Tad C. Theimer

ECTOMYCORRHIZAL FUNGAL COMMUNITY STRUCTURE OF PINYON PINES GROWING IN TWO ENVIRONMENTAL EXTREMES

We used molecular techniques to examine the ectomycorrhizal fungal com- munity associated with pinyon pine (Pinus edulis) growing in two soil types in a semiarid region of northern Arizona: cinder soils low in nutrients and moisture, and sandy-loam soils with higher moisture and nutrient levels. Pinyon performance (e.g., growth, repro- duction, water stress) has been shown to be markedly lower in cinder than in sandy-loam environments. Fungal community composition and richness were determined using RFLP (restriction fragment length polymorphism) analysis of ectomycorrhizal root tips collected from three sites within each soil type. Several patterns emerged from these analyses. First, communities in both cinder and sandy-loam soils were dominated by one or a few abundant ectomycorrhizal types, a species abundance pattern common to many plant and animal communities. Second, unlike the pattern for many other organisms, ectomycorrhizal fungal type (species) richness was not correlated with measures of ecosystem productivity such as soil nutrient and moisture levels; cinder and sandy-loam soils had similar numbers of ectomycorrhizal fungal types (range of 15-19 fungal types for both soil types). Third, soil type and fungal community com- position were linked, as cluster analysis demonstrated greater similarity of fungal com- munities from sites within soil types than between them. Differential amplification using primers with enhanced specificity for basidiomycetes indicated that an average of 85% of the ectomycorrhiza found at the sandy-loam sites were members of the subphylum Basid- iomycotina, whereas over half (mean 5 52%) of the ectomycorrhiza at the cinder sites were formed by members of other fungal groups, probably the subphylum Ascomycotina. Fourth, a preliminary survey of 14-45 ectomycorrhizal root tips from each of 20 trees at one cinder site indicated that trees were dominated by one or a few ectomycorrhizal RFLP types. However, the same RFLP types did not dominate on all trees, and dominant types showed considerable spatial variation. Fifth, the RFLP patterns of some fungal sporocarps matched those of ectomycorrhizal root tips, but many did not, indicating that many of the ectomycorrhizal fungi at these sites fruit infrequently, whereas other fungi with more abun- dant sporocarps may not form ectomycorrhiza. This emphasizes the need to characterize the ectomycorrhizal communities formed on the plant roots themselves, rather than char- acterization based on sporocarps alone, particularly in arid environments. Finally, the dif- ferences in ectomycorrhizal fungal communities we observed between soil types supported the concept that conserving fungal diversity requires conservation of host plant species over their entire range, not just typical sites. If future studies corroborate these patterns, our results suggest that abiotically stressful environments are important to include in these conservation efforts.

Traffic Volume Alters Elk Distribution and Highway Crossings in Arizona

Abstract We used 38,709 fixes collected from December 2003 through June 2006 from 44 elk (Cervus elaphus) fitted with Global Positioning System collars and hourly traffic data recorded along 27 km of highway in central Arizona, USA, to determine how traffic volume affected elk distribution and highway crossings. The probability of elk occurring near the highway decreased with increasing traffic volume, indicating that elk used habitat near the highway primarily when traffic volumes were low (<100 vehicles/hr). We used multiple logistic regression followed by model selection using Akaikes Information Criterion to identify factors influencing probability of elk crossings. We found that increasing traffic rates reduced the overall probability of highway crossing, but this effect depended on both season and the proximity of riparian meadow habitat. Elk crossed highways at higher traffic volumes when accessing high quality foraging areas. Our results indicate that 1) managers assessing habitat quality for elk in areas with high traffic-volume highways should consider that habitat near highways may be utilized at low traffic volumes, 2) in areas where highways potentially act as barriers to elk movement, increasing traffic volume decreases the probability of highway crossings, but the magnitude of this effect depends on both season and proximity of important resources, and 3) because some highway crossings still occurred at the high traffic volumes we recorded, increasing traffic alone will not prevent elk–vehicle collisions. Managers concerned with elk–vehicle collisions could increase the effectiveness of wildlife crossing structures by placing them near important resources, such as riparian meadow habitat.

Seed scatterhoarding by white-tailed rats: Consequences for seedling recruitment by an Australian rain forest tree

The role of white-tailed rats (Uromys caudimaculatus) as dispersers of seeds of the Australian tropical rain forest tree Beilschmiedia bancrof ii, (Lauraceae) was investigated by following the fates of seeds and seedlings over 2 y. Fruits of this tree are too large to be consumed by any avian frugivore except the southern cassowary (Casuarius casuarius), and the only other native mammal capable of dis- persing the seeds is the musky rat kangaroo (Hypsiprimnodon moschatus). However, neither of these species has been documented to disperse the seeds of this tree. During a mast year, white-tailed rats cached seeds an average of 13 m from parent trees in a variety of microsites. Although none of the 61 cached seeds followed in this study survived to germination, comparison of seed, cache and seedling distri- butions suggested that most seedlings arose from rat-cached seeds. White-tailed rats cached seeds in both mast and non-mast years, but the time seeds remained on the forest floor and in caches was significantly shorter in non-mast years, sug- gesting that synchronous seed production increases the probability that some caches survive to germination. Because white-tailed rats are the most common and widespread native mammal capable of dispersing large-seeds, this study sug- gests that they may play an important role in the seed and seedling dynamics of large-seeded tree species in Australian tropical rain forests.

