Tad Theimer - Academia.edu (original) (raw)

Papers by Tad Theimer

Research paper thumbnail of Extreme drought alters frequency and reproductive success of floaters in Willow Flycatchers

The Auk, 2018

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Increased Visitation at Urban Water Sources by Bats and Raccoons: Implications for Cross-species Transmission of Rabies

We examined the potential for urban water sources to act as centers for rabies transmission from ... more We examined the potential for urban water sources to act as centers for rabies transmission from bats to mesocarnivores in the arid southwestern United States where free water is often limited. Because residential housing can act as den and roost sites for both mesocarnivores and bats, we also examined the effect of housing density on abundance. Using ultrasonic acoustic recorders to assess bat activity and camera traps to estimate mesocarnivore abundance, we compared 14 pairs of wet and dry locations over two years by surveying twice during the summer, once prior to summer monsoons and once during the monsoon season, when surface waters were more available. Number of calls for all bat species combined were greater at wet sites compared to dry sites and calls of two bat species often associated with rabies, big brown bat (Eptesicus fuscus) and silver-haired bat (Lasionycteris noctivagans), were recorded more at wet sites than dry sites in the monsoon season. In both years, raccoons ...

Research paper thumbnail of Managing an outbreak of bat rabies in terrestrial wildlife in Flagstaff, Arizona: Past, Present, and Future

Research paper thumbnail of A Preliminary Field Trial of Bait Stations for the Delivery of Oral Rabies Vaccine: Can Varying Diameter Exclude Non-Target Species?

Proceedings of the Vertebrate Pest Conference, 2006

Research paper thumbnail of Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores

Journal of wildlife diseases, Apr 17, 2017

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the ... more Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks ( Mephitis mephitis ). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore specie...

Research paper thumbnail of Temporal variation in the arthropod community of desert riparian habitats with varying amounts of saltcedar (Tamarix ramosissima)

Journal of Arid Environments, 2008

ABSTRACT We used Malaise traps to examine the aerial arthropod community in riparian habitats dom... more ABSTRACT We used Malaise traps to examine the aerial arthropod community in riparian habitats dominated by native willow, exotic saltcedar, or a mixture of these two tree species in central Arizona, USA. Over the course of three sampling periods per year in 2003 and 2004, native habitats had significantly greater diversity (Shannon–Wiener) and supported different arthropod communities compared to exotic habitats, while mixed habitats were intermediate in terms of diversity and supported an arthropod community statistically indistinguishable from the exotic site. The composition of arthropod communities varied significantly between the two years, and there was an approximately two-fold difference in richness and diversity. Overall, we documented complex interactions indicating that differences among the arthropod communities of riparian habitats may be driven not only by the composition of native and exotic tree species making up these habitats, but also by year and season of arthropod sampling.

Research paper thumbnail of Terrestrial vertebrates promote arbuscular mycorrhizal fungal diversity and inoculum potential in a rain forest soil

Ecology Letters, 2002

We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore comm... more We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore communities and mycorrhizal inoculum potential (MIP) of a tropical rain forest soil by comparing plots where terrestrial vertebrates had been excluded for 3 years to adjacent control plots. We extracted spores from soil using sucrose density gradient centrifugation and assayed MIP by growing seedlings of maize (Zea mays) and a rain forest tree (Flindersia brayleana) in intact soil cores from exclosure and control plots. Control plots had significantly higher spore abundance, species richness and diversity than exclosures. Spore community composition also differed significantly between exclosure and control plots. Seedlings of both plant species grown in control cores had significantly higher arbuscular-mycorrhizal colonization than those grown in exclosure cores. This study suggests that loss of vertebrates could alter rates of mycorrhizal colonization with consequences for community and ecosystem properties.

Research paper thumbnail of Ectomycorrhizal Fungal Community Structure of Pinyon Pines Growing in Two Environmental Extremes

Ecology, 1998

We used molecular techniques to examine the ectomycorrhizal fungal community associated with piny... more We used molecular techniques to examine the ectomycorrhizal fungal community 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, reproduction, 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 composition were linked, as cluster analysis demonstrated greater similarity of fungal communities 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 Basidiomycotina, whereas over half (mean ϭ 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 abundant sporocarps may not form ectomycorrhiza. This emphasizes the need to characterize the ectomycorrhizal communities formed on the plant roots themselves, rather than characterization based on sporocarps alone, particularly in arid environments. Finally, the differences 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.

