Elizabeth A. Flaherty

Estimating Leaf Area Index in Southeast Alaska: A Comparison of Two Techniques

The relationship between canopy structure and light transmission to the forest floor is of particular interest for studying the effects of succession, timber harvest, and silviculture prescriptions on understory plants and trees. Indirect measurements of leaf area index (LAI) estimated using gap fraction analysis with linear and hemispheric sensors have been commonly used to assess radiation interception by the canopy, although the two methods often yield inconsistent results. We compared simultaneously obtained measurements of LAI from a linear ceptometer and digital hemispheric photography in 21 forest stands on Prince of Wales Island, Alaska. We assessed the relationship between these estimates and allometric LAI based on tree diameter at breast height (LAIDBH). LAI values measured at 79 stations in thinned, un-thinned controls, old-growth and clearcut stands were highly correlated between the linear sensor (AccuPAR) and hemispheric photography, but the latter was more negatively biased compared to LAIDBH. In contrast, AccuPAR values were more similar to LAIDBH in all stands with basal area less than 30 m2ha−1. Values produced by integrating hemispheric photographs over the zenith angles 0–75° (Ring 5) were highly correlated with those integrated over the zenith angles 0–60° (Ring 4), although the discrepancies between the two measures were significant. On average, the AccuPAR estimates were 53% higher than those derived from Ring 5, with most of the differences in closed canopy stands (unthinned controls and old-growth) and less so in clearcuts. Following typical patterns of canopy closure, AccuPAR LAI values were higher in dense control stands than in old-growth, whereas the opposite was derived from Ring 5 analyses. Based on our results we advocate the preferential use of linear sensors where canopy openness is low, canopies are tall, and leaf distributions are clumped and angles are variable, as is common in the conifer forests of coastal Alaska.

Winter Preference for Weed Seed and Waste Grain by Native Mice in Row-Crop Agriculture

Consumption of weed seeds and waste grains by seed predators is an important ecosystem service that helps to regulate weed and volunteer crop populations in many agricultural systems. The prairie deer mouse is found in a variety of sparsely vegetated habitats throughout the central United States and is the dominant vertebrate seed predator in row-crop fields (corn and soybean) in this region. Evaluating the preferences of prairie deer mice for common agricultural weed seeds and waste grain is important to understand the potential ability of native mice to regulate volunteer crops and weed populations. We evaluated winter seed preference of deer mice using cafeteria-style feeding trials presented within row-crop fields in central Indiana and used compositional analysis to compare proportional consumption of seeds from five common agricultural weeds (common ragweed, common cocklebur, common lambsquarters, velvetleaf, and giant foxtail) and two grains (corn and soybean) during overnight feeding trials. Prairie deer mice significantly preferred corn to all other available seed types. Ragweed and soybean were also readily consumed and were preferred over seeds other than corn. Giant foxtail was intermediately preferred. Our results show that prairie deer mice have clear preferences for certain seeds commonly available in row-crop fields; mice likely contribute to reduction of waste grain and some weed seed populations. Nomenclature: Common cocklebur, Xanthium strumarium L.; common ragweed, Ambrosia artemisiifolia L.; common lambsquarters, Chenopodium album L.; giant foxtail, Setaria faberi Herrm.; velvetleaf, Abutilon theophrasti Medik.; corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Seasonal Foraging by Forest Mice Enhances Loss of Weed Seeds from Crop—Field Edges

Abstract Native seed predators, such as mice (Peromyscus spp.) and ground beetles (Carabidae), consume weed seeds and waste grain within agricultural fields and thus provide a potentially important service to farmers. Most previous investigations of agricultural seed predation services have focused on within-field factors that affect rates of seed removal and consumption by field-resident seed predators. However, seasonal migrants from adjacent non-crop habitats may also contribute to removal of weed seed, particularly along field edges. We investigated whether rates of weed seed removal within fields increased during summer crop growth when Peromyscus leucopus noveboracensis (White-Footed Mouse), a ubiquitous forest-dwelling rodent in the eastern US, seasonally migrates into crop fields from adjacent forested woodlots. We used exclosure experiments to quantify the relative number of Setaria faberi (Giant Foxtail) seeds removed from seed trays by vertebrate and invertebrate seed predators within 4 corn fields in central Indiana during 4 different stages of crop growth (emergence [May], vegetative [July], reproductive [August], post-harvest [November]). Seed-removal experiments were coupled with live trapping of rodents and pitfall sampling of invertebrates to identify seed predators. Vertebrates (mice) contributed nearly twice as much (∼50%) to seed removal compared to invertebrates (∼25%), irrespective of season. Rates of invertebrate consumption differed among seasons but were not affected by distance from forest—field edge. Rates of seed removal by mice significantly interacted with season and distance from field edge, with higher rates of seed loss near forest—field edges during July and August even though mouse abundance showed no strong association with distance. Increased seed loss near (within 90 m) forest—field edges was presumably due to consumption by seasonally field-resident White-footed Mice, which constituted the majority (>70%) of mouse captures near field edges. Peromyscus maniculatus bairdii (Prairie Deer Mouse) is a year-round resident in crop fields and most likely contributed to seed loss nearer field interiors, where they comprised >90% of the rodents caught. Although non-crop habitats are often overlooked as a source of seed predation services, our results indicate that forest-dwelling White-footed Mice likely supplement rates of in-field predation on weed seed. Future investigations of seed-predation services should consider the role of resident and seasonally opportunistic seed predators in regulation of weed populations in crop fields.

