1. Senescence, the physiological decline that results in decreasing survival and/or reproduction with age, remains one of the most perplexing topics in biology. Most theories explaining the evolution of senescence (i.e. antagonistic pleiotropy, accumulation of mutations, disposable soma) were developed decades ago. Even though these theories have implicitly focused on unitary animals, they have also been used as the foundation from which the universality of senescence across the tree of life is assumed.
2. Surprisingly, little is known about the general patterns, causes and consequences of whole-individual senescence in the plant kingdom. There are important differences between plants and most animals, including modular architecture, the absence of early determination of cell lines between the soma and gametes, and cellular division that does not always shorten telomere length. These characteristics violate the basic assumptions of the classical theories of senescence and therefore call the generality of senescence theories into question.
3. This Special Feature contributes to the field of whole-individual plant senescence with five research articles addressing topics ranging from physiology to demographic modelling and comparative analyses. These articles critically examine the basic assumptions of senescence theories such as age-specific gene action, the evolution of senescence regardless of the organism's architecture and environmental filtering, and the role of abiotic agents on mortality trajectories.
4. Synthesis. Understanding the conditions under which senescence has evolved is of general importance across biology, ecology, evolution, conservation biology, medicine, gerontology, law and social sciences. The question ‘why is senescence universal or why is it not?’ naturally calls for an evolutionary perspective. Senescence is a puzzling phenomenon, and new insights will be gained by uniting methods, theories and observations from formal demography, animal demography and plant population ecology. Plants are more amenable than animals to experiments investigating senescence, and there is a wealth of published plant demographic data that enable interpretation of experimental results in the context of their full life cycles. It is time to make plants count in the field of senescence.

1. In animals, age-associated disorders are believed to be connected to shifts in the antioxidant/pro-oxidant balance in favour of oxidative stress. However, the contribution of oxidative stress to ageing in long-lived perennials has not been explored to date.
2. Here, we tested age- and sex-related changes in several photo-oxidative stress markers in Borderea pyrenaica, a small dioecious geophyte relict of the Tertiary with one of the longest life spans ever recorded for a non-clonal herb (more than 300 years). Given that survival increases with age in B. pyrenaica, we hypothesized that oxidative stress does not increase with ageing because the species develops improved anti-oxidant defence.
3. In three field samplings performed during 2008, 2010 and 2011 in the Central Pyrenees (NE Spain), we examined the effects of ageing and sex on photosynthetic pigment levels, PSII integrity (F_v /F_m ratio), lipid peroxidation, and the extent of photo and anti-oxidant protection in chloroplasts. Furthermore, we explored whether age and sex affect plant response to severe natural desiccation.
4. Both male and female plants maintained chlorophyll levels intact, as well as the F_v/F_m ratio and the levels of lipid peroxidation, irrespective of age. This finding suggests the absence of age-associated oxidative stress at the organismal level. Furthermore, photoprotection mechanisms were found to be similarly efficient in the oldest individuals as in juvenile plants, in terms of xanthophyll cycle de-epoxidation and accumulation of low-molecular-weight antioxidants (carotenoids and tocopherols). Indeed, females over 100 years of age were the most resistant to severe desiccation, maintaining higher leaf hydration levels, less chlorophyll degradation and better PSII integrity under stress than females below 100 years, males below or above 100 years, and juveniles.
5. Synthesis. Neither males nor females of the extraordinarily long-lived B. pyrenaica show age-dependent signs of oxidative stress. This observation suggests that age-induced oxidative stress is not a universal feature of ageing in perennial plants. Indeed, females older than 100 years showed signs of negative senescence, in that they registered improved physiological performance with increasing age.

Neither males nor females of the extraordinarily long-lived Borderea pyrenaica show age-dependent signs of oxidative stress. This observation suggests that age-induced oxidative stress is not a universal feature of ageing in perennial plants. Indeed, females older than 100 years showed signs of negative senescence, in that they registered improved physiological performance with increasing age.

1. Senescence is characterized by a decline in survival, fecundity and reproductive value with age among adult individuals. Simple age-dependent life cycles progress forward through developmental stages, with each successive stage being characterized by age-specific vital rates. In contrast, size- or stage-based life cycles for perennial plants are more complex and often include stasis and retrogression to previous vegetative or reproductive life stages, indicating possible slowing or even reversing the developmental progress.
2. Many plants remain in nonemergent, below-ground stages during the growing season (prolonged dormancy), which may affect the process of senescence. Stasis in the dormant stage implies that senescence is interrupted while plants are below-ground.
3. We explored the underlying assumptions of size- or stage-based life cycle graphs and developed four different demographic models for how prolonged dormancy may mediate the relationship between age and vital rates. We then tested these models using more than 20 years of demographic data on 2 perennial herbs, Astragalus scaphoides and Silene spaldingii.
4. Results from model fitting suggest that prolonged dormancy interacts with the age dependence of vital rates. The model using true biological age (time since germination) of emergent and dormant plants to estimate vital rates was never the best model for our data. For both species, the model assuming that dormancy resets plants to the same postdormant state experienced earlier in life independent of their predormant age resulted in the best fit, though not for every vital rate.
5. Older Astragalus plants had declining annual survival probabilities and reproductive value, suggesting senescence. Silene showed the opposite pattern for reproductive value that increased with age, indicating negative senescence.
6. Synthesis. Using long-term demographic data from two perennial herbs, this study shows mixed evidence for senescence in perennial plants. Our results indicate that prolonged dormancy interacts with the age dependence of vital rates and may sometimes retard the process of senescence.

We develop a modelling framework for how prolonged dormancy may affect senescence in perennial plants. Using this framework for long-term demographic data from two perennial herbs, the present study shows mixed evidence for senescence in perennial plants. Our results indicate that prolonged dormancy interacts with the age-dependence of vital rates and may sometimes retard the process of senescence.

1. Senescence is usually viewed as increased age-specific mortality or decreased age-specific fecundity due to the declining ability of natural selection to remove deleterious age-specific mutations with age. In herbaceous perennial plants, trends in age-specific mortality are often confounded by size. Age-indeterminate senescence, where accumulated physiological damage varies strongly with environment, may be a better model of senescence in these species.
2. We analysed trends in size and fertility in Plantago lanceolata, using a long-term demographic census involving > 10 years and > 8000 individuals in four cohorts. We used elasticity and pairwise invasion analysis of life-history function parameterized age × stage matrices to assess whether the force of natural selection declined with age. Then, we used reverse age analysis of size and fertility to assess whether age-indeterminate senescence occurred. Reverse age analysis uses longitudinal data for individuals that have died to look at trait patterns as a function of both age and remaining time to death. We hypothesized that (i) the strength of natural selection would decline strongly with age, and (ii) physiological condition would deteriorate for several years prior to death.
3. Both elasticity and invasion analyses suggested that the strength of natural selection through mortality declined strongly with age once size was accounted for. Further, reverse age analyses showed that individuals shrank for 3 years prior to death, suggesting physiological decline. Inflorescence production declined with age, and also declined in the 3 years prior to death regardless of overall age.
4. Synthesis. The hypothesis that plants escape senescence generally assumes that plants can continue to grow larger and increase reproduction as they get older. The results here show that size and reproduction decline with age and the rates of these declines towards death are life span- and age dependent. Further research is needed to delineate the importance of age-determinate vs. age-indeterminate factors in senescence patterns across species.

