1 Colonization and development of oribatid mite communities (Acari: Oribatida) on post-industrial dumps Piotr Skubała
3 Colonization and development of oribatid mite communities (Acari: Oribatida) on post-industrial dumps Honour species Pay attention to small organisms W a l t e r & P r o c t o r ( )
4 PRACE NAUKOWE UNIWERSYTETU ŚLĄSKIEGO W KATOWICACH NR 2219
5 Colonization and development of oribatid mite communities (Acari: Oribatida) on post-industrial dumps Piotr Skubała Wydawnictwo Uniwersytetu Śląskiego Katowice 2004
6 Editor o f Series: Biologia Paweł Migula Reviewers Mieczysław Górny Wojciech Niedbała
7 Contents Preface - soil as the basis for civilization... 9 Acknowledgements Chapter 1 Introduction Oribatid mites - life hidden in the soil Oribatids perform an important ecological service Contribution of oribatids to global biodiversity Oribatids in biomonitoring studies...21 Chapter 2 Save our dumps (SOD) as an entity Post-industrial dumps as a unique experiment for ecologists A chance to test successional theories Oribatids on dumps...27 Chapter 3 Objectives of the study Chapter 4 Environmental setting Dumps and their surroundings - history, origin, deposits and other considerations General remarks Details of the post-industrial dumps Soil on post-industrial dumps and in adjacent biotopes Vegetation on post-industrial dumps and adjacent biotopes 43
8 Chapter 5 Material and m ethods Collection, extraction, separation and identification of mites Statistical analyses Basic indices Similarities and differences Associations and correlations Multivariate analysis Analysis of dispersal Soil analysis Chapter 6 Sampling strategy...59 Chapter 7 Oribatid mites on post-industrial dumps - characteristics of c o m m u n itie s Pioneer oribatid communities in extreme habitats Formation of oribatid mite communities - rate of development Abundance Species richness Species diversity Structural changes Species abundance relationship Spatial distribution Vertical distribution Oribatid systematic cohorts on dumps Oribatids on contaminated dumps Developmental stages of oribatid communities Similarities and differences Driving factors and the formation of oribatid communities Direct long-term studies of succession Chapter 8 Colonizers and persisters on dum ps Chapter 9 Ways of migration, pool of colonizers Chapter 10 Oribatid mites in assemblages of m esofauna Chapter 11 Succession theories applicable to oribatids on dumps..170
9 Chapter 12 Biodiversity of oribatid fauna on dumps and in nearby biotopes Remarks on selected oribatid species (subspecies) new for the Polish fa u n a a n d fo r U p p er S ile s ia Chapter 13 Conclusions R eferen ces Streszczenie Zusammenfassung Appendices (on CD-ROM) 1. Basic data on the post-industrial dumps studied 2. Particle-size analysis of the soil at the study sites 3. Soil structure and colour in soil layers at the study sites 4. Physical and chemical properties of the upper (A) and lower (B) sections of soil samples from Chorzów (4a), Katowice Wełnowiec (4b), Zabrze Biskupice (4c), Zabrze Makoszowy (4d), Katowice Murcki (dump) (4e), Katowice Murcki (sedimentation tank) (4f) and Brzeszcze (4g), from which oribatid mites were extracted 5. Check-list of plant species on the study dumps and in the neighbouring biotopes 6. Check-list of oribatid species on the study dumps and in the neighbouring biotopes 7. General view of the study sites at seven localities (34 colour photos) 8. SEM-photos of selected oribatid species
