Transcript K = Carrying capacity

CHAPTER 52 - POPULATION
ECOLOGY
Themes:
Heritable Information, Interaction
with the Environment, Regulation,
Evolution
Objectives:
• Two important characteristics of a population are density and the
spacing of individuals
• Demography is the study of factors that affect the growth and
decline of populations
• Life histories are diverse, but show patterns in their variability
• Limited resources mandate trade-offs between survival and
reproduction
• Exponential model of population - idealized population in an
unlimited environment
• Logistic model of population – incorporates the idea of carrying
capacity
• Negative feedback
• Population boom and bust cycles
• What is the carrying capacity for humans?
Root Words
•
•
•
•
•
•
Co –
Demo –
- graphy
Itero –
Semel –
- parity
(I) Population Dispersion:
1. Most common is clumped (ex. Humans). Why?
Because resources for us are usually in certain areas.
2. Know Other patterns – What organism would fit these patterns?
Note: Make sure you know the definition of Population.
(II) Life History:
1. R-selected populations (are opportunistic species) – usually
fish and marine invertebrates.
a. Usually small species that do not care for their young.
b. Large # of offspring in one reproductive episode/lifetime.
c. Survivorship is low. Populations fluctuate dramatically.
d. Curve # 3 Fig. 52.3. (Next slide).
Fig. 52.3 Survivorship Curves
(III) Population Density - # of organisms per area.
Formula : Organisms/area = 50 squirrels per 1 sq.mile.
(IV) Density – Independent Factor- Any factor influencing
population that acts to reduce population by the same %, regardless of
the size of the population.
Examples: earthquakes, tornadoes
(V) Density-Dependent Factor – Any factor influencing
population regulation that has a greater impact as population
density increases.
Examples – accumulation of toxic wastes; competition for
nutrients; predation.
(VI) K = Carrying capacity : maximum stable population size
that the environment can support over a long period of time. Many
times this is determined by energy limitations.
K selected species – equilibrium species.
K selected species – equilibrium species.
1. Repeated production of smaller # of offspring – better
endowed for survival.
2. Slow to mature, parental care. Usually large terrestrial vertebrates
(like humans). Offspring have a good chance of survival. Often
determined by the energy limitations of the organism
3. This is not the way most populations occur.
4. Fits the logistic equation.
5. Fits curve I in Fig. 52.3.
6. Differ among different
species but not within a given
species.
Cohorts – Group of
individuals of the same age.
Mark-Recapture Method – 1 Question : Process of Science
1. Used to estimate fish and wildlife populations –
populations that are very mobile.
2. Traps placed in area of study. Trapped animals are tagged
then immediately released.
3. After a period of time traps are set again. (enough time to
allow marked animals to randomly mix with the rest of the
pop.).
Formula (population sized N) =
# marked in the first catch x total # in second catch
# of recaptures in second catch
Big-bang Reproduction – A life history in which adults have but
a single reproductive opportunity to produce large numbers of
offspring. Also called semelparity ( Latin, semel – once & parito –
to beget) Example: Typical of the pacific salmon.
Certain things must occur:
1. Many gametes are produced by the parents at
reproductive maturity.
2. Could be that reproduction is triggered by an
“unpredictable” event.
3. A life span that could requires a number of years of
maturing before reproduction.
Life Tables – deal with mortality rates, fate of
cohorts newborns & organisms throughout their
lifetime.
Life Tables do
not show
Carrying
capacity!!
Good Table to show (r) vs (K) selected
populations.
Allele effect– Individuals may have a more difficult time surviving
or reproducing if the population size is too small.
1.Example – an individual plant may have a difficult
time surviving a strong wind but if there
were more individuals the chance of this
plant surviving would be increased.
2. Example -Predator might be more likely to be spotted if
a large number of prey are together than it
would be by a single prey animal.
4. Thus the allele effect is a density dependent factor
Demography – study of vital statistics that affect population
size.
Fig. 52.22 – Age Structure of Three Nations.
1. Which country will have the best chance of decreasing in the future?
Why?
2. Which country will be the most stable over a long period of time? Why?
3. Which country will have the worst future unemployment? Why?
4.Which country will probably experience ZPG? (Zero Pop. Growth) Why?
ZPG is
when # of
deaths = #
of births in
a given
time.
Figure from the Test: (5 questions)
HINTS: What is a Barnacle? Pg. 624.
How would any tree fit into this survivorship curve?
What is meant by molting? Pg. 615.
What curve would be impossible?