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Geographic variation in the reproductive traits of animal‐pollinated plants can be shaped by spatially variable selection imposed by differences in the local pollination environment. We investigated this process in Babiana ringens (Iridaceae), an enigmatic species from the Western Cape region of South Africa. B. ringens has evolved a specialized perch facilitating cross‐pollination by sunbirds and displays striking geographic variation in perch size and floral traits. Here, we investigate whether this variation can be explained by geographic differences in the pollinator communities. We measured floral and inflorescence traits, and abiotic variables (N, P, C, and rainfall) and made observations of sunbirds in populations spanning the range of B. ringens. In each population, we recorded sunbird species identity and measured visitation rates, interfloral pollen transfer, and whether the seed set of flowers was pollen limited. To evaluate whether competition from co‐occurring sunbird‐pollinated species might reduce visitation, we quantified nectar rewards in B. ringens and of other co‐flowering bird‐pollinated species in local communities in which populations occurred. Variation in abiotic variables was not associated with geographical variation of traits in B. ringens. Malachite sunbirds were the dominant visitor (97% of visits) and populations with larger‐sized traits exhibited higher visitation rates, more between‐flower pollen transfer and set more seed. No sunbirds were observed in four populations, all with smaller‐sized traits. Sunbird visitation to B. ringens was not associated with local sunbird activity in communities, but sunbird visitation was negatively associated with the amount of B. ringens sugar relative to the availability of alternative nectar sources. Our study provides evidence that B. ringens populations with larger floral traits are visited more frequently by sunbirds, and we propose that visitation rates to B. ringens may be influenced, in part, by competition with other sunbird‐pollinated species., We demonstrate that geographic variation in floral morphology is correlated with pollinator visitation rate. Pollinator visitation rates appear to be influenced by competition with plants in the surrounding community. This suggests that competition may play a role in shaping floral evolution.

Summary Dispersal and dormancy are important risk-reducing strategies in unpredictable environments. Negative covariation between these strategies is theoretically expected, but empirical evidence is limited and inconsistent. Moreover, covariation may be affected by other life-history traits and may vary across levels of biological organization. We assessed dispersal (vertical fall time of fruits, a proxy for wind dispersal ability) and dormancy (germination fractions measured during germination trials) in populations of 15 annual and 12 perennial wind-dispersed species in six Asteraceae genera from South Africa. Dormancy was higher in annuals than in perennials, whereas fall time was largely determined by evolutionary history. Controlling for phylogeny, dispersal and dormancy was negatively associated across species and life-history categories. Negative covariation between dispersal and dormancy was not evident at either the individual level (except for seed heteromorphic species) or the population level. Our study provides rare empirical support for the theoretical expectation of tradeoffs between dormancy and the alternative risk-reducing strategies, perenniality and dispersal, but refutes the expectation of increased dispersability in perennials. Although negative covariation between dispersal and dormancy at the species level appears not to be a simple consequence of upscaling individual-level mechanistic tradeoffs, our findings suggest that selection for one strategy may constrain evolution of the other.

Summary Since co-flowering plants often share pollinators, their fecundity is likely affected by pollen transfer within and among plant species. Changes in pollinator visitation rates (e.g. through facilitation or competition for pollinators) are usually thought to exert the predominant influence on plant fecundity. However, the transfer of conspecific relative to heterospecific pollen between individuals may also play an important role. Indeed, the relative importance of these determinants of fecundity is expected to depend on the density, relative abundance and spatial arrangement of con- and heterospecifics. We investigated the effects of con- and heterospecific density and spatial distribution pattern on pollinator visitation and plant fecundity within and between two annual, self-incompatible co-flowering species [Dimorphotheca pinnata and Ursinia cakilefolia (Asteraceae)] by manipulating their relative abundance, overall patch density and dispersion patterns in experimental arrays in Namaqualand, South Africa. We quantified pollinator visitation rates and fruit set in arrays of varying density and aggregation. This enabled us to determine which mechanism(s) were driving variation of fecundity, particularly through their influence on visitation rates, mate availability and heterospecific pollen interference. To test whether autogamy offers reproductive assurance when individuals are scattered among a dense population of heterospecifics, we included an autogamous species (U. anthemoides) in a separate experiment. We found that increased fecundity with increasing conspecific density was not the result of higher visitation rates, but rather increased mate availability. Furthermore, increased spatial aggregation of conspecifics at low density significantly increased fecundity through reduced heterospecific interference. In contrast to results for self-incompatible species, fruit set in U. anthemoides was consistently high and unaffected by scattered distribution patterns. This suggests that autogamy may offer reproductive assurance when mates are limited and the potential for interspecific pollen transfer (IPT) is high. Synthesis. In this study of annual daisies, variation in fruit set is primarily driven by factors that affect the transfer of conspecific relative to heterospecific pollen, independent of pollinator visitation rate. Our findings demonstrate that mate limitation and IPT negatively affect fruit set and that these effects can be mitigated by intraspecific aggregation and the ability to autonomously self-pollinate.