11 We know more about the movement of celestial bodies than about the soil underfoot. L eo n a r d o D a V in c i, c ir c a s Preface - soil as the basis for civilization For centuries soil and the life in it were of little interest to humankind. Two centuries ago, in 1788, Gilbert White called our attention to life in the soil. He discussed seven functions of earthworms: by boring, perforating, and loosening the soil, and rendering it pervious to rains and the fibres of plants, by drawing straws and stalks of leaves and twigs into it; and, most of all, by throwing up such infinite numbers of lumps of earth called worm-casts [...] (A lle n, 1900). The value of earthworms in the soil system is better known from Charles Darwin s classic book The formation o f vegetable mould through the action o f worms with observations on their habits. However, soil biology began to develop after the Second World War. There was no comprehensive publication on the soil fauna until 1950 when two books with the same title Bodenbiologie written by Kuhnelt and Franz, summarised the knowledge of soil fauna up to that time (V eeresh & R a ja gopal, 1988). The situation has not changed much since. There are only a few academic books on soil biology, and these are not new ones; and soil science is rarely taught at universities, at least in Poland. The true enigma is that although decomposition is the equal of photosynthesis in ecosystem importance, and half or more of terrestrial biodiversity may be tied to the soil-litter system, the study of soil biology has been neglected (W a lt e r & P r o c t o r, 1999). The soil is a living organism of fabulous complexity. Soil systems contain some of the most species-rich communities in nature. Most authors describe soil communities as being amongst the most species-rich components of terrestrial ecosystems (A n d erso n, 1975a, 1978; G h ila r o v, 1977; S ta n to n, 1979). Well-developed temperate woodland soils may contain up to a thousand species of soil fauna
12 (A n d erson, 1975a). The calculation made by Fittakau & K lin g e (1973) is even more impressive; they estimated that 80% of the total animal biomass in the Amazonian rainforest is soil fauna. U s h e r et al. (1979) used impressive words to describe soil communities as the poor man s tropical rainforest. It is noteworthy that only a proportion of all the soil animal species has been described and very little is known about their role, community structure and dynamics. Research concerning soil is not purely an academic subject. The soil is the very basis of earth s productivity. It is fundamental to agriculture and forestry, water purification and biogeochemical cycling, and is the grounding for civilization (B e h a n - P e lle t ie r & N e w to n, 1999). This is particularly true where human activity tends to induce irreversible disturbances (Lebru n, 1979). At a time when demographic pressure is too high, and when the needs of human population are intense and immense, it is wise to realize that the soil is central to human survival. Meanwhile, soil biology has fallen somewhat behind advances in the understanding of other types of communities ( G i l l e r, 1996). Soils are still the least understood habitats on Earth, while also being among the most biologically diverse (B e h a n - P e lle tie r & N e w to n, 1999). From both theoretical and applied perspectives, this state of affairs is surprising from three points of view ( G ille r, 1996). 1. Firstly, in terms of the importance of soils to global biodiversity. 2. Secondly, in terms of the ecosystem processes, in particular those that occur in the soil. The soil performs a fundamental role as the location where 60% to 90% of terrestrial primary production is decomposed. Soil fauna appears to be the major regulatory agent of soil processes affecting the physical and chemical fertility of soils. Moreover, a full understanding of above-ground ecosystem processes is not possible without consideration of processes occurring in the soil (M ay, 1997; O s le r & B e a ttie, 2001). 3. Thirdly, soil fauna can offer a suite of bioindicators for classification of soils and detection of disturbances and pollution. The place of mites, which are the subject of this study, within the soil, is important. Their quantitative and qualitative roles in energy flow are not fundamental; however, their interactions with other members of soil biota are of great ecological meaning. The contribution of Acarology to the understanding of our black box, which may be a good description of the soil system, could be immense.