Genetic variation across the historical range of the wild turkey (Meleagris gallopavo).

Genetic differences within and among naturally occurring populations of wild turkeys (Meleagris gallopavo) were characterized across five subspecies’ historical ranges using amplified fragment length polymorphism (AFLP) analysis, microsatellite loci and mitochondrial control region sequencing. Current subspecific designations based on morphological traits were generally supported by these analyses, with the exception of the eastern (M. g. silvestris) and Florida (M. g. osceola) subspecies, which consistently formed a single unit. The Gould’s subspecies was both the most genetically divergent and the least genetically diverse of the subspecies. These genetic patterns were consistent with current and historical patterns of habitat continuity. Merriam’s populations showed a positive association between genetic and geographical distance, Rio Grande populations showed a weaker association and the eastern populations showed none, suggesting differing demographic forces at work in these subspecies. We recommend managing turkeys to maintain subspecies integrity, while recognizing the importance of maintaining regional population structure that may reflect important adaptive variation.

SPATIAL AND TEMPORAL MIGRATION PATTERNS OF WILSON’S WARBLER (WILSONIA PUSILLA) IN THE SOUTHWEST AS REVEALED BY STABLE ISOTOPES

Abstract We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson’s Warbler (Wilsonia pusilla) migrating through five sites spanning a cross-section of the species’ southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial patterns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all five migration sites, we found a significant negative relationship between the date Wilson’s Warblers passed through the sampling station and δD values of their feathers. These data were consistent with a pattern of “leap-frog” migration, in which individuals that bred the previous season at southern latitudes migrated through migration stations earlier than individuals that had previously bred at more northern latitudes. We documented that this pattern was consistent across sites and in multiple years. This finding corroborates previous research conducted on Wilson’s Warbler during the fall migration. In addition, mean δD values became more negative across sampling stations from west to east, with the mean δD values at each station corresponding to different geographic regions of the Wilson’s Warblers’ western breeding range. These data indicate that Wilson’s Warblers passing through each station represented a specific regional subset of the entire Wilson’s Warbler western breeding range. As a result, habitat alterations at specific areas across the east-west expanse of the bird’s migratory route in the southwestern United States could differentially affect Wilson’s Warblers at different breeding areas. This migration information is critical for management of Neotropical migrants, especially in light of the rapid changes presently occurring over the southwestern landscape. Patrones Espaciales y Temporales de la Migración de Wilsonia pusilla en el Sudoeste Detectados Mediante Isótopos Estables

Functional and numerical responses of predators: where do vipers fit in the traditional paradigms?

Snakes typically are not considered top carnivores, yet in many ecosystems they are a major predatory influence. A literature search confirmed that terrestrial ectotherms such as snakes are largely absent in most discussions of predator‐prey dynamics. Here, we review classical functional and numerical responses of predator‐prey relationships and then assess whether these traditional views are consistent with what we know of one group of snakes (true vipers and pitvipers: Viperidae). Specifically, we compare behavioural and physiological characteristics of vipers with those of more commonly studied mammalian (endothermic) predators and discuss how functional and numerical responses of vipers are fundamentally different. Overall, when compared to similar‐sized endotherms, our analysis showed that vipers have: (i) lower functional responses owing primarily to longer prey handling times resulting from digestive limitations of consuming large prey and, for some adults, tolerance of fasting; (ii) stronger numerical responses resulting from higher efficiency of converting food into fitness currency (progeny), although this response often takes longer to be expressed; and (iii) reduced capacity for rapid numerical responses to short‐term changes in prey abundance. Given these factors, the potential for viperids to regulate prey populations would most likely occur when prey populations are low. We provide suggestions for future research on key issues in predator‐prey relationships of vipers, including their position within the classical paradigms of functional and numerical responses.

Hairy woodpecker winter ecology in ponderosa pine forests representing different ages since wildfire