Research paper thumbnail of Terrestrial vertebrates alter seedling composition and richness but not diversity in an Australian tropical rain forest

Ecology, 2011

Although birds and mammals play important roles in several mechanisms hypothesized to maintain pl... more Although birds and mammals play important roles in several mechanisms hypothesized to maintain plant diversity in species-rich habitats, there have been few long-term, community-level tests of their importance. We excluded terrestrial birds and mammals from fourteen 6 x 7.5 m plots in Australian primary tropical rain forest and compared recruitment and survival of tree seedlings annually over the subsequent seven years to that on nearby open plots. We re-censused a subset of the plots after 13 years of vertebrate exclusion to test for longer-term effects. After two years of exclusion, seedling abundance was significantly higher (74%) on exclosure plots and remained so at each subsequent census. Richness was significantly higher on exclosure plots from 1998 to 2003, but in 2009 richness no longer differed, and rarefied species richness was higher in the presence of vertebrates. Shannon's diversity and Pielou's evenness did not differ in any year. Vertebrates marginally increased density-dependent mortality and recruitment limitation, but neither effect was great enough to increase richness or diversity on open plots relative to exclosure plots. Terrestrial vertebrates significantly altered seedling community composition, having particularly strong impacts on members of the Lauraceae. Overall, our results highlight that interactions between terrestrial vertebrates and tropical tree recruitment may not translate into strong community-level effects on diversity, especially over the short-term, despite significant impacts on individual species that result in altered species composition.

Research paper thumbnail of Polygyny and Extra-Pair Paternity in a Population of Southwestern Willow Flycatchers

The Condor, 2006

Although polygyny can potentially increase male reproductive success, the benefits of this strate... more Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extrapair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 6 0.35 offspring per season, compared to 1.15 6 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extrapair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.

Research paper thumbnail of Age, Habitat, and Yearly Variation in the Diet of a Generalist Insectivore, the Southwestern Willow Flycatcher

Research paper thumbnail of Tamarisk Biocontrol Using Tamarisk Beetles: Potential Consequences For Riparian Birds in the Southwestern United States

The Condor, 2011

... in article. Dennison, P., P. Nagler, K. Hultine, E. Glenn, and J. Ehleringer. 2009. Remote mo... more ... in article. Dennison, P., P. Nagler, K. Hultine, E. Glenn, and J. Ehleringer. 2009. Remote monitoring of tamarisk defoliation and evapotranspiration following salt cedar leaf beetle attack. Remote Sensing of Environment 113:1462–1472. ... Drost, CA, EH Paxton, MK Sogge, and MJ ...

Research paper thumbnail of Population biology of White-crowned Sparrows: Residence time and local movements of juveniles

Behavioral Ecology and Sociobiology, 1982

A field study of the ranging behavior of post-fledging White-crowned Sparrows (Zonotrichia leucop... more A field study of the ranging behavior of post-fledging White-crowned Sparrows (Zonotrichia leucophrys nuttalli) was carried out in undisturbed natural habitat in the Point Reyes National Seashore, Marin Co., California, USA. Forty-three first-brood juveniles, with tail feathers still growing, were banded at an estimated average age of 27 days and re-trapped an average of an additional 24 days for a total minimum time in residence in the immediate natal area of 51 days (Table 1). The distance from the site of first capture to subsequent recapture sites was about 60 m until age 35 days; then the distance increased to about 250 m by age 50 days (Fig. 2). These data indicate that the average juvenile White-crowned Sparrow completes at least the first 50 days of life in its natal area. Experimental work on song ontogeny has previously demonstrated that the sensitive period for song learning ends at about 50 days. Hence, young in our study population probably learn their natal dialect prior to any major dispersal movements. The correspondence between residence time and song learning would have the consequence of perpetuating song dialects as geographically structured populations.