13 Acknowledgements The author would like to thank Mrs Ewa Skipirzepa, Ms Sabina Słomian and Dr. Aleksander Stodółka for excellent technical assistance. I must especially acknowledge Ms Krystyna Pilarczyk for her great effort in sampling, extracting and sorting the microarthropods. I wish to express my grateful thanks to Prof. Wojciech Niedbała (A. Mickiewicz University in Poznań) and Prof. Stanisław Seniczak (University of Technology and Agriculture in Bydgoszcz) for confirming identifications of Phthiracaridae and juvenile forms, respectively. I am also grateful to Dr. Zbigniew Wilczek and Dr. Gabriela Woźniak (University of Silesia) for making phytosociological surveys of the study sites. Many thanks to Dr. Tomasz Zaleski (Agriculture Academy in Cracow) for undertaking chemical and physical analyses of soil and Dr. Ryszard Kulik (University of Silesia) for taking excellent photos of the study sites. I wish to thank Dr. hab. Jerzy Błoszyk (A. Mickiewicz University in Poznań) and Dr. Ritva Niemi (University of Turku, Finland) for making SEM-photos of selected oribatid species. I warmly thank Dr. John Parker (Forest Research, Alice Holt Lodge, United Kingdom) for checking the manuscript. Last but not least I thank my wife Elvira and daughter Kaja for their forbearance in the period of my scientific inquiries and preparation of the book. The studies were supported by grant project No. 6 P04F from the Polish State Committee for Scientific Research and by the grant projects Colonization of post-industrial dumps by saprophagous oribatid mites (Acari: Oribatida) (1998) and Studies on succession of oribatid communities (Acari: Oribatida) on post-industrial dumps (1999) from the University of Silesia. I dedicate this book to those scientists whom I have met in Poland and abroad and who have supported me in my scientific career by interesting discussions and helpful comments. Special thanks to Prof. Paweł Migula (University of Silesia) and Prof. Henryk Skolimowski (Ann Arbor University in Michigan, U.S.A., Department of Ecological Philosophy at Technical University in Łódź) who have always shown personal interest in my scientific and private life and have supported me in the fields of ecology and environmental philosophy.
15 Mites (Acari) are representatives o f the taxonomic dilem ma facing researchers who study soil ecosystem processes. B e h a n - P e lletie r & N e w to n (1999) Chapter i. Introduction 1.1. Oribatid mites - life hidden in the soil Oribatida or moss mites are small, chelicerate arthropods, important representatives of mites (Acari). Mites are ubiquitous and, with the exception of the open oceans, they exist in every sort of terrestrial, aquatic, arboreal and parasitic habitat ( W a lt e r & P r o c t o r, 1999). They are found at eveiy elevation and every latitude, from the Arctic to the Antarctic. Mites have a diversity of function in the ecosystem, as shown by the range of feeding guilds to which they belong (M o o r e et al., 1988). They include predators, parasites, fungal feeders, root feeders, bacterial feeders, omnivores, and scavengers (K ra n tz, 1978). Ignoring mites, however, is a mistake. They are not passive inhabitants of ecosystems; rather they are strong interactors, important indicators of disturbance in ecosystems and major components of biological diversity (W a lt e r & P r o c t o r, 1999). More than any other habitat, the soil litter stratum is the province of mites. Two-thirds of the mite fauna occur in this habitat (W a lt e r et al., 1996). Any true understanding of the soil system must include knowledge of the mite fauna. Oribatid mites have successfully invaded all compartments of the biosphere (B ern in i, 1986). They constitute the main component of acarine populations in the soil. They are not confined to the soil, however, and may occur in considerable numbers in the aboveground parts of vegetation, among aquatic plants, in stored food, in the marine littoral zone, and in house dust. Temperate forests with well-developed surface organic layers and a predominance of fungal over bacterial decomposition are home to the highest diversities of oribatids. Oribatid mites can comprise about 50% of the
