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Many marine bacteria have evolved to grow optimally at either high (copiotrophic) or low (oligotrophic) nutrient concentrations, enabling different species to colonize distinct trophic habitats in the oceans. Here, we compare the genome sequences of two bacteria, Photobacterium angustum S14 and Sphingopyxis alaskensis RB2256, that serve as useful model organisms for copiotrophic and oligotrophic modes of life and specifically relate the genomic features to trophic strategy for these organisms and define their molecular mechanisms of adaptation. We developed a model for predicting trophic lifestyle from genome sequence data and tested >400,000 proteins representing >500 million nucleotides of sequence data from 126 genome sequences with metagenome data of whole environmental samples. When applied to available oceanic metagenome data (e.g., the Global Ocean Survey data) the model demonstrated that oligotrophs, and not the more readily isolatable copiotrophs, dominate the ocean's free-living microbial populations. Using our model, it is now possible to define the types of bacteria that specific ocean niches are capable of sustaining. microbial adaptation and ecology | microbial genomics and metagenomics | monitoring environmental health | trophic adaptation

The Grand Bank ecosystem has undergone significant shifts during the past two decades owing to oceanographic and fishing effects. Effects on upper trophic level seabirds (dietary shifts, reduced reproductive performance) have been mediated through changes in the biology and behaviour of capelin (Mallotus villosus (Muller, 1776)), the focal forage species. To explore for effects at lower trophic levels, we combine dietary (1987-1988, 2003-2006) and distributional (1966-1990, 1998-1999) data for Leach's storm-petrel (Oceanodroma leucorhoa (Vieillot, 1818)), a small, abundant, and highly pelagic seabird. Fish and crustaceans formed the bulk of nestling diet at two colonies, with fish dominating in all sampling periods and years (occurrence >70%, reconstructed mass >75%). Five families were represented, but mature myctophids (glacier lanternfish (Benthosema glaciale (Reinhardt, 1837)), horned lanternfish (Ceratoscopelus maderensis (Lowe, 1839)), Protomyctophum arcticum (Lutken, 1892)) and sandlance (genus Ammodytes L., 1758) dominated. Crustaceans occurred frequently but typically comprised ≤ 10% by mass; Hyperia galba (Montagu, 1813) dominated this prey class. General diet composition was similar through time with birds relying heavily on myctophid fishes in 1987-1988 and 2003-2006. Crustacean diversity, however, declined with fewer species of hyperiid amphipods and no small euphausiids (genus Thysanoessa Brandt, 1851) consumed in 2003-2006. The latter parallels changes in spring diets of capelin and winter diets of murres (genus Uria Brisson, 1760) in the region. Associations of storm-petrels with deep water are consistent with the predominance of mesopelagic prey in their diets. L'ecosysteme du Grand Banc a subi d'importants changements au cours des deux dernieres decennies a cause d'effets oceaniques et halieutiques. Les effets sur les oiseaux marins de niveau trophique superieur (changements alimentaires, performance reproductive reduite) se sont produits par l'intermediaire de modifications de la biologie et du comportement des capelans (Mallotus villosus (Muller, 1776)), leur espece fourrage principale. Pour explorer les effets aux niveaux trophiques inferieurs, nous avons combine des donnees d'alimentation (1987-1988, 2003-2006) et de repartition (1966-1990, 1998-1999) sur l'oceanite cul-blanc (Oceanodroma leucorhoa (Vieillot, 1818)), un petit oiseau marin, abundant et hautement pelagique. Les poissons et les crustaces forment l'essentiel du regime alimentaire des petits au nid dans deux colonies et les poissons dominent dans toutes les periodes et annees d'echantillonnage (frequence >70 %, masse reconstitue e >75 %). Cinq familles sont representees, mais les myctophides matures (la lanterne glaciaire (Benthosema glaciale (Reinhardt, 1837)), la lampe cornee (Ceratoscopelus maderensis (Lowe, 1839)), Protomyctophum arcticum (Lutken, 1892)) et les lancons (le genre Ammodytes L., 1758) predominent. Les crustaces sont frequents, mais representent typiquement ≤ 10 % de la masse; Hyperia galba (Montagu, 1813) domine cette classe de proies. Le regime alimentaire general reste le meme au cours du temps et les oiseaux etaient fortement dependants des poissons myctophides en 1987-1988 et en 2003-2006. La diversite des crustaces a cependant diminue et les oiseaux ont consomme un nombre reduit d'especes d'amphipodes hyperiides et aucun euphausiide (le genre Thysanoessa Brandt, 1851) en 2003-2006. Ces observations s'accordent avec des changements similaires dans les regimes alimentaires des capelans au printemps et des marmettes (le genre Uria Brisson, 1760) en hiver dans la region. L'association des oceanites avec les eaux profondes est en accord avec la predominance de proies mesopelagiques dans leur regime. [Traduit par la Redaction], Introduction The productive waters of the Grand Bank of eastern Canada provide important habitat for a diversity of large vertebrate predators. Globally significant concentrations of marine birds include, for example, [...]

