Reserve mass and dispersal investment in relation to geographic range of plant species: phylogenetically independent contrasts

Journal of Biogeography (1996) 23, 329–338

Reserve mass and dispersal investment in relation to geographicrange of plant species: phylogenetically independent contrasts

W E and M W School of Biological Sciences and Research Unit for Biodiversity and Bioresources,Macquarie University, NSW 2109, Australia

Abstract. Recent studies have reported conflicting which differed not only in seed mass but also in dispersalevidence about correlations between seed size and plant modes and growth forms. Finally, comparing species withinspecies geographic range sizes. Using phylogenetically Acacia and Eucalyptus having similar seed size but differentindependent contrasts (PICs) within genera, we found no dispersal modes, we found that bird dispersal (in Acacia)consistent differences in reserve mass between species with and possession of a wing for wind dispersal (in Eucalyptus)similar dispersal morphology and ‘wide’ versus ‘narrow’ was associated with wider geographic range compared togeographic ranges. There was also no tendency within genera lower-investment dispersal modes. Taken together, thesefor broad ranged species to be those that allocate a larger comparisons indicate that seed size is not itself important aspercentage of the resources invested in each diaspora to a factor influencing breadth of geographic range. Dispersaldispersal structures. PICs were also constructed between mode and growth form may have an influence, however,species having a tenfold difference in seed size. In these and seed size differences may be associated with contrastsPICs, the larger seeded species often occupied a greater in dispersal mode or growth form.number of regions than species with smaller seed sizes. This

Key words. Seed size, dispersal mode, growth form,result was generated primarily through the comparison ofspecies from different genera, families or higher level taxa geographic range.

geographic isolation and subsequent species differentiationINTRODUCTION

(Levins, 1970; Quinn & Hastings, 1988; Gilpin, 1987;Harrison, Murphy & Ehrlich, 1988; Smith & Peacock, 1990;Of the many recent studies of plant species range sizesHanson, 1991).(Gentry, 1986; Hodgson, 1986; Gaston, 1990; Ricklefs &

Populations of widely-dispersed species might beLatham, 1992), two studies have specifically tested rangesustained in a wider range of habitats due to the ‘rescuesize–seed attribute correlations in plant species (Aizen &effect’ from neighbouring populations (Pulliam, 1988;Paterson, 1990; Oakwood et al., 1993). These studies haveHanson, 1991; Carter & Prince, 1987; Fahrig & Merriam,presented contradictory evidence about correlations of seed1985; Morriss, 1991). This might result either in a widerattributes with geographic ranges. Aizen & Paterson (1990)range of habitat-types being occupied by local populationsshowed that the extent of geographic range size waswithin a geographical range, or in a wider overallpositively correlated with acorn volume (seed size) in Northgeographical range. The relationship of dispersal distanceAmerican Oaks (Quercus L), while Oakwood et al. (1993)to seed mass is complicated, however. Larger seeds arereported a weak tendency for species with larger diasporesassociated with dispersal by vertebrates (Oakwood et al.,to have narrower geographic ranges in two semi-arid and1993) and thus are assumed to achieve comparatively largeone temperate Australian data sets. This tendency was onlydispersal distances. However, small wind-dispersed seedsapparent within growth forms and dispersal modes. In themay also travel long distances, are produced in greaterinland but not the coastal flora, species adapted for dispersalnumbers and are a feature of widespread, ruderal-typeby vertebrates tended to occupy wider geographic ranges,species (Grime, 1977, 1979; Grime, Hodgson & Hunt, 1988).had larger seed sizes, and tended to belong to taller growthThese species also display wide range areas.forms.

