American Journal of Botany 90(9): 1328±1332. 2003.

FLORAL LONGEVITY AND REPRODUCTIVE ASSURANCE: SEASONAL PATTERNS AND AN EXPERIMENTAL TEST WITH LATIFOLIA ()1

BEVERLY J. RATHCKE2

Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, Michigan 48109-1048 USA

Floral longevity is assumed to re¯ect a balance between the bene®t of increased pollination success and the cost of ¯ower main- tenance. Flowers of (Ericaceae), mountain laurel, have a long duration and can remain viable up to 21 d if unpollinated. I experimentally tested whether this long duration increases pollination success by clipping stigmas to reduce functional ¯oral longevity to 3±4 d. Clipping stigmas decreased fruit set from 65% to only 10%. Flowers with natural life spans were not pollination-limited, demonstrating that long ¯oral duration ensured female reproductive success. The long ¯oral duration of K. latifolia was unique in this site (the Great Swamp, Rhode Island, USA). Co¯owering in summer had a mean ¯oral life span of 3.4 d. Spring-¯owering species had signi®cantly longer mean ¯oral durations (7.2 d). These duration differences may re¯ect seasonal variation in pollinator availability. However, K. latifolia ¯owers in summer, when its bumble bee pollinators are abundant but it is a poor competitor for bees because its ¯owers produce little nectar. The long ¯oral duration allows K. latifolia to outlast co¯owering competitors and attract suf®cient pollinators. I hypothesize that the long ¯oral duration of K. latifolia functions as a mechanism for competitive avoidance and reproductive assurance.

Key words: competition for pollinators; competitive avoidance; Ericaceae; ¯oral longevity; ¯owering phenology; fruit set; Great Swamp, Rhode Island; induced ¯oral senescence; Kalmia latifolia; pollination limitation; reproductive assurance.

In pollination studies, much attention has focused upon ¯o- have demonstrated that longer durations of ¯oral life increase ral traits that assure successful pollination by increasing the fruit or seed set of ¯owers in the ®eld. attraction or rewards for animal pollinators (e.g., Waser, 1983; Here I present an experimental test of the pollination bene®t Bell, 1985; Real and Rathcke, 1991; Caruso, 2000) or by in- of long ¯oral duration for mountain laurel, Kalmia latifolia L. creasing the effectiveness of pollen transfer (e.g., Campbell et (Ericaceae). Flowers can remain viable for 2±3 wk if unpol- al., 1996). More recently, it has been recognized that ¯oral linated, and they rapidly senesce after pollination (Rathcke, longevity (the length of time a ¯ower remains open and func- 1988a; Nagy et al., 1999). I reduced the functional longevity tional) is a trait that could ensure successful pollination in of ¯owers by clipping stigmas and then compared fruit sets habitats where pollinators are sparse or uncertain (Primack, (fruits initiated per number of ¯owers) of experimental and 1985; Ashman and Schoen, 1994, 1996; Khadari et al., 1995). control ¯owers. I also did procedure controls, and I tested For example, growing in alpine habitats, which typically whether control (naturally pollinated) ¯owers were pollination have few, unpredictable pollinators, have longer ¯oral dura- limited by augmenting ¯owers with cross-pollen. I compare tions than plants at lower elevations with more abundant, pre- the ¯oral longevity of K. latifolia with other species dictable pollinators (Arroyo et al., 1981; Stratton, 1989; Bing- growing in the same habitat and for different ¯owering seasons ham and Orthner, 1998; Blionis and Vokou, 2001; Blionis et (spring and summer). I discuss possible reasons for the main- al., 2001). Ashman and Schoen (1994, 1996) have proposed a tenance of long ¯oral duration in this species. mathematical model in which the duration of ¯oral life is de- termined by a balance between female ®tness accrual rates MATERIALS AND METHODS (pollen receipt), male ®tness accrual rates (pollen dissemina- This study was done in the Great Swamp, Rhode Island, USA (41Њ29Ј N, tion), and the cost of ¯ower maintenance (see also Charnov, 72Њ32Ј W) (for a description of the site, see Rathcke [1988a, b]). Kalmia 1996). By measuring pollen deposition and removal and esti- latifolia, mountain laurel, is a tall evergreen shrub that grows in the understory mating maintenance costs, Ashman and Schoen (1994) found of forests and on mountains in eastern North America. Shrubs have tubular, a signi®cant positive correlation between ¯oral longevities ob- pink-white ¯owers displayed in in¯orescences (corymbs) of 10±300 ¯owers, served in the ®eld and predicted ¯oral longevities for 11 and individual shrubs may have thousands of ¯owers open at the same time. species. However, they note that there was not a close quan- Bumble bees were the only ¯ower visitors and pollinators of K. latifolia (Rath- titative ®t and that environmental factors, including pollina- cke, 1988a, b). In this low elevation habitat, ¯owers do not self-pollinate tion, may in¯uence ¯oral longevity in the ®eld. Also, they did (Rathcke, 1988a), although ¯owers can self-pollinate at the end of ¯ower life not measure effects on fruit or seed set. No experimental tests in a montane habitat in Virginia (Rathcke and Real, 1993; Levri, 1998; Nagy et al., 1999). Fruits are dry capsules with hundreds of tiny seeds.

