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University of Regina
Maryann Vaughan

BIRTH AND DEATH RATES  ecologists use estimates of pop’n densities to estimate the rate at which births, deaths and movements take place in a pop’n and study how rates are influences by environmental factors  the number of individuals in a pop’n at given time is equal to the # present at some time in past plus the # born between then and now, minus the # tht died, plus the # that immigrated into teh pop’n, minus the # that emigrated  life table-created by tracking a group of individuals born at the same time (cohort) and determining the # that are still alive at later dates (survivorship)  used to predict future trends in pop’n  study of the seed-eating cactus finch-210 birds that hatched in 1978, followed until 1991, only 3 alive; mortality rates high during first yr then dropped for several yrs, then increase later; survival of birds depends on seed production which is related to rainfall  graphs are helpful for highlighting important changes in pop’ns  survivorship curves fall into 3 patterns: o most individuals survive for most of their potential life span and die about the same age o probability of surviving to the next yr is abt the same over most of the life span once individuals are a few months old o produce a large # of offspring, each of which receives little investment of energy  high death rates of young individuals are followed by high survival rates 54.2 HOW DO ECOLOGICAL CONDITIONS AFFECT LIFE HISTORIES  life history: describes how organism allocates its time and energy among the variance activities that occupy its life  female rockfish continue to grow throughout their lives; larger females are much more productive than smaller females b/c the # of eggs a female produces is proportional to her size; older, larger females produce eggs with larger oil droplets-provide energy to newly hatched- grow faster and survive better  guppies living in predator-free areas upstream from those waterfalls have low mortality rates; those that live below the falls have high mortality rates; david reznick reared 240 guppies from high-predation and low predation sites; supplied some with plentiful food and others with limited; where no predators were present, guppies from high-predation sites matured earlier, reproduced more 54.3 WHAT FACTORS INFLUENCE POPULATION DENSITIES  as the # of individuals in a pop’
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