Ecosphere

Plant invasions often lead to homogenization of the plant community, but the potential for plant invasions to cause homogenization of other trophic levels is under-studied in many systems. We tested whether the bird community in Phragmites australis-invaded marsh would exhibit spatial and temporal taxonomic homogenization compared to remnant cattail and meadow marsh. We compared the bird community using marsh invaded by P. australis and remnant, uninvaded marsh vegetation in a year with average water depths and a year with above-average water depths in the coastal marshes of a World Biosphere Reserve. Our results demonstrate strong evidence for spatial and temporal homogenization of the wetland bird community following P. australis invasion. The birds present in P. australis-invaded marsh were a nested subset of those present in remnant marsh, and total beta diversity decreased when water depths were above average. In contrast, total beta diversity was high in remnant marsh vegetation and stable between the two years. The distinctively structured vegetation zones in remnant (uninvaded) marsh yields structural complexity and habitat heterogeneity that supports greater taxonomic turnover in the bird community. Our study provides evidence that invasion by a plant has resulted in biological homogenization of the wetland bird community.

Grazing lawns are important food sources in nutrient poor savannas for free-roaming mammalian herbivores. It has been hypothesized that increased grazing pressure by mammalian herbivores can create and maintain patches of lawn grass. We tested whether the application of specific nutrients, nitrogen (N), phosphorus (P) or in combination with calcitic and dolomitic lime (Ca), in a nutrient poor African savanna, would make the grass sward more nutrient rich, which would attract mammalian herbivores to graze more frequently. We investigated the grazing patterns of six species of mammalian herbivores, namely, blue wildebeest (Connochaetes taurinus), Burchells zebra (Equus quagga burchellii), common eland (Taurotragus oryx), impala (Aepyceros melampus), square-lipped rhinoceros (Ceratotherium simum) and warthog (Phacochoerus africanus). We show that the addition of N attracts and increases the grazing pressure for three of the herbivore species, namely, blue wildebeest, Burchells zebra and impala. Our findings suggest that these often abundantly present mammalian herbivores with intermediate body mass, attracted to grazing lawns by the addition of N, can maintain grazing lawns. Conservation implicationsArtificial fertilization with nitrogen attracts large free-roaming herbivore species to localized grazing lawns, stimulating the creation and expansion of high nutrient quality lawn grasses in nutrient poor savannas. This results in a nutrient high food source which would normally not be available in nutrient poor savannas.

Over the last several decades, peat has been extracted from bogs of temperate, populated regions of Eastern Canada, leaving large areas devoid of vegetation if unrestored. For the last 25 years, projects have been conducted in these regions to re-establish vegetation and facilitate recolonization by wildlife. We tested whether vegetation structure and bird species assemblages 10 to 20 years post extraction differ among natural, unrestored and restored bogs at the scales of individual sites and entire bogs. We conducted bird counts and vegetation surveys between 1993 and 2019, using both point counts (309 sites) and Autonomous Recording Units (80 sites). According to our vegetation surveys, restoration of sites that were previously used for peat harvesting accelerated the establishment of Sphagnum and herbaceous strata, but ericaceous and tree strata were unaffected over a 17-year period. None of the bird species with large home ranges were associated specifically to natural, unrestored, or restored areas at the bog level. Bird species diversity was similar in restored and natural sites, but lower in unrestored sites. Alder Flycatcher and American Goldfinch occupied restored and unrestored sites more frequently than natural sites, independent of the number of years post extraction. Occupancy of restored sites by Palm and Yellow-rumped Warblers increased over the years, reaching levels similar to those in natural sites 20 years after restoration was implemented. Occupancy of restored sites by Song and Savannah sparrows increased from 1993-2019 and diverged from their declining occupancy of natural sites. Species assemblages of restored and unrestored sites differed significantly from those of natural sites soon after peat extraction ceased or post restoration. But assemblages from restored and unrestored sites became progressively similar to those of natural sites during the first 20 years, especially in restored sites. We conclude that bird species assemblages of restored bog sites are converging toward those of natural sites, and that restoration provides novel habitats for regionally declining species, e.g., Savannah Sparrows.

