significant quantities for a small proportion of the year (short CPI), which will
lead to a high annual P/B. Even taxa achieving a relatively large body mass can
have relatively high annual P/Bs if they follow this life-history pattern (Huryn,
2002 ). The second pattern – of greater interest from a bioenergetic perspective –
is multiple generations year^1 , each with a short CPI. This pattern is common
for many stream invertebrates, such as chironomid midges, black flies and
many baetid mayflies (Benke & Parsons, 1990 ; Benke & Jacobi, 1994 ; Benke,
1998 ). Given the universal constraints of eukaryotic anabolism, organisms with
the very short CPIs (e.g.<1 month) tend to have a very low body mass.
Given this simple relationship it should not be surprising therefore that body
size and development time are correlatedandthat body size is closely related to
annual and daily P/B (Fig.4.10, right). Yet there are so many exceptions to this
relationship, as suggested by the wide scatter of data when annual P/B is plotted
against body mass (Fig.4.10, right), that it can hardly be considered a rule. This is
because taxa with a small body mass exhibit a wide range of annual P/Bs – from
very low to very high – while those with a large body mass tend to have
low annual P/Bs. For example, annual P/Bs for the often diminutive larvae of
the family Chironomidae (Diptera) range over four orders of magnitude
(<1–258; Butler, 1982 ; Benke, 1998 ; reviewed by Huryn & Wallace, 2000 ) while
their biomass usually ranges within a single order of magnitude. Obvious factors
underlying this variation are those directly affecting anabolic processes, such as
temperature and food quality and quantity. For example, it should be no sur-
prise that temperature, along with body size, explains a significant amount of
variation in time-specific P/Bs among populations (Plant & Downing, 1989 ;
Benke, 1993 ; Morin & Dumont, 1994 ; also see sources cited in the caption of
Fig.4.10). Furthermore, much variation in these data is because animals are
from multiple ecosystems representing a wide range of other factors such as
food quality and quantity. In spite of the poor fit (Fig.4.10, right; r^2 ¼0.31), it is
clear that high annual P/B can be demonstrated in small size classes.
The significant bioenergetic role that taxa with small body size may play within
food webs should never be underestimated. Although population biomass is
usually low for such taxa, high annual P/Bs can lead to enormous levels of
production of macrofaunal invertebrates (e.g. 65–135 gm DM m^2 yr^1 ,Jackson&
Fisher, 1986 ;Benke, 1998 ; reviewed by Huryn & Wallace, 2000 ). Unfortunately,
empirical knowledge of the production dynamics of meiofaunal benthic inverte-
brates as well as the smaller size-range of macrofauna remains primitive. Recent
attempts at quantifying meiofaunal production for stream and lake benthic
invertebrate communities indicate that levels may be similar to those estimated
for macrofauna (Bergtold & Traunspurger, 2005 ;Steadet al., 2005).
BIOMASS TURNOVER AND BODY SIZE 71