Steven M. Ostoja

Effects of Rodent Species, Seed Species, and Predator Cues on Seed Fate

Abstract Seed selection, removal and subsequent management by granivorous animals is thought to be a complex interaction of factors including qualities of the seeds themselves (e.g., seed size, nutritional quality) and features of the local habitat (e.g. perceived predator risk). At the same time, differential seed selection and dispersal is thought to have profound effects on seed fate and potentially vegetation dynamics. In a feeding arena, we tested whether rodent species, seed species, and indirect and direct predation cues influence seed selection and handling behaviors (e.g., scatter hoarding versus larder hoarding) of two heteromyid rodents, Ord’s kangaroo rat (Dipodomys ordii) and the Great Basin pocket mouse (Perognathus parvus). The indirect cue was shrub cover, a feature of the environment. Direct cues, presented individually, were (1) control, (2) coyote (Canis latrans) vocalization, (3) coyote scent, (4) red fox (Vulpes vulpes) scent, or (5) short-eared owl (Asio flammeus) vocalization. We offered seeds of three sizes: two native grasses, Indian ricegrass (Achnatherum hymenoides) and bluebunch wheatgrass (Pseudoroegneria spicata), and the non-native cereal rye (Secale cereale), each in separate trays. Kangaroo rats preferentially harvested Indian ricegrass while pocket mice predominately harvested Indian ricegrass and cereal rye. Pocket mice were more likely to scatter hoard preferred seeds, whereas kangaroo rats mostly consumed and/or larder hoarded preferred seeds. No predator cue significantly affected seed preferences. However, both species altered seed handling behavior in response to direct predation cues by leaving more seeds available in the seed pool, though they responded to different predator cues. If these results translate to natural dynamics on the landscape, the two rodents are expected to have different impacts on seed survival and plant recruitment via their different seed selection and seed handling behaviors.

Ant Assemblages in Intact Big Sagebrush and Converted Cheatgrass-Dominated Habitats in Tooele County, Utah

ABSTRACT. Biological invasions are one of the greatest threats to native species in natural ecological systems. One of the most successful invasive species is Bromus tectorum L. (cheatgrass), which is having marked impacts on native plant communities and ecosystem processes. However, we know little about the effects of this invasion on native animal species in the Intermountain West. Because ants have been used to detect ecological change associated with anthropogenic land use, they seem well suited for a preliminary evaluation of the consequences of cheatgrass-driven habitat conversion. In our study, we used pitfall traps to assess ant community assemblages in intact sagebrush and nearby cheatgrass-dominated vegetation. Ant abundance was about 10-fold greater in cheatgrass-dominated plots than in sagebrush plots. We also noted differences in diversity and evenness between habitat types at both the species and the functional-group levels of organization. At the species level, Shannons diversity index was greater in sagebrush plots than in cheatgrass-dominated plots. However, at the functional-group level, Simpsons and Shannons diversity indices and the Brillouin evenness index were greater in cheatgrass-dominated plots than in sagebrush plots. Further, common species / functional groups tended to be more abundant while less common species / functional groups tended to be less abundant in cheatgrass-dominated plots compared to intact sagebrush plots. Patterns appear to be at least partially related to resource availabilities. This initial survey of ant communities from intact-native and altered vegetation types may be indicative of similar trends of biodiversity shifts throughout the Intermountain West where cheatgrass has successfully replaced native species. We also discuss the implications of ant communities on land management activities, specifically in the context of aridland restoration.

