Ds. Glazier, Trade-offs between reproductive and somatic (storage) investments in animals: a comparative test of the Van Noordwijk and De Jong model, EVOL ECOL, 13(6), 1999, pp. 539-555
Classical life-history theory predicts 'trade-offs' between reproductive an
d somatic investments. However, empirical studies have shown that intraspec
ific phenotypic correlations between these two resource investments are oft
en positive or nonsignificant, rather than negative as predicted. The model
of Van Noordwijk and De Jong (1986) was proposed to explain these unexpect
ed results. According to their model, positive correlations between reprodu
ctive and somatic investments will result if individual variation in resour
ce acquisition exceeds that of resource allocation, whereas negative correl
ations will result if individual variation in resource allocation exceeds t
hat of resource acquisition. To test this model, I used body storage/condit
ion as an index of somatic investment because it is usually strongly relate
d to level of resource acquisition. I predicted that laboratory studies sho
uld more often show negative correlations between reproductive and somatic
investments than field studies, because individual variation in resource ac
quisition is expected to be lower in controlled laboratory environments tha
n in variable natural environments. A literature review revealed that corre
lations between somatic (storage) investment and reproductive investment (e
stimated as clutch/litter mass, number of offspring per clutch/litter, or n
umber of clutches/litters) among conspecific breeding female animals are mo
re often positive (15 species) or nonsignificant (17 species) than negative
(6 species). Moreover, as expected, five of six negative correlations were
observed in laboratory studies, whereas 13 of 15 positive correlations wer
e observed in field studies. It is concluded that future empirical and theo
retical work on life histories should consider individual variation in both
resource acquisition and allocation and the interaction between the two.