Scopul nostru este sprijinirea şi promovarea cercetării ştiinţifice şi facilitarea comunicării între cercetătorii români din întreaga lume.
Autori: Stanescu Manu Minodora
Editorial: p.250, 2007.
CHAPTER I THE RESEARCH HYSTORY OF MITES POPULATIONS
1.1 Taxonomy……………………………………………………… ….3
1.2.1 External morphology…………………………..9
1.2.2 Reproduction……………………………….. .29
1.2.3 Postembryonic developmental stages….………29
CHAPTER II BIOLOGICAL AND ECOLOGICAL CHARACTERIZATION OF MITES (ACARI: MESOSTIGMATA)…..31
CHAPTER III CHARACTERIZATION OF THE STUDIED FORESTRY ECOSYSTEMS
3.1 Abiotical factors………………………………………………….42
3.1.2 Relative humidity..……………………………….. …..53
3.2 Soils….………………………………………………………….. 67
CHAPTER IV METHODS AND WORK TECHNICS
4.1 Choosing of the necessary number of samples…………………..74
4.2 Techniques of the samples extractions and sortation…………….75
4.2.1 Techniques of soil sample extraction.………………….75
4.2.2 Methods of sortation of the mites fauna ………………76
4.2.3 Growings in the lab conditions…………………………..77
4.3 Statistical analyse………………………………………………..78
CHAPTER V STRUCTURAL CHARACTERISTICS OF THE MITES POPULATIONS
5.1 Taxonomical and numerical structure of the mites populations………………………………………….……….88
5.1.1 The structure of the taxonomical diversity……………88
5.1.2 Relative abundance.…………………………………..96
5.1.6 Variation coefficient….……………………………….109
5.1.7 Specific diversity…………………………….. ……..110
5.1.9 Spatial distribution…………………………………..129
18.104.22.168 Simple correlations…………………………136
22.214.171.124 Multiple correlations……………………..141
5.2 Dynamics of the mites populations.……………………………146
CHAPTER VI BIOMASS AND PRODUCTIVITY OF THE MITES POPULATIONS
The Arthropoda phylum, Chelicerata subphylum, Arachnida class, Acari subclass, is characterized by a large diversity of shapes, dimensions and structures. This diversity allowed to sharing the Acari subclass in two suprataxa: Parasitiformes and Acariformes (Zakhvatkin, 1952). Suprataxon Parasitiformes is composed by the following orders: Notostigmata, Tetrastigmata, Mesostigmata, Metastigmata and Acariformes: Astigmata, Cryptostigmata, Prostigmata. Order Mesostigmata is reprezented by five suborders: Gamasina, Antennophorina, Microgyniina, Sejina and Uropodina (Evans O.G, 1979).
Studies regarding the biodiversity of mites are few. However, their biodiversity from the temperate zone was more studied as that from the thropical and subthropical zones. This gap is dued of the small dimensions of these arthopods, to the high diversity of the taxa and to the dificulty in their identification. These invertebrates with small dimension aren’t observed in the extraction process. Their indentification in field is almost impossible and can’t replace the disection, permanent slides and microscopical examinations. Allthrought studies of their diversity are few, recently estimation shows that the number of mite species is about 1.000.000. One of the causes of this taxonomical diversity is trophic diversity.
The knowledges in the mites systematic are more diversified and the ecology is not studied enough. The mites are present in almost habitats: terrestrial, aquatic, in tree, parasites on micro mammals, being cosmopolitan species. The optimal bioedaphical conditions for their development determined a very reach mites fauna, represented about 80% from the number of individuals from soil fauna.
In nature, mites can have a positive role. Regarding the position and the role of the gamasids populations in trophic structure of the pedofauna, these studies give us informations about the importance of the acarofauna in the energy and matter flows, at different trophic levels. The role of the predatorous mites is important for the understanding their influence in soil system, especially on the limit between soil and litter.
Gamasids influence the dynamics of other invertebrate populations like: nematodes, enchytreids, earthworms, carabids, springtails, aphids, dipterans, others mites. The majority of the functional groups of invertebrates are not included in decomposers level. This aspect have impact on the decomposing process, by regulating the others invertebrates populations. The activity in soil of the gamasids as the second and the third consumers in ecosystem, consist in transformation of the primary and the second organic matter.
The existence of the qualitative and quantitative statistical parameters, which characterized the structure and functions of the soil mites populations, parameters which are influenced by the abiotical factors, allows their utilization as bioindicators for the forestry ecosystems soils.
Taking account of the fact that this study was realized on the soil level, the subject of this PhD thesis was predatorous mites, belonging to the Mesostigmta order, Gamasina suborder.
In Romania the study of these mites was not so developed. The published papers till now had a systematic approach, their ecology being not studied enough. In Bucegi massif isn’t a complex study of the gamasids populations, till now.
Taking account of these aspects, we consider that was necessary a realization of the complex study of the gamasids.
This PhD thesis brings numerous informations and new data about mites ecology. Were followed these objectives: the analyse of the faunistic spectrum of the studied ecosystems, the identifications of the main abiotic factors (temperature, humidity, acidity of the air and soil), the structure, distribution, spatial and temporal dynamics of these communities, the influence of the abiotical factors on the structure of the mites populations, their importance in transmition of the energy in soil of the forestry ecosystems.
The structural and functional differences of the gamasids populations were analysed by comparing three types of forestry ecosystems (with Fagus sylvatica, Abies alba and Picea abies), in two periods of study (september 2001- august 2002 and september 2002- august 2003) and on two levels of soil (litter-fermentation and humus).
The conclusions mentioned on the end of each chapter were concentrated in the last chapter of the thesis, characterizing the mites populations from the studied ecosystems, in space and time limits of this research.
For the realization of these objectives were analysed 2016 soil samples, with 24311 adults individuals and 6152 immature individuals, from the three types of ecosystems, on different altitude ( from 950 meters to 1350 meters)
The thesis was structure in six chapters and included 220 pages, one map, 46 tables, 165 figures, 144 bibliographic titles.
All my gratitude to the Prof. PhD. Marian Traian Gomoiu for acceptance to be the coordinator of this paper. I would like to thank to Prof. PhD. Marin Falcã for the scientifical support.
All my respect and gratitude to the PhD Honciuc Viorica, which initiated my in all phases of the realization of this thesis and which guided me constantly in my research carear.
I would like to thank to PhD. Ilinca Juvara-Balş, to researcher Iavorski Vasilica and to PhD. Dariusz Gwiazdowicz, for their support in taxonomical identification, to PhD Bândiu C-tin and to PhD Mihaela Paucã–Comãnescu, for identification and description of the studied ecosystems. For the prelevations of samples from field I would like to thank to Vladu Emilia and for prelucrations in laboratry to Iosif Rodica.