 Premise of the study: The showiness of fl displays is usually explained as an adaptation to attract pollinators. However, selection for less attractive displays imposed by non-pollinating agents, particularly herbivores, may balance pollinator-driven selection for highly visible infl orescences. We investigated whether infl orescence architecture, particularly the unusual groundlevel fl owering associated with a specialized bird perch in Babiana ringens may have originated, in part, as an adaptive response to mammalian herbivory.  Methods: We measured levels of herbivory by antelope in populations of B. hirsuta , the putative sister species of B. ringens , which possesses the likely ancestral form of infl orescence architecture. To test for position-dependent effects of herbivory on fl owers, we compared the herbivory rates and seed production of manipulated infl orescences in a fi eld experiment. We predicted that fl owers at the base of infl orescences would suffer less herbivory than those in apical positions.  Results: We found herbivore damage to flin 50% of naturally occurring B. hirsuta plants. Manipulated infl orescences with only basal fl owers, and consequently similar infl orescence architecture to B. ringens , experienced signifi cantly lower herbivory and higher seed set than infl orescences manipulated to have only apical fl owers.  Conclusions: Our results are consistent with the hypothesis that position-dependent herbivory on infl orescences could have played a role in the evolution of infl orescence design. More specifi cally, position-dependent herbivory may have selected for the loss of apical fl owers. Position-dependent herbivory may have contributed toward the evolution of a naked infl orescence axis, a structure that characterizes B. ringens and functions as a bird perch facilitating cross-pollination by sunbirds.

BACKGROUND AND AIMS Floral variation, pollination biology and mating patterns were investigated in sunbird-pollinated Babiana (Iridaceae) species endemic to the Western Cape of South Africa. The group includes several taxa with specialized bird perches and it has been proposed that these function to promote cross-pollination. METHODS Pollinator observations were conducted in 12 populations of five taxa (B. ringens subspp. ringens, australis, B. hirsuta, B. avicularis, B. carminea) and geographic variation in morphological traits investigated in the widespread B. ringens. Experimental pollinations were used to determine the compatibility status, facility for autonomous self-pollination and intensity of pollen limitation in six populations of four taxa. Allozyme markers were employed to investigate mating patterns in four populations of three species. KEY RESULTS Sunbirds were the primary pollinators of the five Babiana taxa investigated. Correlated geographical variation in perch size, flower size and stigma-anther separation was evident among B. ringens populations. Experimental pollinations demonstrated that B. ringens and B. avicularis were self-compatible with variation in levels of autonomous self-pollination and weak or no pollen limitation of seed set. In contrast, B. hirsuta was self-incompatible and chronically pollen limited. Estimates of outcrossing rate indicated mixed mating with substantial self-fertilization in all species investigated. CONCLUSIONS Despite the possession of specialized bird perches in B. ringens and B. avicularis, these structures do not prevent considerable selfing from occurring, probably as a result of autonomous self-pollination. In eastern populations of B. ringens, smaller flowers and reduced herkogamy appear to be associated with a shift to predominant selfing. Relaxed selection on perch function due to increased selfing may explain the increased incidence of apical flowers in some populations.