Climate change likely will lead to increasingly favourable environmental conditions for many parasites. However, predictions regarding parasitism's impacts often fail to account for the likely variability in host distribution and how this may alter parasite occurrence. Here, we investigate potential distributional shifts in the meningeal worm, Parelaphostrongylosis tenuis, a protostrongylid nematode commonly found in white-tailed deer in North America, whose life cycle also involves a free-living stage and a gastropod intermediate host. We modelled the distribution of the hosts and free-living larva as a complete assemblage to assess whether a complex trophic system will lead to an overall increase in parasite distribution with climate change, or whether divergent environmental niches may promote an ecological mismatch. Using an ensemble approach to climate modelling under two different carbon emission scenarios, we show that whereas the overall trend is for an increase in niche breadth for each species, mismatches arise in habitat suitability of the free-living larva vs. the definitive and intermediate hosts. By incorporating these projected mismatches into a combined model, we project a shift in parasite distribution accounting for all steps in the transmission cycle, and identify that overall habitat suitability of the parasite will decline in the Great Plains and southeastern USA, but will increase in the Boreal Forest ecoregion, particularly in Alberta. These results have important implications for wildlife conservation and management due to the known pathogenicity of parelaphostrongylosis to alternate hosts including moose, caribou and elk. Our results suggest that disease risk forecasts which fail to consider biotic interactions may be overly simplistic, and that accounting for each of the parasite's life stages is key to refining predicted responses to climate change.

Shifts of distributions have been attributed to species tracking their fundamental climate niches through space. However, several studies have now demonstrated that niche tracking is imperfect, that species' climate niches may vary with population trends, and that geographic distributions may lag behind rapid climate change. These reports of imperfect niche tracking imply shifts in species' realized climate niches. We argue that quantifying climate niche shifts and analyzing them for a suite of species reveal general patterns of niche shifts and the factors affecting species' ability to track climate change. We analyzed changes in realized climate niche between 1984 and 2012 for 46 species of North American birds in relation to population trends in an effort to determine whether species differ in the ability to track climate change and whether differences in niche tracking are related to population trends. We found that increasingly abundant species tended to show greater levels of niche expansion (climate space occupied in 2012 but not in 1980) compared to declining species. Declining species had significantly greater niche unfilling (climate space occupied in 1980 but not in 2012) compared to increasing species due to an inability to colonize new sites beyond their range peripheries after climate had changed at sites of occurrence. Increasing species, conversely, were better able to colonize new sites and therefore showed very little niche unfilling. Our results indicate that species with increasing trends are better able to geographically track climate change compared to declining species, which exhibited lags relative to changes in climate. These findings have important implications for understanding past changes in distribution, as well as modeling dynamic species distributions in the face of climate change.

Monitoring plant and animal phenology is a critical step to anticipating and predicting changes in species interactions and biodiversity. Because phenology necessarily involves frequent and repeated observations over time, citizen scientists have become a vital part of collecting phenological data. However, there is still concern over the accuracy and precision of citizen science data. It is possible that training citizen scientists can improve data quality though there are few comparisons of trained and untrained citizen scientists in the ability of each to accurately and precisely measure phenology. We assessed how three types of observers-experts, trained citizen scientists that make repeated observations, and untrained citizen scientists making once-per-year observations-differ in quantifying temporal change in flower and fruit abundance of American mountain ash trees (Sorbus americana Marsh.) and arthropods in Acadia National Park, Maine, USA. We found that trained more so than untrained citizen science observers over- or under-estimated abundances leading to precise but inaccurate characterizations of phenological patterns. Our results suggest a new type of bias induced by repeated observations: A type of learning takes place that reduces the independence of observations taken on different trees or different dates. Thus, in this and many other cases, having individuals make one-off observations of marked plants may produce data as good if not better than individuals making repeated observations. For citizen science programs related to phenology, our results underscore the importance of (a) attracting the most number of observers possible even if they only make one observation, (b) producing easy-to-use and informative data sheets, and

