Congeneric Plant Species Research Articles

Distributions of non‐native and native plants are not determined by the same environmental factors

Abstract Global environmental change will cause shifts in species communities, with non‐native species likely replacing native ones at an unprecedented rate. This will have consequences for biodiversity and ecosystem services, in addition to the ecological and economic damage caused by those non‐native species that are invasive. Understanding general patterns driving distributions of native and non‐native species is therefore vital, but no study has compared yet whether environmental variables that correlate with a species' presence differ between the two groups other than at local scale and often with very limited sample size. In this study, we focus on 141 native and non‐native congeneric plant species pairs at the scale of Switzerland. In the framework of correlative species distribution models, we used newly developed methods for efficient automated selection of a parsimonious number of predictor environmental variables to determine which ones, out of a large candidate set in eight classes, have the strongest explanatory power for both species groups. Our results indicated that variables influence the two groups in significantly different ways. Climate was by far the strongest determinant of both native and non‐native species distributions, although it had significantly more explanatory power in native species models. Models for non‐native species were significantly more influenced by anthropogenic factors, land use variables and forest cover. The presence of non‐native species was also associated with habitats with a significantly lower mean naturality value than native species. These findings provide novel empirical evidence for the different environmental factors driving native and non‐native plants' distributions and guidance for non‐native species management. Practical implications: species distribution models are an increasingly frequently advised tool for conservation management and our results provide guidelines on which covariates should be specifically considered to assess the habitat suitability of non‐native versus native species. The distributions of the former group of species are particularly important to research, as, in time, they may turn invasive. In addition, areas close to infrastructure should be scanned regularly for incipient colonizations by non‐native species, especially in as yet uninvaded areas, such as high mountains.

Flowering phenology patterns promotes pollination facilitation in coexisting Anthurium species from a mountain forest in Colombia

AbstractCo-flowering congeneric plant species may either experience competition for the services of shared pollinators or facilitation when together, they attract a higher number and diversity of pollinators. In this study, we evaluate whether temporal segregation in flowering time and temporal partition of shared pollinators operate among sympatric Anthurium species as mechanisms to reduce competition to attract potential pollinators. We investigated flowering phenology, the intra-e interspecific synchrony, and the composition of the flower visitor community of seven coexisting Anthurium species biweekly for a whole year in Native and Pine forests. We also analyzed the structure of Anthurium -flower visitor networks and the functional role of species. Flowering was continuous thorough the year for most Anthurium species, but their flowering peaks were segregated significantly in time. Although the flowering periods of these species overlapped, flower visitor communities were very dissimilar among Anthurium species, sharing only a tiny fraction of insects that function as connectors among species in the network. The partition of potential pollinators in a fine temporal scale occurred through the rewiring of shared flower visitors to the most abundant flowering Anthurium species. On the other hand, a high number of inflorescences attracted larger abundance and richness of insect visitors. Facilitation occurred almost throughout the year, while competition occurred during the flowering peak, where a particular species was the best competitor increasing the constancy of pollinators. This study highlights the role of facilitation and competition as mechanisms that together shape the use of potential pollinator resources between sympatric congeneric plant species.

Comparative epigenetic and genetic spatial structure in Mediterranean mountain plants: a multispecies study.

Changes in epigenetic states can allow individuals to cope with environmental changes. If such changes are heritable, this may lead to epigenetic adaptation. Thus, it is likely that in sessile organisms such as plants, part of the spatial epigenetic variation found across individuals will reflect the environmental heterogeneity within populations. The departure of the spatial epigenetic structure from the baseline genetic variation can help in understanding the value of epigenetic regulation in species with different breadth of optimal environmental requirements. Here, we hypothesise that in plants with narrow environmental requirements, epigenetic variability should be less structured in space given the lower variability in suitable environmental conditions. We performed a multispecies study that considered seven pairs of congeneric plant species, each encompassing a narrow endemic with habitat specialisation and a widespread species. In three populations per species we used AFLP and methylation-sensitive AFLP markers to characterise the spatial genetic and epigenetic structures. Narrow endemics showed a significantly lower epigenetic than genetic differentiation between populations. Within populations, epigenetic variation was less spatially structured than genetic variation, mainly in narrow endemics. In these species, structural equation models revealed that such pattern was associated to a lack of correlation between epigenetic and genetic information. Altogether, these results show a greater decoupling of the spatial epigenetic variation from the baseline spatial genetic pattern in endemic species. These findings highlight the value of studying genetic and epigenetic spatial variation to better understand habitat specialisation in plants.

