Anthony J. Krzysik

Effects of drought on desert tortoise movement and activity

We monitored movement and activity patterns of 38 desert tortoises (Gopherus agassizii) at 2 locations in the southcentral Mojave Desert during 2 consecutive years differing markedly in winter rainfall. During the first year, winter precipitation was 225% greater than the long-term average for this region, whereas a drought the following year resulted in precipitation that was 25% of the long-term average. These winter rains produced 2 distinct patterns of annual plant productivity: a bloom of annuals the first year, followed by their complete absence the second year. As measured by radiotelemetry, home range size, the number of different burrows used, average distances traveled per day, and levels of surface versus burrow activity were significantly reduced in both populations during the drought year. The pooled distribution of between-observation distances traveled showed a shift favoring shorter-distance movements during the drought year. Differences in levels of winter precipitation between years and the resulting variation of winter annual biomass in the spring appear to play a significant role in desert tortoise movement and activity patterns. Future management and conservation plans for the desert tortoise should consider weather and productivity as important factors influencing annual home range size, number of burrows used, average distances traveled, and activity levels.

Developmental instability in Rhus copallinum L.: Multiple stressors, years, and responses

Developmental instability, as assessed by leaf fluctuating asymmetry and stem internode allometry, was examined at nine sites, representing three levels of disturbance, over multiple years. Site selection was based on land‐use disturbance classes related to training of mechanized infantry and other land management activities at Fort Benning, Georgia. Developmental instability varied among sites and years, and there was a strong site‐by‐year interaction for many traits. Indeed, depending on the year, the same site could be ranked as having the greatest and least amount of leaf fluctuating asymmetry. Burning a site the year prior to collecting the leaves profoundly influenced measures of leaf fluctuating asymmetry. In the absence of recent burning, leaf fluctuating asymmetry declined with increasing disturbance, but burning the year prior to collecting the leaves reversed this trend. Total plant cover, proportion of bare ground, and amount of plant litter influenced the amount of leaf asymmetry in a site‐dependent manner. Overall, burning influenced the levels of developmental instability more than either disturbance or microhabitat variables such as total plant cover, which should reflect competition in a plant’s immediate neighborhood.

Ant Community Composition Across a Gradient of Disturbed Military Landscapes at Fort Benning, Georgia

Abstract Military training, soil texture, and ground cover influence ant communities at Fort Benning, a military installation in west-central Georgia. We sampled 81,237 ground-dwelling ants (47 species in 20 genera) with pitfall traps at 40 sites on a continuum from nearly pristine forest to highly disturbed training areas. We also measured 15 environmental variables related to vegetation and soil. Sites disturbed by military training had fewer trees, less canopy cover, more bare ground, and more compact soils with shallower A-horizons than comparable undisturbed sites. Pheidole bicarinata, Dorymyrmex smithi, and Pogonomyrmex badius dominated the most highly disturbed sites. Competitively submissive myrmicines, such as Aphaenogaster and Crematogaster, and formicines, such as Camponotus and Formica, were abundant in the undisturbed sites. Solenopsis invicta occurred in all but the least disturbed sites. Ant community composition was a useful indicator of disturbance at Fort Benning.

Photosynthesis and Fluctuating Asymmetry as Indicators of Plant Response to Soil Disturbance in the Fall‐Line Sandhills of Georgia: A Case Study Using Rhus copallinum and Ipomoea pandurata

We examined net photosynthesis, transpiration, stomatal conductance, and leaf fluctuating asymmetry on two species (Rhus copallinum and Ipomoea pandurata) as indicators of stress at nine sites across a gradient of soil disturbance at Fort Benning, Georgia. There were three sites for each of three disturbance levels. Physical habitat disturbance was caused by activities associated with infantry training, including mechanized elements (tanks and personnel carriers) and foot soldiers. In addition, we examined the influence of prescribed burns and microhabitat effects (within meter‐square quadrats centered about the plant) on these measures of plant stress. Net photosynthesis declined with increasing disturbance in the absence of burning for both species. However, when sites were burned the previous year, net photosynthesis increased with increasing disturbance. Developmental instability in Rhus, as measured by fluctuating asymmetry, also declined with increasing disturbance in the absence of burning but increased with disturbance if sites were burned the previous year. Developmental instability was much less sensitive to burning in Ipomoea and in general was lowest at intermediate disturbance sites. Microenvironmental and microhabitat effects were weakly correlated with measures of plant stress when all sites were combined. However, higher correlations were obtained within site categories, especially when the recent history of prescribed burning was used as a category. Finally, using all of the combined data in a discriminant function analysis allowed us to correctly predict the disturbance level of more than 80% of the plants. Plant stress is responsive to both large‐scale perturbations, such as burning, and microhabitat parameters. Because of this, it is important to include macro‐ and microhabitat parameters when assessing stress. Similarly, we found a combination of developmental and physiological indicators of stress was superior to using them separately.