population: carrying capacity and limiting factors in natural systems
DESCRIPTION
What is earth's planetary carrying capacity for a modern, industrialized humanity with a properous standard of living for all? Explores limits and population limiting factors in real-world and biospheric systems.TRANSCRIPT
What Every Citizen Should Know About Our Planet
Copyright 2012, The Wecskaop Project.All rights reserved.
This presentation is a courtesy of
The Wecskaop Project
It is entirely free for use by scientists, students, and
educators anywhere in the world.
Part One
Carrying Capacity
How many individuals can a particular ecosystem [or
planet] indefinitely support over a long period of time
while continuing to function and without suffering severe
or irreparable damage?
For scientists, the answer to such a question constitutes the system's carrying capacity
How many individuals can a particular ecosystem [or
planet] indefinitely support over a long period of time
while continuing to function and without suffering severe
or irreparable damage?
Since ecosystems are finite in their size and resources, each
has an upper limit to the population that it can support
while continuing to
and also provide the assorted ecological services
that allow a given population to exist
provide food resources withstand impacts and damage tolerate or withstand wastes maintain, perpetuate, and repair itself
Phytoplankton in the oceans, such as these
diatoms, producemore than half ofthe oxygen that
we breathe
So w
isdo
m re
com
men
ds p
rote
cting
the
m a
nd d
oing
them
no
harm
Since ecosystems are finite in their size and resources, each has an upper limit to the population
that it can support while continuing to
and also provide the assorted ecological services
that allow a given population to exist
provide food resources withstand impacts and damage tolerate or withstand wastes maintain, perpetuate, and repair itself
Examples of crucial ecological services include each day’s production and replacement of most of the molecular O2 that we and most other animals con-sume every few seconds
The fifty species of diatoms in the image above, forinstance, are examples of phytoplankton in the earth’s oceans
that produce more than half of the oxygen that we breathe
Wha
t hap
pens
if w
e de
stro
y th
em o
r dim
inis
h th
eir n
umbe
rs o
r wea
ken
thei
r abi
lity
to fu
nctio
n?
Pollination of vast percentages of flowering
plants everywhere,
and dramatic contributions to the
production of rainfall by the process of
transpiration.
Other ecological services include, for instance,
Wha
t hap
pens
if w
e de
stro
y th
em o
r dim
inis
h th
eir n
umbe
rs ?
Environmental carrying capacities need not necessarily involve foodand water, but can also reflect critical limits to the damages, wastes,
eradications, and impacts that they can safely withstand – and totheir capabilities for self-perpetuation, maintenance, and self-repair
Imagine an elevator, for example, thatcan safely accommodate 18 passengers and yet
83 or 247 or 1058 passengers begin to squeeze aboard
It is easy to understand that thestresses of excessive loading
virtually ensure failures in oneor more components, triggering thecollapse of the entire system and the
destruction of both the vehicleand its passengers
Not
ice
that
this
is q
uite
dif
fere
nt th
an M
alth
us’s
ass
essm
ents
invo
lvin
g fo
od;
So th
at th
e sc
ienc
e an
d un
ders
tand
ings
toda
y ar
e fa
r br
oade
r
A similar unsettling scenario can beenvisioned if one imagines
an aircraft of finite size,
only to notice that a line of more and more and more persons
continue to endlesslyboard the aircraft
It is thus important to appreciate that
carrying capacity inbiological and biospheric systems
is commonly far MORE than
simply a matter offood, or water, or “resources”
Overshoot
Thus, more and more persons endlessly boarding anelevator or aircraft or vehicle or planet
of finite capacity constitutesan egregiously-unwise behavior
Thresholds
A behavior that invites transgressions of at least one or more
Limits
Tipping Pointsand/or
Thousands of examples of thresholds, limits, and tipping points (both known and unknown) exist in
real-world natural and biospheric systems
As two quick examples of thresholds in real-world systems:
One instance in a biological system can be seen in human blood which has buffers that maintain its pH at a mildly alkaline 7.4 level. Seemingly small transgressions, how-
ever, beyond pH 7.3 (lower limit) or 7.5 (upper limit) result in acidosis or alkalosis, both of which are potentially fatal.
Real-world thresholds
All three classical examples experienced 99%-plus die-offs and collapse at a time when the combined bodies or cells of each of the populations physically-occupied roughly 2/1000ths of 1% of their surrounding environment that appeared to remain theoretically-available to them
All three classical examples experienced 99%-plus die-offs and collapse at a time when the combined bodies or cells of each of the populations
physically-occupied roughly 2/1000ths of 1% of their surrounding environment that appeared to remain theoretically-available to them
All t
hree
cla
ssic
al e
xam
ples
exp
erie
nced
99%
-plu
s di
e-off
s an
d co
llaps
e at
a ti
me
whe
n th
e co
mbi
ned
bodi
es o
r cel
ls o
f eac
h of
the
popu
latio
ns
phys
ical
ly-o
ccup
ied
roug
hly
2/10
00th
s of
1%
of t
heir
surr
ound
ing
envi
ronm
ent t
hat a
ppea
red
to re
mai
n th
eore
tical
ly-a
vaila
ble
to th
em
Not a very wisepolicy, was it?
Part Two
Limiting Factors
Examples of Limits, J-curves,Thresholds, and Limiting Factors
Also notice that this graph of human population growth over the past 10,000 years
is an extremeJ-curve
How worrying shouldJ-curves be?
Unfortunately, humankind first learned with horror what J-curves can do from unspeakably
deadly events at the close of World War II
Physicists know that exponential progressions and their resulting graphs
which are known as
J-curves
exhibit a decided tendency to obliterate everything
around themselves in every direction
A graph of this shape on the display monitorsof a nuclear power plant would send theplant’s engineers scrambling for the exits
Key Ideas
Appendix One
How Large is a Billion?
Appendix Two
What is Earth’s carrying capacityfor a modern, industrializedhumanity with a prosperous
standard of living for all?
Appendix Three
Links and Other Resources