The hypothesis that plants escape senescence generally assumes that plants can continue to grow larger and increase reproduction as they get older. The results here show that size and reproduction decline with age and the rates of these declines toward death are lifespan- and age-dependent. Further research is needed to delineate the importance of age-determinate vs. age-indeterminate factors in senescence patterns across species.

1. Senescence (an increase in the mortality rate or force of mortality, or a decrease in fertility, with increasing age) is a widespread phenomenon. Theories about the evolution of senescence have long focused on the age trajectories of the selection gradients on mortality and fertility. In purely age-classified models, these selection gradients are non-increasing with age, implying that traits expressed early in life have a greater impact on fitness than traits expressed later in life. This pattern leads inevitably to the evolution of senescence if there are trade-offs between early and late performance.
2. It has long been suspected that the stage- or size-dependent demography typical of plants might change these conclusions. In this paper, we develop a model that includes both stage- and age-dependence and derive the age-dependent, stage-dependent and age×stage-dependent selection gradients on mortality and fertility.
3. We applied this model to stage-classified population projection matrices for 36 species of plants, from a wide variety of growth forms (from mosses to trees) and habitats.
4. We found that the age-specific selection gradients within a life cycle stage can exhibit increases with age (we call these contra-senescent selection gradients). In later stages, often large size classes in plant demography, the duration of these contra-senescent gradients can exceed the life expectancy by several fold.
5. Synthesis. The interaction of age- and stage-dependence in plants leads to selection pressures on senescence fundamentally different from those found in previous, age-classified theories. This result may explain the observation that large plants seem less subject to senescence than most kinds of animals. The methods presented here can lead to improved analysis of both age-dependent and stage-dependent demographic properties of plant populations.

Theories for the evolution of senescence focus on the decline with age in the magnitude of the selection gradient on age-specific mortality. This decline implies that mortality late in life has less impact on fitness than mortality early in life. The demography of plants, however, often depends on size or stage rather than on age alone. We develop an age-stage classified model and show that in such a population the selection gradient on mortality may increase, rather than decrease, with age within a stage, leading to contra-senescent selection.

1. Demographic senescence, the decay in fertility and increase in the risk of mortality with age, is one of the most striking phenomena in ecology and evolution. Comparative studies of senescence patterns of plants are scarce, and consequently, little is known about senescence and its determinants in the plant kingdom.
2. Senescence patterns of mortality can be classified by distinguishing between two metrics: pace and shape. The pace of mortality captures the speed at which life proceeds and can be measured by life expectancy, while the shape of mortality captures whether mortality increases (‘senescence’), decreases (‘negative senescence’) or remains constant over age (‘negligible senescence’).
3. We extract mortality trajectories from ComPADRe III, a data base that contains demographic information for several hundred plant species. We apply age-from-stage matrix decomposition methods to obtain age-specific trajectories from 290 angiosperm species of various growth forms distributed globally. From these trajectories, we survey pace and shape values and investigate how growth form and ecoregion influence these two aspects of mortality using a Bayesian regression analysis that accounts for phylogenetic relationships using a resolved supertree.
4. In contrast to the animal kingdom, most angiosperms (93%) show no senescence. Senescence is observed among phanerophytes (i.e. trees), but not among any other growth form (e.g. epiphytes, chamaephytes or cryptopyhtes). Yet, most phanerophytes (81%) do not senesce. We find that growth form relates to differences in pace, that is, life span, as woody plants are typically longer lived than nonwoody plants, while differences in shape, that is, whether or not angiosperms senesce, are related to ancestral history.
5. Synthesis: The age trajectory of mortality captures a fundamental life-history pattern for a species that is crucial to ecological understanding. We contribute to ecological knowledge by surveying these patterns across angiosperms. The novelty and strength of our study lies in the comprehensiveness of the data set, the use of a novel Bayesian analysis that accounts for phylogenetic history and in the distinction between metrics of pace and shape as two separate aspects of mortality. We believe that our approach could prove useful in future comparative studies of mortality patterns.

Frequency distribution of shape values for different growth forms. The dashed gray vertical line marks the boundary of senescence. Below this point, species show negative senescence, at that point species show negligible senescence and above that point species show senescence.

1. The diversity of pathogens on highly abundant introduced hosts has been positively correlated with time since introduction, geographical range of the introduced species and diversity of invaded habitats. However, little is known about the ecological effects of pathogen accumulation on non-native invasive plants.
2. Pathogen accumulation on invasive plant species may result from ecological processes such as high plant densities, expanding geographical ranges and pathogen dispersal from the native range, or evolutionary mechanisms such as host range shifts and adaptation of native pathogens to invasive species.
3. Over time pathogen accumulation may cause decline in the density and distribution of invasive plants and facilitate recovery of native species. Alternatively, pathogens might build up on invasive species and then spill back onto co-occurring native species, further exacerbating the effects of invasions.
4. Synthesis. Research efforts should focus on determining the long-term outcomes of pathogen accumulation on invasive species. Such research will require multifaceted approaches including comparative studies of diverse invasive species and habitats, experimental manipulations of hosts and pathogens in nature and controlled environments, and predictive models of host-pathogen interactions within an invasion framework. Results of this research will improve our understanding and ability to predict the outcomes of biological invasions.

Here we briefly review the patterns and potential mechanisms of pathogen accumulation on invasive plant species and outline the primary needs for future research. We provide conceptual models to describe the potential outcomes of pathogen accumulation for invasive and resident native species and describe observational, experimental, and modeling research approaches.

