Unitary vs Modular organisms Modular organisms grow by repeated interations of its parts modules into an adult of indeterminate form coral poison oak Currencies energy nutrients time Allocation Genet genetic individual all the biomass that derived from single embryo Ramet subunit of genet that is physiologically viable as an autonomous fragment growth activity maintenance Reproduction offspring quality offspring quantity 1 2 Life history tradeoffs Life history trade offs of plants or animals Fig 52 6 Campbell Allocation to reproduction comes at expense of individual s own growth and possibly survival and vice versa Starting growth early in the season entails risk of freezing If reproductive resources allocated to larger seeds plant makes fewer so incurs more predation risk and risk of bad luck unfavorable microsites Dispersal reduces competition with parent but increases risk of unsuitable habitat modular unitary Unitary organisms develop from zygote to adult with determinant form Bet hedging by sea rocket half the seed 3 pod floats half sinks If resources are stored rather than spent on offspring a plant can quickly replace tissue lost to grazing fire wind and can survive over periods of starvation e g deciduous trees in winter 4 Population biology Trade offs Demography study of how the vital rate of individuals birth death growth affect structure and dynamics of populations Population group of potentially interbreeding individuals same species co occur in time and space 5 density number of individuals per area or volume size structure age distribution sex ratio ratio 6 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 Parent Ganet chicks 52 2 52 3 7 A peck apart 8 Intraspecific interactions between individuals of the same species vs Interspecific interactions between individuals of different species 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 9 T52 1 T52 1 10 Of course long before you mature most of you will be eaten T52 2 T52 2 11 52 3 52 5 12 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 13 Age structure of human population reflects age specific birth and death rates 14 Huge effect of age of first reproduction on population size in an expanding population B 3 N 4 9 B 8 N 4 8 Years B 2 N 4 16 A 1 A 2 A 4 B brood size N t population size at time t A age at 1st reproduction 15 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 16 dN dt b Nt d Nt b d Nt r Nt Nt Noert e 2 71828 base natural logarithm r intrinsic rate of natural increase is the per capita population growth under the most favorable of environmental circumstances probably at low density 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 b Nt d Nt b d Nt r Nt closed population r b d per capita rate of population growth time 1 17 18 If r 0 Density N r 0 population grows dN rN dt Time Human Population Explosion exponentially If r 0 population is in a stable equilibrium zero population r 0 growth although individuals turn over some die and are replaced by new births If r 0 population r 0 declines exponentially until it goes 19 extinct Billions of people 1650 0 5 1850 1 1930 2 1975 4 2000 6 20 Billions of people 1650 0 5 1850 1 1930 2 1975 4 2000 6 21 22 Campbell Fig 52 13 density dependence in per capita birth and death rates due to intraspecific within species competition mutually adverse interaction Per capita per individual birth or death rates 52 20 52 22 23 24 Demographic transition change from ZPG due to high death rate to ZPG due to low birth rate Numbers in Population r describes population growth at low density K describes density at which population stops growing K Logistic equation dN dt rN K N K 0 Time 25 Campbell Fig 52 11 26 r vs K selected life history traits r selected traits K selected traits K carrying capacity of population in a given environment Short life span Small size High predator vulnerability Weak competitor Good disperser Many small offspring Early reproduction K depends on both the environment and the organism in question Long life span Large size Low vulnerability to predators Strong competitor Slower disperser Fewer but better provisioned offspring Late reproduction 27 overshoot 28 Change in limiting factor Territoriality can produce this type of population growth e g speed limit versus regulation by enforcement of minimum and maximum speed N Density independent factors 29 Period of looser regulation Time 30 Analogy speed limit 60 mph regulated strictly 55 65 or loosely 40 80 Speeding Rapid population growth Fig 52 23 Campbell Ecological footprint footprint Estimate of land and water area needed to produce all resources a nation consumes and to absorb all the waste it generates rate r Strong densitysteering dependent feedbacks Distracted drivers Time lags in feedbacks Over N Time 31 Correlates 32 with K N
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