Integrating plant stoichiometry and feeding experiments: state-dependent forage choice and its implications on body mass.

Intraspecific feeding choices comprise a large portion of herbivore foraging decisions. Plant resource quality is heterogeneously distributed, affected by nutrient availability and growing conditions. Herbivores navigate landscapes, foraging not only according to food qualities, but also energetic and nutritional demands. We test three non-exclusive foraging hypotheses using the snowshoe hare (Lepus americanus): (1) herbivore feeding choices and body conditions respond to intraspecific plant quality variation; (2) high energetic demands mitigate feeding responses; and (3) feeding responses are inflated when nutritional demands are high. We measured black spruce (Picea mariana) nitrogen, phosphorus and terpene compositions, as indicators of quality, within a snowshoe hare trapping grid and found plant growing conditions to explain spruce quality variation (R2 < 0.36). We then offered two qualities of spruce (H1) from the trapping grid to hares in cafeteria-style experiments and measured their feeding and body condition responses (n = 75). We proxied energetic demands (H2) with ambient temperature and coat insulation (% white coat) and nutritional demands (H3) with the spruce quality (nitrogen and phosphorus content) in home ranges. Hares with the strongest preference for high-quality spruce lost on average 2.2% less weight than hares who ate the least high-quality spruce relative to low-quality spruce. The results supported our energetic predictions as follows: hares in colder temperatures and with less-insulative coats (lower % white) consumed more spruce and were less selective towards high-quality spruce. Collectively, we found variation in plant growing conditions within herbivore home ranges substantial enough to affect herbivore body conditions, but energetic stats mediate plant-herbivore interactions.

Population genetics and biogeography of the lungwort lichen in North America support distinct Eastern and Western gene pools.

PREMISE: Populations of species with large spatial distributions are shaped by complex forces that differ throughout their ranges. To maintain the genetic diversity of species, genepool-based subsets of widespread species must be considered in conservation assessments. METHODS: The population genetics of the lichenized fungus Lobaria pulmonaria and its algal partner, Symbiochloris reticulata, were investigated using microsatellite markers to determine population structure, genetic diversity, and degree of congruency in eastern and western North America. Data loggers measuring temperature and humidity were deployed at selected populations in eastern North America to test for climatic adaptation. To better understand the role Pleistocene glaciations played in shaping population patterns, a North American, range-wide species distribution model was constructed and hindcast to 22,000 years before present and at 500-year time slices from then to the present. RESULTS: The presence of two gene pools with minimal admixture was supported, one in the U.S. Pacific Northwest and one in eastern North America. Western populations were significantly more genetically diverse than eastern populations. There was no evidence for climatic adaptation among eastern populations, though there was evidence for range-wide adaptation to evapotranspiration rates. Hindcast distribution models suggest that observed genetic diversity may be due to a drastic Pleistocene range restriction in eastern North America, whereas a substantial coastal refugial area is inferred in the west. CONCLUSIONS: Taken together the results show different, complex population histories of L. pulmonaria in eastern and western North America, and suggest that conservation planning for each gene pool should be considered separately.

Forage stoichiometry predicts the home range size of a small terrestrial herbivore.

Home range size of consumers varies with food quality, but the many ways of defining food quality hamper comparisons across studies. Ecological stoichiometry studies the elemental balance of ecological processes and offers a uniquely quantitative, transferrable way to assess food quality using elemental ratios, e.g., carbon (C):nitrogen (N). Here, we test whether snowshoe hares (Lepus americanus) vary their home range size in response to spatial patterns of C:N, C:phosphorus (P), and N:P ratios of two preferred boreal forage species, lowbush blueberry (Vaccinium angustifolium) and red maple (Acer rubrum), in summer months. Boreal forests are N- and P-limited ecosystems and access to N- and P-rich forage is paramount to snowshoe hares' survival. Accordingly, we consider forage with higher C content relative to N and P to be lower quality than forage with lower relative C content. We combine elemental distribution models with summer home range size estimates to test the hypothesis that home range size will be smaller in areas with access to high, homogeneous food quality compared to areas of low, heterogeneous food quality. Our results show snowshoe hares had smaller home ranges in areas where lowbush blueberry foliage quality was higher or more spatially homogenous than in areas of lower, more heterogeneous food quality. By responding to spatial patterns of food quality, consumers may influence community and ecosystem processes by, for example, varying nutrient recycling rates. Our reductionist biogeochemical approach to viewing resources leads us to holistic insights into consumer spatial ecology.

