Flowering Phenology of Co-Occurring Asteraceae: a Matter of Climate, Ecological Interactions, Plant Attributes Or of Evolutionary Relationships Among Species?

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Org Divers Evol (2011) 11:9–19 DOI 10.1007/s13127-011-0038-2

ORIGINAL ARTICLE

Flowering phenology of co-occurring Asteraceae: a matter of climate, ecological interactions, plant attributes or of evolutionary relationships among species?

Carolina Torres & Leonardo Galetto

Received: 4 June 2010 /Accepted: 10 January 2011 /Published online: 23 February 2011 # Gesellschaft für Biologische Systematik 2011

Abstract We analyzed the flowering phenodynamics of 43 intermediate values for frequency of visits and number of Asteraceae species co-occurring in natural populations of species of floral visitors, seed dispersal mechanisms other Chaco Serrano forests in central Argentina. We explored than anemochory, and herbaceous growth form. In addition, the potential influence of factors such as photoperiod and all but one species belonging to early-branching tribes climate (variations in temperature, rainfall, and frost), (tribes phylogenetically close to the root of the Asteraceae animal-plant interactions (richness of floral visitors, fre- tree) were grouped together and clustered in the same quency of visits), some plant attributes (plant growth form, region of the two-dimensional PCA ordination. All species seed dispersal mechanism), and evolutionary relationships belonging to the late-branching tribes (Asteroideae subfam- among species on flowering phenodynamics. Cluster ily tribes) included in group 1 were separated from the Analysis (CA) and Principal Component Analysis (PCA) other Asteroideae species in the PCA. In conclusion, it were the multivariate statistical methods used to analyze seems that climatic factors restrict the phenological period emerging patterns associated with these co-occurring of most species, and that plant attributes and taxonomic species. Null-model analyses were used to evaluate whether membership are strongly related to flowering phenodynam- flowering times are aggregated, segregated, or random. ics in this group of Asteraceae studied. Results showed that flowering phenology was significantly correlated with the seasonal variation in temperature, Keywords Compositae . Photoperiod and climate . photoperiod, rainfall, and frost. The multivariate statistical Evolutionary relationships . Plant-animal interactions . methods separated all the species in three groups: 1) species Flowering phenology. Argentina with short flowering time, large plant floral display, high frequency of visits by a large number of species of floral visitors, anemochorous fruits, and shrubby growth form, Introduction with a tendency to a segregated flowering pattern; 2) species with long flowering time, small plant floral display, Flowering phenology is one of the most studied traits in plants low frequency of visits by few insect species, anemocho- because it has potential significance for plant ecology and rous fruits, and herbaceous growth form; and 3) species evolution (e.g. Fenner 1998; Rathcke and Lacey 1985;Sakai with long flowering time, small plant floral display, 2001;Schemskeetal.1978). The pattern of flowering can affect plant fitness (LeBuhn 1997;RathckeandLacey1985), C. Torres (*) : L. Galetto and hence the survival and establishment of species. The Instituto Multidisciplinario de Biología Vegetal, Universidad analysis of flowering strategies is a complex issue, because – Nacional de Córdoba Consejo Nacional de Investigaciones the latter are the result of an interacting set of environmental Científicas y Técnicas, Córdoba, Argentina conditions, plant-animal interactions, and plant attributes e-mail: [email protected] (Armbruster 1995). Furthermore, flowering strategy can be a L. Galetto conservative trait within taxonomic groups (e.g. Kochmer e-mail: [email protected] and Handel 1986; Wright and Calderon 1995). 10 C. Torres, L. Galetto

