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Ecological characteristic of rare species : the case of parasitic hymenoptera

Ulrich W.

Polish Journal of Ecology

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2001

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Vol. 49, nr 4

379-389

EN

Ecological characteristic of relatively rare (singleton) hymenopteran species sampled in a beech forest on limestone are studied. No marked differences between singleton and non-singleton species occurred in regard to guild membership, stratum of host attack and phenology. There was however a strong effect of sample size on the fraction of singletons. Body size and phylogenetic position also appeared to influence rarity, but it proofed to be difficult to separate the effects of both variables. Rare species appeared to have larger density fluctuations but - in line with the theory of local mate competition - lover sex rations than more common species. Brachypterous and apterous species had lower fractions of singletons. This result contradicts theoretical expectations of metapopulation models.

2

The Hymenoptera of a dry meadow on limestone : species composition, abundance and biomass

Ulrich W.

Polish Journal of Ecology

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1999

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Vol. 47, no 1

29-47

EN

In 1986 and 1988 the hymenopterous fauna of a semixerophytic meadow on limestone near Gottingen (FRG) was studied using ground-photo-eclectors. A total of 4982 speciments belonging to 475 different species were collected. Extrapolations from double-log functions revealed that there may be as many as 1330 parasitoid species present per year. 455 of the 475 species were parasitoids. 155 of them attack dipterans. 48 lepidopterans, 36 beetles, 23 wasps, 22 plant hoppers and 13 aphids, 47 of the species are egg-parasitoids and parasitoids of miners, ectophytophages count for 44 of the wasp species. The abundance of the wasp fauna was rather high (1120+-53 ind. m^-2 a^-1 (1986) and335 +-42 ind. m^-2 a^-1 (1988). Most abundant were the parasitoids of miners, gall-makers and the eggparasitoids. Compared with the high abundance the biomass was low. In 1986 the wasps weighed a total of 194 +-24 mgDW m^-2 a^-1 and in 1988 only 69+-20 mgDW m^-2 a^-1. The parasitoids of ectophytophagous lepidopter ans and coleopterans counted for more than half of the whole biomass.

3

Temporal stability of community structure of the parasitic Hymenoptera in a beech forest on limestone

Ulrich W.

Polish Journal of Ecology

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1999

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Vol. 47, no 3

257-270

EN

The stability of the community structure of the parasitic Hymenoptera of a beech forest on limestone (northern FRG) was studied. The annual number of species was around 350 to 450 with a high degree of species turnover. In a comparison of the study years the species identity of the abundant species turned out to be low and their dominance rank order was highly variable. The yearly sequence of emergence appeared to be constant. Density fluctuations of the species were high and positively correlated with mean density and negatively with the weight of the species. No clear common temporal trends in density could be detected. Host guild, stratum of host attack or number of generations did not detectably influence the degree of density fluctuations of the species. The findings are discussed in the context of concepts of stability and classifications of communities and it is concluded that this hymenopteran community is best described as non-interactive and non-stable.

4

Species composition, coexistence and mortality factors in a carrion-exploiting community composed of necrophagous Diptera and their parasitoids (Hymenoptera)

Ulrich W.

Polish Journal of Ecology

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1999

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Vol. 47, no 1

49-72

EN

In a beech forest on limestone, the community of carrion (dead Arion ater slugs) exploiting Diptera and their parasitoids (Hymenoptera) was studied. The carcass sustained 17 species of Diptera and 12 of Hymenoptera. With the exception of Kleidotoma psiloides (Eucoilidae), all of the parasitoid species bred were polyphagous and attacked all of the fly species present. The populations of the fly and wasp species were highly aggregated. The degree of aggregation depended in an inversely manner on the density. The dispersion of the parasitoids was independent from the number of hosts. Diptera, which lay their eggs in a late stage of decay, showed a negative correlation between aggregation and the weight of the slugs. There was no interspecific competition detectable between the fly species. The parasitoids did compete markedly only at high levels of parasitism. The parasitoids showed only a weak (negative) density dependent reaction to the numeber of hosts present. The degree of density dependence was more pronounced in the more infrequent species. The total parasitoid numbers increased in a linear manner with increasing host densities, and therefore the overall parasitism rate was roughly constant for different host numbers. Large predators and necrophages (Silphidae, Carabide, Arion ater) had a high impact on the mortality of the flies and wasps. in experimental boxes that allowed free access to these species, they totally prevented the development of phorid flies and their parasitoids.

5

Morphology and ecology of the parasitic Hymenoptera : analysis of three morphological parameters and their relationship to environmental factors

Ulrich W.

