Search publications of the members of the Royal Belgian institute of natural Sciences
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Plumage characteristics and return rate of one-year-old tropical Roseate Terns
- We report an unusually high return rate (16\%) of one-year-old Roseate Terns (Sterna dougalli) to their natal colony on Aride Island, Seychelles, in 2005. Detailed accounts of these birds are provided in terms of timing of arrival, breeding status, and plumage characteristics, and compared with those of two other age classes (2-year-olds and 3 to 6 year-olds) in the same colony and with temperate populations. One-year-old individuals returned on average three weeks later than older birds and did not attempt to breed. Their immature plumage dress ('portlandica phase') differed from their one-year-old temperate counterparts, with most birds showing several characteristics of adults in full breeding plumage, such as red bill and red legs, long tail-streamers, and absence of a dark carpal bar. Contrary to expectations from temperate studies, nonbreeding two-year-old individuals did not retain any characteristic of the portlandica plumage, and were virtually inseparable from breeding adults. The ad hoc return rate of Roseate Tern one-year-olds found in this particular year is high compared to recapture/resighting data from colonies in temperate areas, but is comparable to observations made at other tropical (Caribbean) breeding colonies. Altogether, these findings suggest that tropical Roseate Terns are prone to return to their natal site earlier than their temperate counterparts, and show a more rapid acquisition of the adult plumage. This may be especially the case in years of good food supply conditions, since the 2005 event coincided with the two (2004-2005) of highest marine productivity recorded in the vicinity of Aride Island over the 1997-2005 period.
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Effects of annual changes in primary productivity and ocean indices on breeding performance of tropical roseate terns in the western Indian Ocean
- We assessed the influence of inter-annual changes in primary productivity and local, regional and large scale ocean indices on the breeding parameters of roseate terns Sterna dougallii on Aride Island, Seychelles, western Indian Ocean. Productivity (chicks per breeding pair), timing of breeding and clutch and egg sizes were monitored annually for 8 yr and correlated with local ocean productivity (denoted by Sea-viewing Wide Field-of-view Sensor, SeaWiFS, estimates of chlorophyll concentration, CC), sea surface temperature and indices recording the status of the Indian Ocean Dipole and of El Niño. The rate of increase in CC between mean laying date and CC peak value was positively related to roseate tern productivity and mean clutch size over the 1998 to 2005 study period. Colony productivity seemed also to be influenced by the Multivariate El Niño Index. In most years, the breeding phenology of roseate terns corresponded to the local increase in CC around Aride, and failure to adjust timing of reproduction to the timing of the phytopankton bloom decreased the probability of breeding success. This is the first study showing that a tropical seabird species is sensitive to inter-annual variations in the intensity and timing of the phytoplankton bloom, which should be connected to annual variations in the availability of its main fish prey (juvenile goatfishes). Overall, these patterns indicate that the reproduction of this top marine predator is dictated by the temporal variability in oceanographic conditions. We suggest that CC data available over the world's oceans may be a useful tool to develop models predicting the fate of colonies of inshore feeding seabirds when other, more conventional, monitoring methods cannot be used. © Inter-Research 2007.
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Rhipicephalus appendiculatus and R. zambeziensis (Acari: Ixodidae) from Zambia: A molecular reassessment of their species status and identification
- The closely related species Rhipicephalus appendiculatus and R. zambeziensis co-occur in a wide area in Zambia. In this area, specimens of both species have been collected on the same individual host at the same time. In addition, specimens that are morphologically intermediate between R. appendiculatus and R. zambeziensis have been found in this area. These observations cast some doubt on the species status of R. appendiculatus and R. zambeziensis. Because the two taxa have varied influences on the epidemiology of East Coast fever (ECF), a cattle disease for which they act as vectors, it is essential that their taxonomic status is clarified and their identification is accurate. Therefore a phylogenetic analysis of nucleotide sequences of the ITS2 and a fragment of the mitochondrial 12S rDNA was performed to reassess the specific status of both taxa. This revealed two well supported clades coinciding with R. appendiculatus and R. zambeziensis as two separate species. In order to facilitate species identification a PCR-RFLP diagnostic assay was developed based on BauI digestion of the ITS2 gene. This assay produced clear diagnostic banding patterns for the two species and is applicable over a wide range of both species' distribution. © 2007 Springer Science+Business Media B.V.
