23. Arthropods Inhabiting Rodent Burrows in. the Karakum Desert

VICTOR A. KRIVOKHATSKY

Abstract

Communities of arthropods were studied in the Repetek Reserve (Karakum Desert) in burrows of desert rodents Rhombomys opimus, Spermophilopsis leptodactylm, Meriones meridianus, and M. libycus. These burrows differ in complexity and structure of arthropod communities. More than 500 species of burrow-inhabiting arthropods possessing various degrees of ecological specialization were discovered, from obligate bothrobionts to species only accidentally found in burrows. Taxonomic composition of the burrow arthropod communities is discussed as well as their trophic, temporal, and spatial structure.

Introduction

Animal burrows and holes contain peculiar ecosystems. In addition to their hosts, these burrows are often inhabited by many other animal species, predominantly arthropods, which are usually called "bothrobionts" or "nidicoles." Here, we refer to a community of an animal burrow as a "heterotrophic burrow consortium." Its core includes the host(s) of the burrow and its nonliving part, the burrow itself. Other animals in this consortium have ecological connections of various degree with its core. The term "bothrobiont," currently used in the morphological-ecological classifications of ecosystems, designates any animal that lives in the holes or burrows, digs its own burrow, and has morphological and ecological adaptations to these conditions. We use the following classification system for animals found in burrows: (1) bothrobionts - species with permanent (obligatory) burrow connections; (2) bothrophiles - species with a strong burrow connection; (3) bothroxenes - species with no obligatory connections; and (4) species alien to the burrow, and only accidentally found there. Studies of burrow ecosystems started in Europe early in this century (Falcoz 1915). In the former USSR, extensive studies were done by Vysotskaya in

V. Fet & K.I. Atamuradov (eds.), Biogeography and Ecology of Turkmenistan, 389-402. © 1994 Kluwer Academic Publishers. Printed in the Netherlands. 390 Victor A. Krivokhatsky

Russia (1953-1978) and Chilkilevskaya in Belorussia (1965-1982). In Middle Asian deserts, research on burrow consortia was started by Ya. Vlasov (or; Vlassov) (1932-1941, Central Karakum Desert) and continued by E. Nelzina ; and her colleagues in the Kizylkum (Nelzina 1966, 1971, 1977; Nelzina et al. 1978) and the author (from 1981 to 1989) in the East Karakum. f In the sand desert, many animal species dig burrows as shelters from external j conditions and as protection from predators. Mammals which dig only? permanent complex burrows include the large gerbil, Rhombomys opimus I Licht., the ground squirrel, Spermophylopsis leptodactylus Licht.; some gerbils j of the genus Meriones (e.g., M. meridianus Pall, and M. libyens Licht.); fox] (Vulpes vulpes L.); and hedgehog (Hemiechinus auritus Gmel.). Some mammals J do not dig their own holes but rather occupy previously made burrows: these f include the active desert predator Vormela peregusna Güld., which uses gerbil burrows after eating the host. Even some birds, such as Oenanthe isabellina . Temm. and Athene noctua Scop., build their nests in gerbil burrows. Many,; lizards, snakes, and tortoises also use previously made burrows as shelters from i extreme temperatures in summer and during the winter months. Numerous ; species of arthropods living in desert conditions strictly inhabit the complex rodent burrows. In the Karakum Desert, arthropod communities of the burrow were studied in detail in two localities: in the southern part of the Central Karakum near Ashkhabad (Vlasov 1932, 1933, 1937a,b, 1941; Vlasov and loff 1937; Vlasov \ and Miram 1937; Vlasov and Kirichenko 1937; Vlasov and Sychevskaya 1937; Vlasov and Shestoperov 1937; Vlasov and Stackelberg 1937) and the Repetek Reserve, in the East Karakum (Krivokhatsky 1981, 1982a,b, 1983, 1984, 1985a,b, 1987,1989; Krivokhatsky and Fet 1982; Krivokhatsky and Kashcheev 1983). During these studies, more that 500 species of burrow-inhabiting arthropods possessing various degrees of ecological specialization were discovered.