Preference and performance of the generalist aphid Myzus persicae on closely and distantly related plant species

AbstractThe ability of herbivorous insects to discriminate suitable host plants for the development of their progeny is not homogenous. Herbivores with broader diets show weaker correlation between oviposition preference and offspring performance in comparison with specialist insects. The neural constraints hypothesis postulates that due to neural limitation, generalist insects would have greater difficulty in processing a large number of stimuli from diverse host plants. Under this framework, it is expected that generalists would be more efficient in discriminating suitable plants when faced with more similar stimuli from closely related plants (simplified environment), and less efficient when faced with more diverse stimuli from unrelated plants (complex environment). In this study, we evaluated this in the generalist aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae). Preference was evaluated as the aphid's ability to discriminate between congeneric plant species or between plants from different families. The congeneric host plants were the cultivated potato, Solanum tuberosum L., the wild potato, Solanum commersonii Dunal, tomato, Solanum lycopersicum L., and eggplant, Solanum melongena L. (Solanaceae). The plant species of different families used were spinach, Spinacia oleracea L. (Amaranthaceae), squash, Cucurbita maxima Duchesne (Cucurbitaceae), and basil, Ocimum basilicum L. (Lamiaceae). Performance was evaluated as the population growth in one generation on whole‐plant conditions and on excised leaves. The results showed positive correlations between settlement and larviposition preferences and the performance of M. persicae for all comparisons between unrelated plant species. Positive correlations between preference and performance were also observed for two of the three comparisons between congeneric plants. These results indicate that M. persicae can efficiently discriminate between suitable plants for their progeny regardless of the degree of relatedness of the plants, which is at odds with the neural constraints hypothesis. The results contribute to the knowledge of host selection mechanisms in generalist herbivores, particularly in an underrepresented insect group.

Correction: Diversity among rare and common congeneric plant species from the Garry oak and Okanagan shrub-steppe ecosystems in British Columbia: implications for conservation

Correction: Diversity among rare and common congeneric plant species from the Garry oak and Okanagan shrub-steppe ecosystems in British Columbia: implications for conservation

Mycorrhiza governs plant-plant interactions through preferential allocation of shared nutritional resources: A triple (13C, 15N and 33P) labeling study.

Plant-plant interactions and coexistence can be directly mediated by symbiotic arbuscular mycorrhizal (AM) fungi through asymmetric resource exchange between the plant and fungal partners. However, little is known about the effects of AM fungal presence on resource allocation in mixed plant stands. Here, we examined how phosphorus (P), nitrogen (N) and carbon (C) resources were distributed between coexisting con- and heterospecific plant individuals in the presence or absence of AM fungus, using radio- and stable isotopes. Congeneric plant species, Panicum bisulcatum and P. maximum, inoculated or not with Rhizophagus irregularis, were grown in two different culture systems, mono- and mixed-species stands. Pots were subjected to different shading regimes to manipulate C sink-source strengths. In monocultures, P. maximum gained more mycorrhizal phosphorus uptake benefits than P.bisulcatum. However, in the mixed culture, the AM fungus appeared to preferentially transfer nutrients (33P and 15N) to P.bisulcatum compared to P. maximum. Further, we observed higher 13C allocation to mycorrhiza by P.bisulcatum in mixed- compared to the mono-systems, which likely contributed to improved competitiveness in the mixed cultures of P.bisulcatum vs. P. maximum regardless of the shading regime. Our results suggest that the presence of mycorrhiza influenced competitiveness of the two Panicum species in mixed stands in favor of those with high quality partner, P. bisulcatum, which provided more C to the mycorrhizal networks. However, in mono-species systems where the AM fungus had no partner choice, even the lower quality partner (i.e., P.maximum) could also have benefitted from the symbiosis. Future research should separate the various contributors (roots vs. common mycorrhizal network) and mechanisms of resource exchange in such a multifaceted interaction.