Novel Glaucomys volans vocalizations in Indiana and evidence of geographic variation in high frequency communication

The study of ultrasonic signaling has provided important insights into the ecology of bats and marine mammals, but it is poorly understood in other mammalian taxa. Recently, ultrasonic and high frequency vocalizations were described in southern flying squirrels (Glaucomys volans) in the southeastern United States and Ontario, Canada. Notable differences in many call characteristics suggest regional variation in G. volans communication. We evaluated this observation of regional variation by examining G. volans communication in a little studied portion of their range, the Central Hardwoods Region of the United States. We recorded calls of wild G. volans near West Point, Indiana, with Anabat II ultrasonic recorders. We described frequency and time characteristics of recorded calls, categorized call syllables into types, and used a canonical discriminant function analysis to refine our classification. Our analyses yielded 11 distinct types of G. volans syllables, 7 of which are unlike any calls described in other portions of the species range. This suggests G. volans either communicates in distinct regional dialects or has a much larger call repertoire than previously known. We recommend the creation of locally specific call libraries across the range of G. volans to ensure accuracy in the study of high frequency communication.

Functional and numerical responses of shrews to competition vary with mouse density

For decades, ecologists have debated the importance of biotic interactions (e.g., competition) and abiotic factors in regulating populations. Competition can influence patterns of distribution, abundance, and resource use in many systems but remains difficult to measure. We quantified competition between two sympatric small mammals, Keen’s mice (Peromyscus keeni) and dusky shrews (Sorex monticolus), in four habitat types on Prince of Wales Island in Southeast Alaska. We related shrew density to that of mice using standardized regression models while accounting for habitat variables in each year from 2010–2012, during which mice populations peaked (2011) and then crashed (2012). Additionally, we measured dietary overlap and segregation using stable isotope analysis and kernel utilization densities and estimated the change in whole community energy consumption among years. We observed an increase in densities of dusky shrews after mice populations crashed in 2012 as expected under competitive release. In addition, competition coefficients revealed that the influence of Keen’s mice was dependent on their density. Also in 2012, shrew diets shifted, indicating that they were able to exploit resources previously used by mice. Nonetheless, increases in shrew numbers only partially compensated for the community energy consumption because, as insectivores, they are unlikely to utilize all food types consumed by their competitors. In pre-commercially thinned stands, which exhibit higher diversity of resources compared to other habitat types, shrew populations were less affected by changes in mice densities. These spatially and temporally variable interactions between unlikely competitors, observed in a relatively simple, high-latitude island ecosystem, highlight the difficulty in assessing the role of biotic factors in structuring communities.

INTERSPECIFIC COMPARISON OF HANTAVIRUS PREVALENCE IN PEROMYSCUS POPULATIONS FROM A FRAGMENTED AGRO-ECOSYSTEM IN INDIANA, USA

abstract:  Comparatively little is known about hantavirus prevalence within rodent populations from the Midwestern US, where two species of native mice, the prairie deer mouse (Peromyscus maniculatus bairdii) and the white-footed mouse (Peromyscus leucopus noveboracensis), are dominant members of rodent communities. We sampled both species in central Indiana and tested individuals for presence of hantavirus antibodies to determine whether seroprevalence (percent of individuals with antibodies reactive to Sin Nombre virus antigen) differed between species, or among different habitat types within fragmented agro-ecosystems. Prevalence of hantavirus antibodies varied significantly between species, with seroprevalence in prairie deer mice (21.0%) being nearly four times higher than in white-footed mice (5.5%). Seroprevalence was almost eight times higher within the interior of row-crop fields (37.7%) occupied solely by prairie deer mouse populations, relative to field edges (5.2%) or adjacent forest habitat (6.1%). In the fragmented Midwestern agro-ecosystem of this study, prairie deer mice appear to be the dominant hantavirus reservoir, with particularly high seroprevalence in populations within the interior of row-crop fields.