Materials and Methods

The original research was conducted by the author in the Repetek Reserve, Turkmenistan, from 1978 to 1988. More than 60,000 specimens of Arthropoda, predominantly insects, were studied. Arthropods were collected from rodent burrows (Rhombomys opimus, Spermophilopsis leptodactylus, and Meriones meridianus) using a number of techniques. One of the methods used (total of 5,600 samples) was extraction of material from the holes using a spoon-like shovel with a long handle and a sieve (a modification of the Shiranovich method). Another technique was installation of burrow traps (glass cylinders filled with formalin) inside and outside of each burrow entrance (a modification of the Barber method of pitfall traps). A total of 850 traps were installed, and invertebrates were sampled every three hours. Additional collecting techniques included light trapping and hand collection. Arthropods Inhabiting Rodent Burrows in the Karakum Desert 391

Fig. 1. Part of the large gerbil burrow (Repetek, February 1979): 1 - entrances, 2 - holes, 3 - feeding and nesting chambers, 4 - depth of the holes, 5 - surface.

Environment in the Rodent Burrows

Types of burrows in the Karakum Desert range from the simple and temporary to the complex and permanent. For example, jerboas dig summer burrows which are used only for one day. These holes are destroyed the next day and lack any bothrobionts. Next in complexity follow the burrows of gerbils, Meriones spp., and the ground squirrel Spermophilopsis leptodactylus. These burrows are permanent, but not complicated. The most complex is the burrow of the large gerbil, Rhombomys opimus. It has two to three levels and a number of holes, passages, and chambers (Fig. 1). The microclimate of R. opimus burrows has been the object of detailed studies (Shiranovich et al. 1965). The temperature in the holes was found to be equal to that of the soil temperature at the same depth. Seasonal and daily fluctuations of the burrow temperatures are less than those on the soil surface. Humidity in the burrow is higher than in the air; it depends on the presence of the animals and decayed food supply, and on the regime of ventilation. Burrows of the large gerbils are peculiar but widespread desert habitats; many desert animals (arthropods as well as vertebrates) cannot exist outside of these burrows. 392 Victor A. Krivokhatsky Table 1. Taxonomic and ecological composition of burrow consortia in the Repetek Reserve

1 8 _ _ Isopoda 1 1 _ _ 100 Scorpiones 4 1 2 1 - 15 Pseudoscorpiones 4 3 - 1 - 20 Solifuga 4 - 1 2 1 10 Aranei 40 12 13 8 6 1 1,180 Gamasoidea 3 - - - 3 1,000 Ixodoidea 6 - 2 2 2 1,500 Myriapoda 1 - - - 1 9 Insecta: 261 106 46 32 58 18 18,730 Collembola 2 - - 2 - 10,000 Protura 1 1 - - - 6 Thysanura 3 1 2 - - 100 Blattodea 4 1 1 - 2 2,240 Orthoptera 6 4 - 1 1 212 Psocoptera 1 1 - - - 10 Homoptera 6 6 - - - 28 Hemiptera 29 29 4 2 4 834 Coleoptera 121 33 31 20 34 3 2,498 Aphaniptera 11 - - - 11 1,670 Neuroptera 3 - - 1 2 75 Hymenoptera 50 32 3 3 2 10 432 Diptera 8 - 3 1 1 3 500 Lepidoptera 15 8 2 1 2 2 124 Vertebrata: 22 2 3 2 15 1,520 Reptilia 10 - 1 - 9 500 Mammalia 9 - 2 1 6 1,000 Aves 3 1 - 2 - 20 Total 345 124 67 49 86 19 25,075

1 - taxonomic groups, 2 - total number of species sampled from the burrows, 3 - alien species, 4 - bothroxenes, 5 - bothrophiles, 6 - bothrobionts, 7 - undetermined species, 8 - total number of animals sampled.

Morphological Structure of the Burrow Arthropod Communities

Morphological structure of a burrow consortium is characterized by classifi- cation of arthropod inhabitants according to their taxonomic composition, trophic level, and distribution.

Taxonomic Structure

The list of arthropod groups found in the rodent burrows in the Karakum Desert is given in the Table 1. below, we give a brief review of large systematic groups, which include Crustacea (Isopoda), several classes of Arachnida (Scorpiones. Pseudoscorpiones, Solifuga, Aranei, Acariformes, and Parasitiformes), Myriapoda, and various orders of Insecta. Arthropods Inhabiting Rodent Burrows in the Karakum Desert 393

Isopoda. In the large Asiatic sawbug genus Protracheoniscus, only one species, P. orientalis Ul., lives in the sandy deserts. This species can dig its own holes only in the moist sand (in Repetek, inside gerbil burrows).

Scorpiones. These are not obligatory bothrobionts and live in natural cavities in the sand desert. Some species, however, such as Mesobuthus eupeus (C.L. Koch) and Orthochirus scrobiculosus (Grube) are commonly found in gerbil burrows.

