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A primary objective of road ecology is to understand and predict how roads affect connectivity of wildlife populations. Road avoidance behavior can fragment populations, whereas lack of road avoidance can result in high mortality due to wildlife-vehicle collisions. Many small animal species focus their activities to particular microhabitats within their larger habitat. We sought to assess how different types of roads affect the movement of small vertebrates and to explore whether responses to roads may be predictable on the basis of animal life history or microhabitat preferences preferences. We tracked the movements of fluorescently marked animals at 24 sites distributed among 3 road types: low-use dirt, low-use secondary paved, and rural 2-lane highway. Most data we collected were on the San Diego pocket mouse (Chaetodipus fallax), cactus mouse (Peromyscus eremicus), western fence lizard (Sceloporus occidentalis), orange-throated whiptail (Aspidoscelis hyperythra), Dulzura kangaroo rat (Dipodomys simulans) (dirt, secondary paved), and deer mouse (Peromyscus maniculatus) (highway only). San Diego pocket mice and cactus mice moved onto dirt roads but not onto a low-use paved road of similar width or onto the highway, indicating they avoid paved road substrate. Both lizard species moved onto the dirt and secondary paved roads but avoided the rural 2-lane rural highway, indicating they may avoid noise, vibration, or visual disturbance from a steady flow of traffic. Kangaroo rats did not avoid the dirt or secondary paved roads. Overall, dirt and secondary roads were more permeable to species that prefer to forage or bask in open areas of their habitat, rather than under the cover of rocks or shrubs. However, all study species avoided the rural 2-lane highway. Our results suggest that microhabitat use preferences and road substrate help predict species responses to low-use roads, but roads with heavy traffic may deter movement of a much wider range of small animal species. Resumen Un objetivo principal de la ecologia de caminos es entender y predecir como afectan los caminos la conectividad de las poblaciones silvestres. El comportamiento de evitacion de caminos puede fragmentar poblaciones, mientras que la falta de evitacion puede resultar en alta mortandad debido a colisiones. Muchas especies animales pequenas enfocan sus actividades a microhabitats particulares dentro de su habitat mayor. Buscamos estudiar como los diferentes tipos de caminos afectan el movimiento de pequenos vertebrados y conocer si ciertas respuestas hacia los caminos pueden ser predecibles basandose en la historia de vida del animal o el microhabitat. Rastreamos los movimientos de animales marcados con fluorescencia en 24 sitios distribuidos entre 3 tipos de caminos: tierra de bajo uso, camino secundario pavimentado de bajo uso, y carretera rural de 2 carriles. La mayoria de los datos que colectamos fueron sobre Chaetodipus fallax, Peromyscus eremicus, Sceloporus occidentalis, Aspidoscelis hyperythra, Dipodomys simulans (tierra, pavimentacion secundaria), y P. maniculatus (solamente en carretera). C. fallax y P. eremicus se movian hacia los caminos de tierra pero no hacia una carretera de baja pavimentacion de anchura similar o hacia la carretera, indicando que evitan los caminos con sustrato pavimentado. S. occidentalis y A. hyperythra se movian hacia la tierra y los caminos secundarios pavimentados pero evitaban la carretera rural de 2 carriles, indicando que pueden evitar el ruido, las vibraciones o el disturbio visual de un constante flujo de trafico. D. simulans no evitaba el camino de tierra ni los caminos secundarios con pavimento. En general, el camino de tierra y los caminos secundarios fueron mas permeables para las especies que prefieren forrajear o tomar el sol en areas abiertas de su habitat en lugar de bajo rocas o arbustos. D. simulans no evito el camino de tierra ni los caminos secundarios pavimentados. Sin embargo todas las especies estudiadas evitaron la carretera de 2 carriles. Nuestros resultados sugieren que las preferencias de uso de microhabitat y sustrato de caminos ayudan a predecir las respuestas de las especies hacia caminos de bajo uso, pero los caminos con trafico pesado pueden disuadir el movimiento de un rango mucho mayor de especies animales pequenas.