Short-Term Vegetation Response Following Mechanical Control of Saltcedar (Tamarix spp.) on the Virgin River, Nevada, USA

Abstract Tamarisk (a.k.a. saltcedar, Tamarix spp.) is an invasive plant species that occurs throughout western riparian and wetland ecosystems. It is implicated in alterations of ecosystem structure and function and is the subject of many local control projects, including removal using heavy equipment. We evaluated short-term vegetation responses to mechanical Tamarix spp. removal at sites ranging from 2 to 5 yr post-treatment along the Virgin River in Nevada, USA. Treatments resulted in lower density and cover (but not eradication) of Tamarix spp., increased cover of the native shrub Pluchea sericia (arrow weed), decreased density and cover of all woody species combined, increased density of both native annual forbs and the nonnative annual Salsola tragus (prickly Russian-thistle), and lower density of nonnative annual grasses. The treated plots had lower mean woody species richness, but greater herbaceous species richness and diversity. Among herbaceous species, native taxa increased in richness whereas nonnative species increased in both species richness and diversity. Thus, efforts to remove Tamarix spp. at the Virgin River reduced vegetative cover contributing to fuel loads and probability of fire, and resulted in positive effects for native plant diversity, with mixed effects on other nonnative species. However, absolute abundances of native species and species diversity were very low, suggesting that targets of restoring vegetation to pre-invasion conditions were not met. Longer evaluation periods are needed to adequately evaluate how short-term post-treatment patterns translate to long-term patterns of plant community dynamics. Nomenclature: Tamarix (tamarisk). Management Implications: Short-term reductions in density and cover of Tamarix spp. can be achieved with mechanical control techniques, as applied on the Virgin River, Nevada, USA. These treatments can also reduce total woody plant cover and may provide some reduction in flammable nonnative annual grass density, but have no net effect on total herbaceous density. Thus, treatments can reduce fuelbeds, and the potential for wildfire where fuel reduction is the principal goal of vegetation management. Nonnative annual forbs, Salsola tragus (Russian-thistle) in particular, can increase indicating that control treatments for Tamarix spp. can facilitate secondary invasion by other nonnative species. Treatments can also increase cover of rhizomatous native woody plants such as Pluchea sericea (arrowweed), and native forbs as a group, as well as increase diversity for various plant guilds. Treatments provided no significant benefit to arboreal native plants such as Prosopis spp. (mesquites) nor mesic taxa including Salix spp. (willows) and Populus fremontii (Fremont cottonwood) that may be of greater value to wildlife. The results of this short-term response study are the foundation for understanding longer-term (i.e. 5+ yr) Tamarix spp. control efficacy or plant community trajectories, and provide a basis to assess how long the initial treatment effects may persist. In addition, it is unknown how the results of mechanical treatments evaluated in this study compare with those of other approaches (e.g. herbicide, fire, biological control, or combinations thereof). Both short and long term effects, and the relative pros and cons of various control techniques, should be considered when developing any Tamarix spp. management plan.

A Network Extension of Species Occupancy Models in a Patchy Environment Applied to the Yosemite Toad (Anaxyrus canorus)

A central challenge of conservation biology is using limited data to predict rare species occurrence and identify conservation areas that play a disproportionate role in regional persistence. Where species occupy discrete patches in a landscape, such predictions require data about environmental quality of individual patches and the connectivity among high quality patches. We present a novel extension to species occupancy modeling that blends traditional predictions of individual patch environmental quality with network analysis to estimate connectivity characteristics using limited survey data. We demonstrate this approach using environmental and geospatial attributes to predict observed occupancy patterns of the Yosemite toad (Anaxyrus (= Bufo) canorus) across >2,500 meadows in Yosemite National Park (USA). A . canorus , a Federal Proposed Species, breeds in shallow water associated with meadows. Our generalized linear model (GLM) accurately predicted ~84% of true presence-absence data on a subset of data withheld for testing. The predicted environmental quality of each meadow was iteratively ‘boosted’ by the quality of neighbors within dispersal distance. We used this park-wide meadow connectivity network to estimate the relative influence of an individual Meadow’s ‘environmental quality’ versus its ‘network quality’ to predict: a) clusters of high quality breeding meadows potentially linked by dispersal, b) breeding meadows with high environmental quality that are isolated from other such meadows, c) breeding meadows with lower environmental quality where long-term persistence may critically depend on the network neighborhood, and d) breeding meadows with the biggest impact on park-wide breeding patterns. Combined with targeted data on dispersal, genetics, disease, and other potential stressors, these results can guide designation of core conservation areas for A . canorus in Yosemite National Park.

