1. Peppy Populations
Chapter 53

2. Population Ecology
Study of populations in relation to the environment

3. I. Population
A group of individuals of a single species in an area at the same time

4. Density The number of individuals per unit area or volume
Estimating: mark/recapture, counting individuals, counting signs (nests, burrow, etc)

5. Estimating Using Mark-Recapture
Capture random sample of individuals
“Mark” them and release
Allow them to mix back in with general population
Capture a second set
Record those that you already marked vs. those not marked

6. Equation for Mark/Recapture
N = mn x
N = population size
m = # of individuals marked in first sample
n = total number of individuals recaptured
x = # of marked animals recaptured

7. You try Original amount marked = 180
Total amount captured in second sample = 44
Amount marked when recaptured = 7
What is the estimated population size?

8. Dispersion Spacing among individuals within a geographic area
Can occur in patterns due to availability of nutrients
Clumped: individuals aggregated in patches
Uniform: evenly spaced, may be due to direct interaction between individuals
Random: unpredictable, occurs in absence of strong attractions or repulsions

9. Fig. 53-4
(a) Clumped
(b) Uniform
(c) Random

10. II. Changes in Population size (Demography)
Additions: birth or immigration
Declines: death or emigration

11. Life Tables
Follow a “cohort” – a group of individuals of the same age – from birth to death

12. Survivorship Curves
Survivorship curves: Plot of numbers in a cohort (same age) still alive at each age.

14. Survivorship Curves Type 1 curve:
Relatively flat at the start, low death rate during early life. Drops steeply in older ages (HUMANS)
Few offspring, good parental care

15. Survivorship Curves
Type II curve: Constant death rate over lifetime (some annual plants, lizards, some rodents)

16. Survivorship Curves
Type III curve: Drops sharply on left side because of high rate of mortality in early life. Flattens out at a certain age.
Lots of young, but little or no parental care (Fish, Spiders)

17. IV. Measuring Population Size (N)
Change in size during time interval = birth - deaths
∆N= bN-dN bN = per capita birth
∆t dN = per capita death
r = per capita birth – per capita death
If r is +, population is growing
If r is -, population is declining
If r is O = Zero population growth – no change in size

18. V. Exponential Population Growth
Ideal conditions, constrained only by life history (life span)
Maximum growth rate - J shaped growth curve, no population can remain here indefinitely

19. Carrying Capacity (K)
Maximum population size that a particular environment can support at a given time
Varies over space and time due to availability of resources
When N is small and K is large, rate of increase is large
When N is large and K is small, rate of increase is small
When N = K, Zero Population growth

20. K = carrying capacity
N = population size
Rmax = maximum rate
of increase

21. Logistic Population Growth
Mathematical model of population growth that incorporates changes in growth rate as population size nears the carrying capacity

23. Many organisms don’t fit this growth model exactly

24. III. Life History
Traits that affect an organism’s schedule of reproduction and survival (birth through reproduction to death)
Big Bang Reproduction (Semelparity)
Lots of babies in one big bang, then die
Salmon, agave (century plants)
Variable, unpredictable environments

25. III. Life History Repeated Reproduction (Iteroparity)
Reproduce annually, few young each time
Lizards
Dependable environments, adults able to survive to breed more than once

26. Effects of Brood Size on Parent survival

27. Life History Bottom Line
It all depends on the survival rate of the offspring
If poor, big bang is favored
If good, repeated is favored

28. VI. Logistic Population Growth (cont)
Life Histories and Logistic Population Growth
K-selection: density dependent selection, for crowded environment, favors adaptations that enable organisms to survive and reproduce with few resources

29. K-selection *Few young *High energy investment in each *Large young
*Slow sexual maturation
*Higher incidence of sexual reproduction
*Long reproductive span
*Lots of parental care
*Many reproductive events (iteroparous)
*Predictable environment
*Population control by density-dependant
*Long life span
*Type I survivorship curve; many survive
*Prone to extinction

30. B. Life Histories and Logistic Population Growth (cont)
2. R-selection: density independent, favors adaptations that favor rapid reproduction

31. r-selection *Many young *Little energy investment in each *Small young
*Rapid sexual maturation
*Higher incidence of asexual reproduction
*Brief reproductive span
*Little or no parental care
*”Big Bang” (semelparous)
*Unpredictable environment
*Population control by density-independant
*Short life span
*Type III survivorship curve; few survive
*Not prone to extinction

32. VII. Population Limiting Factors
Density Dependent (negative feedback)
Death rate rises as population density rises
Density Independent
Birth/Death rate don’t change with population density

33. VII. Density Dependent Regulation
Factors causing negative feedback
Resource limitation (sets up competition)
Territoriality
Availability of nesting sites
Health of organisms: crowded plants tend to be smaller than those with lots of space
Predation: predators can preferentially feed on most abundant prey
Accumulation of toxic waste
Disease: rate of spread higher in high densities

34. Describe what you think is shown in this graph

35. C. Population Dynamics
Looks at interactions between biotic and abiotic factors
Fluctuations with regularity that can’t be explained by chance alone

36. VIII. Human Population Growth
Human population has been growing exponentially for 300 years but cannot continue to do so indefinitely – growth rate is slowing
OVER 7.2 BILLION PEOPLE!
Demographic Transition
going from
Zero population growth = high birth-high death TO
Zero population growth = low birth - low death

37. How does this happen? Some countries regulate birth rate (China)
Voluntary contraception
Family planning
Social change - more working women, emphasis on career
Delayed reproduction

38. B. Age Structure Relative number of individuals of each age
Reveal populations growth trends and future social conditions

41. C. Earth’s Carrying Capacity
How many people/organisms can the earth hold?????

42. Ecological Footprint
Aggregate land and water area required by each person, city or nation to produce all the resources it consumes and to absorb all the waste it generates
Can measure in terms of land, photosynthetic products, nonrenewable resources etc.
i.e. – Estimates say that humans should use about 1.7 hectares per person of ecologically productive and – In the US a typical person uses 10 hectares

43. Fig
Log (g carbon/year)
13.4
9.8
5.8
Not analyzed