Diversity among rare and common congeneric plant species from the Garry oak and Okanagan shrub-steppe ecosystems in British Columbia: implications for conservation

It is often assumed that the northern peripheral populations of species’ ranges are genetically depauperate due in part to founder effects from postglacial colonization. The majority of federally protected plant species are peripheral in Canada, yet we have little information about their patterns of genetic diversity and structure. In British Columbia, the majority of these protected plant species occur in two threatened habitats: the Garry oak and Okanagan shrub-steppe ecosystems. Using universal noncoding chloroplast DNA markers, we investigated genetic diversity and genetic structure in four rare and common plant species pairs inhabiting these two ecosystems. We found that rare species had lower genetic diversity than their common congeners, and detected contrasting patterns of regional diversity and structure based on ecosystem. Species from the Garry oak ecosystem showed lower genetic diversity in the northern deglaciated region and significant differentiation between regions, likely due to limited dispersal between Vancouver Island and the mainland. Species from the Okanagan shrub-steppe, however, tended to have uniform diversity across their range and lack regional structure. This study provides an important first look at the phylogeographic patterns of four rare plant species in British Columbia.

Eco-evolutionary causes and consequences of rarity in plants: a meta-analysis.

Species differ dramatically in their prevalence in the natural world, with many species characterized as rare due to restricted geographic distribution, low local abundance and/or habitat specialization. We investigated the ecoevolutionary causes and consequences of rarity with phylogenetically controlled metaanalyses of population genetic diversity, fitness and functional traits in rare and common congeneric plant species. Our syntheses included 252 rare species and 267 common congeners reported in 153 peer-reviewed articles published from 1978 to 2020 and one manuscript in press. Rare species have reduced population genetic diversity, depressed fitness and smaller reproductive structures than common congeners. Rare species also could suffer from inbreeding depression and reduced fertilization efficiency. By limiting their capacity to adapt and migrate, these characteristics could influence contemporary patterns of rarity and increase the susceptibility of rare species to rapid environmental change. We recommend that future studies present more nuanced data on the extent of rarity in focal species, expose rare and common species to ecologically relevant treatments, including reciprocal transplants, and conduct quantitative genetic and population genomic analyses across a greater array of systems. This research could elucidate the processes that contribute to rarity and generate robust predictions of extinction risks under global change.

Context dependency of biotic interactions and its relation to plant rarity

AbstractAimBiotic interactions can determine rarity and commonness of species, however, evidence that rare and common species respond differently to biotic stress is scarce. This is because biotic interactions are notoriously context dependent and traits leading to success in one habitat might be costly or unimportant in another. We aim to identify plant characteristics that are related to biotic interactions and may drive patterns of rarity and commonness, taking environmental context into account.LocationSwitzerland.MethodsIn a multispecies experiment, we compared the response to biotic interactions of 19 rare and 21 widespread congeneric plant species in Switzerland, while also accounting for variation in environmental conditions of the species' origin.ResultsOur results restrict the long‐standing hypothesis that widespread species are superior competitors to rare species to only those species originating from resource‐rich habitats, in which competition is usually strong. Tolerance to herbivory and ambient herbivore damage, on the other hand, did not differ between widespread and rare species. In accordance with the resource‐availability hypothesis, widespread species from resource‐rich habitats where more damaged by herbivores (less defended) than widespread species from resource‐poor habitats—such a growth‐defence trade‐off was lacking in rare species. This indicates that the evolutionary important trade‐off between traits increasing competitive ability and defence is present in widespread species but may have been lost or never evolved in rare species.Main conclusionsOur results indicate that biotic interactions, above all competition, might indeed set range limits and underlines the importance of including context dependency in studies comparing traits of common and rare or invasive and non‐invasive species.

Shared mycorrhizae but distinct communities of other root-associated microbes on co-occurring native and invasive maples.

