Invasive species are especially problematic when introduced into ecosystems with native congeners. The extent to which niches overlap in space determines whether the introduced species threatens the native one or the native species can escape competition or the effect of control. We compared the spatial distribution in relation to landscape and land-use/ land-cover variables of introduced and native Phragmites australis (common reed) in a landscape of protected freshwater wetlands in Quebec, Canada. Results showed that the wetlands still serve as refuges for native P. australis. At this stage of invasion, native and introduced P. australis occupy distinct spatial niches, the more abundant native type in low marsh and areas of lesser human impacts, the introduced one closer to roads and drier land covers. For now, native P. australis largely escapes competition, and the lack of spatial overlap could reduce opportunities for hybridization. Our study also suggests that invasion foci could still be controlled without endangering the native type. Whether the heterogeneous wetland conditions and the different spatial niches will be sufficient to allow long-term coexistence of native and introduced P. australis remains to be seen, but the situation needs to be closely monitored, especially in wetlands protected for biodiversity conservation.

The brown creeper (Certhia americana) is one of the forest bird species most sensitive to partial harvesting in North America. We examined the detailed response of this species and its food (bark-dwelling invertebrates) during the 3^rd and 4^th year after experimental selection harvesting (30–10% basal area removal) in northern hardwood forest. Relative to control plots, nest densities in treated plots were ca 50% lower. Because the density of nesting substrates was not significantly lower in treated plots than in controls, we investigated whether foraging substrates could be the limiting factor. Specifically, we tested for a treatment effect on 1) the abundance and species composition of bark invertebrate assemblages; 2) the biomass of bark invertebrates per unit area; and 3) the frequency of food provisioning. As predicted, treatment had a significant negative effect on food provisioning rate, though not on invertebrate biomass, when accounting for year effects. There was also no evidence for a treatment effect on the structure of bark invertebrate assemblages, which was mainly influenced by cumulative degree days. Selection harvesting thus appeared to reduce the amount of food delivered to brown creeper nestlings, unless greater amounts of food were delivered per feeding trip in treated plots. The lower density of foraging substrates in treated plots (77 versus 112 stems ha^-1 in controls) may require that adults perform longer foraging trips. Future studies should determine whether this extra effort has short- or long-term consequences for adults and nestlings.

The mountain pine beetle (MPB) infested 1.6 million ha of forest in Colorado and southern Wyoming from 1996 to 2010, causing extensive tree mortality, especially in lodgepole pine forests. Identifying the extent to which MPB outbreaks have occurred in the past will further our understanding of the current outbreak's causes and consequences. We explore the use of dendroecological methods to reconstruct a prior MPB outbreak event, which occurred in northwestern Colorado in the early 1980s. We used coarse-scale maps of MPB and GIS layers of suitable MPB habitat based on stand attributes to identify 15 stands of probable MPB activity in the 1980s. At 9 sites where field observations indicated probable past MPB activity, we collected tree cores from canopy host trees and subcanopy non-host (Engelmann spruce and subalpine fir) and host trees. The relatively synchronous dates of death of host trees determined by crossdating against live or recently killed trees (i.e., after 1996) confirmed that host trees had died in the 1980s period of reported MPB activity. Tree cores from subcanopy trees of both host and non-host species were used to detect accelerated radial growth (i.e., growth releases) of surviving trees following the death of canopy trees. Over 90% of subcanopy host and non-host trees sampled showed increased radial growth following the 1980s outbreak when evaluated 1) through visual inspection of ring-width series and 2) using a mathematical kernel to identify a period of ≥ 150% growth increase maintained for at least 5 y. Over half of the canopysize lodgepole pines that survived the 1980s outbreak also accelerated their growth rates following the 1980s outbreak, although less sharply and for a shorter duration than the subcanopy trees. These results demonstrate the feasibility of using dendroecological methods to detect previous MPB outbreaks in lodgepole pine forests in Colorado over the past several decades and also identify limitations for extending reconstruction efforts back in time beyond the documentary record.

