organization. When scaled beyond the level of the individual, production is a
flow or flux per unit of time (e.g., amount of biomass formed per unit of area per
unit of time, mg m^2 yr^1 or mg m^2 d^1 ). Estimating secondary production is
labor intensive, when compared with estimates of abundance or biomass alone.
One must also be able to either follow cohorts through time, know biomass-
specific growth rates (for instance, mg mg^1 d^1 ), or know mean developmental
times (cohort production interval or CPI, d) (Benke & Huryn, 2006).
The rate of production is conveniently expressed as either the cohort or time-
specific (e.g. daily or annual) biomass turnover. The cohort biomass turnover
(P/B over the length of the CPI) ranges within one order of magnitude (2–8,
Fig.4.10, left), and 5 has long been used as a proxy for expected cohort P/B
(Waters, 1969 ). This relative consistency is due to the limited range of the
logarithm of the ratio of the mass of the final to initial larval mass (Waters,
1987 ). The cohort P/B shows a strong positive relationship with body size
because the relative increase in body mass during the CPI is greatest for taxa
attaining a large body mass (Fig.4.10, left).
The cohort P/B can be easily converted to a time-specific biomass turnover rate
if one knows the approximate length of a population’s CPI because the annual
P/B is approximated as 5365/CPI. For example, if a CPI¼30 days, then the
associated annual P/B 5 365/3060. In this example, biomass would replace
itself 60 times throughout the year and the biomass turnover time would be 365/60
or12 days. Similarly, the daily P/B can be approximated as 51/300.17. The
daily P/B is essentially the same as g, the daily biomass growth or turnover rate
(see Benke & Huryn, 2006 , for algorithm used to calculate g).
In summary, an organism with a CPI that approximates 1-year will show
annual P/Bs ranging from2 to 8. One that has a CPI 1-year will show a low
annual P/B (e.g.<2, Huryn & Wallace, 1986 ), and one that has a CPI 1-year will
show a high annual P/B (e.g.>20, Benke, 1998 ). The annual P/B for most species
of freshwater invertebrates was once widely believed to vary from<5 (species
with CPIs longer than a year) to about 5–10 (species with CPIs6 months to
1 year; Waters, 1977 ; Banse & Mosher, 1980 ). However, detailed studies of
species in warm-water systems have shown that CPIs can be<1 month and
daily g can be>0.1 d^1 ; thus, annual P/B can be substantially greater than 10 or
even 100 (Benke & Parsons, 1990 ; Benke & Jacobi, 1994 ; Benke, 1998 ; Jackson &
Fisher, 1986 ; reviewed by Huryn & Wallace, 2000 ). In fact, some species living in
coldwater environments can also have relatively high growth rates and short
CPIs (Huryn & Wallace, 1986 ; Nolte & Hoffman, 1992 ) resulting in annual P/B
ranging well above 20 (reviewed by Huryn & Wallace, 2000 ).
Two very different life-history patterns underlie high rates of biomass turn-
over. The first is a single generation year^1 followed by a long period of devel-
opmental quiescence (e.g. resting egg). In such cases, biomass will be present in
BIOMASS TURNOVER AND BODY SIZE 69