1 Manuscript received 22 November 2002; revision accepted 18 April 2003. Reduction of ¯oral durationÐFor the experiment, I tagged four budded The author thanks Lee Kass, Carol Landry, Hitashi Sato, Rachel Simpson, in¯orescences on each of 14 shrubs. For each shrub, two in¯orescences were and two anonymous reviewers, who provided many helpful suggestions on the manuscript; Irene Stuckey, who provided a home for me near the Great assigned to controls and two were assigned to experimental treatments. For Swamp so I could do this research; and William Crepet, who provided me each assigned in¯orescence, new ¯owers (in anthesis) were tagged with color- with an of®ce and facilities in the L. H. Bailey Hortorium during my sab- coded yarn every 2 d throughout the ¯owering season (12±29 June). To reduce batical at Cornell University. the functional ¯oral longevity for female function, I clipped the stigmas of 2 E-mail: [email protected]. all ¯owers after they had been receptive (glistening and sticky) for 3±4 d. I 1328 September 2003] RATHCKEÐFLORAL LONGEVITY OF KALMIA LATIFOLIA 1329

TABLE 1. Percentage fruit sets of Kalmia latifolia ¯owers with natural TABLE 2. Percentage fruit sets of Kalmia latifolia ¯owers in controls ¯oral longevities and with reduced functional longevities (3±4 d) and in two experimental treatments: (1) with stigmas pollinated and created by clipping stigmas (means Ϯ 1 SD). Fruit set ϭ 100 (fruit/ subsequently clipped and (2) with stigmas clipped and styles im- ¯owers), N ϭ number of plants (number of ¯owers). Difference mediately pollinated (means Ϯ 1 SD). Fruit set ϭ 100 (fruit/¯ow- between control and treatment was tested using Friedman's non- ers), N ϭ number of plants (number of ¯owers). Difference be- parametric t test with plant as the sample unit. The asterisk denotes tween control and treatment was tested using Friedman's nonpara- a signi®cant difference; probability level is shown. metric t test with plant as the sample unit. NS indicates no signif- icant difference. Treatment N Fruit set (%) P Fruit Natural longevity 14 (612) 65 Ϯ 17.7* Ͻ0.0001 Treatment N set (%) Signi®cance Reduced longevity 14 (568) 10 Ϯ 8.3 Control 14 (612) 65 Ϯ 17.7 NS Pollinated, then clipped 9 (224) 61 Ϯ 16.2 Control 14 (612) 65 Ϯ 17.7 not tested chose 3±4 d because most other shrubs that co¯owered with K. latifolia in Clipped, then pollinated 9 (149) 0 June had ¯oral longevities of 3±4 d (Rathcke, 1988b). Stigmas were clipped with scissors just below the sticky surface, and the scissors were sterilized with ethanol after each use. Experimental ¯owers and control ¯owers were same family (Ericaceae), the same comparisons were made using only eri- exposed to natural pollination, and subsequent fruit sets were measured and caceous shrubs. compared. I also did a procedural control treatment to ascertain whether stigma clip- Statistical analysesÐDifferences in fruit sets among different treatments ping harmed ¯owers or normal fruit development. I augmented other ¯owers were tested with nonparametric Friedman's paired-sample sign tests because with cross-pollen and clipped their stigmas the following day. To determine percentage data are not distributed normally and because individual shrubs whether stigma clipping would preclude subsequent pollination and fertiliza- can differ in fruit set for other reasons and can be considered blocks. In this tion as assumed, I clipped stigmas of virgin ¯owers and immediately added test, the ranking in one block (plant) is independent of the ranking in another pollen to the remaining styles. Fruit sets were compared between these treat- block (Sokal and Rohlf, 1981). Tests are based on plants (blocks), not ¯owers, ments and controls. although the numbers of ¯owers are shown. Differences in ¯oral longevities of different species were tested with Student's t tests because the data met Fruit setÐFruit set was calculated as the percentage of ¯owers that initi- the assumption of homogeneity of variances based on Bartlett's tests. Statis- ated fruits. Percentage fruit set was calculated for each in¯orescence, and a tical analyses