Available data suggest that biotic and abiotic factors can group of species. Plant growth form can restrict flowering influence the initiation and duration of flowering (e.g. possibilities (Bertiller et al. 1991;Lieberman1982; Seghieri Brody 1997; Losos 2000; Madeira and Fernandes 1999; et al. 1995). On the other hand, fruit dispersal characteristics Sakai 2002; Smith-Ramírez and Armesto 1994; Waser can be related to flowering and fruit-ripening dates (e.g. 1983). The main abiotic factors that may shape plant Bolmgren and Lönnberg 2005; Oberrath and Böhning-Gaese phenological patterns are photoperiod (e.g. Diekmann 2002). In this way, Bolmgren and Lönnberg (2005)found 1996; Marco and Páez 2002; Wright and van Schaik early flowering in fleshy-fruited taxa when comparing mean 1994), temperature (e.g. Ashton et al. 1988; Fitter et al. flowering times between fleshy- and dry-fruited plants (but 1995; Marques et al. 2004), and rainfall (e.g. Borchert see Lönnberg 2004). This pattern could be interpreted as an 1996; Murali and Sukumar 1994). Although below-freezing evolutionary interdependence between flowering and fruiting temperatures (i.e. frosts) can also limit plant growth and phases. Then, if the main causes influencing flowering times determine flowering phenology, they have received little are related to fruit dispersal mechanisms, it is reasonable to attention (Inouye 2000). If the main causes influencing the expect that anemochorous fruits may be synchronized with flowering times are related to abiotic factors, it is the windiest months, and that zoochorous fruits (epizoocho- reasonable to expect similar patterns of phenodynamics rous in the case of Asteraceae species) may be independent within a group of co-occurring species. of abiotic conditions. Flowering phenology could also be shaped by biotic Finally, many studies have indicated that flowering time is a factors such as the appropriate time for reproduction or conservative trait within evolutionary lineages (e.g. Jennings growth (e.g. Ashton et al. 1988;MuraliandSukumar1994; 2001; Johnson 1992; Kochmer and Handel 1986; Smith- Pleasants 1980; Smith-Ramírez et al. 1998; Stiles 1975, Ramírez and Armesto 1994; Smith-Ramírez et al. 1998; 1977; Yeboah Gyan and Woodell 1987). If the availability or Wright and Calderon 1995; but see Silvertown et al. 2001). efficiency of pollinators affects sexual reproduction of Consequently, additional phenological studies about co- animal-pollinated plants, some hypotheses about phenolog- occurring species and phylogenetically related species, like ical trait-patterns may be deduced from the literature. the one presented here, have become of great importance According to the adaptationist school of thought, co- toward understanding certain patterns of flowering phenology occurring species must differ significantly in their reproduc- by taking into consideration several concurrent forces. tive phenology to increase the opportunities for pollination However, only few studies have analyzed the phenological (i.e. phenological character displacement among species due traits of species belonging to the same family, e.g. to competition; e.g. Feinsinger 1987; Levin and Anderson Wheelwright (1985; Lauraceae), Ashton et al. (1988; 1970). The resulting expected flowering pattern is a regular Dipterocarpaceae), Milton (1991; Moraceae), Smith-Ramírez temporal segregation among species sharing common et al. (1998; Myrtaceae), or to the same genus, e.g. Fleming pollinators (e.g. Ashton et al. 1988;Pleasants1980; Stiles (1985; Piper),Friedeletal.(1994; Acacia), Madeira and 1975, 1977; Yeboah Gyan and Woodell 1987). However, in Fernandes (1999; Chamaecrista). Although Asteraceae is an many natural communities, patterns of flowering do not fulfil interesting group to be analyzed in comparative studies due to predictions of the competition theory (e.g. Agren and its high richness of species easily found in small areas, there Fagerström 1980; Armbruster and McGuire 1991;Rathcke are surprisingly few phenological studies carried out on this 1988a), and tests of temporal flowering have shown patterns widespread family (e.g. Baskin et al. 1993 on ten North to be aggregated, segregated (e.g. Gotelli and Graves 1996; American Asteraceae; Gross and Werner 1983 on Solidago). Murali and Sukumar 1994; Poole and Rathcke 1979;Sakai Although many discrepancies have been pointed out 2002; Smith-Ramírez et al. 1998) or to be indistinguishable with respect to the use of comparative methods (e.g. from what would be expected by chance alone (e.g. Fleming Abouheif 1999; Ackerly 2000; Felsenstein 1985, 1988; and Partridge 1984;Rathcke1984; Wright and Calderon Freckleton 2000; Harvey and Pagel 1991; Losos 1999; 1995). The absence of clear phenological patterns indicates Pagel 1992; Pagel and Harvey 1992; Price 1997; Westoby that pollinator-mediated selection is weak or nonexistent et al. 1995), most authors have concluded that it is basic to (Ollerton and Lack 1992). apply this methodology only when a well-resolved phylo- Some supplementary ideas explain why existing competi- genetic tree of the studied species is available. Therefore, in tion for pollinators is difficult to detect when flowering the absence of a tree of this type for mapping traits of our phenology is analyzed. For example, by selecting plant traits group of species, and in order to apply the comparative related to other reproductive phases such as the best time of method with this group of species, we used a recently fruit dispersal or leaf sprouting, the evolution of flowering published phylogenetic tree of tribes and subfamilies of phenology may be constrained (Pico and Retana 2000). Thus, Asteraceae (Fig. 1; adapted from Panero and Crozier 2008; it is relevant to analyze the relationship between some plant Panero and Funk 2008) to discuss some general tendencies attributes and flowering phenology within a closely related in a rough taxonomic framework. Flowering phenology of co-occurring Asteraceae 11

In our study, we examined the flowering phenodynamics Serranita and Los Aromos), on natural populations of the (flowering time, flowering time length, and plant floral 43 Asteraceae species, as detailed in Table 1. The study site display) of 43 species of the Asteraceae family co-occurring (31º44′S, 64º26′W, with a 1.5 km radius) is located on the in natural populations in central Argentina. We explored the eastern slope of the Sierras Chicas, at 650 m above sea potential influences on flowering phenodynamics of factors level. such as photoperiod and climate (variations in temperature, We recorded the flowering phenology of each species rainfall, and frost), animal-plant interactions (richness of over the course of 2 years (from August 1998 to August floral visitors, frequency of visits), some plant attributes 2000). Records were kept at weekly intervals on a (plant growth form, seed dispersal mechanism), and minimum of ten individuals per species. A species was evolutionary relationships among species. considered in bloom when open flowers were seen on 25% Specifically, we expected for this group of co-occurring or more of the monitored individuals (Dafni 1992). The Asteraceae species that (A) photoperiod and climate would number of flowering species per month was calculated as limit the flowering season to some favorable months, (B) the number of different species recorded in bloom during those species sharing common pollinators would show a each calendar month, averaged for this month over the regular temporal segregation of flowering time within a study period. Flowering time length of each species was competitive scenario, (C) perennial species would show estimated as the 2-year mean of the number of weeks in spaced flowering times within the favourable season and which the species flowered within each 12-month period. more synchronized (i.e. aggregated) ones than annual The species were classified as presenting (A) large plant species, (D) those species with anemochorous fruits would floral displays (>100 daily active inflorescences) or (B) be more synchronized during the windiest months than small plant floral displays (<100 daily active inflorescen- those species with epizoochorous fruits. Furthermore, ces), according to the mean number of capitula with open considering some relationships found in previous studies flowers simultaneously offered by each individual. between different floral traits (nectar composition, corolla, pollen and stigma morphology, richness of floral visitors) Climate data and photoperiod records and the phylogeny of tribes (Torres 2000; Torres and Galetto 2002, 2007), we expected that flowering phenody- The normal climate in the study area is dry-temperate namics would be related to the taxonomic membership in with a mean annual temperature of 17.3°C. Mean this group of Asteraceae species. monthly maximum temperatures reached 29.5°C in February; mean monthly minimum temperatures descended to 4°C in July. Annual total rainfall over a Material and methods 10-year period averaged 866 mm. Climate data were the latest available records from the nearest meteorological Study site and phenological data station at Córdoba Airport, ca. 50 km from the study site. We used the monthly 10-year average for the The study was conducted in Chaco Serrano forests in following climatic variables recorded during the period Argentina, Córdoba Province (Dept. Santa María, near La 1981–1990: total rainfall; number of days with frost; maximum, minimum, and median temperature. We also considered mean monthly photoperiod. Considering that this group of species seems to show highly seasonal flowering, we performed a cluster analysis to identify the group of months in which species do not flower because of unfavorable climatic conditions. Statistical analyses determined two major seasons: (1) a rainy, warm, and long-day season without frosts, from October to April, and (2) a dry, cold, and short-day season with frequent frosts, from May to September. Because flowering of most studied species occurs between October and April, we named this period “the rainy flowering season”. These months are characterized by mean total rainfall higher than 56 mm andmeanmediantemperatureshigherthan17°C.This Fig. 1 Diagram of phylogenetic relationships between Asteraceae taxa studied in this work (adapted from Panero and Crozier 2008; period is also determined by the absence of frosts from Panero and Funk 2008) October until April. 12 C. Torres, L. Galetto

