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International audience; It has been argued that the mechanisms structuring ecological communities may be more generalizable when based on traits than on species identities. If so, patterns in the assembly of community-level traits along environmental gradients should be similar in different places in the world. Alternatively, geographical change in the species pool and regional variation in climate might result in site-specific relationships between community traits and local environments. These competing hypotheses are particularly untested for animal communities. Here we test the geographical constancy of trait-based assembly patterns using a widespread multi-trophic community: aquatic macroinvertebrates within bromeliads. We used data on 615 invertebrate taxa from 1,656 bromeliads in 26 field sites from Mexico to Argentina. We summarized invertebrate traits with four orthogonal axes, and used these trait axes to examine trait convergence and divergence assembly patterns along three environmental gradients: detrital biomass and water volume in bromeliads, and canopy cover over bromeliads. We found no overall signal of trait-based assembly patterns along any of the environmental gradients. However, individual sites did show trait convergence along detrital and water gradients, and we built predictive models to explore these site differences. Sites that showed trait convergence along detrital gradients were all north of the Northern Andes. This geographical pattern may be related to phylogeographical differences in bromeliad morphology. Bromeliads with low detritus were dominated by detritivorous collectors and filter feeders, where those with high detritus had more sclerotized and predatory invertebrates. Sites that showed the strongest trait convergence along gradients in bromeliad water were in regions with seasonal precipitation. In such sites, bromeliads with low water were dominated by soft-bodied, benthic invertebrates with simple life cycles. In less seasonal sites, traits associated with short-term desiccation resistance, such as hard exoskeletons, were more important. In summary, we show that there are strong geographical effects on the trait-based assembly patterns of this invertebrate community, driven by the biogeography of their foundational plant species as well as by regional climate. We suggest that inclusion of biogeography and climate in trait-based community ecology could help make it a truly general theory.

Humans are modifying the availability of nutrients such as nitrogen (N) and phosphorus (P), and it is therefore important to understand how these nutrients, independently or in combination, influence the growth and nutrient content of primary producers. Using meta-analysis of 118 field and laboratory experiments in freshwater, marine and terrestrial ecosystems, we tested hypotheses about co-limitation of N and P by comparing the effects of adding N alone, P alone, and both N and P together on internal N (e.g. %N, C:N) and P (e.g. %P, C:P) concentrations in autotroph communities. In particular, we tested the following predictions. First, if only one nutrient was limiting, addition of that nutrient should decrease the concentration of the other nutrient, but addition of the non-limiting nutrient would have no effect on the internal concentration of the limiting nutrient. If community co-limitation was occurring then addition of either nutrient should result in a decrease in the internal concentration of the other nutrient. Community co-limitation could also result in no change – or even an increase – in N concentrations in response to P addition if P stimulated growth of N fixers. Finally, if biochemically dependent co-limitation was occurring, addition of a limiting nutrient would not decrease, and could even increase, the concentration of the other, co-limited nutrient. We found no general evidence for the decrease in the internal concentration of one nutrient due to addition of another nutrient. The one exception to this overall pattern was marine systems, where N addition decreased internal P concentrations. In contrast, P addition increased internal N concentrations across all experiments, consistent with co-limitation. These results have important implications for understanding the roles that N and P play in controlling producer growth and internal nutrient accumulation as well as for managing the effects of nutrient enrichment in ecosystems. Synthesis On a global scale, humans have doubled nitrogen (N) inputs and quadrupled phosphorus (P) inputs relative to pre-industrial levels. N and P fertilization influences autotroph internal nutrient concentrations and ratios and thereby affects a variety of community and ecosystem processes, including decomposition and consumer population dynamics. It is therefore critical to understand the effects of nutrient additions on the growth and nutrient concentrations of primary producers. We used meta-analysis to evaluate the responses of autotroph internal N and P concentrations to additions of N, P, and N+P and make inferences about limitation and co-limitation of N and P across marine, terrestrial, and freshwater ecosystems. We found little evidence for single-nutrient limitation, highlighting the fact that multiple nutrients generally limit primary production.

