No abstract

Human activities are increasing the size, frequency, and severity of disturbance across earth's ecosystems including deserts. Ants are important drivers of ecosystem function and are good bioindicators of ecosystem sensitivity to disturbance and change. Rodents also play an important role in ecosystem response to disturbance and often compete with ants for resources. The purpose of our study was to test the main and interactive effects of fire, rodent activity, and time on ant forager abundance, species richness, and diversity, as well as changes in ant mound density and disk area in the Great Basin Desert. We experimentally applied burn and rodent exclusion treatments and used pitfall traps to collect ants each month from April through October from 2014 to 2016. Over the three‐year period, burned areas had lower richness and diversity than unburned areas. Rodent exclusion had minimal effects on the ant community, and there was not a significant rodent exclusion interaction with fire. Treatment effects varied by month and year. The western harvester ant, Pogonomyrmex occidentalis, was the most abundant ant species, comprising about 70% of the total ants captured. Shifts in ant diversity following fire were driven by positive responses of harvester ants to burned habitat conditions. In contrast, all other ant species when analyzed together had lower forager abundance in burned plots, which drove lower ant diversity in burned plots. Ant forager abundance, richness, and diversity increased each year of the study in all plots; however, richness and diversity remained lower in burned areas than in unburned areas each year. Structural equation modeling shows that the effects of fire on ant community diversity are partially mediated through the plant community. While rodents affected the plant community, those effects do not seem to transfer over to the ant community. Pogonomyrmex occidentalis mound density was higher in burned areas, but disk area was smaller. Our results suggest that fire has adverse effects on ant community diversity. This could have long‐lasting effects on ecosystem function in the face of a changing fire regime in deserts of North America caused by invasive annual plants.

Recent increases in the frequency and size of desert wildfires bring into question the impacts of fire on desert invertebrate communities. Furthermore, consumer communities can strongly impact invertebrates through predation and top‐down effects on plant community assembly. We experimentally applied burn and rodent exclusion treatments in a full factorial design at sites in both the Mojave and Great Basin deserts to examine the impact that fire and rodent consumers have on invertebrate communities. Pitfall traps were used to survey invertebrates from April through September 2016 to determine changes in abundance, richness, and diversity of invertebrate communities in response to fire and rodent treatments. Generally speaking, rodent exclusion had very little effect on invertebrate abundance or ant abundance, richness or diversity. The one exception was ant abundance, which was higher in rodent access plots than in rodent exclusion plots in June 2016, but only at the Great Basin site. Fire had little effect on the abundances of invertebrate groups at either desert site, with the exception of a negative effect on flying‐forager abundance at our Great Basin site. However, fire reduced ant species richness and Shannon's diversity at both desert sites. Fire did appear to indirectly affect ant community composition by altering plant community composition. Structural equation models suggest that fire increased invasive plant cover, which negatively impacted ant species richness and Shannon's diversity, a pattern that was consistent at both desert sites. These results suggest that invertebrate communities demonstrate some resilience to fire and invasions but increasing fire and spread of invasive due to invasive grass fire cycles may put increasing pressure on the stability of invertebrate communities.

The reconstruction of twist torque in the Main Parachute Risers of the Capsule Parachute Assembly System (CPAS) has been successfully used to validate CPAS Model Memo conservative twist torque equations. Reconstruction of basic, one degree of freedom drop tests was used to create a functional process for the evaluation of more complex, rigid body simulation. The roll, pitch, and yaw of the body, the fly-out angles of the parachutes, and the relative location of the parachutes to the body are inputs to the torque simulation. The data collected by the Inertial Measurement Unit (IMU) was used to calculate the true torque. The simulation then used photogrammetric and IMU data as inputs into the Model Memo equations. The results were then compared to the true torque results to validate the Model Memo equations. The Model Memo parameters were based off of steel risers and the parameters will need to be re-evaluated for different materials. Photogrammetric data was found to be more accurate than the inertial data in accounting for the relative rotation between payload and cluster. The Model Memo equations were generally a good match and when not matching were generally conservative. Nomenclature BET