Table 1 Plant attributes and floral visitors of 43 Asteraceae species growing in the Chaco Serrano forests of La Serranita-Los Aromos; subfamily assignment after Panero and Funk (2008)

Nr. Species Growth Dispersal Status c No. of floral visitor Total frequency Floral Cluster forms a mechanisms b speciesd of visits e display f membership g

MUTISIOIDEAE 01 Chaptalia integerrima PH A N ––SS 02 Ch. nutans PH A N ––SS 03 Trichocline reptans PH A N 7 18 S S 04 Trixis divaricata subsp. discolor SA N5 38L S CARDUOIDEAE 05 Carduus thoermeri AH A A 7 71 S S CICHORIOIDEAE 06 Hypochaeris chillensis PH A N 5 28 S S 07 H. microcephala PH A N ––SS 08 H. radicata PH A A ––SS 09 Sonchus oleraceus AH A NAT 7 19 S S 10 Taraxacum officinale PH A A 7 24 S S 11 Vernonia mollissima SS A N 12 60 S S 12 V. nudiflora SS A N 6 85 L M ASTEROIDEAE 13 Achyrocline tomentosa SS A N ––LM 14 Baccharis articulata S A N 11 420 L M 15 B. pingraea PH A N 12 101 L M 16 B. rufescens SA N––LM 17 B. salicifolia SA N––LM 18 Grindelia pulchella var. discoidea SS O N 7 82 S I 19 Heterothalamus alienus SO N––LM 20 Solidago chilensis PH A N 20 488 L M 21 Senecio pampeanus PH A N 17 155 L M 22 Gaillardia megapotamica PH A E 9 45 S S 23 Helenium argentinum PH A E 7 16 S S 24 Schkuhria pinnata AH O N ––SI 25 Tagetes minuta AH O N ––SI 26 Acmella decumbens var. affinis PH O N 13 46 S I 27 Angelphytum aspilioides SS O N 13 26 S I 28 Bidens pilosa AH O N 17 146 S I 29 Cosmos sulphureus AH O A 10 45 S I 30 Flourensia campestris S O E 6 141 L M 31 Galinsoga parviflora AH O N ––SI 32 Parthenium hysterophorus AH O N ––SI 33 Zexmenia buphthalmiflora PH O E 7 59 S I 34 Zinnia peruviana AH O N 4 15 S I 35 Eupatorium argentinum SS A N 3 24 L S 36 E. arnottianum SS A N ––LM 37 E. clematideum PH A N ––SS 38 E. hookerianum SA N––LM 39 E. inulifolium S A N 11 342 L M 40 E. subhastatum SS A N ––SS 41 E. viscidum SA N––LM 42 Mikania urticifolia V A N 12 231 L M 43 Stevia satureifolia SS A N 3 4 S S a AH annual herb, PH perennial herb, S shrub, SS subshrub, V vine b A anemochory, O other mechanisms c A adventitious, E endemic, N native, NAT naturalized d see text in Material and methods section e measured as number of capitula visited; see Material and methods section f L large plant floral display (>100 capitula daily), S small plant floral display (<100 capitula daily) g M ‘massive blooming’, S ‘sparse blooming’, I ‘intermediate’ group of species; see Results section Flowering phenology of co-occurring Asteraceae 13