were done using SYSTAT, version 5.01 (Systat Inc., Evanston, mean was calculated for each individual shrub for each treatment. Fruit ini- Illinois, USA). tiation after a month of development was assumed to indicate that ¯owers had been successfully pollinated and fertilized. Previous studies showed that RESULTS little fruit abortion occurs after initiation, so these values also closely re¯ect ®nal fruit set (Rathcke, 1988a). Seeds were not measured. Floral longevity experimentÐFlowers with reduced func- tional ¯oral longevity had only 10% fruit set, whereas control Pollination limitationÐTo test for pollination limitation of fruit set of ¯ow- ¯owers with natural longevities had 65% fruit set (Table 1). ers, I compared the fruit set of naturally pollinated ¯owers to the fruit set of Reduced ¯oral longevity resulted in 85% pollination limitation ¯owers augmented with cross-pollen. In the pollen-augmentation treatment, of fruit set. Stigma clipping did not harm ¯owers or fruit de- all open ¯owers on one in¯orescence on each of the experimental shrubs were velopment. The mean fruit set of ¯owers that were hand-pol- augmented every 2 d with cross-pollen mixed from four other distant shrubs. linated and then clipped on the following day was not signif- The pollination limitation of entire plants was not determined because each icantly different from the mean fruit set of hand-pollinated, shrub typically has thousands of ¯owers. It is known that augmented polli- unclipped ¯owers (Table 2). Stigma clipping precluded sub- nation of a subset of ¯owers on a plant may in¯uence the fruit set of other sequent pollination and fertilization as assumed; stigmas of ¯owers or may reduce fruit set in subsequent years because of resource re- virgin ¯owers that were clipped and the styles pollinated pro- allocation (Zimmerman and Pyke, 1988). However, the experimental ¯owers duced no fruit (Table 2). in these shrubs were usually Ͻ1% of the total ¯owers on a shrub and seem unlikely to have strongly affected the fruit set of other in¯orescences. Pollination limitationÐMean fruit sets of naturally polli- A relative index of pollination limitation (PL) was calculated based on fruit nated ¯owers and pollen-augmented ¯owers were not signi®- sets (FS) of control ¯owers with natural longevity (control) and of experi- cantly different, indicating that fruit set was not limited by mental ¯owers with shortened longevity (experimental) as follows: pollination (Table 3). PL ϭ 100 (% FS of control Ϫ % FS of experimental)/(% FS of control) If the fruit sets of control and experimental ¯owers are equal, then PL ϭ 0%. Comparisons of ¯oral longevitiesÐShrubs that ¯owered in If fruit set were zero for experimental ¯owers and 100% for control ¯owers, spring had longer ¯oral longevities of 6±9 d (Table 4) and a then PL would equal 100% (Rathcke, 2000).

TABLE 3. Percentage fruit sets of Kalmia latifolia ¯owers with natural Comparisons of ¯oral longevitiesÐIn a previous study, longevities of pollination and with augmented cross-pollen (means Ϯ 1 SD). Fruit bagged ¯owers were measured for other shrub species growing in this site set ϭ 100 (fruit/¯owers), N ϭ number of plants (number of ¯ow- (Rathcke, 1988b). Flowers were bagged with bridal veiling to exclude polli- ers). Difference between the control and treatment was tested using nators, and ¯owers were individually tagged, color-coded by day of opening, Friedman's nonparametric t test with plant as the sample unit. NS and monitored daily until ¯owers senesced. For ®ve of these species, the ¯oral indicates no signi®cant difference. longevities of naturally pollinated ¯owers were also measured and compared Fruit with that of unpollinated ¯owers (Rathcke, 1988b). Treatment N set (%) Signi®cance For this study, the mean ¯oral longevities of spring and summer ¯owering Ϯ shrubs were compared to each other and to K. latifolia. To test whether the Natural pollination 14 (612) 65 17.7 NS Augmented pollination 14 (537) 50 Ϯ 16.2 ¯oral longevity of K. latifolia re¯ected a trait shared with other species in the 1330 AMERICAN JOURNAL OF BOTANY [Vol. 90