CHAPTER I THE RESEARCH HYSTORY OF THE MITES POPULATIONS (ACARI: MESOSTIGMATA)
Acarology apperead and developed as a branch of biology in the begining of XIX century, once with the discovery and perfectation of the microscope.
In taxonomical and morphological research in the world, we could distinguish the following phases:
1758-1806, the first studies on the mites, with describing of the genus “ Acarus“ by Linné; introduction in zoology of the natural classification methods by C.L.Koch, Latreile, Leach, Duger, De Geer;
1884-1927, studies in external morphology and anatomy of the gamasids, describing of the new species, by A.D.Michael, Berlese, Oudemans and J.N. Halbert;
1940-1943, improving of the systematic criterias of the gamasids, through their classification in Mesostigmata cohort, Gamasina subcohort;
1944-1953, realization of a catalogue with describing of 360 species of mesostigmatids, “ A synonymic catalogue of the British Acari”, by F.A. Turk;
1957-1981, apearance of many papers with revisions and introductions of a new systematical criteria, describing of a new species, by G.O Evans, N. Hirschmann, M.C. Ghiliarov, N.G. Bregetova, Vera Halaskova, Bhattcharyya, E. Lindquist, W. M. Till. K.H. Kyatt, Athias Henriot C.;
1981 – 2003, development of the taxonomy studies of gamasids, by W. Karg, W. Witalinski, C. Blaszak.
In ecological research in the world, we distinguished the following phases:
1961, the appearance of the first studies in gamasids ecology, made by W Karg;
1970-1982, studies regarding the influence of the abiotical factors on some structural parameters of the gamasids populations, the first studies on the functional characteristics of these mites, made by D.C. Coleman and J.T. McGinnis, C.A. Edwards, J.R. Lofty, J.R. Harris, M.B. Usher, Athias Henriot C., G.O. Evans, G.W. Krantz, W.M. Till, W. Karg, M. Luxton;
1982-1989, the continuation of the ecological studies, underlining the importance in the trophic structure of the gamasids, by: E. Lindquist, W. Walter, G.W. Krantz, M.B. Usher, P.R. Davis, M.F.B. Bowring, Koehler H., Ilinca Juvara Balş, Marc Baillod;
1990-2004, appearance of many papers about gamasids ecology, of the first studies of their behavior and phoretic mechanisms, made by: Axel Christian, Andrea Ruf, Koehler M, Stanislav Kaluz, Ineta Salmane, G.W. Krantz, L. Lundqvist, K. Schmolzer, A. Kofler, Czeslaw Blaszak, J. Bloszyk, Daria Bajerlein, R. Ehrnsberger, R. Schuster, Paul H. Krogh, Buryn, B. Brandal., D.E. Walter, H.C. Proctor, W. Karg, R. Norton.
In Romania, the researches regarding systematic and ecology of the mites followed these phases:
1962-1965, for the first time in our country was been made a taxonomical description of the gamasids, by Prof. Feider Z., Libertina Solomon and Marie Hamer;
1970-1977, new contributions on the systematic and ecology studies of the mesostigmatids species, made by Prof. Feider Z., Iulia Mironescu, V.Gh. Radu, Mariana Domocoş, Ilinca Juvara Balş, Vasilica Iavorski;
1978-1982, the continuation of the taxonomical and ecological studies of the edaphic mites, identification of 132 gamasids species and of some characteristic groups for the different soil class, by Adriana Georgescu, Viorica Honciuc;
1982-2005, systematical and ecological research of the gamasids from different forestry ecosystems in Romania, natural or man–created, by Honciuc Viorica, Adina Cãlugãr and Minodora Stãnescu.
1.2 MORFOLOGY AND REPRODUCTION
Gamasids have the body covered with chitinous shields. Their dimensions are between 0,2-2 mm in lenght. Many small species are not so chitinously. Their body is composed by gnathosoma – the trophical and the smallest region with sensory functions and idiosoma, which present the appendices.
Gnathosoma is formed by:
– appendices (chelicerae and palps);
– sternal elements of the chelicerae and pediplaps.
Idiosoma is formed by:
– podosoma, which presents ambulatory appendices;
The dorsal surface of the podosoma is called podonotum and the dorsal and ventral part of opisthosoma, opisthonorum and respectively opisthogaster.
By the morphological point of view gamasids are describe in this way:
1. Many of small species are very weak sclerotized, but in general idiosoma is partial covered with some brown shields. Idiosoma is divided in many regions and tubular gnathosoma is mobile and articulated to it, being protected by a camerostom. The ventral region of the gnathosoma presents a maximum number of four pairs of seta. The external mala presents corniculus. Gnathotectum is present. All species have an unpaired tritosternum, but the parasitic forms have a pair of lacinia or only one, but divided. All larval stages have a sternal shield, exception making the larva. The genital orifice is situated in intercoxal region. At female this orifice is protected by one, three or four shields and at male by one or two shields. Each anal valve, on the larval stages has maximum one seta.
2. Chelicera is three articulated and can presents some modification on the parasitic forms. The movable digit at male presents a spermatodactyl. The main part of the chelicerae has a dorsal seta and two lyrifissure. Pedipalps have five free podomers and an ambulacrum (apotele), represented by an entire, two, three, four-tined movable claw-like structure, situated at the inner basal angle of the tarsus.
3. The legs present movable coxa and are articulated to the idiosoma. They have six podomeres and an ambulacrum. The first leg has sensorial function. In some cases, the leg can retracts in some deep cavities of the idiosoma. On the lateral part of the coxal region II-IV exists a pair of stigma. Peritreme is expanding anteriorly, having the shape of a fine channel. Exceptions are made by the larval and endoparasitic forms, which don’t have respiratory systems.
The types of reproduction on Mesostigmata are tectospermy and podospermy. Parthenogenesis at gamasids is represented by the arrhenotoky reproduction (haploids males from unfertilized eggs and diploid females from egg receiving spermatosoa), observed on species from Macrochelidae, Macronyssidae, Phytoseiidae and Laelaptidae families and thelytoky reproduction (mainly females from unfertilized eggs, males absent or rare, and if present, do not mate), at species from Glyptholaspis, Holostaspella, Areolaspis and Macrocheles genera.
The post-embryonic developmental cycle of the Mesostigmata comprises a hexapod larva, two octopod nymphal stages (protonymph and deuteronymph) and the adult (male or female).