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Genetic variation in Rhipicephalus appendiculatus (Acari: Ixodidae) from Zambia: Correlating genetic and ecological variation with Rhipicephalus appendiculatus from eastern and southern Africa
- Based on their ecology, Rhipicephalus appendiculatus ticks from eastern and southern Africa have been divided into three groups. We investigated how two geographic genetically differentiated stocks of R. appendiculatus from the southern and the eastern provinces of Zambia, representing two ecological groups, i.e., southern African and transition groups, respectively, genetically compare to stocks from east Africa (Rwanda) and southern Africa (Zimbabwe and South Africa). The ITS2 and two mitochondrial genes segments, 12s rDNA and COI, were used in the investigations. The ITS2 tree did not show support for differentiation into any groups, while the two mitochondrial genes trees (12s rDNA and COI) showed two genetically differentiated groups: an east African genetic group which included specimens from Rwanda and the plateau area of the eastern province of Zambia, and a southern African genetic group represented by specimens from South Africa, Zimbabwe and specimens collected on the fringes of the eastern province plateau in the Nyimba district of Zambia. This suggests that the two geographically differentiated stocks of the southern and eastern provinces of Zambia might be part of two wider geographic genetically differentiated R. appendiculatus groups that extend beyond Zambia. Stocks of "transition" ecology (eastern province) belong to the east African genetic group and the differences in ecology within this genetic grouping may be due to genetic polymorphism, phenotypic plasticity, and other local factors.
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Further evidence for geographic differentiation in R. appendiculatus (Acari: Ixodidae) from Eastern and Southern provinces of Zambia
- Studies in the biology, ecology and behaviour of R. appendiculatus in Zambia have shown considerable variation within and between populations often associated with their geographical origin. We studied variation in the mitochondrial COI (mtCOI) gene of adult R. appendiculatus ticks originating from the Eastern and Southern provinces of Zambia. Rhipicephalus appendiculatus ticks from the two provinces were placed into two groups on the mtCOI sequence data tree. One group comprised all haplotypes of specimens from the Eastern province plateau districts of Chipata and Petauke. The second group consisted of a single haplotype of specimens from the Southern province districts and Nyimba, an Eastern province district on the fringes of the valley. This variation provides additional evidence to the earlier observations in the 12S rDNA and ITS2 data for the geographic subdivision of R. appendiculatus from Southern province and Eastern province plateau. The geographic subdivision further corresponds with differences in body size and diapause between R. appendiculatus from these geographic areas. The possible implications of these findings on the epidemiology of East Coast fever (ECF) the disease for which R. appendiculatus is one of the vectors are discussed. © 2007 Springer Science+Business Media B.V.
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Conodont biostratigraphy of shallow marine Givetian deposits from the Radom-Lublin area, SE Poland
- Detailed conodont data were obtained from 66 samples in 9 deep wells representative of three palaeogeographic regions of the Mid Devonian epicontinental basin of southeastern Poland: (1) the elevated part of the East European Platform representing the basin margin, (2) the Lublin Graben with a larger proportion of open marine systems, (3) the Radom Area characterized by more offshore, purely marine deposition and larger subsidence rates in the Radom Area. The 1344 specimens collected were assigned to 8 genera: Icriodus, Polygnathus, Ancyrodella, Belodella, Mehlina, Neopanderodus, Pandorinellina and Skeletognathus, and 38 taxa of species or subspecies rank. The vertical distribution of the conodont assemblages studied in particular sections is highly irregular and discontinuous with many barren intervals controlled by less suitable palaeocological conditions, mostly representing restricted and/or very shallow-water facies. We found only a single index species characteristic of deeper marine facies, as applied in the standard conodont zonation. Therefore the biostratigraphic interpretation also takes into account the total range of all taxa found in particular samples, established after a critical analysis of adequately published total ranges of these taxa. The stratigraphic ranges of the following taxa were modified: Icriodus arkonensis arkonensis, I. a. walliserianus, I. eslaensis, I. platyobliquimarginatus, I. subterminus, I. aff. I. subterminus, Polygnathus ansatus, P. latifossatus, P. linguiformis linguiformis, P. timorensis and P. varcus. As a result of the stratigraphic analysis of the conodont assemblages we distinguished five zones in the Givetian of the studied area, i.e. the rhenanus/varcus, ansatus, hermanni, norrisi (=lower part of Lower falsiovalis Zone) zones, and also two informal units, the subterminus and insita faunas. We documented the co-occurrence of I. subterminus and P. latifossatus which supports the earlier supposition of Rogers (1998) that the Lower subterminus Fauna may partly correspond to the Lower hermanni Zone.
