RFLP Analysis of Mitochondrial DNA to Evaluate Genetic Variation in Striped Red Mullet (Mullus surmuletus L.) and Red Mullet (Mullus barbatus L.) Populations

The genetic differentiation of striped red mullet (Mullus surmuletus) and red mullet (Mullus barbatus) was investigated in 6 Mediterranean populations of each species by means of restriction fragment length polymorphism analysis of mitochondrial DNA. Three segments amplified by polymerase chain reaction (control region, COI, and 12S–16S ribosomal RNA) were digested with 20 restriction endonucleases, revealing 71 haplotypes for M. surmuletus and 30 for M. barbatus. For the two species nucleotide diversity was equally distributed within and among populations, leading to N _ST values of 0.545 and 0.500 for M. surmuletus and M. barbatus, respectively. However, intrapopulation and interpopulation genetic structuring appeared to be much higher for M. surmuletus than for M. barbatus (1.88% vs. 0.46% of mean intrapopulation nucleotide diversity; 1.94% vs. 0.47% of mean interpopulation nucleotide diversity; 0.055% vs. 0.002% of net interpopulation divergence). Furthermore, 81.69% of the haplotypes observed for M. surmuletus were unique, whereas 70.29% of M. barbatus individuals were grouped in 3 common haplotypes. Given that fishing pressure and population sizes are similar for both species, this differentiation could be attributed to differences in biological parameters and life histories between the two species, coupled with oceanographic conditions prevailing in the studied area. Received July 25, 2000; accepted December 29, 2000     

Difference in diet and size‐related trophic level in two sympatric fish species,the red mullets Mullus barbatus and Mullus surmuletus,in the Gulf of Lions (north‐west Mediterranean Sea)

Stable‐isotope ratios (δ¹⁵N and δ¹³C) and diet of the red mullets Mullus barbatus and Mullus surmuletus were analysed in two zones differently subjected to the Rhône River runoff in the Gulf of Lions (north‐west Mediterranean sea) in May and October 2004. δ¹⁵N and δ¹³C increased significantly with fish size in M. barbatus in both zones and seasons, whereas no significant trend was evidenced in M. surmuletus. A clear size‐related shift in diet was observed in M. barbatus, with an increase in polychaete and shrimp consumption with size and a decrease in small crustacean consumption. In M. surmuletus, a diet shift was observed only between medium and large individuals. Large M. surmuletus preyed on shrimps, polychaetes, bivalves, ophiurids and amphipods, and ingested prey of lower mean mass than M. barbatus of similar size. Difference in size‐related increase in δ¹⁵N between the two mullid fish species were related to difference of trophic level of their main prey. Sub‐surface deposit‐feeding polychaetes, carnivorous polychaetes, shrimps and brachyurans presented higher δ¹⁵N values than bivalves, small crustaceans and ophiurids. The lower δ¹³C values observed in M. barbatus compared to M. surmuletus were related to a higher consumption of sub‐surface polychaetes in the former species. Significantly, lower δ¹³C were recorded in fishes collected off the Rhône River, particularly in spring, suggesting an influence of river inputs as a source of particular organic matter for mullids in this zone after the flooding season. Thus, these closely related sympatric fish species displayed diet divergences that were reflected in their stable isotopic signatures.     

Fragmentation, habitat composition and the dispersal/predation balance in interactions between the Mediterranean myrtle and avian frugivores

