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▪ Abstract Mutualisms occur when interactions between species produce reciprocal benefits. However, the outcome of these interactions frequently shifts from positive, to neutral, to negative, depending on the environmental and community context, and indirect effects commonly produce unexpected mutualisms that have community-wide consequences. The dynamic, and context dependent, nature of mutualisms can transform consumers, competitors, and parasites into mutualists, even while they consume, compete with, or parasitize their partner species. These dynamic, and often diffuse, mutualisms strongly affect community organization and ecosystem processes, but the historic focus on pairwise interactions decoupled from their more complex community context has obscured their importance. In aquatic systems, mutualisms commonly support ecosystem-defining foundation species, underlie energy and nutrient dynamics within and between ecosystems, and provide mechanisms by which species can rapidly adjust to ecological variance. Mutualism is as important as competition, predation, and physical disturbance in determining community structure, and its impact needs to be adequately incorporated into community theory.

Marine larvae are consumed by a wide variety of generalist fishes and particle-feeding invertebrates, but larvae of any particular species probably constitute a small and variable portion of the diet for these consumers. Because virtually all consumers can ingest small quantities of noxious compounds with minimal detrimental effects, it is uncertain that toxic chemicals in larvae could be consumed in quantities sufficient to select for predator recognition and avoidance. Despite this, chemically defended larvae do occur. We show that, at low doses, secondary metabolites (the didemnins) from adults and larvae of the Caribbean tunicate Trididemnum solidum induced vomiting in fish, resulting in rapid learned aversion to the didemnin-defended food. The particle-feeding anemone Aiptasia pallida did not learn to avoid the chemically defended food. When anemones ingested the chemical equivalent of 15 larvae/d, representing <2% of the mass of their total daily diet, the didemnins in the larvae significantly reduced: (1) growth of adults by 82%, (2) combined growth of adults and daughter clones by 76%, (3) production of daughter clones by 44%, and (4) average mass of individual daughter clones by 41%. At higher water temperatures, anemones cloned more rapidly, but the negative effects of consuming didemnins also occurred more rapidly. Significant differences in the number of daughter clones produced between treatment and control anemones occurred after only 4 d at seawater temperatures of 27°-29°C vs. 32 d at seawater temperatures of 18°-21°C. Thus consumption of even very small quantities of secondary metabolites can decrease consumer fitness substantially and select for predators that recognize and avoid chemically defended larvae, as do many consumers that co-occur with Trididemnum solidum larvae. This is the first rigorous demonstration that consumption of marine secondary metabolites can decrease consumer fitness when ingested at ecologically realistic doses.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 188:169-178 (1999) - doi:10.3354/meps188169 Reduced mobility is associated with compensatory feeding and increased diet breadth of marine crabs John J. Stachowicz*, Mark Hay** University of North Carolina at Chapel Hill, Institute of Marine Sciences, Morehead City, North Carolina 28557, USA Present addresses: *University of Connecticut, Department of Marine Sciences, 1084 Shennecossett Rd., Groton, Connecticut 06340, USA. E-mail: jstach@uconnvm.uconn.edu **School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA ABSTRACT: Direct effects of predation have been widely recognized as important in affecting prey population dynamics and evolution. However, less attention has been devoted to the consequences of indirect effects of predators on prey behavior. For example, to avoid predation many animals restrict their activities to physical refugia and adopt low-mobility lifestyles, yet the consequences of these anti-predator behaviors for foraging and diet selection are relatively unknown. In this study we examine the relationships between mobility, feeding preferences, and compensatory feeding for 3 species of marine decapod crabs feeding on seaweeds in North Carolina, USA. Low mobility and high site fidelity of crabs were associated with a broad, non-selective diet and compensatory feeding. The majid Mithrax forceps exhibited the lowest mobility, highest site fidelity, and least selective diet of the 3 species, whereas another majid Libinia dubia was intermediate in both mobility and selectivity, and the xanthid Panopeus herbstii had the greatest mobility and narrowest diet. Of these 3 crabs, only M. forceps compensated for low food quality by increasing consumption rates in single food-species feeding assays. This may be because M. forceps is resistant to (or tolerant of) seaweed chemical defenses, while other crab species are not. The ability to consume, and presumably subsist on, a wide variety of potential foods including those defended from more mobile consumers may facilitate a low-mobility lifestyle, allowing the crab to minimize movement and reduce exposure to predators. Low mobility and high site-fidelity may thus facilitate the formation and use of associational refuges with sessile benthic organisms that are resistant to predators; these associations can have important community and ecosystem-wide consequences. KEY WORDS: Associational refuge · Compensatory feeding · Crabs · Diet breadth · Mobility Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 188. Publication date: November 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 336:211-223 (2007) - doi:10.3354/meps336211 Population