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Detecting algae blooms in European waters
- A near real-time algal bloom detection service has been developed for European waters. Daily chlorophyll a data from Envisat/MERIS and Aqua/MODIS are compared to a predefined threshold map to determine whether an algal bloom has occurred. The design of the threshold map takes account of two factors. Firstly, over European waters regional differences in typical and extreme levels of chlorophyll a span two orders of magnitude. A concentration, e.g. 2 μg/1, that would be considered as a bloom concentration in one region could correspond to a relatively low concentration in another region. Secondly, the errors in satellite chlorophyll a can be significant in coastal waters effectively giving an artificial background level in satellite images. To account for these two factors a threshold map has been designed using satellite chlorophyll a data from a previous year, with separate threshold maps for each sensor to take account of sensor-specific bias. This threshold is defined here as the top 10\% level of a previous year's chlorophyll a data. The results of algal bloom detection in various regions are analysed in terms of bloom timing, duration and strength. Differences between the performance for the MERIS and Aqua sensors are also discussed.
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Early release of eggs and embryos in a brooding ancient asexual ostracod: Brood selection or a gambling strategy to increase fecundity?
- Asexual lineages lack the means to purge their genomes of (deleterious) mutations through recombination. Evolutionary theory thus predicts that such lineages will be prone to early extinction. In brooding animals, brood selection might provide a mechanism to counter the accumulation of mutations. Of the three putative ancient asexual animal groups, only the darwinulid ostracods are brooders. Here, we test the incidence of egg and juvenile abortion in a darwinulid species, Penthesilenula brasiliensis, under two temperature treatments. Part of the offspring is released without brooding (close to 30\% in one treatment). The majority of these aborted eggs hatches and develops. As it is unlikely that females are such bad judges of offspring quality, either the surviving animals will present deficiencies later on in development (brood selection) or early egg release can be a (bet-hedging) strategy to increase fecundity in favourable conditions. © 2007 Springer Science+Business Media B.V.
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The updated check list of Dolichopodidae (Diptera) of the Czech Republic and Slovakia: Background information, data and considerations
- The 1997 check list of Dolichopodidae of the Czech Republic and Slovakia has recently been reviewed and updated. The new species list includes 346 species with 22 species added as new to the fauna of the Czech Republic. While the check list itself is published elsewhere, largely unpublished new records of Hercostomus argentifrons, H. nigrilamellatus, Medetera adjaniae, M. melancholica and M. setiventris are presented here, together with data on their distribution in Europe and their biology and ecology. The status of the newly added Sympycnus desoutteri is discussed. H. argentifrons is recorded here for the first time from the Czech Republic (Bohemia; Moravia) and background information is given on its discovery. While the Czech fauna with 324 species can be considered well known, the fauna of Slovakia is definitely much richer than its current national list of 217 species suggests. In the latter country, in particular surveys of sandy habitats with heathland or peatmoor, saltmarshes, reedmarshes, humid forests on loamy soils, and of rothole and saprun microhabitats on trees might quickly yield new species records. © 2007 Institute of Zoology, Slovak Academy of Sciences.
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A review of Palaearctic Teuchophorus, with a new species from Bulgaria (Diptera: Dolichopodidae)
- The Palaearctic species of Teuchophorus are reviewed and a key provided to males. T. chaetifemoratus is described as new from Bulgaria. The male of this species is easily recognized by the ventral and posteroventral rows of strong curved bristles on the hind femur and, in contrast to all other Palaearctic species, its hind tibia does not show any peculiar chaetotaxy. It shares the same habitat preference as most of its Western European congeners, whereas Mediterranean species occur in more open habitats. T. simplex Mik is recorded for the first time from Bulgaria. T. bisetus Loew is reinstated as a distinct species, whereas T. tenuemarginatus Strobl most probably does not belong to Teuchophorus and is regarded as nomen dubium. In contrast to the literature, European, African and some Oriental Teuchophorus species have 6 dorso-central bristles instead of 5, and the entire generic range encompasses 4 to 6 dorsocentral bristles. Two morphological features are found in both sexes of all Teuchophorus species and are the only reliable characters to separate this genus from Sympycnus (sensu lato): the oblique position of crossvein dm-cu and the anterior bend at the base of the distal section of vein M1. Copyright © 2007 Magnolia Press.
