| The goal of this research is to evaluate the utility of stable isotopic analysis of small
mammal remains for reconstructing paleoecological conditions on the Snake River Plain over the
Holocene. Isotopic compositions in animals are derived from the plants they consume, which are
in turn strongly mediated by climatic conditions. Strong relationships between plant isotopic
compositions and climate have been found at global scales, however, variability in responses
exists at smaller scales. To begin to address this, my dissertation consists of two distinct, yet
related inquiries. The first examined whether the nitrogen isotopic composition of plants were
useful indicators of climate in a sagebrush steppe ecosystem of southern Idaho, evaluated at two
spatial scales. The second focused on using isotopic values in small mammal tissues to
reconstruct Holocene paleoenvironments of the Snake River Plain. With regard to the first, my
initial results found a complex relationship between plant isotopic compositions and climate. At
large gradients, foliar isotopic compositions follow expected trends of enrichment with
increasing temperatures, however, at smaller spatial scales, trends were opposite than expected –
higher isotopic values were observed with lower temperatures. This may be due to the narrower
range in climate measures or local biogeophysical traits that influence nitrogen cycling within
this system. Plant responses at both scales may also be limited by inclusion of only one
vegetation type and limited sampling. In terms of the second component, I show that various
forms of data from small mammals can provide new insight into ecological and climatic changes
over long periods of time, especially important in the Snake River Plain where other data sources are limited. Isotopic data from the generalist herbivores provided greater information due to their
opportunistic feeding habits, recording a warmer/drier early to mid-Holocene transitioning into
cooler/wetter conditions in the late period. The carbon isotope data also suggest changing
vegetation patterns with greater proportions of C4-CAM plants during the warmer and drier
period. Changes in skull size in the late period also supports morphological assessments as
another means to gain insight into ecological changes occurring in concert with climatic
evolution across the Holocene in southern Idaho.
Keywords: stable isotopes, nitrogen, climate, paleoenvironment, bone collagen, bone carbonate |