Research paper thumbnail of Spatial and Temporal Migration Patterns of Wilson’s Warbler (Wilsonia Pusilla) in the Southwest as Revealed by Stable Isotopes

The Auk, 2007

AяѠѡџюѐѡ.-We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson's Wa... more AяѠѡџюѐѡ.-We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson's Warbler (Wilsonia pusilla) migrating through fi ve sites spanning a cross-section of the species' southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial paĴ erns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all fi ve migration sites, we found a signifi cant 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 paĴ ern 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 paĴ ern was consistent across sites and in multiple years. This fi nding 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 diff erent geographic regions of the Wilson's Warblers' western breeding range. These data indicate that Wilson's Warblers passing through each station represented a specifi c regional subset of the entire Wilson's Warbler western breeding range. As a result, habitat alterations at specifi c areas across the east-west expanse of the bird's migratory route in the southwestern United States could diff erentially aff ect Wilson's Warblers at diff erent 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.

Research paper thumbnail of Does dominance determine how far dark-eyed juncos, Junco hyemalis, migrate into their winter range?

Animal Behaviour, 1989

The behavioural dominance hypothesis suggests that differential migration among individuals of a ... more The behavioural dominance hypothesis suggests that differential migration among individuals of a species of bird is due solely to social interactions that force subordinate individuals (often a class, e.g. female or young birds) to migrate farther into the winter range than dominant individuals (often a class, e.g. male or old birds). Here, this hypothesis was tested with two experiments. In the first experiment, the prediction was tested that dominance acts within a sex-age class and influences migration distance. The outcomes of interactions within dyads of dark-eyed juncos, Junco hyemalis, were observed. Each dyad consisted of a junco caught in winter in Michigan matched with another of the same sex-age class caught in Indiana, which is situated farther south and therefore farther into the winter range of this species. Michigan birds were dominant in only half of the experimental dyads (21 of 41 dyads), which is inconsistent with the prediction of the dominance model. In the second experiment the prediction was tested that members of a sex-age class that migrates farther into the winter range should be subordinate to members of a different class that migrates a shorter distance. Young males that wintered in Michigan were pitted against old males that wintered in Indiana. In 19 of 25 dyads, the more southern-wintering old males were dominant, which also is counter to the prediction of the dominance hypothesis. These results indicate, at the very least, that in migratory J. h. hyemalis, dominance does not play as important a role in determining latitude of winter residence as has been suggested.

Research paper thumbnail of The effect of seed dispersion on the foraging success of dominant and subordinate dark-eyed juncos, Junco hyemalis

Animal Behaviour, 1987

Laboratory experiments were conducted to determine the effect of seed dispersion on the rate of s... more Laboratory experiments were conducted to determine the effect of seed dispersion on the rate of seed consumption by dark-eyed juncos, Junco hyemalis, feeding in dyads and in triads. In the dyad experiments, dominants consumed significantly more seeds than subordinates when seeds were clumped in a patch of 0.09 m 2, but subordinates obtained as many seeds as dominants when food was dispersed in a larger 1-44-m 2 patch. In the triad experiments, there was a significant difference in seed consumption between dominants, intermediates and subordinates when food was dispersed in patches of 0.09 m 2 and 1.44 m 2, but there was no significant difference between ranks when it was dispersed in a larger 2-88-m 2 patch. Dominants had significantly more agonistic interactions with intermediates than with subordinates. This was not related to differences in distances maintained between birds. Dispersion of seeds in the environment can have a marked effect on whether dominants realize an immediate foraging advantage over subordinates.

