Download 1. What factors determine distribution and abundance of organisms

Big ecology questions:
1. What factors determine
distribution and
abundance of organisms ?
2. What limits and regulates
populations ?
3. How will organisms,
ecosystems or the planet
respond to changes in
climate, land use, or other
biota (extinctions,
invasions, changes in
traits) ?
Niches
(a la Hutchinson’s 1957 “hypervolume”)
• Niche: the limits, for all important
environmental factors (conditions and
resources), within which individuals of a
species can survive, grow, and reproduce
– Fundamental Niche: : The largest ecological niche
an organism or species can occupy in the absence of
adverse biotic interactions
– Realized Niche: The portion of the Fundamental
Niche occupied by a species subject to adverse biotic
interactions
Resources, conditions, and
the fundamental niche
• What determines the distribution and
abundance of species?
– In part, their tolerance of conditions,
and their need for certain resources
*condition: abiotic environmental factor that
varies in space and time and affects the
performance of organism
**resource: all things consumed (used up) by
organisms (space, nutrients, water, prey, holes
for refuge, etc)
Performance is generally nonlinear across a range of intensities of an
abiotic condition: more is good, even more is bad…
Homeostasis harder to
maintain when organism is
further outside of its
favorable range.
Performance of
species
Reproduction
Growth
s
g r
r g
s
cold
hot
Condition (e.g., temperature)
Survival
A resource can become a condition at high
or low levels, e.g., light, oxygen, water.
Distributions of organisms determined by cooccurrence of a number of critical (potentially
limiting) resources and conditions:
Phase diagrams
BTH Fig 2.2b
Light
grows
dies
Soil moisture
Light
grows
dies
Nitrogen
Stickleback Fundamental Niche
Salt, 30 ppt
Tolerates more salinity at colder
temperatures
Salinity
Tolerates warmer
temperatures at lower
salinity osmoregulatory
Stickleback
survives, grows
Fresh 0 ppt
Without
parasite
cold
warm
Temperature
“stress”—fish spends
metabolic energy to
avoid water loss
through gills, so has
less energy to spend
on other life
functions (e.g.
reproduction)
Salt, 30 ppt
Salinity
Without
parasite
Realized stickleback
niche if gill parasite is
present.
Realized Niche
with gill parasite,
tolerates narrower
range of conditions
H1. Gills damaged so can’t
osmoregulate as efficiently
H2. Parasites more
abundant under warmer or
more saline conditions
Fresh 0 ppt
Temperature
Degree days for ectotherms (BTH p. 33)
• For each 10oC rise in temperature, rate of biological
enzymatic processes often roughly doubles, until enzymes
denature (Q10 = 2)
• When growth or development increases nearly linearly
with temperature, “degree-days” rather than days
predict phenology (seasonal progression of biological
events—bud burst, insect emergence, etc.)
– With a physiological threshold = 10oC, mite takes 24 days to
develop at 15oC, and 8 days at 25oC. Development requires 120
degree-days above threshold at both temperatures.
0.2
% development completed day-1 0.1
0
10
20
30
Wessels 1997: “For the southern boundary, I have traced a line
where the proportions of eastern red cedar to common juniper in old
pastures is roughly equal….the change in species is due to decreasing
winter temperatures, to which the upright red cedar is less tolerant.”
Time dependencies
• Acclimatization (“acclimation in the lab): shifts in the
response of an organism to a condition caused by the
regime it has experienced in the past.
– E.g. trees can tolerate lower temperatures in
October than they can if surprised in mid-summer,
because they’ve induced new types of proteins and
restructured cell membrane phospholipids.
• Are organisms limited by the maximum level of a
condition, or by whether it lasts a certain period of
time?
– Crayfish or starfish displaced by short bursts of
fast flow, but if current increases gradually, may
hunker down and hold on
– Saguaro cacti can tolerate freezing if there is a
daily thaw, but can’t take it if freezing
temperatures last more than 30 hours.
Size dependencies
surface
Surface drag
FreeStream
velocity
Depth (cm)
Boundary layer
bed
Velocity (cm s-1)
Biomechanics at Berkeley: Mimi Koehl, Bob Full
Reynolds Number:
(Flow velocity x Object diameter)/ kinematic viscosity of fluid
High values—turbulence and form drag matter
Low values---viscosity and friction drag matter
Vogel (1981) Life in moving fluids
Neritic: nearshore subtidal
Benthos: life on substrate or
bed of sea, lake, spring, or
rivers and streams
Plankton: passive drifters
Nekton: active swimmers
zooplankton
phytoplankton
Stoichiometry
(Sterner and Elser 2002)
• Study of balance of
energy and multiple
chemical elements in
living systems
• Redfield Ratio (atoms):
C (106): N (16): P(1)
• Plants: C:N and C:P
generally higher than in
animals (varies among
taxa, tissues, age
groups)
• Detritus even worse
Redfield Ratio
Animal C:N:P
Plant C:N:P
Sterner and Elser 2002
Animals show
more strict
stoichiometric
homeostasis
than plants
Problem for
herbivores and
detritivores:
to get enough N
and P
Supplemental reading
Chapin, F. S., III, and G. R. Shaver. 1985. Individualistic growth response of
tundra plant species to environmental manipulations in the field. Ecology 66:564576.
Chapin, F.S., III. l980. The mineral nutrition of wild plants. Annu. Rev.
Ecol. Syst. ll:233-260
Sterner, R. W., and J. J. Elser. 2002. Ecological Stoichiometry: The biology of
elements from molecules to the biosphere. Princeton University Press, Princeton
NJ.
Thompson, D. A. 1942 (1917). On Growth and Form. Cambridge Univ. Press,
Cambridge, UK.
Vogel, S. 1981. Life in moving fluids. Princeton Univ. Press, Princeton, N.J.
Web sites:
http://cbc.berkeley.edu/thisweek.html (seminar
postings)
http://bie.berkeley.edu/index.htm (Berkeley Institute
of the Environment)