Germination and growth of native and invasive plants on soil associated with biological control of tamarisk ( Tamarix spp.)

Introductions of biocontrol beetles (tamarisk beetles) are causing dieback of exotic tamarisk in riparian zones across the western United States, yet factors that determine plant communities that follow tamarisk dieback are poorly understood. Tamarisk-dominated soils are generally higher in nutrients, organic matter, and salts than nearby soils, and these soil attributes might influence the trajectory of community change. To assess physical and chemical drivers of plant colonization after beetle-induced tamarisk dieback, we conducted separate germination and growth experiments using soil and litter collected beneath defoliated tamarisk trees. Focal species were two common native (red threeawn, sand dropseed) and two common invasive exotic plants (Russian knapweed, downy brome), planted alone and in combination. Nutrient, salinity, wood chip, and litter manipulations examined how tamarisk litter affects the growth of other species in a context of riparian zone management. Tamarisk litter, tamarisk litter leachate, and fertilization with inorganic nutrients increased growth in all species, but the effect was larger on the exotic plants. Salinity of 4 dS m−1 benefitted Russian knapweed, which also showed the largest positive responses to added nutrients. Litter and wood chips generally delayed and decreased germination; however, a thinner layer of wood chips increased growth slightly. Time to germination was lengthened by most treatments for natives, was not affected in exotic Russian knapweed, and was sometimes decreased in downy brome. Because natives showed only small positive responses to litter and fertilization and large negative responses to competition, Russian knapweed and downy brome are likely to perform better than these two native species following tamarisk dieback. Nomenclature: Downy brome, Bromus tectorum L.; Russian knapweed, Acroptilon repens (L.) DC.; tamarisk, Tamarix spp.; red threeawn, Aristida purpurea Nutt. var. longiseta (Steud.) Vasey; sand dropseed, Sporobolus cryptandrus (Torr.) Gray. Management Implications: Following control of tamarisk, riparian land managers often seek to establish a native plant community, but secondary weed invasions can thwart such efforts. Soil conditions are among the factors that determine plant community composition following tamarisk die-back after biocontrol by tamarisk beetles. Soils that have been dominated by tamarisk for decades generally have a thick layer of tamarisk leaf litter and are higher in nutrients, organic matter, and salts than nearby soils. Mechanical removal of dead or dying tamarisk can leave behind wood chips or debris. Greenhouse experiments showed that such soils are not harmful to two native species, red threeawn and sand dropseed, but generally had positive effects on the growth of two common invasive exotic plants, Russian knapweed and downy brome, when plants were grown alone or in competition. Russian knapweed even showed a slight positive growth response to small increases in salinity. A thick layer of tamarisk wood chips was detrimental to plant germination, but a thin layer of wood chips increased growth slightly. Russian knapweed and downy brome are likely to do well after tamarisk dieback where soils are enriched in nutrients from tamarisk litter and beetle frass, so managers should be prepared for secondary invasion by these species following tamarisk removal if they occur nearby. Further experimentation should elucidate when a thin layer of wood chips might benefit plant growth. However, soil conditions vary from site to site. Soil testing and assessment of which native species grow nearby could suggest desirable native species to plant to facilitate establishment of the plant community of interest.

