Ad. Huryn, TEMPERATURE-DEPENDENT GROWTH AND LIFE-CYCLE OF DELEATIDIUM (EPHEMEROPTERA, LEPTOPHLEBIIDAE) IN 2 HIGH-COUNTRY STREAMS IN NEW-ZEALAND, Freshwater Biology, 36(2), 1996, pp. 351-361
1. Measurements of larval growth rates were used to produce an empiric
al model for examining factors influencing patterns of size structure
and emergence period for populations of the leptophlebiid mayfly Delea
tidium (lillii group) in two high-country streams (South Island, New Z
ealand). Growth rates were measured in situ by enclosing groups of lar
vae and natural stream substrata in growth chambers. 2. Multiple regre
ssion analysis showed that temperature explained most variation among
growth rates in both streams. Growth rates were also significantly rel
ated to larval size, although the effect was minor compared with tempe
rature. A significant relationship between larval biomass per chamber
and growth rate was shown at only one site. 3. Growth models based on
multiple regression equations (R(2) = 0.70-0.84) simulated the extende
d emergence period and complex size structure observed for populations
of Deleatidium in the field. Larvae hatching from eggs deposited befo
re mid-February (austral summer) probably emerge as adults before May
(minimum cohort duration approximate to 3 months). Larvae hatching aft
er mid-February probably do not emerge as adults until the following s
ummer because of low growth rates during winter (maximum cohort durati
on approximate to 11 months). 4. On average, there are probably two ge
nerations of Deleatidium per year (bivoltine) at the study sites. The
presence of numerous overlapping cohorts throughout summer, however, r
esults in an extended emergence period and complex size structure.