Principles of terrestrial ecosystem ecology.pdf

Table 10.1. Basic properties
of water and air that influence
ecosystem processes.
plankton from the euphotic zone, the uppermost
layer of water where there is enough light
to support photosynthesis. Coping with this frequent
disturbance requires rapid cell division,
small size, and, for larger organisms, the capacity
to swim. The small size of phytoplankton
results in a high surface to volume ratio that
maximizes their effectiveness in absorbing
nutrients. Many marine plankton are particularly
small (nanoplankton are 2 to 20mm in
diameter, and picoplankton are less than 2mm
in diameter) and have a competitive advantage
where nutrients are extremely dilute.
Picoplankton, for example, account for half of
the plankton biomass of the highly nutrientimpoverished
tropical oceans (Valiela 1995).
The size and lifespan of marine organisms
increases going up the food chain (Fig. 10.1).
The size of aquatic organisms determines
their feeding strategy.Water is a polar molecule
Generation time (d) [log scale]
10 5
10 4
10 3
10 2
10
1
0.1 10 2
0.1
Ecosystem Properties 225
Property Water Air Ratio of water to air
Oxygen concentration (ml L -1 ) 7.0 209.0 1:30
Diffusion coefficient (mm s -1 )
Oxygen 0.00025 1.98 1:8000
Carbon dioxide 0.00018 1.55 1:9000
Density (kg L -1 ) 1.000 0.0013 800:1
Viscosity (cP) 1.0 0.02 50:1
Heat capacity (cal L -1 (°C) -1 ) 1000.0 0.31 3000:1
Data from Moss (1998).
Marine Terrestrial
Plants Herbivores
Carnivores
10 5
Figure 10.1. Body size and generation time for
organisms in the ocean (Steele 1991) and on land of
dominant plants, herbivores, and carnivores. In
the ocean the dominant plants (picoplankton and
that sticks to the surface of organisms. The
movement of small organisms and particles is
impeded by these viscous forces. Large organisms,
in contrast, can swim, and their speed is
largely determined by inertia. The Reynolds
number (Re) is the ratio of inertial to viscous
forces and is a measure of the ease with which
organisms can move through a viscous fluid like
water.
Re = (10.1)
The movement of organisms through water is
not strongly impeded for organisms with a large
length (l) and velocity (v) and under conditions
of low kinematic viscosity (Vk) (Fig. 10.2). Small
planktonic organisms must deal with life at a
low Reynolds number, where viscous forces
are much stronger than inertial forces. At these
small sizes, swimming and filter feeding are
lv
Vk 10 8
0.1 10 2
Length (µm) [log scale]
Herbivores and
carnivores
10 5
Plants
10 8
nanoplankton) are generally smaller than the herbivores
that feed on them, whereas on land, the dominant
plants are often as large or larger than the
herbivores that eat them.