Synthesis The tissue chemistry of plants can influence ecosystem processes including growth, herbivory, and decomposition. Our comparison of nitrogen and phosphorus in over 1700 autotroph taxa demonstrates that latitudinal trends in tissue chemistry are consistent across non-vascular and vascular species in freshwater, terrestrial, and marine ecosystems. Tissue chemistry varies most within species and taxonomic lineages, yet the nitrogen to phosphorus ratio within individuals is strikingly similar among species in different ecosystems. These results shed new light on existing hypotheses, suggesting that light (e.g. photon flux) and growing season duration are primary drivers of latitudinal gradients in tissue chemistry, but providing little support for temperature, nutrient supply, or soil substrate age. Photoautotroph nitrogen (N) and phosphorus (P) tissue concentrations can influence ecosystem function via processes including growth, decomposition, and consumption, and may reflect traits maintaining coexistence. Studies in terrestrial systems have led to hypotheses that latitudinal trends in the N and P content of leaves may be driven by soil substrate age, environmental temperature, or season length; however, terrestrial patterns alone cannot differentiate these mechanisms. Here, we demonstrate that broad geographical patterns of N and P in freshwater and marine multicellular photoautotrophs are concordant with those in terrestrial ecosystems. Our > 6800 record database reveals that mean tissue N and P increase with latitude in all ecosystems, but P increases more rapidly, causing N:P to decline; mean N:P scaling within individuals also is identical among systems, despite very different evolutionary environments. A partitioning of the variance in these data suggests that species composition and local environmental context likely lead to the variation observed within a latitudinal band. However, the consistency of trends in photosynthetic tissue chemistry across Earth’s ecosystems suggests that biogeographical gradients in insolation and growing season length may constrain tissue N and P, whereas global trends in temperature, nutrient supply, and soil substrate age are unlikely to generate the consistent latitudinal trends among ecosystems. Thus, this cross-ecosystem comparison suggests a new hypothesis, global patterns of insolation, while also providing a new perspective on other mechanisms that have been hypothesized to underlie latitudinal trends in photosynthetic tissue chemistry.

Category: Ankle Arthritis Introduction/Purpose: As an alternative to ankle replacement, ankle arthrodesis remains a mainstay in the treatment of end- stage arthritis. Arthroscopic techniques for ankle arthrodesis have more recently been developed, although there has been limited research exploring the cost of arthroscopic (AAA) versus open ankle arthrodesis (OAA), and comparing ankle fusions to replacement (TAA). We hypothesize that resource use after AAA will be lower than that after OAA, and both will be lower than TAA. Methods: We performed a retrospective review of a prospectively collected database. The COFAS database was used to identify patients with >2 years of follow up who have undergone AAA, OAA or Hintegra TAA at St Paul’s Hospital between 2003-2010. Ninety patients with TAA, 52 with AAA and 56 with OAA met our inclusion criteria. The following data were documented: patient demographics (age, gender, presence of diabetes, inflammatory arthritis or any smoking history), factors related to the index surgery (type of surgery, OR time, length of stay) and factors relating to the post-operative course (number of unplanned post-operative clinic visits, OR time for re-operations, length of stay for additional hospital admissions). For all significant comparisons, p < 0.05. Results: AAA required less primary surgery OR time and shorter primary hospital stay vs. TAA and OAA. Patients required more additional follow-up visits for TAA and OAA vs. AAA. TAA required more additional days in hospital compared to OAA or AAA. For each primary TAA, on average an additional seven clinic visits, 60 minutes of revision surgery, three days in hospital were required on top of the cost assigned for the primary arthroplasty. For each primary AAA, an additional four clinic visits, 23 minutes of revision surgery and one day in hospital were required. For each primary OAA, an average additional five clinic visits, three minutes of revision OR time, and 0.2 days of additional hospital stay were required. Conclusion: Using several measures of resource use, we find that arthroscopic ankle fusions compare favourably to both ankle replacements and open ankle fusions. We also show that resource utilization measurements can be a useful surrogate for complications, and that resource utilization can demonstrate the practical implications of complications for patients, surgeons and health care providers or payers.

Background This study examined the evolution of damage control resuscitation (DCR) and outcomes in severe traumatic hemorrhage (STH) at a large Canadian trauma center. Methods This was a retrospective cohort study of trauma patients admitted to a level 1 trauma center between 2005 and 2010, who received 10 or more units of packed red blood cells within 24 hours of admission. Demographic and clinical findings were compared between survivors and nonsurvivors. Results Forty-five patients were included. Twenty-five percent of patients were coagulopathic at admission. Early crystalloid use declined over the study period. The mean 24-hour fresh-frozen plasma:platelets:packed red blood cells ratio was 1:1:2. Hemorrhage-related mortality was 69%. No pedestrians survived STH. A total of 1,032 blood product units were used in the first day for nonsurvivors. Conclusions Principles of DCR crept into clinical practice even before the implementation of a formal STH protocol. DCR appeared to reduce the intensive care unit length of stay but not mortality. STH is associated with heavy use of blood bank resources and high mortality rates. Futility of resuscitative efforts may be predictable by mechanism and early physiological markers.