16 to ta l m ic ro a rth ro p o d fa u n a (G onzalez & S eastedt, 2000). D e n s itie s o f or m o re m ite s p e r s q u a re m e tre in th e u p p e r 10 cm o f s o il a re c o m m o n ly rep o rte d (P etersen, 1982). R ajski (1961) r e c o r d e d in th e P rim a e v a l B ia ło w ie ż a F o re s t a c o u n t o f 1 m illio n o r ib a tid m ite s p e r s q u a re m e tre. B u t e v e n th e d rie s t, h o tte s t o r c o ld e s t o f so ils a re d o m in a te d b y A c a ri, a n d its m o s t c o n s p ic u o u s r e p re s e n ta tiv e s - o rib a tid m ite s (W alter & P roctor, 1999). N u m e r ou s p e c u lia r, e p h e m e ra l a n d s m a ll h a b ita ts, s u c h a s d u n g, b ird n ests, lic h e n th allu s, m o ss es, fu n g a l m ycelia, m u s h ro o m s, th e in s id e o f c o n ife r n e e d le s, fo o d p ro d u c ts, etc., a re c o lo n iz e d b y o rib a tid s (L ebrun & V an Straalen, 1995). E v en m ore p e c u lia r m ic ro h a b ita ts can p r o v id e a h o m e fo r o r ib a tid s, e.g. lu m b r ic id g a lle r ie s (L ebrun & W auth y, 1981), a e ria l ro o ts o f o rc h id s (D enmark & W o o dring, 1965), c a v itie s o f c u rc u lio n id b e e tle e ly tra s (G ressit et al., 1966), o r a n t n e s ts (A oki et al., 1994). E v e n th e m a n -m a d e e n v iro n m e n t h a s b e e n in v a d e d b y so m e e n d e m ic s p e c ie s b e lo n g in g to th e d o m e s tic g e n u s Cosmochthonius o r s p e c ie s o f Trimalaconothrus liv in g in e n v ir o n m e n ts su c h a s s w im m in g p o o ls (Tagami et a l., 1992). O lszanow ski (1996) fo u n d o rib a tid s in an a q u a riu m. O rib a tid s a re a lso fre q u e n tly a d o m in a tin g g r o u p a m o n g m ic r o a r th r o p o d s o n p o s t - in d u s t r ia l w a s te la n d s (D avis, 1963; S kubała, 1995). N o in fo rm a tio n is a v a ila b le c o n c e rn in g th e g ro u n d -w a te r s u b s y s te m, a lth o u g h o rib a tid s c o u ld liv e in u n d e rg ro u n d s tre a m s a n d la k es, as s u g g e s te d b y th e ir p r e s en c e in c o ld s p rin g s (L ebrun & V an S traalen, 1995). In c o n c lu s io n w e ca n s a y th a t a ll n ic h e s c o n ta in in g o rg a n ic m a tte r c o n te n t a re c o lo n iz e d b y o rib a tid s, u s u a lly in h ig h n u m b ers. Oribatid mites constitute the order richest in species in the subclass Acari. Together with the Actinedida (Prostigmata), Acaridida (Astigmata) and Endeostigmata they constitute a group of mites of common origin called the Acariformes (Z a c h vatk in, 1947) or Actinotrichida (H am m en, 1972). Their evolutionary history is apparently a long one. They have the richest fossil record of any mite group, dating back to the Devonian, or million years ago (C oleman & C rossley, 1996). The origin and phylogeny of the mites and oribatids is not clear yet. And the systematics of the Oribatida is therefore not finally accepted by the society of acarologists. The Oribatida are grouped in two supercohorts: Oribatida Inferiores or lower oribatid mites and Oribatida Superiores or higher oribatid mites (G randjean, 1954, 1969). Lower oribatid mites include five cohorts - the Palaeosomata, Enarthronota, Parhyposomata, Mixonomata and Desmonomata (G r an d je an, 1954, 1969). Oribatida Inferiores may be broadly characterized as species with contiguous genital and anal shields occupying the entire length of the genitoanal field, and with leg tibiae and genua of uniform length and shape