Aim Our aim was to test the degree to which nectar production predicts hummingbird abundances at large spatial scales compared with other large-scale environmental variables.Location Arizona, Colorado, New Mexico and Utah, USA.Methods We surveyed nectar producing flowers at 67 sites in the summer of 2008 and converted flower densities to nectar production using data obtained from the literature. We derived a model of nectar production and used this to create a nectar production map for the study region. We then tested the degree to which nectar production predicted the abundance and occupancy of blackchinned (Archilochus alexandri) and broad-tailed (Selasphorus platycercus) hummingbirds with zero-inflated Poisson regression. Abundance data were taken from the North American Breeding Bird Survey. We compared the predictions made from nectar production to those made from temperature, precipitation, growing degree-days, elevation and primary productivity. ResultsWe found that black-chinned hummingbird abundance was best predicted by the abundance of conspecifics in a surrounding 20-km neighbourhood as opposed to any of the environmental variables. Their occupancy varied independently of any underlying spatial or environmental variation. Broad-tailed hummingbird abundance was best predicted by average temperature. Nectar was a weak predictor of both species' abundance and occupancy.Main conclusions Of the variables we measured, no single one is a key predictor of spatial variation of hummingbird abundance. It is possible that breeding abundances respond to local habitat characteristics that do not correlate strongly with large-scale environmental variability. Within the breeding season, hummingbird abundance and occupancy may depend on factors unrelated to nectar production and hummingbirds may not disperse to track spatial variation in nectar production.

Aim Ecological niche theory states that realized niche breadth should increase with population growth. This relationship has been studied extensively in the context of density‐dependent habitat selection, and there is evidence that animal populations at higher density occupy a wider range of vegetation types. To our knowledge, no previous studies have investigated the relationship between population growth and climate niche breadth (i.e. the range of climatic conditions occupied). Here we aim to estimate the influence of population trend, as well as changes in distribution, on realized climate niche breadth. Location North America. Methods We estimated changes in realized climate niche breadth and distribution between 1980 and 2012 for 46 bird species using data from the North American Breeding Bird Survey (BBS) and standard ecological niche modelling techniques. We analysed changes in niche breadth in relation to population trends and distributional changes from the BBS for these same species. Results Changes in realized climate niche breadth were significantly and positively associated with population growth, as reflected by BBS population trends, and with changes in distributional extent. Using variance partitioning, we showed that 44.2% of the variation in change in niche breadth can be explained by population trend, and that roughly half of this was independent of changes in distribution. Conclusions Realized climate niche breadth is variable on an ecological time‐scale as a function of population trend. Mechanisms associated with changes in distribution and those acting within current species range limits appear to be equally important in driving this relationship. Observed changes in niche breadth may violate distribution modelling assumptions of niche conservatism. Studying how population growth influences realized climate niche breadth is therefore important for understanding dynamic species distributions, responses to climate change and our ability to model future species distributions.

Aim Geographical disparities in the effect of the environment on population dynamics have been shown to follow a core-periphery gradient when peripheral populations are less abundant and occur in marginal habitat. Whether the gradient in environmental influence occurs in the absence of a gradient in abundance is not known. We tested whether duck populations on the periphery of their main breeding region were more strongly affected by environmental stochasticity and less abundant than at the core. Location The Prairie Pothole Region of central United States and CanadaMethods We used the North American Waterfowl Breeding Population and Habitat Survey to model the dynamics of 10 duck species at 1059 sites spanning 1961-2012. We used the North American Breeding Bird Survey to measure abundance at the same sites, averaged over the same time span. We used structural equation models to characterize relationships among a site's distance from the regional centre, a site's abundance, and the degree to which a site's ducks were affected by environmental stochasticity.

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One intriguing hypothesis about range limits of species along environmental gradients is that interspecific interference competition limits the activity of the better exploitation competitor. The hypothesis works if the costs of interference and (or) exploitation vary along the gradient. However, in some systems, species turnover happens over gradients that may be too short to induce changes in costs associated with competition. An example is breeding Black-chinned Hummingbirds (Archilochus alexandri (Bourcier and Mulsant, 1846)) and Broad-tailed Hummingbirds (Selasphorus platycercus (Swainson, 1827)) in western Colorado, USA, where turnover happens over ∼400 m. We recorded foraging and chasing activity of the two species at feeders and found that their foraging activity changed with elevation but interspecific competition did not. Because the foraging activity of the two species changed inversely with each other, it may be the presence of Black-chinned Hummingbirds rather than active interference that limits the activity of Broad-tailed Hummingbirds. Importantly, the relationship between foraging activity and elevation depended on the distance between the two feeders, which shows that relationships with elevation are contingent on other factors such as spatial distribution of resources. Our results suggest that interspecific differences in flight performance are not manifested over the short elevation gradient and do not account for changes in activity. Flight performance may indirectly affect patterns in breeding-season activity by influencing how species interact with other competitors during the nonbreeding season.