9780521861724htl 1..2

Understanding relationships with temperature, and improving biomass estimates

The widespread inverse relationships between temperature experienced

during ontogeny and both final body and offspring size in ectotherms (Atkinson,

1994 ;Atkinsonet al., 2001) has been termed the ‘temperature–size rule’ (TSR;

Atkinson, 1996 ). This plastic response of body size has been described as a

‘life-history puzzle’, because reduced growth rate (observed at lower temper-

atures) typically favours smaller, not the observed larger, body size (Berrigan &

Charnov, 1994 ;Atkinson&Sibly, 1997 ;Day&Rowe, 2002 ; Angilletta &

Dunham, 2003 ; Angillettaet al., 2004). However, life-history models can be

produced that are capable of accounting for the TSR (Kozłowski, Czarnołe ̨ski &

Dan ́ko, 2004 ), and these now need testing.

The TSR has been quantified for diverse protists (Atkinson, Ciotti &

Montagnes, 2003 ), which may be useful to ecologists wanting to estimate bio-

mass and predict rates of production (if biomass is estimated by cell counts

multiplied by an average cell volume for each species). Incorporating into

biomass estimates the cell-volume reduction of2.5% relative to volume at a

reference temperature (15 8 C) per 8 C increase (Atkinsonet al., 2003) could avoid

errors of about 25% over a 10 8 C range. However, as this result was derived for

exponentially growing (log-phase) populations, and optimal size can be influ-

enced by population growth rate (see discussion of Eq. (3.1), and section on

Predicting life-history plasticity), further work should establish the relationship

for non-growing populations.

0

20

40

60

80

100

120

Low predation High predation

Mature male mass (mg)

12.5

13

13.5

14

14.5

15

15.5

16

16.5

17

Low predation High predation

Mature male length (mm)

(a) (b)

Figure 3.3Least squares means (1 SE, rarely extending beyond symbol) of size at maturity

of adult male guppies,Poecilia reticulata, from high and low predation sites on the north slope

(solid line) and south slope (broken line) of the Northern Range Mountains, Trinidad (data

extracted from Figures 2c and 4d in Reznick and Ghalambour ( 2005 ), and redrawn:

(a) data from field-collected fish; (b) data obtained under common garden conditions for each

pair of high and low predation sites, though north slope populations were reared under

lower food levels and at a different time from south slope fish). This illustrates co-gradient

variation in adult size, with smaller size under high predation selection.

42 D. ATKINSON AND A. G. HIRST