This is the same power point we are using in class.

1. Ch 36 Population Ecology
Goals
• Define population, density, dispersion, and demography.
• Explain how age structure, generation time, & sex ratio are important in
determining the growth & decline of a population.
• Explain what a survivorship curve shows & describe the 3 types.
• Define life history & explain why trade-offs must be made between
putting energy into reproduction & survival.
• Discuss 3 basic factors that determine an organisms life history.
• Distinguish between exponential growth & logistic growth. (no math
please)
• Explain how density – dependent & density independent factors regulate
population growth.
• State the current human population & explain why it’s so high and still
growing.
• Explain why different countries have different population growth rates.

2. Ch 36 Population Ecology
Population –
• single species
• rely on same resources
• influenced by similar env factors
• high chance of interacting
2 important characteristics - density & spacing (dispersion)
• Clumped, uniform, random

4. Demography - study of factors that affect
the growth & decline of pops
• Additions - thru births or immigration
• Eliminations –thru deaths or emmigration

5. Most important factors that determine growth
& decline of pop:
• Age structure – the # of individuals of each age.
• Ex: a pop with large % of individuals at prime
reproductive age will grow faster than one with a large %
of individuals who are older. (baby boomers)
• sex ratio – proportion of individuals of each sex
• # of females - good indicator of births
• # of males - less sig b/c they can mate w/ several females.
•Ex: deer hunting regs let you kill more bucks than does

6. Also important in determining growth &
decline:
• generation time – ave span between the
birth of individuals & the birth of their
offspring
• small orgs have short gen times
resulting in faster pop growth

7. Survivorship Curves
• a plot of # in a pop still alive @ each age
• 3 types:
• Type I – humans & large mammals that have few offspring
but take good care of them
• Type III – fishes & marine invertebrates
• Type II – mortality is constant over the lifespan –
rodents, birds

8. Life history – the traits that affect an
orgs schedule of reproduction & death
• Limited resources mandate tradeoffs b/t
investments in reproduction & survival
• Remember – Darwinian fitness is measured by how
many offspring survive to produce their own
offspring
• Trade – offs are involved – “should I invest E in my
survival or in my reproduction?”
• Experiments have been done that show if less eggs
are layed, the female lives longer – this shows the
trade – off.

9. 3 basic questions determine an orgs life history:
1. # rep events per lifetime
• Just once?
• Ex:
• many times?
• Ex: perenial plants, mammals
2. # of offspring per rep episode
• if chances of parent surviving to reproduce again are low, then…
• if chances of parent surviving to reproduce again are high, then …
• if chances of offspring survival are low, then …. Ex:
• if chances of offspring survival are high, then ... Ex:
3. Age @ 1st rep
• if delay first reproduction, then benefits are -
• if delay first reproduction, drawbacks are –

10. 3 basic questions determine an orgs life history:
1. # rep events per lifetime
• just once /many – when cost to parents of staying alive between
broods is great
• Ex: mosquito & pacific salmon
• many times /few each time – when parents are likely to survive but
immature individuals are not
• Ex: perenial plants, mammals
2. # of offspring per rep episode
• if chances of parent surviving to reproduce again are low, than have
many
• if chances of parent surviving to reproduce again are high, then have
few cause need to put E into own self survival
• if chances of offspring survival are low, then many. Ex: insects &
dandelions
• if chances of offspring survival are high, then few. Ex: mammals
3. Age @ 1st rep
• if delay first reproduction, then benefits are - don’t need to put E
into courtship, nest building, gamete production, or migration to
breeding areas
• if delay first reproduction, drawbacks are – may die before producing
any offspring at all.

11. 2 population growth models:
• Exponential growth – when reproductive rate is greater
than 0. Makes a J shaped curve.
– Carrying capacity not reached
• Logistic growth – when limiting factors restrict size of
the population to carrying capacity (K) of the habitat.
Makes an S shaped

12. POPULATION LIMITING FACTORS
Density dependent factors - regulate pop growth by varying
with density.
• As density increases, the density – dependent factor
intensifies, regulating the pop growth even more.
• Sometimes the density – dependent factor determines
the carrying capacity (K)
• Examples of how density – dependent factors regulate
pop growth:
Density independent factors - are unrelated to pop size –
they affect the same % of individuals regardless of pop
density.
• Examples of density – independent factors
• A mix of density – dependent & density – independent
factors probably limits the growth of most pops

13. Some pops have regular boom & bust cycles

14. HUMAN POP GROWTH
growing almost exponentially for centuries. Why so high?
• birthrates increased & deathrates decreased when we became farmers
instead of hunters & gatherers.
• Industrial revolution decreased death rates, esp infant
• Better nutrition , medical care, & sanitation
What factors may limit our growth?
• Food –technology has helped us keep up. Do better if all vegetarians
• Space? - seem to be few limits on how closely humans can be crowded
• Limited resources –metals & fossil fuels
• own wastes
Diff countries have diff pop growth rates – Why?
• age structures
• Sweden – uniform age distribution
• Mexico – many more of reproductive age
• US – fairly even except baby boomers from post WW2 (1945)
What makes our fate in terms of pop growth diff from other orgs is that we can
consciously control it. It’s up to us!

15. Mexico – past & present

17. Human pop growth

19. Current est world pop of humans:
6,768,181,146 (July 2010 est.)
By country:
https://www.cia.gov/library/publications/the-
world-factbook/rankorder/2119rank.html