TABLE 4. Floral longevities for shrubs ¯owering in spring (May) and shrubs had longer mean ¯oral durations (7.2 d) than summer- summer (June and July) in the Great Swamp, Rhode Island, USA. ¯owering shrubs. This seasonal difference in ¯oral duration Modes in days shown. (Table modi®ed from Table 3 in Rathcke, 1988b). may re¯ect the seasonal change in pollinator abundance ob- served in this habitat. In spring, all pollinators are scarce and No. bees are infrequent, consisting mostly of a few queen bumble Family Species days bees starting their colonies and a few species of solitary bees, Spring-¯owering shrubs mostly Andrena. In addition, weather is often unfavorable to Ericaceae baccata 6 pollinator activity. In contrast, bee pollinators are abundant in Ericaceae Vaccinium atrococcum 8 summer because bumble bee colonies have produced many Ericaceae 9 workers and many solitary bee species are present (Rathcke, Caprifoliaceae Viburnum cassinoides 6 1988a, b). Low pollinator abundance in different habitats has Summer-¯owering shrubs often been related to longer ¯oral durations in these habitats Ericaceae Kalmia latifolia 8 (Arroyo et al., 1981; Primack, 1985; Stratton, 1989; Bingham Ericaceae 4 and Orthner, 1998; Blionis et al., 2001; Blionis and Vokou, Ericaceae Rhododendron viscosum 4 Ericaceae 3 2001). In this one habitat, the seasonal change in pollinator Ericaceae ligustrina 4 abundance is accompanied by a seasonal change in ¯oral lon- Clethraceae Clethra alnifolia 3 gevities, but it cannot explain the long ¯oral duration of K. Aquifoliaceae Ilex glabra female 5 latifolia because it blooms in summer when its bumble bee Aquifoliaceae Ilex opaca female 4 pollinators are abundant. Liliaceae Smilax glauca male 2 Although pollinator abundance is lower in spring, the longer ¯oral life spans of spring-¯owering shrubs could also re¯ect cooler temperatures, which may reduce metabolism and slow mean of 7.2 d (Table 5), whereas shrubs that ¯owered in sum- development. Arroyo et al. (1981) reported that mean longev- mer had ¯oral longevities of 3±4 d (Table 4) and a mean of ity of ¯owers was 4.1 d at a low elevation site (2320 m asl) 3.4 d (Table 5). The mean ¯oral longevities were signi®cantly and 9.0 d at a high elevation site (3550 m asl) in the Andes, different for summer- and spring-¯owering shrubs (Table 5). and they attributed the difference to slower ¯oral development The ¯oral longevity of K. latifolia was signi®cantly longer at cooler temperatures. However, cooler temperatures could be than that of other summer-co¯owering shrubs (Table 5). The a proximate cue for the ultimate factor of low pollinator avail- ¯oral longevity of K. latifolia was not signi®cantly different ability. In either circumstance, K. latifolia again is an excep- from the mean ¯oral longevity of spring-¯owering shrubs (Ta- tion because it blooms during the warmer days of June but ble 5), but the maximum ¯oral longevity of K. latifolia (21 d) has long ¯oral duration. was much longer than that found for any other shrub species The long ¯oral duration of K. latifolia is not a trait shared in this community. by other shrubs in the same family (Ericaceae) that were grow- Shrubs in the Ericaceae showed a similar seasonal pattern ing in this site. Kalmia latifolia has greater ¯oral longevity in ¯oral longevities; spring-¯owering species had longer ¯oral than other ericaceous species that co¯ower in summer, includ- life spans than summer-¯owering species (Table 6). The ¯oral ing one congeneric species, K. angustifolia (Table 6). Al- longevity of K. latifolia was signi®cantly longer than that of though the mean ¯oral longevity (8 d) of K. latifolia was not other summer-¯owering ericaceous shrubs and was similar to signi®cantly different from spring-¯owering Ericaceae, the that of spring-¯owering ericaceous shrubs (Table 6). maximum ¯oral longevity for K. latifolia,upto21d,was much longer than the ¯oral maximum of any other shrub in DISCUSSION the community. These experimental results demonstrate that long ¯oral du- The long ¯oral duration of 21 d in K. latifolia is unusual ration can signi®cantly increase successful pollination and fruit for plant species in general. Floral longevities of 2 wk or lon- set in K. latifolia. Flowers with natural longevities were not ger have been reported for relatively few species. These spe- pollination-limited, whereas ¯owers with reduced longevities cies include some orchids (Primack, 1985), two ®g species (3±4 d) showed 85% pollination limitation of fruit set. Long (Khadari et al., 1995), and some wind-pollinated species (Pri- ¯oral duration lasting up to 21 d is clearly advantageous to mack, 1985), and their long ¯ower durations have been attri- female ®tness in K. latifolia, and is unique in this site. Other buted to low probabilities of pollination (Primack, 1985). Most shrubs that co¯ower in summer with K. latifolia had a mean plant species have ¯oral longevities of 2±4 d (Primack, 1985; life span of only 4.2 d for bagged ¯owers. Spring-¯owering Stratton, 1989). Tropical species often have ¯oral longevities

