Generalist Strategy Research Articles

Individual specialization in the use of space by frugivorous bats.

Natural populations are not homogenous systems but sets of individuals that occupy subsets of the species' niche. This phenomenon is known as individual specialization. Recently, several studies found evidence of individual specialization in animal diets. Diet is a critical dimension of a species' niche that affects several other dimensions, including space use, which has been poorly studied under the light of individual specialization. In this study, which harnesses the framework of the movement ecology paradigm and uses yellow-shouldered bats Sturnira lilium as a model, we ask how food preferences lead individual bats of the same population to forage mainly in different locations and habitats. Ten individual bats were radiotracked in a heterogeneous Brazilian savanna. First, we modelled intraspecific variation in space use as a network of individual bats and the landscape elements visited by them. Second, we developed two novel metrics, the spatial individual specialization index (SpatIS) and the spatial individual complementary specialization index (SpatICS). Additionally, we tested food-plant availability as a driver of interindividual differences in space use. There was large interindividual variation in space use not explained by sex or weight. Our results point to individual specialization in space use in the studied population of S. lilium, most probably linked to food-plant distribution. Individual specialization affects not only which plant species frugivores consume, but also the way they move in space, ultimately with consequences for seed dispersal and landscape connectivity.

Trophic strategies of three predatory pelagic fish coexisting in the north-western Mediterranean Sea over different time spans

Understanding the trophic ecology of marine predators is pivotal to assess their ecological role in the ecosystems and develop management actions. Despite the ecological importance of predatory pelagic fish species, the trophic role that individual species play within marine communities in many marine basins, such the Mediterranean Sea, remains unclear. In the present study, we aimed to provide new integrative information about the trophic ecology at different temporal scales of Atlantic bonito (Sarda sarda), little tunny (Euthynnus alletteratus) and swordfish (Xiphias gladius) in the north-western Mediterranean Sea. To quantify the trophic habits of these three species, we used stable isotopic analysis and isotopic mixing models from different tissues that integrate trophic information at different temporal scales (~1 month for liver, ~ several months for muscle, >1 year for fin). We found clear and consistent differences in the trophic habits among the three species and time spans within the same species. Although preying mainly on clupeiforms, Atlantic bonito and little tunny present a temporal segregation in the species preference, with Atlantic bonito preying mainly on European sardine and round sardinella at long-term, while little tunny preyed mainly on European anchovy. In the other hand, swordfish shows a more generalist trophic strategy with high preference for demersal prey. This study emphasises the utility of this integrative approach for trophic studies due to its capacity for monitoring trophic habits over different time spans.

A Bayesian Account of Generalist and Specialist Formation Under the Active Inference Framework.

This paper offers a formal account of policy learning, or habitual behavioral optimization, under the framework of Active Inference. In this setting, habit formation becomes an autodidactic, experience-dependent process, based upon what the agent sees itself doing. We focus on the effect of environmental volatility on habit formation by simulating artificial agents operating in a partially observable Markov decision process. Specifically, we used a “two-step” maze paradigm, in which the agent has to decide whether to go left or right to secure a reward. We observe that in volatile environments with numerous reward locations, the agents learn to adopt a generalist strategy, never forming a strong habitual behavior for any preferred maze direction. Conversely, in conservative or static environments, agents adopt a specialist strategy; forming strong preferences for policies that result in approach to a small number of previously-observed reward locations. The pros and cons of the two strategies are tested and discussed. In general, specialization offers greater benefits, but only when contingencies are conserved over time. We consider the implications of this formal (Active Inference) account of policy learning for understanding the relationship between specialization and habit formation.

