Dakota skipper (Hesperia dacotae Skinner) andPoweshiek skipperling (Oarisma poweshiek Parker) (Lepidoptera: Hesperiidae) are endemic prairie species that are threatened in Canada. Surveys during the brief adult flight period are necessary to quantify population sizes, but dates of adult emergence vary widely from year to year (up to 24 days) and populations are geographically distant from one another (150-250 km). To predict adult emergence of H. dacotae and O. poweshiek, we used local weather station data to calculate the number of degree days accumulated between March 1 and adult emergence using two different models in seven different years between 2002 and 2013. We also compared the number of degree days accumulated at the soil surface where larvae and pupae reside to those accumulated using weather station data. We recommend that surveys for Dakota skipper begin when degree day accumulations (from weather stations) reach a threshold of 575 (standard model) or 600 (double sine model) in the south central portion of Manitoba and 550 (standard model) or 575 (double sine model) in the southwest region of Manitoba. For Poweshiek skipperling surveys should be considered after degree day accumulations reach 575 (standard model) or 625 (double sine model). Degree days accumulated at the soil surface were 20-30 % greater than those calculated using weather station data in Dakota skipper sites, and 1-12 % greater in Poweshiek skipperling sites. Using our models, we predicted adult emergence to within 48 h of emergence in 2011, 2012 and 2013.

The Poweshiek skipperling (Oarisma poweshiek) is a critically endangered grassland butterfly with six populations remaining in the United States and Canada. The single Canadian population, with the largest remaining contiguous habitat, includes less than ~50 observed individuals and extirpation is potentially imminent. Captive breeding is underway and there is a need to locate suitable sites for reintroduction and habitat management. Species distribution models (SDMs) predict habitat quality and guide management decisions. Most SDMs rely on statistical validation as a surrogate metric for accuracy, with presence‐only SDMs usually reporting area under the curve (AUC). Although experts have long cautioned against relying on statistical validation alone, accuracy is rarely field‐validated. We developed a presence‐only SDM using the maximum entropy (Maxent) method to predict probability of occurrence for the Poweshiek skipperling and determine environmental covariates associated with high probability of occurrence. We collected two independent datasets to (a) calibrate our model to predict categories of habitat quality (using factor analysis) and (b) compare expected and observed habitat quality to calculate model accuracy. Statistical validation showed that we predicted presence‐absence of training data with high accuracy (AUC = 0.98). Covariates responsible for most of the variation in probability of occurrence included soil drainage, habitat patch size, and land use type. Only 0.4% of the study area was expected to represent good‐excellent habitat with the remaining 99.6% medium‐poor. Our model predicted novel habitat quality with 81% accuracy (better than chance). Poor‐medium habitat was predicted more accurately (92%) than good‐excellent habitat (54%). Our model showed better accuracy than most other field‐validated SDMs reviewed. We reiterate calls for greater field‐validation of SDMs: if we had relied on statistical validation alone, perceived accuracy of our model would be inflated. Finally, managers can use our results to reliably exclude predicted poor‐medium habitats as candidates for Poweshiek skipperling habitat management or reintroduction.

The present study investigated the effect of artificial defoliation on weekly radial xylem production in trembling aspen (Populus tremuloides Michx.). It was hypothesized that defoliated trees would show reduced xylem and vessel production and thinner secondary walls in fibres. Two adjacent natural forest sites were selected within Winnipeg, Manitoba. Microcores were extracted weekly from the stems of 30 aspen trees from May to October 2002. Ten aspen trees were defoliated using pole pruners between 22 June and 6 July. Measurements included weekly xylem increment, annual vessel characteristics, and late growing season fibre dimensions. No significant difference in overall ring width was observed; however, trees from both groups showed a significant reduction in ring width in 2002. The ratio of radial growth in 2002 / radial growth in 2001 was significantly less in defoliated trees, suggesting a higher reduction in radial growth due to defoliation. Sigmoidal regression models suggested early growth cessation in defoliated trees. No significant differences in vessel characteristics were observed between groups; however, the diameter and lumen width of fibres was significantly reduced in defoliated trees. It is speculated that a shorter radial growing season may have led to a reduced cell elongation period. An early cessation of the radial growing season associated with a reallocation of carbohydrates to produce a second flush of leaves could explain the reduced size of fibres from defoliated trees.Key words: wood anatomy, diffuse porous, image analysis, radial growth, cell dimension, dendrochronology.

Species distribution models (SDMs) use spatial relationships between species occurrence and habitat (predictor) variables to generate maps of habitat suitability across a region of interest. These maps are frequently used in recovery planning efforts for endangered species, but they are influenced by data availability, selection of predictor variables, and choice of model type. Ground validation is necessary to robustly evaluate map accuracy, but it is rarely done, making it difficult to determine which modeling approach is best-suited for a given species or region. To address this uncertainty, we used two SDM types (Maxent and GLM) and two methods of selecting predictor variables to build four SDMs for an endangered prairie butterfly (Dakota skipper, Hesperia dacotae) in two regions of Manitoba, Canada. We then conducted field-based habitat suitability assessments at 120 locations in each region to enable direct comparisons of model output and accuracy. We found that soil type and surrounding landcover (grassland versus cropland) were important predictors of species occurrence regardless of region, predictor selection method, or model type. Cross-validation statistics indicated that most SDMs performed well (AUC > 0.7), but ground validation revealed that the habitat suitability maps they generated were inaccurate (Cohen’s kappa < 0.4). Maxent models produced more accurate maps than GLMs, likely because false species absences adversely affected the latter, but only one Maxent-based map was accurate enough to help locate sites for future field investigations (Cohen’s kappa > 0.3). Our results emphasize the importance of ground-validating SDM-based habitat suitability maps before incorporating them into species recovery plans.

Habitat loss and edge effects resulting from habitat fragmentation are key processes implicated in the decline of bee populations globally. Their effects on wild bees and their pollination services in natural ecosystems are poorly understood, particularly in North American prairies. Our objectives were to determine whether natural habitat loss and edge effects affect bee abundance and pollination services in the Northern Great Plains. We sampled bee abundance and pollination services along transects beginning at road or tree edges in grasslands located in Manitoba, Canada. We measured bee abundance using pan traps, and pollination services using seed-set of Brassica rapa (L.) (Brassicales: Brassicaceae) phytometers. We collected local-scale habitat data by measuring occurrence of flowering species, vegetation type, and vegetation structure, and we measured habitat amount at 1-km radii using GIS analysis of landscape cover. Increasing amounts of habitat loss resulted in declines in bee abundance, and sometimes in pollination services. Results varied with bee life-history: proximity to road edges negatively affected social bees, and litter depth had negative effects on below- ground-nesting bees. Surprisingly, few effects on bees led to corresponding impacts on pollination services. This suggests that conservation of intact natural habitat across the northern Great Plains is important for maintaining resilient and diverse bee communities, but that efforts to conserve bee populations cannot be assumed to also maintain all associated pollination services.