Research paper thumbnail of Increased Lesser Earless Lizard (Holbrookia maculata) Abundance on Gunnison's Prairie Dog Colonies and Short Term Responses to Artificial Prairie Dog Burrows

The American Midland Naturalist, 2003

Research paper thumbnail of Striped Skunk Relative Abundance in Flagstaff, Arizona: Implications for Rabies Spread and the Current TVR Program

Proceedings of the 25th Vertebrate Pest Conference, 2012

Potentially fatal wildlife diseases like rabies are of increasing concern, due to human effects o... more Potentially fatal wildlife diseases like rabies are of increasing concern, due to human effects on the environment that could alter wildlife behavior and population dynamics in ways that increase disease prevalence. Wildlife population abundance is a key factor, affecting both disease outbreak and rate of disease spread, and understanding how population abundance changes across landscapes is crucial for developing predictive models to control and manage wildlife diseases. We investigated how urbanization in Flagstaff, AZ influenced skunk population abundance by simultaneously trapping 6 pairs of suburban and wildland study sites for 200 trap-nights between June and September 2011. The number of unique skunks captured at the 6 suburban locations ranged from 3-14 (mean = 6.5) while the number trapped at the 6 wildland sites ranged from 0-2 (mean = 0.5). We also reviewed data gathered as part of the trap-vaccinate-release (TVR) program carried out from 2004-2010 by USDA APHIS Wildlife ...

Research paper thumbnail of Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the ... more Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks (Mephitis mephitis). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore species ...

Research paper thumbnail of Geographic variation in the plumage coloration of willow flycatchers Empidonax traillii

The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races... more The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races) can advance ecological research efforts by determining connectivity between the non-breeding and breeding grounds for migrant species, identifying the origin of migrants, and helping to refine boundaries between subspecies or geographic races. Multiple methods are available to identify taxonomic groups (e.g., morphology, genetics), and one that has played an important role for avian taxonomists over the years is plumage coloration. With the advent of electronic devices that can quickly and accurately quantify plumage coloration, the potential of using coloration as an identifier for distinct taxonomic groups, even when differences are subtle, becomes possible. In this study, we evaluated the degree to which plumage coloration differs among the four subspecies of the willow flycatcher Empidonax traillii, evaluated sources of variation, and considered the utility of plumage coloration to assign subspecies membership for individuals of unknown origin. We used a colorimeter to measure plumage coloration of 374 adult willow flycatchers from 29 locations across their breeding range in 2004 and 2005. We found strong statistical differences among the mean plumage coloration values of the four subspecies; however, while individuals tended to group around their respective subspecies' mean color value, the dispersion of individuals around such means overlapped. Mean color values for each breeding site of the three western subspecies clustered together, but the eastern subspecies' color values were dispersed among the other subspecies, rather than distinctly clustered. Additionally, sites along boundaries showed evidence of intergradation and intermediate coloration patterns. We evaluated the predictive power of colorimeter measurements on flycatchers by constructing a canonical discriminant model to predict subspecies origin of migrants passing through the southwestern U.S. Considering only western subspecies, we found that individuals can be assigned with reasonable certainty. Applying the model to migrants sampled along the Colorado River in Mexico and the U.S. suggests different migration patterns for the three western subspecies. We believe that the use of plumage coloration, as measured by electronic devices, can provide a powerful tool to look at ecological questions in a wide range of avian species.

Research paper thumbnail of Extreme drought alters frequency and reproductive success of floaters in Willow Flycatchers

The Auk, 2018

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

Research paper thumbnail of Increased Visitation at Urban Water Sources by Bats and Raccoons: Implications for Cross-species Transmission of Rabies

We examined the potential for urban water sources to act as centers for rabies transmission from ... more We examined the potential for urban water sources to act as centers for rabies transmission from bats to mesocarnivores in the arid southwestern United States where free water is often limited. Because residential housing can act as den and roost sites for both mesocarnivores and bats, we also examined the effect of housing density on abundance. Using ultrasonic acoustic recorders to assess bat activity and camera traps to estimate mesocarnivore abundance, we compared 14 pairs of wet and dry locations over two years by surveying twice during the summer, once prior to summer monsoons and once during the monsoon season, when surface waters were more available. Number of calls for all bat species combined were greater at wet sites compared to dry sites and calls of two bat species often associated with rabies, big brown bat (Eptesicus fuscus) and silver-haired bat (Lasionycteris noctivagans), were recorded more at wet sites than dry sites in the monsoon season. In both years, raccoons ...