1. There has been much debate on the impact of large herbivores on biodiversity, especially given that large mammals are becoming locally extinct in many places.
2. The use of evolutionary information on community structure has typically been limited to evaluating assembly processes, for example, competition or habitat filtering, whereas a lack of long-term experiments has precluded the test of predictions considering more complex biotic interactions.
3. Reconstructing the complete phylogeny of the trees and shrubs of the Kruger National Park from DNA data, we tested for phylogenetic signal in antiherbivory traits and compared the phylogenetic structure of communities under various degrees of herbivore pressure using experimental plots spanning several decades.
4. We show that all antiherbivory traits examined demonstrated weak but significant phylogenetic signal, and that exclusion of large herbivores results in impoverished species diversity in restructured communities. Surprisingly, we also show that reduction in species diversity coupled with community reorganization does not necessarily result in a decrease in phylogenetic diversity, and that community responses to herbivore exclusion depend on initial structure.
5. Synthesis. Extinction of large mammal herbivores will have cascading effects on plant diversity; however, impacts on plant community structure are contingent on initial conditions. This research has implications for best practice when managing large herbivores and natural habitats.

Extinction of large mammal herbivores will have cascading effects on plant diversity; however, impacts on plant community structure are contingent on initial conditions. This research has implications for best practice when managing large herbivores and natural habitats.

1. Non-random spatial patterns are a common feature of plant communities. However, the mechanisms leading to their formation remain unknown. The clonal dispersal ability of a species, that is, the average length of spacers between ramets, is commonly acknowledged to influence spatial patterns in clonal plants, although this relationship remains to be demonstrated. Moreover, the clonal dispersal ability of neighbouring species may influence environmental conditions and trigger modifications in clonal characteristics of a focal species. Thus, not only the clonal dispersal ability of a species, but also that of its competitors may influence the fine-scale spatial pattern of a species.
2. In this article, we compared spatial patterns (in terms of colonization and occupation of space) of species with low (L), intermediate (I) or high (H) clonal dispersal abilities. Twelve species were classified within three groups of clonal dispersal (L, I or H) based on their average spacer lengths, and seven types of experimental assemblages consisting of species from one, two or three dispersal groups were studied. Two questions were addressed: (i) does the species clonal dispersal ability influence their spatial patterns and (ii) are species fine-scale spatial patterns affected by the clonal dispersal of neighbours? Species spatial patterns were recorded for each assemblage and were then analyzed using point pattern analysis.
3. Despite strong species-specific effects, L-species displayed the highest level of local aggregation, which is indicative of limited space colonization, and the lowest level of local co-occurrence with other species, which is indicative of a high level of space occupation. The opposite pattern was observed in H-species, while that of I-species was intermediate. The species spatial patterns were modified by the clonal dispersal ability of competitors.
4. Synthesis. This study emphasizes the importance not only of clonal dispersal but also of biotic interactions and, more precisely, of plant neighbour characteristics, in the spatial patterning of grassland plant communities.

Using a garden experiment, we investigated some mechanisms responsible for spatial patterning in grasslands. We compared the spatial patterns of plant species differing in their clonal dispersal abilities and grown in several types of assemblages. Our results highlight that species spatial patterns not only depended on the clonal dispersal ability of species, but were also modified by the clonal dispersal ability of neighbours.

1. Habitat filtering (HF, trait convergence) and niche differentiation (ND, trait divergence) are known to impact upon plant community structure. Both processes integrate individual responses to the abiotic environment and biotic interactions. Thus, it is difficult to clearly identify the underlying abiotic and biotic factors that ultimately impact community structure by looking at community-level patterns of trait divergence or convergence alone.
2. We used a functional trait-based and multiscale approach to assess how biotic interactions and aridity determine the functional structure of semi-arid shrublands sampled along a large aridity gradient in Spain. At the regional scale, we investigated functional differences among species (axes of specialization) to identify important traits for community assembly. At the community scale, we evaluated the relative impact of HF and ND on community structure using a null model approach. Finally, at the plant neighbourhood scale, we evaluated the impact of biotic interactions on community structure by investigating the spatial patterns of trait aggregation.
3. The shrub species surveyed can be separated along four axes of specialization based on their above-ground architecture and leaf morphology. Our community scale analysis suggested that the functional structure of semi-arid communities was clearly non-random, HF and ND acting independently on different traits to determine community structure along the aridity gradient. At the plant neighbourhood scale, the spatial distribution of species was also clearly not random, suggesting that competition and facilitation impacted on the observed changes in the functional diversity of shrubland communities along the aridity gradient.
4. Synthesis: Our results demonstrated that HF and ND acted simultaneously on independent traits to jointly determine community structure. Most importantly, our multiscale approach suggested that competition and facilitation interplayed with aridity to determine this structure. Competition appeared to be constant along the aridity gradient and explained the high functional diversity observed in semi-arid shrublands. Facilitation affected subordinate and rare species and, thus, may act to enhance the biodiversity of these ecosystems. Finally, the framework employed in our study allows moving forward from the examination of patterns to the development of mechanistic trait-based approaches to study plant community assembly.

Using a novel trait-based and multiscale approach, we show that competition and facilitation jointly determine the functional structure of Mediterranean shrublands along a large aridity gradient. Competition mostly impacted on dominant plant species whereas facilitation affected subordinate and rare species. Overall, shift from competition to facilitation appears to be trait-dependent along the aridity gradient.

1. Abiotic variables are critical drivers of succession in most primary seres, but how their influence on biota changes over time is rarely examined. Landslides provide good model systems for examining abiotic influences because they are spatially and temporally heterogeneous habitats with distinct abiotic and biotic gradients and post-landslide erosion.
2. In an 18-year study on 6 Puerto Rican landslides, we used structural equation models to interpret the changing effects of abiotic influences (landslide dimensions, slope, aspect, elevation, parent material and related soil properties) on seed plants (density and diversity), tree fern density, scrambling fern cover, canopy openness and soil development (nitrogen, soil organic matter, pH and cation exchange capacity).
3. Seven years after landslide formation, catchment size (the landslide area above the point of measurement) was the key abiotic factor influencing plants. The larger the catchment the greater was the diversity and density of seed plants. Conversely, the smaller the catchment the greater was the density of tree ferns and the cover of scrambling ferns.
4. Eighteen years after landslide formation, landslide slope was the key abiotic influence. The greater the slope, the lower was the density and diversity of seed plants and the greater was the scrambling fern cover.
5. Aspect, particularly east-facing slopes exposed to wind disturbances, positively influenced tree fern densities at both 7 and 18 years and negatively influenced seed plants and scrambling ferns at 18 years. Soils were least developed, that is, had lowest soil nitrogen and organic matter concentrations, after 18 years on steep slopes (like seed plants); soils were most developed near landslide edges, on hurricane-exposed slopes (like tree ferns) and where there were high soil potassium concentrations.
6. Synthesis. Abiotic variables have important influences on plant succession on landslides and the relative influence of different abiotic variables changes with time. Improved predictability of temporal dynamics will rely not only on understanding the effects of initial disturbances and subsequent biological responses but also on the different and changing influences exerted by each abiotic variable.

