Likely to interact and breed Described by boundaries and size Density and Dispersion Density number of individuals per unit area or volume Dispersion pattern of spacing among individuals within the boundaries of the population Density A Dynamic Perspective Mark Recapture Method estimate the size of wildlife populations Immigration influx of new individuals from other areas Emigration movement of individuals out of a population and into other locations Patterns of Dispersion Clumped Patches Plants and fungi in areas of nutrients Swarm to increase chances of mating Defense Uniform Evenly spaced from direct interactions Territoriality defense of a bounded physical space against encroachment by other individuals Random Unpredictable spacing Independent of other individuals Demographics Study of the vital statistics of populations and how they change over time Main interests birth and death rates Life Tables Age specific summaries of the survival pattern of a population Constructed following cohort group of individuals of the same age from birth until death Determine number of individuals that die in each age group Survivorship Curves Graphic method of representing some of the data in a life table Indicate rates of death Type I flat at the start drops steadily with increased age Type II constant death rate Type III drop sharply at start and then flatten Dynamic Biological Processes Influence Population Density Dispersion and Demographics Density and Dispersion Demographics cont Reproductive Rates Reproductive Table fertility schedule age specific summary of reproductive rates in a population Constructed by measuring the reproductive output of a cohort from birth until death The Exponential Model Describes Population Growth in an Idealized Unlimited Environment Unlimited growth does not occur in nature Studying population growth in an ideal unlimited environment reveals how fast a population is capable of growing and the conditions under which rapid growth might actually occur Per Capita Rate of Increase Change in population Births Immigrants Deaths Emigrants N B D t N is population size t is time B is births D is deaths B bN N bN mN t N is population size t is time B is births m is per capita death rate r b m per capita rate of increase Zero Population Growth Rate occurs when the per capita birth and death rates are equal N rN t N r inst N t Usually measured instantaneously Exponential Growth Exponential Population Growth population increase when members have access to abundant food and are free to reproduce at their physiological capacity N r max N t The Logistic Model Describes how a Population Grows more Slowly as it Nears its Carrying Capacity Carrying Capacity K maximum population size that a particular environment can sustain Energy shelter refuge nutrients water and nesting sites are all limiting factors The Logistic Growth Model Logistic Population Growth per capita rate of increase approaches zero as the carrying capacity is reached K N N r max N t K K N represents no growth As N approaches K the growth rate drops The Logistic Model Describes how a Population Grows more Slowly as it Nears its Carrying Capacity cont The Logistic Model and Real Populations Logistic model assumes the populations adjust instantaneously to growth and approach carrying capacity smoothly Populations to not adjust instantaneously to growth Allele effect individuals may have a more difficult time surviving or reproducing if the population size is too small Important in conservation biology to predict how rapidly population might increase Life History Traits are Products of Natural Selection Life History traits that affect an organism s schedule of reproduction and survival Includes when reproduction begins how often it reproduces and how many offspring it produces Evolution and Life History Diversity Evolution accounts for the diversity of life Semelparity one shot pattern of big bang reproduction matures for a few years releases thousands of seeds eggs and then dies Iteroparity repeated reproduction organisms produce few but large offspring 2 factors contribute to evolution of semelparity vs iteroparity Survival rate of the offspring Likelihood that the adult will survive to reproduce again When survival rate is low semelparity is more common Iteroparity is more common in dependable environments Trade offs and Life Histories Cannot produce as many as semelparity or as well as iteroparity Tradeoff between reproduction and survival Populations with high death rates produce a lot of smaller organisms K Selection density dependent selection selection for traits that are sensitive to population density high densities near carrying capacity maximise K r Selection selection for traits that maximise reproductive success in uncrowded environments low densities maximise r per capita rate of increase Many Factors that Regulate Population Growth and Density Dependent Population Change and Population Density Density Independent a birth or death rate that does not change with population density Density Dependent death rate rises as population density rises Birth rate is usually dependent and death rate is independent Mechanisms of Density Dependent Population Regulation Feedback regulation applies to population dynamics W o negative feedback btwn population density and birth death rates a population would never stop growing Increased density causes growth rates to drop by affecting reproduction growth and survival Many Factors that Regulate Population Growth and Density Dependent cont Population Dynamics Population dynamics population fluctuations from year to year or place to place influenced by many factors and in turn affect other species Stability and Fluctuation Weather and competition can cause even the largest of species to see significant increases decreases in their population Population Cycles Scientific Inquiry Some populations undergo regular boom and bust cycles Immigration Emigration and Metapopulations Immigration and emigration are particularly important when a number of local populations are linked forming a metapopulation Populations in metapopulation can be thought of as occupying discrete patches of suitable habitat in a sea of otherwise unsuitable The Human