Human‐induced fragmentation and disturbance of natural habitats can shift abundance and composition of frugivore assemblages, which may alter patterns of frugivory and seed dispersal. However, despite their relevance to the functioning of ecosystems, plant‐frugivore interactions in fragmented areas have been to date poorly studied. I investigated spatial variation of avian frugivore assemblages and fruit removal by dispersers and predators from Mediterranean myrtle shrubs (Myrtus communis) in relation to the degree of fragmentation and habitat features of nine woodland patches (72 plants). The study was conducted within the chronically fragmented landscape of the Guadalquivir Valley (SW Spain), characterized by ~1% of woodland cover. Results showed that the abundance and composition of the disperser guild was not affected by fragmentation, habitat features or geographical location. However, individual species and groups of resident/migrant birds responded differently: whereas resident dispersers were more abundant in large patches, wintering dispersers were more abundant in fruit‐rich patches. Predator abundances were similar between patches, although the guild composition shifted with fragmentation. The proportion of myrtle fruits consumed by dispersers and predators varied greatly between patches, but did not depend on bird abundances. The geographical location of patches determined the presence or absence of interactions between myrtles and seed predators (six predated and three non‐predated patches), a fact that greatly influenced fruit dispersal success. Moreover, predation rates were lower (and dispersal rates higher) in large patches with fruit‐poor heterospecific environments (i.e. dominated by myrtle). Predator satiation and a higher preference for heterospecific fruits by dispersers may explain these patterns. These results show that 1) the frugivore assemblage in warm Mediterranean lowlands is mostly composed of fragmentation‐tolerant species that respond differently to landscape changes; and 2) that the feeding behaviour of both dispersers and predators influenced by local fruit availability may be of great importance for interpreting patterns of frugivory throughout the study area.     

Local and systemic responses induced by aphids in Solanum tuberosum plants

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Homoptera: Aphididae) are serious pests of potato (Solanum tuberosum L.) (Solanaceae), notably in transmitting several plant viruses. Heterospecific interactions may occur between these two species as they are often seen at the same time on the same potato plant in the field. As aphid infestation is known to induce both local and systemic changes, we conducted experiments to determine the effect of previous infestation on probing behaviour and feeding‐related parameters. We used the DC electrical penetration graph technique to characterize the influence of previous infestation by conspecific M. persicae or by heterospecific Ma. euphorbiae on M. persicae feeding behaviour at both local and systemic levels, i.e., on previously infested leaves and on non‐previously infested leaves of infested plants, respectively. Conspecific and heterospecific infestation led to similar modification of M. persicae feeding activities. However, the effects of previous infestation occurring at the local level were opposite to those observed at the systemic level. Myzus persicae food acceptance was slightly enhanced on previously infested leaves, whereas it was inhibited on non‐infested leaves of infested plants, which indicated an induced resistance mechanism. Our results advance the understanding of the mechanisms involved in aphid–host plant acceptance and colonization processes on potato plants in conspecific and heterospecific situations.     

Floral neighborhood influences pollinator assemblages and effective pollination in a native plant

Pollinators represent an important intermediary by which different plant species can influence each other’s reproductive fitness. Floral neighbors can modify the quantity of pollinator visits to a focal species but may also influence the composition of visitor assemblages that plants receive leading to potential changes in the average effectiveness of floral visits. We explored how the heterospecific floral neighborhood (abundance of native and non-native heterospecific plants within 2 m × 2 m) affects pollinator visitation and composition of pollinator assemblages for a native plant, Phacelia parryi. The relative effectiveness of different insect visitors was also assessed to interpret the potential effects on plant fitness of shifts in pollinator assemblage composition. Although the common non-native Brassica nigra did not have a significant effect on overall pollinator visitation rate to P. parryi, the proportion of flower visits that were made by native pollinators increased with increasing abundance of heterospecific plant species in the floral neighborhood other than B. nigra. Furthermore, native pollinators deposited twice as many P. parryi pollen grains per visit as did the nonnative Apis mellifera, and visits by native bees also resulted in more seeds than visits by A. mellifera. These results indicate that the floral neighborhood can influence the composition of pollinator assemblages that visit a native plant and that changes in local flower communities have the potential to affect plant reproductive success through shifts in these assemblages towards less effective pollinators.     