17 (K ra n tz, 1978). The great majority of described Oribatida belongs to Oribatida Superiores. The supercohort may be broadly characterized as aptychoid species with rounded, generally well separated genital and anal fields on a distinct ventral shield, and with leg tibiae distinctly longer and of a different shape than the adjacent genua. It comprises two cohorts - the Brachypylina and the Poronota. Cohortal separation is based on presence or absence of dorsal pores and pteromorphae (K ra n tz, 1978). Oribatids are a highly morphologically diverse group of mites. The species diversity and the variability within species greatly differ in separate morpho-ecological types. K riv o lu ts k y (1965, 1968, and 1995) divided oribatids into 6 groups, including 16 morpho-ecological types. These groups are: inhabitants of the soil surface; small dwellers in narrow soil pores; deep-soil weakly sclerotized oribatids; inhabitants of the substrate, able to widen the pores; non-specialized forms; and inhabitants of wet habitats and aquatic systems. Oribatid mites in general have conservative life histories. N o r t o n (1994) claimed that a low metabolic rate is the driving force of the oribatid life cycle. A low metabolism results in slow development, low reproductive output, limited body size and energy storage, and a long adult life. Iteroparity is common in oribatids and X-selected species prevailed because of the energy costs of maintenance requirements and dispersal (Fig. 1). All these characteristics may result in low metabolism slow develodment low fertility limited body size and energy storage long life 1 stable populations _ rapid increase in abundance long development and long life Fig. 1. Oribatid mite life strategy survival during food shortage
18 ra th e r sta b le p o p u la tio n s as d e m o n s tra te d b y m a n y a u th o rs (Lebrun, 1964; M itc h e ll, 1977; Schatz, 1985). T h e d e v e lo p m e n t tim e o f o r i b a tid s is g e n e ra lly lo n g a n d is w o rth y o f re g is tra tio n in th e Guinness Book o f Records. T h e re c o rd in th is c o n te x t is h e ld b y th e b o re a l in h a b ita n t Ceratozetes kananaskis. Its m ea n d e velo p m en t tim e is 770 d a ys, w h ile th e a d u lt life s p a n a p p ro a c h e s 4 y e a rs (M itc h e ll, 1977). L o n g d e v e lo p m e n t a n d lo n g life re s u lts in a lo w c a p a c ity fo r p o p u la tio n in crease. O rib a tid s a re a b le to su rvive fo r a lo n g p e rio d d u rin g fo o d sh o rta g e. T h e s e c o n s tra in e d K a ttrib u te s a re p le s io ty p ic fo r o rib a tid s a n d h a ve o fte n p la y e d a ro le in p re a d a p ta tio n o f s p ecies in v a d in g e x tre m e h a b ita ts (B ücking et a l., 1998). M o s t o f th e s e c h a r a c te r is tic s a re u n u s u a l a n d illu s tra te w h y O r ib a tid a a re an ex cep tio n w ith in th e a ca ro lo gica l w o rld (Lebrun & Van Straalen, 1995). Thelytokous parthenogenesis is again peculiar to oribatids. Many hundreds of species of oribatids are parthenogenetic, and never produce functional male offspring (W alter & P roctor, 1999). Approximately 10% of the species studied exhibit this clonal mode of gene-pool transmission and maintenance. Perhaps 1% of known insect species and 0.1% of known members of the animal kingdom are obligated parthenogens. In this respect, oribatid mites present a striking anomaly (Lebrun & V an Straalen, 1995; N orton & Palmer, 1991). Surprisingly, knowledge of feeding biology of oribatid mites is poor and the available information is in part contradictory. Unlike the vast majority of other Arachnida, which adopted a carnivorous mode of life, oribatids are, for the most part, vegetarian. Gut content analyses indicate that most oribatid mites ingest a wide range of food materials including spores of various fungal species, living and dead plant material, moss, lichens, conifer pollen and carrion (B ehan- P elletier & H ill, 1983). Dietary features include poor nutritive value of ingested food, relatively low ingestion rates, and consequent minimal assimilation rates (B e r th et, 1964a; L uxto n, 1972, 1979; W a llw o r k, 1983), which constrain their life-history parameters (N o r to n, 1994). Mites link together many components of soil food webs and a study of their behaviour can shed light on our understanding of ecosystem functioning (W alter & P r o cto r, 1999). Unfortunately, rather little information is available on their relationships with other soil biota in comparison with other soil arthropods (W allwork, 1983). Let s consider the present knowledge on the role of oribatid mites in the soil system.