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Long-term studies on productivity of Roseate Terns and Lesser Noddies on Aride Island, Seychelles
- This paper summarises up to 16 years of data on the productivity of Roseate Terns and Lesser Noddies on Aride Island, Seychelles, in order to assess: (1) the magnitude of variation in reproductive parameters, (2) the factors influencing their breeding success, and (3) whether common factors influenced the productivity of the two species. With the exception of 2002, the productivity of Lesser Noddies on Aride Island was always higher than that of Roseate Terns. The frequent mass mortalities of chicks on Aride were more common for Roseate Terns (an almost null productivity occurred in 44\% of the years) than for Lesser Noddies (productivity less than 0.10 chicks per breeding pair occurred in only 20\% of the years). Hatching success of both species was positively correlated, but there was no correlation for productivity, which suggests that stochastic variation in short-term food availability affected both species differently. Our results indicate that food shortage is the main factor explaining the breeding success of both species on Aride; the impact of other factors, such as tick infestation, depended upon the extent of food shortage. The underlying causes of food shortage are difficult to predict, although annual variation in marine productivity seems to be the ultimate factor determining productivity of Roseate Terns and Lesser Noddies. Copyright © NISC Pty Ltd.
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Sapphicorhynchus, a new early Givetian rhynchonellid (brachiopod) genus from western New York State, USA, and Sapphicorhynchidae, n. fam
- A new genus, Sapphicorhynchus, type species S. sappho (HALL, 1860), is described from the early Givetian of western New York State. The presence of the species in older and younger strata of New York, in other States of the United States of America, in the Province of Ontario (Canada), and outside North America is rejected. The genus is designated the type for the new family Sapphicorhynchidae. It is compared to the emended middle Eifelian genus Oligopthycherhynchus SARTENAER, 1970, type species O. hexatomus (SCHNUR 1851), and the early Givetian genus Cupularostrum SARTENAER, 1961, to which Sapphicorhynchus sappho is assigned in recent literature.
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The late Eifelian rhynchonellid (brachiopod) genus Isopoma TORLEY, 1934, and Isopomidae n. fam
- Fortunate circumstances have recently allowed to collect specimens of the late Eifelian Isopoma brachyptyctum (SCHNUR 1853) from its type locality (Blankenheim, Blankenheimer Mulde, Eifel area). For the first time internal characters were investigated by means of transverse serial sections of topotypic material. Apart from its original description, this species, designated as the type species of the genus Isopoma TORLEY 1934, was only known so far by its lectotype. A full description of Isopoma is given, and its original description by TORLEY, based on late Givetian specimens from Sauerland unduly identified as I. brachyptyctum, is disregarded. A new family, Isopomidae, type genus Isopoma, is established. A better understanding of Isopoma made it possible to assess the validity of the various species and subspecies assigned to the genus at one time or another.
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Did Pleistocene glaciations shape genetic patterns of European ostracods? A phylogeographic analysis of two species with asexual reproduction
- Nested clade analyses (NCA) and likelihood mapping were applied to DNA sequence data of the ribosomal ITS1 and mitochondrial COI region from two non-marine ostracod species. The aim was to test whether Pleistocene glaciations may have shaped genetic and geographic patterns. According to the results from both types of analyses, evidence was lacking for any kind of geographic grouping of European (and one African) population from the putatively ancient asexual ostracod, Darwinula stevensoni. This counters the possibility that a recent selective sweep could have caused the low intraspecific, genetic diversity observed in this species. One of the most cited hypotheses to explain geographic parthenogenesis invokes faster, postglacial colonization by asexual lineages. However, no evidence for northern 'range expansion' of asexual haplotypes was found for Eucypris virens, a species with geographic parthenogenesis. Rather, the outcome of the NCA reveals that phylogeographic relationships are characterized by 'restricted dispersal with isolation by (geographic) distance'. This result suggests that either no faster, postglacial range expansion of asexuals occurred in E. virens or, that patterns of subsequent colonization became 'overwritten' by more recent dispersal events. Likelihood mapping provides evidence for the second scenario because genetic instead of geographic clustering was statistically supported. © 2006 Springer Science+Business Media B.V.