How an invasive alga species (<Emphasis Type="Italic">Caulerpa taxifolia</Emphasis>) induces changes in foraging strategies of the benthivorous fish <Emphasis Type="Italic">Mullus surmuletus</Emphasis> in coastal Mediterranean ecosystems

The foraging behaviour variability of three striped red mullet (Mullus surmuletus L. 1758) populations with respect to the vegetation cover was examined along the French Mediterranean coasts. We tested both the carrying capacity of different habitats and the hypothesis of a food segregation by the invasive alga Caulerpa taxifolia (Vahl) C. Agardh, on the functioning of benthic fish populations. The results indicated a significant site effect on M. surmuletus foraging behaviour and movements. The vegetation cover may play an important role in modifying the striped red mullet cost of foraging (sampling effort) and thus its strategy of prey capture. As long as the cover of marine phanerogams and/or macrophyte algae (Caulerpaceae) increases, the foraging budget and the distances covered in search of prey decrease significantly. Similarly, the striped red mullet increases the prospected sample periods to augment its foraging success, swimming above the bottom. These changes are related to the development of a dense superficial network of plagiotropic rhizomes and stolons, and to the reduction of space between fronds that limits the accessibility to resources and may increase intra-specific food competition. The role of C. taxifolia does not differ from that of other marine phanerogams but induces significant changes in the structure of Mullidae populations at the local level. The rapid expansion of Caulerpaceae in the Mediterranean Sea could constitute a real threat for the balance of the marine coastal biodiversity and the ecology of M. surmuletus, which is considered a flagship species for coastal Mediterranean demersal fisheries.     

Plant and soil effects on bacterial communities associated with Miscanthus × giganteus rhizosphere and rhizomes

Bacterial assemblages, especially diazotroph assemblages residing in the rhizomes and the rhizosphere soil of Miscanthus × giganteus, contribute to plant growth and nitrogen use efficiency. However, the composition of these microbial communities has not been adequately explored nor have the potential ecological drivers for these communities been sufficiently studied. This knowledge is needed for understanding and potentially improving M. × giganteus – microbe interactions, and further enhancing sustainability of M. × giganteus production. In this study, cultivated M. × giganteus from four sites in Illinois, Kentucky, Nebraska, and New Jersey were collected to examine the relative influences of soil conditions and plant compartments on assembly of the M. × giganteus‐associated microbiome. Automated ribosomal intergenic spacer (ARISA) and terminal restriction fragment length polymorphism (T‐RFLP) targeting the nifH gene were applied to examine the total bacterial communities and diazotroph assemblages that reside in the rhizomes and the rhizosphere. Distinct microbial assemblages were detected in the endophytic and rhizosphere compartments. Site soil conditions had strong correlation with both total bacterial and diazotroph assemblages, but in different ways. Nitrogen treatments showed no significant effect on the composition of diazotroph assemblages in most sites. Endophytic compartments of different M. × giganteus plants tended to harbor similar microbial communities across all sites, whereas the rhizosphere soil of different plant tended to harbor diverse microbial assemblages that were distinct among sites. These observations offer insight into better understanding of the associative interactions between M. × giganteus and diazotrophs, and how this relationship is influenced by agronomic and edaphic factors.     

Pre-copulatory isolation in sympatric Melolontha species (Coleoptera: Scarabaeidae)

1 The two most abundant cockchafer species in Europe, the forest cockchafer Melolontha hippocastani Fabr. and the European cockchafer Melolontha melolontha L., tend to form calamitous mass breedings with casual reports on sympatric and simultaneous occurrence. 2 Both species are known to use feeding‐induced green leaf volatiles (GLV) as primary attractants (sexual kairomones) for mate finding. The attractiveness of GLV is enhanced by the sex pheromones 1,4‐benzoquinone in M. hippocastani and toluquinone in M. melolontha. Phenol attracts males from both species. All three compounds are present in females of both species. 3 In the present study, it is confirmed that only male M. melolontha perform the typical swarming flight at dusk, as has already been shown for M. hippocastani. Furthermore, whether swarming Melolontha males were cross‐attracted to heterospecific females, and whether males could discriminate olfactorily between conspecific and heterospecific females, was tested in the field. 4 Males of both species preferred females when given the choice between females and males of the other species. However, they preferred conspecific females when females from both species were offered simultaneously. 5 The results suggest that species‐specific pheromone blends contribute to precopulatory reproductive isolation in sympatric populations of M. melolontha and M. hippocastani, but are not mutually exclusive or indispensable prerequisites for mate finding as in other insects.     