19 1.2. Oribatids perform an important ecological service The dormant microbes require the kiss of arthropod Prince Charm ings to awaken. W a lt e r & P r o c to r ( ) The sheer numbers of oribatids, at least in most soil systems, suggest that they play key, but still virtually unexplored, roles in their environment (soil). It is generally accepted today that oribatid mites are responsible for the indispensable process of antiphotosynthesis, achieving this by small, multiple and complementary stages that are a direct result of the species diversity of this group (W a llw o r k, 1976). Mites play an essential part in the biological fertility of the soil and they affect soil energetics. Their activity contributes greatly to organic decomposition, the synthesis of humus, the restitution of biogenic elements, and the stimulation of fungal and bacterial metabolism (C r o s s le y, 1977a; Lebru n, 1979; N o r t o n, 1986; R u sek, 1975). It is noteworthy that oribatids are the most important group of arachnids from the standpoint of direct and indirect effects in the development and maintenance of soil structure in organic horizons (M o o r e et al., 1988; N o r t o n, 1986). Many species sequester calcium and other minerals in their thickened cuticle (N o rto n & B e h a n -P e lle tie r, 1991). Thus, their bodies may form important sinks for nutrients, especially in nutrient-limited environments (C r o s s le y, 1977b). F o u r m a jo r p rin c ip le s ca n be ta k e n in to a c c o u n t c o n c e rn in g th e p a rtic u la r fu n c tio n s o f o rib a tid m ites. The result of mechanical breakdown and fragmentation is to increase the active surface of litter, enhancing its colonization by microorganisms, especially saprophytic fungi. The oribatid activity facilitates and accelerates the leaching of hydrosoluble elements and hydration of the organic matter (B e h a n -P e lle tie r & H ill, 1983; C u rry, 1969; Witkamp, 1971). The digestive transit ensures physical and chemical change as well as biological breakdown. This is accompanied by a mixing of mineral and organic elements and microorganisms (Lebru n, 1979). The production of faecal pellets creates a highly fertile environment. It facilities growth of roots and the germination of seeds (H a a r lö v, 1960; Lebru n, 1979; Pande & B e r t h e t, 1973). The consumption of dead roots by saprophagous oribatids is also of great importance because it considerably increases soil porosity and the development of humus (Lebru n, 1979). 2 - Colonization. 17
20 T h e g ra z in g o f m ite s s tim u la te s m ic r o flo ra l a c tiv ity. T h is fu n c tio n m a y b e o f m a jo r im p o r ta n c e. T h e y a id th e d is p e r s a l o f b a c te r ia a n d fu n g i, b o th e x te rn a lly o n th e ir b o d y s u rfa c e a n d b y in g e s tin g s p o re s th a t s u rv iv e p a s s a g e th r o u g h th e ir a lim e n ta ry tra c t (B ehan-p elletier & W alte r, ). M ic ro b e s h a v e lim ite d a b ilitie s to m o v e fro m o n e re s o u rc e p a tc h to a n o th er. O n c e th e e n e rg y in a p a r tic u la r p a tc h h a s b e e n e x p e n d e d, m ic r o b a l b io m a s s s h u ts d o w n a n d re m a in s d o rm a n t u n til n e w re s o u r c e s b e c o m e a v a ila b le. L avelle ( ) d e s c rib e d th is p h e n o m e n o n as th e S le e p in g B e a u ty P a r a d o x. W alter 8s P roctor ( ) c la im e d th a t d o rm a n t m ic ro b e s re q u ire th e»k