In recent decades, fish ecologists have become increasingly aware of the need for spatially comprehensive sampling. However, a corresponding reflection on the temporal aspects of research has been lacking. We quantified the seasonal timing and extent of freshwater fish research. Since reviewing all prior work was not feasible, we considered two different subsets. First, we compiled the last 30 years of ecological research on juvenile Pacific salmon and trout (Oncorhynchus spp.) (n = 371 studies). In addition to the aggregate, we compared groups classified by subject matter. Next, to evaluate whether riverscape ecology has embraced space at the expense of time, we compiled research across taxa in which fish were enumerated in a spatially continuous fashion (n = 46). We found that ecological Oncorhynchus spp. research was biased towards summer (40% occurred during June-August) and the month of June in particular, at the expense of winter work (only 13% occurred during December-February). Riverscape studies were also biased toward summer (47% of studies) and against winter (11%). It was less common for studies to encompass multiple seasons (43% of ecological Oncorhynchus spp. studies and 54% of riverscape studies) and most were shorter than 4 months (73% of ecological Oncorhynchus spp. studies and 81% of riverscape studies). These temporal biases may cause researchers to overemphasize ecological phenomena observed during summer and limit our ability to recognize seasonal interactions such as carry-over effects or compensatory responses. Full year and winter studies likely hold valuable insights for conservation and management.

BackgroundNon-random species co-occurrence is of fundamental interest to ecologists. One approach to analysing non-random patterns is null modelling. This involves calculation of a metric for the observed dataset, and comparison to a distribution obtained by repeatedly randomising the data. Choice of randomisation algorithm, specifically whether null model species richness is fixed at that of the observed dataset, is likely to affect model results. This is particularly important in cases when there is high variation in species richness between sampling units in the observed data. MethodsHere I demonstrate the effects of accounting for variation in species richness. I use the C-score, a metric measuring species segregation as "checkerboard units", applied to 289 datasets. First, I run null models in which sites are equally likely to be occupied (fixed-equiprobable algorithm). I do this both for the original datasets, and for the same datasets where occurrences are randomised with the species richness distribution fixed (pre-randomised datasets). Second, I run null models that fix site species richness to that observed (fixed-fixed algorithm). ResultsFor real datasets, using the fixed-equiprobable algorithm (sites are equally likely to be colonised), C-score standardised effect size (SES) was positively related to variability in species richness between sites within a dataset. This effect was also found for pre-randomised datasets, indicating that variability in species richness can be exclusively responsible for detection of non-random species co-occurrence. When using the fixed-fixed algorithm (richness is constrained to that of real sites), there was no relationship between SES and variability in species richness. There was also a reverse in the effect direction, with 94% of significant tests indicating a lower C-score than expected for the fixed-equiprobable algorithm, but 98% of significant tests indicating a higher C-score than expected for the fixed-fixed algorithm. DiscussionI speculate that when variation in species richness is high, fewer checkerboard units are possible, regardless of segregation between species. Therefore, use of fixed-equiprobable algorithms in situations where real species richness is highly variable between sites within a dataset will yield significant results, even if species co-occur randomly within the constraints of the species richness distribution. Consequently, use of such tests makes the a priori assumption that high within-dataset variation in species richness indicates non-random species co-occurrence. I recommend using algorithms that explicitly take into account species richness distributions when one wants to eliminate the effect of richness variation in terms of producing significant but spurious positive co-occurrence results. Alternatively, non-null mechanistic models can be created, in which hypothesised species assembly processes must be explicitly stated and tested.