Abstract.--Fruits and seeds, green foliage, and animal matter composed the seasonal diets of Peromyscus pectoralis in central Texas. Based on changes in foods consumed, five distinct seasons were delineated. Trophic [...]

We quantify the trophic positions of subtropical open-ocean zooplankton species using amino acid-specific (AA) stable nitrogen isotopic compositions. We model animal trophic position by computing trophic [sup.15]N enrichment of glutamic acid relative to phenylalanine, and find that trophic position for primary copepod consumers (Oithona spp., Neocalanus robustior) and secondary copepod consumers (Pleuromamma xiphias and Euehaeta rimana) varied little over a 5-10-yr period in the North Pacific Subtropical Gyre (NPSG; mean [+ or -] SD: 2.1 [+ or -] 0.1 and 2.9 [+ or -] 0.1, respectively). Comparison of AA [sup.15]N enrichment patterns in different copepod species suggests that trophic [sup.15]N enrichment is most consistent in glutamic acid, aspartic acid, and alanine, 'trophic' AAs that are intimately involved in the citric acid cycle and energy production. We further test equations involving these trophic AAs and 'source' AAs (which appear to retain the nitrogen isotopic composition of the food-web base), and find that such compound-specific models give results that are identical to those calculated using whole-animal (bulk) stable isotopic compositions. However the benefits of our AA-based approach (i.e., the relatively few samples needed for precise TP estimation, elimination of the need for concurrent prey isotopic analyses, and the ability to utilize formalin-preserved specimens from archived collections), make this a powerful technique for the quantitative assessment of trophic position within the pelagic food web. We further discuss how stable isotopic analyses provide a new perspective on the structure of open-ocean food webs and can be used to trace large seasonal fluctuations in nitrogen source in the NPSG.

By influencing nutrient mineralization in the soil, decomposers may affect the performance of plants and their associated herbivores. The strength of above--belowground linkages may therefore depend on the availability of nutrients in ecosystems. We investigated the dependency of decomposer- and leaf-herbivore-mediated changes in plant performance on soil nutrient availability in microcosm systems. In separate treatments, Poa annua was used as host plant for the herbivore and was grown in combination with different herb species: Plantago lanceolata, Trifolium repens, and Sanguisorba minor. At three different levels of nutrient availability, the impact of Collembola (Folsomia candida) and aphids (Rhopalosiphum padi), as well as their interacting effects on plant performance, were investigated. We further assessed the effects of Collembola on the performance of aphids and vice versa, as well as the effects on element contents in P. annua and soil nutrients. Collembola increased total aboveground biomass and biomass of single plant species (except T. repens) only at low and moderate nutrient availability, whereas the negative effects of aphids on P. annua and total aboveground biomass were highest at high nutrient availability. Collembola decreased relative root allocation. The negative effect of aphids on plant biomass was more pronounced in the presence of Collembola. Nitrogen concentration in shoots of P. aroma was increased by Collembola. Aphids decreased the nitrogen concentration in grass shoots only when Collembola were present. These interacting effects can be related to indirect effects of decomposers on herbivore performance. At low and moderate nutrient availability, aphid numbers strongly increased due to decomposers, whereas at high nutrient availability this effect was much weaker. In turn, aphid herbivory increased the number of Collembola only at high nutrient availability. We conclude that the role of both below- and aboveground food webs for the dynamics of vegetation depend on each other and the availability of nutrients in ecosystems. This suggests that nutrient enrichment of ecosystems may have important consequences for above--belowground linkages and their effects on natural communities. Key words: above-belowground linkages; decomposers; herbivores; microcosms; nutrient availability; plant communities; trophic interactions.