Abiotic variables have important influences on plant succession on landslides and the relative influence of different abiotic variables changes with time. Improved predictability of temporal dynamics will rely not only on understanding the effects of initial disturbances and subsequent biological responses but also on the different and changing influences exerted by each abiotic variable.

1. Trait-based approaches are increasingly used to obtain an insight into the functional aspects of plant communities. Since measuring traits can be time-consuming, large international databases of plant traits are being compiled to share the effort. From these databases, average trait values are often extracted per species by averaging trait values of individuals over multiple populations and habitats. However, the accuracy of such aggregated information from regional databases as a surrogate for on-site measurements has seldom been tested.

2. For the local species pool (aggregated at the habitat-level) and the plant communities on the plots (aggregated at the community-level), we quantified how accurately trait values for each species measured at the plot (plot scale) and those averaged per species and site (site scale) can be estimated from those retrieved from a North-west-European trait database. We analysed three widely used plant traits, canopy height (CH), leaf dry matter content (LDMC) and specific leaf area (SLA), of species occurring in a wet meadow and a salt marsh.

3. Database values more accurately predicted traits aggregated at the habitat-level than those aggregated at the community-level. In addition, traits with lower plasticity, such as LDMC, were more accurately predicted by database values. The performance of database values also depended upon the habitat studied, for example, habitat-level SLA values were accurately predicted by database values in the wet meadow but inaccurately predicted in the salt marsh.

4. Synthesis. This study reveals that the accuracy of traits retrieved from a database depends on the level of aggregation (lower at community-level), the trait (lower in plastic traits) and the habitat type (lower in extreme habitats). For studies focussing on processes mainly acting at the site scale (e.g. trait–environment relationships), traits retrieved from a regional database and filtered according to habitat will probably lead to good results. Whereas studying processes acting at the plot scale (e.g. niche partitioning), requires the additional effort of measuring traits on-site.

This study reveals that the accuracy of traits retrieved from a database depends on the level of aggregation (lower at community level), the trait (lower in plastic traits) and the habitat type (lower in extreme habitats). For studies focussing on processes mainly acting at the site scale (e.g. trait-environment relationships) traits retrieved from a regional database and filtered according to habitat will probably lead to good results. Whereas studying processes acting at the plot scale (e.g. niche partitioning), requires the additional effort of measuring traits on-site.

1. Increased shrub growth has been observed across the Arctic with recent climate warming trends, whilst many populations of caribou and reindeer (Rangifer) have been in decline. Paradoxically, our current understanding of the impacts of caribou and reindeer in altering trajectories of Arctic vegetation change is almost entirely dependent on studies with relatively high density semi-domesticated herds in Fennoscandia. With many wild herd populations across the Arctic presently at much lower densities, it is important to understand the impact of low intensity browsing on shrub biomass and the soil nutrient pools that fuel it.

2. We used exclosures that have been in place for 5 years in mesic birch hummock tundra in the central Canadian low Arctic to investigate the impact of caribou exclusion on tundra shrub biomass, tissue chemistry and plant and soil nitrogen (N) pools. Over the study period, the migratory tundra caribou herd in the region declined from 25% to 7% of its previous population maximum.

3. Caribou exclusion significantly enhanced the above-ground biomass components of one deciduous shrub (Betula glandulosa) and two evergreen shrubs (Vaccinium vitis-idaea and Rhododendron subarcticum). In particular, exclusion doubled B. glandulosa leaf biomass and increased V. vitis-idaea old leaf biomass 1.7 times, with the strongest effects in evergreens present in tissues > 1 year old, indicating a legacy of browsing from the earlier years of the experiment when the caribou population was higher. Meanwhile, Vaccinium uliginosum biomass and overall vascular plant diversity tended to decline with exclusion. Caribou exclusion increased B. glandulosa leaf N pools by 0.15 g N m⁻² (equivalent to 12% of the total vascular plant community annual N requirement for apical growth). Altogether exclusion did not alter total above-ground N pools, but rather led to a redistribution of shoot biomass and N, enhancing spatial variability in a key growth-limiting resource for tundra plants.

4. Synthesis. Excluding caribou during a population low resulted in ecologically significant changes in the distribution of plant above-ground biomass and nitrogen, further increasing the dominance of the three most abundant shrubs. These findings demonstrate that, despite uncertainty in herd recovery, Rangifer browsing impacts to both deciduous and evergreen shrub species should be considered for more robust projections of Arctic vegetation change.

Caribou exclusion during a population low resulted in ecologically significant changes in the distribution of plant above-ground biomass and nitrogen, further increasing the dominance of the three most abundant shrubs. These findings demonstrate that, despite uncertainty in herd recovery, Rangifer browsing impacts to both deciduous and evergreen shrub species should be considered for more robust projections of Arctic vegetation change.

1. Multiple plant species are engaged in defensive mutualisms with members of the third trophic level. However, mutualisms are prone to exploitation by low-quality symbionts that do not provide the adequate service to their host. Can mutualisms proceed only when hosts identify their symbionts in advance or continuously monitor their activity, or are there other mechanisms to avoid the invasion of mutualisms by exploiters?
2. High-reward species amongst Mesoamerican Acacia myrmecophytes are dominantly colonized by defending mutualistic ants, whereas about 50% of the low-reward hosts are inhabited by non-defending exploiters. I followed the development of recently founded ant colonies on a high-reward and a low-reward Acacia host species over 7 months, to investigate whether reward production correlates with a preferred maintenance of defending ants on the respective hosts.
3. Ant diversity decreased sooner on high-reward than on low-reward hosts, and mutualistic ants were more likely to finally dominate the high-reward hosts. I observed an increased frequency of mutualists replacing parasites at high initial rates of reward production. Apparently, higher nectar provisioning by the host plants shifted the competitive balance between mutualistic and parasitic ants. Independently of the causal reason for the different secretion rates, producing more nectar thereby favours the maintenance of defending mutualists on high-reward hosts.
4. Synthesis. The aggressiveness that enables ants to outcompete other ants also underlies their defensive effect against herbivores. I conclude that hosts can preferably associate with high-quality mutualists without measuring their effectiveness. Mutualisms remain stable when partner screening is based on traits that are relevant for the mutualistic interaction, with no need for the host to have information on the quality or identity of the symbiont.

Defensive ant–plant mutualisms are challenged by non-defending exploiter ants. However, the hosts can favour the persistence of defending mutualists by nourishing them with high amounts of extrafloral nectar, thereby enhancing their energy supply and thus their competitive capacities. Mutualisms remain stable when partner screening is based on traits of direct relevance for the mutualistic interaction.