Previous studies about relationships between seedAizen & Paterson (1990) suggested that larger seed masscharacteristics and species range sizes have taken phylogenyincreases the capacity for seedlings to establish in a widerinto account in only a limited way. The study of Aizen andrange of habitats (Westoby, Leishman & Jurado, 1992), thePatterson was confined to a single genus. Even within thisconsequence of which is wider range sizes in extant species.study, aspects of the evidence were questioned on bothOakwood et al. (1993), seeking to account for the widerstatistical and taxonomic grounds (Jensen, 1992). In therange sizes in fleshy-fruited vertebrate-dispersed species,

suggested that wider dispersal might reduce the chances of patterns reported by Oakwood et al. (1993) comparisons

1996 Blackwell Science Ltd 329

330 Will Edwards and Mark Westoby

between different dispersal modes and seed sizes were to a distributional data reported here. We have used these dataas an indication of the extent of occurrence (sensu Gaston,considerable extent also comparisons between different plant

families (though it was shown that the tendency for 1991, 1994) of each species and the variety of conditionsover which each species exists.vertebrate-dispersed species to have wider geographic ranges

in the inland floras applied within several families). Inthe present paper we take phylogeny into account more Diaspore, reserve and dispersal investment massrigorously, using phylogenetically independent contrasts. Seeds were obtained from commercial suppliers of nativeWe ask the following two questions. plant seeds though additional mass and dissection data were

also available from existing databases (Jurado, Westoby &(1) Do widely distributed species tend to have larger (orNelson, 1991; Leishman & Westoby, 1992; Westoby, Ricesmaller) seed sizes than narrowly distributed ones?& Howell, 1990). All species for which seed size information

We address this question in two ways. First, we compare was available were classified according to the within-familyseed size differences between species with different classification of Hnatiuk (1990) and the higher ordergeographic range sizes, and secondly, we compare range classifications of Cronquist (1988). Means size wassizes between species with differing seed sizes. determined by weighing twenty diaspores of each species

individually using a Cahn 29 microbalance with a resolution(2) Do widely distributed species tend to invest largerto 0.001 mg. The five diaspores closest to the mean wereamounts in dispersal structures?then dissected into the component parts of reserve (embryo

Similar to the first question, we investigate this also as two plus endosperm), dispersal structure (fleshy fruit, elaiosome,smaller questions. First, we compare the amount invested pappus etc.—where applicable) and seed coat. Each of thein dispersal structures between congeneric species pairs seed components from these five replicates was individuallyhaving similar dispersal morphology (and syndrome) though weighed to determine what proportion it represented of thediffering range sizes. Second, we compare the effects of total diaspore mass.dispersal mode on geographic distribution between For each analysis, as many PICs as possible werecongeneric species pairs similar in both seed size and growth constructed that satisfied the criteria of divergence on theform. If it is true that seed size rather than other plant seed attribute in question. For analyses involving geographiccharacteristics determines range size, then we should expect range size as the species attribute, we chose ‘wide’ andto find, for any given seed size, similar geographic ranges ‘narrow’ distributed species such that the range of thebetween species independent of other plant and seed narrowly distributed species was always embedded withinattributes. the range of the widely distributed species, in order that

comparisons would reflect differences in breadth ofgeographic range rather than in the actual geographic

METHODSlocation of the range. Details of PICs and species are givenunder each analysis.

Phylogenetically independent contrasts

A phylogenetic contrast is a pair of species that have Dispersal modes and growth formsdiverged in some attribute of interest, together with the Dispersal mode is a categorization according tophylogenetic branch-pair from the common ancestor up morphological attributes of the diaspore. The sameto the extant species. A set of contrasts are said to be categories and criteria were used in the studies of Joradophylogenetically independent (PICs) where the divergences et al. (1991), Leishman & Westoby (1992), and Westoby etfollow independent phylogenetic paths in each contrast al. (1990). Growth form classifications were determined withrelative to the other contrasts in the same set. Each contrast reference to Beadle (1976), Beadle et al. (1986), Boland etwithin a set of PICs therefore represents a separate al. (1984), Brooker & Kleining (1983), Burbidge & Greyevolutionary episode of divergence for the criterion (1970), Costerman (1981), Cronin (1988), Cunningham etattribute, and for whatever other attributes may prove also al. (1981), Fairley & Moore (1989), Harden (1991), Jessopto have diverged (Armstrong & Westoby, 1993; Burt, 1989).1

(1981), Simmons (1981) and Simpfendorfer (1975).