Generalized mycorrhizal interactions and fungal enemy release drive range expansion of orchids in southern Florida

AbstractA species’ ability to establish and spread is influenced by different types of biotic interactions encountered in a new range. Species with high dependency on biotic interactions, such as orchids, are believed to have low ability to expand ranges. Using a comparative approach, we addressed the role of below‐ground biotic interactions in the naturalization and spread of two introduced orchids. Using fungus‐specific DNA primers and symbiotic germination trials, we identified the types of fungal taxa associated with Cyrtopodium flavum and Eulophia graminea, two invasive orchids in southern Florida, with that of two native congeners, C. punctatum and E. alta. We quantified the degrees of mycorrhizal specificity as well as associations with pathogenic fungi. We identified a total of 57 distinct fungal taxa, collected from a total of 104 root samples (67 adults and 37 seedlings), and 111 protocorms derived from fungal baits in southern Florida and southwest China. We found that invasive orchids were capable of associating with a broader range of mycorrhizal fungi than co‐occurring native congeners (i.e., generalist strategy). Concurrently, invasive orchid species were less likely to harbor pathogenic fungal groups (Ascomycete) than native congeners, suggesting enemy release played a role as well in these orchids’ naturalization and spread. These findings provided insights into the complex roles of mycorrhizal symbioses in range expansions.

Description and ecology of a new species of the cricket genus Endecous (Orthoptera: Grylloidea: Phalangopsidae) in the speleological province of Arcos-Pains-Doresópolis, Southeastern Brazil.

A new cricket species of the genus Endecous Saussure, 1878 is described in the present work found in the speleological province of Arcos-Pains-Doresópolis, which belongs to the limestone group Bambuí, Brazil. Moreover, the spatial distribution of the new species was related to the species Eidmanacris sp., which co-occurs with the former in several caves. Relationships between species abundance and horizontal projection, number of entrances and environmental stability of the caves where these species coexist were evaluated. The presence of bilateral symmetry in individuals of Endecous painensis n. sp. perhaps due to environmental stress caused by mining activities surrounding the cave was also tested. Endecous crickets are commonly observed in the caves, for which the preference by distinct microhabitats and generalist strategies may be key factors explaining colonization and segregation in relation to other cricket species in subterranean habitats. The generalist lifestyle of the here described species may attenuate the effects environmental stresses over development.

Crossing extreme habitat boundaries: Jack‐of‐all‐trades facilitates invasion but is eroded by adaptation to a master‐of‐one

AbstractThe invasion of new environments can be a key instigator of adaptive diversification, but the likelihood of such invasions succeeding can depend on the attributes of would‐be invaders. Chief among these seems to be a generalist or ‘jack‐of‐all‐trades’ phenotype.Yet, despite the obvious link between habitat transitions and adaptation, we know surprisingly little about how phenotypes that might initially allow taxa to transition between habitats subsequently evolve or influence post‐invasion differentiation.We tested how a generalist phenotype of a broad diet and behavioural plasticity in marine blenny fish has facilitated the repeated invasion of extreme environments—particularly land—and how the conditions post‐invasion have impacted that generalist phenotype and associated trophic morphology.Our data show that a wide diet and plasticity in being able to shift between environments freely have been instrumental in the progressive invasion of land by amphibious blennies. Once established, however, terrestrial blennies have experienced strong stabilizing selection for a restricted diet, little to no plasticity and a highly specialized morphology. Instead of promoting diversification, the invasion of land appears to offer only a limited niche for survival, constraining descendent blennies to a specific adaptive phenotype.While our study supports the view that generalism facilitates invasion and that habitat transitions instigate adaptation, it also shows a generalist strategy is not optimal for successful establishment and new environments may offer fewer (not more) opportunities for diversification. This has broad implications for how taxa might be expected to respond or adapt to abrupt environmental change more generally.A freeplain language summarycan be found within the Supporting Information of this article.