1. There has been much recent interest in understanding how functional traits of vascular plant species drive ecological processes such as herbivory and litter decomposition. In plants, these two processes are often driven by the same or similar suites of traits and therefore correlate across species. However, few studies have considered how traits of plant-like life forms such as lichens determine species differences in their effects on ecological processes. This is despite the significant contribution of lichens to carbon and nutrient cycling in many environments.
2. We collected 28 lichen species that differed in their growth form, substrate type and capacity to fix N, and determined key traits for each species. For each species, we performed a feeding bioassay using the generalist snail Cepaea hortensis and carried out a laboratory bioassay to assess decomposability. We did these tests both with intact lichen material containing natural concentrations of carbon-based secondary compounds (CBSCs), and material that had been acetone rinsed to reduce concentrations of CBSCs, to evaluate the effect of CBSC on palatability and decomposability.
3. We found that reducing CBSC concentrations greatly increased palatability for 17 species, and decomposability of 10 species. However, decomposability was correlated with several lichen traits while palatability was not, regardless of whether or not CBSCs were removed, and we therefore found no relationship between decomposability and palatability across species. Decomposability and palatability both varied, but in contrasting directions, among N-fixing vs. non-fixing lichens, lichens with different growth forms and those from contrasting substrate types. As such, N-fixing lichens had higher decomposition rates but lower consumption rates than non-fixing lichens, while foliose species had higher decomposition rates but lower consumption rates than fruticose species.
4. Synthesis: We have shown that lichen CBSCs regulate key processes such as lichenivory and decomposition, that lichen decomposability but not palatability are related to traits, and that these two processes are unrelated across species. These results highlight the potential role of lichen species differences in influencing ecosystem processes relating to decomposition and nutrient cycling and the role that grazers may play in driving this.

We have shown that lichen carbon-based secondary compounds (CBSCs) regulate key processes such as lichenivory and decomposition, that lichen decomposability but not palatability are related to traits, and that these two processes are unrelated across species. These results highlight the potential role of lichen species differences in influencing ecosystem processes relating to decomposition and nutrient cycling and the role that grazers may play in driving this.

1. The loss of suitable habitats is one of the main causes behind the loss of species and communities. Habitat fragmentation, that is, the division of the remaining habitat into small and isolated fragments, often co-occurs with the process of habitat loss. The spatial division of habitats decreases connectivity among local populations and generally has a negative effect on population viability, but it can also have a positive effect for some species, for example, due to released competition pressure.
2. In both animals and plants, certain characteristics such as low dispersal ability and narrow ecological niche are known to be associated with fragmentation vulnerability, but in fungi, systematic analyses have so far been lacking. With their small and highly dispersive spores, fungi could be mainly resource-limited, not dispersal-limited.
3. In this study, we analysed spatial occurrence data on 119 species of wood-inhabiting fungi to identify the species characteristics that are associated with high extinction risk and fragmentation vulnerability in particular. We modelled resource use and connectivity dependence separately for each species using the presence–absence data on 98 318 dead trees in 496 sites located on a gradient in the duration and intensity of land use in eastern Fennoscandia. We then related species' responses to connectivity to their resource-use patterns, life-history characteristics and red-list status.
4. Our results show that red-listed species are highly specialized in their resource use and suffer from loss of connectivity at three spatial scales: along the large-scale gradient, at the landscape scale and at the scale of a forest stand. In contrast, many of the non-red-listed generalist species are actually more likely to occur (per resource unit) in fragmented managed forests than well-connected natural forests.
5. Synthesis. We show that the expected number of red-listed species per a fixed amount of similar resources (dead trees) can be even more than 10 times higher in well-connected than in fragmented surroundings, and thus, protecting high-quality areas that are well connected is conservationally more effective than protecting small fragments distributed across the landscape.

We show that the expected number of red-listed species per a fixed amount of similar resources (dead trees) can be even more than 10 times higher in well-connected than in fragmented surroundings, and thus protecting high-quality areas that are well connected is conservationally more effective than protecting small fragments distributed across the landscape.

1. The alteration and transformation of the areas surrounding native forests due to anthropogenic disturbance can result in differences near this newly created boundary, termed ‘edge effects’.
2. Our study describes the consequences of edge creation over two successive stages in the life cycle of a hemi-parasitic mistletoe (Tristerix corymbosus), which determine its reproductive success, in temperate austral forests.
3. We assessed how flower production and pollinator visits change with distance to the nearest forest edge and how these changes affect fruit set, fruit and seed size, and fruit removal by seed dispersers.
4. Edge effects were dominated by fruit removal, which increased with the distance to the edge, height in the canopy and fruit availability. As a result, plant reproduction (in terms of seeds produced and fruits removed, which putatively leads to higher seed dispersal) decreased strongly near to forest edges. In contrast, visitation rates of the main pollinator (the hummingbird) were unaffected by edges, and their strong effects on fruit set (including the alleviation of quality pollen limitation arising in the forest interior) might be mitigating the decrease in bumblebee visitation near to forest edges.
5. Synthesis. Our study shows clearly how secondary and tertiary responses to forest edges acted in opposite directions (increasing or decreasing plant reproductive performance), highlighting the need to study several successive processes that impact upon plant fitness under disturbance. Preserving relatively large patches of old-growth forest with low perimeter/area ratios would be key to the habitat requirements of the main disperser and pollinator and thus for mistletoe reproductive performance.

The alteration and transformation of the areas surrounding native forests due to anthropogenic disturbance can lead to ‘edge effects’. Our study shows clearly how secondary and tertiary responses to forest edges acted in opposite directions (increasing or decreasing plant reproductive performance), highlighting the need to study several successive processes that impact upon plant fitness under disturbance.

1. Individual performance is a function of an individual's traits and its environment. This function, known as an environmental filter, varies in space and affects community composition. However, filters are poorly characterized because dispersal patterns can obscure environmental effects, and few studies utilize longitudinal data linking individual performance to environment.
2. We model the effects of environmental filters on demographic rates of nearly all tree species (99) in a 25-ha subtropical rain forest plot. We develop a hierarchical Bayesian model of environmental filtering, drawing inspiration from classic studies of intraspecific natural selection. We characterize the specific environmental gradients and trait axes most important in filtering of demographic rates across species.
3. We found that stronger filtering along a given trait axis corresponded to less spatial variation in the value of favoured traits.
4. Environmental gradients associated with filtering were different for growth versus survivorship.
5. Species maximum height was under the strongest filtering for growth, with shorter species favoured on convex ridges. Shorter stature species may be favoured on ridges because trees on ridges experience higher wind damage and lower soil moisture.
6. Wood density filtering had the strongest effects on survival. Steep slopes and high available P in the soil favoured species with low-density wood. Such sites may be favourable for fast-growing species that exploit resource-rich environments.
7. Synthesis: We characterized trait-mediated environmental filters that may underlie spatial niche differentiation and life-history trade-offs, which can promote species coexistence. Filtering along trait axes with the strongest effects on local community composition, that is, traits with the strongest filtering, may necessarily have a weaker potential to promote species coexistence across the plot. The weak spatial variation in filters with strong effects on demography may result from long-term processes affecting the species pool that favour habitat generalist strategies.

