Perithemis Tenera Research Articles

Life History and Size Structure of Larval Dragonfly Populations

Comparative data on emergence, adult activity, and larval development were used to interpret patterns of phenology, voltinism, and developmental synchrony in a 14-species assemblage of dragonflies (Odonata:Anisoptera). Interspecific differences in these characteristics provided an opportunity to interrelate life history, population size structure, and the potential for intra- and interspecific interactions. Larval populations of most species comprised an extraordinary size range of individuals at any one time. In many species, this intraspecific size variability was primarily due to developmental asynchrony within generations (e.g., Libellula lydia, Celithemis elisa, Perithemis tenera). Oviposition in these species occurred throughout most of the summer so that the timing of instar development varied considerably among broods. By fall, the largest larvae in these populations were 5 to 10 times the size of smaller conspecifics. In other asynchronous breeders, an even wider size range of co-occurring conspe...

Mutual Predation in Assembled Communities of Odonate Species

Larval individuals from six anisopteran species were added to artificial ponds so that each pond contained an equal number and size distribution of each species. Half of these ponds were exposed to an additional anisopteran, Anax junius. Interodonate predation in Anax—free ponds was size dependent, with the smallest species, Perithemis tenera, experiencing the highest mortality. Predation in ponds containing Anax was not size dependent, but was species dependent. Plathemis lydia individuals were not significantly affected by Anax, probably due to the tendency of Plathemis to dig deeply into the sediment. Pe. tenera was shown to have a different allometric relationship between head width and body volume than the other six dragonfly species. We postulate that this is correlated with its small size and is an adaptation to increase the range of prey available to it.

Odonate Guild Composition: Experiments with Colonization History and Fish Predation

Fewer than half of the anisopteran odonate species that oviposited in a North Carolina farm pond successfully metamorphosed from that pond. Odonates metamorphosed during two periods: early April though early June, and late May through early September. I used an experiment designed for variance analysis to measure the impact of fish and early—breeding odonates on the abundance and species composition of late—breeding odonates. Odonates recruited naturally in open—topped screened pens that either excluded or contained fish. I placed pens in the pond either during or after the early species breeding season to alter the abundance of larval early breeders. Fish exclusion increased the combined abundances of all anisopteran species 5—10 times above abundances in pens containing fish. However, fish also facilitated the recruitment of one species, Perithemis tenera. Placement of fish exclusion pens in late June instead of early May reduced abundance of early breeders and increased abundances of two late breeders, Perithemis tenera and Pachydiplax longipennis. Early—breeders did not reduce late—breeder recruitment in pens with fish. Abundances of early and late breeders were significantly negatively correlated in pens without fish, but abundances of the same species were not significantly correlated in pens with fish. Different histories of colonization by early breeders influenced interspecific interactions among odonates only if fish were absent. Most variation in the composition of experimental communities was explained by a hierarchy of negative effects of fish on odonate abundance, and negative effects of early—breeders on late—breeders in the absence of fish.

The Impact of Fish Exclusion on the Abundance and Species Composition of Larval Odonates: Results of Short‐Term Experiments in a North Carolina Farm Pond

Under natural conditions in a man—made North Carolina farm pond, a single small species, Perithemis tenera, numerically dominates a littoral assemblage of larval dragonflies. Censuses of exuvia of larvae metamorphosing from the pond in three successive years demonstrated a consistent negative correlation between numerical dominance in the assemblage and species—specific size in the final larval instar. This pattern suggested that size—dependent processes, such as vertebrate predation, might structure the odonate assemblage. Exclusion of vertebrate predators from patches of emergent vegetation by screen exclosures for 3 mo increased total abundances of larval odonates by an order of magnitude. Dominance shifted from small species to species of intermediate size, especially Pachydiplax longipennis, where fish were excluded. The largest species remained rare and were unaffected by fish exclusion. Four odonate species were facultatively multivoltine, completing larval development within 1—2 mo after colonization of the fish exclosures. Fish exclusion also increased the abundance of large microcrustacea, especially the cladoceran Simocephalus serrulatus. large microcrustacea increased in abundance despite a corresponding increase in the abundance of their macroinvertebrate predators, where fish were excluded. The usual dominance of small Perithemis in this assemblage was a probable consequence of differentially heavy predation by fish on moderate—size species, and the unexplained failure of large species to recruit well under experimental or natural conditions. These results support the general importance of predation in structuring freshwater communities and document an important mode of population regulation operating during the aquatic larval phase of the odonate complex life cycle.

Odonata in the Florida Soybean Agroecosystem

Thirty-five species of Odonata, including 4 families of Anisoptera and 3 families of Zygoptera, were observed in Florida soybean fields. Where possible, time of flight, flight pattern, feeding habits, and prey taken were recorded. Nine species appeared to be numerous enough and sufficiently selective in feeding habits to be capable of affecting prey populations. Three dragonfly species possibly may affect prey of economic importance. These were Erythemis simplicicollis (Say) which fed on Heliothis zea (Boddie), H. viriscens (Fabricius), and Pseudoplusia includens (Walker); Pachydiplax longipennis (Burmeister) which fed on alate imported fire ants, Solenopsis saevissima richteri Forel and Mexican bean beetle, Epilachna varivestis Mulsant; and Perithemis tenera seminole Calvert which fed on dolichopodid flies. Only 1 species of damselfly, Anomalagrion hastatum (Say) was consistently associated with soybean culture.