Floral visitors and frequency of visits riod [hours], (III) total rainfall [mm], and (IV) number of days with frosts. Because of the strong correlations among The number of floral visitor species and total frequency of the independent variables, the stepwise method was used visits were estimated for most Asteraceae species. A total of for multiple regression analyses. Mean maximum, median, 2 h of observations were made on each plant species, in and minimum monthly temperatures showed similar four periods of 30 min equally distributed during the correlations; thus, only median temperatures were used morning and afternoon on different sampling days. For in the regression tests. These analyses, based on rainfall, each 30-min period, we delimited six different squares of temperature, frost, and photoperiod means, were run using 1m2 in which two variables (number of floral visitor data of the respective month prior to phenological species, total number of inflorescences visited by all observations. individuals) were recorded during 5-min periods for each In order to characterize the different groups of species to square. The number of inflorescences included within each be included in the null model, we used clustering square was very variable (range 1–300) because of differ- techniques (K-Means Cluster Analysis; Digby and ences in the reproductive strategies of the studied species Kempton 1996). Through this approach we obtained sets (squares may contain many inflorescences of only one of species classified according to species differences in individual in shrubby and densely flowered species, or few flowering times, plant growth form, seed dispersal mech- inflorescences of different individuals in herbaceous species anism, plant floral display, number of floral visitor species, with small floral displays). In order to compare species with and frequency of visits. We carried out a one-way analysis very different vegetative and flowering traits, sampling was of variance (ANOVA) using the final clusters as groups for standardized as the mean number of visits received by an each variable, individually using SPSS (1999). For descrip- inflorescence (i.e. as total number of visits/number of tive purposes, F values are provided to interpret the observed capitula). differences between the conglomerates (i.e. not as the statistical null hypothesis that the centers of the conglom- Plant attributes and evolutionary relationships erates are equal; Digby and Kempton 1996; SPSS 1999). Multiple regression and cluster analyses were performed Plant growth form (shrub, subshrub, annual herb, perennial according to methods described in Sokal and Rohlf (1995) herb, or vine) and actual status for Argentina (adventitious, and Tabachnick and Fidell (1996). We used the statistical endemic, native, or naturalized) were obtained from program package SPSS Inc. (1992). In addition, we used Zuloaga and Morrone (1999) and from field observations. multivariate Principal Component Analysis (Digby and The species were also classified as either anemochorous or Kempton 1996) to analyze emerging flowering phenology non-anemochorous (i.e. mainly epizoochorous) according patterns in this group of co-occurring species by consider- to their pappus morphology (plumed or non-plumed ing flowering phenology, plant traits and evolutionary achenes, respectively). Evolutionary relationships between relationships. the subfamilies and tribes (Fig. 1) were based on recently All null-model analyses were conducted with EcoSim published phylogenetic trees in Panero and Crozier (2008) 6.0 software in which “flowering midpoints” and “length of and Panero and Funk (2008). the flowering time” were used as indicators of flowering time in each species (Gotelli and Entsminger 2001). Data analyses EcoSim performs Monte Carlo randomizations to create “pseudo-communities” (Pianka 1986), then statistically We employed Hierarchical Cluster Analysis to determine compares the distribution in these randomized group of different climatic seasons (Digby and Kempton 1996; species to those in the real data matrix. Null-model analyses SPSS 1999). We selected the between-group average were used to evaluate whether flowering times are linkage method measured by squared Euclidian distance aggregated, segregated, or random. We used “flowering sinceweintendedtoanalyzethe similarities between midpoint” as each entry of the matrix representing the groups of months by considering the average values of flowering time of a particular species (i.e. the number of the four climatic variables. Pearson correlation and multiple week at the center of the flowering period). Those species regression analyses were performed with the number of that flower year-round were excluded from null-model flowering species in each month, starting and ending dates analyses, because midpoints are unrealistic indicators of of flowering for each species as the dependent variables, flowering times. We performed two null-model analyses and climatic factors as independent variables; it should be (one including all species, the other excluding exotic noted that these factors are not necessarily independent species). Considering that strong correlations were found from each other. Four mean monthly climatic predictors between climatic variables and flowering times (Table 2), were tested: (I) median temperature [in°C], (II) photope- and that most species do not flower under the climatic 14 C. Torres, L. Galetto

Table 2 Correlations between monthly numbers of Asteraceae phenological observations; values represent Pearson’s correlation species flowering in the Chaco Serrano forests of La Serranita-Los coefficients (* = P<0.05, ** = P<0.01) Aromos and means of climatic variables for the month prior to

Climatic variable No. of species flowering No. of species beginning flowering No. of species finishing flowering

Photoperiod [h] 0.89** 0.73** −0.37 Total rainfall [mm] 0.91** 0.51* −0.06 Average temperature [°C] 0.96** 0.53* 0.01 Frost [No. of days] −0.85** −0.51* 0.01

conditions of the dry season, we limited the phenological Null-model analysis showed that the observed variance space to the rainy season so that every position along the in segment length (0.60) between flowering midpoints for resource axis was assigned the same probability of Asteraceae species was not significantly different from the occupation (Cole 1981; Pleasants 1990). In addition, we expected variance (0.61, P=0.55 for all species (native + used the “segment length” metric of EcoSim that is exotic); 0.87, P=0.20 for native species only). Thus, the calculated between adjacent species (i.e. using the length observed distribution of one of the parameters used to of the flowering time of each species) to analyze patterns of characterize phenology (i.e. midpoints) within the rainy flowering phenology. We used the variance of segment season need not reflect anything but stochastic events. lengths that measures the overall tendency for even spacing of all species (Gotelli and Entsminger 2001). The more Influences of ecological factors and taxonomic membership regular the spacing of species, the more similar in size the on flowering phenology segments are and, consequently, the smaller the variance in segment length is for a group of species. The randomization Cluster analysis allowed us to group species according to process was repeated 5000 times to create a frequency their differences in flowering time length, plant growth distribution of variances against which the observed form, seed dispersal mechanism, plant floral display, variance could be compared. number of floral visitor species, and frequency of visits. The following three groups were found (Table 3). (1) Species with comparatively short flowering times, large Results plant floral display, and high frequency of visits of a great number of floral visitor species. Most of these species were Influences of climatic factors and photoperiod on flowering anemochorous and shrubby plants. For simplicity, we phenology named this group ‘massive blooming species’. (2) Species with comparatively long flowering times, small plant floral The number of species flowering in each calendar month display, and low frequency of visits of few insect species. was very variable (2–31 species; Fig. 2). The maximum All species in this group had anemochorous fruits and were occurred in December and January (Fig. 2), whereas in mostly herbaceous. We named this group ‘sparse blooming August only two non-native species had open flowers species’. (3) Species with long flowering times, small plant (Taraxacum officinale and Sonchus oleraceus, which are floral display, and seed dispersal mechanisms other than the only species that flower year-round; Fig. 3b). anemochory. Most of these species were herbaceous plants. All climatic variables were significantly correlated with We named this group ‘intermediate species’ because of the number of species flowering in each month (Table 2). their comparatively intermediate values of frequency and The stepwise regression process indicated that mean the number of floral visitor species. In summary, floral plant median temperature was the best predictor for the number display, dispersal mechanism, frequency of visits, and of species flowering in each month (adjusted R2=0.92, growth form showed the greatest differences among the P<0.01). Similarly, all climatic variables were significantly three groups, whereas flowering time length and the correlated with the number of species that begin to flower number of floral visitor species showed lesser differences in each month (Table 2), but the photoperiod was the best (Table 3). predictor (adjusted R2=0.48, P<0.01). On the other hand, With the exception of Vernonia nudiflora, all species no significant correlations were found between the number belonging to the subfamilies Mutisioideae, Carduoideae, of species that stop flowering in each month and the and Cichorioideae were classified within the ‘sparse climatic variables (Table 2). blooming’ group, while the other two clusters were Flowering phenology of co-occurring Asteraceae 15