Individual performance is a function of an individual's traits and its environment. This function, known as an environmental filter, varies in space and affects community composition. We characterized trait-mediated environmental filters that underlie spatial niche differentiation and life history trade-offs for individuals in a tree community. The trait axes with the strongest filtering (a & c) and greatest variation in filters are shown (b & d).

1. Recent interest in the importance of short-term, transient responses in population dynamics has prompted the development of many new methods for describing transient responses in population models. Many of these methods focus on the largest possible responses for a model, thus providing a description of the ‘transient potential’ of a model that does not depend on knowledge of initial conditions in the population.
2. This study uses long-term demographic data from five perennial plant species to evaluate how well measures of transient potential reflect actual transient responses in the populations. I used previously published matrix population models to create a set of initial conditions derived from empirically-based simulations for each population. Maximum transient responses within this set of initial conditions were then compared with responses used in describing transient potential.
3. Transient responses based on empirical modeling results were smaller than responses used for measures of transient potential.
4. Realized responses were strongly correlated with the distance between the current demographic structure in the population and the asymptotically stable stage structure of the model (SSD).
5. Theoretical transient potential was predictive of the amount of variation in distance from SSD observed in each population in the simulations.
6. Synthesis. Methods based on largest possible responses tend to overemphasize the role of transient dynamics. These results suggest that traditional, asymptotic analyses may be appropriate in many cases. Measures of transient potential can be helpful for identifying species and situations that may be prone to larger transient responses, but do not necessarily indicate that transient dynamics are more important in those systems.

Methods based on largest possible responses tend to overemphasize the role of transient dynamics. These results suggest that traditional, asymptotic analyses may be appropriate in many cases. Measures of transient potential can be helpful for identifying species and situations that may be prone to larger transient responses, but do not necessarily indicate that transient dynamics are more important in those systems.

1. Understanding the variation in hereditary symbiont frequency among host populations is a prerequisite to predict symbiont fixation processes. However, the mechanisms driving this variation remain elusive. Exploring the mechanisms responsible for the observed variability on an ecological time scale requires simultaneous study of fitness differentials between symbiotic (S) and non-symbiotic (NS) hosts, and the symbiont transmission rates to host offspring.
2. We studied these two key mechanisms using a grass–endophyte symbiosis in the alpine grass Festuca eskia. Plants from four native populations varying in endophyte frequencies (ranging from 13% to 100%), and environmental conditions (water availability, and grazing pressure) were transplanted in a common garden. Soil nutrient levels were manipulated to assess genetic and environmental differences within and among populations in fitness-related traits (i.e. traits linked to clonal growth, sexual reproduction and resource acquisition).
3. A fitness differential favouring S over NS plants was detected in all studied populations: in heavily grazed populations, sexual reproduction was higher in S compared with NS plants, whereas in minimally grazed populations, clonal growth increased. Results showed a positive correlation between endophyte transmission rates and population endophyte symbiotic frequencies. The population endophyte transmission rates were not affected by soil resource level.
4. According to selection pressures acting in each population, symbiotic plants appear to perform better in all F. eskia populations. The correlation between endophyte frequencies and transmission, and the positive effect of S on NS plants under our experimental conditions, indicated a predominant role of endophyte transmission in endophyte frequency variation in F. eskia. The endophyte transmission rate variation is genetically based at the population level and can be explained by a trade-off with a specific host trait subjected to strong selection; here, we suspected traits linked to plant resource acquisition.
5. Synthesis: Our study provides evidence for the (i) dominant role of endophyte transmission and its responsibility for endophyte frequency variation in a native grass when compared with fitness differential process between S and NS plants at an ecological time scale, and (ii) genetically based variation in endophyte transmission rates. We also confirm the population specificity of positive endophyte effects in a native grass.

Theoretically, two mechanisms might contribute to variation in hereditary symbiont frequency among host populations: the impact of symbioses on host fitness, and symbiont transmission to offspring. We studied both mechanisms using a grass-endophyte symbiosis in a native grass. We showed that transmission: (i) drives symbiont frequency variation in host populations, (ii) is not directly linked to the impact of symbiosis on host fitness, and (iii) is genetically based at population level.

1. Environmental gradients may influence a plant's physiological status and morphology, which in turn may affect plant–plant interactions. However, little is known about the relationship between environmental variation, physiological and morphological variability of plants and variation in the balance between competition and facilitation.
2. Mountain ranges in dry environments have opposing altitudinal environmental gradients of temperature and aridity, which limit plant growth at high and low elevations. This makes them particularly suitable for exploring the relationships between environmental conditions, plant phenotype and plant–plant interactions. We hypothesized that different environmental stressors will differently affect the physiological status of a nurse plant. This, then, manifests itself as variation in nurse plant morphological traits, which in turn mediates plant–plant interactions by altering microhabitat conditions for the nurse and associated species.
3. In an observational study, we measured a series of functional traits of Arenaria tetraquetra cushions as indicators of its physiological status (e.g. specific leaf area, relative water content) and morphology (e.g. cushion compactness, size). Measurements were taken along the entire elevation range where A. tetraquetra occurs. Furthermore, we analysed how these functional traits related to soil properties beneath cushions and the number of associated species and individuals compared with open areas.
4. Cushions at high elevation showed good physiological status; they were compact and large, had higher soil water and organic matter content compared with open areas and showed the strongest facilitation effect of the whole elevation gradient – that is, the highest increase in species richness and abundance of beneficiaries compared with open areas. Physiological data at low elevation indicated stressful abiotic conditions for A. tetraquetra, which formed loose and small cushions. These cushions showed less improved soil conditions and had reduced facilitative effects compared with those at high elevation.
5. Synthesis. Functional traits of the nurse species varied distinctively along the two opposing stress gradients, in parallel to the magnitude of differences in microenvironmental conditions between cushions and the surrounding open area, and also to the facilitation effect of cushions. Our data, therefore, provides a strong demonstration of the generally overlooked importance of a nurse plant's vigour and morphology for its facilitative effects.