Research paper thumbnail of Managing an outbreak of bat rabies in terrestrial wildlife in Flagstaff, Arizona: Past, Present, and Future

Research paper thumbnail of A Preliminary Field Trial of Bait Stations for the Delivery of Oral Rabies Vaccine: Can Varying Diameter Exclude Non-Target Species?

Proceedings of the Vertebrate Pest Conference, 2006

Research paper thumbnail of Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores

Journal of wildlife diseases, Apr 17, 2017

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the ... more Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks ( Mephitis mephitis ). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore specie...

Research paper thumbnail of Temporal variation in the arthropod community of desert riparian habitats with varying amounts of saltcedar (Tamarix ramosissima)

Journal of Arid Environments, 2008

ABSTRACT We used Malaise traps to examine the aerial arthropod community in riparian habitats dom... more ABSTRACT We used Malaise traps to examine the aerial arthropod community in riparian habitats dominated by native willow, exotic saltcedar, or a mixture of these two tree species in central Arizona, USA. Over the course of three sampling periods per year in 2003 and 2004, native habitats had significantly greater diversity (Shannon–Wiener) and supported different arthropod communities compared to exotic habitats, while mixed habitats were intermediate in terms of diversity and supported an arthropod community statistically indistinguishable from the exotic site. The composition of arthropod communities varied significantly between the two years, and there was an approximately two-fold difference in richness and diversity. Overall, we documented complex interactions indicating that differences among the arthropod communities of riparian habitats may be driven not only by the composition of native and exotic tree species making up these habitats, but also by year and season of arthropod sampling.

Research paper thumbnail of Terrestrial vertebrates promote arbuscular mycorrhizal fungal diversity and inoculum potential in a rain forest soil

Ecology Letters, 2002

We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore comm... more We examined whether terrestrial vertebrates affected the arbuscular mycorrhizal fungal spore communities and mycorrhizal inoculum potential (MIP) of a tropical rain forest soil by comparing plots where terrestrial vertebrates had been excluded for 3 years to adjacent control plots. We extracted spores from soil using sucrose density gradient centrifugation and assayed MIP by growing seedlings of maize (Zea mays) and a rain forest tree (Flindersia brayleana) in intact soil cores from exclosure and control plots. Control plots had significantly higher spore abundance, species richness and diversity than exclosures. Spore community composition also differed significantly between exclosure and control plots. Seedlings of both plant species grown in control cores had significantly higher arbuscular-mycorrhizal colonization than those grown in exclosure cores. This study suggests that loss of vertebrates could alter rates of mycorrhizal colonization with consequences for community and ecosystem properties.

Research paper thumbnail of Ectomycorrhizal Fungal Community Structure of Pinyon Pines Growing in Two Environmental Extremes

Ecology, 1998

We used molecular techniques to examine the ectomycorrhizal fungal community associated with piny... more We used molecular techniques to examine the ectomycorrhizal fungal community 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, reproduction, 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 composition were linked, as cluster analysis demonstrated greater similarity of fungal communities 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 Basidiomycotina, whereas over half (mean ϭ 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 abundant sporocarps may not form ectomycorrhiza. This emphasizes the need to characterize the ectomycorrhizal communities formed on the plant roots themselves, rather than characterization based on sporocarps alone, particularly in arid environments. Finally, the differences 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.

Research paper thumbnail of Terrestrial vertebrates alter seedling composition and richness but not diversity in an Australian tropical rain forest

Ecology, 2011

Although birds and mammals play important roles in several mechanisms hypothesized to maintain pl... more Although birds and mammals play important roles in several mechanisms hypothesized to maintain plant diversity in species-rich habitats, there have been few long-term, community-level tests of their importance. We excluded terrestrial birds and mammals from fourteen 6 x 7.5 m plots in Australian primary tropical rain forest and compared recruitment and survival of tree seedlings annually over the subsequent seven years to that on nearby open plots. We re-censused a subset of the plots after 13 years of vertebrate exclusion to test for longer-term effects. After two years of exclusion, seedling abundance was significantly higher (74%) on exclosure plots and remained so at each subsequent census. Richness was significantly higher on exclosure plots from 1998 to 2003, but in 2009 richness no longer differed, and rarefied species richness was higher in the presence of vertebrates. Shannon's diversity and Pielou's evenness did not differ in any year. Vertebrates marginally increased density-dependent mortality and recruitment limitation, but neither effect was great enough to increase richness or diversity on open plots relative to exclosure plots. Terrestrial vertebrates significantly altered seedling community composition, having particularly strong impacts on members of the Lauraceae. Overall, our results highlight that interactions between terrestrial vertebrates and tropical tree recruitment may not translate into strong community-level effects on diversity, especially over the short-term, despite significant impacts on individual species that result in altered species composition.