CHAPTER II BIOLOGICAL AND ECOLOGICAL CHARACTERIZATION OF THE MITES (ACARI: MESOSTIGMATA)
In conception of Van der Drift (1955) „soil fauna” includs those animals which spend the entire or only a part of life in soil. The criterions of clasification for the invertebrates soil fauna are: the dimension of body, adaptation of the humidity and food conditions, habitats, etc. In soil fauna are included invertebrates with very important role in descomposing process of the vegetal matter, having a big contribution to the soil genesis, like: sprintails, nematods, earthworms, enchytreids and mites.
The mites lives in many habitats: soil, litter, nest of birds, on plants, on animals. The soil offers the best condition for their development. The free species from soil depend by its structure, by the composition of detritus, the amount of humus and water. In arable soils, on one square meter will be found between 5.000 and 100.000 individuals, and in soils of forestry ecosystems and meadows, between 10.000 and 150.000 individuals. The maximum number of individuals in soil is till 5 cm depth, decreasing progressively till 25-30 cm depth. Their existance in the favourite ecosystems, where have a reach food resources depends by the abiotical factors, like: relative humidity, temperature and pH.
In world is known about 650 species of gamasids, belonging to the 90 genera and 20 families, till now. In Romania were identified 273 species, which represents about 42,66% from the total number of species known in the world.
Analysing the position and the role of the gamasids populations in trophic structure of the pedofauna, the results of this study gives us informations regarding the importance of the mites fauna in the matter and energy flows in different trophic levels. Taking account of their food preferences, we could share the gamasids in different categories: omnivorous, phytophagous, parasite, nematophagous and predatorous.
From all researches regarding the ecological role of the gamasids in terrestrial ecosystems, in trophic structure of the pedofauna, the gamasids were considered as second and third descomposers.
CHAPTER III CHARACTERIZATION OF THE STUDIED FORESTRY ECOSYSTEMS
The researches were made in Bucegi massif, in three types of forestry ecosystems.
Ecosystems with Fagus sylvatica is situated on 1200 m altitude, having a south exposure and a small slope, by 100.
Ecosystems with Abies alba is situated at 950-1000 meters altitude, on Valea Urlãtoarei and it has a north-north west exposure and a slope of 100-150.
The ecosystem with Picea abies is situated on 1350 meters altitude, in Valea cu Brazi and has a south exposure and a slope about 350.
3.1 ABIOTIC FACTORS
Climatic characterization of the research periods (september 2001-august 2002; september 2002-august 2003) was based by the description of the monthly evolution of the maximal, minimal and average temperature, of the precipitations and of the humidity, in the air and in the soil.
From the atmospheric point of view, in period september 2001- august 2002 was recorded an increased humidity and a decreased temperature. In period september 2002- august 2003, the situation was changed. Was recorded a increased values of the temperatures and a decreased values of the humidities.
In the soil, the monthly and seasonally evolutions of the temperatures are characteristics for the temperate zone, being favorable for the development of the gamasids fauna. The values of the relative humidities of the soil showed that the ecosystems with Fagus sylvatica and Abies alba had an increased humidities and the ecosystem with Picea abies had low values of this abiotic factor.
In ecosystem with Fagus sylvatica, the soil was less acid, dued the increased composition of calcium from litter. In ecosystem with Abies alba, the acidity of the soil was more decreased in comparation with the other ecosystem, dued the differences in composition of the vegetable matter. In ecosystem with Picea abies, the composition of the vegetable matter, the increased humidity and the presence of the micromycetes determined the highest acidity of the soil.
Pedoclimatical conditions of the studied surfaces are different, depending on the altitude. In ecosystems with Fagus sylvatica, the type of soil is brown eumesobasic of forest with clayey-sandy fine texture, of the medium depth, with a superior productivity and with the horizon A partial damaged.
In ecosystems with Abies alba, the soil is brown of forest, reach in humus and sandy. The parenteral matter is formed by the conglomerates of Bucegi.
In ecosystems with Picea abies, the soil is litosoil cambic, relatively superficial (30 – 35 cm), with a strong washing of the litter and humus layer. The parenteral matter is made by a various resources.
3. 3 VEGETATION
In Bucegi massif, at the middle mountain level are beech forest, fir-tree forests, and deciduous forests. The spruce forests are found at the high altitude, beginning from 1300 meters, in shadowed positions of the mountain. The fir-tree forests occupied small surfaces, depending of some relief shapes.
The beech forest is characterized by the association Symphyto cordati – Fagetum Vida (59) 63 (Sanda Vasile, 2002). The fir-tree forest is characterized by the association Abietetum dacicum Beldie 67; facies Oxalis – Pleurozium Beldie 1967; and the spruce forest by the association Leucanthemo waldsteinii – Piceetum Krajina 1933 (Sanda Vasile, 2002).
CHAPTER IV METHODS AND WORK TECHNICS
4.1 THE CHOOSING OF THE NUMBER OF SAMPLES
For a correctly analyse of the dynamics of the mites fauna, the researches were made taking account by the number and dimensions of the samples, by their periodicity and by the structure of the soil layers.
The researches of the mites fauna were made monthly, in period september 2001- august 2002, (the Ist period) and in period september 2002- august 2003 (the IInd period), in surfaces of 50 m x 50 m. Each surface was shared in smaller areas, with sides of 1 m. Periodical, on fixed data were prevailed random samples (14 in each surface). In the end of research, in this way was analysed as much as possible a big area from the studied ecosystems.
4.2 PREVAILING TECHNICS AND EXTRACTION OF THE SAMPLES
The samples of fauna of mites were collected with a random stratification method, with a metal core, by 10 x 10 x 10 cm dimensions. The levels were separated in the moment of collecting, in the same day, taking account of the macro-morphological criterions in: litter and fermentation layer (OLF) and humus layer (OH). The studied layers had variable dimensions and that’s why the densities of the populations were reported to the square meter. Through this method is possible to shows the heterogeneity of the biotopes and the ecology of the gamasids populations.
The extraction of the gamasids was made in 10-14 days, by Berlese –Tullgren method, modified by Balogh (1956). The samples have been kept in refrigerator, till next extraction. In toto were analysed 2016 samples. The numbering and identification of the mites were made by a binocular Zeiss and a microscope MC3. The conservation of the gamasids fauna was made in an alcohol and glycerin mixture. All identified species are in mites collection of the Institute of Biology – Ecological Stationary from Posada.
The growing in the laboratory condition of the mites were made in one year and gave us information about the productivity of the following species: Veigaia nemorensis (Mesostigmata: Veigaidae) and Neopodocinum mrciaki (Mesostigmata: Macrochelidae).. These species are kept in plastic boxes, on the culture medium formed by vegetable charcoal and CaCO3 (9:1), on 27 C0 temperature and 85%- relative humidity. The food was represented by different live soil invertebrates: springtails, enchytreids, nematodes, immature of oribatids. Their extraction was made manually, from samples collected from the same ecosystems. Their feeding was made at every three days.
