Graduate Thesis Or Dissertation
 

Effect of adult aquatic insect life history on return to Lookout Creek, H. J. Andrews Experimental Forest, Oregon

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  • Aquatic insects that emerge out of streams to mate represent a potential energy flux to terrestrial food webs. The relative success of an individual aquatic adult insect is whether it survives long enough to produce offspring, i.e. mate and return to the stream to oviposit eggs. Some characteristics of the adult stage of aquatic insects are thought to be responses to aerial and terrestrial predation from riparian insectivores. These characteristics and behaviors may result in differential numbers of returning individuals to the stream. In summer 2001 we measured emergence and return of adult aquatic Ephemeroptera, Plecoptera and Trichoptera at Lookout Creek, a 4th order western Oregon montane stream located in H.J. Andrews Experimental Forest. As a group, Plecoptera had the highest proportion of returning adults (P{retum} 0.37), Ephemeroptera the second highest (P{return}=O.28), and Trichoptera the lowest (P {return}=0. 18). The range in return proportion among families within an order was large but among species within a family or genus they were surprisingly similar. Concurrently, we assessed the associations between adult behavior, specifically diel activity, the longevity of the adult stage, and length of emergence period with adult return to the stream. Six out ofseven Trichoptera species were nocturnal at our study site, but only two out of six Plecoptera and four out of seven Ephemeroptera exhibited higher activity at night than during the day. Calculated values of diel activity at the species level ranged widely, even among congenerics. Simple linear regression of our measure of die! activity on return proportion was moderately significant (R² = 0.42, p <0.02) at the family level but the relationship was weak at the species level (R² = 0.22, p <0.08). As expected, Trichoptera species averaged longer adult stages than Plecoptera (1-4 weeks vs. 0.5-1.5 weeks). Also, most Trichoptera species had extended emergence periods of 8 weeks or longer, while many Plecoptera and all but one Ephemeroptera had emergence periods of 6 weeks or shorter. Overall, species with shorter adult life stages had greater return proportions, but this relationship was marginally significant (R² = 0.23, p <0.05). A stronger negative relationship existed between emergence period length and return proportion (R² 0.34 p <0.02). The similarity in return proportion in closely related species indicates that factor(s) producing difirential return numbers are important at the genus and species level. However, similarities in did behavior, adult longevity, or emergence period durations did not occur among closely related species. We conclude, therefore, that despite some evidence of a relationship between the three life history dimensions and return proportion, the absence of similar patterns within or among taxa shows that other factors are more important influences on determining how many insects survive to oviposition.
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