dynamics of the non-native crab Petrolisthes armatus invading the South Atlantic Bight at densities of thousands m–2 A. L. Hollebone, M. E. Hay* School of Biology, Georgia Institute of Technology, 311 Ferst Drive, Atlanta, Georgia 30332-0230, USA *Corresponding author. Email: mark.hay@biology.gatech.edu ABSTRACT: The green porcelain crab Petrolisthes armatus recently invaded oyster reefs of the South Atlantic Bight. In 2 estuaries of coastal Georgia, USA, crab densities reached peak densities of 4000 to 11000 crabs m–2 in some periods and locations. Densities generally were higher in the low versus the high intertidal and in the lower versus upper regions of the estuaries. In warmer months, 20 to 90% of adult females were gravid, recruits were dense, and population levels were high. In colder months, densities dropped by 64 to >99%. Male:female ratios were near 1:1 across times and locations. Maximum mean densities of P. armatus in Georgia were 37 times the highest densities recorded in the presumptive native range. Crabs in the new range reproduced at a smaller size, and the percentage of gravid females was similar between the old and new range. Thus, population fecundity in Georgia exceeds that of the native range by more than 1 order of magnitude. Densities of native mud crabs in the genera Panopeus and Eurypanopeus were unrelated to, or positively correlated with, densities of the exotic crabs; correlations were never significantly negative. The impact of Petrolisthes armatus on native communities is unclear, but could be considerable if this filter-feeding crab impacts oysters, which are the foundation species of inshore reefs. KEY WORDS:Marine invasion · Invasive species · Exotic species · Crab densities · Population dynamics · Species boundaries Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 336. Online publication date: April 27, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Abstract Long‐standing theory predicts that the intensity of consumer–prey interactions declines with increasing latitude, yet for plant–herbivore interactions, latitudinal changes in herbivory rates and plant palatability have received variable support. The topic is of growing interest given that lower‐latitude species are moving poleward at an accelerating rate due to climate change, and predicting local interactions will depend partly on whether latitudinal gradients occur in these critical biotic interactions. Here, we assayed the palatability of 50 seaweeds collected from polar (Antarctica), temperate (northeastern Pacific; California), and tropical (central Pacific; Fiji) locations to two herbivores native to the tropical and subtropical Atlantic, the generalist crab Mithraculus sculptus and sea urchin Echinometra lucunter . Red seaweeds (Rhodophyta) of polar and temperate origin were more readily consumed by urchins than were tropical reds. The decline in palatability with decreasing latitude is explained by shifts in tissue organic content along with the quantity and quality of secondary metabolites, degree of calcification or both. We detected no latitudinal shift in palatability of red seaweeds to crabs, nor any latitudinal shifts in palatability of brown seaweeds (Phaeophyta) to either crabs or urchins. Our results suggest that evolutionary pressure from tropical herbivores favored red seaweeds with lower palatability, either through the production of greater levels of chemical defenses, calcification, or both. Moreover, our results tentatively suggest that the “tropicalization” of temperate habitats is facilitated by the migration of tropical herbivores into temperate areas dominated by weakly defended and more nutritious foods, and that the removal of these competing seaweeds may facilitate the invasion of better‐defended tropical seaweeds.

Abstract Aim The aim was to evaluate the hypothesis that biotic interactions are more intense in the tropics using reef fishes (from both functional and taxonomic perspectives), the crucial consumers on most reefs. Location Fifteen reef locations between 34°N and 27°S in the Western Atlantic. Time period 2011–2014. Major taxa studied Reef fishes. Methods We quantified fish feeding pressure on the benthos across 61° of latitude in the Western Atlantic via 1,038 10 min videos of 2 m 2 reef areas, where every fish feeding on the benthos was identified, had its total length estimated, and the number of bites on the reef substratum was counted. Fish were assigned to functional groups based on diet and feeding modes. Benthic cover estimates were also obtained through visual assessments from the videos. Results We documented feeding rates that were 2‐ to 22‐fold higher in tropical versus extratropical locations. This pattern was driven mainly by an interaction between fish functional group and temperature, with herbivory dominating in tropical regions ( c . 20‐fold higher), shifting to omnivory in temperate regions of both Hemispheres. Feeding by invertivores was common across all latitudes. Consumer species composition differed between Northern and Southern Hemispheres, but functional groups were similar, and their feeding changed in a similar manner with temperature regardless of Hemisphere. Main conclusions Our results support the hypothesis that biotic interactions, especially plant–herbivore interactions, are more intense in the tropics. These findings help to explain the lower palatability of tropical versus extratropical seaweeds and suggest that herbivory is favoured in warm conditions but omnivory in colder waters. The functional approach indicated that factors associated with latitude or temperature have selected for similar feeding functions among the different species occupying these geographical regions. Understanding the shifting trophic interactions across latitudes might help to predict the impacts of global changes on ecosystem function as tropical species move polewards and contact temperate systems.