Data collectionAnalysis

Geographic range informationThe Census of Australian Vascular Plants (Hnatiuk, 1990) Do widely distributed species tend to have larger (or

smaller) seed sizes than narrowly distributed ones?was used to collate data on the number of species withineach genus and the geographic range of each species. PICs from two complementary data sets were used to

investigate the relationship between reserve mass andHnatiuk (1990) divided the Australian continent into ninety-seven regions based on the biogeographic zones recognized geographic range. In one set of comparisons, PICs were

chosen to represent contrasts of geographic range, and seedby the relevant herbaria in each state, and listed the recordedoccurrence of all species in each region. The census thus reserve mass was compared. In the complentary set of

comparisons, PICs were chosen to represent contrasts ofprovides broad continental based distributionalinformation. These descriptions have been the basis of all seed reserve mass, and geographic range was compared.

Blackwell Science Ltd 1996, Journal of Biogeography, 23, 329–338

Seed size and geographic range 331

TABLE 1. The number of congeneric species pairs comprising a(i) Comparisons of seed size between species with differentsingle contrast within each genus in analysis 1 and 3. Details forgeographic range sizes.the construction of each pair is given within the text. Column A

We compared reserve mass using PICs constructed from represents the number of species used for comparisons of reserveweights between widely and narrowly distributed species; Columnspecies in forty-one genera. Comparisons were based onB, the number of pairs used for comparisons of proportional‘wide’ and ‘narrow’ geographic distributions. Species withinvestment in dispersal between widely and narrowly distributed‘wide’ geographic distributions were those recorded in tenspecies.

or more biogeographic regions and species with ‘narrow’Family Genus A Bgeographic distributions in five or fewer regions. For all

comparisons the range of the narrowly distributed speciesLamiaceae Westringia 1 1was required to be ‘embedded’ within the range of theAsteraceae Brachycome 1 1widely distributed species with which it was compared. Each Helichrysum 3 1

genus represents one contrast in the total data set. For some Olearia 1 1genera, each side of the PIC was an average of more than Convolvulaceae Convulvulus 1

Chenopodiaceae Atriplex 1one species (Table 1). While using average values does allowFabaceae Daviesia 2 2for an unbalanced design (e.g. comparing three wide versus

Pultenaea 3 3five narrow), we chose to use equal numbers on either sideSwainsona 1 1of a contrast. When data for more than one species pairGompholobium 1 1

per genus was available, the average reserve mass of all Mimosaceae Acacia 6 6species on either side of a contrast was used. In those Euphorbiaceae Poranthera 1 1instances when, for example, the average of three widely Oxalidaceae Oxalis 1

Rutaceae Boronia 1 1distributed species is compared with the average for threeEriostemon 1 1narrowly distributed species, each narrowly distributedZieria 1 1species was embedded within the range of a single widely

Sapindaceae Dodonaea 2 1distributed one. Myrtaceae Eucalyptus 9 9

Baeckea 1(ii) Comparisons of range sizes between species with differingAngophora 1seed sizes.Melaleuca 4Kunzea 1For this analysis we chose twenty-two species pairs in whichLeptospermum 4the difference in reserve mass between each member was

Tremandraceae Tetratheca 1 1approximately an order of magnitude, and compared theProteaceae Banksia 4 1number of regions in which they have been recorded.

