Impacts of late Quaternary environmental change on the long-tailed ground squirrel(Urocitellus undulatus)in Mongolia

Impacts of Quaternary environmental changes on mammal faunas of central Asia remain poorly understood due to a lack of comprehensive phylogeographic sampling for most species.To help address this knowledge gap,we conducted the most extensive molecular analysis to date of the long-tailed ground squirrel （Urocitellus undulatus Pallas 1778） in Mongolia,a country that comprises the southern core of this species＇ range.Drawing on material from recent collaborative field expeditions,we genotyped 128 individuals at two mitochondrial genes （cytochrome b and cytochrome oxidase Ⅰ;1797 bp total）.Phylogenetic inference supports the existence of two deeply divergent infraspecific lineages （corresponding to subspecies U.u.undulatus and U.u.eversmanni）,a result in agreement with previous molecular investigations but discordant with patterns of range-wide craniometric and external phenotypic variation.In the widespread western eversmanni lineage,we recovered geographically-associated clades from the：（a） Khangai,（b） Mongolian Altai,and （c） Govi Altai mountain ranges.Phylogeographic structure in U.u.eversmanni is consistent with an isolation-by-distance model;however,genetic distances are significantly lower than among subspecies,and intra-clade relationships are largely unresolved.The latter patterns,as well as the relatively higher nucleotide polymorphism of populations from the Great Lakes Depression of northwestern Mongolia,suggest a history of range shifts into these lowland areas in response to Pleistocene glaciation and environmental change,followed by upslope movements and mitochondrial lineage sorting with Holocene aridification.Our study illuminates possible historical mechanisms responsible for U.undulatus genetic structure and contributes to a framework for ongoing exploration of mammalian response to past and present climate change in central Asia.

Rodent burrow network dynamics under human-induced landscape transformation from desert to steppe in Kalmykian rangelands

Rodents play an important role in rangelands through the engineering of extensive burrow systems,which pro­vides key habitats for many animal and plant species.We have analyzed the long-term variation in the abun­dance and distribution of rodent burrows in grazing ecosystems of southern Russia(Kalmykia)under the land­scape change from desert to steppe caused by the drastic reduction of livestock after the collapse of the USSR in the early 1990s.We conducted burrow surveys in the“desert”(1980)and“steppe”(2017)periods on 193-km transects.We found considerable changes in burrow abundance and distribution,as well as evidence of desert habitat fragmentation and isolation caused by the expansion of tall-grass communities.Burrows of the open-dwelling diurnal ground squirrel(Spermophilus pygmaeus),the dominant and the keystone species during the“desert”period,almost completely disappeared from the rodent burrow network by 2017,indicating signifi­cant habitat loss.In contrast,the burrows of the folivorous social vole(Microtus socialis)which was rare in the 1980s,became abundant and ubiquitously distributed.The burrow density of the desert-dwelling psammophi­lous midday gerbil(Meriones meridianus)decreased,while the distances between occupied patches increased,indicating desert habitat fragmentation and loss of population connectivity.Burrows of the folivorous tamarisk gerbils(M.tamariscinus)were recorded only sporadically in both 1980 and 2017.The observed changes in the rodent burrow network,the key component of grazing ecosystems,correlate with rodent species ecology and can have long-term and important consequences for ecosystem functioning.

Breeding versus survival:proximate causes of abrupt population decline under environmental change in a desert rodent,the midday gerbil(Meriones meridianus)

Studying abrupt ecological shifts under gradual environmental change caused,in particular,by human activi­ty is important for understanding the fundamental aspects and underlying mechanisms of ecological resilience.One of the rare well-documented examples of an abrupt ecological shift is the delayed step transition of the population of a desert rodent,the midday gerbil(Meriones meridianus),from high-abundance(1994-2002)to low-abundance(2003-2017)regimes.This was in response to landscape transformation from desert to steppe caused by the drastic reduction of livestock in the rangelands of southern Russia after the collapse of the USSR in the early 1990s.In this study,we tested whether demographic parameters were correlated with the observed abrupt downward population shift.We found that reproductive activity(the percentage of breeding females,the number of litters,fecundity and the number of young recruited per female)showed no trend over time and did not differ between periods of high and low abundance.In contrast,the adult sex ratio(SR=males:females)de­creased significantly with time and was as much as twice more female-biased for the low-abundance population regime.However,SR was not related to any reproductive parameter,including the percentage of breeding fe­males.We conclude that proximate reasons for an abrupt population decline in M.meridianus are not associat­ed with the changes in breeding patterns or mate limitation caused by the Allee effect but relate to the increased mortality as a result of the desert landscape being fragmented by steppezation.The mortality is expected to be higher for males as the mobile and dispersing sex.