4.3 STATISTICAL ANALYSE
The characterization of the ecology of mites population was made by analysing the following statistical parameters: relative abundance (Ar), frequency (F), constancy (C), dominance (D), variation coefficient (CV), numerical density (no. of ind./sq.m.), specifically diversity (index Shannon-Wiener=H(S)), similarity (index Jaccard – q), spatial distribution (index Morisita-Iδ), simple correlations (r), multiple correlations (R), biomass (mg.d.w./sq.m.) and productivity (mg.d.w./sq.m./year). Was used Microsoft Office XP-Excel 2005 system.
CHAPTER V STRUCTURAL CHARACTERISTICS OF THE MITES POPULATIONS
5.1 TAXONOMICAL AND NUMERICAL STRUCTURE OF THE MITES POPULATIONS
In studied forestry ecosystems, the taxonomical structure of the gamasids was composed by 11 families (Epicriidae, Parasitidae, Veigaidae, Ameroseiidae, Aceosejidae, Rhodacaridae, Macrochelidae, Pachylaelaptidae, Laelaptidae, Eviphididae and Zerconidae), with 39 genera and 96 species. These species are belonging to the four trophic categories: 62 predatorous, 17 omnivorous, 15 poliphagous and 2 phyphagous.
From all 96 indentified species, 19 are new for the mites fauna from Romania: Leptogamasus parvulus, Leptogamasus obesus, Paragamasus similis, Lysigamasus neoruncatellus, Lysigamasus truncus, Pergamasus alpinus, Epicriopsis rivus, Cheroseius sp., Zerconopsis remiger, Dendrolaelaps rotundus, Dendrolaelaps foveolatus, Dendrolaelaps willmanni, Dendrolaelaps samsinaki, Rhodacarellus kreuzi, Protogamasellus sp., Macrocheles insignitus, Zercon arcuatus, Zercon athiasi and Zercon tatrensis.
The spatial dynamics of the taxonomical structure of the gamasids shows a maximum number of species in ecosystems with Abies alba (78 species), in ecosystems cu Fagus sylvatica was recorded a closed value (71 species) and the minimum value in ecosystem with Picea abies (67 species) (Figure no.49).
Figure no.49: Spatial dynamics of the number of gamasids species in studied forestry ecosystems, from Bucegi massif.
Analysing the taxonomic spectrum of the gamasids populations from all three ecosystems, predatorous species were dominant, followed by the poliphagous and omnivorous species. The phytophagous species were recorded the most decreased number of individuals.
The evolution of the trophic analyse was constant, with little fluctuations in ecosystems with Picea abies and Fagus sylvatica. From 49 identified predatorous species, in this ecosystem was recorded 38. In ecosystem with Fagus sylvatica from a total of 14 omnivorous species was recorded only 6 (Figure no.50).
Figure no.50: Dynamics of the taxonomic structure of the gamasids in studied forestry ecosystems, from Bucegi massif.
The temporal dynamics of the taxonomic structure of the gamasids showed two distict periods: the first one (september 2001-august 2002) and the second one (september 2002- august 2003). In these three ecosystems was recorded a decreasing of the total number of identified species from the first period to the second, dued to the changing of the abiotic factors (fluctuation of the humidity and temperature, man influence) (Figure no.51).
Figure no.51: Temporal dynamics of the number of gamasids species from the studied forestry ecosystems, from Bucegi massif.
Investigations made in these forestry ecosystems showed the presence of some characteristic species. In ecosystem with Fagus sylvatica the characteristic species were: Paragamasus vagabundus, Veigaia kochi, Gamasolaelaps multidentatus, Gamasolaelaps excisus, Dendrolaelaps samsinaki, Rhodacarellus silesiacus, Macrocheles insignitus.
In ecosystems with Abies alba were identified the following characteristic species: Leptogamasus obesus, Leptogamasus variabilis, Arctoseius brevicheles, Asca bicornis, Dendrolaelaps willmanni, Geholaspis mandibularis, Olopachys scutatus, Prozercon fimbriatus. For ecosystem with Picea abies, the characteristic species were: Holoparasitus excisus, Leptogamasus doinae, Pergamasus alpinus, Hypoaspis montana, Zercon athiasi and Zercon tatrensis.
The analyse of the relative numerical abundances of the gamasids populations revealed some common species for all three forestry ecosystems, dominant in the mites structure: Paragamasus similis, Veigaia nemorensis, Neopodocinum mrciaki, Eviphis ostrinus. In ecosystems with Fagus sylvatica species Veigaia cerva and Veigaia paradoxa, were characteristic species for the beech forest (Index IV, Table no 3, 4). For the ecosystems with Abies alba the most important functional species were Rhodacarellus kreuzi and Prozercon traegardhi (Index V, Table no 3, 4). These have preferences for the coniferous forests with an increased humidity of the soil, and in ecosystems with Picea abies, the following species had recorded the high values of the relative numerical abundances: Pergamasus laetus, Leptogamasus tectegynellus, Pergamasus athiasae, Zercon triangularis, Zercon fageticola, species who have preferences for the coniferous forest situated on the mountain zones (Index VI, Table no 3, 4). Distribution in soil layers of these mites revealed a higher numerical abundance in litter and fermentation layer, in comparation with the humus layer. This distribution was demonstrated by the values of the Morisita index, which indicate the aggregation tendency of the gamasids. Species who aggregate are in general predatorous, which depend of the food resources. The favorable climate conditions (relative humidity of the soil over 60%; pH between 3,6 and 5,23) determined the colonization of the litter and fermentation layer with fungivorous species (springtails, enchytreids, nematodes, oribatids), which represents the food resource for the gamasids.
Bio-edaphical conditions from all three ecosystems determined an increased number of the euconstant and constant species. In ecosystems with Fagus sylvatica, dued to the stability of the environment, was recorded the most increased number of euconstant and constant species.
Negative influences of the man interventions (wood cuttings) in ecosystem with Abies alba determined a decreasing of the euconstant and constant species and a increasing of the accidentally species. The big trophic diversity caused favorable conditions for the development of accidentally species.
26,04% from the total number of species are belonging to the 8,9,10 frequency classes. Species with the most wide ecological valence were: Paragamasus similis, Leptogamasus parvulus, Veigaia nemorensis, Neopodocinum mrciaki, Hypoaspis aculeifer.
The values of the diversity indices Shannon-Wiener demonstrated that in ecosystem with Abies alba were favorable conditions for a specifical diversity closed to the maximum, in comparison with ecosystem with Picea abies, where bio-edaphical conditions (altitude, slope and temperature) determined a minimal diversity. Ecosystem with Fagus sylvatica recorded an average specifical diversity (Index IV, V, VI; Table no 3, 4).