BackgroundAcross a variety of anthropogenic and natural contexts, fire can reoccur in a previously burned location. However, effects of subsequent fire on preexisting pyrogenic organic matter (PyOM) stocks are difficult to discern. Laboratory experiments offer a powerful approach to investigating how subsequent fire impacts the preexisting PyOM. AimsWe aimed to design a highly repeatable laboratory method to effectively measure the impacts of subsequent fires on PyOM at different soil depths while addressing key limitations of previous methods. MethodsJack pine (Pinus banksiana Lamb.) log burns were used to parameterize realistic heat flux profiles. Using a cone calorimeter, these profiles were applied to buried jack pine PyOM to simulate variable reburn fire intensities. Key resultsIn general, higher heat flux and shallower depths led to more mass loss of PyOM from combustion and more heat exposure. ConclusionsOur reburn method offers a highly replicable way to simulate specific fire scenarios. Conditions that result in more heat exposure (higher heat fluxes, shallower depths) are likely to lead to more loss of PyOM in subsequent fires. ImplicationsThe customizable method could simulate different fire scenarios to investigate spatial variability within a given fire event, or to study the effects of fire on different types of biomass or organisms, such as microbes. Summary textOur paper illustrates a laboratory method to better quantify loss of preexisting PyOM in soil after a fire. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/605814v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@10e9104org.highwire.dtl.DTLVardef@152cb49org.highwire.dtl.DTLVardef@a04c41org.highwire.dtl.DTLVardef@1ee543d_HPS_FORMAT_FIGEXP M_FIG C_FIG

The U.S. Fish and Wildlife Service monitors species-specific waterfowl (ducks, seaducks, geese, and brant) harvest through two hunter surveys, one that estimates the total harvest for each waterfowl group, and a second that estimates the species composition of each waterfowl group. Point estimates for species-specific harvest can be computed by multiplying the estimated total harvest by the estimated proportion of the total harvest of each species. However, to date, no uncertainty estimates have been available. Here, we combine these two data sources to provide species-specific harvest estimates at the state and flyway level while characterizing the uncertainty via Bayesian estimation. We take a similar approach to Smith et al. (2022), providing both estimates that treat yearly data as independent and estimates that share information across years via a random walk process. We then discuss the advantages and disadvantages of each approach.

Our understanding of soil microarthropod (Acari and Collembola) community assembly and dynamics is somewhat limited compared to aboveground communities. Understanding the processes involved in assembly and the spatial scales at which they occur would help answer the age old question of how so many species and individuals can coexist in soil. We use a microcosm experiment using intact soil cores to explore the processes of selection and dispersal taking place at the micro-spatial scale. We do this by manipulating available pore space and population density, which allows us to indirectly investigate the role of dispersal and biotic interactions in shaping microarthropod community dynamics. Results suggest that there are processes limiting abundance and that communities are sometimes held at abundances below those which the environment could accommodate by abiotic factors. Food and space did not appear to drive the observed patterns; however, findings suggest that abiotic factors may influence dynamics in the field.

Species are shifting their ranges in response to climate change. There remain many unknowns about relative impacts of range-expanding ecosystem engineers between historical and expanded habitats, however. The mud fiddler crab Minuca pugnax (=Uca pugnax) is shifting its range northward likely due to increased warming in the Gulf of Maine. A burrowing crab, M. pugnax affects ecosystem functioning in salt marshes south of Cape Cod, Massachusetts with unknown effects in expanded marsh habitats over 150km to the north. We therefore studied the M. pugnax range expansion to determine the extent that range expanding ecosystem engineers are influencing ecosystem functioning expanded ranges relative to historical habitats. We installed in 2017 and 2018 a series of crab-inclusion cages at both the UMass Boston Nantucket Field Station (historical range) and the Plum Island Estuary Long Term Ecological Research site (PIE-LTER, expanded range). For each site, year, and block, we measured in the beginning and end of the three-month experiment metrics of sediment strength, primary production, and decomposition. We developed and tested causal models using structural equation modeling (SEM) to determine direct and indirect effects of fiddler crabs on ecosystem functions. Despite site, year, and block variability, local environment influenced burrow density, which directly affected sediment strength and indirectly affected primary production in both ranges. Overall, understanding range-expanding ecosystem engineers in historical ranges was predictive for how they influence expanded habitats, despite inter-site heterogeneity. Therefore, it is critical to study relative impacts of range-expanding ecosystem engineers to understand total impacts of global range shifts.