accounting for 61.7% of the total variation. Close relationships were observed on axis 1 between species scores and ‘flowering length’ and ‘life form’, on axis 2 between species scores and ‘mode of dispersion’ and ‘taxonomic membership’ (Fig. 4). Again with the exception of Vernonia nudiflora, all species in Mutisioideae, Carduoideae, and Cichorioideae (i.e. in early-branching tribes; Fig. 1) were grouped together and appeared in the same region of the two-dimensional PCA ordination (Fig. 4). In contrast, all species belonging to the late-branching tribes (of Aster- oideae subfamily) included within ‘massive blooming Fig. 2 Number of Asteraceae species growing in Chaco Serrano species’ were separated from the other Asteroideae species forests of La Serranita-Los Aromos that bear flowers during each in the plot (Fig. 4). month of the year; for calculation, see text in Material and methods Section We analyzed separately each cluster pattern of flowering midpoints. Null-model analysis for native species exclusively composed of taxa belonging to tribes of the belonging to the ‘massive blooming’ group (Fig. 3a) Asteroideae subfamily (Table 1; Fig. 1). showed an observed variance (1.91) lower than expected Principal Component Analysis showed that the principal (4.03), and generated a tail probability of 0.07. On the two axes provide separate ordinations of the species other hand, null-model analyses were unrealistic for the Fig. 3 Flowering phenology of 43 Asteraceae species in Chaco Serrano forests of La Serranita- Los Aromos separated in three groups: (A) ‘massive blooming’, (B) ‘sparse blooming’, (C) ‘intermediate’ species (see Results Section). Numbers indicate the species detailed in Table 1; lines represent their flowering times; ♦ = flowering midpoint (week in center of recorded flowering period) 16 C. Torres, L. Galetto

Table 3 Plant attributes and floral visitors according to cluster membership of 43 Asteraceae species growing in the Chaco Serrano forests of La Serranita-Los Aromos; values represent means ± SD or percentage shares by species, as applicable

Species cluster Flowering period Growth Dispersal No. of floral Total frequency Floral [weeks] forms mechanisms visitor species of visits a displays b

‘Massive blooming’ 8±4 20% herbs 86% anemochory 11.9±4.5 245.4±43.4 100% L 73% shrubs 14% others 7% vines ‘Sparse blooming’ 25.2±2.5 71% herbs 100% anemochory 6.5±2.5 31.5±19.2 88% S 29% shrubs 12% L ‘Intermediate’ 21.3±9.9 82% herbs 100% others 10.1±4.1 59.9±40.5 100% S 18% shrubs a measured as number of capitula visited; see text in Material and methods section b L large plant floral display (>100 capitula daily), S small plant floral display (<100 capitula daily)

‘sparse blooming’ and ‘intermediate’ groups of species, plant characteristics and/or particularities of animal-plant because midpoints may not be representative indicators of interactions. In general in this group of co-occurring flowering phenology in species with long flowering times Asteraceae, species with flowers visited by few insect (Fig. 3b, c). species at low frequencies exhibited long blooming times, whereas those visited by a great number of species at high frequencies showed shorter flowering times and a tenden- Discussion cy to separation of their flowering midpoints. In this group of ‘massive blooming’ Asteraceae species, the tendency Influences of climatic factors and photoperiod on flowering for flowering times to be distributed throughout the rainy season could greatly contribute to reduced reproductive As typically occurs in floras of temperate forests (e.g. interference, mainly for those plant species that require Diekmann 1996; Fitter et al. 1995; Marques et al. 2004; pollinators to set seeds. Previously, Torres and Galetto Smith-Ramírez and Armesto 1994), the flowering phenol- (2008) studied the dependence on floral visitors for seed ogy of the studied species was significantly correlated with production in seven of the 14 ‘massive blooming’ seasonal variation in several, to some degree non- Asteraceae species. Five species could not set seeds in independent variables: temperature, photoperiod, rainfall, the absence of floral visitors (Baccharis articulata is and frosts. A shared response of species to specific climatic dioecious; Senecio pampeanus, Flourensia campestris, cues should result in synchronous flowering. However, Vernonia nudiflora,andMikania urticifolia are not although flowering phenology in central Argentina appears autogamous); two species (Solidago chilensis and Eupa- to be largely constrained by climatic seasonality (since torium arnottianum) produced more fruits by natural photoperiod and climate are shaping broad patterns of pollination than by autogamy (Torres and Galetto 2008). flowering within this group of co-occurring species), the Nevertheless, although the above pattern is interesting, the studied Asteraceae species showed some diversification in available data are insufficient for conclusions about the their flowering times and flowering midpoints within the advantages of flowering time segregation in this group of favorable period (rainy season). native ‘massive blooming’ Asteraceae. On the other hand, flowering phenodynamics can also be Influences of ecological factors and taxonomic membership related to the taxonomic membership of the studied species. on flowering Most taxa belonging to tribes grouped within the subfamilies Cichorioideae, Carduoideae, and Mutisioideae Although it is clear that seasonality in climatic factors exhibited long flowering times and smaller plant floral plays a major role in shaping broad phenology patterns, displays. The data also showed that these species are less the particularities of phenological diversification within frequently visited by a lower number of insect species in the rainy season are not surprising. Flowering phenody- comparison with species grouped in tribes within the namics potentially integrate a large number of selective subfamily Asteroideae. Considering the tribes of Cichor- forces caused by biotic factors such as optimization of ioideae, Carduoideae, and Mutisioideae as early-branching pollination and seed dispersal (Hamann 2004). Thus, or basal within Asteraceae, and the tribes of Asteroideae as biotic factors can influence phenological traits because of late-branching or derived (Panero and Funk 2008), it can be Flowering phenology of co-occurring Asteraceae 17