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Annotated checklist of the rotifers (Phylum Rotifera), with notes on nomenclature, taxonomy and distribution
- Phylum Rotifera comprises about 2030 known species classified in three main groups, the marine Seisonida (3 species), the Monogononta (1570 species) and the unique, exclusively parthenogenetic Bdelloidea with 461 clonal species. Here I present an annotated checklist of the taxon, giving the global distribution of the valid species. This checklist contains over 3,000 available names at the genus- and species-group level, including valid names and a non-comprehensive list of synonyms. A number of taxonomic and nomenclatural suggestions following from the review is presented. Suggestions include several new synonyms and two nomina nova: Dissotrocha kostei for Dissotrocha aculeata Koste, 1996 non Ehrenberg, 1838 (stat. nov., ex. Dissotrocha hertzogi aculeata) and Lepadella zigzag for Lepadella bractea Myers, 1934 non (Ehrenberg, 1838). This contribution also describes features of an on-line, global names database of the Rotifera, on which this checklist is based. Copyright © 2007 Magnolia Press.
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Note on a highly diverse rotifer assemblage (Rotifera: Monogononta) in a Laotian rice paddy and adjacent pond
- During August 1999, the authors conducted a sampling campaign in the PDR Laos, in order to contribute to the chorology of rotifers in the region. Two samples, collected from a rice paddy and an adjacent pond near Vientiane, Laos, contained a total of 135 rotifer species including several that appear new to science or that warrant taxonomical or biogeographical comments. No new species can be named, but Cephalodella boettgeri KOSTE and Floscularia armata SEGERS are recorded for the second time ever after their description from South America, and Parencentrum lutetiae (HARRING and MYERS) and Polyarthra luminosa KUTIKOVA are new to Southeast Asia. This raises the number of rotifers recorded from Laos from 9 to 130. The diversity recorded is remarkable, especially when compared with that of similar habitats in the Thai part of the floodplain of River Mekong and its tributaries. Different agricultural practices may account for the difference in species richness. Similar highly diverse rotifer faunas are known to occur in natural, tropical and subtropical floodplain systems only. This accords with the view that rice paddies can be regarded as artificial wetlands or floodplain systems, which, if managed taking biodiversity concerns into account, may have a potential for the conservation of freshwater biodiversity. © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.
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A new species of the genus Hesperempis Melander (Diptera: Empididae) from Siberia
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Revision of the genus Elaphropeza Macquart (diptera: Hybotidae) from the Oriental Region, with a special attention to the fauna of Singapore
- The genus Elaphropeza Macquart from the Oriental region is revised. In addition to the 79 known species (including seven new combinations of species previously placed within Drapetis Meigen) 51 new species are described and illustrated. The study is mainly based on freshly collected material in Singapore (544 samples, year cycle in eight stations and numerous hand captures). Smaller samples were available from Malaysia, Thailand and Cambodia. Of the 51 new species only 43 have been given a name: E. acantha sp. nov., E. asexa sp. nov., E. asiophila sp. nov., E. belumut sp. nov., E. benitotani sp. nov., E. bezzii sp. nov., E. bulohensis sp. nov., E. chekjawa sp. nov., E. combinata sp. nov., E. crassicercus sp. nov., E. darrenyeoi sp. nov., E. demeijerei sp. nov., E. equalis sp. nov., E. feminata sp. nov., E. flavicaput sp. nov., E. furca sp. nov., E. limosa sp. nov., E. luanae sp. nov., E. luteoides sp. nov., E. malayensis sp. nov., E. meieri sp. nov., E. melanderi sp. nov., E. modesta sp. nov., E. monacantha sp. nov., E. monospina sp. nov., E. murphyi sp. nov., E. neesoonensis sp. nov., E. ngi sp. nov., E. pauper sp. nov., E. pluriacantha sp. nov., E. riatanae sp. nov., E. sime sp. nov., E. singaporensis sp. nov., E. singulata sp. nov., E. sivasothii sp. nov., E. spicata sp. nov., E. spiralis sp. nov., E. sylvicola sp. nov., E. temasek sp. nov., E. tiomanensis sp. nov., E. ubinensis sp. nov., E. yangi sp. nov., E. yeoi sp. nov. Eight species known only as females are briefly diagnosed but not named. Species (including type materials in most cases) described by C.R. Osten-Sacken, M. Bezzi, J.C.H. de Meijere, R. Senior-White, A.L. Melander and K.G.V. Smith were examined and re-described. Neotypes have been designated for E. calcarifera Bezzi, E. melanura Bezzi, E. formosae Bezzi and E. scutellaris Bezzi. Elaphropeza exul Osten-Sacken, 1882 is transferred as Crossopalpus exul (Osten-Sacken) comb. nov. Elaphropeza formosae Bezzi sensu Quate, 1960 re-described by L.W. Quate from Micronesia, is considered a new species and a new name is given: E. quatei sp. nov. All species of Elaphropeza are divided into two main species groups: E. biuncinata group and E. ephippiata group. Phylogenetic relationships within Elaphropeza are provisionally outlined. Some interesting morphological features and phenology of the species are discussed. Fourteen species have been found exclusively in mangroves. A key is given to the species of the Oriental Region (Indian subcontinent, Southeast Asia, Philippines and Taiwan, but excluding certain species of the Chinese mainland that proved to be different from the rest of the Oriental Region). A check list of the Oriental species is provided. Copyright © 2007 · Magnolia Press.