Given their relatively small body size, high thermoregulatory costs, and low metabolic rate, we tested the hypothesis that red squirrels (Tamiasciurus hudsonicus) would employ bouts of daily torpor to save energy during winter. We collected data on body temperature (T_b) using surgically implanted data loggers for squirrels in the Cypress Hills region of Saskatchewan, where extended periods of cold snowy weather make foraging difficult and should lead to high levels of energy expenditure. Based on over 8000 measurements from 4 animals over 3 winters, we found no evidence for torpor use. However, T_b was lowest in January and highest in September and May, and mean monthly T_b was correlated with mean monthly ambient temperature (T_a). Given that taxonomically related species can and do use torpor, it remains to be determined what makes heterothermy in this species costly to the extent that its use is precluded.

Distyly is a common reproductive strategy in the family Rubiaceae. Studies on tropical species of the genus Psychotria present several cases of atypical distyly, e.g., the absence of reciprocal positioning of sexual organs between morphs, anisoplethy, limited pollen availability, and monomorphy. To describe the floral polymorphism and reproductive ecology of Psychotria nervosa, I studied the proportion of morphs, the floral morphology, the number of inflorescences, flowers, and fruits set between morphs, and the diversity and behaviour of floral visitors in 2 natural populations of the species in a seasonally dry tropical forest in Mexico. Psychotria nervosa is a distylous species; both populations presented a 1:1 morph ratio, with reciprocal positioning of sexual organs between morphs, as well as a suite of ancillary floral traits associated to polymorphism. The diversity and behaviour of the floral visitor assemblage caused a higher fruit set in the longstyled morph than in the short-styled morph in both populations. Furthermore, the highest fruit set was observed in the most morphologically reciprocal population.

Seedlings germinating from large seeds are known to endure hazards such as shading, competition, and litter coverage better than seedlings germinating from small seeds. However, few studies have assessed the relationships between seed size and recruitment comparing plant communities with different structures in order to establish the conditions under which a seed-size advantage prevails. Here, seeds from 20 species varying in seed size from 0.05 to 17.8 mg were sown in 6 different vegetation types, representing a gradient from open grassland to closed canopy coniferous forest. We hypothesized that the effect of seed size on recruitment is generally positive, but that there is a stronger positive effect of seed size in closed than in open communities. Our results provided only limited support for this hypothesis. Firstly, the results varied between years, suggesting that any seed size advantage may depend on factors varying on an annual basis. Secondly, although there were trends of significantly positive relationships between seed size and seedling emergence, seedling survival, and recruitment success, particularly in relatively more closed vegetation types, the strongest positive effects of seed size were found in intermediate (semi-open) habitats along the gradient. We conclude that the filtering of species into the investigated communities is only weakly related to seed size, and that several factors other than canopy probably influence the link between seed size and recruitment.

The distribution and abundance of dominant species and their relationships with soil and climate were investigated using a variety of multivariate statistics across 30 plots that spanned 50 000 km² of the Sonoran Desert. Relationships between the distribution of Carnegiea gigantea and several of its nurse plant species (Ambrosia deltoidea, Ambrosia dumosa, Cercidium microphyllum, Larrea tridentata, Prosopis spp., Olneya tesota) were documented. A general east-west gradient was observed where temperature increases and precipitation decreases westwards and calcium levels, total organic carbon, particle size, and soil pH increase westwards. Western areas with high temperatures and low precipitation may have elevated levels of calcite and thus a high pH; the low rainfall limits calcium dilution within the soil. The gradient in soil pH likely governs the range of several species (e.g., Ambrosia deltoidea, A. dumosa, and Larrea tridentata) that were delineated by calcic soils in western areas from eastern regions with lower soil pH and higher precipitation. Thus, the distribution of the dominant species reflects a temperature—precipitation—calcium—pH gradient. We found that the pH gradient follows the precipitation gradient as much as the dominant species follow the pH or rainfall gradients. Although climate is thought to dominate the distributions of these species, we found that soil pH and texture are intimately intertwined and that their removal from analyses resulted in poorer explanatory power of species distributions.