Intraspecific phenotypic variation in ecologically important traits is widespread and important for evolutionary processes, but its effects on community and ecosystem processes are poorly understood. We use life history differences among populations of alewives, Alosa pseudoharengus, to test the effects of intraspecific phenotypic variation in a predator on pelagic zooplankton community structure and the strength of cascading trophic interactions. We focus on the effects of differences in (1) the duration of residence in fresh water (either seasonal or year-round) and (2) differences in foraging morphology, both of which may strongly influence interactions between alewives and their prey. We measured zooplankton community structure, algal biomass, and spring total phosphorus in lakes that contained landlocked, anadromous, or no alewives. Both the duration of residence and the intraspecific variation in foraging morphology strongly influenced zooplankton community structure. Lakes with landlocked alewives had small-bodied zooplankton year-round, and lakes with no alewives had large-bodied zooplankton year-round. In contrast, zooplankton communities in lakes with anadromous alewives cycled between large-bodied zooplankton in the winter and spring and small-bodied zooplankton in the summer. In summer, differences in feeding morphology of alewives caused zooplankton biomass to be lower and body size to be smaller in lakes with anadromous alewives than in lakes with landlocked alewives. Furthermore, intraspecific variation altered the strength of the trophic cascade caused by alewives. Our results demonstrate that intraspecific phenotypic variation of predators can regulate community structure and ecosystem processes by modifying the form and strength of complex trophic interactions. Key words: alewife, Alosa pseudoharengus; interspecific variation; intraspecific variation; keystone species; life history differences; predator identity; size-selective predation; trophic cascade; zooplankton.

Understanding and predicting the consequences of trophic interactions for community processes requires knowledge of the role of food availability, which is often wrongly conflated with prey abundance. For prey animals in groups, this is not fully understood. Previous work has shown that oystercatchers more frequently attack solitary rather than aggregated limpets and are more successful in predation attempts on singletons. It has also been demonstrated that an attack on one limpet in a group alerts the entire group, all of which then clamp down and become unavailable. I show that Eurasian Oystercatchers (Haematopus ostralegus L.) attack only one limpet in a group and then move on to attack another individual limpet, and I also demonstrate that the distance they move is greater than the distance at which groups of limpets have been known to detect attacks. Thus in the oystercatcher--limpet predator--prey system on rocky shores, groups of limpets are actually one prey item independently of the number of limpets in the group. This has implications for assessment of food supply for avian predators on rocky shores, with consequences for our understanding of previously documented trophic cascades. Key words: behavior; Eurasian Oystercatcher; Haematopus ostralegus; limpet; Patella spp.; predation; prey availability; trophic cascade.

The traditional trophic cascades model is based on consumer resource interactions at each link in a food chain. However, trophic-level interactions, such as mesocarnivore release resulting from intraguild predation, may also be important mediators of cascades. From September 2001 to August 2004, we used spatial and seasonal heterogeneity in wolf distribution and abundance in the southern Greater Yellowstone Ecosystem to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus), accounts for high rates of coyote predation on pronghorn (Antilocapra americana) fawns observed in some areas. Results of this ecological perturbation in wolf densities, coyote densities, and pronghorn neonatal survival at wolf-free and wolf-abundant sites support the existence of a species-level trophic cascade. That wolves precipitated atrophic cascade was evidenced by fawn survival rates that were four-fold higher at sites used by wolves. A negative correlation between coyote and wolf densities supports the hypothesis that interspecific interactions between the two species facilitated the difference in fawn survival. Whereas densities of resident coyotes were similar between wolf-free and wolf-abundant sites, the abundance of transient coyotes was significantly lower in areas used by wolves. Thus, differential effects of wolves on solitary coyotes may be an important mechanism by which wolves limit coyote densities. Our results support the hypothesis that mesopredator release of coyotes contributes to high rates of coyote predation on pronghorn fawns, and demonstrate the importance of alternative food web pathways in structuring the dynamics of terrestrial systems. Key words: Antilocapra americana; Canis latrans; Canis lupus; carnivore competition: mesopredator release hypothesis; predator-prey; Program MARK.