How do genes flow? Identifying potential dispersal mode for the semi-aquatic lichen Dermatocarpon luridum using spatial modelling and photobiont markers.

BACKGROUND: Landscape genetics is an interdisciplinary field that combines tools and techniques from population genetics with the spatially explicit principles from landscape ecology. Spatial variation in genotypes is used to test hypotheses about how landscape pattern affects dispersal in a wide range of taxa. Lichens, symbiotic associations between mycobionts and photobionts, are an entity for which little is known about their dispersal mechanism. Our objective was to infer the dispersal mechanism in the semi-aquatic lichen Dermatocarpon luridum using spatial models and the spatial variation of the photobiont, Diplosphaera chodatii. We sequenced the ITS rDNA and the ß-actin gene regions of the photobiont and mapped the haplotype spatial distribution in Payuk Lake. We subdivided Payuk Lake into subpopulations and applied four spatial models based on the topography and hydrology to infer the dispersal mechanism. RESULTS: Genetic variation corresponded with the topography of the lake and the net flow of water through the waterbody. A lack of isolation-by-distance suggests high gene flow or dispersal within the lake. We infer the dispersal mechanism in D. luridum could either be by wind and/or water based on the haplotype spatial distribution of its photobiont using the ITS rDNA and ß-actin markers. CONCLUSIONS: We inferred that the dispersal mechanism could be either wind and/or water dispersed due to the conflicting interpretations of our landscape hypotheses. This is the first study to use spatial modelling to infer dispersal in semi-aquatic lichens. The results of this study may help to understand lichen dispersal within aquatic landscapes, which can have implications in the conservation of rare or threatened lichens.

Stoichiometric distribution models: ecological stoichiometry at the landscape extent.

Human activities are altering the fundamental geography of biogeochemicals. Yet we lack an understanding of how the spatial patterns in organismal stoichiometry affect biogeochemical processes and the tools to predict the impacts of global changes on biogeochemical processes. In this contribution we develop stoichiometric distribution models (StDMs), which allow us to map spatial structure in resource elemental composition across a landscape and evaluate spatial responses of consumers. We parameterise StDMs for a consumer-resource (moose-white birch) system and demonstrate that we can develop predictive models of resource stoichiometry across a landscape and that such models could improve our predictions of consumer space use. With results from our study system application, we argue that explicit consideration of the spatial patterns in organismal elemental composition may uncover emergent individual, population, community and ecosystem properties that are not revealed at the local extents routinely used in ecological stoichiometry. We discuss perspectives for further developments and application of StDMs to advance three emerging frameworks for spatial ecosystem ecology in an era of global change; meta-ecosystem theory, macroecological stoichiometry and remotely sensed biogeochemistry. Progress on these emerging frameworks will allow for the integration of ecological stoichiometry and individual space use and fitness.

Assessing post-industrial land cover change at the Pine Point Mine, NWT, Canada using multi-temporal Landsat analysis and landscape metrics.

