Population biology Demography study of how the vital rates of individuals birth death growth migration affect structure and dynamics of populations Population group of potentially interbreeding individuals same species co occur in time and space density number of individuals per area or volume size structure age distribution sex ratio ratio BIDE Equation for change in population size N N numbers in population Births Immigration Deaths Emigration 1 Dispersion pattern of distribution of individuals in space clumped even or random every site has an equal probability of being occupied by an individual independent of locations of other individuals 2 Parent Ganet chicks 3 Intraspecific interactions between individuals of the same species vs Interspecific interactions between individuals of different species A peck apart 4 Of course long before you mature most of you will be eaten Life and reproductive table summary of age or size specific rates of survival and fecundity progeny per individual Constructed by following a cohort a group of individuals of the same age from birth until they all die or by other methods that approximate this ideal approach 5 6 7 8 9 10 Age structure of human population reflects age specific birth and death rates Cohort life table for reproductives only ax number surviving to age x lx proportion original cohort alive at time age x mx fecundity of individual at age x lx mx number of progeny contributed per original individual of age x Basic Reproductive Rate Ro lx mx Ro is sum of progeny produced per original individual at the end of the cohort s life If Ro 1 population grows 11 12 Population growth Nt number of individuals at time t N Births Deaths population closed to migration N Births Immigration Deaths Emigration open pop N t rate of change dN dt rate of change over very small time interval dN dt b Nt d Nt b d Nt r Nt Nt Noert e 2 71828 base natural logarithm r per capita rate of increase N numbers of individuals in population t time b per capita birth rate number of births Nt 1time 1 time 1 if Nt 1000 and there were 34 births in a year b 0 034 year 1 d per capita death rate deaths Nt 1 time 1 time 1 if Nt 1000 and there were 16 deaths in a year d 0 016 year 1 dN dt bNt dNt b d Nt r Nt closed population r b d per capita rate of population growth time 1 r 0 Density N dN rN dt Nt Noert r 0 r 0 Time 13 If r 0 population grows exponentially If r 0 population is in a stable equilibrium zero population growth although individuals turn over some die and are replaced by new births If r 0 population declines exponentially until it goes 15 extinct 14 Elephants in Kruger National Park South Africa 16 Billions of people 1650 0 5 1850 1 1930 2 1975 4 2000 6 17 18 Huge effect of age of first reproduction on population size in an expanding population B 3 N 4 9 K carrying capacity of population in a given environment B 8 N 4 8 Years B 2 N 4 16 Campbell Fig 52 11 A 1 A 2 K depends on both the environment and the organism in question A 4 B brood size N t population size at time t A age at 1st reproduction 19 20 Campbell Fig 52 13 density dependence in per capita birth and death rates due to intraspecific within species competition Territoriality can produce this type of population growth Per capita per individual birth or death rates mutually adverse interaction overshoot Density independent factors 21 Change in limiting factor e g speed limit versus regulation by enforcement of minimum and maximum speed 22 Analogy speed limit 60 mph regulated strictly 55 65 or loosely 40 80 Rapid population growth rate r steering Strong densitydependent feedbacks Distracted drivers Time lags in feedbacks Speeding Over N Period of looser regulation Time N 23 Time 24 Demographic transition change from ZPG due to high death rate to ZPG due to low birth rate r vs K selected life history traits r selected traits K selected traits Short life span Small size High predator vulnerability Weak competitor Good disperser Many small offspring Early reproduction 25 Long life span Large size Low vulnerability to predators Strong competitor Slower disperser Fewer but better provisioned offspring Late reproduction 26
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