Generalists versus specialists in fluctuating environments: a bet‐hedging perspective

Bet‐hedging evolves in fluctuating environments because long‐term genotype success is determined by geometric (rather than arithmetic) mean fitness across generations. Diversifying bet‐hedging produces different specialist offspring, whereas conservative bet‐hedging produces similar generalist offspring. However, many fields, such as behavioral ecology and thermal physiology, typically consider specialist versus generalist strategies only in terms of maximizing arithmetic mean fitness benefits to individuals. Here we model how environmental variability affects optimal amounts of phenotypic variation within and among individuals to maximise genotype fitness, and we disentangle the effects of individual‐level optimization and genotype‐level bet‐hedging by comparing long‐term arithmetic versus geometric mean fitness. For traits with additive fitness effects within lifetimes (e.g. foraging‐related traits), genotypes of similar generalists or diversified specialists perform equally well. However, if fitness effects are multiplicative within lifetimes (e.g. sequential survival probabilities), generalist individuals are always favored. In this case, geometric mean fitness optimization requires even more within‐individual phenotypic variation than does arithmetic mean fitness, causing individuals to be more generalist than required to simply maximize their own expected fitness. In contrast to previous results in the bet‐hedging literature, this generalist conservative bet‐hedging effect is always favored over diversifying bet‐hedging. These results link the evolution of behavioral and ecological specialization with earlier models of bet‐hedging, and we apply our framework to a range of natural phenomena from habitat choice to host specificity in parasites.

Feeding ecology of black scorpion fish (Scorpaena porcusLinnaeus, 1758) in SE Black Sea region, (Ordu) Turkey

AbstractBlack scorpion fish (Scorpaena porcus) is an important species for both artisanal and industrial fisheries in the Turkish Black Sea, with 306 tonnes landed in 2017. The diet composition of this species was investigated through the examination of their stomach contents. A total of 621S. porcus(ranging from 12.79–765.5 g) were caught by trammel net in the south-eastern Black Sea (Turkish waters) from December 2015 to November 2016. The importance of prey items in the diet ofS. porcuswas assessed using the Index of Relative Importance (%IRI). Overall, the dominant species was the isopodIdotea balthica(52.8%IRI) followed by decapods (38.5%IRI) and teleosts (8.7%IRI). Seasonal variations in the diets were observed, with isopods predominant in autumn (>85%IRI), teleosts in winter (>77%IRI) and decapod crustaceans (>78%IRI) in spring and summer. The modified Costello's graphical analysis evinced a specialist feeding strategy forS. porcusduring winter, spring and autumn while a shift to generalistic feeding strategy was exhibited in summer by a limited number ofS. porcusindividuals.

Defining Cyanobacterial Species: Diversity and Description Through Genomics

Cyanobacteria were the first oxygenic photosynthersizers, evolving ∼3.5 bya, they have since radiated into one of the most diverse and widely distributed phyla of bacteria. Cyanobacterial diversification occurs through ecological adaptation, facilitated by asexual reproduction, homologous recombination and horizontal gene transfer, and selection pressures on ecotypes leading to speciation. Delimiting cyanobacterial species is, thus, fraught with difficulties and a clear taxonomy has not yet been universally accepted. This review discusses diversity and description of cyanobacteria: covering traditional and new methods to define species boundaries and concluding with a focus on the advances made through genomics. Examples from the genera Raphidiopsis, Microcystis, and Prochlorococcus are used throughout. Genome plasticity allows cyanobacteria to rapidly adapt and be resilient to environmental changes, illustrating the means of their persistence, and is an important aspect of their biology. Genomics has revealed generalist and specialist genome strategies, intraspecific diversity, and genome evolution in response to environmental stimuli. New taxonomic definitions will need to account for intraspecific genetic variation, with a species classification that is relevant to a species concept and scientific endeavors. Capturing intraspecific diversity with comparative genomics may provide a new path to species classification. This is demonstrated with two case studies; comparison of available genomes shows differing species delineation of Raphidiopsis and Microcystis. In both genera, species boundaries occur at ∼96% average nucleotide identity (ANI), where homologous recombination is constrained, but speciation of Raphidiopsis raciborskii, R. brookii, and R. curvata has occurred through geographic isolation, whereas available data on Microcystis contain at least 15 species, reflecting, to differing extents, different ecotypes, which may co-exist. Both case studies question the relative importance of species-specific versus habitat specific gene pools as drivers of inter- and intraspecific diversity.