Ecology Letters (2011) 14: 852–862 Abstract Synergistic interactions between multiple limiting resources are common, highlighting the importance of co-limitation as a constraint on primary production. Our concept of resource limitation has shifted over the past two decades from an earlier paradigm of single-resource limitation towards concepts of co-limitation by multiple resources, which are predicted by various theories. Herein, we summarise multiple-resource limitation responses in plant communities using a dataset of 641 studies that applied factorial addition of nitrogen (N) and phosphorus (P) in freshwater, marine and terrestrial systems. We found that more than half of the studies displayed some type of synergistic response to N and P addition. We found support for strict definitions of co-limitation in 28% of the studies: i.e. community biomass responded to only combined N and P addition, or to both N and P when added separately. Our results highlight the importance of interactions between N and P in regulating primary producer community biomass and point to the need for future studies that address the multiple mechanisms that could lead to different types of co-limitation.

Plant-herbivore interactions mediate the trophic structure of ecosystems. We use a comprehensive data set extracted from the literature to test the relative explanatory power of two contrasting bodies of ecological theory, the metabolic theory of ecology (MTE) and ecological stoichiometry (ES), for per-capita and population-level rates of herbivory across ecosystems. We found that ambient temperature and herbivore body size (MTE) as well as stoichiometric mismatch (ES) both constrained herbivory, but at different scales of biological organization. Herbivore body size, which varied over 11 orders of magnitude, was the primary factor explaining variation in per-capita rates of herbivory. Stoichiometric mismatch explained more variation in population-level herbivory rates and also in per-capita rates when we examined data from within functionally similar trophic groups (e.g. zooplankton). Thus, predictions from metabolic and stoichiometric theories offer complementary explanations for patterns of herbivory that operate at different scales of biological organization.

Conservationists have proposed that maintaining key elements of the original land-cover type in modified landscapes may mitigate the detrimental effects of land-cover change on residual species. We tested this hypothesis for aquatic insect communities in tank-forming bromeliads in forested and non-forested habitats in Costa Rica. Bromeliad tanks hold much of the standing water in this region and therefore provide an important resource for insects with aquatic larval stages. We quantified the relative importance of land-use type and the bromeliad-specific “local” environment on the insect community, and also the effect of land-use type on this local environment. Insect species responded to both land-use type and the local environment, with these variables explaining a total of 36% of species densities. The local environment independently explained 19% of insect densities, while land-use type explained 17%, mainly through its modification of the local environment. Local environmental conditions wer...

The cycles of the key nutrient elements nitrogen (N) and phosphorus (P) have been massively altered by anthropogenic activities. Thus, it is essential to understand how photosynthetic production across diverse ecosystems is, or is not, limited by N and P. Via a large-scale meta-analysis of experimental enrichments, we show that P limitation is equally strong across these major habitats and that N and P limitation are equivalent within both terrestrial and freshwater systems. Furthermore, simultaneous N and P enrichment produces strongly positive synergistic responses in all three environments. Thus, contrary to some prevailing paradigms, freshwater, marine and terrestrial ecosystems are surprisingly similar in terms of N and P limitation.

Consumer and resource control of diversity in plant communities have long been treated as alternative hypotheses. However, experimental and theoretical evidence suggests that herbivores and nutrient resources interactively regulate the number and relative abundance of coexisting plant species. Experiments have yielded divergent and often contradictory responses within and among ecosystems, and no effort has to date reconciled this empirical variation within a general framework. Using data from 274 experiments from marine, freshwater, and terrestrial ecosystems, we present a cross-system analysis of producer diversity responses to local manipulations of resource supply and/or herbivory. Effects of herbivory and fertilization on producer richness differed substantially between systems: ( i ) herbivores reduced species richness in freshwater but tended to increase richness in terrestrial systems; ( ii ) fertilization increased richness in freshwater systems but reduced richness on land. Fertilization consistently reduced evenness, whereas herbivores increased evenness only in marine and terrestrial ecosystems. Producer community evenness and ecosystem productivity mediated fertilization and herbivore effects on diversity across ecosystems. Herbivores increased producer richness in more productive habitats and in producer assemblages with low evenness. These same assemblages also showed the strongest reduction in richness with fertilization, whereas fertilization increased (and herbivory decreased) richness in producer assemblages with high evenness. Our study indicates that system productivity and producer evenness determine the direction and magnitude of top-down and bottom-up control of diversity and may reconcile divergent empirical results within and among ecosystems.

