MODELING PLASTICITY IN RODENT RESPONSES TO THE LUNAR CYCLE FOLLOWING HABITAT MODIFICATION
|Jackson L Tenney; University of Nevada, Reno; email@example.com; Kevin T Shoemaker, Danielle C Miles|
It is well established that many rodent species alter their activity levels across the different phases of the lunar cycle. Previous studies indicate that perceived predation risk from increased moonlight can alter foraging activity to an extent that causes population shifts comparable to those caused by actual predation. However, the extent to which these behavioral cycles within rodent populations are plastic is not yet understood. Conifer woodland removal projects, used by land management agencies to restore sagebrush habitat, provide geographically dispersed experimental replicates to measure potential activity and population shifts in response to increased exposure to moonlight from reduced canopy cover. To assess how habitat changes translate to behavioral shifts in rodent populations, we conducted a 4-year BACI study design across five project regions in the northern Great Basin. We assessed weekly recapture rates as a metric of activity for over 5,000 capture occasions of 24 rodent species. Our trapping efforts spanned the vegetation gradient from open sagebrush to dense woodland cover within each transect and included diurnal-species control groups. This allowed us to isolate changes in the relationship between activity and moonlight, increasing our understanding of how rodent populations vary their behaviors in response to habitat change.
TRANSLOCATION OF THE SAN JOAQUIN ANTELOPE SQUIRREL (AMMOSPERMOPHILUS NELSONI) IN THE CARRIZO PLAIN
|Patrick R Anderson; California Polytechnic State University; firstname.lastname@example.org; Craig M. Fiehler, William T. Bean|
In arid and semi-arid environments, burrowing mammals play a key role in increasing landscape heterogeneity through facilitative (positive) species interactions. The loss of burrowing mammal populations can consequently lead to negative effects cascading through the ecosystem; it is therefore critical to understand these facilitative interactions for conservation and management. For instance, accounting for facilitative interactions during translocation could improve success rates. To investigate the importance of burrow facilitation on San Joaquin antelope squirrel (Ammospermophilus nelsoni) translocation success, we designed a program for antelope squirrels using a natural experiment, with paired sites selected for the presence and absence of a burrowing facilitator, the giant kangaroo rat (Dipodomys ingens). We radio collared 98 antelope squirrels from core habitat within the Carrizo Plain. We then translocated 68 to uninhabited lands in their historical range, half to a site with giant kangaroo rats and half without. We compared survival, dispersal and movement, and home range size across the three treatment groups. Our study highlights the importance of considering facilitative interactions when selecting release sites for translocation and planning restoration campaigns.
IT'S GETTING HOTTER IN HERE: SALT MARSH HARVEST MOUSE SURVIVAL AND RECOVERY FOLLOWING WILDFIRE
|Melissa K Riley; CDFW, UC Davis; email@example.com; Katie Smith, Laureen Barthman-Thompson, Sarah Estrella|
Climate change is cited as one of the main threats to endangered species, especially those with small populations that are susceptible to stochastic events that can be exacerbated by such change. An example of this in California is the increase in the frequency and intensity of wildfires. In Suisun Marsh, the occurrence of wildfires has increased in recent years threatening species like the endangered salt marsh harvest mouse (Reithrodontomys raviventris, SMHM). SMHM are endemic to the marshes of the San Francisco Bay Estuary and have been listed as endangered since the 1970s. While populations are thriving in Suisun Marsh, recent wildfires almost completely burned the vegetation at several SMHM conservation areas. The objective of this study was to quantify how SMHM and associated small mammal populations responded after wildfire events. In most cases SMHM were shown to be resilient, with populations rebounding within one year. However, in areas where vegetation regrowth has been slow, populations remain low. Understanding the response of SMHM to catastrophic events like wildfires will allow managers to better implement conservation efforts in the future as well as understand the effects of management tools like prescribed burns.
