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Ch52 - Ch52 Population Ecology(cond 1 fecundity is also a...

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Ch52: Population Ecology (con’d) 1. “fecundity” is also a key part of a life table; it’s defined as # of females produced by each female. 2. An organism’s “life history” consists of how it allocates its resources to growth, repro, and activity related to survival. SURVIVAL VS REPRODUCTION. 3. Ex) In France, 50% of 1-yr-old female L. Vivipara lizards reproduce, but they don’t all survive. Fecundity is high but survivorship is low in France. Even within the species, there’s variation in life-history traits. 4. Life-history traits form a continuum. Orgs w/ low fecundity have high survivorship n tend to grow slowly, and invest time in traits that help them survive. 5. The mustard plant Araidopsis thaliana grows to sexual maturity fast, but only live a few months. However, life-history traits can change if conditions change. 6. A population’s growth rate is change in # of Indivs in popu (N) per unit time (t). 7. If NO immigration OR emigration is occurig: growth rate=N.r. R is the “per-capita rate of increase” and is the diff bet (r=b-d) birth rate n death rate. 8. If birth rates r as high as possible and death rate r as low, then r reaches maximum called “intrinsic rate of increase”, rMax. Each species w/ certain life history has characteristic Rmax that does NOT change. But @ any time, the “per-capita rate of increase” of each popu is likely to be much LOWER THAN RMAX. 9. A population’s r is also likely to be diff from r values of other populations of SAME species and to CHANGE over time 10. “Exponential popu growth” occurs when r doesn’t change over tim e. It doesn’t depend on # of indivs in population. When increases in size of popu do not affect r, growth is “density independent” Exponential growth is observed when ppl found new habitats, but can’t continue. Exponential growth is indep of population size 11. However, when “popu density”--# of indivs per unit area—gets very high, popu’s per-capita birth rate shud decrease n death rate increases, so r declines. So in the natural world, it’s mostly density DEPENDENT. 12. Carrying capacity, K, can change depending on conditions. If population is below the Carrying capacity, the popu shud continue to grow. It shud be proportional to (K-N)/K, which is the proportion of “unused resources n space”.When N is small, it’s close to 1, and growth rate is high. This is called “logistic growth equation” and describes “logistic population growth”—change in growth rate that occurs as function of popu size. 13. Density-dependent growth for popu has 3 sections: exponential growth, then begins to decline(N increases, density dependent), growth rate reaches 0 @ carrying capacity (graph is FLAT) 14. populations change as a result of BOTH density-Independent n dependent factors.
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