This study demonstrates the generally overlooked importance of a nurse plant's vigor and morphology for its facilitative effects. Functional traits of the cushion plant Arenaria tetraquetra ssp. amabilis varied distinctively along two opposing stress gradients, in parallel to the magnitude of differences in micro-environmental conditions between cushions and the surrounding open area, and also to the facilitation effect of cushions.

1. According to the insurance hypothesis, more diverse plant communities are more likely to be resistant to drought. Whilst many experiments have been carried out to determine the effects of plant diversity on plant community insurance, the results are still contradictory.
2. Here, we conducted a drought experiment where we tested whether the presence of subordinate species increases plant community insurance. In Swiss Jura grassland, we combined a removal experiment of subordinate species with a summer drought event using rainout shelters.
3. Plant community composition was determined after the drought and based on biomass measurements; we estimated resistance, recovery and resilience of the plant community for each combination of treatments. Moreover, to assess drought impacts on water-use efficiency (WUE), we analysed carbon isotope ratios (δ¹³C values) in plant leaves of two dominants and two subordinates collected at the end of the drought period.
4. We showed that subordinate species are more resistant to drought and increased community resistance by enhancing their above-ground biomass production during the imposed drought. These patterns were associated with decreased competitiveness of dominant species whose biomass decreased during drought. Significant increase in δ¹³C values in plant tissue under drought indicated a better WUE for the measured species. Interestingly, the WUE was significantly higher in plots where subordinates were removed. Recovery and resilience were not affected by the summer drought, but the absence of subordinates reduced overall above-ground biomass in both watered and drought plots.
5. Synthesis. We demonstrated that, independent of plant diversity, the presence of drought-resistant subordinate species increases plant community insurance against drought and, hence, is important for the functioning of grassland ecosystems.

While many experiments have been carried out to determine the effects of plant diversity on plant community insurance to drought, the results are still contradictory. Here, we demonstrated that, independent of plant diversity, the presence of drought-resistant subordinate species increases plant community insurance against drought and hence is important for the functioning of grassland ecosystems.

1. Understanding the processes responsible for macro-scale spatial and temporal phenological patterns is a critical step in developing predictive phenological models. While phenological responses may involve the integration of multiple environmental cues, the spring phenology of many plant and animal species appears to be especially sensitive to temperature.
2. As a result of the success of citizen science schemes in mobilizing amateur naturalists, for some parts of the world, there now exist extensive data sets of phenological timings, spanning many species, locations and years. In macroecology, two types of models – time windows and growing degree-days – are widely used to predict phenology on the basis of temperature.
3. Here, we compare the performance of the two methods in predicting spatiotemporal variation in the timing of Quercus robur first leafing. The methods agree on the time at which leafing becomes sensitive to temperature and provide weak support for a delay in initiation of thermal sensitivity with increasing latitude due to a day-length requirement. Both methods explain c. 50% of the variation in first dates and identify plasticity, rather than local adaptation, as the major cause of spatial covariation between temperature and phenology. For a 1°C rise in spring temperatures we predict that a plastic response of first leafing will give rise to an advance of about seven days.
4. Synthesis: Time-window and growing degree-day methods provide remarkably congruent insights into the processes underpinning geographic variation in Quercus robur first leafing dates. We find that a spatially invariant plastic response to temperature dominates spatiotemporal phenological variation, which means that it may be reasonable to substitute space for time to project how this species will respond to climate change. This study demonstrates the contribution that top-down macroecological approaches can make to our understanding of the processes that give rise to intraspecific phenological variation.

Time-window and growing degree-day methods provide remarkably congruent insights into the processes underpinning geographic variation in Q. robur first leafing dates. We find that a spatially invariant plastic response to temperature dominates spatiotemporal phenological variation, which means that it may be reasonable to substitute space for time to project how this species will respond to climate change. This study demonstrates the contribution that top-down macroecological approaches can make to our understanding of large-scale phenological processes.

1. Macroclimatic variation along latitudinal gradients provides an excellent natural laboratory to investigate the role of temperature and the potential impacts of climate warming on terrestrial organisms.
2. Here, we review the use of latitudinal gradients for ecological climate change research, in comparison with altitudinal gradients and experimental warming, and illustrate their use and caveats with a meta-analysis of latitudinal intraspecific variation in important life-history traits of vascular plants.
3. We first provide an overview of latitudinal patterns in temperature and other abiotic and biotic environmental variables in terrestrial ecosystems. We then assess the latitudinal intraspecific variation present in five key life-history traits [plant height, specific leaf area (SLA), foliar nitrogen:phosphorus (N:P) stoichiometry, seed mass and root:shoot (R:S) ratio] in natural populations or common garden experiments across a total of 98 plant species.
4. Intraspecific leaf N:P ratio and seed mass significantly decreased with latitude in natural populations. Conversely, the plant height decreased and SLA increased significantly with latitude of population origin in common garden experiments. However, less than a third of the investigated latitudinal transect studies also formally disentangled the effects of temperature from other environmental drivers which potentially hampers the translation from latitudinal effects into a temperature signal.
5. Synthesis. Latitudinal gradients provide a methodological set-up to overcome the drawbacks of other observational and experimental warming methods. Our synthesis indicates that many life-history traits of plants vary with latitude but the translation of latitudinal clines into responses to temperature is a crucial step. Therefore, especially adaptive differentiation of populations and confounding environmental factors other than temperature need to be considered. More generally, integrated approaches of observational studies along temperature gradients, experimental methods and common garden experiments increasingly emerge as the way forward to further our understanding of species and community responses to climate warming.

Macroclimatic variation along latitudinal gradients provides an excellent opportunity to investigate the role of temperature and the potential impacts of climate warming on terrestrial organisms. We review the use of latitudinal gradients for ecological climate-change research, in comparison with altitudinal gradients and experimental warming, and illustrate their use and caveats with a meta-analysis of latitudinal intraspecific variation in life-history traits of plants.