Detecting the influence of rare stressors on rare species in Yosemite National Park using a novel stratified permutation test

Statistical models often use observational data to predict phenomena; however, interpreting model terms to understand their influence can be problematic. This issue poses a challenge in species conservation where setting priorities requires estimating influences of potential stressors using observational data. We present a novel approach for inferring influence of a rare stressor on a rare species by blending predictive models with nonparametric permutation tests. We illustrate the approach with two case studies involving rare amphibians in Yosemite National Park, USA. The endangered frog, Rana sierrae, is known to be negatively impacted by non-native fish, while the threatened toad, Anaxyrus canorus, is potentially affected by packstock. Both stressors and amphibians are rare, occurring in ~10% of potential habitat patches. We first predict amphibian occupancy with a statistical model that includes all predictors but the stressor to stratify potential habitat by predicted suitability. A stratified permutation test then evaluates the association between stressor and amphibian, all else equal. Our approach confirms the known negative relationship between fish and R. sierrae, but finds no evidence of a negative relationship between current packstock use and A. canorus breeding. Our statistical approach has potential broad application for deriving understanding (not just prediction) from observational data.

Short-term Response of Holcus lanatus L. (Common Velvetgrass) to Chemical and Manual Control at Yosemite National Park, USA

One of the highest priority invasive species at both Yosemite and Sequoia and Kings Canyon national parks is Holcus lanatus L. (common velvetgrass), a perennial bunchgrass that invades mid-elevation montane meadows. Despite velvetgrass being a high priority species, there is little information available on control techniques. The goal of this project was to evaluate the short-term response of a single application of common chemical and manual velvetgrass control techniques. The study was conducted at three montane sites in Yosemite National Park. Glyphosate spot-spray treatments were applied at 0.5, 1.0, 1.5, and 2.0% concentrations, and compared with hand pulling to evaluate effects on cover of common velvetgrass, cover of other plant species, and community species richness. Posttreatment year 1 cover of common velvetgrass was 12.1% ± 1.6 in control plots, 6.3% ± 1.5 averaged over the four chemical treatments (all chemical treatments performed similarly), and 13.6% ± 1.7 for handpulled plots. This represents an approximately 50% reduction in common velvetgrass cover in chemically- treated plots recoded posttreatment year 1 and no statistically significant reduction in hand pulled plots compared with controls. However, there was no treatment effect in posttreatment year 2, and all herbicide application rates performed similarly. In addition, there were no significant treatment effects on nontarget species or species richness. These results suggest that for this level of infestation and habitat type, (1) one year of hand pulling is not an effective control method and (2) glyphosate provides some level of control in the short-term without impact to nontarget plant species, but the effect is temporary as a single year of glyphosate treatment is ineffective over a two-year period. Nomenclature: Glyphosate; common velvetgrass, Holcus lanatus L. Management Implications: This study was designed to evaluate short-term effects of a single application of chemical and mechanical control techniques on Holcus lanatus L. (common velvetgrass) cover and nontarget plant cover and species richness. Our results showed that various glyphosate concentrations were equally effective at reducing cover of common velvetgrass, and that there were no statistically significant effects of treatments on nontarget cover and species richness. A one-time spot spray application was effective at reducing common velvetgrass in the post-treatment year 1, but not longer. These spot-spray herbicide treatments, even at the highest concentrations, did not have detrimental effects on nontarget species. This is particularly important where land management objectives are not just to control invasive plant infestations but also to support native species, special status plants, or traditionally used plants (i.e., plants species that are important in ongoing American Indian traditional cultural practices such as those involving ceremony, subsistence and artistry). Despite the lack of herbicide impacts to nontarget species at any of the concentrations evaluated, the lowest concentration (0.5%) would be recommended because higher concentrations were no more effective at controlling velvetgrass. Despite the statistically significant reduction in common velvetgrass cover during posttreatment year 1, 6.3% common velvetgrass cover still remained, and the reduced cover effect was gone by posttreatment year 2. This study suggests that glyphosate treatments could be an option to control common velvetgrass, but one application will not maintain control after the first year. In order to gain long-term control, managers could experiment with glyphosate treatments repeated annually or even multiple times per year to control infestations. Hand pulling common velvetgrass at these densities for only one year was ineffective at controlling common velvetgrass. Moreover, studies have suggested that repeated hand pulling of velvetgrass and the associated soil disturbance could promote local increases in non-native species.