BackgroundBiological invasions are major drivers of environmental change that can significantly alter ecosystem function and diversity. In plants, soil microbes play an important role in plant establishment and growth; however, relatively little is known about the role they might play in biological invasions. A first step to assess whether root microbes may be playing a role in the invasion process is to find out if invasive plants host different microbes than neighbouring native plant species.MethodsIn this study we investigated differences in root associated microbes of native sugar maple (Acer saccharum Marsh.) and exotic Norway maple (A. platanoides L.) collected from a forested reserve in eastern Canada. We used microscopy to examine root fungi and high-throughput sequencing to characterize the bacterial, fungal and arbuscular mycorrhizal communities of both maple species over one growing season.ResultsWe found differences in root associated bacterial and fungal communities between host species. Norway maple had a higher bacterial and fungal OTU (operational taxonomic units) richness compared to sugar maple, and the indicator species analysis revealed that nine fungal OTUs and three bacterial OTUs had a significant preference for sugar maple. The dominant bacterial phyla found on the roots of both maple species were Actinobacteria and Proteobacteria. The most common fungal orders associated with the Norway maple roots (in descending order) were Helotiales, Agaricales, Pleosporales, Hypocreales, Trechisporales while the Agaricales, Pleosporales, Helotiales, Capnodiales and Hypocreales were the dominant orders present in the sugar maple roots. Dark septate fungi colonization levels were higher in the sugar maple, but no differences in arbuscular mycorrhizal fungal communities and colonization rates were detected between maple species.DiscussionOur findings show that two congeneric plant species grown in close proximity can harbor distinct root microbial communities. These findings provide further support for the importance of plant species in structuring root associated microbe communities. The high colonization levels observed in Norway maple demonstrates its compatibility with arbuscular mycorrhizal fungi in the introduced range. Plant-associated microbial communities can affect host fitness and function in many ways; therefore, the observed differences suggest a possibility that biotic interactions can influence the dynamics between native and invasive species.

LAESI mass spectrometry imaging as a tool to differentiate the root metabolome of native and range-expanding plant species

Main conclusionLAESI-MSI, an innovative high-throughput technique holds a unique potential for untargeted detection, profiling and spatial localization of metabolites from intact plant samples without need for extraction or extensive sample preparation.Our understanding of chemical diversity in biological samples has greatly improved through recent advances in mass spectrometry (MS). MS-based-imaging (MSI) techniques have further enhanced this by providing spatial information on the distribution of metabolites and their relative abundance. This study aims to employ laser-ablation electrospray ionization (LAESI) MSI as a tool to profile and compare the root metabolome of two pairs of native and range-expanding plant species. It has been proposed that successful range-expanding plant species, like introduced exotic invaders, have a novel, or a more diverse secondary chemistry. Although some tests have been made using aboveground plant materials, tests using root materials are rare. We tested the hypothesis that range-expanding plants possess more diverse root chemistries than native plant species. To examine the root chemistry of the selected plant species, LAESI-MSI was performed in positive ion mode and data were acquired in a mass range of m/z 50–1200 with a spatial resolution of 100 µm. The acquired data were analyzed using in-house scripts, and differences in the spatial profiles were studied for discriminatory mass features. The results revealed clear differences in the metabolite profiles amongst and within both pairs of congeneric plant species, in the form of distinct metabolic fingerprints. The use of ambient conditions and the fact that no sample preparation was required, established LAESI-MSI as an ideal technique for untargeted metabolomics and for direct correlation of the acquired data to the underlying metabolomic complexity present in intact plant samples.