Research paper thumbnail of Polygyny and Extra-Pair Paternity in a Population of Southwestern Willow Flycatchers

The Condor, 2006

Although polygyny can potentially increase male reproductive success, the benefits of this strate... more Although polygyny can potentially increase male reproductive success, the benefits of this strategy could be offset by losses to extra-pair paternity or reduced offspring survival. We developed microsatellite markers to assess the influence of extrapair offspring (EPO) on reproductive success and paternity in monogamous and polygynous pairs of the facultatively polygynous Southwestern Willow Flycatcher (Empidonax traillii extimus). Based on genotypes of 140 offspring from 56 clutches over six years, 14% of nestlings in our study population were extra-pair offspring, with 23% of all successful nests containing at least one EPO. We found that polygynous males produced 2.11 6 0.35 offspring per season, compared to 1.15 6 0.18 for monogamous males. This increased reproductive success was due primarily to the increased number of nests of polygynous males, as the number of offspring per pair did not differ between monogamous and polygynous males. Twenty of the 140 genotyped nestlings were extrapair offspring. Sires could be assigned to 16 of these; one polygynous male sired two EPO in one nest, two monogamous males sired eight EPO in two nests, and four nonterritorial males sired six EPO in four nests. Overall, these results indicate that in this population, females of polygynous males did not raise a disproportionate number of EPO as a result of the polygynous mating strategy of their mate, and that both territorial and nonterritorial males sired EPO.

Research paper thumbnail of Age, Habitat, and Yearly Variation in the Diet of a Generalist Insectivore, the Southwestern Willow Flycatcher

Research paper thumbnail of Tamarisk Biocontrol Using Tamarisk Beetles: Potential Consequences For Riparian Birds in the Southwestern United States

The Condor, 2011

... in article. Dennison, P., P. Nagler, K. Hultine, E. Glenn, and J. Ehleringer. 2009. Remote mo... more ... in article. Dennison, P., P. Nagler, K. Hultine, E. Glenn, and J. Ehleringer. 2009. Remote monitoring of tamarisk defoliation and evapotranspiration following salt cedar leaf beetle attack. Remote Sensing of Environment 113:1462–1472. ... Drost, CA, EH Paxton, MK Sogge, and MJ ...

Research paper thumbnail of Population biology of White-crowned Sparrows: Residence time and local movements of juveniles

Behavioral Ecology and Sociobiology, 1982

A field study of the ranging behavior of post-fledging White-crowned Sparrows (Zonotrichia leucop... more A field study of the ranging behavior of post-fledging White-crowned Sparrows (Zonotrichia leucophrys nuttalli) was carried out in undisturbed natural habitat in the Point Reyes National Seashore, Marin Co., California, USA. Forty-three first-brood juveniles, with tail feathers still growing, were banded at an estimated average age of 27 days and re-trapped an average of an additional 24 days for a total minimum time in residence in the immediate natal area of 51 days (Table 1). The distance from the site of first capture to subsequent recapture sites was about 60 m until age 35 days; then the distance increased to about 250 m by age 50 days (Fig. 2). These data indicate that the average juvenile White-crowned Sparrow completes at least the first 50 days of life in its natal area. Experimental work on song ontogeny has previously demonstrated that the sensitive period for song learning ends at about 50 days. Hence, young in our study population probably learn their natal dialect prior to any major dispersal movements. The correspondence between residence time and song learning would have the consequence of perpetuating song dialects as geographically structured populations.

