BIOB50H3 Chapter Notes - Chapter L#9: Geometric Distribution, Mountain Pine Beetle, Heath Hen
CHAPTER 11: POPULATION DYNAMICS (LECTURE #9) 249-262
-eutrophication: increase in the nutrient content of an ecosystem
washing down fertilizers has serious effect on aquatic communities b/c
phytoplankton concentrations increase, and oxygen decreases Mnemopsis jellyfish
was introduced ate lots of zooplankton (who are phytoplanktons main consumers)
led to little zoo plankton, lots of phytoplankton phytoplankton decompose =
bacteria at bottom decomposed them = bacteria activity increased = less oxygen =
less fish
INTRODUCTION
- can summarize effects on population size w/ equation
Nt = pop. Size at time t
B = # of births
D = # of deaths
I = immigration
E = emigration
- Ecologists use term population dynamics to refer to how populations change in
abundance over time
PATTERNS OF POPULATION GROWTH (11.1)
- Most observed patterns of pop. Growth can be grouped into 4 types: exponential,
logistic, population fluctuations, and regular population cycles (special type of
fluctuation)
Exponential growth can occur when conditions are favourable
- In exponential growth, population increases/decreases by a constant proportion at each
point in time
Reproduce in synchrony
Reproduce continuously
- Exponential growth doesn’t occur indefinitely, but if conditions are favourable, can
increase exponentially for a limited time (eg. Good weather for sev. Years, enters new
env. grows rapidly until density dependent factors regulate its numbers)
Eg. How dispersal leads to exponential growth Cattle egret (bubulcus ibis ibis)
lived in meditaraneean before, but since 1900s, have colonized new regions
(including NA and SA) bonce reached Florida pop. Increased w/ r = 0.11, until
stabalized by the 1980s
Jump dispersal events: species that successfully colonize new geographic regions on
their own by long-distance moving local pop. In the region then increase in rise,
while also occupying nearby habitat
In Logistic growth, the population approaches an equilibrium
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- Pop. Appear to be relatively stable # of indiv. First
increases in size, then fluctuates a relatively small
amount around what appears to be the maximum
sustainable population size
Pop. Growth doesn’t match predictions of logistic
growth precisely eg. Sheep abundance in
Tasmania are similar to S-shape curve, but roughly
apply concept of logistic growth to any pop. Whose
numbers increase initially but then level off and
fluctuate around the carrying capacity
oDoes not
match logistic
equation b/c “K” is assumed to be constant
for it to be constant
however, birth/deaths
rate must not change
yearly rarely ever
happens in nature
- birth/death rate may take on a
range of values thus K change
over time when K changes, we
can expect population size to
fluctuate around an average K value
All populations fluctuate in size
-population fluctuations: population
size rises and falls over time
can be erratic
increases/decreases in
abundance from overall mean
some fluctuations can be really
small, while sometimes
outbreaks happen: # of
individuals in a population explode (eg. Mnemiopsis outbreak in 2 years exploded
1000 fold)
-some outbreaks have huge ecological effects eg. Mountain pine beetle has killed
millions of trees across BC, Canada
Some species exhibit population cycles
- Alternating periods of high and low abundance in intervals of time
Factors can be: hormonal or behavioural responses to crowding
DELAYED DENSITY DEPENDENCE (11.2)
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Document Summary
Chapter 11: population dynamics (lecture #9) 249-262 eutrophication: increase in the nutrient content of an ecosystem. Washing down fertilizers has serious effect on aquatic communities b/c phytoplankton concentrations increase, and oxygen decreases mnemopsis jellyfish was introduced ate lots of zooplankton (who are phytoplanktons main consumers) Led to little zoo plankton, lots of phytoplankton phytoplankton decompose = bacteria at bottom decomposed them = bacteria activity increased = less oxygen = less fish. Introduction can summarize effects on population size w/ equation. Ecologists use term population dynamics to refer to how populations change in abundance over time. Growth can be grouped into 4 types: exponential, logistic, population fluctuations, and regular population cycles (special type of fluctuation) Exponential growth can occur when conditions are favourable. In exponential growth, population increases/decreases by a constant proportion at each point in time. Exponential growth doesn"t occur indefinitely, but if conditions are favourable, can increase exponentially for a limited time (eg. good weather for sev.
