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Стрекозы: конкуренция личинок

Wissinger-S Mcgrady-J

Intraguild Predation and Competition Between Larval

Dragonflies - Direct and Indirect Effects on Shared Prey

Source: ECOLOGY 1993, Vol 74, Iss 1, pp 207-218

We conducted manipulative field experiments in artificial

ponds to quantify the predatory impact of larvae of a migratory

dragonfly (Tramea lacerata) on a common resident dragonfly

species (Erythemis simplicicollis), and on damselflies as shared

prey of the two dragonflies. We found that the combined

predatory effects of the two dragonflies on damselflies were not

additive. To determine the underlying cause of non-additive

predation rates in the field, we conducted a second experiment

in laboratory aquaria to isolate the impact of each predator on

the consumption rates of the other. Dragonfly consumption rates

of damselflies in single-predator treatments were compared to

those in the presence of heterospecifics or conspecifics with

their menta (mouthparts) surgically modified so that they could

not capture prey.

In the laboratory experiment, de-mented Tramea reduced the

consumption rates of Erythemis to less than half of that

observed when Erythemis foraged alone. Erythemis numbers were

also reduced by Tramea predation. Erythemis had neither effect

on Tramea. Both of the negative effects of Tramea on Erythemis

will have indirect positive effects on damselflies. The

''behavioral'' component (reduced Erythemis foraging rate)

should be more important than the ''trophic link'' (reduced

Erythemis numbers) indirect effect. Together these indirect

positive effects will allay, but not completely compensate for,

the direct negative effects of Tramea predation on damselflies.

These results illustrate how an asymmetric potential for

intraguild predation can lead to asymmetries in interference

competition and to non-additive effects on prey mortality. The

addition or removal of predators that interact in this manner to

or from communities should have only a small net effect on prey

because of compensating direct and indirect effects. This may

explain why predator manipulations have often had unpredictable

or undetectable effects on freshwater benthic communities.

Стрекозы: питание имаго.

Ecological Entomology Volume 25 Issue 2 Page 239 - May 2000

Critical Appraisal Fitness and body size in mature odonates

Natalia Sokolovska, Locke Rowe and Frank Johansson*

The relationship between body size and fitness components in odonates was examined using a meta-analysis of 33 published studies. There was a positive and significant overall effect of body size on mating rate and lifetime mating success among males. There was also a weaker but still significant positive effect of body size on survivorship of males. The relationship between body size, mating rate, longevity, and lifetime mating success differed significantly between males of territorial and nonterritorial species. The effect of body size was significant for all fitness components in territorial species but significant only for longevity and lifetime mating success in nonterritorial species. Effect sizes appeared to be strongest on longevity in both sexes, and on male mating rate in territorial species. Other effect sizes, even when significant, were small. Despite a much smaller data set, female fitness also increased significantly with body size. Both clutch size and longevity showed a significant positive relationship with body size. These results suggest that there is a general fitness benefit to large size in odonates. Nevertheless, significant heterogeneity is apparent in this effect, which can be attributed to sex, mating system, and fitness component. Finally, these analyses point to inadequacies in the current data that need further study before the potentially rich patterns in size effects on fitness can be explored more thoroughly.

Стрекозы: биоиндикация пестицидов.

Authors: Takamura-K Hatakeyama-S Shiraishi-H

Odonate Larvae as an Indicator of Pesticide Contamination

APPLIED ENTOMOLOGY AND ZOOLOGY 1991, Vol 26, Iss 3, pp 321-326

The abundance of odonate larvae was surveyed in a river

system at two upstream stations surrounded by rice fields

lacking aerial spraying of pesticides, two midstream stations

surrounded by rice fields with and without aerial spraying, and

four downstream stations surrounded by sprayed fields. Species

diversity and numbers of individuals were much lower at the

downstream stations. Pesticide contamination from ground

spraying occurred at one upstream station as well as one

midstream and all downstream stations. Damage to the odonate

larvae was not clearly evident except at one downstream station.

Damage by the aerially sprayed insecticides seemed appreciable

at the downstream stations. The distribution of odonate larvae

in a river may be restricted by pesticide contamination and thus

can indicate pesticide contamination.

Стрекозы: расселение имаго.

Kelvin F. Conrad, Karen H. Willson, Katherine Whitfield, Ian F. Harvey, Chris J. Thomas and Thomas N. Sherratt

Characteristics of dispersing Ischnura elegans and Coenagrion puella (Odonata): age, sex, size, morph and ectoparasitism

Ecography Volume 25 Issue 4 Page 439 - August 2002

In this study we assessed whether individuals of the damselfly species Ischnura elegans and Coenagrion puella that moved between ponds differed in their mean characteristics from individuals that did not move. Overall, the sex (female) and species (C. puella) that spent the most time away from the breeding site was more likely to move between ponds. Ischnura elegans males that dispersed had significantly longer forewings than males that did not, while male C. puella parasitised by water mites were more likely to disperse than unparasitised males. There was no evidence for differences in dispersal rates among the female colour forms of either I. elegans or C. puella. In general, the differences in dispersal characteristics between sexes and species could be explained by underlying variation in activity and mobility. The majority of dispersal between breeding sites by C. puella and I. elegans did not appear to be directed, but probably arose from chance movements occasionally taking individuals to a different pond from which they emerged.

Стрекозы. Распределение имаго.


Volume 25 Issue 4 Page 459 - August 2002

Distribution and habitat specialization of species affect local extinction

in dragonfly Odonata populations

Esa Korkeamaki and Jukka Suhonen

The object of our study was to determine the effect of distribution and habitat specialization of odonate species on local extinction in streams in central Finland. We studied the local extinction of the 20 most abundant dragonfly (Odonata) species in 34 small creeks and brooks in central Finland. The historical presence of each studied species in our research area was confirmed using existing records gathered between 1930 and 1975. A minimum of five records was available for each species. During the summers of 1995 and 1996, we investigated the current persistence of 219 separate populations with historical presence. In total, 98 historical populations were vanished. As predicted, we found that species with a narrow distribution were less persistent than species with a broad distribution. Therefore, the extinction risk of a species was inversely related to the width of its regional distribution. Using reference works, species were categorized into two main breeding habitat types: lotic species or lentic species. The species main habitat type was a significant predictor of local extinction risk after statistical removal of the effect of regional distribution on extinction risk. The lotic species had lower local extinction risk than other species. Altogether, the highest extinction risk was found in habitat-specialist species associated with peatlands, probably due to loss of natural breeding habitat. On the other hand, extinction risk was lower in widely distributed habitat generalist species than true lotic species. The local extinction within species was more common in small dynamic upstream than in larger stable downstream habitats. The results of this study are consistent with meta-population theory.

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