iss«o f a rth r o p o d»p rin c e C h a rm in g s «to a w a k e n. T h u s, m ic r o b ia l p r o p a g u le s a re m ix e d w ith fre s h re s o u rc e s in th e fa e c a l p e lle ts a n d a re tra n s p o r te d to n e w sites. S o m e d a ta s u p p o rt th e v ie w th a t o rib a tid s a re e s s e n tia l fo r e f fic ie n t d e c o m p o s itio n a n d n u trie n t cy c lin g. N e a rly 5 6 % o f th e n e t p r o d u c tio n o f fu n g i is c o n s u m e d b y m y c o p h a g o u s m ite s p e c ie s (M c B r a y e r et a l., 1974). B u tc h e r et al. ( ) e s tim a te d th a t a d u lt o rib a tid m ite s d ire c tly m e ta b o lis e o n ly 1.8% o f th e e n e rg y in fo re s t litter, e v e n th o u g h in on e y e a r th e y in g e s t an a m o u n t o f m a te ria l e q u a l to a b o u t 5 0 % o f a n n u a l le a f fall. G h ila r o v ( ) p ro v e d th a t o rg a n ic d e c o m p o s itio n is five tim e s fa ster w h e n m ic ro o rg a n is m s a n d m ite s w o r k to g e th e r th a n b y m ic ro o rg a n is m s a lo n e. E v e n th o u g h th e s e g e n e ra l c h a ra c te ris tic s o f o rib a tid m ite s are k n o w n, th e ro le o f m o s t m ite s p ecies in e c o s y s te m fu n c tio n in g is u n cle a r, a s is th e ca s e w ith o th e r g ro u p s o f s o il o rg a n is m s (B e h a n - P e lle t ie r & N e w to n, 1999). In v ie w o f th is, a n d s in c e th e y n o r m a lly e x c e e d m o s t o th e r a rth ro p o d s in a b u n d a n c e a n d d iv e rs ity (see n e x t p a rt o f th is c h a p ter), o rib a tid m ite s sh o u ld b e regard e d as k e y in d u s tr y a n im a ls in d e c o m p o s e r fo o d c h a in s (W a llw o r k, 1983).
21 We must take it for granted that a large part of the mite fauna of the world will remain unsampled, unnamed, and unclassified (not to mention unwept, unhonoured, and unsung) for decades to come. M a y ( ) 1.3. Contribution of oribatids to global biodiversity Exploring the diversity of life will be one of the essential topics in 21st century ecology. The importance of biodiversity arises from the fact that the world depends on self-sustaining biological systems that include many kinds of organisms. Knowledge of biodiversity is required to understand the natural and artificial changes it may undergo. Furthermore, such knowledge permits the wise use and management of ecosystems, both as elements of natural heritage and as reservoirs of actual and potential resources. Biological diversity has been used to refer to almost any measure (taxonomic, numerical, genetic, etc.) of the variety of organisms that live in a particular place. Three dominant themes can be distinguished in this field, namely: a c c o u n tin g fo r th e d iv ersity, d e te rm in in g h o w th is d iv e rs ity is m a in ta in ed, e n u m e ra tin g p rin c ip a l fu n c tio n s p ro v id e d b y th e d iv e rs ity o f life. M o n ito rin g th e v ita lity o f soil b io ta is on e o f th e a c c e p te d is s u e s to b e fo u n d in th e G lo b a l D iv e rs ity A s s e s s m e n t (H eywood & G ardner, 1995). T h e ra tio n a le fo r in c lu d in g a rth ro p o d s in b io d iv e rs ity s tu d ies h as b e e n e s ta b lis h e d (D idham et al., 1996; E hrlich, 1988; W ilson, 1988; V erhoef & B russard, 1990; W inchester, 1997). T h e c o n trib u tio n o f m ite s to g lo b a l b io d iv e rs ity is fa r fro m b e in g a p p re c i a te d. M ite a n d o r ib a tid b io d iv e r