Lecture 19 - BIO220

statistical problem 1 they are taking obser ved data

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ases K (ppl s urvive longer to reproductive age) -birth control will reduce r. -Statistical Problem 1: They are taking obser ved data and trying to project it for ward i nto the future -Statistical Problem 2: Extrapolating beyond obser ved data is always a risk -Biological Problem 1: No option for oscillation to settle into K capacity (shoots up, crashes b ack down, eventually settles at K) The real human trajectory can’t be modeled simply • Growth (r) depends on balance of fertility rates (bx) and mortality (inverse of Lx) • Birth rates have been high for much of human history, but death rates dropped radically during the 19th 20th centuries • Changes in health care raised r – First vaccination & hygiene, then antibiotics, insecticides (Locke Rowe’s lectures) • Changes in agriculture raised K Ricklefs Ch. 12 -Differing degrees of oscillation due to the lag time from when D dependence is introduced -Green: approaches K, never gets above it Red&Blue: Density D occurs, but it has a time lag. Increased D effects will be felt in the f uture, not immediately. -Perhaps Allee was right.. we are just in the middle of a massive overshoot! -Perhaps there will be a correction and then it will come back down (We have no evidence to s uggest or refute this). Current guesses about trajectory • UN: rate is slowing, might level off at about 9 billion • In 1970, growing at about 2% per year, now down to about 1.2%, a big change… • …but still growing exponentially! • At present, adding 74 million per year • Leveling off requires less birth or more death Three scenarios (United Nations) Optimistic: In lower projections, declines are due to drops in fertility – Genetics, machines,...
View Full Document

Ask a homework question - tutors are online