Pseudoscorpiones. Among the false scorpions there is an ecological group living in caves, bird nests, and burrows. In the Karakum Desert such species as Olpium pallipes Luc. and Geogarypus shulovi Beier are obligatory bothrobiontes.

Solifuga. Solpugids Galeodes fumigatus Walter and G. turcomanicus Birula can use burrows as shelters during the day. This group needs more taxonomic study.

Aranei. Some spider families include many bothrobiont and bothrophile species. In Repetek Reserve, these include Minosia karakumensis Spassky, Berlandina afghana Denis, and Minosiella intermedia Denis (Gnaphosidae); Theridium varians Hahn., Steatoda grossa (C.L. Koch), and Latrodectus tredecimguttatus (Rossi) (Theridiidae); Artema transcaspica Spassky (Pholcidae); Micaria sp. (Micariidae); Hersiliola sp. (Hersiliidae); Zodarion raddei Simon (Zodariidae); Evippa onager (Simon) (Lycosidae); and Trachelocamptus asiaticus Tanasevitsch (Linyphiidae). Some of these spiders in their natural habitats are bothrobionts, but they may also inhabit human habitations (Artema transcaspica, Steatoda grossa).

Acariformes. Very small mites belonging to Gamasoidea are common nidicoles on rodents and in rodents' nests. The best known species from the gerbil burrows in the Repetek Reserve are Eulaelaps stabularis C.L. Koch and Androlaelaps angsticutis Breg.

Parasitiformes. Several tick species (Ixodidae and Argasidae) are rodent para- sites during various developmental stages. In R. opimus burrows are found larvae of Haemaphysalis numidiana turanica Pom., adults and nymphs of Hyalomma asiaticum P. Sch. et Sch., and all stages of Ornithodoros tartakovski Olen.

Myriapoda, Chilopoda. Several specimens of Scutigera coleoptrata Latr. were found only twice, in the outermost holes of the large gerbil burrows in June 1980 and in May 1982, during the days following extraordinary summer rains.

Insecta

Collembola. Willowsia samarkandica Mart, outnumbers all other insects of the burrow communites in the Repetek Reserve. Unlike other desert springtails, this species is an obligatory bothrobiont. 394 Victor A. Krivokhatsky

Thysanura. Two species, Ctenolepisma mauritanica Luc. and Apteryskenoma turanica Kaplin, inhabit soils in Repetek and can be treated as bothroxenes.

Blattodea. Two species of cockroaches from the familiy Polyphagidae (Polyphaga pellucida Redt, and Arenivaga roseni Br.-W.) are obligatory bothrobionts. P. pellucida lives in the burrows as well as in all other desert habitats; A. roseni is found only in vegetation-stabilized sands.

Orthoptera. A grasshopper species, Lesina mutica Br.-W (Henicidae), and a cricket, Eremogryllodes vlasovi (Mir.) (Gryllidae), are obligatory bothrobionts.

Hemiptera. In the arid zone, about 90 species of true bugs are known from the burrows. The majority (Anthocoridae, Stenocephalidae, and Coreidae) sometimes use holes as a wintering place and as a summer shelter from the high daily temperatures. Another family, Reduviidae, has also trophic connections with the burrows. True bugs of the genus Stirogaster and Oncocephalus are cavity-living bugs, and such species as Reduvius christophi Jak., R. fedtschenkianus Osh., and Holotrichius tristis Jak. are typical bothrobiont predators.

Coleoptera. There are more than 1,000 species of 55 families of beetles known from animal burrows worldwide. About 20 families of beetles have obligatory connections with the desert burrows. More than 300 species of beetles from the rodent burrows are known in the Karakum Desert. Among those, 70 are bothrobionts and bothrophiles: e.g., Taphoxenus psammophylis Znoiko and Anthia mannerheimi Chd. (Carabidae); Gnathoncus pygmaeus Krysh. and Eremosaprinus vlasovi Rchdt. (Histeridae); Cholevinus fuscipes Men. (Catopidae); Conosoma lineata Kasch., Mycroglotta nidicola Fairm. and Aleochara jacobsoni Kirshbl. (Staphylinidae); Eremasus cribratus Sem., Thynorycter chlamidatus Sem. et Medv., and Onthophagus vlasovi Medv. (Scarabaeidae); lachnogya squamosa Men., Netuschilia hauseri Rtt., Cyphogenia gibba F.-W, Blaps fausti Seidl., B. sculettata F.-W, Nanoblaps hiemalis Sem. et Bog. and Aphaleriapigmaea F.-W. (Tenebrionidae); Attagenus fasciolatus Sols. (Dermestidae); Ptinus latro F. (Ptinidae); Gronops sp. (Curculionidae); as well as species of Cucujidae, Cryptophagidae, Lathridiidae, and Anthicidae. Weevils of the genera Mesostylus and Gronops commonly use burrows as wintering places. Other beetles have trophic connections inside the burrows (they can be saprophages, predators, etc.).

