Demography - Principles of Biology - Lecture Slides, Slides of Biology

Download Demography - Principles of Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! • Life tables used to study demography Population ecology Where have all the sea otters gone? – Cohort life table = life table based on individuals of same age (i.e. a cohort) followed from birth to death • Survivorship (lx): proportion of individuals that survive from birth to age x Age (x) Number Alive (Nx) Survivorship (lx) 0 843 =843/843 = 1.000 1 722 =722/843 = 0.856 2 527 =527/843 = 0.625 3 316 =316/843 = 0.375 • lx= Nx/N0 Docsity.com • Life tables Population ecology Where have all the sea otters gone? – Mortality (Mx): Proportion of individuals that die between ages x and x+1 Age (x) Number Alive (Nx) Mortality (Mx) 0 843 =(843-722)/843= 0.143 1 722 =(722-527)/722 = 0.270 2 527 =(527-316)/527 = 0.400 3 316 – Mx= (Nx-Nx+1)/Nx Docsity.com Population ecology Where have all the sea otters gone? • Life tables summarize life-history traits – Life-history trait = traits associated with organism’s life cycle • age at first reproduction (maturity) • number of offspring (fecundity) • number of reproductive bouts (parity) – Semelparity = reproduce once in lifetime – Iteroparity = reproduce multiple times during lifetime • lifespan (aging) Docsity.com • Life-history traits Population ecology Where have all the sea otters gone? – Life histories involve trade-offs – Resources limited; if resources used for one life- history trait then fewer resources available for another life-history trait • Increased fecundity in birds correlates with higher mortality Docsity.com • Life-history traits Population ecology Where have all the sea otters gone? – Many other life history trade-offs observed • Early vs. late fecundity • Number and size of offspring – Nestling weight is smaller when clutch sizes are larger in Great tits – Uta lizards with surgically reduced clutch sizes produce larger eggs Docsity.com • Population growth Population ecology Where have all the sea otters gone? – Exponential growth • Population growth rate increases as population size increases Population size (N) Time (t) Population growth rate (dN/dt) is slope Docsity.com • Population growth Population ecology Where have all the sea otters gone? – Example of exponential population growth Docsity.com • Population growth Population ecology Where have all the sea otters gone? – Does population growth continue without limits? • Number of resources usually prevent populations from growing exponentially • Carrying capacity (K) = maximum number of individual that an environment can support – Population growth rate = 0 when population reaches carrying capacity – At carrying capacity, population birth rate = population death rate Docsity.com