Relatedness with plant species in native community influences ecological consequences of range expansions

Global warming is enabling many plant species to expand their range to higher latitudes and altitudes, where they may suffer less from natural aboveground and belowground enemies. Reduced control by natural enemies can enable climate warming‐induced range expanders to gain an advantage in competition with natives and become disproportionally abundant in their new range. However, so far studies have only examined individual growth of range expanders, which have common congeneric plant species in their new range. Thus it is not known how general is this reduced effect of above‐ and belowground enemies and how it operates in communities, where multiple plant species also interact with each other. Here we show that range‐expanding plant species with and without congenerics in the invaded habitats differ in their ecological interactions in the new range. In a community‐level experiment, range‐expanding plant species, both with and without congenerics, suppressed the growth of a herbivore. However, only range expanders without congenerics reduced biomass production of the native plant species. In the present study, range expanders without congenerics allocated more biomass aboveground compared to native plant species, which can explain their competitive advantage. Competitive interaction and also biomass allocation of native plants and their congeneric range expanders were similar. Our results highlight that information about species phylogenetic relatedness with native flora can be crucial for improving predictions about the consequences of climate warming‐induced range expansions.

Belowground Plant-Herbivore Interactions Vary among Climate-Driven Range-Expanding Plant Species with Different Degrees of Novel Chemistry.

An increasing number of studies report plant range expansions to higher latitudes and altitudes in response to global warming. However, consequences for interactions with other species in the novel ranges are poorly understood. Here, we examine how range-expanding plant species interact with root-feeding nematodes from the new range. Root-feeding nematodes are ubiquitous belowground herbivores that may impact the structure and composition of natural vegetation. Because of their ecological novelty, we hypothesized that range-expanding plant species will be less suitable hosts for root-feeding nematodes than native congeneric plant species. In greenhouse and lab trials we compared nematode preference and performance of two root-feeding nematode species between range-expanding plant species and their congeneric natives. In order to understand differences in nematode preferences, we compared root volatile profiles of all range-expanders and congeneric natives. Nematode preferences and performances differed substantially among the pairs of range-expanders and natives. The range-expander that had the most unique volatile profile compared to its related native was unattractive and a poor host for nematodes. Other range-expanding plant species that differed less in root chemistry from native congeners, also differed less in nematode attraction and performance. We conclude that the three climate-driven range-expanding plant species studied varied considerably in their chemical novelty compared to their congeneric natives, and therefore affected native root-feeding nematodes in species-specific ways. Our data suggest that through variation in chemical novelty, range-expanding plant species may vary in their impacts on belowground herbivores in the new range.

The influence of residence time and geographic extent on the strength of plant–soil feedbacks for naturalised Trifolium

Abstract Release from natural enemies is considered an important mechanism underlying the success of plants introduced to new regions, but the degree to which alien plant species benefit from enemy release appears highly variable and context‐dependent. Such variation could arise if enemy release is a transient phenomenon, whereby alien plant species initially escape but subsequently accumulate enemies in their new regions. To evaluate this hypothesis in terms of soil biota, we used 11 Trifolium (clover) species introduced to New Zealand from Europe to test whether species resident for longer or with a larger geographic extent in New Zealand were more adversely affected by soil communities in the introduced range, as expected if species have accumulated inhibitory soil biota over time. We used plant–soil feedback (PSF) experiments to compare the effect of soil biota on the growth of the Trifolium species in soil from their introduced (New Zealand) and native (Spain and the United Kingdom) ranges. We applied a novel statistical approach aimed at isolating the impact of antagonistic soil biota by accounting for variation in plant growth due to mutualistic rhizobia bacteria. The between‐range differences in PSF varied considerably among the Trifolium species: some species were released from inhibitory PSF in the introduced range, but the majority experienced similar PSF in both ranges. Averaged over all 11 Trifolium species, PSF was less inhibitory in the introduced than in the native range, implying some release from soil‐borne enemies. However, neither residence time nor geographic extent in the introduced range was significantly correlated with the strength of release from inhibitory PSF. Synthesis. Our multispecies study provides some evidence that alien plants can escape antagonistic soil biota in their introduced range, but highlights how plant–soil feedback responses can be highly variable among congeneric plant species in the same region. Our results do not support the hypothesis that the release from inhibitory plant–soil feedback is transient, questioning the generality of this phenomenon.