Fig. 4 Plot of PCA scores for 43 co-occurring Asteraceae species in spond to the variables included in the PCA. Symbols: ▽ = species Chaco Serrano forests of La Serranita-Los Aromos, showing first two grouped in tribes of Mutisioideae, = Carduoideae, ▼ = Cichor- principal component axes from analysis of flowering phenology ioideae, ○ = species grouped in tribes of Asteroideae, ● = ‘massive considering plant traits and taxonomic membership. Vectors corre- blooming’ species grouped in tribes of Asteroideae

said that phenological and reproductive strategies are the phenological strategies of ‘massive blooming’ or related to taxonomic membership. Consequently, the ‘sparse blooming’ would be two equally efficient alter- observed patterns of flowering phenology are in accordance natives to attract pollinators. with the reported tendency of Asteraceae species to evolve To conclude, it seems that climatic factors restrict the in order to attract the greatest quantity of floral visitors, i.e. phenological period of most species, and that plant “generalists” (Torres and Galetto 2002). For example, some attributes and taxonomic membership are strongly related traits such as long blooming time or few open flowers per to the flowering phenodynamics in the group of Asteraceae day may confer several advantages to plants, including high studied. Nevertheless, future experimental studies aiming to mate diversity, tolerance to rare pollinators (Rathcke compare these phenological and reproductive strategies 1988b), low risk of reproductive failure resulting from may provide new evidence on the extraordinary diversifi- harsh weather (Bawa 1983), and unpredictable peaks of cation of the family Asteraceae. visitation. If we take into account all these traits, this kind of flowering represents a bet-hedging strategy (Bolmgren et al. 2003). Furthermore, short episodes of massive blooming Acknowledgements We sincerely thank two anonymous reviewers, Olaf Bininda-Emonds, and Sasa Stefanovic for constructive criticisms, can influence, among many other factors, the diversity and suggestions and encouragement, Nick Waser, Diego P. Vázquez, and frequency of visits of potential pollinators by attracting Marcelo A. Aizen for useful evaluation and detailed comments on more insects through a great offer of resources (reviewed in early versions of the manuscript, Claudio Sosa for insect identifica- Lane 1996). Waser et al. (1996) stated that it would be risky tions, Nicolás Soria for improvements to the figures, and Laura Bruno for careful text editing. The study was supported by Consejo Nacional to conclude that lineages always evolve to attract few de Investigaciones Científicas y Técnicas (CONICET), Agencia specialized pollinators, as has been commonly assumed for Nacional de Promoción Científica y Tecnológica, Secretaría de more evolutionary derived families (Faegri and van der Pijl Ciencia y Tecnología de la Universidad Nacional de Córdoba, and 1966), including Asteraceae (Mani and Saravanan 1999). Agencia Córdoba Ciencia. Thanks are due the Academia Nacional de Ciencias Exactas, Físicas y Naturales and to CONICET for fellow- Considering that Asteraceae species constitute a principal ships to the first author. LG and CT are members of Carrera del component in most terrestrial ecosystems (Bremer 1994), Investigador from CONICET. 18 C. Torres, L. Galetto