1. Alpine plants are at high risk because of climate change. Assessing the performance of alpine plant species across different altitudes is useful for predicting how they may respond to changing climate. Adaptation and plasticity of early life stages are of particular interest since seed germination and seedling establishment could be crucial life-history stages for environmental tracking and population persistence of sexually reproducing plants.
2. To evaluate past adaptation and the potential to accommodate future climate conditions, seeds and seedlings of Erysimum capitatum were reciprocally transplanted between alpine and low-altitude sites.
3. When grown in a common field environment, E. capitatum from alpine and lower-altitude populations differed from each other in germination, size and morphological traits. Planting altitude also influenced those traits, indicating that population differentiation and plasticity to altitudinal conditions both contributed to differences in the performance of high- vs. low-altitude plants. Seeds tended to germinate more in their native habitat than in the foreign habitat. Alpine plants survived more than low-altitude plants at high altitude, and they suffered higher mortality when they were planted in low-altitude sites. The production of multiple rosettes, a characteristic morphology of alpine E. capitatum, was negatively associated with survival at low altitude. In contrast to alpine populations, a survival advantage of low-altitude populations in low-altitude sites was not evident in this experiment.
4. Synthesis. Because climate change is projected to cause alpine environments to become more similar to low-altitude environments, alpine Erysimum capitatum is expected to suffer reduced seedling recruitment and higher mortality as a direct response to altered environment and possibly as a result of past adaptation to high altitude. In particular, the production of multiple rosettes, an adaptive trait to the current alpine environment, would constrain plant survival should those environments come to resemble low altitude. Moreover, the limited fitness advantage of low-altitude E. capitatum in low-altitude conditions suggests that environmental tracking by low-altitude populations might have a limited role in maintaining future populations.

As an effort to predict how alpine plant species may respond to climate change, we examined local adaptation and plasticity to altitude using Erysimum capitatum—a mustard that occurs in a broad altitudinal range. The results imply that alpine E. capitatum would suffer reduced seedling recruitment and higher mortality as a direct response to altered environment and possibly as a result of past adaptation to high altitude. In addition, environmental tracking by low-altitude populations is predicted to have a limited role in maintaining future populations.

1. Whether plant competition grows stronger or weaker across a soil fertility gradient is an area of great debate in plant ecology. We examined the effects of competition and soil fertility and their interaction on growth rates of the four dominant tree species in the sub-boreal spruce forest of British Columbia.
2. We tested separate soil nutrient and moisture indices and found much stronger support for models that included the nutrient index as a measure of soil fertility.
3. Competition, soil fertility and their interaction affected radial growth rates for all species.
4. Each species supported a different alternate hypothesis for how competitive interactions changed with soil fertility and whether competition intensity was stronger or weaker overall as soil fertility increased depended on the context, specifically, species, neighbourhood composition and type of competition (shading vs. crowding).
5. The four species varied slightly in their growth response to soil fertility.
6. Individual species had some large variations in the shapes of their negative relationships between shading, crowding and tree growth, with one species experiencing no net negative effects of crowding at low soil fertility.
7. Goodness-of-fit was not substantially increased by models including competition–soil fertility interactions for any species. Tree size, soil fertility, shading and crowding predicted most of the variation in tree growth rates in the sub-boreal spruce forest.
8. Synthesis. The intensity of competition among trees across a fertility gradient was species- and context-specific and more complicated than that predicted by any one of the dominant existing theories in plant ecology.

Whether plant competition grows stronger or weaker across a soil fertility gradient is an area of great debate in plant ecology. The intensity of competition among trees across a fertility gradient in a multi-species forest was species- and context-specific and more complicated than predicted by any one of the dominant existing theories in plant ecology.

1. Soil nitrogen (N) occurs in a range of chemical forms from simple inorganic compounds, such as nitrate () and ammonium (), to organic compounds, such as amino acids. Plants differ in their capacity to use these various forms, which might influence the distribution of species across environmental nutrient gradients.
2. We tested the hypothesis that the distribution of understorey palm species along a soil N gradient in a tropical montane forest in Panama is related to preferences for different chemical forms of N. We conducted a field experiment using ¹⁵N-labelled ammonium, nitrate and glycine to examine whether tropical plants show preferences for, or are flexible in, their use of chemical forms of soil N.
3. All species used N from inorganic and organic sources and showed no preference for chemical forms of N. However, across all species, the overall N acquisition pattern was glycine ≥ nitrate ≥ ammonium. Species from low-nutrient sites dominated by ammonium and organic N forms had inherently slow N uptake rates.
4. Synthesis. Patterns in the distribution of understorey palms were related to nitrogen (N) uptake rates rather than preferences for N chemical forms. Down-regulation of N uptake rates may be an important adaptation for plant species associated with low-N soils, with plasticity in N acquisition patterns from various N sources important in alleviating competition for soil N.

We found that patterns in the distribution of understorey palms were related to nitrogen (N) uptake rates rather than preferences for N chemical forms. Down-regulation of N uptake rates may be an important adaptation for plant species associated with low N soils, with plasticity in N acquisition patterns from various N sources important in alleviating competition for soil N.

1. Pollinator sharing can offer powerful insights into the floral traits associated with the evolution of a pollination system and the consequences of floral differences for pollinator behaviour. Here, we investigate the first known case of pollinator sharing between two sexually deceptive plant genera. Floral manipulations were used to test the importance of floral traits for pollinator behaviour and pollination efficiency. We also explored the ecological differences enabling species co-occurrence.
2. Drakaea livida and Caladenia pectinata (Orchidaceae) exhibit dramatic differences in floral display and the insectiform appearance of the labellum, yet both are pollinated by sexually attracted males of the thynnine wasp Zaspilothynnis nigripes. Because of the prevalence of cryptic species in some genera of thynnine wasps, we confirmed pollinator sharing by a mark–recapture study and sequencing of the mtDNA CO1 region.
3. Floral dissections revealed that semiochemicals used to attract the pollinator are released from the labellum in D. livida and sepaline clubs in C. pectinata. Drakaea livida was more efficient at converting pollinator attraction into potential pollen deposition leading to higher fruit set. Floral manipulations showed that pollinator contact with the labellum increases when it is the point of semiochemical release. However, sexual attraction to the labellum remained infrequent in C. pectinata in all experimental treatments.
4. While their distribution and climatic range show extensive overlap, the differences in edaphic requirements of the two orchid species suggest that they rarely co-occur. Therefore, the potential cost of sharing the same pollinator species is not realized.
5. Synthesis. This case of pollinator sharing confirms that morphological traits do not place a strong constraint on the evolution of sexual deception. However, interspecific differences in floral traits have important consequences for converting attraction into pollination, suggesting that selection can act to increase efficiency at multiple steps of the pollination process. This system provides a novel opportunity to elucidate the chemical, visual and morphological adaptations underpinning the evolution of sexual mimicry.

Synthesis. This case of pollinator sharing confirms that morphological traits do not place a strong constraint on the evolution of sexual deception. However, interspecific differences in floral traits have important consequences for converting attraction into pollination, suggesting that selection can act to increase efficiency at multiple steps of the pollination process. This system provides a novel opportunity to elucidate the chemical, visual and morphological adaptations underpinning the evolution of sexual mimicry.