Paleoecology of Beringian “packrat” middens from central Yukon Territory, Canada

Rodent middens from ice-rich loess deposits are important new paleoenvironmental archives for Eastern Beringia. Plant macrofossils recovered from three middens associated with Dawson tephra (ca. 24,000 ¹⁴C yr B.P.) at two sites in Yukon Territory include diverse graminoids, forbs, and mosses. These data suggest substantial local scale floristic and habitat diversity in valley settings, including steppe-tundra on well-drained soils, moist streamside meadows, and hydric habitats. Fossil arctic ground squirrel burrows and nesting sites indicate that permafrost active layers were thicker during Pleistocene glacial periods than at present on north-facing slopes.     

Desertification and animal biodiversity in the desert grasslands of North America

Studies of breeding birds and small mammals were conducted at a series of sites that form a gradient of severity of desertification. Desert grassland sites represented the least changed landscape units and mesquite coppice dunes represented the most severe degradation, an irreversibly degraded landscape unit. The hypothesis that desertification reduces species diversity was not supported by the data. Species richness and diversities (Shannon-Weaver H′) of breeding birds were higher in the desertified areas than in the grassland with one exception. Data from a site dominated by the exotic African grass,Eragrostis lehmanniana, in south-eastern Arizona showed that breeding bird diversity was lower at that site than at a site in the same region that was dominated by native grasses. Species richness, diversity (H′), and abundance of small mammals were also higher in desertified areas than in desert grassland. Most grassland species of birds and mammals persist in the desertified habitats and species that are characteristic of shrublands colonize desertified desert grasslands. This accounts for the increases in species richness. However some species such as the banner-tailed kangaroo rat,Dipodomys spectabilis, are eliminated when grassland degrades to mesquite coppice dune or eroded creosotebush communities. These data suggest that other measures of faunal biodiversity such askeystone speciesmay be better measures of the impact of desertification on animal biodiversity.     

Spacing behaviour between two desert rodents, the golden spiny mouseAcomys russatusand the bushy-tailed gerbilSekeetamys calurus

Nest and feeding behaviour patterns were compared between two sympatric species, the bushy-tailed gerbilSekeetamys calurusand the golden spiny mouseAcomys russatus, in order to assess nest site and food as possible resources of competition. The way the species interact under laboratory conditions was also compared. WhileS. calurusused a nest into which they removed bedding material, only two out of sixA. russatusdid so, while in at least half of the studied cases they were found roosting outside of the nest inside the enclosure. When introduced into the same enclosure,S. caluruswas the dominant species and in five out of 12 casesS. calurusinhabited the nest abandoned byA. russatus, and in seven casesA. russatuswas found resting in the enclosure. UnlikeA. russatus,S. calurusaccumulated food inside its nest and also protected the food resource in the enclosure againstA. russatus. It seems that different nest and feeding behavioural patterns can reduce competition between these two sympatric species.     

A bio-available strontium isoscape for eastern Beringia: a tool for tracking landscape use of Pleistocene megafauna

Numerous paleoecological questions concern the mobility of ancient fauna in eastern Beringia. Strontium (Sr) isotope ratio (⁸⁷Sr/⁸⁶Sr) analysis has emerged as a powerful tracer for determining the provenance of ancient biological materials. However, it is important to characterize ⁸⁷Sr/⁸⁶Sr variation across a landscape. We measured the ⁸⁷Sr/⁸⁶Sr composition of teeth from present-day, herbivorous rodents (n = 162) sampled from across eastern Beringia to estimate bio-available ⁸⁷Sr/⁸⁶Sr values. We compiled these data with the very limited number of previously published ⁸⁷Sr/⁸⁶Sr values from the region. We then used this dataset and a machine learning, random-forest regression to predict bio-available ⁸⁷Sr/⁸⁶Sr variations across eastern Beringia. As a case study using our new ⁸⁷Sr/⁸⁶Sr map (isoscape), we measured the ⁸⁷Sr/⁸⁶Sr and oxygen stable isotope values (δ¹⁸O) of five radiocarbon-dated steppe bison from eastern Beringia and compared these to our ⁸⁷Sr/⁸⁶Sr isoscape and a δ¹⁸O isoscape to estimate the probable landscape use of these ancient fauna. Our model and isoscape provide important foundations for a wide range of additional applications, including studies of the paleo-mobility of other fauna, ancient people and present-day fauna in eastern Beringia.