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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.

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.

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.

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.

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.