TABLE 5. Comparisons of ¯oral longevities of shrubs in the Great Swamp, Rhode Island, USA, between different seasons and with Kalmia latifolia (means Ϯ 1 SD). Signi®cant differences were tested by Student's t tests. Asterisks denote signi®cant differences; probability levels are shown. NS indicates no signi®cant difference. See Table 4 for species names.

Comparison N (species) Floral longevity (d) P Spring-¯owering shrubs 4 7.2 Ϯ 1.50* Ͻ0.01 Summer-¯owering shrubs, K. latifolia excluded 8 3.4 Ϯ 1.06 Summer-¯owering shrubs, K. latifolia excluded 8 3.4 Ϯ 1.06* Ͻ0.01 Summer-¯owering K. latifolia 1 8 Spring-¯owering shrubs 4 7.2 Ϯ 1.50 NS Summer-¯owering K. latifolia 1 8 September 2003] RATHCKEÐFLORAL LONGEVITY OF KALMIA LATIFOLIA 1331

TABLE 6. Comparisons of ¯oral longevities of ericaceous shrubs in the Great Swamp, Rhode Island, USA, between different seasons and with Kalmia latifolia (Ericaceae) (means Ϯ 1 SD). Signi®cant differences were tested by Student's t tests. Asterisks denote signi®cant differences; probability levels are shown. NS indicates no signi®cant difference. See Table 4 for species names.