Total Bee Dependence on One Flower Species Despite Available Congeners of Similar Floral Shape

Extreme specialization is a common phenomenon in antagonistic biotic interactions but it is quite rare in mutualistic ones. Indeed, bee specialization on a single flower species (monolecty) is a questioned fact. Here, we provide multiple lines of evidence on true monolecty in a solitary bee (Flavipanurgus venustus, Andrenidae), which is consistent across space (18 sites in SW Iberian Peninsula) and time (three years) despite the presence of closely related congeneric plant species whose flowers are morphologically similar. The host flower (Cistus crispus, Cistaceae) is in turn a supergeneralist, visited by at least 85 insect species. We uncover ultraviolet light reflectance as a distinctive visual cue of the host flower, which can be a key mechanism because bee specialization has an innate basis to recognize specific signals. Moreover, we hypothesized that a total dependence on an ephemeral resource (i.e. one flower species) must lead to spatiotemporal matching with it. Accordingly, we prove that the bee’s flight phenology is synchronized with the blooming period of the host flower, and that the densities of bee populations mirror the local densities of the host flower. This case supports the ‘predictable plethora’ hypothesis, that is, that host-specialization in bees is fostered by plant species providing predictably abundant floral resources. Our findings, along with available phylogenetic information on the genus Cistus, suggest the importance of historical processes and cognitive constraints as drivers of specialization in bee-plant interactions.

Modularity in ecological networks between frugivorous birds and congeneric plant species

Abstract:Ecological and evolutionary factors influence the presence of modules in species interaction networks, and these modules usually cluster functional similar species. But whether closely related species form modules is still unknown. We tested whether the interaction networks formed by frugivorous birds andMiconiaplants are modular and evaluated how modules were divided. To do so, we gathered from the literature data concerning four networks ofMiconiaand their frugivorous birds (three from Brazilian savanna and one from a rain forest in Panama). We quantified modularity using binary and weighted algorithms and also tested the relationship between bird traits (body mass, dietary specialization, migratory behaviour and phylogeny) in relation to within- and among-module connectivity indices (candzvalues). If considering only binary information, networks did not present distinct modular structure. Nevertheless, by including interaction strength, modules can be detected in all fourMiconia-bird networks. None of the bird traits, however, was related with the connectivity indices. The possible fluctuation of frugivorous bird abundance coupled with the asynchronic fruiting period ofMiconiamight favour the formation of temporal modules comprising birds and plant species with phenological overlap, ensuring seed dispersal and facilitating the coexistence in sympatry. Bird traits had little effect on the role that each species plays within the modular network, probably because the frugivorous assemblages were dominated by small-bodied and opportunistic species.

Ecological host-range of Lilioceris cheni (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera

Open-field host-specificity testing assesses the host-range of a biological control agent in a setting that permits the agent to use its full complement of host-seeking behaviors. This form of testing, particularly when it includes a no-choice phase in which the target weed is killed, may provide the most accurate assessment of the ecological host-range of an agent. We conducted a two-phase field host-specificity test with experienced and naïve adults of Lilioceris cheni Gressitt and Kimoto (Coleoptera: Chrysomelidae), a biological control agent of Dioscorea bulbifera L. (Dioscoreales: Dioscoreaceae). We followed field tests with a no-choice laboratory consumption study with the congeneric plant species that received test feeding in the field, and an additional field evaluation of spillover risk. Both experienced and naïve adults strongly preferred D. bulbifera to non-targets in the field. Within 47h post-release, 90% of the released beetles that remained in the plots were found on D. bulbifera. In the laboratory no-choice test, the beetles consumed significantly more D. bulbifera and survived longer on this plant than the non-targets. All naïve beetles in the Dioscorea sansibarensis and Dioscorea villosa treatments and 75% of naïve beetles on Dioscorea floridana died within 7d. Potted plants of the native D. floridana experienced minor test feeding in the spillover experiment when surrounded by large populations of L. cheni in the field. At the end of this experiment, L. cheni eggs and/or larvae were present on 83% of D. bulbifera plants but none of the D. floridana plants. We conclude that L. cheni is host-specific to D. bulbifera and does not pose a spillover risk to the native D. floridana.

A mutualistic endophyte alters the niche dimensions of its host plant.

