1. Generalist enemies can regulate low-density forest insect populations, and are widely considered to cause greater mortality in more diverse habitats. Forest tent caterpillars (Malacosoma disstria Hübner; FTC) are a major defoliator of aspen (Populus tremuloides Micheaux) in the boreal forest, a region with a mosaic of forest stand types. This heterogeneity may influence FTC outbreaks if generalist predation or parasitism differs among stands of different tree composition.2. Using exclusion experiments we estimate predation and parasitism of FTC across multiple life-history stages in low-density populations occupying both aspen (low diversity) and mixedwood stands (high diversity).3. Arthropod and avian generalist predators were responsible for most natural enemy-caused mortality of immature FTC, but their relative impacts varied among FTC life-history stages. Contrary to expectation, predation on late instar larvae and pupae was higher in the less diverse aspen stands and early instar mortality did not differ.4. By considering multiple life-history stages, our results provide a more comprehensive view of natural enemy-caused morality of immature FTC. Because generalist predation on FTC was higher in aspen than in mixedwood stands, we suggest that FTC populations may be slower to reach outbreak levels in aspen stands.

Accounting for climate change in invasive species risk assessments improves our understanding of potential future impacts and enhances our preparedness for the arrival of new non-native species. We combined traditional risk assessment for invasive species with habitat suitability modeling to assess risk to biodiversity based on climate change. We demonstrate our method by assessing the risk for 15 potentially new invasive plant species to Alberta, Canada, an area where climate change is expected to facilitate the poleward expansion of invasive species ranges. Of the 15 species assessed, the three terrestrial invasive plant species that could pose the greatest threat to Alberta’s biodiversity are giant knotweed (Fallopia sachalinensis), tamarisk (Tamarix chinensis), and alkali swainsonpea (Sphaerophysa salsula). We characterise giant knotweed as ‘extremely invasive’, with 21 times the suitable habitat between baseline and future projected climate. Tamarisk is ‘extremely invasive’ with a 64% increase in suitable habitat, and alkali swainsonpea is ‘highly invasive’ with a 21% increase in suitable habitat. Our methodology can be used to predict and prioritise potentially new invasive species for their impact on biodiversity in the context of climate change.

ABSTRACT. Across North America, grassland songbirds have undergone steep population declines over recent decades, commonly attributed to agricultural intensification. Understanding the potential interactions between the impacts of climate change on the future distributions of these species and the availability of suitable vegetation for nesting can support improved risk assessments and conservation planning for this group of species. We used North American bioclimatic niche models to examine future changes in suitable breeding climate for 15 grassland songbird species at their current northern range limits along the boreal forest-prairie ecotone in Alberta, Canada. Our climate suitability projections, combined with the current distribution of native and tame pasture and cropland in Alberta, suggest that some climate-mediated range expansion of grassland songbirds in Alberta is possible. For six of the eight species projected to experience expansions of suitable climate area in Alberta, this suitable climate partly overlaps the current distribution of suitable land cover. Additionally, for more than half of the species examined, most of the area of currently suitable climate was projected to remain suitable to the end of the century, highlighting the importance of Alberta for the long-term persistence of these species. Some northern prairie-endemic species exhibited substantial projected northward shifts of both the northern and southern edges of the area of suitable climate. Baird's Sparrow (Ammodramus bairdii) and Sprague's Pipit (Anthus spragueii), both at-risk grassland specialists, are predicted to have limited climate stability within their current ranges, and their expansion into new areas of suitable climate may be limited by the availability of suitable land cover. Our results highlight the importance of the preservation and restoration of remaining suitable grassland habitat within areas of projected climate stability and beyond current northern range limits for the long-term persistence of many grassland songbird species in the face of climate change.Réactions projetées de passereaux de prairie nord-américains aux changements climatiques et à la disponibilité de l'habitat à la limite nord de leur aire en Alberta, Canada RÉSUMÉ. Partout en Amérique du Nord, les passereaux de prairie ont subi d'importantes baisses de population au cours des dernières décennies, qu'on attribue le plus souvent à l'intensification de l'agriculture. La compréhension des interactions potentielles entre les impacts des changements climatiques sur la future répartition de ces espèces et la disponibilité de végétation favorable à leur nidification peut contribuer à améliorer l'évaluation des risques et la planification des mesures de conservation pour ce groupe d'espèces. Nous avons utilisé des modèles de niches bioclimatiques afin d'examiner les variations futures du climat favorable pour la nidification de 15 passereaux de prairie à la limite nord de leur aire actuelle le long de l'écotone forêt boréale-prairie en Alberta, au ...

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