References Fitter, A. H., Fitter, R. S. R., Harris, I. T. B., & Williamson, M. H. (1995). Relationships between first flowering date and temperature in the flora of a locality in central England. Functional Ecology, 9,55–60. Abouheif, E. (1999). A method for testing the assumption of Fleming, T. H. (1985). Coexistence of five sympatric Piper (Piper- phylogenetic independence in comparative data. Evolutionary aceae) species in a tropical dry forest. Ecology, 66, 688–700. Ecology Research, 1, 895–909. Fleming, T. H., & Partridge, B. L. (1984). On the analysis of Ackerly, D. D. (2000). Taxon sampling, correlated evolution, and phenological overlap. Oecologia, 62, 344–350. independent contrasts. Evolution, 54, 1480–1492. Freckleton, R. P. (2000). Phylogenetic tests of ecological and Agren, G. I., & Fagerström, T. (1980). Increased or decreased evolutionary hypotheses: checking for phylogenetic indepen- separation of flowering times? The joint effect of competition dence. Functional Ecology, 14, 129–134. for space and pollination in plants. Oikos, 35, 161–164. Friedel, M. H., Nelson, D. J., Sparrow, A. D., Kinloch, J. E., & Armbruster, W. S. (1995). The origins and detection of plant Maconochie, J. R. (1994). Flowering and fruiting of arid zone community structure: reproductive versus vegetative processes. species of Acacia in central Australia. Journal of Arid Environ- Folia geobotanica & phytotaxonomica, 30, 483–497. ments, 27, 221–239. Armbruster, W. S., & McGuire, D. (1991). Experimental assessment Gotelli, N. J., & Entsminger, G. L. (2001). EcoSim: Null models of reproductive interactions between sympatric Aster and software for ecology. Version 6. Burlington, VT: Acquired Erigeron (Asteraceae) in interior Alaska. American Journal of Intelligence Inc. & Kesey-Bear. http://homepages.together.net/- Botany, 78, 1449–1457. gentsmin/ecosim.htm. Accessed 15 March 2002. Ashton, P. S., Givnish, T. J., & Appanah, S. (1988). Staggered Gotelli, N. J., & Graves, G. R. (1996). Null models in ecology. flowering in the Dipterocarpaceae: New insights into floral Washington, D.C.: Smithsonian Institution. induction and the evolution of mast fruiting in the aseasonal Gross, R. S., & Werner, P. A. (1983). Relationships among flowering tropics. The American Naturalist, 132,44–66. phenology, insect visitors, and seed-set of individuals: experi- Baskin, J., Baskin, C., & Leck, M. (1993). After ripening pattern mental studies on four co-occurring species of goldenrod during cold stratification of achenes of ten perennial Asteraceae (Solidago: Compositae). Ecological Monographs, 53,95–117. from eastern North America, and evolutionary implication. Plant Hamann, A. (2004). Flowering and fruiting phenology of a Philippine Species Biology, 8,61–65. submontane rain forest: climatic factors as proximate and Bawa, K. S. (1983). Patterns of flowering in tropical plants. In C. E. ultimate causes. Journal of Ecology, 92,24–31. Jones & R. J. Little (Eds.), Handbook of experimental pollination Harvey, P. H., & Pagel, M. (1991). The comparative method in biology (pp. 394–410). New York: Scientific and Academic evolutionary biology. Oxford: Oxford University Press. Editions. Inouye, D. W. (2000). The ecological and evolutionary significance of Bertiller, M. B., Beeskow, A. M., & Coronato, F. (1991). Seasonal frost in the context of climate change. Ecology Letters, 3,457–463. environmental variation and plant phenology in arid Patagonia Jennings, W. B. (2001). Comparative flowering phenology of plants in (Argentina). Journal of Arid Environments, 21,1–11. the western Mojave desert. Madrono, 48, 162–171. Bolmgren, K., & Lönnberg, K. (2005). Herbarium data reveal an Johnson, S. D. (1992). Climatic and phylogenetic determinants of association between fleshy fruit type and earlier flowering time. flowering seasonality in the Cape flora. Journal of Ecology, 81, International Journal of Plant Sciences, 166, 663–670. 567–572. Bolmgren, K., Eriksson, O., & Linder, H. P. (2003). Constrasting Kochmer, J. P., & Handel, S. N. (1986). Constraints and competition flowering phenology and species richness in abiotically and in the evolution of flowering phenology. Ecological Mono- biotically pollinated angiosperms. Evolution, 57, 2001–2011. graphs, 56, 303–325. Borchert, R. (1996). Phenology and flowering periodicity of Neotrop- Lane, M. A. (1996). Pollination biology of compositae. In P. D. S. ical dry forest species: evidence from herbarium collections. Caligari&D.J.N.Hind(Eds.),Compositae: Biology & Journal of Tropical Ecology, 12,65–80. utilization. Proceedings of the International Compositae Confer- Bremer, K. (1994). Asteraceae: Cladistics & classification. Portland: ence, Kew, 1994 (pp. 61–80). Kew: Royal Botanic Gardens. Timber. LeBuhn, G. (1997). Timing is everything: New perspectives on floral Brody, A. K. (1997). Effects of pollinators, herbivores, and seed phenology. Trends in Ecology & Evolution, 12,4–5. predators on flowering phenology. Ecology, 78, 1624–1631. Levin, D. A., & Anderson, W. W. (1970). Competition for pollinators Cole, B. J. (1981). Overlap, regularity, and flowering phenologies. The between simultaneously flowering species. The American Natu- American Naturalist, 117, 993–997. ralist, 104, 455–467. Dafni, A. (1992). Pollination ecology. A practical approach. Oxford: Lieberman, D. (1982). Seasonality and phenology in a dry tropical Oxford University Press. forest in Ghana. Journal of Ecology, 70, 791–806. Diekmann, M. (1996). Relationship between flowering phenology of Lönnberg, K. (2004). Flowering phenology and distribution in fleshy perennial herbs and meteorological data in deciduous forests of fruited plants. Plant Ecology, 9,1–25. Sweden. Canadian Journal of Botany, 74, 528–537. Losos, J. B. (1999). Uncertainty in the reconstruction of ancestral Digby, P. G. N., & Kempton, R. A. (1996). Multivariate analysis of character states and limitations on the use of phylogenetic ecological communities. London: Chapman and Hall. comparative methods. Animal Behaviour, 58, 1319–1324. Faegri, K., & van der Pijl, L. (1966). The principles of pollination Losos, J. B. (2000). Ecological character displacement and the study ecology. Oxford: Pergamon. of adaptation. Proceedings of the National Academy of Sciences/ Feinsinger, P. (1987). Effects of plant species on each other’s Biology, 97, 5693–5695. pollination: Is community structure influenced? Trends in Madeira, J. A., & Fernandes, G. W. (1999). Reproductive phenology Ecology & Evolution, 2, 123–126. of sympatric taxa of Chamaecrista (Leguminosae) in Serra do Felsenstein, J. (1985). Phylogenies and the comparative method. The Cipó, Brazil. Journal of Tropical Ecology, 15, 463–479. American Naturalist, 125,1–15. Mani, M. S., & Saravanan, J. M. (1999). Pollination ecology and Felsenstein, J. (1988). Phylogenies and quantitative characters. Annual evolution in compositae (Asteraceae). Enfield: Science. Review of Ecology and Systematics, 19, 445–471. Marco, D. E., & Páez, S. A. (2002). Phenology and phylogeny of Fenner, M. (1998). The phenology of growth and reproduction in animal-dispersed plants in a Dry Chaco forest (Argentina). plants. Perspectives in Plant Ecology, 1,78–91. Journal of Arid Environments, 52,1–16. Flowering phenology of co-occurring Asteraceae 19