There is an increasing need to move beyond evaluating the effect of land use on stream communities by only studying local variables, and instead incorporate a metacommunity perspective which integrates environmental and spatial factors across larger spatial scales. The use of molecular tools (DNA metabarcoding) to identify bioindicator groups, such as aquatic macroinvertebrates, can provide greater taxonomic resolution to explore patterns in stream metacommunities. In this study, we collected aquatic macroinvertebrates from streams in southern Ontario which spanned a gradient of agricultural disturbance and used DNA metabarcoding to identify the species composition from these samples. We address a significant knowledge gap in previous stream aquatic macroinvertebrate metacommunity studies by incorporating molecular identification as well as a temporal component. We observed that a combination of local habitat conditions, regional agricultural land use, and spatial position influenced aquatic macroinvertebrate community composition, suggesting there is an interaction between environmental filtering and dispersal processes that structures these communities. However, aquatic macroinvertebrate communities were also highly dissimilar between streams and composed of many rare species, and a large percentage of unexplained variation suggests that there is a strong stochastic component to community assembly. We also observed that there is a seasonal component to metacommunity dynamics, with different water quality variables being significant to community composition in each sampling month. While we expected that an increased percentage of surrounding agricultural land use would result in more homogenous macroinvertebrate communities, we only detected this relationship in May and found evidence that a larger riparian buffer width can mitigate the effects of agricultural land use. We demonstrate the utility of DNA metabarcoding for revealing patterns in metacommunity dynamics that may not be detectable using coarse taxonomic identifications, and reveal the importance of incorporating a seasonal component when evaluating the influence of land use on community composition.

Previous research has shown that host diversity and heterogeneity promote parasite abundance and heterogeneity by creating additional niches for parasites to occupy. Central Alberta, Canada, sees a diverse array of native and migratory species each year. A previous snail-trematode survey conducted at six lakes in central Alberta from 2013-2015 uncovered 79 trematode species. However, analyses suggested that additional species remained to be uncovered. To build on this baseline, we conducted further snail-trematode collections from 2019 to 2022 at eight reclaimed wetland sites in various stages of reclamation, along with one established lake in Alberta. Across the nine sites, we collected 22,397 snails, of which 1,981 were infected with digenean trematodes. We also documented broader biodiversity at these sites using traditional survey techniques. Through DNA barcoding, we identified 74 trematode species infecting five snail species. Among these were 23 trematode species not previously reported in central Alberta and nine putative novel species. In addition, we observed several previously unreported snail-trematode interactions. While trematode richness did not vary significantly with the wetland reclamation stage, host identity did influence richness: Physa gyrina hosted significantly more trematode species than Planorbella trivolvis. When combined with data from the earlier survey, sample completeness analyses indicate that we captured 100% of the dominant species and 99% of the typical species, but only 63% of the overall species diversity in central Alberta. These findings underscore that trematode diversity in central Alberta remains underestimated and highlight the continued value of long-term and host-inclusive sampling efforts.

Trophic cascades, or indirect effects of predators on non-adjacent lower trophic levels, have become paradigmatic in ecology, though they are thought to be stronger in aquatic ecosystems. Most research on freshwater trophic cascades focused on temperate lakes, where fish are present and where Daphnia tend to dominate the zooplankton community. These studies identified that Daphnia often play a key role in facilitating trophic cascades by linking fish to algae with strong food web interactions. However, Daphnia are rare or absent in most tropical and subtropical lowland freshwaters, and fish are absent from small and temporary water bodies, where invertebrates fill the role of top predator. While invertebrate predators are ubiquitous in freshwater systems, most have received little attention in food web research. Therefore, we aimed to test whether trophic cascades are possible in small warmwater ponds where small invertebrates are the top predators and Daphnia are absent. We collected naturally occurring plankton communities from small fishless water bodies in central Texas and propagated them in replicate pond mesocosms. We removed zooplankton from some mesocosms, left the plankton community intact in others, and added one of two densities of the predaceous insect Neoplea striola to others. Following an incubation period we then compared biomasses of plankton groups to assess food web effects between the trophic levels including whether Neoplea caused a trophic cascade by reducing zooplankton. The zooplankton community became dominated by copepods which prefer large phytoplankton and exhibit a fast escape response. Perhaps due to these qualities of the copepods and perhaps due to slow consumption rates by Neoplea on key grazers, no evidence for food web effects were found other than somewhat weak evidence for zooplankton reducing large phytoplankton. More research is needed to understand the behavior and ecology of Neoplea, but trophic cascades may generally be weak or absent in fishless low-latitude lowland water bodies where Daphnia are rare.