This study investigates land cover change near the abandoned Pine Point Mine in Canada's Northwest Territories. Industrial mineral development transforms local environments, and the effects of such disturbances are often long-lasting, particularly in subarctic, boreal environments where vegetation conversion can take decades. Located in the Boreal Plains Ecozone, the Pine Point Mine was an extensive open pit operation that underwent little reclamation when it shut down in 1988. We apply remote sensing and landscape ecology methods to quantify land cover change in the 20 years following the mine's closure. Using a time series of near-anniversary Landsat images, we performed a supervised classification to differentiate seven land cover classes. We used raster algebra and landscape metrics to track changes in land cover composition and configuration in the 20 years since the mine shut down. We compared our results with a site in Wood Buffalo National Park that was never subjected to extensive anthropogenic disturbance. This space-for-time substitution provided an analog for how the ecosystem in the Pine Point region might have developed in the absence of industrial mineral development. We found that the dense conifer class was dominant in the park and exhibited larger and more contiguous patches than at the mine site. Bare land at the mine site showed little conversion through time. While the combination of raster algebra and landscape metrics allowed us to track broad changes in land cover composition and configuration, improved access to affordable, high-resolution imagery is necessary to effectively monitor land cover dynamics at abandoned mines.

Ecoregion and community structure influences on the foliar elemental niche of balsam fir (Abies balsamea (L.) Mill.) and white birch (Betula papyrifera Marshall).

Changes in foliar elemental niche properties, defined by axes of carbon (C), nitrogen (N), and phosphorus (P) concentrations, reflect how species allocate resources under different environmental conditions. For instance, elemental niches may differ in response to large-scale latitudinal temperature and precipitation regimes that occur between ecoregions and small-scale differences in nutrient dynamics based on species co-occurrences at a community level. At a species level, we compared foliar elemental niche hypervolumes for balsam fir (Abies balsamea (L.) Mill.) and white birch (Betula papyrifera Marshall) between a northern and southern ecoregion. At a community level, we grouped our focal species using plot data into conspecific (i.e., only one focal species is present) and heterospecific groups (i.e., both focal species are present) and compared their foliar elemental concentrations under these community conditions across, within, and between these ecoregions. Between ecoregions at the species and community level, we expected niche hypervolumes to be different and driven by regional biophysical effects on foliar N and P concentrations. At the community level, we expected niche hypervolume displacement and expansion patterns for fir and birch, respectively-patterns that reflect their resource strategy. At the species level, foliar elemental niche hypervolumes between ecoregions differed significantly for fir (F = 14.591, p-value = .001) and birch (F = 75.998, p-value = .001) with higher foliar N and P in the northern ecoregion. At the community level, across ecoregions, the foliar elemental niche hypervolume of birch differed significantly between heterospecific and conspecific groups (F = 4.075, p-value = .021) but not for fir. However, both species displayed niche expansion patterns, indicated by niche hypervolume increases of 35.49% for fir and 68.92% for birch. Within the northern ecoregion, heterospecific conditions elicited niche expansion responses, indicated by niche hypervolume increases for fir of 29.04% and birch of 66.48%. In the southern ecoregion, we observed a contraction response for birch (niche hypervolume decreased by 3.66%) and no changes for fir niche hypervolume. Conspecific niche hypervolume comparisons between ecoregions yielded significant differences for fir and birch (F = 7.581, p-value = .005 and F = 8.038, p-value = .001) as did heterospecific comparisons (F = 6.943, p-value = .004, and F = 68.702, p-value = .001, respectively). Our results suggest species may exhibit biogeographical specific elemental niches-driven by biophysical differences such as those used to describe ecoregion characteristics. We also demonstrate how a species resource strategy may inform niche shift patterns in response to different community settings. Our study highlights how biogeographical differences may influence foliar elemental traits and how this may link to concepts of ecosystem and landscape functionality.

Herbivore Impacts on Carbon Cycling in Boreal Forests.

Large herbivores can have substantial effects on carbon (C) cycling, yet these animals are often overlooked in C budgets. Zoogeochemical effects may be particularly important in boreal forests, where diverse human activities are facilitating the expansion of large herbivore populations. Here, we argue that considering trophic dynamics is necessary to understand spatiotemporal variability in boreal forest C budgets. We propose a research agenda to scale local studies to landscape extents to measure the zoogeochemical impacts of large herbivores on boreal forest C cycling. Distributed networks of exclosure experiments, empirical studies across gradients in large herbivore abundance, multiscale models using herbivore distribution data, and remote sensing paired with empirical data will provide comprehensive accounting of C source-sink dynamics in boreal forests.