Taking account of the existence of the same category of the primary producers (coniferous) and of the same type of soil, between gamasids populations from ecosystems with Picea abies and Abies alba, characterized by the vegetal associations Leucanthemo waldsteinii – Piceetum and Abietetum dacicum was a high level of similarity. The smaller level of similarity was recorded between populations of gamasids from ecosystems with Picea abies and Fagus sylvatica, characterized by the vegetal associations Leucanthemo waldsteinii – Piceetum and Symphyto cordatai – Fagetum, dued to the differences of the vegetable layers and of the pedological and climatic characteristics.
The influence of the abiotic factors on the structure of the mites populations was demonstrated by the simple and multiple correlation coefficients. The seasonal analyse of these coefficients showed that the increasing of the temperature determined a decreasing of the numerical abundances of the gamasids populations. It is known that these species on a temperature over 250 C migrate in sol, till 15 cm depth. Increasing of the relative humidity and of the acidity of soil influenced in a positive way the evolution of the gamasids. In these environmental conditions was created a favorable habitat for the development of the others invertebrates groups, which represent the thropical source for the predatorous mites.
5.2. DYNAMICS OF THE GAMASIDS POPULATIONS
In period of study 2001-2003 the most increased numerical density of the gamasids was recorded in ecosystems with Picea abies (86.693 no.of ind./sq.m.), followed by the ecosystem with Fagus sylvatica (48.672 no.of ind./sq.m.) and the most decreased in ecosystem with Abies alba (38.272 no.of ind./sq.m.). The temporal dynamics showed the impact of the abiotical factors and of human interventions on the annual values of this parameter in the second period of study. Were recorded a decreasing of numerical density with 53,24% in ecosystem with Picea abies, with 32,14% in forest with Abies alba and with 24,11% in ecosystem with Fagus sylvatica. Seasonal dynamics present maximum and minimum values, in autumn and in summer, in the first period and at the beginning of the spring and in winter, in second period.
In ecosystem with Fagus sylvatica, in period september 2001- august 2002, the numerical density was very increased (27.672 no.of ind./sq.m.- adults, 3443 no.of ind./sq.m.- immatures), in comparison with period september 2002- august 2003, when the decreased values of the temperature and of the humidities determined a smaller values of this statistical parameter (21.000 no.of ind./sq.m.- adults and 3.765 no.of ind./sq.m.- immatures) (Figure no.108).
Figure no.108: The density (no.of ind./sq.m.) of the gamasids species (adults + immatures) from ecosystem with Picea abies, in first and second period of study.
In ecosystem with Abies alba in first period, the gamasids had an increased density (22.800 no.of ind./sq.m.- adults, 5.342 no.of ind./sq.m.- immatures), in comparison with the second period, when the numerical density of species was recorded important decreasing (15.472 no.of ind./sq.m.- adults, 2.458 no.of ind./sq.m.-immatures) (Figure no.114).
Figure no.114: The density (no.of ind./sq.m.) of the gamasids species (adults + immatures) from ecosystem with Abies alba, in first and second period of study.
In ecosystem with Picea abies, in first period, the numerical density of the adults was 59.072 no.of ind./sq.m. and of the imature of 2.686 no.of ind./sq.m., in comparation with the second period, when was recorded important decreasing (27.621 no.of ind./sq.m. and 1.373 no.of ind./sq.m.) (Figure no.120). This decreasing was dued to the washing of the litter and layer layer by the abundant precipitations, from the second period of the study, damaging the habitat of mites.
Figure no.120: The density (no.of ind./sq.m.) of the gamasids species (adults + immatures) from ecosystem with Picea abies, in first and second period of study.
Monthly and seasonally oscillations of the numerical densities of the gamasids populations have a favorable evolution in autumn (recording to the maximum values) in the both periods of the study. This aspect was directly correlated with the temperature and humidity, which provided a favorable microclimate for the development of mites.
Regarding the vertical distribution of the individuals and the influence of the abiotic factors, the obtained data are not different in these three ecosystems. We observed that the litter and fermentation layer was more populated then humus layer.
In studied ecosystems the ratio adults / immatures was constantly higher that 1, presenting fluctuation on the whole period of the study. In first period this ratio recorded values between 41 and 5, and in the second period decreased from 25 to 3. This evolution demonstrated that the gamasids populations were permanently modified by the appearance of the immature stages, characteristic phenomenon for the gamasids populations from anterior biotopes (Figure no. 106; 107). The appropriate monthly values of the ratio adults/immatures presented the same rectilinear evolution in the both research period. In spring, the number of gamasids species increased dued to the development of the immatures of gamasids (period of the year favorable for the ontogenetic evolution of the majority of the invertebrates from forestry ecosystems).
Figure no.106: The ratio adults/immatures of the gamasids populations in studied forestry ecosystems, from the first period.
Figure nr.107: The ratio adults/immatures of the gamasids populations in studied forestry ecosystems, from the second period.
From the 96 identified species, 23% were numerical dominant: Pergamasus laetus, Paragamasus similis, Paragamasus sp., Lysigamasus neoruncatellus, Leptogamasus tectegynellus, Leptogamasus parvulus, Vulgarogamasus zschokkei, Veigaia nemorensis, Veigaia cerva, Veigaia exigua, Rhodacarellus kreuzi, Neopodocinum mrciaki, Macrocheles montanus, Macrocheles decoloratus, Geholaspis longispinosus, Hypospis aculeifer, Pachylaelaps furcifer, Pachyseius humeralis, Eviphis ostrinus, Zercon triangularis, Zercon fageticola, Prozercon kochi, Prozercon traegardhi and from these 75% were important in structure and function of the gamasids populations, through their double valence as euconstant – eudominant and constant-dominant elements.
CHAPTER VI . THE BIOMASS AND THE PRODUCTIVITY OF THE MITES POPULATIONS
6.1 THE BIOMASS
The role of the gamasids as intermediate link in energy flow from soil was underlined by showing the dynamics of the biomass and productivity. In soil of spruce forest, the 67 species recorded a total average biomass of 296,20 mg.d.w./sq.m. In beech forest the 71 species have a total average biomass by 166,3 mg.d.w./sq.m. and in fir-tree forest, all 67 identified species recorded a total average biomass by 130,77 mg.d.w./sq.m. Making a comparison between the two periods of the study, the values of this parameter decreased in the second year with 41,52%, dued to the man negative influence (Figure no.130).
Figure no.130: Monthly dynamics of the gamasids biomass (mg.d.w./sq.m.) in soil layers, from the forestry ecosystems, from the first and second periods.