Wetland ecosystems are known for their carbon storage potential due to slow decomposition rates and high carbon fixation rates. However, nutrient addition from human activities affects this carbon storage capacity as the balance of fixed and respired carbon shifts due to plant and microbial communities. Ongoing atmospheric deposition of nutrients could be changing wetland plant-microbe interactions in ways that tip the balance from carbon storage to loss. Therefore, examining microbial community patterns in response to nutrient enrichment is important to understanding nutrient effects on carbon storage potential. In this study, we hypothesized that fertilization of a low nutrient ecosystem leads to increased organic carbon input from plant biomass into the soil and results in increased soil bacterial diversity and modifications to soil bacterial community composition. As such, increased soil nutrients and carbon resources provide more energy to support increased microbial growth rates, which can result in wetland carbon losses. To test this hypothesis, we used bacterial community-level and soil chemical data from the long-term wetland ecology experiment at East Carolina Universitys West Research Campus (established in 2003). Specifically, we examined the extent that long-term effects of nutrient enrichment affect wetland microbial communities and plant biomass, which are factors that can affect carbon storage. We collected soil cores from fertilized and unfertilized test plots. We extracted genomic DNA from soil samples and conducted 16S rRNA targeted amplicon sequencing to characterize the bacterial community composition. In addition, we measured plant above and belowground biomass and soil carbon content. Results revealed an increase in aboveground plant biomass, soil carbon, and bacterial diversity. In contrast, belowground plant biomass and microbial biomass were similar in fertilized and unfertilized plots. To further examine bacterial community changes to nutrient enrichment, we compared the relative abundance of fast growing copiotrophic and slow growing oligotrophic bacteria of a subset of taxa putatively identified as belonging to either life history strategy. These taxa-level results revealed a decrease in oligotroph relative abundance and little to no change in copiotroph relative abundance of a subset of bacterial taxa. If there is a community-wide shift in the proportion of oligotroph to copiotroph life history strategies, this would have a negative impact on organic carbon storage since oligotrophic bacteria respire less carbon than copiotrophic bacteria over the same amount of time. Taken together, this study provided evidence that long-term nutrient enrichment influences wetland soils in ways that decrease their carbon storage potential of important carbon sinks.

Decadal changes in abundance of marine organisms along the Australian coastline were reported in a recent Nature paper by Edgar et al. (2023). We reexamine the data used in that paper, and show that the conclusion of a 59% decline in weedy seadragons (Phyllopteryx taeniolatus) cannot be justified based on these data. The data are too sparse, especially for the final survey years of 2020 and 2021, and it is this sparsity in combination with particular modelling choices made by Edgar et al. (2023) that drives their results. While not specifically considered here, it is likely that these issues also affect the results on numerous other species reported in Edgar et al. (2023).

Plants can cultivate soil microbial communities that affect subsequent plant growth through a plant-soil feedback (PSF). Strong evidence indicates that PSFs can mediate the invasive success of exotic upland plants, but many of the most invasive plants occur in wetlands. In North America, the rapid spread of European Phragmites australis cannot be attributed to innate physiological advantages, thus PSFs may mediate invasion. Here we apply a two-phase fully-factorial plant-soil feedback design in which field-derived soil inocula were conditioned using saltmarsh plants and then were added to sterile soil mesocosms and planted with each plant type. This design allowed us to assess complete soil biota effects on intraspecific PSFs between native and introduced P. australis as well as heterospecific feedbacks between P. australis and the native wetland grass, Spartina patens. Our results demonstrate that native P. australis experienced negative conspecific feedbacks while introduced P. australis experienced neutral conspecific feedbacks. Interestingly, S. patens soil inocula inhibited growth in both lineages of P. australis while introduced and native P. australis inocula promoted the growth of S. patens suggestive of biotic resistance against P. australis invasion by S. patens. Our findings suggest that PSFs are not directly promoting the invasion of introduced P. australis in North America. Furthermore, native plants like S. patens seem to exhibit soil microbe mediated biotic resistance to invasion which highlights the importance of disturbance in mediating introduced P. australis invasion.