Low costs of adaptation to dietary restriction.

Dietary restriction (DR) is the most successful and widespread means of extending organismal lifespan. However, the evolutionary basis of life extension under DR remains uncertain. The traditional evolutionary explanation is that when organisms experience DR, they allocate endogenous resources to survival and postpone reproduction until conditions improve. However, this life-extension strategy should be maladaptive if DR continues for multiple generations due to trade-offs between longevity and reproduction. To test this prediction, we subjected the budding yeast Saccharomyces cerevisiae to 1800 generations of evolution on restricted versus non-restricted diets. Adaptation to a non-restricted diet improved reproductive fitness by 57%, but provided a much smaller (14%) advantage on a restricted diet. By contrast, adaptation to DR resulted in an approximately 35% increase in reproductive fitness on both restricted and non-restricted diets. Importantly, the life-extending effect of DR did not decrease following long-term evolution on the restricted diet. Thus, contrary to theoretical expectations, we found no evidence that the life-extending DR response became maladaptive during multigenerational DR. Together, our results suggest that the DR response has a low cost and that this phenomenon may have evolved as part of a generalist strategy that extends beyond the benefits of postponing reproduction.

Spatial and temporal variation in prey color patterns for background matching across a continuous heterogeneous environment.

In heterogeneous habitats, camouflage via background matching can be challenging because visual characteristics can vary dramatically across small spatial scales. Additionally, temporal variation in signaling functions of coloration can affect crypsis, especially when animals use coloration seasonally for intraspecific signaling (e.g., mate selection). We currently have a poor understanding of how wild prey optimize background matching within continuously heterogeneous habitats, and whether this is affected by requirements of intraspecific signaling across biological seasons. Here, we quantified color patterns of a wild population of shore skink (Oligosoma smithi), a variably colored lizard endemic to New Zealand, to (a) investigate whether background matching varies across a vegetation gradient; (b) assess potential signaling functions of color; and (c) to determine whether there is a trade‐off between requirements for crypsis and intraspecific signaling in coloration across seasons. Although all pattern types occurred throughout the vegetation gradient, we found evidence for background matching in skinks across the vegetation gradient, where dorsal brightness and pattern complexity corresponded with the proportion of vegetation cover. There was also a significant disparity between ventral color (saturation) of juveniles and adults, and also between sexes, suggestive of sex recognition. However, there was little indication that color was condition‐dependent in adults. Despite some evidence for a potential role in signaling, crypsis did not greatly differ across seasons. Our study suggests that selection favors a mix of generalist and specialist background matching strategies across continuously heterogeneous habitats.

Adolescent SBIRT implementation: Generalist vs. Specialist models of service delivery in primary care

BackgroundDrug, alcohol, and tobacco use among adolescents pose significant short- and long-term health consequences and are associated with more severe use as adults. Screening, brief intervention, and referral to treatment in primary care settings has the potential to deliver preventive interventions to a diverse range of adolescents, but optimal implementation of these services needs to be determined. The purpose of this study was to compare implementation of two different SBIRT service delivery models in primary care settings. MethodsThis cluster-randomized trial assigned 7 primary care clinics of a federally qualified health center to implement brief interventions (BI) using a Generalist model (4 sites), in which BIs were delivered by the primary care provider (PCP), or a Specialist model (3 sites), in which BIs were delivered by a behavioral health counselor (BHC) for adolescent patients ages 12–17 years. Implementation was tracked through the clinic's electronic health record, spanning 9639 clinic visits over 20 months. Multilevel logistic regression modeling was used to compare Generalist and Specialist strategies on penetration of BI for patients scoring ≥2 on the CRAFFT substance use screen, delivered by the PCP in the Generalist sites, and via warm hand-off to a BHC in the Specialist sites. ResultsApproximately 62% of adolescent patient visits were screened with the CRAFFT (with <4% screening positive with a CRAFFT score ≥ 2). The Generalist Condition had significantly higher self-reported penetration of BI delivery than the Specialist Condition (38% vs. 8%; Adjusted Odds Ratio = 6.53; p = .005). DiscussionDespite having co-located behavioral health services at all sites, a Specialist approach to providing BI was less effectively implemented than a Generalist approach in this FQHC. BI delivered by PCPs rather than by hand-off to a BHC may ensure greater penetration of these services in primary care settings. Both implementation models provided a framework for identifying and intervening with adolescent primary care patients whose substance use might have otherwise gone undetected.