The rate of species loss is increasing at a global scale, and human-induced extinctions are biased toward predator species. We examined the effects of predator extinctions on a foundation species, the eastern oyster (Crassostrea virginica). We performed a factorial experiment manipulating the presence and abundance of three of the most common predatory crabs, the blue crab (Callinectes sapidus), stone crab (Menippe mercenaria), and mud crab (Panopeus herbstii) in estuaries in the eastern United States. We tested the effects of species richness and identity of predators on juvenile oyster survival, oyster recruitment, and organic matter content of sediment. We also manipulated the density of each of the predators and controlled for the loss of biomass of species by maintaining a constant mass of predators in one set of treatments and simultaneously using an additive design. This design allowed us to test the density dependence of our results and test for functional compensation by other species. The identity of predator species, but not richness, affected oyster populations. The loss of blue crabs, alone or in combination with either of the other species, affected the survival rate of juvenile oysters. Blue crabs and stone crabs both affected oyster recruitment and sediment organic matter negatively. Mud crabs at higher than ambient densities, however, could fulfill some of the functions of blue and stone crabs, suggesting a level of ecological redundancy. Importantly, the strong effects of blue crabs in all processes measured no longer occurred when individuals were present at higher-than-ambient densities. Their role as dominant predator is, therefore, dependent on their density within the system and the density of other species within their guild (e.g., mud crabs). Our findings support the hypothesis that the effects of species loss at higher trophic levels are determined by predator identity and are subject to complex intraguild interactions that are largely density dependent. Understanding the role of biodiversity in ecosystem functioning or addressing practical concerns, such as loss of predators owing to overharvesting, remains complicated because accurate predictions require detailed knowledge of the system and should be drawn from sound experimental evidence, not based on observations or generalized models. Key words: Callinectes sapidus; crab; Crassostrea virginica; ecosystem functioning; extinction; foundation species; identity effect; Menippe mercenaria; oyster; Panopeus herbstii; predator-prey interaction; trophic interaction.

Predator-prey communities are ubiquitous in ecology, but introduced predators can drive native species to extinction within island systems, prompting the eradication of such exotics. Ecological theory predicts that elimination of top-introduced predators from islands can lead to the counterintuitive decline of native prey populations through the ecological release of smaller introduced species in a process termed 'mesopredator release.' We show, in accordance with mesopredator release theory and counter to conservation goals for a New Zealand island reserve, that initial eradication of cats on Little Barrier Island led to reduced breeding success of Cook's petrels, which also are vulnerable to predation by a mesopredator, the Pacific rat. The rat's impact on prey productivity varied with elevation within the island. Rat eradication was followed by a rise in petrel productivity, in support of both ecological theory and practical conservation management goals. It appears that interactions among introduced predators, native prey, and environmental gradients can drive counterintuitive and spatially heterogeneous responses to predator eradications from islands. Location-specific, ecosystem-level understanding is essential for predicting the outcomes of such restoration management techniques. habitat gradients | introduced predator eradications | island restoration | trophic cascade | Cook's petrel