The biomass was obtained by reporting of the average individual weight of a 10 gamasids to the values of the numerical abundances of all species. These ten species were: Epicrius mollis, Paragamasus similis, Vulgarogamasus zschokkei, Porrhostaspis lunulata, Pergamasus athiasae, Veigaia nemorensis, Macrocheles decoloratus, Geholaspis longispiosus, Eviphis ostrinus, Zercon fageticola. The obtained biomass represents 42.75% from the total average biomass of the gamasids from the soil in ecosystem with Fagus sylvatica, 50,7% in ecosystem with Abies alba and 39,98% in ecosystem with Picea abies.
Influenced by the abiotic factors (temperature, humidity and pH), the seasonal dynamics of the biomass recorded the most increased values in september and octomber and the most decreased in december and january. In autumn, the soil humidity and the thickness of the litter and fermentation layer were optimal factors for the development of invertebrates populations, wich represents food resource for mites. In this way the recorded biomass in this time of the year was more increased. In winter, the metabolism and the activity of the mites were more decreased, and the biomass and productivity had a descendent evolution.
In organic layers of the soil, the maximum values of the biomass were recorded in the both periods of the study, in litter and fermentation layer (455,42 mg.d.w./sq.m.) and the minimum values in humus layer (137,74 mg.d.w./sq.m.).
The big importance of species Veigaia nemorensis and Neopodocinum mrciaki in structure of the gamasids populations, by their increased numerical abundances was an argue for the analysing of their biomass in laboratory conditions. The annual average biomass of the Veigaia nemorensis represented 25,56% from the total average biomass recorded in forest with Fagus sylvatica, 19,53% in ecosystem with Abies alba and 14,34% in ecosystem with Picea abies. Neopodocinum mrciaki brought a contribution with 24,56% in beech forest, with 11,83% in fir-tree forest and with 7,94% to the total biomass in spruce forest.
5.2 THE PRODUCTIVITY
The highest productivity of the gamasids populations was recorded in ecosystem with Picea abies (28,85 mg.d.w./sq.m./year) and the lowest in ecosystem Abies alba (-56,87 mg.d.w./sq.m./year). This negative influence is determined by the man influence (wood cuttings). In ecosystem with Fagus sylvatica the productivity was – 4,10 mg.d.w./sq.m./year. Comparing the productivities from the two periods of study in analysed ecosystems, we showed that in the first year was recorded the most increased value (56,21 mg.d.w./sq.m./year) and in the second year this value decreased (-27,26 mg.d.w./sq.m./year). The causes of this oscillated evolution were the differences of humidities of soil and the man intervention from the second period of study (Figure no.151).
Figure nr.151: Monthly dynamics of the gamasids productivity (mg.d.w./sq.m./year) in soil layers, from the forestry ecosystems, in the first and second periods.
The seasonal dynamics showed maximum values of the productivity in autumn and in spring, dued to the favorable environmental conditions (the increased humidity of soil) and to the appearance of the imature stages of other invertebrates – the food resource for the gamasids. That’s way the populations of mites was increasing.
In soil, on the litter and fermentation layer, the gamasids had an important role in fixation of the energy by accumulation of biomass, in comparation with the humus layer, where their energetical contribution was more decreased. The cause of this phenomenon is the migration in soil of these invertebrates.
From all identified species, the most important (by their numerical abundances and biomass) in structure and function of mites populations were species Veigaia nemorensis and Neopodocinum mrciaki. These predatorous mites were growing in laboratory conditions and was analysed their productivity. Because of the trophic spectrum and of the reduced experimental space, these species recorded a decreased productivy. The gamasids are a very fast and mobile species, which are in a continous process of the food looking, like: larva of insects, enchytreids, nematods, springtails, imature of oribatids, pollen, fungi. This trophical spectrum in laboratory conditions cloud not be provided, which influenced the results.
The intitled paper: ”Ecological researches of mites populations (Acari: Mesostigmata) from soils of some forestry ecosystems from Bucegi massif” brings many new informations. These objectives were followed: the biological and ecological characterization of the mites populations; the charaterization of the studied forestry ecosystems; the identification of the main abiotic factors (temperature, humidity, pH ); the analyse of the faunistical spectrum of the studied ecosystems; the analyse of the structural particularities of the mites populations and of their dynamics; the influence of the abiotic factors on the structure of the gamasids populations; the role as intermediate link in energy flow at soil level.
The ecological researches on the gamasids populations were made for the first time in Bucegi massif. The ecological contributions on these populations were the analyses on the structural particularities, which involved a study of their taxonomical spectrum. Were identified 11 families, 39 genera and 96 species. The identified species were classified in four trophic categories: 62 predatorous, 17 omnivorous, 15 polyphagous and 2 phytophagous. This classification certified that the gamasids were represented mostly by the predatorous species, which had an important ecological role in trophic structure of the pedofauna, as the third level consumers.
In ecosystem with Abies alba were identified 78 species, in ecosystems with Fagus sylvatica 71 species and in ecosystems with Picea abies 67 species. The contribution on the knowledge of the mites fauna consisted in identification of 19 new for the fauna of Romania.
The variations of the spatial dynamics of the specifically diversity and of the trophic structure between the populations of mites from the studied forestry ecosystems were caused by the pedological, climatical and vegetal differences.
Based on the frequencies and numerical abundances of the gamasids species, for the first time in forestry ecosystems from Bucegi massif was studied the level of ecological plasticity and preferences of the gamasids for a certain type of forestry ecosystem.
Were identified common species for the three types of forestry ecosystems and characteristics species for each forest. 45 species have big ecological valences; 9 species are characteristics for the ecosystem with Fagus sylvatica, 10 species for ecosystem with Abies alba and 6 species in ecosystem with Picea abies. The common species were more abundant than the characteristic ones. We can conclude that the relationship between the gamasids fauna was not directly correlated with the type of vegetation or soil.
In ecosystem with Fagus sylvatica, the characteristic identified species were: Paragamasus vagabundus, Veigaia transisalae, Veigaia kochi, Gamasolaelaps multidentatus, Gamasolaelaps excisus, Dendrolaelaps samsinaki, Rhodacarellus silesiacus, Cheroseius sp., Macrocheles insignitus. The ecological researches demonstrated that the temperature and humidity fluctuations, the low acidity of the soil influenced the specifical composition of the gamasids populations, dominated being those belonging to the Rhodacaridae family (Gamasolaelaps multidentatus, Gamasolaelaps excisus, Dendrolaelaps samsinaki, Rhodacarellus kreuzi), which can easily adapt to the unfavorable environmental conditions, dued to the small dimensions of their body.