Research paper thumbnail of Spatial and Temporal Migration Patterns of Wilson’s Warbler (Wilsonia Pusilla) in the Southwest as Revealed by Stable Isotopes

The Auk, 2007

AяѠѡџюѐѡ.-We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson's Wa... more AяѠѡџюѐѡ.-We used stable hydrogen isotopes (δD) to identify the breeding locations of Wilson's Warbler (Wilsonia pusilla) migrating through fi ve sites spanning a cross-section of the species' southwestern migration route during the springs of 2003 and 2004. Determining the temporal and spatial paĴ erns of migration and degree of population segregation during migration is critical to understanding long-term population trends of migrant birds. At all fi ve migration sites, we found a signifi cant 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 paĴ ern 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 paĴ ern was consistent across sites and in multiple years. This fi nding 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 diff erent geographic regions of the Wilson's Warblers' western breeding range. These data indicate that Wilson's Warblers passing through each station represented a specifi c regional subset of the entire Wilson's Warbler western breeding range. As a result, habitat alterations at specifi c areas across the east-west expanse of the bird's migratory route in the southwestern United States could diff erentially aff ect Wilson's Warblers at diff erent 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.

Research paper thumbnail of Does dominance determine how far dark-eyed juncos, Junco hyemalis, migrate into their winter range?

Animal Behaviour, 1989

The behavioural dominance hypothesis suggests that differential migration among individuals of a ... more The behavioural dominance hypothesis suggests that differential migration among individuals of a species of bird is due solely to social interactions that force subordinate individuals (often a class, e.g. female or young birds) to migrate farther into the winter range than dominant individuals (often a class, e.g. male or old birds). Here, this hypothesis was tested with two experiments. In the first experiment, the prediction was tested that dominance acts within a sex-age class and influences migration distance. The outcomes of interactions within dyads of dark-eyed juncos, Junco hyemalis, were observed. Each dyad consisted of a junco caught in winter in Michigan matched with another of the same sex-age class caught in Indiana, which is situated farther south and therefore farther into the winter range of this species. Michigan birds were dominant in only half of the experimental dyads (21 of 41 dyads), which is inconsistent with the prediction of the dominance model. In the second experiment the prediction was tested that members of a sex-age class that migrates farther into the winter range should be subordinate to members of a different class that migrates a shorter distance. Young males that wintered in Michigan were pitted against old males that wintered in Indiana. In 19 of 25 dyads, the more southern-wintering old males were dominant, which also is counter to the prediction of the dominance hypothesis. These results indicate, at the very least, that in migratory J. h. hyemalis, dominance does not play as important a role in determining latitude of winter residence as has been suggested.

Research paper thumbnail of The effect of seed dispersion on the foraging success of dominant and subordinate dark-eyed juncos, Junco hyemalis

Animal Behaviour, 1987

Laboratory experiments were conducted to determine the effect of seed dispersion on the rate of s... more Laboratory experiments were conducted to determine the effect of seed dispersion on the rate of seed consumption by dark-eyed juncos, Junco hyemalis, feeding in dyads and in triads. In the dyad experiments, dominants consumed significantly more seeds than subordinates when seeds were clumped in a patch of 0.09 m 2, but subordinates obtained as many seeds as dominants when food was dispersed in a larger 1-44-m 2 patch. In the triad experiments, there was a significant difference in seed consumption between dominants, intermediates and subordinates when food was dispersed in patches of 0.09 m 2 and 1.44 m 2, but there was no significant difference between ranks when it was dispersed in a larger 2-88-m 2 patch. Dominants had significantly more agonistic interactions with intermediates than with subordinates. This was not related to differences in distances maintained between birds. Dispersion of seeds in the environment can have a marked effect on whether dominants realize an immediate foraging advantage over subordinates.