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Effects of environmental stress on the condition of Littorina littorea along the Scheldt estuary (The Netherlands)
- The condition of the periwinkle Littorina littorea, expressed in terms of its shell morphology, reproductive impairment (i.e. female sterility/intersex, male penis shedding), trematode infestation load, lipid reserves and dry/wet weight ratio, was determined in function of environmental stress along the polluted Western and relatively clean Eastern Scheldt estuary (The Netherlands). The upstream increasing pollution and decreasing salinity levels along the Western Scheldt estuary (Fig. 1) are reflected in the dry/wet weight ratio and lipid content of the periwinkles. Compared to the Eastern Scheldt, female intersex (i.e. indicator of TBT pollution) and sterility occurred more frequently in the Western Scheldt estuary, while male penis shedding was even restricted to the latter estuary. The highest population intersex and sterility incidence was found near the harbour of Vlissingen and reflects potential nautical activities. The number of trematode infested periwinkles did not differ between both estuaries, although local sampling site differences were detected within each estuary, reflecting the complex interactions that exist among parasites, hosts and the local environment. Finally, both estuaries were maximally discriminated from each other based on the shell weight of the periwinkles using a canonical discriminant analysis. Periwinkles with the heaviest shells were found in the Western Scheldt estuary and may reflect growth rate or structural population differences caused by the less favourable living conditions in the Western Scheldt estuary. © 2007 Elsevier B.V. All rights reserved.
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Sinkhole formation above underground limestone quarries: A case study in South Limburg (Belgium)
- Historical records were used for the compilation of a database of sinkholes resulted from collapses of abandoned shallow underground limestone quarries (mines) in two villages in Belgian South Limburg. During the last 350 years the formation of such sinkholes caused at least 38 casualties, but more often it caused a change in topography and damage to public and private property. The objective of this study is to better understand the spatial and temporal patterns of quarry collapse-related sinkholes in the study area. Apart from sinkhole locations and ages, the compiled database provides information on the dimensions of the area affected and the damage caused by sinkhole formation, as well as the causal factors of sinkholes. One hundred seventy-three sinkholes have been reported since 1665, but most (80\%) reported sinkholes postdate 1965. Sinkhole dimensions provided information on the type of collapse. Seven large sinkholes, displacing a total sediment volume of 480,000 m3, resulted from large-scale roof breakdown after pillar failure. The smaller sinkholes were the result of fall of the overburden into galleries after local roof collapse or suffosion of a solution pipe. In total, these small sinkholes displaced 12,300 m3 of sediment. At present almost all large underground quarries in the study area have been affected by sinkholes. These features were caused by natural and anthropogenic factors, and occur in zones with thin roofs, where pillars were affected by pillar robbing, or on locations with inappropriate sewerage systems above quarries. The formation of sinkholes was often reported in spring during years with high moisture contents in the overburden, caused by high groundwater recharge or above average precipitation. With increasing time since quarry abandonment, quarries become more susceptible to pillar creep and bending of the roof. Hence, if no appropriate mitigation measures are taken to reduce such deterioration processes, the number of sinkholes is expected to increase. © 2007 Elsevier B.V. All rights reserved.