The Athabasca Sand Dunes in northern Saskatchewan are a unique landscape characterized by large areas of active sand dunes. The dunes are of high conservation value as they support 10 endemic vascular plant taxa, including 9 sand dune specialists: Achillea millefolium var. megacephala, Armeria maritima ssp. interior, Deschamp sia mackenzieana, Salix brachycarpa var. psammophila, Salix silicicola, Salix turnorii, Salix tyrrellii, Stellaria arenicola, and Tanacetum huronense var. floccosum. This paper describes the patterns of distribution, abundance, and environmental affinity of the Athabasca endemic flora and assesses the implications of these patterns for the conservation status of the species. Extensive field surveys found large populations of Deschampsia mackenzieana, Salix brachycarpa, Salix silicicola, Salix turnorii, Salix tyrrellii, Stellaria arenicola, and Tanacetum huronense. With the exception of S. brachycarpa the abundant species were widely distributed across the dune landscape. Two species, Achillea millefolium and Armeria maritima, had relatively small populations that were concentrated in limited environments within the dune landscape (wet dune slack and gravel pavements respectively). Few immediate external threats were observed, and flowering, seed set, and seedling establishment were observed for all taxa. The small populations and limited environmental breadth of Achillea millefolium and Armeria maritima indicate that the conservation status of these species should be re-examined.

The ideal free distribution (IFD) model predicts that consumers match the distribution of resources across habitat patches and that this association should lead to equal individual fitness among individuals in a population. Here we studied to what extent predators utilize different prey groups and if the resulting spatial patterns relate to the reproductive success of individuals in a population of a web-building spider species (Phylloneta impressa, Theridiidae). Web-building spiders, their prey remains, egg sacs, and spiderlings were collected in a wheat field, and coordinates of web sites were recorded for spatial point pattern analysis using pair and mark correlation functions. Spiders were aggregated in the study area, but only post-reproductive females were aggregated over the full range of spatial scales. Web-owners in clusters caught a higher proportion of hemipteran prey than expected by the mean, suggesting that the availability of this prey type contributed to the clustering of individuals and the higher reproductive success of females in clusters. However, 2 abundant prey groups (Syrphidae and Hymenoptera) were not more common than expected by the mean at any distance, and another prey group (Elateridae) was even less common in webs close to each other. At least 2 prey groups (Hemiptera and Elateridae) showed deviations from the assumption of the IFD model that predators in clusters should have similar prey capture success compared to predators that are not located in clusters. Both prey groups include many cereal pest species, and our results suggest that spatially explicit information about prey utilization and predator fitness may contribute to a better understanding of the role of natural enemies in biological control.

We used an information-theoretic model comparison approach to investigate the influence of forest stand attributes resulting from wildfire on the occupancy of winter habitats by barren-ground caribou (Rangifer tarandus groenlandicus) in the Northwest Territories, Canada. We used field data describing forest stand and understory attributes to develop multinomial regression models. These analyses identified a combination of ground cover type and tree volume (i.e., stand basal area) as best able to describe the observed selection of feeding sites. An observed increase in the percent ground cover of lichen had a positive influence on site selection, while an increase in the percent rock cover and basal area of conifer trees had a negative influence on selection of feeding sites by caribou. The most parsimonious regression model predicted site use with an accuracy of 87%. Lastly, we used published equations to determine the biomass of fruticose lichens on experimental and control sites classified as unburned. Our data indicated that fruticose lichen biomass on the winter range of the Bathurst herd of barren-ground caribou was high compared to winter habitats of caribou in Alaska and the Yukon Territory, and falls in the general range of lichen values reported for winter habitats of the more easterly Beverly herd, as well as portions of Saskatchewan, Manitoba, and Ungava. Overall, the analyses of feeding-site selection suggest that Bathurst caribou forage in areas with a high percentage cover and biomass of lichen, and that future increased incidence and severity of forest fires could cause a temporary decrease in the quality of winter habitat available to the Bathurst herd.