Neuroptera. Ant-lion larvae (Myrmeleontidae) use burrows for making their sandpits inside gerbil holes (Morter semigriseus Kriv.) or live under sandy cover in the burrows (Acanthaclisis pallida McLachlan and A. curvispura Kriv.).

Hymenoptera. Some wasps and bees from the families Mutillidae, Vespidae, Sphecidae, and Apidae build their nests in the rodent burrows. Vespa orientalis Arthropods Inhabiting Rodent Burrows in the Karakum Desert 395

F., Psenpulavskii Kazenas, and Nomioidespulverosus Handl.'can either dig their own holes, or use holes of the rodent burrows. Parasitic wasps from the families Ichneumonidae, Braconidae, Eucoliidae, Encyrtidae, Pteromalidae, Torymidae, Ceraphronidae, Platygastridae, and Dryinidae were found in the Repetek Reserve in the burrows of Rhombomys opimus. A true trophic connection was discovered between the dauber wasp Chlorion regale Sm. (Sphecidae) and the grasshopper Lesina mutica Br.-W (Henicidae). Some ants (Formicoidea) commonly use the holes as an underground subway.

Diptera. Many species of flies use burrows as a shelter from the hot weather; some of them have trophic connections with the burrow and its host. Larvae of Caenophanomyia insignis Lw. (Therevidae) are very common bothrobionts feeding on live and dead insects. Other flies (e.g., Dolichopodidae, Helomyzidae, and Spheroceridae) also have trophic connections with the burrows. Sand flies (Phlebotomidae) live in the burrows as larvae, and also as adults which suck host's blood.

Aphaniptera. All fleas, as gerbil parasites, use the mammals' nests for larval development and for host availability. In the Repetek Reserve, eleven flea species are found. Most numerous are Xenopsylla hirtipes Rorth., X. conformis Wagn., Coptopsylla olgae Wagn., and Ceratophyllus turcmenicus Vlasov et loff.

Lepidoptera. Butterflies in the desert can hide themselves during the very hot hours of the day in the shadow of the burrow entrances. Some night moths (Noctuidae) use rodent holes as day shelters, and some Momphidae (Calycobathra calligoni Sinev and Ascelenia decolorella Sinev), use them obligatorily for shelter during the winter months. Some Tineidae larvae (Anamallota repetekiella Zag.) could evolve in the rodent burrows.

Trophic Structure. All burrow arthropods can be classified in several ecological groups characterized by their trophic connections within burrow communities.

Hematophages. - blood-feeding parasites of the burrow hosts (e.g., ticks Eulaelaps stabularis and Ornithodoras tartakovski, and fleas Xenopsylla hirtipes, X. conformis, and Coptopslla olgae);

Entomophages. - predators and parasitoids of the arthropods (e.g., spiders Minosiella intermedia and Zodarion raddei, and true bug Reduvius christophi);

Saprophages. - arthropods which feed on decaying plant or animal tissues (e.g., springtail Willowsia samarkandica, cockroaches Polyphaga pellucida and Arenivaga roseni, cricket Eremogryllodes vlasovi, beetle larvae Attagenus fasciatus, and fly larvae Caenophanomyia insignitis); 396 Victor A. Krivokhatsky Table 2. Phenology fcf selected species of burrow arthropods in the Repetek Reserve

Species/stage Months

J FMAMJ J AS OND

Xenopsylla conformi (Aphaniptera: Pulicidae) ova + + + + + + + ____ + larvae — + + + + ______pupa + + + + + + + + + + + + adult + + + + + + + --- + +

Reduvius christophi (Hemiptera: Reduviidae) ova ---+ ______larvae, 1 instar --- + + + ______larvae, 2 instar ----+ + + + + ___ larvae, 3 instar -----+ + + + + + - larvae, 4 instar + —-- — — — + + + + + larvae, 5 instar + + + + ---- + + + + adult --- + + + + + ____

Caenophamomyia insignis (Diptera: Therevidae) ova ----+ + + _____ larvae + + + + + - + + + + + + pupa — — — + + ______adult ----+ + + _____

Attagenus fasciolatus (Coleoptera: Dermestidae) ova -----+ + + ____ larvae + + + + + + + + + + + + pupa ----+ + + _____ adult -----+ + _____

Minosiella intermedia (Aranci: Gnaphosidae) ova + + + + + + ______juveniles, young — + + + + + + _____ juveniles, medium + —+ + + + + + + + + + subadults + + — — — + + + + + + + adult males + + + + ---- + + + + adult females + + + + +"+ -- + + + +

Conventional Aphages. - a group which does not feed in burrows (includes many species that are rarely found in burrows).

