Secondary Production and Consumer Energetics - Fundamentals of Ecosystem Science - page 56

TABLE 3.2 Overview of methods used to estimate secondary production (for details, see Downing and
Rigler 1984; Benke 1984; Kemp et al. 1993; Servais 1995 ).

Organism Method Data Requirements Limitations

Bacteria Tracers (radioactive

nucleotides or amino
acids)

Uptake of label Subject to large errors because of

(1) critical assumptions about fate
and use of label and nonradioactive
analogues, which may be hard to test;
(2) uncertain conversion factors to get
from uptake of label to carbon
production

Fungi Ergosterol synthesis

(from radioactive
acetate)

Uptake of label into ergosterol Method still under development;

potential problems similar to those
for bacterial production

Animals with
recognizable
cohorts

Increment
summation, mortality
summation, Allen
curve

Density and body size of animals
at frequent intervals over the life
of the cohort

Data intensive

Animals
without
recognizable
cohorts

Growth increment
summation,
instantaneous growth

Density, body size, and growth
rates of animals in various size
classes throughout the year

Data intensive; growth rates often
measured in the lab and extrapolated
to the field

Egg ratio Density and development time of

eggs, body mass of animals at
death

Suitable only in the special case in
which the body mass at death is
known

Size-frequency
(“Hynes method”)

Density and body size of animals
in various size classes throughout
the year

Data intensive

Any organism Empirical models Population biomass; perhaps body

size, temperature, habitat type

Subject to large error; may be data
intensive

amounts of 14 C-labeled acetate, which is incorporated into ergosterol, a chemical com-
pound that occurs only in fungi. Organic carbon production is estimated from the amount
of radiolabeled ergosterol measured after the incubation. To get annual production of
microbes, incubations are run throughout the year in the various parts of the ecosystem
under study. Although relatively simple in spirit, these radiotracer methods make impor-
tant assumptions about the biochemical uptake, production, and destruction of labeled
compounds, and factors for converting from uptake of radiolabel to production of organic
carbon may be difficult to estimate. Thus, estimates of microbial production often have
large (or uncertain) errors and must be interpreted cautiously.
Animal production is sometimes estimated as the product of standing biomass and the
turnover rate of that biomass. Because turnover rates often change with animal size or
age, the population usually is divided into size-classes. Thus,

X

P 5 B i g i ð 3 : 5 Þ

i