DEMOGRAPHICS OF LESTES DISJUNCTUS DISJUNCTUS (ODONATA, ZYGOPTERA) IN A RIVERINE WETLAND

I investigated the demographics of Lestes disjunctus disjunctus inhabi ting a riverine wetland adjacent to the St. Marys River, Michigan. The areal extent of cover types within the 4.03-ha study area was measure d and the densities of all life stages of L. d. disjunctus in separate cover types were converted to population estimates. Data were then an alyzed using life-table techniques. The 1982 cohort oviposited an esti mated 944 300 eggs in the 4.03-ha study area. Mortality in the egg sta ge was estimated to be 22.6%, of which 6.0% was associated with hatchi ng and 16.6% was attributed to habitat loss. Survival through all larv al instars was 5.5%. Mean larval production was 135 mg dry mass.m(-2). year(-1). The mortality rate was greatest in final-instar larvae. Inst ars F-8 through F-6 dispersed from wracks to Sparganium eurycarpum bed s. The female:male ratio of instars F-2 through F was 1.08:1.00 and va ried from 1.91:1.00 to 1.01:1.00 in the adult stage. An estimated 20 1 00 adult females emerged from the 4.03-ha study area, yielding a survi val rate from the egg to adult stage of 4.3%. Lower potential fecundit y in 1983 (45.2 eggs/female) than in 1982 (73.5 eggs/female), combined with low survival, yielded a net reproductive rate (R(0)) of 0.97 and a population rate of increase (r) of -0.03.