In ecosystem with Abies alba, characteristic species were: Holoparasitus rotulifer, Leptogamasus obesus, Leptogamasus variabilis, Arctoseius brevicheles, Asca bicornis, Dendrolaelaps willmanni, Amblyseius sp., Geholaspis mandibularis, Olopachys scutatus, Prozercon fimbriatus. These species are in majority predatorous, the limitative factor of their development being the food. The existence of a favorable bioedaphical conditions (the layer of litter and fermentation with a developed stratum of moos in proportion of 95%, which determined an increased humidity of soil) provided a good habitat for the others populations of invertebrates, which represent the food resource for these mites.
In ecosystem with Picea abies, the taxonomical structure revealed some characteristic species: Holoparasitus excisus, Leptogamasus doinae, Pergamasus alpinus, Hypoaspis montana, Zercon athiasi and Zercon tratensis. These species prefer the forests from a high altitude. Comparing the soils of the studied forestry ecosystems, in beech forest the acidity is more increased, dued to the differences of the vegetable matter composition, of soil humidity and of the presence of the fungi.
The ecological researches on the gamasids populations confirmed that these species had preferences for the hygromesophytic habitats. Comparing the taxonomical structure of the mites populations from the studied forestry ecosystems, in fir-tree forest the abiotic factors (the increased humidity and the acidity of soil) and the structure of soil (mull-moder humus) had determined the highest number of species. In ecosystem with Picea abies, the number of the identified species was the lowest, caused by the high altitude and by the washings of the litter and fermentation layer.
Another ecological contributions on the study of the gamasids were the identification of the common species, eudominant, euconstant, from the litter-fermentation layer and from humus layer. These were: Paragamasus similis, Veigaia nemorensis, Neopodocinum mrciaki, Eviphis ostrinus.
In ecosystem with Fagus sylvatica species Veigaia cerva and Veigaia paradoxa are characteristic for the beech forest. In ecosystem with Picea abies, characteristic species were: Pergamasus laetus, Leptogamasus tectegynellus, Pergamasus athiasae, Zercon triangularis, Zercon fageticola. In ecosystem with Abies alba, the most important functional species were: Rhodacarellus kreuzi, Hypoaspis aculeifer, Pachyseius humeralis, Prozercon kochi, having preferences for the coniferous forests with an increased humidity of the soil
Another important contribution on the ecological study on the mites from some soil from forestry ecosystems from Bucegi massif was the analyse of the specifical diversity in relation with bio-edaphical conditions. Along the two years of study, the specifical diversity had an oscillatory evolution. In spatial dynamics, in ecosystem with Abies alba, in comparison with ecosystem with Picea abies, gamasids populations had recorded a diversity very closed to the maximum hypothetical one, dued to the favorable bio-edaphical conditions (altitude, slope and temperature). On the soil layers, in humus was identified the highest diversity. The mull-moder humus from the beech and fir-tree forests with a reach organic matter action as an additional trophic substrate, increasing the habitat. In ecosystem with Picea abies, the washing of the litter and fermentation layer determined a decreasing of the specifical diversity. In temporal dynamics, period september 2001- august 2002 provided favorable conditions for an increased diversity, in comparison with period september 2002- august 2003, when dued to the macro and microclimatic changes and to the man interventions (the wood cuttings), the values of this parameter decreased.
Ecological researches on the gamasids populations confirmed the fact that these species had in majority a negative binomial distribution. On the litter and fermentation layer, species which had the aggregation tendency on maximum were: Pergamasus quisquiliarum, Gamasodes spiniger, Arctoseius cetratus, Melichares juradeus, Dendrolaelaps rotundus, Rhodacarellus kreuzi and in humus layer: Pergamasus quisquiliarum, Arctoseius cetratus, Leitneria granulata, Rhodacarellus kreuzi, Zercon triangularis şi Zercon romagniolus.
The aggregation is allways influenced by the different biotical and abiotical factors as: interspecifical relationships, temperature, relative humidity of the air and soil, the structure of the microhabitats, the development stages of the gamasids populations, their morphological and physiological modifications, the availability of the food resource. The low level of the homogeneity and the high number of species, reflects the diversity of soil, of the vegetable layer and especially the mobility of the mites.
Species which had this aggregation tendency were most of them predatorous, which depended of food accessibility. The high percentage of the aggregation tendency recorded to the litter and fermentation layer, in comparation with the humus layer, were dued to the favorable environmental conditions (the relative humidity higher that 60%, the increased acidity) for the colonization with species which feed with fungi (springtails, enchytreids, nematods, oribatids) – the food resource for the mites.
The influence of the food source availability on the aggregate distribution of the gamasids is not demonstrated yet, this relation beeing an important subject of study in the future.
Another contribution to the ecological studies of the gamasids in forestry ecosystems from Bucegi massif is the similarity between the populations from the studied biotopes.
Between gamasids populations from the ecosystems with Picea abies and with Abies alba were a high similarity, taking account of the existance of the same category of the primary producers (conifers), of the same type of soil. The identified common species for these forests were: Gamasodes spiniger, Leioseius lawrencei, Dendrolaelaps foveolatus, Pachylaelaps pectinifer, Zercon peltatus, Zercon peltadoides, Zercon triangularis, Zercon pinicola and Zercon carpathicus.
The lowest similarity were recorded between structure of the mites populations from ecosystems with Picea abies and Fagus sylvatica, caused by the pedological and the vegetation differences, only three species being common: Eugamasus monticolus, Iphidozercon venustulus and Pachylaelaps latior.
The same structure of the soil, the small differences of the temperature and humidity allowed identification of 9 common species, in soil of ecosystems with Abies alba and Fagus sylvatica: Holoparasitus minimus, Paragamasus motasi, Paragamasus sp., Veigaia paradoxa, Epicriopsis rivus, Leitneria granulata, Macrocheles decoloratus, Pachylaelaps magnus and Olopachys vysotskajae.
This analyse showed that the structure elements of the herbaceous and shrubs layers, the chemical and morphostructural characteritics of soil, the specifical micro and macroconditions for each biotope provided particular configurations of the structures of the gamasids populations.
These ecological characteritics confirmed researches made by Adriana Georgescu in similar ecosystems from Romania, in period 1978-1982. According to them were identified characteristics species for the type of soil and for the vegetable associations: Olopachys scutatus, Olopachys vysotskajae, Macrocheles montanus, Laseioseius berlesei, Parasitus fucorum, Veigaia transisalae.
The analyse of the dynamics of the populations structure of the adults and immatures mites was another ecological contribution to their study. The monthly, seasonaly and annualy variations were been established. The original contribution of this thesis is dynamics study on time and space scale of the mites populations structure from some forestry soils from Bucegi massif, taking account of the environmental factors.
