Entomology

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    Nutrient co-limitation of primary producer communities
    (Blackwell, 2011) Harpole, Stanley; Ngai, Jacqueline; Cleland, Elsa; Seabloom, Eric; Borer, Elizabeth; Bracken, Matthew; Elser, James; Gruner, Daniel; Hillebrand, Helmut; Shurin, Jonathan; Smith, Jennifer
    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.
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    Nutrient regulation by an omnivore and the effects on performance and distribution
    (2009) Pearson, Rachel Estelle Goeriz; Gruner, Daniel S; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Omnivores have a unique interaction with their nutritional environment because they have adapted to consume food from different trophic levels. To successfully navigate their variable resources, omnivores must maintain some level of nutrient regulation. To explore the effects of nutrient regulation by an omnivore, I used a salt marsh katydid, Conocephalus spartinae. To first address the ability of Conocephalus to perform on a wide range of diets and to regulate their nutritional intake, I used artificial diets that differed in relative amounts of protein and carbohydrate (Chapter 1). I found that Conocephalus survival decreased on a high protein diet due in part to a decrease in lipid stores but growth was not affected by diet. In a second experiment Conocephalus showed a degree of nutrient regulation as evidenced by the difference in what they actually ate and the predicted consumption if they had been feeding equally on the diets presented in each treatment. However, I did not find evidence for tight macronutrient regulation. Next I explored capacity of Conocephalus to regulate their nutrient intake (nitrogen and lipid) when fed naturally co-occurring prey (Chapter 2). I first established that the prey differed in their protein and lipid content and that these differences were related to the size of the prey species. When Conocephalus were fed different prey species individuals showed no differences in either growth or survival. In the final experiment, I found that Conocephalus did show evidence of a degree of nitrogen and lipid regulation because they did not feed equally on all of the prey species offered. Lastly, I documented the relationship between the ability of Conocephalus to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that Conocephalus aggregates in areas of high plant quality but that their numbers do not correspond to areas of high prey density. However, I found that katydid growth and survival was enhanced by prey availability but not plant quality. Overall, I documented how an organism like an omnivore relates to its nutritional environment and how nutrient regulation might affect performance and distribution. Last, I documented the relationship between the ability of katydids to locate plant and prey resources and the effect that these resources have on omnivore performance (Chapter 3). I found that katydids aggregate in areas of high plant quality but that their numbers do not correspond to areas of high prey density.
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    Global analysis of nitrogen and phosphorus limitation of primary producers in freshwater, marine and terrestrial ecosystems
    (Ecology Letters, 2007-12) Elser, James; Bracken, Matthew; Cleland, Elsa; Gruner, Daniel; Harpole, Stanley; Hillebrand, Helmut; Ngai, Jacqueline; Seabloom, Eric; Shurin, Jonathan; Smith, Jennifer
    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.