Direct Evidence of Central European Forest Refugia During the Last Glacial Period Based on Mollusc Fossils
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Quaternary Research 82 (2014) 222–228 Contents lists available at ScienceDirect Quaternary Research journal homepage: www.elsevier.com/locate/yqres Direct evidence of central European forest refugia during the last glacial period based on mollusc fossils Lucie Juřičková ⁎, Jitka Horáčková, Vojen Ložek Charles University in Prague, Faculty of Science, Department of Zoology, Viničná 7, CZ-12844 Prague 2, Czech Republic article info abstract Article history: Although there is evidence from molecular studies for the existence of central European last glacial refugia for Received 4 October 2013 temperate species, there is still a great lack of direct fossil records to confirm this theory. Here we bring such ev- Available online 6 March 2014 idence in the form of fossil shells from twenty strictly forest land snail species, which were recorded in radiocarbon-dated late glacial or older mollusc assemblages of nine non-interrupted mollusc successions situated Keywords: in the Western Carpathians, and one in the Bohemian Massif. We proposed that molluscs survived the last glacial Central European last glacial refugia Late glacial period period in central Europe in isolated small patches of broadleaf forest, which we unequivocally demonstrate for Surviving of temperate species two sites of last glacial maximum age. © 2014 University of Washington. Published by Elsevier Inc. All rights reserved. Introduction studies (e.g., Pfenninger et al., 2003; Pinceel et al., 2005; Kotlík et al., 2006; Ursenbacher et al., 2006; Benke et al., 2009) reveal very complex, One of the central paradigms of European paleoecology is the alter- often taxon-specific, patterns of species range dynamics. But molecular nation of glacial and interglacial faunas via large-scale migrations, phylogeography provides neither direct evidence of past distributions where whole communities shifted southwards to the Mediterranean nor the entire context of the paleoenvironment including the composi- refuge during glacial periods and northwards during interglacial periods tion of species assemblages. Though some direct evidence exists for pol- (e.g., De Lattin, 1967). However, it has been called into question during len and plant remains (e.g., Birks, 2003; Magri et al., 2006; Jankovská the past two decades by an increasing amount of evidence from central and Pokorný, 2008), snails (Ložek, 2006) and mammals (e.g., Horáček, European last glacial refugia for temperate species, sometimes called 2006; Sommer and Nadachowski, 2006; Sommer and Zachos, 2009), cryptic refugia because of their small area and difficult detection. there is still great work remaining for paleontologists to complete the Where then did temperate species survive during the last glacial mosaic of our knowledge on glacial/interglacial species ranges shifts. period? Much coincident as well as contradictory evidence has been Land snails can be used as relatively independent proxy for paleoeco- discovered. Some authors even consider the Mediterranean region to logical reconstructions because of their close relationships to geological be an area of paleo-endemism rather than a source for northwards background and microclimatic conditions but not to particular plant spe- postglacial colonization (Bilton et al., 1998). A review of the current cies (e.g., Ložek, 1964, 2000; Davies, 2008). Although their shells persisted knowledge was given by Schmitt and Varga (2012), which asked in only in calcium-rich environments, such environments covered a wide the title of their review whether extra-Mediterranean refugia are the spectrum of humidity and elevation and there were usually a large abun- rule or exception during species range shifts. They answer that, in fact, dance of snails (Ložek, 2000). Unlike pollen, which is commonly used for they are a bit of both. Instead of the above-mentioned simple model, a reconstruction of the paleoenvironment, snail shells can be identified to more complicated situation is taking shape, with many small refugia species level, which is essential if we wish to elucidate shifts in ranges. situated both in the Mediterranean and/or far from it having hosted Moreover, snails are usually fossilized directly in places where they various species during various periods, which then spread to various lived or in close surroundings, thus we have direct paleo-faunistic records directions at various times. We know the current situation, but particu- at our disposal, which is again crucial. Finally, a representative network of lar phases of this confused process remain largely undescribed. sites in the critical area, where cryptic refugia have been indicated to be The majority of evidence for central European