Mutualisms can play important roles in influencing species coexistence and determining community composition. However, few studies have tested whether such interactions can affect species distributions by altering the niches of partner species. In subalpine meadows of the Rocky Mountains, USA, we explored whether the presence of a fungal endophyte (genus Epichloë) may shift the niche of its partner plant, marsh bluegrass (Poa leptocoma) relative to a closely related but endophyte-free grass species, nodding bluegrass (Poa reflexa). Using observations and a 3-year field experiment, we tested two questions: (i) Do P. leptocoma and P. reflexa occupy different ecological niches? and (ii) Does endophyte presence affect the relative fitness of P. leptocoma versus P. reflexa in the putative niches of these grass species? The two species were less likely to co-occur than expected by chance. Specifically, P. leptocoma grew closer to water sources and in wetter soils than P. reflexa, and also had higher root colonization by mycorrhizal fungi. Endophyte-symbiotic P. leptocoma seeds germinated with greater frequency in P. leptocoma niches relative to P. reflexa niches, whereas neither endophyte-free (experimentally removed) P. leptocoma seeds nor P. reflexa seeds showed differential germination between the two niche types. Thus, endophyte presence constrained the germination and early survival of host plants to microsites occupied by P. leptocoma. However, endophyte-symbiotic P. leptocoma ultimately showed greater growth than endophyte-free plants across all microsites, indicating a net benefit of the symbiosis at this life history stage. Differential effects of endophyte symbiosis on different host life history stages may thus contribute to niche partitioning between the two congeneric plant species. Our study therefore identifies a symbiotic relationship as a potential mechanism facilitating the coexistence of two species, suggesting that symbiont effects on host niche may have community-level consequences.

Top-down control of root-feeding nematodes in range-expanding and congeneric native plant species

Climate warming may result in range expansion of species towards previously colder environments, and it has been demonstrated that in the new range successfully range-expanding plant species can be less attacked by aboveground and belowground enemies than congeneric natives. Plant enemies may be controlled naturally by complex bottom-up and top-down interactions with their hosts, however, little is known about how these interactions may operate in the new range. Here, we examine how root-feeding nematodes are controlled in the root zone of successfully range-expanding plant species in comparison with congeneric plant species native to the new range. As range-expanding plant species can have less negative soil feedback than congeneric natives, we tested the hypothesis that top-down control of root-feeding nematodes may be strongest on range-expanding plant species. To test this, we grew four pairs of range-expanding plant species and their native congeners in field soil, to which we added soil microbes, nematodes, or microarthropods from the new habitat. Addition of soil microorganisms and microarthropods reduced the numbers of root-feeding nematodes, being strongest when microorganisms were added. Opposite to our expectation, nematode control was not more effective in the root zone of range-expanding than native plant species. We conclude that top-down control of root-feeding nematodes is highly plant species-specific and that top-down control of these nematodes in the root zone of range-expanding plant species can be as effective as in the root zone of congeneric natives.

Potential impacts of climate change on insect communities: a transplant experiment.

Climate change will have profound impacts on the distribution, abundance and ecology of all species. We used a multi-species transplant experiment to investigate the potential effects of a warmer climate on insect community composition and structure. Eight native Australian plant species were transplanted into sites approximately 2.5°C (mean annual temperature) warmer than their native range. Subsequent insect colonisation was monitored for 12 months. We compared the insect communities on transplanted host plants at the warmer sites with control plants transplanted within the species' native range. Comparisons of the insect communities were also made among transplanted plants at warmer sites and congeneric plant species native to the warmer transplant area. We found that the morphospecies composition of the colonising Coleoptera and Hemiptera communities differed markedly between transplants at the control compared to the warmer sites. Community structure, as described by the distribution of feeding guilds, was also found to be different between the controls and transplants when the entire Coleoptera and Hemiptera community, including non-herbivore feeding guilds, was considered. However, the structure of the herbivorous insect community showed a higher level of consistency between plants at control and warm sites. There were marked differences in community composition and feeding guild structure, for both herbivores and non-herbivores, between transplants and congenerics at the warm sites. These results suggest that as the climate warms, considerable turnover in the composition of insect communities may occur, but insect herbivore communities may retain elements of their present-day structure.