An altitudinal comparison of caterpillar (Lepidoptera) assemblages on Ficus trees in Papua New Guinea

Aim This analysis of caterpillar (Lepidoptera) beta‐diversity between tropical lowlands and highlands attempts to separate the effects of between‐site (1) turnover of herbivore species on particular host plants, (2) changes in host use by herbivores, and (3) turnover of plant species on changes in herbivore assemblages. Location Two rain forest areas 130 km and 1700 altitudinal metres apart were studied in Papua New Guinea: one in the lowlands (100 m a.s.l.) on the northern coast of the island and one in the central New Guinean cordillera at 1800 m a.s.l. Methods The analysis is based on caterpillar feeding records obtained by quantitative sampling and rearing of caterpillars from four Ficus species studied in the mountains and 21 Ficus species and 62 plant species from other genera and families studied in the lowlands, including three Ficus species studied in both areas. Results Only 17% of species feeding on Ficus in the highlands also occurred in the lowlands. These species represented 1–46% of individuals in caterpillar assemblages on particular Ficus hosts. Widespread species included both Ficus specialists and generalists feeding on numerous plant families. Some of the Ficus specialists changed their preferred host species with altitude. High species turnover was not explained by changes in the species composition of host plants with altitude as lowland and montane assemblages feeding on the same Ficus species showed high turnover. Despite the rarity of widespread caterpillars, the lowland and montane Ficus assemblages were remarkably similar in their dominance structure, species richness, host specificity, generic composition and familial composition. Main conclusions Ficus‐feeding Lepidoptera assemblages between tropical lowlands and highlands are characterized by substantial species turnover not explained by altitudinal changes in the composition of the vegetation. Further, species‐rich plant genera can support caterpillar assemblages with relatively low beta‐diversity compared with species‐poor genera as caterpillars can switch their host preferences from one congeneric host species to another along an altitudinal gradient. Closely related plant species can thus represent a broad, continuously distributed resource along such gradients.     

Sexual differentiation and seasonal variation in response to conspecific and heterospecific acoustic signals

Interspecific territoriality is frequently reported between closely related species; however, few studies have demonstrated interspecific territoriality between distantly related species living in sympatry. We conducted playback experiments to investigate territorial behaviour in male and female White‐bellied Wrens (Uropsila leucogastra) in response to simulated conspecific and heterospecific intruders during the breeding and non‐breeding seasons. We explored whether heterospecific songs of the Happy Wren (Pheugopedius felix), a distantly related species and ecological competitor, elicited antagonistic responses from focal White‐bellied Wrens, and whether such responses differed between the sexes. We also examined whether male and female responses to conspecific and heterospecific rivals varied with season. We found that male White‐bellied Wrens always responded to conspecific song, and responded significantly more to heterospecific song compared to a control stimulus (Tropical Parula, Setophaga pitiayumi). In contrast, although female White‐bellied Wrens responded strongly to conspecific song, their response to heterospecific song did not differ significantly from the control stimulus. The proportion of males that responded to heterospecific songs and the proportion of females that responded to conspecific songs varied seasonally, showing significantly lower responses during the breeding season. The intense responses of male White‐bellied Wrens to playback of heterospecific songs suggest that they recognise ecological competitors based on their vocal signals. Furthermore, the decrease in agonistic interactions during the breeding season is in line with the hypothesis that aggressive behaviour may be detrimental to reproductive and parental activity, and the hypothesis that heterospecific animals pose less of a threat during the breeding season.     