Grevillea 1 1Phylogenetic relationships of each pair are shown in Fig. Hakea 2 11. Because seed size (reserve mass) within genera was rarely Isopogon 1 1found to span an order of magnitude, only four of the Persoonia 3 1

Rhamnaceae Cryptandra 1 1comparisons used in this study were between species withinDilleniaceae Hibbertia 2 2genus. Of the remaining eighteen comparisons, twelve wereEpacridaceae Leucopogon 2 2between genus within family, and six between families (see

Epacris 1Fig. 1). Unlike the previous test, we were not always able Casuarinaceae Allocasuarina 3 3to select species of different seed sizes which satisfied the Cyperaceae Carex 1criterion of overlapping occurrence. As regions are not the Gahnia 1

Lepidosperma 1 1same size, it was important that we did not compare speciesPoaceae Aristida 1occupying many small versus a few large regions as theRestionaceae Restio 1 1number of regions could then be a misleading measure ofXanthorrhoeaceae Xanthorrhoea 1geographic range. Because of this we also calculated for Lomandra 2 2

each species in this analysis measures of latitudinal andlongitudinal spread (following Oakwood et al., 1993). Thelatitudinal spread measure was the distance between the

We compared the mass of the dispersal structure as anorthernmost boundary of the northernmost regionproportion of the total diaspore mass in twenty-sixoccupied by the species, and the southernmost boundary ofcongeneric PICs also used previously (Table 1). Thisthe southernmost region; similarly for longitudinal spread.represents the number of pairs for which information onIn the event, these measures of latitudinal and longitudinaldispersal structure mass was available. In this analysis thespread were very closely correlated with the number ofsame restriction on pair selection was used in the comparisonregions occupied in all comparisons, and accordingly weof seed size between species with different geographic rangereport results only in terms of the numbers of regionssizes.occupied.

(ii) Congeneric species similar in both seed size and growthDo widely distributed species tend to invest larger amounts form though differing dispersal modes.in dispersal structures?(i) Congeneric species of similar dispersal morphology Most genera include only a single dispersal mode. This

study is thus confined to two Australian genera, Acacia andthough differing in range size.



Genus/Species D G

Disphyma clavellatum 2 1Atriplex holocarpa 4 5Chenopodium melanocarpum 4 1Ptilotus atriplicifolius 3 5Portulaca oleracea 4 1Rumex brownii 4 1Abutilon fraseri 3 1Sisymbrium erysimoides 4 1Pittosporum phylliraeoides 1 3Sollya heterophylla 3 3Acacia victoriae 2 2Lotus cruentus 4 1Banksie aemula 1 5Banksia conferta 2 5Isopogon anemonifolius 2 1Hakea sericea 2 5Eucalyptus terminalis 1 5Eucalyptus populnea 1 1Angophora costaca 1 1Syncarpia glomulifera 1 1Cryptandra arbutiflora 3 2Dodonaea viscosa 2 2Leichardtia australis 1 5Solanum lasiophyllum 4 3Nicotiana umbratica 4 1Convolvulus remotus 4 1Evolvus alsinoides 4 1Morgania floribunda 4 1Stylidium affine 4 1Stylidium amoenum 4 1Calotis cuneifolia 4 4Minuria denticulata 4 5Centipeda thespidioides 4 1Helipterum floribundum 4 5Helichrysum bracteatum 4 5Helichrysum apiculatum 4 5Pterocaulon sphacelatum 4 5Senecio magnificus 4 5Cymbopogon obtectus 5 5Sporobous caroli 5 1Diplanche fusca 5 5Tripogon loliiformis 5 1Haemodorum spicatum 4 1Conostylis juncea 4 1

Family

Aizoaceae

ChenopodiaceaeAmaranthaceaePortulacaceaePolygonaceaeMalvaceaeBrassicaceae

PittosporaceaeMimosaceaeFabaceae

Proteaceae

Myrtaceae

RhamnaceaeSapindaceaeAsclepiadaceae

Solanaceae

ConvulvulaceaeScrophulariaceae

Stylidiaceae

Asteraceae

Poaceae

Haemodoraceae

FIG. 1. Phylogenetic relationships of the contrasts used to analyse the relationship of seed size differences and geographic range. Each pairis an order of magnitude difference in seed reserve mass. Also included are the growth form (G) and dispersal modes (D) for each species(for growth form; 1, tree; 2, shrub; 3, subshrub; 4, forb; 5, grass: for dispersal mode; 1, unassisted; 2, ant; 3, vertebrate dispersed (fleshyfruit or aril); 4, external adhesion to animals; 5, wind, possessing distinct structures for increasing air resistance).