Although the ecological effects of invasions often become obvious soon after introduced species become established, more gradual effects may take years to manifest and can thus require long-term data for quantification. We analyzed an 8-year record of stable isotope data on Argentine ants (Linepithema humile) from southern California to infer how the trophic position of this widespread invasive species changes over time as native ant species are displaced. We couple this longitudinal analysis with a biregional comparison of stable isotope data ([[delta].sup.15]N) on ants from Argentina (native range) and California (introduced range) to quantify (i) how the trophic position of L. humile differs between native and introduced populations, and (ii) how relative trophic position as estimated by [[delta].sup.15]N values of Argentine ants compare with those of other ants at the same site. Both long-term and biregional comparisons indicate that the Argentine ant's relative trophic position is reduced at sites with a longer history of occupation. Over the course of 8 years, the relative trophic position of L. humile remained high at the leading edge of an invasion front but declined, on average, behind the front as native ants disappeared. Relative to native populations, where L. humile is among the most carnivorous of ants, Argentine ants from California occupied lower trophic positions. These results support the hypothesis that Argentine ants shift their diet after establishment as a result of resource depletion and increasing reliance on plant-based resources, especially honeydew-producing Hemiptera. Our results demonstrate the value of long-term and biregional data in uncovering ecological effects of invasions. biological invasions | stable isotopes | food webs

Predicting the dynamics of ecosystems requires an understanding of how trophic interactions respond to environmental change. In Antarctic marine ecosystems, food web dynamics are inextricably linked to sea ice conditions that affect the nature and magnitude of primary food sources available to higher trophic levels. Recent attention on the changing sea ice conditions in polar seas highlights the need to better understand how marine food webs respond to changes in such broad-scale environmental drivers. This study investigated the importance of sea ice and advected primary food sources to the structure of benthic food webs in coastal Antarctica. We compared the isotopic composition of several seafloor taxa (including primary producers and invertebrates with a variety of feeding modes) that are widely distributed in the Antarctic. We assessed shifts in the trophic role of numerically dominant benthic omnivores at five coastal Ross Sea locations. These locations vary in primary productivity and food availability, due to their different levels of sea ice cover, and proximity to polynyas and advected primary production. The [delta][sup.15]N signatures and isotope mixing model results for the bivalves Laternula elliptica and Adamussium colbecki and the urchin Sterechinus neumeyeri indicate a shift from consumption of a higher proportion of detritus at locations with more permanent sea ice in the south to more freshly produced algal material associated with proximity to ice-free water in the north and east. The detrital pathways utilized by many benthic species may act to dampen the impacts of large seasonal fluctuations in the availability of primary production. The limiting relationship between sea ice distribution and in situ primary productivity emphasizes the role of connectivity and spatial subsidies of organic matter in fueling the food web. Our results begin to provide a basis for predicting how benthic ecosystems will respond to changes in sea ice persistence and extent along environmental gradients in the high Antarctic. Key words: Antarctica; benthic food webs; coastal sea ice; omnivory; Ross Sea; spatial subsidies; stable isotopes.

Insectivorous birds and ants co-occur in most terrestrial communities, and theory predicts that emergent properties (i.e., nonadditive effects) can determine their combined influence on arthropods and plants. In a three-year factorial experiment, I investigated whether the effects of birds on pine and its arthropods differed based on the presence of ants that were predators of most arthropods, but mutualists with tended aphid species. Birds and ants reduced the abundance of most herbivorous and carnivorous arthropods in an additive fashion, with the effects of ants being stronger than those of birds. In sharp contrast, the opposing influences of birds and ants on tended aphid species interacted strongly; ants only increased tended aphid abundance in the absence of birds, while birds only reduced their abundance in the presence of ants. This interaction was mirrored in total herbivore abundance because tended aphids dominated the herbivore community, l develop a novel lexicon to discuss the emergent properties from these effects of opposing sign (predation, mutualism). Despite having emergent effects on herbivores, birds indirectly increased pine wood and foliage growth to a similar extent whether or not ants were present, while ants had no detectable effects. Birds also indirectly increased the abundance of some pine phloem monoterpenes, but these effects differed based on the presence or absence of ants. Thus, I report on a novel yet possibly widespread indirect interaction between intraguild predators, herbivore mutualists, and plant traits (growth, secondary chemistry) mediated through a species-rich community of arthropods. Key words: ant-aphid mutualism; Cinara; emergent property; Formica podzolica; indirect effect; multiple predator effect; negative-biased interaction; phloem monoterpenes; Pinus ponderosa; positive-biased interaction; tritrophic interaction; trophic cascade.