In the premontane rain forests of northwest Costa Rica, patches of secondary forest can contain high densities of large Vriesea spp. bromeliads. Such patches contain an average of 6,470 ± 1,080 (s.e.) larvae ha-1 of the bromeliad-dwelling pseudostigmatid, Mecistogaster modesta, ca 3 6× higher than larval densities that we previously reported for adjacent primary forest. Using a new method to partition landscape variation in populations, we show that secondary forest has higher larval densities than primary forest because of higher bromeliad abundance (13% of effect), greater bromeliad size (33%), and greater larval abundance in bromeliads of similar size (54%). The last effect reflects additional effects of forest type after accounting for differences in the quantity of larval habitat. We use surveys of prey communities in bromeliads and adult densities in the two forest types to show that these additional effects of forest type are more likely due to adult behaviour, not larval resource limitati...

Summary 1 Foraging by geese has led to vegetation loss in salt marshes along the Hudson Bay coast and lesser snow geese are increasingly grazing inland freshwater marshes. We determined whether different nutrients limit the growth of forage plants in the two habitats, and whether these differences affect the nutritional quality of vegetation available to geese at La Perouse Bay, Manitoba. 2 Results from fertilization experiments indicate that primary productivity in the salt marsh is both nitrogen and phosphorus limited, whereas the freshwater marsh is phosphorus limited. Total amounts of calcium, magnesium and potassium in above-ground biomass per unit area showed similar differences in limitation. 3 Leaves of preferred forage species have higher nutrient concentrations (nitrogen, phosphorus, calcium, potassium, magnesium, sodium) and lower C : N and C : P ratios than alternative forage. The main forage species in the salt marsh ( Puccinellia phryganodes ) has higher nutrient content per unit mass, for nitrogen, magnesium, calcium and sodium, than the major freshwater marsh species( Carex aquatilis ). The difference in nutritional quality of forage between the marshes is likely to have had consequences for goose fitness, and may have contributed to the reported declines in gosling survivorship and size. 4 At moderate grazing intensities, seasonal growth of salt-marsh forage is maintained by addition of nitrogen and, to a lesser extent, phosphorus from high numbers of goose faeces to swards. In contrast, the low densities and low phosphorus content of goose faeces in the phosphorus-limited freshwater marsh mean that plants are unlikely to recover rapidly from the effects of grazing. As a consequence, the freshwater marsh is likely to become increasingly less productive as foraging intensifies. 5 Nutrient gradients in vegetation across an ecotone and changes in foraging behaviour have resulted in adverse effects on both the growth rates of individuals and the population structure of a herbivore.

Objective The measurement of functional outcomes in pelvic fracture patients remains difficult for authors. The authors aimed to test the construct validity, respondent burden, floor and ceiling effects, and patient perception of 3 previously published pelvic outcome questionnaires. Design Prospective case series. Setting Level I Trauma Center. Patients Those with surgically treated Orthopaedic Trauma Association (OTA) B and C pelvic ring disruption at greater than 12 months after treatment. Intervention None. Main outcome measurement Majeed Pelvic Score, Orlando Pelvic Score, Iowa Pelvis Score, Short Form-36, and Short Musculoskeletal Functional Assessment (SMFA). Results The authors recruited 38 patients, 15 OTA C and 23 OTA B fractures, who had a mean of 57 months from surgery (13-115 months). Patients cited recreational/mobility difficulty (30), emotional stress and family strain (24), employment and financial difficulty (17), sleep disturbance and anxiety (9), and sexual function (6) as the most important consequences of their injuries. Each of the 3 pelvic outcome questionnaires showed a high correlation with the Physical Component Score of the SF-36, and both indices of the SMFA. None had a high correlation with the Mental Component Score of the SF-36, indicating that these scores do not capture psychologic distress and well-being, social functioning, and overall vitality. All 3 questionnaires demonstrated ceiling effects, with 21%, 18%, and 15% of respondents reporting the highest possible scores on the Iowa, Majeed, and Orlando scores, respectively. The time for completion was 3.6 ± 0.4 minutes for the Iowa score, 7.4 ± 0.4 for the Orlando score (not including radiographic assessment), and 2.6 ± 0.2 for the Majeed score. Fifteen patients preferred the Iowa score, 12 the Orlando score, and 11 the Majeed instrument. Conclusions Three previously published pelvic outcome instruments were found to have strong construct validity based on correlation with the Physical Component Score of the SF-36 and both indices of the SMFA. Subjects identified mental and emotional outcomes as important consequences of their injury; however, none of the pelvic questionnaires measure these domains, as they all correlate poorly with the Mental Component Score of the SF-36. Ceiling effects limit the utility of the all 3 current instruments, and their reliability and responsiveness over time remain unknown. No currently available outcome instrument seems to captures all of the important consequences of these injuries.