Pollen competition between two sympatric Orchis species (Orchidaceae): the overtaking of conspecific of heterospecific pollen as a reproductive barrier

The frequency of hybrid formation in angiosperms depends on how and when heterospecific pollen is transferred to the stigma, and on the success of that heterospecific pollen at fertilising ovules. We applied pollen mixtures to stigmas to determine how pollen interactions affect siring success and the frequency of hybrid formation between two species of Mediterranean deceptive orchid. Plants of Orchis italica and O. anthropophora were pollinated with conspecific and heterospecific pollen (first conspecific pollen then heterospecific pollen and vice versa) and molecular analysis was used to check the paternity of the seeds produced. In this pair of Mediterranean orchids, competition between conspecific and heterospecific pollen functions as a post‐pollination pre‐zygotic barrier limiting the frequency of the formation of hybrids in nature. Flowers pollinated with heterospecific pollen can remain receptive for the arrival of conspecific pollen for a long time. There is always an advantage of conspecific pollen for fruit formation, whether it comes before or after heterospecific pollen, because it overtakes the heterospecific pollen. The conspecific pollen advantage exhibited in O. italica and O. anthropophora is likely to result from the reduced germination of heterospecific pollen or retarded growth of heterospecific pollen tubes in the stigma and ovary. Overall, the results indicate that our hybrid zone represents a phenomenon of little evolutionary consequence, and the conspecific pollen advantage maintains the genetic integrity of the parental species.     

Asymmetric conspecific sperm precedence in relation to spawning times in the Montastraea annularis species complex (Cnidaria: Scleractinia)

In broadcast spawners, prezygotic reproductive isolation depends on differences in the spatial and temporal patterns of gamete release and gametic incompatibility. Typically, gametic incompatibility is measured in no‐choice crosses, but conspecific sperm precedence (CSP) can prevent hybridization in gametes that are compatible in the absence of sperm competition. Broadcast spawning corals in the Montastraea annularis species complex spawn annually on the same few evenings. Montastraea franksi spawns an average of 110 min before M. annularis, with a minimum gap of approximately 40 min. Gametes are compatible in no‐choice heterospecific assays, but it is unknown whether eggs exhibit choice when in competition. Hybridization depends on either M. franksi eggs remaining unfertilized and in proximity to M. annularis when the latter species spawns or M. franksi sperm remaining in sufficient viable concentrations when M. annularis spawns. We found that the eggs of the early spawning M. franksi demonstrate strong CSP, whereas CSP appears to be lacking for M. annularis eggs. This study provides evidence of diverging gamete affinities between these recently separated species and suggests for the first time that selection may favour CSP in earlier spawning species when conspecific sperm is diluted and aged and is otherwise at a numeric and viability disadvantage with heterospecific sperm.     

The effects of heterospecific mating frequency on the strength of cryptic reproductive barriers

Heterospecific mating frequency is critical to hybrid zone dynamics and can directly impact the strength of reproductive barriers and patterns of introgression. The effectiveness of post‐mating prezygotic (PMPZ) reproductive barriers, which include reduced fecundity via heterospecific matings and conspecific sperm precedence, may depend on the number, identity and order of mates. Studies of PMPZ barriers suggest that they may be important in many systems, but whether these barriers are effective at realistic heterospecific mating frequencies has not been tested. Here, we evaluate the strength of cryptic reproductive isolation in two leaf beetles (Chrysochus auratus and C. cobaltinus) in the context of a range of heterospecific mating frequencies observed in natural populations. We found both species benefited from multiple matings, but the benefits were greater in C. cobaltinus and extended to heterospecific matings. We found that PMPZ barriers greatly limited hybrid production by C. auratus females with moderate heterospecific mating frequencies, but that their effectiveness diminished at higher heterospecific mating frequencies. In contrast, there was no evidence for PMPZ barriers in C. cobaltinus females at any heterospecific mating frequency. We show that integrating realistic estimates of cryptic isolation with information on relative abundance and heterospecific mating frequency in the field substantially improves our understanding of the strong directional bias in F1 production previously documented in the Chrysochus hybrid zone. Our results demonstrate that heterospecific mating frequency is critical to understanding the impact of cryptic post‐copulatory barriers on hybrid zone structure and dynamics, and that future studies of such barriers should incorporate field‐relevant heterospecific mating frequencies.     