Indicator species are typically used to infer the presence of other biota or specific environmental conditions. Here we use indicator species to quantify the hydrological niche of their corresponding vegetation communities within Coastal Upland Swamps of the Sydney Basin Bioregion, Australia. Swamp vegetation organizes naturally into five recognised communities, thought to occupy distinct positions along a hydrological gradient. However, longwall mining reduces hydro-period, potentially impacting the observed vegetation. We modelled the hydrological niche for each community using the relative frequency of 20 vascular plant indicator species (four for each community) and time series soil moisture data from 11 unmined sites across four swamps. We then used this model to predict indicator species frequencies in 3 mine-impacted sites. Indicator species were modelled as a function of the average number of days-per-year that swamps remained saturated at the base of the root zone (30 cm below surface). Hydrological niches were well differentiated for four communities with the estimated optimal mean annual days-per-year saturated ranging from Restioid heath at 16 [<16, 29] (mean {+/-} [95% uncertainty]) to Ti-tree thicket at 352 [322, >353]. Banksia thicket 96 [65, 154] and Cyperoid heath 257 [204, 297] communities were intermediate. However, Sedgeland indicator species showed limited variation with changing saturation, and their hydrological niche remains unclear. The model under-predicted the frequency of Cyperoid heath and over-predicted Banksia thicket indicator species in mine-impacted sites, suggesting vegetation is not yet in equilibrium with hydrology. Results suggest indicator species can provide a reliable basis for determining the hydrological niche of wetland plant communities, which can in turn predict community-level impacts of hydrological change.

Many shorebird species are rapidly declining (Piersma et al. 2016; Munro 2017; Studds et al. 2017), but it is not always clear why. Deteriorating and disappearing habitat, e.g. due to intensive agriculture (Donal et al. 2001; Kentie et al. 2013; Kentie et al. 2018), river regulation (Nebel et al. 2008) or mudflat reclamation (Ma et al. 2014; Larson 2017), and hunting (Reed et al. 2018; Gallo-Cajiao et al. 2020) are some of the documented causes. A recent study suggests yet another possible cause of shorebird decline: a global increase in nest predation (Kubelka et al. 2018). The authors compiled an impressive dataset on patterns of nest predation in shorebirds and their analyses suggest that global patterns of nest predation have been disrupted by climate change, particularly in the Arctic. They go as far as to conclude that the Arctic might have become an ecological trap (Kubelka et al. 2018). Because these findings might have far-reaching consequences for conservation and related political decisions, we scrutinized the study and concluded that the main conclusions of Kubelka et al. (2018) are invalid (Bulla et al. 2019a). The authors then responded by reaffirming their conclusions (Kubelka et al. 2019b). Here, we evaluate some of Kubelka et al.s (2019b) responses, including their recent erratum (2020), and show that the main concerns about the original study still hold. Specifically, (1) we reaffirm that Kubelka et al.s (2018) original findings are confounded by study site. Hence, their conclusions are over-confident because of pseudo-replication. (2) We reiterate that there is no statistical support for the assertion that predation rate has changed in a different way in the Arctic compared to other regions. The relevant test is an interaction between a measure of time (year or period) and a measure of geography (e.g., Arctic vs the rest of the world). The effect of such an interaction is weak, uncertain and statistically non-significant, which undermines Kubelka et al.s (2018) key conclusion. (3) We further confirm that the suggested general increase in predation rates over time is at best a weak and uncertain trend. The most parsimonious hypothesis for the described results is that the temporal changes in predation rate are an artefact of temporal changes in methodology and data quality. Using only high-quality data, i.e. directly calculated predation rates, reveals no overall temporal trend in predation rate. Below we elaborate in detail on each of these points. We conclude that (i) there is no evidence whatsoever that the pattern in the Arctic is different from that in the rest of the world and (ii) there is no solid evidence for an increase in predation rate over time. While we commend Kubelka et al. for compiling and exploring the data, we posit that the data underlying their study, and perhaps all currently available data, are not sufficient (or of sufficient quality) to test their main hypotheses. We call for standardized and consistent data collection protocols and experimental validation of current methods for estimating nesting success.