Research paper thumbnail of Increased Lesser Earless Lizard (Holbrookia maculata) Abundance on Gunnison's Prairie Dog Colonies and Short Term Responses to Artificial Prairie Dog Burrows

The American Midland Naturalist, 2003

Research paper thumbnail of Striped Skunk Relative Abundance in Flagstaff, Arizona: Implications for Rabies Spread and the Current TVR Program

Proceedings of the 25th Vertebrate Pest Conference, 2012

Potentially fatal wildlife diseases like rabies are of increasing concern, due to human effects o... more Potentially fatal wildlife diseases like rabies are of increasing concern, due to human effects on the environment that could alter wildlife behavior and population dynamics in ways that increase disease prevalence. Wildlife population abundance is a key factor, affecting both disease outbreak and rate of disease spread, and understanding how population abundance changes across landscapes is crucial for developing predictive models to control and manage wildlife diseases. We investigated how urbanization in Flagstaff, AZ influenced skunk population abundance by simultaneously trapping 6 pairs of suburban and wildland study sites for 200 trap-nights between June and September 2011. The number of unique skunks captured at the 6 suburban locations ranged from 3-14 (mean = 6.5) while the number trapped at the 6 wildland sites ranged from 0-2 (mean = 0.5). We also reviewed data gathered as part of the trap-vaccinate-release (TVR) program carried out from 2004-2010 by USDA APHIS Wildlife ...

Research paper thumbnail of Ecological Potential for Rabies Virus Transmission via Scavenging of Dead Bats by Mesocarnivores

Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the ... more Multiple species of bats are reservoirs of rabies virus in the Americas and are occasionally the source of spillover infections into mesocarnivore species. Although rabies transmission generally is assumed to occur via bite, laboratory studies have demonstrated the potential for rabies transmission via ingestion of rabid animals. We investigated the ecological potential for this mode of transmission by assessing mesocarnivore scavenging behavior of dead bats in suburban habitats of Flagstaff, Arizona. In autumn 2013, summer 2014, and autumn 2015, we placed 104 rabies-negative bat carcasses either near buildings, in wildland areas, or in residential yards and then monitored them with trail cameras for 5 d. Overall, 52 (50%) bat carcasses were scavenged, with 39 (75%) of those scavenged by striped skunks (Mephitis mephitis). Within our study area, striped skunks had a higher ecological potential to contract rabies via ingestion of bat carcasses compared to other mesocarnivore species ...

Research paper thumbnail of Geographic variation in the plumage coloration of willow flycatchers Empidonax traillii

The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races... more The ability to identify distinct taxonomic groups of birds (species, subspecies, geographic races) can advance ecological research efforts by determining connectivity between the non-breeding and breeding grounds for migrant species, identifying the origin of migrants, and helping to refine boundaries between subspecies or geographic races. Multiple methods are available to identify taxonomic groups (e.g., morphology, genetics), and one that has played an important role for avian taxonomists over the years is plumage coloration. With the advent of electronic devices that can quickly and accurately quantify plumage coloration, the potential of using coloration as an identifier for distinct taxonomic groups, even when differences are subtle, becomes possible. In this study, we evaluated the degree to which plumage coloration differs among the four subspecies of the willow flycatcher Empidonax traillii, evaluated sources of variation, and considered the utility of plumage coloration to assign subspecies membership for individuals of unknown origin. We used a colorimeter to measure plumage coloration of 374 adult willow flycatchers from 29 locations across their breeding range in 2004 and 2005. We found strong statistical differences among the mean plumage coloration values of the four subspecies; however, while individuals tended to group around their respective subspecies' mean color value, the dispersion of individuals around such means overlapped. Mean color values for each breeding site of the three western subspecies clustered together, but the eastern subspecies' color values were dispersed among the other subspecies, rather than distinctly clustered. Additionally, sites along boundaries showed evidence of intergradation and intermediate coloration patterns. We evaluated the predictive power of colorimeter measurements on flycatchers by constructing a canonical discriminant model to predict subspecies origin of migrants passing through the southwestern U.S. Considering only western subspecies, we found that individuals can be assigned with reasonable certainty. Applying the model to migrants sampled along the Colorado River in Mexico and the U.S. suggests different migration patterns for the three western subspecies. We believe that the use of plumage coloration, as measured by electronic devices, can provide a powerful tool to look at ecological questions in a wide range of avian species.