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Abstract
I designed six experiments to assess the physiological and ecological mechanisms that allow two sympatric species of tiger beetles (Cicindela togata and Cicindela circumpicta) to coexist in the eastern Nebraska Salt Marsh.
The salt marsh is periodically flooded and I found Cicindela larvae to survive immersion and anoxia for about 6 days in typical summertime temperatures and longer at lower temperatures. I hypothesized that one mechanism of flood survival is by facultative anaerobiosis; during anoxia, larvae depress metabolic rates and conduct anaerobic metabolism. Compared with larvae of Amblycheila cylindriformis (a tiger beetle species whose habitat is never flooded), C. togata survived longer, depressed metabolism further, and utilized different anaerobic pathways during the first 24 hours of anoxia.
Beyond seasonal flooding, tiger beetle larvae (sedentary predators) face prolonged starvation compared to adults (active foragers). I hypothesized that during periods of starvation, adult and larval tiger beetles use fat body reserves differently because of differing foraging strategies. Whole body triacylglycerol and phospholipid compositions differed between fed and starved beetles.
To test niche differentiation, I investigated the influences of soil salinity and shade on oviposition choices by females of the two tiger beetle species. I found resource use consistent with niche partitioning. I also quantified potential prey availability by placing sticky traps in exposed and shaded areas of the salt flat; the captures were dominated by Dolichopodidae and Cicindelidae.
Finally, I conducted a series of experiments to document niche shifts and intraguild predation by C. circumpicta on C. togata. Cicindela togata serves as intraguild prey for C. circumpicta. Behaviorally, C. togata uses different microhabitats and shifts its foraging behavior, taking longer to feed in the presence of C. circumpicta.
The biological significance of these findings lies in an appreciation of the physical and ecological community of predators that share a relatively harsh and food-limited habitat.