In spatial dynamics, the ecological researches revealed that the microclimatic particularities caused distinct characteristics of the mites populations. The ecosystem with Picea abies offered the best enviromnental conditions, beiing recorded the most increased number of individuals (86.693 no.of ind./sq.m.). In ecosystem with Fagus sylvatica the environmental condition were not so favorable, beeing recorded 48.672 no.of ind./sq.m. In these two ecosystems, the gamasids was a stable and complex comunity. The comunity of gamasids from forest with Abies alba was in ecological unbalance, dued to the man intervention, beeing recorded only 38.272 no.of ind./sq.m.
In temporal dynamics, in period september 2001 – august 2002 were recorded 110.544 no.of ind./sq.m. and in perioad september 2002 – august 2003, 64.093 no.of ind./sq.m. These fluctuations reflects the negative impact in the fir-tree forest of the man intervention (the wood cuttings) and of the modifications of the abiotic factors (decreasing of the soil humidity and increasing of the temperature). These abiotic parameters were key factors for the evolution of the gamasids populations.
From the numerical poit of view, in soil layers, the dynamics of the gamasids fauna showed a predominance of the populations in litter and fermentation layer (120.694 no.of ind./sq.m.), in comparation with humus layer (45.701 no.of ind./sq.m.). Abiotic factors and pedological structure caused this difference. Mull- moder humus from the soil of fir-tree and beech forests was a favorable substratum for the gamasids populations.
The ratio adults/imatures was favorable to the matures and had fluctuation on the research period. In spatial and temporal dynamics the adults represented about 90% from all population, in all three ecosystems. The dynamics of the demographical structure showed an increasing of the numerical densities of the imatures from 8.909 no.of ind./sq.m., in the first period to the 10.158 no.of ind./sq.m., in the second one. In this way was demonstrated that the gamasids populations were permanently modified by the appearence of the immature stages. However, the identified immature stages were weak represented in comparation with adults. These two stages of developement could have different ecological niches. This aspect was study in Romania only at Zerconidae family by Adina Cãlugãr, in 2003.
Allthrough geographical viewpoint the three studied ecosystems were very similar and were under the influences of the same abiotic factors, between populations of gamasids were some differences of the maximum and minimum moments and in the time when were produced the migration in soil. These differences were influenced by the specifical structure of the gamasids populations and by the distinct microclimatic conditions.
The correlated influence of the environmental factors on the numerical structure of the mites populations was demonstrated by the values of the simple and multiple correlations indices. Their analyse allowed to establish some ecological aspects:
– the increasing of the temperature determined a decreasing of the numerical abundances of the gamasids populations. In these conditions only some small species can adapt, like: Rhodacarellus kreuzi, Rhodacarellus silesiacus, Asca bicornis,
– the increasing of the relative humidity and of the soil acidity determined a high values of the numerical abundances. This fact confirms that the gamasids species prefer the hygromesophillic habitats,
– the synergic action of the temperature and humidity has a big influence on the numerical abundances values, in both layers of the soil,
– the synergic action of the temperature and of the pH had a small influence on the numerical structure of the gamasids populations;
– the synergic action of the humidity and of the pH had an importnat influence the gamasids populations, by developening of a favorable conditions to the fungi, which represents the food resource for the soil invertebrates.
Another analised ecological aspect was the functional characterization of the mites populations. Was studied two parameters: biomass and productivity. An original contribution was the quantification of the total biomass, by reporting of the individual average weight of the 10 species to the total numerical abundances. These ten species are: Epicrius mollis, Paragamasus similis, Pergamasus athiasae, Vulgarogamasus zschokkei, Neopodocinum mrciaki, Veigaia nemorensis, Macrocheles decoloratus, Geholaspis longispinosus, Eviphis ostrinus, Zercon fageticola. Their biomass represented 44,4% from the total biomass of the gamasids from the forestry ecosystems.
The spatial and temporal dynamics of the biomass and productivity showed an important influence of the abiotic factors. In spatial dynamics the highest biomass and productivity were recorded by the gamasids populations from the spruce forest, and the lowest on those from beech forest. The increasing of the number of accidentally species from the soil of ecosystem with Abies alba determined high values of the total biomass and a decreasing of the productivity.
In soil, making a comparison between litter-fermentation layer and humus layer, the first one through his trophical diversity provided the best conditions for the biomass accumulation of the species and for an increased values of their productivity.
The temporal dynamics of the biomass and productivity of the gamasids reached the highest values in autumn, when the increased soil humidity and the thickness of the litter and fermentation layer were favorable factors for the invertebrates’ development, the food resource for these mites. In winter, the metabolism and activity of mites were lower, involving a decreasing of the biomass and of the productivity.
These studies confirm others researches made in similar forestry ecosystems from Romania in Retezat and Cãlimani mountains, by Libertina Solomon (1982) and by Adriana Georgescu (1988).
The big importance in structure of the mites populations of the species Veigaia nemorensis and Neopodocinum mrciaki, by their increased numerical abundances constituted an argue to analyse their biomass and productivity in laboratory conditions. The spruce forest ofered the best life conditions to Veigaia nemorensis, the quantified biomass representing 14,34% from the total value of this parameters, 19,53% from those to the fir-tree forest and 25,56% from those to the beech forest.
Biomass evolution of the Neopodocinum mrciaki was different. This mite contributed with 24,56% to the total value of the annual biomass from the beech forest, with 11,83% from fir-tree forest and with 7,94% from spruce forest. These researches confirmed the studies made by D.C. Coleman and J.T. McGinnis (1970), Athias-Henriot C. (1978), Libertina Solomon (1982) and Adriana Georgescu(1988), which demonstrated that the Veigaia nemorenis has the biggest ponderable dominance from all identified gamasids.
Because of the trophical spectrum, of the reduced experimental space and to the increased rate of the mortality, these species recorded a decreased productivy. The gamasids are a very fast and mobile species, which are in a continous process of the food looking. Their trophical spectrum in laboratory conditions could not be provided, which influenced the results.
The annual productivity of the gamasids populations was decreased, confirming in this way that the mites have a small contribution to the energy flow of the invertebrates fauna from soil. The chitinous structure of the gamasids, the energetical losses dued by their high mobility, their strictly trophic preferences caused the energetical losses. For a better clarification of this aspect is necessary the continuation of these studies.
The results of this thesis have not only theoretical importance but can be useful in environmental protection programmes. The existence of quantitative and qualitative parameters, which characterize the structure and functions of the edaphic mites populations and are influenced by the abiotic and biotic factors, allowes the usage of this group as bioindicators for the soil. This paper brings new contributions to the scientifical knowledge of the mites and it can be a base for a future researches.
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Cuvinte cheie: mites populations, structure, dynamics, distribution, biomass, productivity