O_LINitrogen (N) is limiting for terrestrial herbivores, particularly over winter. Caribou (Rangifer tarandus) have adapted to seasonal scarcity of N by accruing muscle mass during the growing season when N is more abundant. C_LIO_LINitrogen stored in muscle tissue is then relied upon during winter to compensate for dietary deficits. Once their diet shifts from N-rich vascular plants to N-poor lichen over winter, caribou can lose [~]30% of their muscle mass. As catabolized N is shed in urine on wintering grounds, caribou could act as elemental transport across seasons and landscapes. Furthermore, if deposited N is taken up by lichen or other winter forage, it might enrich the nitrogen-poor winter diet of caribou in the future. C_LIO_LIWe tested this potential transport via three steps. We analysed Cladonia spp. lichen and vascular plants upon which caribou forage across Fogo Island, Newfoundland, using %N content as our metric of forage quality. We then compared seasonal habitat selection responses to forage quality by caribou using integrated step selection analyses. In summer, caribou selected areas with higher vascular plant %N but did not select nor avoid Cladonia quality. In contrast, caribou selected sites with higher quality Cladonia in winter but responded neutrally to vascular plant quality. C_LIO_LIWe compared seasonal distributions of caribou to determine whether nitrogen consumed in summer and deposited in winter would occur in spatially discrete locations. Population-level kernel density estimates for summer and winter in this island herd were mostly non-overlapping, lending credence to the potential landscape effects of N transport. C_LIO_LIWhen viewed together with established seasonal changes in woodland caribou physiology, sociality, and forage preferences, the shifts in habitat selection and seasonal ranges we observe here could serve as an adaptive strategy for caribou to recycle N and mitigate winter nutrient scarcity. C_LI

Abundance and distribution of earthworms in agricultural fields is frequently proposed as a measure of soil quality assuming that observed patterns of abundance are in response to improved or degraded environmental conditions. However, it is not clear that earthworm abundances can be directly related to their edaphic environment, as noted in Darwins final publication, perhaps limiting or restricting their value as indicators of ecological quality in any given field. We present results from a spatially explicit intensive survey of pastures within United Kingdom farms, looking for the main drivers of earthworm density at a range of scales. When describing spatial variability of earthworm abundance within any given field, the best predictor was earthworm abundance itself within 20 - 30 m of the sampling point; there were no consistent environmental correlates with earthworm numbers, suggesting that biological factors (e.g. colonisation rate, competition, predation, parasitism) drive or at least significantly modify earthworm distributions at this spatial level. However, at the national scale, earthworm abundance is well predicted by soil nitrate levels, density, temperature and moisture content, albeit not in a simple linear fashion. This suggests that although land can be managed at the farm scale to promote earthworm abundance and the resulting soil processes that deliver ecosystem services, within a field, earthworm distributions will remain patchy. The divergence in the interpretative value of earthworm abundance as an ecological indicator is a function of spatial scale, corresponding to species specific biological factors as well as a response to environmental pressures. Species abundance can effectively be used as ecological indicators, even if, at first, distributions seem random. However, care must be exercised, in the sampling design for the indicator species, if its abundance is to be used as a proxy for environmental quality at a particular scale (e.g. a management scale such as field scale).

Ants are vital ecosystem engineers that can influence soil properties, subsequent soil processes, and associated biota via underground nest construction. Harvester ants consume seeds and are often found in arid areas, frequently altering soil chemistry and bulk density of the soils in and around their nest sites. Many species of harvester ants also intentionally remove vegetation around nest openings, creating cones or discs of bare soil that may further alter soil temperatures. However, much of the work investigating the impacts of harvester ants on soil properties has occurred in shrubland and grassland settings rather than suburban environments. We aimed to determine if Pogonomyrmex barbatus (Smith) (Hymenoptera: Formicidae) nests in a suburban habitat in the Lower Rio Grande Valley in Texas similarly altered soil properties. First, we measured active nest disc size to determine changes and colony persistence. Then we assessed soil compaction and surface temperature along a gradient centered on the disc. We found that disc size did not increase throughout the two-year observation period and that nests with smaller discs were less likely to persist between years. While we did not observe any changes in surface temperature across the gradient, we found a significant increase in soil compaction with greater distance from the center of the disc. These data indicate that increased nest size increases the extent of soil impacted. The impacts of nests reducing soil compaction, particularly within a suburban landscape with precipitation run-off issues and a highly disturbed plant community should be addressed in future studies.