Temporal and Spatial Structure of the Burrow Arthropod Communities

Temporal Structure

Changes in the structure of the burrow consortium in time can be studied in terms of daily activities, seasonal dynamics, and multi-year changes and Arthropods Inhabiting Rodent Burrows in the Karakum Desert 397 successions. The temporal structure of the arthropod'burrow communities depends on the climate and weather changes, and on the availability or absence of the burrow hosts (Krivokhatsky 1981,1982,1982b, 1983,1984,1985,1985b).

Seasonal Dynamics In the East Karakum, four basic seasons can be defined regarding the burrow communities. In April, burrow communities contain high numbers of parasites and saprophages, an increasing number of predators, and the highest abundance of conventional aphages. By July and August, the abundance of parasites in the external holes of rodent burrows reaches its annual minimum; entomophages and saprophages show the highest abundance. Also, this season is characterized by the highest number of the species which hide in burrows in the daytime. In November, the second peak of abundance of all the trophic groups is exhibited. In January, animal abundance is minimal, due to migration from the external holes to the deep burrows. These dynamics are dependent on the time of species development (Table 2) and on their migrations. In general, migrations from the external holes to the deep burrows from spring to summer and from fall to winter are typical for the burrow communities.

Daily Activity The dynamics of the daily activity are very similar to the temperature dynamics in different seasons. A peak of activity in spring and summer is detected during cool morning hours, but in winter the activity curve closely follows the curve for the daily temperature changes (Fig. 2). Different bothrobiont species exhibit two types of daily activity characterized by single-peak and double-peak curves. In different seasons activity of a species may shift from one type to another.

8 H I» 17 20 23 2 5

Fig. 2. Temperature dependence of daily activity of the burrow arthropods in Repetek in 1979 (Krivokhatsky 1981): 1 - number of specimens per trap, 2 - soil surface temperature (°C). 398 Victor A. Krivokhatsky

One can observe different curves of activity for the same species in the deep burrow and in the external holes. This effect depends on the migratory activity because most arthropods do not stay in burrows day and night; they may spend the day in the burrows and night in the soil surface, or vice versa.

Multi-year Changes and Successions Climatic changes from year to year can produce delays or accelerations of the individual development of arthropod species, and of burrow communities as a whole. The population of Rhombomys opimus in the East Karakum Desert exhibits a 14-year cycle. In different points of this cycle the abundance of gerbils changes. Consequently, the structure of the burrow arthropod communities also changes. Some stages of the 14-year burrow consortia succession have been simulated (Fig. 3). Following the gerbil depression of 1979-1980, some rodents in the Repetek Reserve left experimental burrows. After short latent period, the structure of burrow consortia started to undergo changes (demutation) toward that of the surrounding soil consortia. The abundance of parasites decreased, and the number of soil saprophages and predators increased. The rate of such demutation varied in different habitats. In sand dunes, demutation proceeded very rapidly and was terminated with the formation of soil communities when the burrow collapsed. In the desert woodlands with stabilized sand where large gerbils live in the depression period, demutation progressed slowly and burrows did not disappear. When numbers of gerbils increased, animals again inhabited their burrows. After the succession toward the burrow consortium climax began, parasites appeared; burrow saprophages and predator species replaced soil arthropods, as shown in the simple model of the successional cycle (Fig. 3). It is interesting to notice that certain burrow consortia located in the desert

Condition of the large gerbil population

High abundance Depression High abundano

1URROW COMMUNITY

Direction ol x" \ Direction ot

Fig. 3. The 14-year dynamics of the large gerbil population and burrow arthropod communities in Repetek. Arthropods Inhabiting Rodent Burrows in the Karakum Desert 399

Fig. 4. Distribution of spiders in the rodent burrow in Repetek (Krivokhatsky and Fet 1982).