Category: Ankle Arthritis Introduction/Purpose: As an alternative to ankle replacement, ankle arthrodesis remains a mainstay in the treatment of end- stage arthritis. Arthroscopic techniques for ankle arthrodesis have more recently been developed, although there has been limited research exploring the cost of arthroscopic (AAA) versus open ankle arthrodesis (OAA), and comparing ankle fusions to replacement (TAA). We hypothesize that resource use after AAA will be lower than that after OAA, and both will be lower than TAA. Methods: We performed a retrospective review of a prospectively collected database. The COFAS database was used to identify patients with >2 years of follow up who have undergone AAA, OAA or Hintegra TAA at St Paul’s Hospital between 2003-2010. Ninety patients with TAA, 52 with AAA and 56 with OAA met our inclusion criteria. The following data were documented: patient demographics (age, gender, presence of diabetes, inflammatory arthritis or any smoking history), factors related to the index surgery (type of surgery, OR time, length of stay) and factors relating to the post-operative course (number of unplanned post-operative clinic visits, OR time for re-operations, length of stay for additional hospital admissions). For all significant comparisons, p < 0.05. Results: AAA required less primary surgery OR time and shorter primary hospital stay vs. TAA and OAA. Patients required more additional follow-up visits for TAA and OAA vs. AAA. TAA required more additional days in hospital compared to OAA or AAA. For each primary TAA, on average an additional seven clinic visits, 60 minutes of revision surgery, three days in hospital were required on top of the cost assigned for the primary arthroplasty. For each primary AAA, an additional four clinic visits, 23 minutes of revision surgery and one day in hospital were required. For each primary OAA, an average additional five clinic visits, three minutes of revision OR time, and 0.2 days of additional hospital stay were required. Conclusion: Using several measures of resource use, we find that arthroscopic ankle fusions compare favourably to both ankle replacements and open ankle fusions. We also show that resource utilization measurements can be a useful surrogate for complications, and that resource utilization can demonstrate the practical implications of complications for patients, surgeons and health care providers or payers.

Synergistic interactions between multiple limiting resources are common, highlighting the importance of co-limitation as a constraint on primary production. Our concept of resource limitation has shifted over the past two decades from an earlier paradigm of single-resource limitation towards concepts of co-limitation by multiple resources, which are predicted by various theories. Herein, we summarise multiple-resource limitation responses in plant communities using a dataset of 641 studies that applied factorial addition of nitrogen (N) and phosphorus (P) in freshwater, marine and terrestrial systems. We found that more than half of the studies displayed some type of synergistic response to N and P addition. We found support for strict definitions of co-limitation in 28% of the studies: i.e. community biomass responded to only combined N and P addition, or to both N and P when added separately. Our results highlight the importance of interactions between N and P in regulating primary producer community biomass and point to the need for future studies that address the multiple mechanisms that could lead to different types of co-limitation.

Nutrient availability and herbivory control the biomass of primary producer communities to varying degrees across ecosystems. Ecological theory, individual experiments in many different systems, and system-specific quantitative reviews have suggested that (i) bottom‐up control is pervasive but top‐down control is more influential in aquatic habitats relative to terrestrial systems and (ii) bottom‐up and top‐down forces are interdependent, with statistical interactions that synergize or dampen relative influences on producer biomass. We used simple dynamic models to review ecological mechanisms that generate independent vs. interactive responses of community-level biomass. We calibrated these mechanistic predictions with the metrics of factorial meta-analysis and tested their prevalence across freshwater, marine and terrestrial ecosystems with a comprehensive meta-analysis of 191 factorial manipulations of herbivores and nutrients. Our analysis showed that producer community biomass increased with fertilization across all systems, although increases were greatest in freshwater habitats. Herbivore removal generally increased producer biomass in both freshwater and marine systems, but effects were inconsistent on land. With the exception of marine temperate rocky reef systems that showed positive synergism of nutrient enrichment and herbivore removal, experimental studies showed limited support for statistical interactions between nutrient and herbivory treatments on producer biomass. Top‐down control of herbivores, compensatory behaviour of multiple herbivore guilds, spatial and temporal heterogeneity of interactions, and herbivore-mediated nutrient recycling may lower the probability of consistent interactive effects on producer biomass. Continuing studies should expand the temporal and spatial scales of experiments, particularly in understudied terrestrial systems; broaden factorial designs to manipulate independently multiple producer resources (e.g. nitrogen, phosphorus, light), multiple herbivore taxa or guilds (e.g. vertebrates and invertebrates) and multiple trophic levels; and ‐ in addition to measuring producer biomass ‐ assess the responses of species diversity, community composition and nutrient status.