Eucalyptus, which are polymorphic for dispersal mode. The genus Acacia is represented by over 800 species inAustralia, most of which are dispersed by ants (O’Dowd &These two genera are the most speciose in Australia. In

both genera, there is one predominant dispersal mode (ant Gill, 1986). In these species, the funicle takes the form ofan oil-rich white appendage known as an elaiosome, whichdispersal in Acacia and unassisted dispersal in Eucalyptus),

and morphologically recognizable, less common dispersal acts as a stimulus for ant dispersal (Sernander, 1906;Westoby et al., 1982, Hughes & Westoby, 1992). In birdmodes (bird and unassisted dispersal in Acacia and wind

dispersal in Eucalytpus). dispersed Acacia species the funicle is expanded and often



Most Eucalyptus seeds lack appendages and have no visibledispersal structures. However, in some species there existextensions of the seed coat which may increase the diameteror length of the longest axis of the seed threefold. Theseextensions clearly act as a means of increasing the airresistance of the falling seed and are distinct from unassistedseeds. We have therefore classified this morphology as windassisted (see Fig. 2b).

We collated information on growth form, seed size, themass of dispersal structure as a percentage of total diasporemass and geographic range for 116 Acacia and ninety-eightEucalyptus species. We found five species of Eucalyptuswhich displayed obvious adaptations for wind dispersal andfive species of Acacia which we classified as being vertebrate(bird) dispersed. For each of these species we selected acongeneric species of similar reserve mass, but differentdispersal morphology for comparison (Table 2, Fig. 2).These comparisons were not designed to be phylogeneticallyindependent. Selection of comparison species was made onthe basis that the difference between reserve mass of thespecies pairs was less than 5%. Where this was not possible(such as in the comparison of Eucalyptus polycarpa versusE. gummifera, and in Acacia oswaldii versus A. complanata)we selected the comparison species with the a priori decisionto always allow for a larger reserve mass in the species withsmaller investment in dispersal. This was done to minimizeany risk of including both larger reserve mass and largerdispersal investment in any one comparison. Geographicranges were described both as number of regions occupiedand as the product of latitudinal spread multiplied bylongitudinal spread, these spreads being estimated asdescribed previously.

Stevens (1989) presented data from several groups oforganisms to support the idea that geographic range size

FIG. 2. Seed characteristics between species pairs having similar increases with increasing latitude, a phenomena he termedreserve mass but differing dispersal modes within genera. Fig. 2a; Rapoport’s Rule. Recent evidence suggests that Rapoport’sAcacia species. Top row, from left are; (1) Acacia tetragonophylla Rule may not apply to all taxa nor has it been shown(∗), A. longifolia (+); (2) A. oswaldii (∗), A. ramulosa (#); Bottom

outside of North America (Rohde, Heap & Heap, 1993;row, from left are; (3) A. coriaceae (∗), A. harpophylla (#); (4) A.Colwell & Hurtt, 1994; Smith, May & Harvey, 1994).melanoxylon, A. verticellata (+); (5) A. salicinia (∗), A. penninervis

(+); Dispersal modes are: (∗) bird dispersed; (+) ant dispersed; Nevertheless, we thought it desirable to check whether(#) unassisted. Fig. 2b; Eucalyptus species. Top row, from left are; effects we observed might be artefacts of Rapoport’s Rule.(1) Eucalyptus dendromorpha (∗), E. incrassata (+); (2) E. beyeri For this purpose we plotted the number of regions in which(∗), E. tessellaris (+); Bottom row, from left are (3) E. terminalis each species occurred against the latitudinal midpoint of(∗), E. nortonii (+) (4) E. polycarpa (∗), E. gummifera (+); (5) E.

each species range.intermedia (∗), E. eximia (+); Dispersal modes are: (∗) wind assisted;(+) unassisted.