2

01

Fig. 5. The distribution of the flea Xenopsylla hirtipes (specimens per each 10 cm of a hole) in the external holes of the large gerbil burrows in Repetek, from February (II) to May (V) 1980. Number of experimental burrows is given in parentheses (Krivokhatsky 1984).

woodlands, in the core of the big gerbil population, have exhibited climax indefinitely without demutation.

Spatial Structure Differences in taxonomic structure of an animal population between different parts of the burrow, and between different burrows, form the spatial structure of the burrow consortium. Some arthropod species can use the entire burrow with all its holes and chambers, whereas other prefer deeper holes, and some live only next to the entrance (Fig. 4). In general, the number of obligatory bothrobionts increases from the entrance toward the depth of the burrow. This pattern, however, may change due to daily and seasonal migrations (Fig. 5). The taxonomic structure of the burrow communities changes from habitat to habitat, and even among the neighboring burrows. According to these 400 Victor A. Krivokhatsky

nt of stabilized

Zodarion raddei Hersiliola sp. "Talanites" sp. Minosiella interned

Potyprtaga pellucida Arenivaga romeni

Heduvius Christoph! Holotrichus tristis Hyalocoris pilicornis

Ale/noeta helopioides Saratrtropus depressi/: Lachnogya squamosa Blaps fausti Arthrodosis castaneut Attagenus tasciolatus

Fig. 6. The habitat distribution of selected burrow arthropods in Repetek. Habitats (plant communities): 1 - Haloxylon persicum, 2 - H. aphyllum, 3 - Calligonum spp. differences, we can distinguish levels of consortia, which include the following: individual (each burrow as a consortium); habitat (for neighboring burrows in the different habitats); population (for the burrows in the different host populations); geographical (for the burrows in the different regions); host- specific (for the different burrow hosts); and host-animal (for the burrow host- bothrobiont species connection) consortia. As an example of such analysis, the similarity between the neighboring large gerbil burrow consortium and ground squirrel burrow consortium (similarity index of flea fauna in the Repetek Reserve is 73%) is higher than the similarity between large gerbil geographical consortia in the East Karakum and North Kizylkum Deserts (20%), or even in the East and Central Karakum Deserts (13%). Such differences are associated with geographical and habitat distribution of species inhabiting a burrow consortium (Fig. 6).

Functional Structure Quantitative data on burrow consortia are limited because of the difficulties of sampling of bothrobionts. Our estimate of total abundance of the burrow arthropods in the Repetek Reserve varies from 0 to 20,000 specimens per one hectare in the desert woodland in the spring period. At the same time, we can more precisely describe the quantitative characteristics of the predator-prey model in the burrow consortium. In the burrows of R. opimus, the optimal ratio between predators and prey species is estimated as 2.5 predators to 7.5 prey items per one burrow hole. This density, however, is not observed in natural conditions. Dynamics of density correspond to hypothetical models of Leslie and Lotka-Volterra (Fig. 7).

Origin of Burrow Communities

Not less than 4,500 insect species inhabit the Repetek Reserve. Of these, about 3% are bothrobionts which cannot exist in the sand deserts outside of rodent Arthropods Inhabiting Rodent Burrows in the Karakum Desert 401

10,0

1.0

JfZ •

0.1 '0.0 100.0

Fig. 7. The quantitative dynamics of predator - prey ratio in two burrow consortia (Nb N2) in Repetek (Krivokhatsky 1987). Note similarity to the hypothetical Leslie model. Ox, Oy - number of specimens per one entrance, for predators and prey, correspondingly.

ANTHROPOGENE

Fig. 8. Origin and evolution of the burrow consortia in the Middle Asian deserts. burrows. The taxonomic position and geographic distribution of these highly specialized species allow us to trace their possible origin and modes of formation of the burrow communities. Different characteristics of various arthropod groups have allowed them to adapt to conditions inside burrows: parasites move into the burrows with their host (or change hosts), saprophages and predators search for food, and many arthropods use the burrow as a shelter in the changing environment. First fossils of burrowing rodents in Middle Asia appear during the Eocene and Oligocene. Evolution of burrowing behavior can be attributed to the general aridization and formation of large open areas. Some of the arthropods which lived in the natural cavities and did not construct their own burrows, could have shifted to life in the rodent burrows during this period. Following stages of the the colonization of burrows by the arthropods, and their subsequent adaptive 402 Victor A. Krivokhatsky evolution, accompanied by the formation of the large sand deserts lacking natural cavities in the Pliocene and the formation of contemporary landscapes in the Holocene (Fig. 8). Modem burrow communities probably were formed essentially in the Holocene.