Floral Comparison N (species) longevity (d) P Spring-¯owering shrubs 3 7.7 Ϯ 1.53* Ͻ0.01 Summer-¯owering shrubs, K. latifolia exluded 4 3.8 Ϯ 0.50 Summer-¯owering shrubs, K. latifolia excluded 4 3.8 Ϯ 0.50* Ͻ0.01 Summer-¯owering K. latifolia 1 8 Spring-¯owering shrubs 3 7.7 Ϯ 1.53 NS Summer-¯owering K. latifolia 1 8 of only 1 d, possibly because of high rates of predation or the size of the ¯oral display and attract more pollinators (Ishii bacterial and fungal decay (Primack, 1985). Risk of disease and Sakai, 2001). However, large ¯oral displays can also in- has been proposed to shorten ¯oral longevities (Shykoff et al., crease geitonogamy (within-plant pollination), which would be 1996). In this study, neither ¯ower predation nor infection of detrimental to K. latifolia because of strong inbreeding de- ¯owers was evident for any of the species, although fungal pression (Rathcke and Real, 1993). The cost from geitonoga- pathogens on leaves have been shown to increase fruit abortion my can be reduced by pollination-induced senescence, which and affect mating in K. latifolia in Virginia (Levri and Real, removes ¯owers from the display when they are pollinated. 1998). The apparent lack of ¯oral predation or disease may Flowers of K. latifolia show pollination-induced senescence; allow long ¯oral duration of K. latifolia in this site. corollas wilt and fall the day after they are successfully pol- What is a possible explanation for the long ¯oral duration linated (Rathcke, 1988a). Pollination-induced senescence can of K. latifolia? I propose that long ¯oral duration is advanta- also direct pollinators to viable ¯owers and increase the effec- geous because K. latifolia is a poor competitor for pollinators tiveness of pollinator visits (van Doorn, 1997). In addition, and that it is a mechanism for competitive avoidance. Flowers ¯exible ¯oral longevity can decrease transpirational water loss of K. latifolia produce little nectar and are infrequently visited and energy costs of maintaining ¯owers (Primack, 1985; Strat- by bumble bees when other shrub species are ¯owering (Rath- ton, 1989), which have been shown to be substantial in some cke, 1988a). Bumble bees are the only pollinators of K. lati- species (Ashman and Schoen, 1997; Galen et al., 1999). folia in this habitat, and they preferentially visit species with Whether the long ¯oral duration of K. latifolia evolved as higher nectar rewards. The long ¯oral duration of K. latifolia a response to competition for pollinators remains speculative. increases the probability that ¯owers will be pollinated after Instead, this trait may have evolved in areas such as montane competing species cease ¯owering (Rathcke, 1988a). Because habitats, where pollinators are sparse or unpredictable as has unpollinated ¯owers remain viable, they extend the ¯owering been reported for other species (Arroyo et al., 1981; Stratton, phenology of K. latifolia into a competition-free period. In 1989; Bingham and Orthner, 1998; Blionis and Vokou, 2001; addition, long ¯oral duration may provide pollination assur- Blionis et al., 2001). The trait may have been maintained when ance when pollinators are scarce and allow K. latifolia to tol- it proved to be advantageous in more favorable sites where erate conditions of low pollinator activity. Such tolerance of competition for pollinators was strong. Other species have low pollinator activity may be an alternative strategy to having evolved self-pollination, rather than long ¯oral duration, for greater attraction or rewards and greater competitive ability reproductive assurance in situations in which pollinators are for pollinators (Rathcke, 1988a). sparse (Baker, 1955; Lloyd, 1980; Fausto et al., 2001). Self- Species that tolerate low resources have been termed ``good pollination has also been invoked as a mechanism for com- response competitors'' in contrast to ``good effect competi- petitive avoidance in Arenaria uni¯ora (Fishman and Wyatt, tors'' that can deplete resources effectively (Goldberg, 1990; 1999). This study suggests that long ¯oral life span can be an Miller and Travis, 1996). The ability of K. latifolia to tolerate alternative to self-pollination under conditions of uncertain low rates of pollinator visitation and its inability to compete pollination and competition. In fact, K. latifolia exhibits both effectively for pollinators make it a good response competitor. long ¯oral duration and the ability to self-pollinate in a mon- Why is K. latifolia a good response competitor, rather than a tane site in Virginia where pollinators are more unpredictable good effect competitor for pollinators? Higher nectar produc- and where competition with other shrubs is also strong (Rath- tion per ¯ower would make it more competitive with co¯ow- cke and Real, 1993; Nagy et al., 1999; B. J. Rathcke, unpub- ering species (Rathcke, 1988a). However, greater nectar re- lished data). Despite having both of these mechanisms for re- wards would probably cause bees to forage longer within in- productive assurance, fruit set was pollination-limited in Vir- dividual shrubs and would promote geitonogamy (within-plant ginia (Rathcke and Real, 1993). In contrast, fruit set was not pollination) and sel®ng (Rathcke and Real, 1993). Because K. pollination-limited in this habitat in Rhode Island, indicating latifolia shows strong inbreeding depression with sel®ng, a that pollinators were more available, especially after compet- strategy of higher nectar rewards could be detrimental to both ing shrubs ceased ¯owering. This greater availability of pol- female and male reproductive success (Rathcke, 1992; Rathcke linators may explain why K. latifolia does not self-pollinate and Real, 1993). Higher nectar production would also be cost- and has only prolonged ¯oral duration as a mechanism for ly in resources. Other traits could also increase attractiveness reproductive assurance in this Rhode Island habitat. (Waser, 1983; Caruso, 2000), but higher rewards would be Floral senescence in K. latifolia is induced by pollen de- necessary to increase the ability of K. latifolia to compete position, rather than pollen removal, which suggests that fe- effectively for pollinators. male function is less rapidly completed than male function Another bene®t of long ¯oral duration can be to increase (Proctor and Harder, 1995; Bell and Cresswell, 1998; Evanhoe 1332 AMERICAN JOURNAL OF BOTANY [Vol. 90 and Galloway, 2002). This response supports the assumption GOLDBERG, D. E. 1990. Components of resource competition in plant com- made here that female function and maintenance of fruit set is munities. In J. B. Grace and D. Tilman [eds.], Perspectives on plant the important factor selecting for long ¯oral duration in K. competition, 27±49. Academic Press, San Diego, California, USA. ISHII,H.S.,AND S. SAKAI. 2001. Effects of display size and position on latifolia. 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