last glacial refugia present based on molecular phylogeography and/or fossil records, is comes from molecular phylogeography, which has been established as also at our disposal (Ložek, 1964, 1982 and unpublished data). a useful tool for this purpose. Current results from many molecular Here we are interested in the last glacial refugia of temperate forest snail species only, because the existence of broadleaf forests in central Europe during the last glacial period is still not yet broadly accepted ⁎ Corresponding author. (Willis et al., 2000; Carcaillet and Vernet, 2001; Svenning et al., 2008). E-mail address: [email protected] (L. Juřičková). Therefore, we searched our database of land snails successions situated http://dx.doi.org/10.1016/j.yqres.2014.01.015 0033-5894/© 2014 University of Washington. Published by Elsevier Inc. All rights reserved. their age ( tain so-called dead carbon sometimes leading toThe an only material over-estimation suitable of for dating was mollusc shells,tion which can using con- the OxCal v4.1 calibration program ( moved from the sediment and identi based on the type of resultingsieve sediment. was Shells dried were and sorted systematically by re- sieving into adried variable number of under fractions laboratory conditions. Afterwards,their the fraction fragments above were the repeatedlyand decanted then if into necessary asieving. also 0.5 After in mm careful hydrogen sieve drying, peroxide. each and were sample Floating was extracted shells disaggregated from and in the water sedimentswithin by 80-cm-wide a excavation combination pits of taken or from open the outcrops. central Mollusc part of shells each lithologically distinguishable layer ( development of the sediment at each site2010 was undisturbed. because 78% of themwe do used not the contain amalgam of any small dead species carbon shells ( for radiocarbon dating Spectrometry) method and calibrated for variable initial USA. Mollusc shells werethe Center measured for by Applied thenon-directly Isotope dated AMS samples. Studies (Accelerator Radiocarbon of analyses Mass weresnails the performed University were in separated, of Georgia, ratherused than only samples using with age-estimation directfrom models radiocarbon our for dating, unpublished database from of whichexisting mollusc these mollusc Holocene successions successions. We across the Czech Republic and Slovakia Material and methods glacial wastelands. al of canopy forest snails in areas considered awhere these few snails decades can ago live. as Our harsh aim is toof provide evidence of snails the surviv- only toforest document species broadleaf occur. We woodlands restricted our asdistinct dataset the radiocarbon-dated to last only this glacial ecological habitat group layers wherein the records Bohemian of Massif and strictly Western Carpathians for such lithologically logical groups ( and fossil shells. The recorded snails wereJu classi not have survived outside of a canopy forest (Lo only those species that are woodland sensu stricto, and which could last glacial maximum (LGM) (approximately 13,500 assemblages are of late glacialwithin age, six non-interrupted are older molluscfound but in fauna not ten directly as mollusc radiocarbon-dated successions assemblages contained old as ( Western the Carpathians) of twenty strictly forest mollusc species were Results successions of the two unpublished pro descriptions, see the papers cited in for detailedsuccessions and information lithology of these about pro mostly particular regional journals successionstion. but Eight of these lack and mollusc successions have radiocarbonproxy, been published site such dating. in as various pollen For or vertebrate mollusccan bones, only can be provide present such in anor indica- a parkland true landscape but canopy also forest. speci NoSuch other species commonly thus used indicate not onlypusilla sparse woodland with light patches debatable species Lo ř i ž Molluscs were determined according to All these mollusc successions were sampled by standard methods We selected ten strictly forest mollusc records from more than 300 Altogether, 46 records (three in Bohemian Massif and 43 in the č ek, 1964 ková's and V. Lo ). The lithology was further used as a proxy to control that the that sometimes also occur in other than broadleaf forest types). Goodfriend and Stipp, 1983 ), i.e. 8 dm Lo Discus ruderatus ž ek, 1964 ž ek's personal comparative collections of recent 3 of spatially discrete sediment samples were ). From these ecological groups we chose , Monachoides incarnatus fi fi Table 1 c microclimatic conditions, which ed under a dissection microscope. fi ). To minimize this dating error, fi les see Supplementary Table 1; les see Supplementary Table 2. ; and for complete mollusc ž fi ek's group 1, excluding Bronk Ramsey, 2009 Lo ed into ten main eco- L.