Spatial Variation in Density of White-footed Mice Along Edges in Fragmented Habitat

Abstract The influence of forest fragmentation and associated habitat edges differentially affects forest-dependent organisms, particularly when certain species are able to use resources from surrounding matrix habitats. The white-footed mouse is a forest habitat generalist and is known to disperse among adjoining farmland habitats, including agricultural matrix, in fragmented agro-ecosystems. However, little is known about spatial variation in population density within adjoining farmland habitats or how this relationship varies seasonally. In addition quantifying the extent to which white-footed mice use agricultural matrix as habitat is important for inferring potential ecosystem services (predation of weed seed and waste grain) rendered within row-crop fields. We used spatially explicit capture-recapture models to estimate density of white-footed mice along a gradient of patch (forest fragment) interior to matrix (crop field) interior that spanned fragmented habitat edges. Spatial variation in population density within adjoining habitats was related to the distance from habitat edge, and the magnitude of this relationship (edge effect) varied among seasons and crop cycles within the agricultural matrix. Within-field densities were greater during periods of summer crop growth relative to spring crop emergence or following fall crop harvest. Populations of white-footed mice in forest fragments appear to seasonally spill over from patch habitat into surrounding agricultural matrix. Acquisition of resources from surrounding agricultural matrix may contribute to the inverse density-area relationship observed for white-footed mice within forested habitat in fragmented landscapes. Furthermore, seasonal foraging within matrix habitat likely provides weed seed predation ecosystem services in row-crop fields.

Diet and food availability of the Virginia northern flying squirrel (Glaucomys sabrinus fuscus): implications for dispersal in a fragmented forest

A history of timber harvest in West Virginia has reduced red spruce (Picea rubens) forests to < 10% of their historic range and resulted in considerable habitat fragmentation for wildlife species associated with these forests. The Virginia northern flying squirrel (Glaucomys sabrinus fuscus) has been described as a red spruce obligate subspecies that must traverse this fragmented landscape to disperse among remnant red spruce patches. Food availability in the forest matrix surrounding red spruce may be a limiting factor to successful dispersal of G. s. fuscus. We examined the diet of flying squirrels using stable isotope analysis and used vegetation surveys to determine the availability of diet items in the habitats encountered by G. s. fuscus in the matrix surrounding red spruce fragments. Stable isotope analysis suggested hypogeous fungi, epigeous fungi, and invertebrates contributed the most to the diet of G. s. fuscus, followed by lichen. Tree buds contributed the least in spring, and beechnuts contributed the least in fall. The vegetation surveys revealed that no habitat type had a greater availability of the diet items that contributed most to the assimilated diet of G. s. fuscus, suggesting that stand age and structure may be more important for diet-item availability than habitat type.

Testing the efficacy of an acoustic lure on bat mist-netting success in North American central hardwood forests

Severe population declines in numerous North American bat species makes population monitoring increasingly difficult. We tested the effectiveness of an acoustic lure at increasing capture success of bats in mist nets. Increasing detection rate is especially relevant for species that have been heavily affected by white-nose syndrome, such as the Indiana bat (Myotis sodalis), little brown bat (M. lucifugus), and northern long-eared bat (M. septentrionalis). We conducted our study at 3 properties in southern Indiana during summer 2014. We set up 7 mist-netting sites at each property, netting 2 times at each site, with and without the use of an UltraSoundGate Player BL acoustic lure. The lure played recordings of various social calls from Myotis, Eptesicus, and Lasiurus spp. recorded in Europe and North America on a loop throughout the mist-net night. A total of 21 bats were caught using the lure, while 46 bats were caught without the use of the lure. We ran a series of zero-inflated Poisson generalized linear models on number of bats captured per trapping night to test whether the lure produced a difference in bat captures overall and for each genus while accounting for additional sources of variability. Using an information theoretical approach, we determined the most parsimonious models for each species grouping. For bats overall and those in the genera Myotis and Eptesicus, the top performing models contained an effect for use of the lure. This effect was positive and significant (P = 0.007) for our Myotis model, while the Eptesicus model showed a marginally significant and negative effect of the lure. We conclude that level of sociality in bat species influences the effectiveness of an acoustic lure on bat capture success. Understanding this distinction can inform when and where the use of an acoustic lure may enhance conservation goals.