Abstract We investigated how changes in vegetation structure and prey resources following wildfire affected the winter ecology of hairy woodpeckers (Picoides villosus) in ponderosa pine (Pinus ponderosa) forests of northern Arizona, USA. Using point-counts, radiotelemetry, and focal bird observation, we assessed the relative abundance, home range size and composition, and habitat use by foraging hairy woodpeckers in 3 stands that had experienced wildfire in 1996, 2000, or 2002. Because we conducted the study over 2 years, we used the 1996 fire to represent 6 and 7 years after fire, while we used the 2000 fire to represent 2 and 3 years after fire in a space-for-time substitution chronosequence analysis. We also assessed bark beetle and woodborer density by x-raying bark samples collected from a subset of trees within burned areas. We detected significantly greater hairy woodpecker relative abundance in burned forests representing 1 and 2 years after fire, and bark beetle and woodborer density was highest in these stands as well. Woodpecker home range size increased across stands representing increasing time since fire. Within a burn, hairy woodpeckers used high-severity burned areas more than moderate-severity burned areas representing 2 and 3 years after fire, but not in areas representing 6 and 7 years after fire. Bark beetle and woodborer densities were also higher in high-severity burned stands representing 2 and 3 years after fire. Hairy woodpeckers used edges of high-severity burned areas more than the interior. We hypothesize that an initial increase in bark beetle and woodborer density following fire allowed for higher woodpecker abundance and smaller home ranges, but as burned forests aged, bark beetle and woodborer density within trees decreased, killed trees fell, and, in response, hairy woodpecker relative abundance decreased and home range size increased. These patterns suggest that high-severity burned areas provide important but ephemeral resources to this dominant primary cavity-nester. The higher bark beetle and woodborer densities and greater use of edges of high-severity burned areas by woodpeckers suggests that salvage logging of these areas could remove potential prey and preferred foraging areas for hairy woodpeckers, especially when trees are removed along severely burned edges.

Intraspecific variation in seed size affects scatterhoarding behaviour of an Australian tropical rain-forest rodent

Vertebrate seed dispersers could impact the evolution of seed size or alter the pattern of seedling recruitment if they responded differently to seeds of varying size (Jordano 1995). For example, models of seed caching by birds and mammals predict that seeds of higher nutritive value should be placed farther from parent trees and in lower densities than lower quality seeds (Clarkson et al. 1986, Stapanian & Smith 1978, Tamura et al. 1999). Comparisons of seed removal rates among tropical tree species in South-East Asia (Blate et al. 1998) and Australia (Osunkoya 1994) failed to show a relationship between seed size and removal rate, although the probability that a seed was scatterhoarded by agoutis (Dasyprocta punctata) in a neotropical rain forest increased with interspecific seed size (Forget et al. 1998). However, interspecific comparisons are often confounded by differences among species in seed characteristics other than size. Studies of intraspecific seed size variation have shown that both red acouchis (Myoprocta acouchy) (Jansen et al. 2002) and agoutis (Hallwachs 1994) cache larger seeds more often than smaller seeds, and transport larger seeds greater distances. Spiny pocket mice (Heteromys desmarestianus) also preferentially removed larger Astrocaryum mexicanum (Palmae) seeds over smaller ones, but smaller seeds were buried farther from the seed source (Brewer 2001). These studies suggest that differences in seed size could affect which seeds are ulti-

Tamarisk biocontrol using tamarisk beetles: Potential consequences for riparian birds in the southwestern United States

Abstract. The tamarisk beetle (Diorhabda spp.), a non-native biocontrol agent, has been introduced to eradicate tamarisk (Tamarix spp.), a genus of non-native tree that has become a dominant component of riparian woodlands in the southwestern United States. Tamarisk beetles have the potential to spread widely and defoliate large expanses of tamarisk habitat, but the effects of such a widespread loss of riparian vegetation on birds remains unknown. We reviewed literature on the effects of other defoliating insects on birds to investigate the potential for tamarisk beetles to affect birds positively or negatively by changing food abundance and vegetation structure. We then combined data on the temporal patterns of tamarisk defoliation by beetles with nest productivity of a well-studied riparian obligate, the Southwestern Willow Flycatcher (Empidonax traillii extimus), to simulate the potential demographic consequences of beetle defoliation on breeding riparian birds in both the short and long term. Our results highlight that the effects of tamarisk biocontrol on birds will likely vary by species and population, depending upon its sensitivity to seasonal defoliation by beetles and net loss of riparian habitat due to tamarisk mortality. Species with restricted distributions that include areas dominated by tamarisk may be negatively affected both in the short and long term. The rate of regeneration and/or restoration of native cottonwoods (Populus spp.) and willows (Salix spp.) relative to the rate of tamarisk loss will be critical in determining the long-term effect of this large-scale ecological experiment.

Effects of Traffic on Elk Use of Wildlife Underpasses in Arizona

Abstract We used video surveillance at 4 wildlife underpasses along 27 km of Arizona State Route 260, USA, to monitor elk (Cervus elaphus) responses to traffic volume and traffic type during underpass use. Passage rates at the highest traffic category (>10–27 vehicles/min) were not lower than passage rates when no vehicles were present, whereas passage rates at low, intermittent traffic volume (>0–1 vehicles/min) were 15% lower. Once elk entered an underpass, semi-trailer trucks were 4 times more likely than passenger vehicles to cause flight behavior when traffic levels were intermittent versus when traffic was continuous. Overall, traffic volumes of >10–27 vehicles per minute did not decrease the effectiveness of wildlife underpasses as a means of mitigating elk population subdivision. However, if flight away from underpasses at intermediate traffic levels causes elk to cross the highway at other points and thereby increases the potential for costly elk–vehicle collisions, we recommend that managers consider measures to reduce traffic noise and visual stimuli, especially those caused by semi-trailer trucks.