s ity m a y b e o n e o f th e r ic h e s t reservo irs o f sp ecies in th e w orld. W alter & P roctor (1999) p re sen te d th e h y p o th e s is a b o u t lik e ly m ite m e g a d iv e rs ity. T h e re a re a p p ro x i m a te ly n a m ed sp ecies o f A c a ri (T a b le 1). R e c e n t estim a te s o f g lo b a l a c a rin e d iv e rs ity ra n ge fro m b e tw e e n h a lf to o v e r 1 m illio n sp ecies (W alter & P roctor, 1999). So th e n u m b e r o f s p ecies o f m ite s d e s c rib e d so fa r is e s tim a te d to re p re s e n t b e tw e e n 4 % a n d 8 % o f to ta l m ite d iv e rs ity. As reg a rd s o rib a tid m ite s, 1 1,0 0 0 s p e c ie s in m o re th a n g e n e ra h a v e b e e n d e s c rib e d ; th e ir to ta l s p e c ie s ric h n e s s c o u ld b e 3 to 10 tim e s h igh er. In te m p e ra te re g io n s, th e a c a ro fa u n a s a re c e r ta in ly d iv e rs e, b u t n o t e x c e p tio n a lly so. If th e A c a ri a re a h y p e r d iv e r s e g ro u p, th e n th e m a jo rity o f th e m w a it to b e e x p lo r e d in th e a c a r o lo g ic a lly u n e x p lo r e d t r o p ic s (W alte r & P roctor, 1999).
22 Current and expected diversity in mites (Acari) Table 1 Families Genera Species Species estimates minimum maximum Opilioacariformes Parasitiformes Holothyrida Ixodida Mesostigmata Total Acariformes Endeostigmata Sarcoptiformes Oribatida Astigmata T rombidiformes Total Total Acari Percentage of species described to date Source: WALTER & PROCTOR (1999) , The future of oribatids with respect to biodiversity does not look very optimistic. Numbers of described taxa increase annually, but the Oribatida although fascinating and diverse, is not widely studied by taxonomists. Only eight scientists work with oribatids in Poland. Data on mites and on oribatid diversity in tropical ecosystems is especially rare (W alter & P roctor, 1999). The reasons for this neglect are the minute size of individuals (0.1 to 3 mm in length), difficulty of identification, their cryptic habits, and their relative lack of economic importance. C o n tin u in g b io d iv e rs ity lo s s e s a n d th e e v e r-w o rs e n in g q u a lity o f th e e n v iro n m e n t a re w e ll-d o c u m e n te d fa cts. S c ie n tis ts d iffe r in e s tim a tio n o f th is p ro cess. A c c o rd in g to c o n s e rv a tiv e c a lc u la tio n s m o re th a n 13 sp ecies b e c o m e e x tin c t e a c h day. A c c o rd in g to p e s s im is tic e s tim a tio n s, it is p o s s ib le th a t 410 sp ecies d is a p p e a r e v e ry d a y (G oodland, 1991). L egal e n v iro n m e n ta l c o n stra in ts to stop lo s ses o f b io d iv e rs ity a re still la rg e ly u n s a tis fa c to ry. T h e s c ie n tific c o m m u n ity d o es in s u ffic ie n t w o rk on th is p ro b lem. L ebrun 8& V an S traalen (1995) u n d e rlin e d th e o b s tin a c y o f s c ie n tis ts w h o w is h to u n d e r s ta n d c o m p le te ly a ll th e m e c h a n is m s in v o lv e d b e fo re s o u n d in g th e a la rm b ells. W alter 8s P roctor (1999) w rite a b o u t th e p re s e n t w o rld fa s c in a te d b y m o le c u la r m a n ia, b u t w h e re little a tte n tio n is g iv e n to d im in is h in g d iv e rs ity a n d th e d e s tru c tio n o f n a tu re. A s regard s a n im a l b io d iv e r s ity, a v e r te b r o c e n tric v ie w is r a r e ly q u e s tio n e d, w h e re a s in v e rte b ra te s m ak e u p 95% o f a n im a l b io d iv e rs ity. Do w e 4,0