Marques, M. C. M., Roper, J. J., & Baggio Salvalaggio, A. P. (2004). Silvertown, J., Dodd, M., & Gowing, D. (2001). Phylogeny and the Phenological patterns among plant life-forms in a subtropical niche structure of meadow plant communities. Journal of forest in southern Brazil. Plant Ecology, 173, 203–213. Ecology, 89, 428–435. Milton, K. (1991). Leaf change and fruit production in six neotropical Smith-Ramírez, C., & Armesto, J. J. (1994). Flowering and fruiting Moraceae species. Journal of Ecology, 79,1–26. patterns in the temperate rainforest of Chiloé, Chile—ecological Murali, K. S., & Sukumar, R. (1994). Reproductive phenology of a and climatic constraints. Journal of Ecology, 82, 353–365. tropical dry forest in Mudumalai, southern India. Journal of Smith-Ramírez, C., Armesto, J. J., & Figueroa, J. (1998). Flowering, Ecology, 82, 759–767. fruiting, and seed germination in Chilean rain forest Myrtaceae: Oberrath, R., & Böhning-Gaese, K. (2002). Phenological adaptation Ecological and phylogenetic constraints. Plant Ecology, 136, of ant-dispersed plants to seasonal variation in ant activity. 119–131. Ecology, 83, 1412–1420. Sokal, R. R., & Rohlf, F. J. (1995). Biometry. The principles and Ollerton, J., & Lack, A. J. (1992). Flowering phenology: An example practice of statistics in biological research (3rd ed.). New York: of relaxation of natural selection? Trends in Ecology & Evolution, W. H. Freeman and Co. 7, 274–276. SPSS Inc. (1992). SPSS for windows: Professional statistics, release Pagel, M. (1992). A method for the analysis of comparative data. 5. Chicago: SPSS Inc. Journal of Theoretical Biology, 156, 431–442. SPSS Inc. (1999). SPSS Base 10.0. Chicago: SPSS. Pagel, M., & Harvey, P. H. (1992). On solving the correct problem: Stiles, F. G. (1975). Ecology, flowering phenology, and hummingbird wishing does not make it so. Journal of Theoretical Biology, 156, pollination of some Costa Rican Heliconia species. Ecology, 56, 425–430. 285–301. Panero, J. L., & Crozier, B. S. (2008). Asteraceae. Sunflowers, Stiles, F. G. (1977). Coadapted competitors: The flowering seasons of daisies. Version 04 April 2008. http://tolweb.org/Asteraceae/ hummingbird-pollinated plants in a tropical forest. Science, 198, 20780/2008.04.04. Accessed 20 October 2010. 1177–1178. Panero, J. L., & Funk, V. A. (2008). The value of sampling anomalous Tabachnick, B. G., & Fidell, L. S. (1996). Using multivariate statistics taxa in phylogenetic studies: Major clades of the Asteraceae (3rd ed.). New York: Harper Collins College. revealed. Molecular Phylogenetics and Evolution, 47, 757–782. Torres, C. (2000). Pollen size evolution: Correlation between pollen Pianka, E. R. (1986). Ecology and natural history of desert lizards. volume and pistil length in Asteraceae. Sexual Plant Reproduc- Princeton: Princeton University Press. tion, 12, 365–370. Pico, F. X., & Retana, J. (2000). Temporal variation in the female Torres, C., & Galetto, L. (2002). Are nectar sugar composition and components of reproductive success over the extended flowering corolla tube length related to the diversity of insects that visit season of a Mediterranean perennial herb. Oikos, 89, 485–492. Asteraceae flowers? Plant Biology, 4, 360–366. Pleasants, J. M. (1980). Competition for bumblebee pollinators in Torres, C., & Galetto, L. (2007). Style morphological diversity of Rocky Mountain plant communities. Ecology, 61, 1446–1459. some Asteraceae species from Argentina: Systematic and Pleasants, J. M. (1990). Null-model tests for competitive displace- functional implications. Journal of Plant Research, 120, 359– ment: The fallacy of not focusing on the whole community. 364. Ecology, 7, 1078–1084. Torres, C., & Galetto, L. (2008). Visitantes florales y sistema Poole, R. W., & Rathcke, B. J. (1979). Regularity, randomness and reproductivo en Asteraceas de Argentina Central: Grado de aggregation in flowering phenologies. Science, 203, 470–471. dependencia entre las plantas y sus polinizadores. Acta botanica Price, T. (1997). Correlated evolution and independent contrasts. Venezuelica, 31, 473–494. Philosophical Transactions of the Royal Society of London, B, Waser, N. (1983). Competition for pollination and floral character 352, 519–529. differences among sympatric plant species: a review of evidence. Rathcke, B. J. (1984). Patterns of flowering phenologies: Testability In C. S. Jones & R. J. Little (Eds.), Handbook of experimental and causal inference using a random model. In D. R. Strong, D. pollination biology (pp. 277–293). New York: Van Nostrand- Simberloff, L. G. Abele, & A. B. Thistle (Eds.), Ecological Reinhold. communities: Conceptual issues and the evidence (pp. 383–393). Waser, N. M., Chittka, L., Price, M. V., Williams, N. M., & Ollerton, Princeton: Princeton University Press. J. (1996). Generalization in pollination systems, and why it Rathcke, B. (1988a). Flowering phenologies in a shrub community: matters. Ecology, 77, 1043–1060. Competition and constraints. Journal of Ecology, 76, 975–994. Westoby, M., Leishman, M., & Lord, J. (1995). Further remarks on Rathcke, B. (1988b). Interactions for pollination among coflowering phylogenetic correction. Journal of Ecology, 83, 727–729. shrubs. Ecology, 69, 446–457. Wheelwright, N. T. (1985). Competition for dispersers, and the timing Rathcke, B., & Lacey, E. P. (1985). Phenological patterns of terrestrial of flowering and fruiting in a guild of tropical trees. Oikos, 44, plants. Annual Review of Ecology and Systematics, 16, 179–214. 465–477. Sakai, S. (2001). Phenological diversity in tropical forests. Population Wright, S. J., & Calderon, O. (1995). Phylogenetic patterns among Ecology, 43,77–86. tropical flowering phenologies. Journal of Ecology, 83, 937–948. Sakai, S. (2002). General flowering in lowland mixed dipterocarp Wright, S. J., & van Schaik, C. P. (1994). Light and the phenology of forests of South-east Asia. Biological Journal of the Linnean tropical trees. The American Naturalist, 143, 192–199. Society, 75, 233–247. Yeboah Gyan, K., & Woodell, S. R. J. (1987). Flowering phenology, flower Schemske, D. W., Willson, M. F., Melampy, M. N., Miller, L. J., colour and mode of reproduction of Prunus spinosa L. (Blackthorn); Verner, L., Schemske, K. M., et al. (1978). Flowering ecology of Rosa canina L. (Dog Rose); and Rubus fruticosus L. (Bramble) in some spring woodland herbs. Ecology, 59, 351–366. Oxfordshire, England. Functional Ecology, 1,261–268. Seghieri, J., Floret, C., & Pontanier, R. (1995). Plant phenology in Zuloaga, F. O., & Morrone, O. (1999). Catálogo de las plantas relation to water availability: Herbaceous and woody species in vasculares de la República Argentina II. Monographs in the savannas of northern Cameroon. Journal of Tropical Ecology, Systematic Botany from the Missouri Botanical Garden, 74. St. 11, 237–254. Louis: Missouri Botanical Garden.