We are interested in understanding the population and community dynamics of spatially and temporally complex environments and are using sage-steppe as a test case for developing those themes. Sage steppe is rapidly declining in extent, due to increasing human population and associated land uses, and remaining sage steppe is increasingly fragmented. Craters of the Moon National Monument and Preserve poses an interesting landscape in which islands of sage-steppe that were isolated by Pleistocene lava flows (kipukas) persist in a temporally variable and historically fragmented environment. This contrasts with the contemporary fragmentation of sage that is caused by regional population increase and development. Our lab is studying the plant communities, the mammals, and the arthropod food webs of the dominant characteristic shrub (Artemisia tridentata, big sagebrush), and is researching the ecological traits and dynamics that influence diversity of plants and animals in fragmented and extensive sage steppe. 

The lava flows on the Snake River Plain in south central Idaho provide the opportunity to study habitat patches that were formed long ago by physical processes and are relatively free of recent land use impacts and to compare these with habitat patches that have been created by recent intensified land use by humans.  The kipukas of Craters of the Moon NM were isolated 2,100-15,000 years ago by lava flows dispensed from the Yellowstone hot spot.  Kipukas have not been farmed or grazed and thus are expected to retain native sage-steppe habitat that has been minimally influenced by human land use practices; these remnant patches of sage steppe within the lava flow matrix provide a likely baseline for sage-steppe ecosystems that are minimally affected by intensive human land use, as well as a baseline by which to estimate expected effects of the now-extensive fragmentation of sage-steppe that is following from more intensive land use in the Intermountain West. However, little literature documents the biology or ecology of these unique habitats, so their potential to provide guidance to land use and land management is largely unrealized. Much of the historical sage-steppe region has been converted to agriculture in the past century, with native vegetation found in discrete patches within a matrix of agricultural land uses.  Approximately 3.5 million of the 10.3 million ha of sage-steppe that were historically present in Idaho have been cleared for agricultural purposes.  Agricultural practices have also led to the invasion of Bromus tectorum (cheatgrass), which has increased fire frequency and contributed to conversion and fragmentation of sage-steppe. 

A pilot study of kipukas at Craters of the Moon National Monument indicated that isolation (distance of a kipuka from an extensive area of sage steppe) may cause low diversity of small mammals on kipukas. Additionally, diversity of small mammals was lower on kipukas that had cheatgrass (Bromus tectorum), an invasive species that is implicated in increased fire frequency and destruction of sagebrush habitat in the Intermountain West. However, the kipukas with cheatgrass were more isolated on average than were those without, and they also tended to be found on the east/west side of the flow, so the effects of isolation, geography, and cheatgrass could not be estimated independently.  Additionally, diversity of small mammals was lower in kipukas than on nearby patches of sage within developed agricultural land. This last result is surprising, given that kipukas would be expected to be of higher quality habitat and more typical sage-steppe than patches within agricultural areas. However, kipukas have been isolated for thousands of years and, if biogeographic constraints are strong, may have undergone significant reduction in populations present, reflecting occasional local extinction of a population that is not reestablished by colonization of individuals dispersing across lava. In contrast, agricultural patches have been formed within the past ca. 100 years, so increased local extinction and reduced successful colonization may be yet to play out.

The galling insects of sage showed a different pattern from that of small mammals.  Neither diversity nor density of galls were related to isolation of kipukas. However, density increased significantly with area, and diversity decreased with area. The patterns contrasted sharply with those of galling insects of sage sampled from patches in agricultural lands. The galling insects of kipukas were at relatively low density, were diverse, and had relatively high levels of parasitism, whereas the galling insects of patches of sage within agriculture occurred at high density, were strongly dominated by a single species, and had very low rates of parasitism.  Again, the data suggested an effect of cheatgrass: species richness of galling insects on kipukas declined with abundance of cheatgrass.

            We have expanded our studies of sage steppe communities and their dynamics, and are studying many more kipukas, several adjacent areas of extensive sage-steppe, and areas of the lava matrix-habitat surrounding kipukas.  Ph.D. student Cameron Pedersen is studying the long-term and large-scale patterns of sage establishment and growth and their influence on diversity of the plant community of kipukas and other sage-steppe. Former ISU undergraduate student Jose Ramirez (now an M.S. student in Entomology at UC-Riverside) continues to work with our lab to complete analysis of the arthropod foodwebs associated with sagebrush (Artemisia tridentata). M.S. student Nicole Talaro is studying the spiders of kipukas and other sage areas, with goals of understanding patterns of diversity and abundance of Salticids (jumping spiders) and their role as top predators in the food web associated with sagebrush.  Ph.D. student Nancy Hampton works primarily in extensive sagesteppe habitat, rather than the fragmented kipukas landscape of Craters of the Moon National Monument and Preserve, but is studying the local and regional ecology of two major insect herbivores of sagebrush, Aroga websteri (the sagebrush defoliator moth, Gelechiidae) and Hemileuca hera hera (the sagebrush sheep moth, Saturniidae).