Individuals within populations: No evidences of individual specialization in the trophic habits of an opportunistic predator

Human activities can affect species in different ways, with some species being unable to cope with the human-driven changes, while others can persist and even benefit from these alterations. The main factors explaining the population dynamics of successful species include their use of food resources derived from human activities and the adaptability in their feeding behavior. Among marine predators, some gull species of the genus Larus, such as the yellow-ledged gull Larus michahellis, are particularly successful within the current context of human-induced global change. While the yellow-ledged gull is considered a generalist and opportunistic predator at the population level, some individuals may show specialisation in feeding habitat and diet. Here, we examined the degree of individual specialisation in the trophic habits and temporal variation in food resource utilisation within a population of this gull in the southwestern Iberian Peninsula. We analysed the isotopic composition (δ15N and δ13C) in blood and different feathers molted throughout the annual cycle for reconstructing the diet of individuals and quantifying the degree of individual specialisation. Individuals of this species in the studied population preferably fed on demersal fish throughout the entire annual cycle, with a low consumption of terrestrial prey and human-related resources. Isotopic values also revealed a generalist feeding behavior in this gull species with a very small proportion of individuals acting as specialists throughout the annual cycle. Taking into account the generalist strategy of this population, management measures should mainly be focused on controlling the availability of demersal sources from fishery discards. Future research should prioritise multispecific approaches to study how general or flexible the behavior is in this winning species.

Generalist Life Cycle Aids Persistence of Alexandrium ostenfeldii (Dinophyceae) in Seasonal Coastal Habitats of the Baltic Sea

In seasonal environments, strong gradients of environmental parameters can shape life cycles of phytoplankton. Depending on the rate of environmental fluctuation, specialist or generalist strategies may be favored, potentially affecting life cycle transitions. The present study examined life cycle transitions of the toxin producing Baltic dinoflagellate Alexandrium ostenfeldii and their regulation by environmental factors (temperature and nutrients). This investigation aimed to determine whether genetic recombination of different strains is required for resting cyst formation and whether newly formed cysts are dormant. Field data (temperature and salinity) and sediment surface samples were collected from a site with recurrent blooms and germination and encystment experiments were conducted under controlled laboratory conditions. Results indicate a lack of seasonal germination pattern, set by an endogenous rhythm, as commonly found with other dinoflagellates from the Baltic Sea. Germination of quiescent cysts was triggered by temperatures exceeding 10°C and combined nutrient limitation of nitrogen and phosphorus or a drop in temperature from 16 to 10°C triggered encystment most efficiently. Genetic recombination was not mandatory for the formation of resting cysts, but supported higher numbers of resistant cysts and enhanced germination capacity after a resting period. Findings from this study confirm that A. ostenfeldii follows a generalist germination and cyst formation strategy, driven by strong seasonality, which may support its persistence and possibly expansion in marginal environments in the future, if higher temperatures facilitate a longer growth season.