Morphological variability of the shape of striped red mullet Mullus surmuletus in relation to stock discrimination between the Bay of Biscay and the eastern English Channel

Truss analysis and length measurements were made on 168 striped red mullet Mullus surmuletus. Multivariate statistical analyses with principal component analysis and partial redundancy analysis (pRDA) were used on these measurements to evaluate the influence of maturity, sex and geographical area distribution on body shape. Truss measurements were important to quantify and discriminate changing body shape, presumably due to changing environmental conditions. Sexual dimorphism was not observed and juveniles could be distinguished from adults based on their body shape. More importantly, M. surmuletus occurring in different geographical areas could be differentiated using this method. Based on pRDA, a significant difference of head morphological dimensions was observed between populations occurring in the eastern English Channel and those occurring in the Bay of Biscay, suggesting that fish from these areas could represent two subpopulations.     

Behavioural and ultrastructural studies on the sedentary platyctenean ctenophore Vallicula multiformis

Feeding habit and diet composition of two colonizing mullids, Upeneus asymmetricus and U. moluccensis, and two indigenous goatfish Mullus barbatus and M. surmuletus (Mullidae), in the eastern Mediterranean were investigated. The most important taxonomic group in the diet of all four species was the Decapoda which were identified to the specific level, enabling precise assessment of trophic partitioning. Leptochela pugnax, a pasiphaeid of Red Sea origin, was by far the most important prey of all mullids studied, which resulted in considerable trophic overlap between all of the species. Trophic separation does not play an important role in resource partitioning of the eastern Mediterranean mullids. Consequently, coexistence between colonizing and indigenous mullids is presumably achieved by spatial segregation.     

Differential Response to Interspecific and Intraspecific Signals Amongst Chickadees

Black‐capped chickadees (Poecile atricapillus) and mountain chickadees (P. gambeli) have a similar vocal repertoire and share many other life history traits; yet, black‐capped chickadees are socially dominant to mountain chickadees where populations overlap. Previous research suggested that in contact zones, both species respond weakly to heterospecific songs during the breeding season, and have suggested minimal interspecific competition. However, both black‐capped and mountain chickadees discriminate between conspecific and heterospecific chick‐a‐dee calls, suggesting attention is paid to interspecific signals. We compared the responses of both black‐capped and mountain chickadees to conspecific and heterospecific chick‐a‐dee calls during the winter, when both species compete for the same food resources. We conducted an aviary playback experiment exposing both species to playback composed of heterospecific and conspecific chick‐a‐dee calls, which had been recorded in the context of finding food sources. Responses from the tested birds were measured by recording vocalizations and behaviour. Black‐capped chickadees responded significantly more to conspecific than to heterospecific stimuli, whereas the subordinate mountain chickadees responded to both mountain and black‐capped chickadee calls. Based upon the reactions to playbacks, our results suggest these two closely related species may differ in their perception of the relative threat associated with intra‐ versus interspecific competitors.     