RESULTSfolded into an elaborate dispersal structure (Davidson &Morton, 1984). In species such as A. melanoxylon R. Br.,the funicle is a fleshy structure, orange to reddish in colour, Do widely distributed species tend to have larger (orand folded in such a way that it may completely (or partially) smaller) seed sizes than narrowly distributed ones?surround the seed (see Fig. 2a). These seeds may also remain (i) Comparisons of seed size between species with differenton the parent plant long after the legume is fully opened. geographic range sizes.This form of dispersal morphology and presentation isindicative of a vertebrate (bird) dispersal syndrome (van We found no systematic tendency for seed reserve mass to

be bigger in congeneric species with ‘wide’ compared toder Pijl, 1982; O’Dowd & Gill, 1986). In other species thefunicle is small and not associated with either bird or ant ‘narrow’ distributions (log reserve mass for narrowly

distributed species plotted against congeneric widelydispersal syndromes, i.e. unassisted (O’Dowd & Gill, 1986;see Fig. 2a). distributed species in Fig. 3a, paired t-test, t=1.76, df=40,

P=0.09).There are over 600 species of Eucalyptus in Australia.



TABLE 2. Diaspore weight, reserve weight, dispersal weight and weight of dispersal structure as percentage of total diaspore weight forfive sets of species pairs from Acacia and Eucalyptus. Species within each pair differ in dispersal mode { (∗) bird dispersed, (+) ant dispersedand (‡) unassisted for Acacia; and (∗) wind dispersed in Eucalyptus). Each pair selected for reserve weights differences less than 5% whereverpossible—see text for explanation.

Genus Species Diaspore Reserve Dispersal Dispersal asweight weight weight % total(mg) (mg) (mg) diaspore

Acaciatetragonophylla∗ 27.175 14.275 8.261 30.398longifolia+ 18.875 14.450 2.081 11.025

oswaldii∗ 119.847 73.778 20.314 16.95ramulosa‡ 159.097 81.315 0.238 0.15

coriacae∗ 70.944 48.274 14.643 20.64hapophylla‡ 50.171 46.400 0.557 1.20

salicinia∗ 62.661 30.988 16.885 26.947penninervis+ 63.387 31.357 3.105 4.95

melanoxylon∗ 19.016 6.975 4.431 23.3verticillata+ 12.331 6.987 1.180 9.57

Eucalyptusintermedia∗ 3.638 2.439 0.206 5.67nortonii 3.117 2.432 n/a n/a

polycarpa∗ 8.713 5.405 0.629 7.22gummifera 9.867 7.295 n/a n/a

terminalis∗ 11.601 8.456 0.498 4.30eximia 11.269 8.473 n/a n/a

tessellaris∗ 3.111 1.817 0.435 14.00beyeri 3.199 1.815 n/a n/a

incrassata∗ 1.651 1.192 0.192 11.65dendromorpha 1.891 1.199 n/a n/a

(ii) Comparisons of geographic range sizes between species differences between the species pair, D and E comparedspecies of differing growth forms through similar dispersalwith differing seed sizes.modes, and O and L compared similar growth forms though

Species with tenfold larger seed sizes, on average, occupied differing dispersal modes.a greater number of regions than their paired species withsmaller seed size (Fig. 3b) (range size for large reserve mass Do widely distributed species tend to invest larger amountsspecies plotted against small reserve mass species in Fig. in dispersal structures?3b, paired t-test, t=2.62, df=21, P=0.016). (i) Congeneric species of similar dispersal morphology

Since these two comparisons ask questions that are though differing in range size.mirror-images of each other, what might account for the

