https://www.jstor.org/stable/pdfplus/3787.pdf

Interactions among coexisting predators- a field experiment with dragonfly larvae

Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounte ...

Conflicting selection pressures on the growth/predation risk trade-off in a damselfly

Several species of coexisting dragonfly larvae were studied for four consecutive years in a 1-ha old farm pond. Larval development, emergence patterns, and adult flight patterns showed that the most abundant species were univoltine and developed relatively synchronously (i.e., like a cohort). Three of the common species emerged in early spring, and the others emerged later in the summer. The common genera with the most similar microhabitat had a distinct temporal separation that may serve in reducing interspecific com- petition. However, coexisting congeneric species had almost identical life histories, supporting the hypothesis that ecological homologues can coexist because of "errors of exploitation" of the dominant species. The larval population dynamics of each dominant species (Ladona deplanata, Epitheca spp., and Celithemis fasciata) was characterized by a constant percentage numerical decline, coupled with a dramatic biomass increase from time of hatching to final instar. Larval mortality during this period averaged 92% per annum, but population biomass increased at least ten- fold during the same period for each species. Comparison of larval estimates with emergence data revealed that at least 80% of the final instars die just before leaving the water to emerge. Life history variations among species smoothed out composite density and biomass trends which averaged about 1,000 individuals/m2 and 2 g dry wt/m2, respectively. In general, pop- ulation dynamics from year to year were quite consistent, indicating a relatively high degree of stability in terms of species composition and densities.

Comparative dynamics and life histories of coexisting dragonfly populations

Tetragoneuria cynosura and Celithemis elisa dominate the larval dragonfly assemblage of Bays Mountain Lake, Tennessee, USA, where they coexist in the extensive submersed macrophyte and allochthonous detritus habitats despite relatively high overlap in both seasonal occurrence and diet. Field enclosure experiments, designed to determine the intensity of intraspecific and interspecific competition at approximately natural densities, were conducted during September 1981 and April 1982. Survival rate for both species was dependent on intraspecific density in September, and that for C. elisa was also affected by the presence of T. cynosura. These effects are attributed to interference (encounter) competition rather than to exploitation (consumption) competition. The mechanism of competition seems to be predation by larger larvae on smaller larvae. No evidence of either exploitation or interference competition was found in the April experiment.

Competition among larval dragonflies a field enclosure experiment

Many animals have two basic traits for avoiding being killed by a predator: behavioral modification and morphological defense. We examined the relationship between antipredator behavior and morphological defense in larvae of three closely related dragonfly species within the genus Leucorrhinia. The three species differ with regard to their morphological defense as expressed in the length of the larval abdominal spines. Results showed that longer abdominal spines provided protection against an attacking fish predator (perch) because the probability of being rejected after an attack was significantly higher in the species with the longest abdominal spines. In contrast to other studies, the species with the strongest morphological defense did not show the least behavioral predator avoidance. Instead, the species with intermediate morphological defense showed the least predator behavioral avoidance. The results suggest that the Leucorrhinia system is a mixture of trait cospecialization (a positive correlation between antipredator behavior and morphological defense) and trait compensation (a negative correlation between antipredator behavior and morphological defense). Differences in the relationship between morphological and behavioral defense between species might be related to abundance patterns of the three species in lakes with and without fish predators.

/pdf/morphological-and-behavioral-defenses-in-dragonfly-larvae-4et6a2ioxc.pdf

Morphological and behavioral defenses in dragonfly larvae: trait compensation and cospecialization

A method for representing individual growth rates of aquatic insects from field sampling is presented using the mean instar number as the age criterion. Various examples are used to show how the method is useful in making both intra— and interspecific comparisons. Significantly different growth rates are shown between populations of the same species in different habitats. Also, an example is presented which shows the possible role of temporal separation in niche differentiation between two similar species. See full-text article at JSTOR

A. C. Benke

Papers

A Method for Comparing Individual Growth Rates of Aquatic Insects with Special Reference to the Odonata