Diet and isotopic niche of eastern sand darter (Ammocrypta pellucida) near the northern edge of its range: a test of niche specificity

Niche specificity can predispose species to population declines during periods of resource limitation, yet trophic niche specificity is poorly known for many small-bodied freshwater fishes. Applying a two-tiered approach involving stomach content and stable isotope analyses, we examined the diet and trophic niche of the threatened eastern sand darter (Ammocrypta pellucida (Putnam, 1863)) and co-occurring fishes in the Thames River, Ontario, Canada. As with previous studies, stomach content analysis revealed that eastern sand darter consumed a variety of benthic organisms including Chironomidae, Cladocera, Ostracoda, Oligochaeta, and Ephemeroptera; however, proportional contributions of prey groups differed based on stable isotope analysis, highlighting the potential for seasonal variation in prey consumption. Despite evidence of a generalist strategy, stable isotope analysis indicated eastern sand darter exhibited a relatively narrow trophic niche relative to co-occurring fishes. Trophic niche overlap was relatively minor between eastern sand darter and drift-feeding fishes (spotfin shiner (Cyprinella spiloptera (Cope, 1867)), emerald shiner (Notropis atherinoides Rafinesque, 1818), and buffalo sp. (genus Ictiobus Rafinesque, 1820)), but was more evident between eastern sand darter and benthic and benthopelagic fishes (johnny darter (Etheostoma nigrum Rafinesque, 1820) and blackside darter (Percina maculata (Girard, 1859))), indicating that competition with these species may be more likely during periods of prey scarcity.

Imperfect camouflage: how to hide in a variable world?

Camouflage is an important anti-predator strategy for many animals and is traditionally thought of as being tightly linked to a specific visual background. While much work focuses on optimizing camouflage against one background, this may not be relevant for many species and contexts, as animals may encounter many different habitats throughout their lives due to temporal and spatial variation in their environment. How should camouflage be optimized when an animal or object is seen against multiple visual backgrounds? Various solutions may exist, including colour change to match new environments or use of behaviour to maintain crypsis by choosing appropriate substrates. Here, we focus on a selection of approaches under a third alternative strategy: animals may adopt (over evolution) camouflage appearances that represent an optimal solution against multiple visual scenes. One approach may include a generalist or compromise strategy, where coloration matches several backgrounds to some extent, but none closely. A range of other camouflage types, including disruptive camouflage, may also provide protection in multiple environments. Despite detailed theoretical work determining the plausibility of compromise camouflage and elucidating the conditions under which it might evolve, there is currently mixed experimental evidence supporting its value and little evidence of it in natural systems. In addition, there remain many questions including how camouflage strategies should be defined and optimized, and how they might interact with other types of crypsis and defensive markings. Overall, we provide a critical overview of our current knowledge about how camouflage can enable matching to multiple backgrounds, discuss important challenges of working on this question and make recommendations for future research.

Persistence, loss and gain: Characterising mature green roof vegetation by functional composition

Like any constructed ecosystem, the vegetation of extensive green roofs (EGRs) will change over time. Although this may influence the desired function and performance, little work has examined the floristic dynamism of EGRs over the long-term. Variations in species composition may be associated with original species (persistent or lost), colonisers (gained), or the effects of spatial heterogeneity. This paper reports on floristic variation of two unmanaged German EGRs twenty years after installation. To evaluate floristic change, the analyses focused on functional composition and plant strategies sensu Grime's CSR theory, referring to the basic adaptive strategies of competition, stress-tolerance and ruderality, and their derivatives. With reference to original documentation, less than half the original species persisted. In spite of the losses, both roofs had entire cover, or nearly so, thanks to colonising species. The generalist strategy (CSR strategists) was the most important functional trait in the observed vegetation, followed by stress-tolerance and then by variations in stress-tolerant ruderality. The functional composition of colonising species was chiefly ruderals, followed by stress tolerators and generalists. The drivers behind these changes relate to the pressures of stress, disturbance and competition, as well as spatial heterogeneity and strategies for dispersal and regeneration, seedbank and propagule sources. This study suggests that long-term floristic diversity may be facilitated by ensuring a diversity of traits and species from the start, by providing spatial heterogeneity, and by considering the mechanisms that support persistence and those which determine colonisation.