Polish Journal of Ecology

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1999

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Vol. 47, no 2

117-133

EN

In the parasitic Hymenoptera of a dry meadow on limestone and a beech forest on limestone (both near Gottingen, FRG) three porphological parameters were analyzed and related to environmental factors: the relative wine surface, the ovipositor length and the relative length of the hind leg (as a measure of body-compactness). Two coefficients of wing surface and one of body-compactness are developed. Wing surface and length of legs turned out to be allometrically related to the thorax volume of the species. Soil living parasitoids had the relatively largest wings and longest hind legs; parasitoids of the canopy level showed the opposite trend. On the dry meadow many more wingless or short winged species occurred than in the beech wood; these species also reached higher densities. In the fully winged species there were more species with smaller wing surfaces on the dry meadow than in the beech wood. Idiobiontic parasitoids appeared to have much higher proportions of wing reduced species to han koinobiontic species. The impact of these differences in morphology on community structure is discussed.

6

The parasitic Hymenoptera in a beech forest on limestone. 3, the role of leaf litter for the parasitoid species

Ulrich W.

Polish Journal of Ecology

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1998

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Vol. 46, no 3

311-326

EN

In a mixed beech forest growing on limestone, the effect of an enhanced and a reduced layer of leaf litter on the emergence of parasitic Hymenoptera (as well as their hosts) was studied. A long term increase (4 years with an initially 5-fold value) of the leaf layer and a short term experiment (1 year, factor 5) resulted in arise of the total density of soil living parasitoids. The abundance of parasitoids which attack hosts in the herb layer or canopy declined. However, in both groups diversity and evenness was lowered. A reduction of the layer of leaf litter resulted in lower densities of the parasitoids of soil living hosts, but higher abundances of the parasitoids of hosts in other strata. The lacking leaf layer caused a reduction in the number of species and lowered both diversity and evenness. The lacking leaf layer also caused changes in the species composition. Experiments with dead snails to attract necrophagous insects and their parasitoids covered by different amounts of leaf litter revealed a species specific reaction to the leaf cover. Total parasitism rates were not reduced under a thick layer of leaf litter. No protective function of the leaf cover could be detected.

7

The parasitic Hymenoptera in a beech forest on limestone. 2, study of the sex ratios and their dependence on ecological factors

Ulrich W.

Polish Journal of Ecology

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1998

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Vol. 46, no 3

291-310

EN

The sex ratio of the parastic Hymenoptera of a beech forest on limestone near Gottingen (FRG) was studied using ground-photo-eclectors. Judged from the mean sex ratios the parasitoids could be separated into 4 groups. Parasitoids of miners and gall-makers had the highest sex ratios (30 to 40% males) and less than 5% of the species were thelytokous. The species which attack soil-living sapro- or mycetophagous Diptera as well as the parasitoids of ectophytophages had (on average) 20 to 30% males and only 1.5% of them were thelytokous. Parasitoids of sap-suckers and egg-parasitoids usually had sex ratios below 20% males and 29% of them were thelytokous. The lowes sex ratios (below 10% males) and the highest number of thelytokous species (30%) were found among hyperparasitoids and parasitoids of soil-living Staphylinidae. No clear trend was detectable between the sex ratio and the density of the species. The density fluctuations and the degree of aggregation of the species influenced the sex ratio. The data are consistent with the hypothesis that K-selected parasitoid species have higher sex ratios on average. Koinobiontic species (mostly parasitoids of gall-makers and miners) had (on average) significantly higher sex ratios if their host lives in the herb or crown layer (32% versus 21%). They also produced more males if they are univoltine (32% versus 22%) and hibernate as larvae or pupae (30% versus 17%). After a MANOVA-analysis the voltinism turned out to be the main infuencing factor. There was a trend towards higher percentages of males in the summer generation.

8

The parasitic Hymenoptera in a beech forest on limestone. 1, species composition, species turnover, abundance and biomass

Ulrich W.

Polish Journal of Ecology

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1998

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Vol. 46, no 3

261-289

EN

Between 1980 and 1987 a beech forest (Fagus sylvatica) on limestone near Gottingen (FRG) was studied using ground-photo-electors. 720 species of Hymenoptera were detected. 669 of the species were parasitoids, 29 phytophagous Tenthredinidae, Cynipidae and Eurytomidae, 9 ants, 4 vespids and 9 nest-building sphecids, megachilids, andrenids and bumble bees. Even after 8 years of sampling a great number of species seems to remain undetected. Estimates of extiction and immigration rates indicate species turnover rates of at least 5 to 10%. The abundance of the parasitic Hymenoptera ranged between 123 +- (1981) and 1078 +- 186 (1984) ind. m^-2 a^-1. The most important groups were the parasitoids of Diptera with 56 +- 15 (1981) to 936 +- 164 (1984) ind. m^-2 a^-1. As judged by the sorting according to parasitoid guild, the parasitoids of gall-makers (23 +- 9 to 880 +- 163 ind. m^-2 a^-1) and the egg-parasitoids (21 +- 17 to 102 +- 33 ind. m^-2 a^-1) reached the highest densities. The biomass of the parasitic wasps ranged between 19 +- 5 (1981) and 170 +- 92 (1987) mg DW m^-2 a^-1 with a mean of 68 mg DW m^-2 a^-1. In comparison with other important insect taxa this is a low value.