PATCH OCCUPANCY OF THE SALT MARSH HARVEST MOUSE: DO PATCH SIZE AND ISOLATION DRIVE OCCURRENCE OF AN ENDANGERED HABITAT SPECIALIST?
|Cody M Aylward; UC Davis ; firstname.lastname@example.org; Laureen Barthman-Thompson, Douglas A. Kelt, Mark Statham, Benjamin N. Sacks|
The salt marsh harvest mouse (SMHM; Reithrodontomys raviventris) is an endangered species restricted to the San Francisco Estuary wetlands. Approximately 90% of historical wetland habitat in the estuary has been destroyed. Modern wetlands primarily consist of relatively small, patchy fragments among a matrix of urban and upland habitat. Restoration and preservation of marsh habitat are among the primary methods of SMHM conservation, and understanding which patches of habitat to prioritize is key to allocating resources optimally. To this end, we developed a non-invasive survey for small mammals and used this technique to survey 48 marsh patches in the San Francisco Estuary. We tested hypotheses derived from island biogeography theory – that SMHM occupancy was related to marsh patch size, and inversely related to patch isolation (as measured by the proportion of marsh and urban habitat surrounding a given patch). We tested the effects of habitat variables and occurrence of potential competitors (western harvest mouse [R. megalotis], house mouse [Mus musculus], and California vole [Microtus californicus]) on SMHM occupancy. We also estimated patterns of occupancy in the three co-occurring species. Preliminary results suggest a strong relationship between SMHM occupancy and patch isolation at a landscape scale, and a moderate relationship with patch size. SMHM occupancy was also moderately increased by high tide escape habitat and inversely related to western harvest mouse occurrence. Western harvest mouse occupancy was positively related to the presence of terrestrial grasses within marsh patches. House mice and voles exhibited no strong habitat associations, although there was a moderate positive relationship between western harvest mouse and house mouse occupancy. Our results suggest that isolation, fragmentation, and encroachment of upland vegetation into marsh habitat are detrimental to SMHM persistence, and conservation of SMHM at the landscape scale may be particularly important.
A NEW FRAMEWORK FOR EVALUATING POTENTIAL HABITAT OF THE SALT MARSH HARVEST MOUSE
|Carla L Angulo; email@example.com; Dr. Katherine R. Smith, Melissa Riley, Sadie Trombley, Monica Zhang|
The endangered salt marsh harvest mouse (Reithrodontomys raviventris; SMHM) is endemic to the marshes of the San Francisco Estuary. This species is actively managed as a habitat specialist dependent on tidal marshes dominated by pickleweed (Salicornia pacifica). In reality, their realized niche is much broader, and recent research has continued to reveal flexibility in their habitat requirements. However, an abundance of research failed to accurately identify the primary constituent elements that determine occupancy and abundance throughout the species range. This lack of a more nuanced understanding of habitat requirements causes challenges for biologists attempting to evaluate the potential for SMHM occupancy at many sites, and presence is often assumed if any pickleweed marsh occurs. Based on recent demographic, diet, and habitat use data we propose that SMHM persistence is dependent upon four primary constituent elements-foraging habitat, refuge habitat, nesting habitat, and dispersal habitat – and describe here the essential characteristics of each of these elements. It is our hope that a standardized framework for evaluating these essential characteristics will provide biologists the tools they need to assess areas of potential SMHM occupancy in a more efficient, effective, and consistent manner, which can streamline permitting decisions and recovery plans.
A RANGE-WIDE ASSESSMENT OF THE RELATIONSHIP BETWEEN SALT MARSH HARVEST MOUSE DENSITIES AND ENVIRONMENTAL CHARACTERISTICS
|Katie Smith; WRA, Inc., UC Davis; firstname.lastname@example.org;|
Though the salt marsh harvest mouse (Reithrodontomys raviventris; SMHM) has been listed as state and federally endangered since the early 1970’s, there has never existed a comprehensive, central repository for survey data. Further, survey methods differ among monitoring entities, and for many older efforts raw data was not retained and only a minimal summary of the methods and results now exists. This lack of an all-inclusive data set has prohibited researchers from performing any large-scale assessments of correlations between SMHM densities, and habitat features and environmental conditions. Localized analyses often contradict one another, and likely provide a misleading picture of SMHM ecology. These deficiencies have had consequences for planning and executing recovery actions such as tidal restoration. Over the past two years myself and my collaborators have compiled the most comprehensive database of SMHM survey data and created a GIS of environmental variables that are likely to impact SMHM populations. Using these tools I performed the first range-wide spatial analysis of the relationship between SMHM occupancy and densities, and environmental variables. The resulting heat maps of SMHM hot spots, high quality but unoccupied patches, and low quality patches will support the effective application of recovery actions.