[MIKE HOLMES]

CV LinkedIn Twitter Contact

RESEARCH DESCRIPTION

I am broadly interested in the effects of anthropogenic climate change on species distribution and biology. Using the Grinnell Resurvey Project as a backdrop, I am investigating how small mammals have responded to climate change over the last century in California's Sierra Nevada Mountains. The GRP has shown that many species mammals in three regions of California (Lassen, Yosemite, Southern Sierras) have responded to warmer temperatures (as is the case in the Yosemite and Southern Sierras transects) by moving upslope, presumably following a thermocline. The biological effects of these shifts is so far unknown. My research investigates biological change in three species of rodent (Family Cricetidae) that show varying elevational responses in the three Grinnellian transects. The three areas of my research include:

1) Morphology: Cranial morphology is often an indicator of dietary change in vertebrates. Using geometric morphometrics and digital imagery of specimens from the Museum of Vertebrate Zoology, I am determining to what extent the crania of four species have changed over the last 8-100 years. The data suggest that species in each of the three transects have changed shape and that there are patterns to that shape change across transects and among taxa. This might provide insight into underlying ecological processes taking place.

2) Isotopes: Stable isotopes can provide us with information on the diet of an individual. Using hair from hsitoric (80-100 years old) and modern MVZ specimens, I am using the stable isotope facility at UC Berkeley to determine dietary shifts in Peromyscus maniculatus across the three GRP transects. P. maniculatus, a habitat and dietary generalist is found throughout the elevational ranges of the GRP. Thus, it has not changed its elevational distribution in California in response to anthropogenic climate change. Thus, if the community composition around populations of P. maniculatus is shifting, this species will be experiencing new dietary items, which may be seen in stable isotopic analysis.

3) Phylogeography: Species responding to climate change must move, adapt or face extirpation or extinction. As small mammals move upslope, areas once favrable to immigration may become gene flow barriers too warm to traverse (eg. low-lying valleys). Additionally, species like P. maniculatus that show no elevational shift may be exhibiting more nuanced shifts such that populations - rather than metapopulations or entire species - might be shifting upslope. Using phylogeographic analysis, I am hoping to see if haplotypes once common to lowland areas are now found in higher elevations. For species such as Neotoma macrotis, which has increased its elevational range in the Southern Sierras transect, I am testing the hypothesis of increased isolation.