Geographic variation in biochemical and physiological traits of the red seaweeds Chondracanthus chamissoi and Gelidium lingulatum from the south east Pacific coast

Diverse phenotypic characteristics have evolved in seaweeds to cope with environmental stress, but these traits can vary among populations of the same species especially if these are distributed along environmental gradients. In this study, natural populations of the carrageenophyte Chondracanthus chamissoi and the agarophyte Gelidium lingulatum from a latitudinal gradient along the Chilean coast (between 20° S and 41° S) were compared. We determined physiological and biochemical traits in field and culture samples. Sulfated polysaccharide contents ranged from 15.4 to 52.7% dry weight (DW) in C. chamissoi and from 10.9 to 25.1% DW in G. lingulatum. Carrageenan amounts were higher in gametophytes than tetrasporophytes and were also, depending on life cycle phase, negatively correlated with the geographic variation of temperature, photosynthetically active radiation (PAR), and chlorophyll a (Chl a), whereas agar showed no significant correlation with these variables. The UV-absorbing mycosporine-like amino acids (MAAs) shinorine and palythine in both species ranged from 0.8 to 6.8 mg g−1 DW and these contents were positively correlated to PAR and Chl a levels at the sampling site. In C. chamissoi variation among populations in their photosynthetic characteristics, pigment concentrations, antioxidant capacity, and MAA contents were persistent after acclimation under common-garden conditions, suggesting ecotypic differentiation in this species. Contrary, G. lingulatum seems to have a more generalist strategy because differences after cultivation were observed only in some photosynthetic parameters and phycobiliprotein concentration. This study confirms that intraspecific differences in phenotypic traits along the same geographic area are strongly dependent on species and life cycle phases.

Foreign firms’ strategic positioning and performance in a host market

PurposeStrategic positioning of foreign firms in a host market is vital for their success. By integrating the resource partitioning theory and the resource-based view, this study aims to investigate foreign firms’ strategic positioning (i.e. their choice of generalist or specialist positioning strategy) and its performance implications in the US market.Design/methodology/approachThe final sample includes 212 foreign companies from 28 countries operating in the US market. Multiple data sources were used to collect data of these foreign companies’ subsidiaries in the USA This study used logistic regression to test its major hypotheses.FindingsThe results of this study suggest that a generalist positioning strategy is positively related to performance in a host market. It is also found that market concentration and local market knowledge moderate this strategic positioning – performance relationship.Research limitations/implicationsFor a foreign firm that enters a host market, market concentration (an industry-level factor) in the host market and the firm’s local market knowledge (a firm-specific factor) play prominent roles in the strategic positioning – performance relationship.Originality/valueThis study offers a novel perspective of international business strategy by applying the lens of resource partitioning theory to study the relationships between multinational enterprises’ strategic positioning and performance. This study contributes to the strategy literature in that it examines the performance implications of firms’ strategic positioning (i.e. generalist or specialist positioning).

Trophic ecology of two co-existing Sub-Antarctic limpets of the genus Nacella: spatio-temporal variation in food availability and diet composition of Nacella magellanica and N. deaurata

Interactions between algae and herbivores can be affected by various factors, such as seasonality and habitat structure. Among herbivores inhabiting marine systems, species of the order Patellogastropoda are considered key organisms in many rocky coasts of the world. Nacella species are one of the most dominant macro-herbivores on the rocky shores of the sub-Antarctic ecoregion of Magellan. However, the importance of its key role must be associated with its trophic ecology. The objective of this work was to evaluate spatial and temporal variabilities in the dietary composition of two intertidal Nacella species, considering grazing on macro- (macroalgae) and microscopic (periphyton) food. The composition of periphyton and the availability of macroalgae in the winter and summer seasons were examined at two localities of the Magellanic province, alongside the gut contents of N. magellanica and N. deaurata. The dietary composition differed between the two Nacella species, as well as between seasons and locations. The differences observed in the diet of the two species of Nacella may be mainly due to their respective distributions in the intertidal zone. Both species presented a generalist strategy of grazing, which is relationed to the seasonality of micro- and macroalgae availability and to the variability of the assemblages between the localities. This research was the first to perform a detailed study of the diet of intertidal Nacella species.