A preliminary assessment of the response of a native reptile assemblage to spot‐spraying invasive Bitou Bush with glyphosate herbicide

During recent work examining the effects of Bitou Bush (Chrysanthemoides monilifera ssp. rotundata) invasion on native reptile assemblages in coastal heathland vegetation in Eastern Australia, unplanned spot‐spraying of glyphosate occurred at some of our experimental sites invaded by Bitou Bush. We used this unexpected herbicide application as an opportunity to provide a preliminary assessment of the short‐term impacts on reptiles of glyphosate spot‐spraying of Bitou Bush. Using an M‐BARCI design, we compared reptile assemblages among uninvaded (reference) sites, invaded (control) sites and invaded and sprayed (impact) sites before and after spraying. We found no significant short‐term (7 – 10 months) differences in reptile abundance, species richness or assemblage composition among invaded, uninvaded and sprayed sites before and after glyphosate application. We cautiously interpret our results to generate a preliminary finding that spot‐spraying of Bitou Bush with glyphosate appears not to have a deleterious effect on reptile assemblages at seven and ten months following herbicide application. While we would not recommend basing management decisions on the outcomes of our study alone, we suggest that our findings can be used to assist in the development of strategic analyses of glyphosate impacts on native flora and fauna.     

Insect diversity and trophic structure differ on native and non‐indigenous congeneric rushes in coastal salt marshes

Displacement of native plant species by non‐indigenous congeners may affect associated faunal assemblages. In endangered salt marshes of south‐east Australia, the non‐indigenous rush Juncus acutus is currently displacing the native rush Juncus kraussii, which is a dominant habitat‐forming species along the upper border of coastal salt marshes. We sampled insect assemblages on multiple plants of these congeneric rushes in coastal salt marshes in Sydney, New South Wales, Australia, and compared the abundance, richness, diversity, composition and trophic structure between: (i) J. acutus and J. kraussii at invaded locations; and (ii) J. kraussii at locations either invaded or not invaded by J. acutus. Although J. acutus supported a diverse suite of insects, species richness and diversity were significantly greater on the native J. kraussii. Moreover, insect assemblages associated with J. kraussii at sites invaded by J. acutus were significantly different from, and more variable than, those on J. kraussii at non‐invaded sites. The trophic structure of the insect assemblages was also different, including the abundance and richness of predators and herbivores, suggesting that J. acutus may be altering consumer interactions, and may be spreading in part because of a reduction in herbivory. This strongly suggests that J. acutus is not playing a functionally similar role to J. kraussii with respect to the plant‐associated insect species assemblages. Consequently, at sites where this non‐indigenous species successfully displaces the native congener, this may have important ecological consequences for community composition and functioning of these endangered coastal salt marshes.     

Mycorrhizal feedback is not associated with the outcome of competition in old‐field perennial plants

The symbiosis between plants and arbuscular mycorrhizal (AM) fungi is hypothesized to be an important contributor to plant–soil feedbacks, which can influence the outcome of inter‐specific competition. Mycorrhizal feedbacks can be conspecific, which affects individuals of the same species, or heterospecific, which affects individuals of a different species. When heterospecific feedbacks are more positive than conspecific feedbacks, heterospecific individuals are expected to outcompete conspecific individuals. To test this hypothesis, we quantified conspecific mycorrhizal feedback for Plantago lanceolata as a focal species, and heterospecific mycorrhizal feedbacks for 21 competitor old‐field species using mycorrhizae cultured with P. lanceolata. We quantified inter‐specific competition against the focal species by growing the 21 old‐field species with and without P. lanceolata in the presence of mycorrhizae cultured with P. lanceolata. Heterospecific and conspecific feedbacks were both positive, and average heterospecific feedbacks exceeded conspecific feedback by 75%. Competition suppressed P. lanceolata biomass by 14% and average competitor biomass was reduced by 44% in the presence of P. lanceolata, and these effects varied with competitor species identity. Contrary to predictions, the magnitude of heterospecific feedbacks did not predict the ability of competitor species to either suppress or resist suppression by P. lanceolata. Instead, the outcome of competition was significantly and positively correlated with intrinsic growth rate, measured as biomass of competitor species five weeks after germination in non‐inoculated conditions. Our findings suggest that species experiencing more positive mycorrhizal feedbacks than a competitor do not necessarily have a competitive advantage. Mycorrhizal mediated soil feedbacks may be less important than intrinsic differences in growth rate in determining competitive outcomes.