We surveyed burned and unburned plots across four habitat reserves in San Diego County, California, USA, in 2005 and 2006, to assess the effects of the 2003 wildfires on the community structure and relative abundance of rodent species. The reserves each contained multiple vegetation types (coastal sage scrub, chaparral, woodland, and grassland) and spanned from 250 m to 1078 m in elevation. Multivariate analyses revealed a more simplified rodent community structure in all burned habitats in comparison to unburned habitats. Reduction in shrub and tree cover was highly predictive of changes in post-fire rodent community structure in the burned coastal sage scrub and chaparral habitats. Reduction in cover was not predictive for the less substantially burned woodlands and grasslands, for which we hypothesized that interspecific competition played a greater role in post-fire community structure. Across vegetation types, generalists and open habitat specialists typically increased in relative abundance, whereas closed habitat specialists decreased. We documented significant increases in relative abundance of the deer mouse (Peromyscus maniculatus Wagner) and Dulzura kangaroo rat (Dipodomys simulans Merriam). In contrast, we found significant decreases in relative abundance for the California mouse (Peromyscus californicus Gambel), San Diego pocket mouse (Chaetodipus fallax Merriam), desert woodrat (Neotoma lepida Thomas), and brush mouse (Peromyscus boylii Baird). Currently, our research program involves assessment of whether habitat conservation plans (HCPs) in southern California provide long-term protection to HCP covered species, as well as preserve ecosystem function. The scenario of increased wildfires needs to be incorporated into this assessment. We discuss our results in relation to management and conservation planning under a future scenario of larger and more frequent wildfires in southern California.

In southern California the Dulzura kangaroo rat (Dipodomys simulans) occurs in shrub-dominated habitats adjacent to forb- or grass-dominated habitats, which support the endangered Stephens's kangaroo rat (D. stephensi). We monitored a number of populations of both species from 1996 through 2000, spanning the 1997- 1998 El Nino Southern Oscillation (ENSO) event. Although populations of D. stephensi were not significantly impacted by this climatic event, D. simulans declined from 10-24 individuals/ha to about 7-12 individuals/ha over a 6- to 8-month period; numbers subsequently continued to decline to 1-2 individuals/ha and failed to recover in the approximately 2.5 years of post-ENSO monitoring. We noticed no signs of sickness or illness among these animals, although adult body masses of D. simulans (but not D. stephensi) declined through the ENSO event, suggesting that food resources for the former species may have been compromised. Alternatively, populations of D. simulans may have been unusually high before the ENSO event, such that the onset of rains merely hastened a predictable winter die-off. Finally, other rodents could have robbed seeds from the food caches of Dulzura kangaroo rats, influencing the ability of the latter to survive the ENSO event. Although this explanation remains speculative, cache pilferage has been demonstrated among other heteromyids, and a recent theoretical study suggests this may be an important mechanism of species coexistence. Further investigations of cache pilferage could enhance our understanding of the ecology and evolution of these diverse small mammal assemblages.

Reanalysis of a recently published data set on the responses of 2 species of kangaroo rats to the 1997-1998 El Nino Southern Oscillation (ENSO) event revealed an error during data manipulation, and underscored the perils associated with electronic data storage, manipulation, and analyses. Renewed analyses revealed that Dipodomys simulans was not catastrophically impacted by the ENSO event. Both species were negatively impacted by 2 separate rainy periods, and both species appeared to recover rapidly. The rate of demographic recovery may be a function of habitat preferences. Dipodomys stephensi occurs in valley bottoms and recovered numerically only after cessation of rains, whereas D. simulans, which occurs on better-drained habitat in adjacent hill slopes, appeared to initiate demographic recovery half way through the rainy period associated with the 1998 ENSO. In contrast, however, D. simulans was not observed to recover for about 5 months after the rainy period in 2000.

The magnitude of sexual dimorphism in size among populations of some small mammals living in different habitats may be a reflection of the degree of habitat partitioning between sexes or nutritional quality of available food. We tested these hypotheses by quantifying between-sex differences in size in populations of the Dulzura kangaroo rat ( Dipodomys simulons ) from several macrohabitat types at regional and local geographic scales. On a regional scale, our results indicated a significant shift in morphology of males and females along a north-south latitudinal gradient. Large kangaroo rats inhabited warm and arid southernmost latitudes, whereas small animals inhabited relatively cool and moist regions to the north. This morphologic gradient represented an increase in size with less seasonal variation in precipitation and temperature. This pattern was clearly counter to Bergmann's rule, but consistent with the hypothesis that temporal variation in availability of food may be an important factor leading to geographic variation in size. External and cranial measures of size dimorphism were not correlated significantly with any major geographic factor, and only cranial measures were associated significantly with variation in climate. At a local level, kangaroo rats living in different vegetation communities within the same latitudinal zone also exhibited significant sexual dimorphism in size; however, macrohabitat heterogeneity appeared to affect males and females equally. Both sexes were larger in Sierran Montane Conifer Forest and Californian Chaparral macrohabitats. Smaller animals occupied Californian Grassland and Coastal-scrub, and Vizcaino vegetation communities. This pattern of variation was observed in all three-way comparisons and suggests the possibility of habitat-mediated phenotypic responses. Finally, only one of eight comparisons involving kangaroo rats living in adjacent plant communities showed a significant two-way interaction between dimorphism and macrohabitat type. Our results, therefore, did not provide strong evidence to substantiate the hypotheses that the magnitude of dimorphism among populations of D. simulans living in different macrohabitats is a reflection of the degree of partitioning between sexes or nutritional quality of available food.