Adult population dynamics and reproductive effort of the fishing spider Dolomedes triton (Araneae, Pisauridae) in central Alberta

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Abstract
A combination of simple enumeration and more intensive Jolly–Seber and Manly–Parr mark–recapture estimation was required to give a complete picture of the population dynamics of adult Dolomedes triton on a small pond in central Alberta. The total number of spiders marked was 142 in 1986 and 210 in 1987, and annual adult emergence, using the population size estimates of the two mark–recapture methods, amounted to ca. 150 and 230 individuals in 1986 and 1987, respectively. The sex ratio was not different from 1:1 in 1986, but in 1987 more than twice as many males emerged than females. Males had significantly shorter observed residence times (life-spans) than females. Contrary to longevity estimates based on the survival probabilities given by the Jolly–Seber model, which were close to those based on enumeration, Manly–Parr survival estimates were strongly biased and even yielded impossible estimates of adult longevity. In both years the median date of male emergence preceded that of females by 5–10 days. Male population size decreased dramatically during the interval when the density of the female population increased, supporting the hypothesis that cannibalism by females is a major source of male mortality. Seventy and 55% of marked females produced egg sacs in 1986 and 1987, respectively. First egg sacs contained 472 ± 18.5 (SE) eggs. Four times as many nursery webs were found in 1986 as in 1987, suggesting that significant losses in female reproductive success occur during the period of egg sac care.

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