Using comparisons within a genus there was no evidencedifferences between Fig. 3a and b? One difference betweento suggest a tendency for broad ranged species to be thosethe two tests is that in Fig. 3a, all PICs were within a genus,that allocate a larger percentage of the resources invested inwhile in Fig. 3b only four PICs were between congenericeach diaspore to dispersal structures, compared to narrowlyspecies (points H, N, Q, U in Fig. 3b). With decreasingranging congeneric species utilizing similar dispersal modestaxonomic relatedness between members of each pair, the(Fig. 3c; paired t-test, t=0.89, df=25, P=0.381).chance of including character trait differences (other than

those in question) increases. Of the twenty-two comparisons,(ii) Congeneric species similar in both seed size and growth

the seven between species of similar dispersal modes andfrom though differing in dispersal modes.

growth forms (points G, I, M, N, Q, T and V) all lay nearthe equality line. The most substantial deviations from the Bird dispersal in Acacia and wind dispersal in Eucalytpus

required greater proportional expenditure on dispersalequality line in Fig. 4 are points J, D, E, F, L and O. Apartfrom point O, all of these comparisons were between species structure than other dispersal modes in Acacia or unassisted

in Eucalyptus (Table 2). In each comparison, the speciesfrom different families or tribes. J and F were comparisonswhich involved both dispersal mode and growth form adopting the more expensive dispersal mode occupied



substantially larger geographic ranges (Fig. 4a and b; pairedt-tests Acacia t=7.69, df=4, P<0.01; Eucalyptus t=3.19,df=4, P<0.05). Species which have undergone dispersalmode shifts have greatly different proportional investmentin dispersal.

This result was not produced as a side effect of Rapoport’srule. In all comparisons, species with latitudinal mid-pointsfurther from the tropics also occurred in fewer regions (Fig.5) and tended to have narrower North–South spread (Table3), contrary to Rapoport’s rule. In eight of the tencomparisons, most of the difference in geographic rangearea was produced through differences in East–West ratherthan North–South range extent (Table 3).

DISCUSSION

Recent reports of correlations between seed mass and plantspecies geographic ranges have shown both positive (Aizen& Paterson, 1990) and negative (Oakwood et al., 1993)correlations. Jensen (1992) disputed the statistical validityof Aizen & Paterson’s (1990) analysis on the grounds thatQuercus represents very distinct sub-genera. Jensen (1992)argued that acorn volume was related to sub-genusmembership, and its correlation with geographic range wasmuch reduced when sub-genera were treated separately.Much of the reported effects therefore was associated withthe single divergence between these two sub-genera (but seealso the response from Aizen & Paterson, 1992). The PICdesign adopted here eliminates the possibility that astatistically significant result can arise from a singleevolutionary divergence.

Using PICs chosen to represent within-genus contrastsof geographic range, we found no tendency for species withwide geographic ranges to have either larger or smallerseeds. Similarly, we found no overall tendency for widelydistributed species to invest proportionately more heavilyin dispersal structures than narrowly distributed congenersusing similar dispersal modes.

When PICs were chosen to represent wide contrasts of

FIG. 3. (a); Log reserve mass of narrowly distributed species plottedagainst log reserve mass for widely distributed species for forty-one congeneric species pair. Diagonal represents position in whichpoints would lie if no difference between species existed (equalityline). (b); Number of regions occupied by species with small reservemass plotted against number of regions occupied by species withlarge reserve mass. Seed masses of each species pair differ by anorder of magnitude (see also Fig. 1). Points G, I, M, N, Q, T andV are comparisons of species of similar growth form and dispersalmodes; Points C, D, E and U are species with similar dispersalmodes though differing growth forms; A, H, L, O, P, R and S arespecies of similar growth form though differing dispersal modes;points B, F, J and K are comparisons of species with both differinggrowth form and dispersal modes. H, N, Q, U are comparisonsbetween congeneric species. Diagonal line represents equality innumber of regions occupied by each pair. (c); Mass of dispersalstructure expressed as a proportion of total diaspore mass fornarrowly distributed species plotted against the same value forwidely distributed species. All twenty-three comparisons are withingenus and within dispersal mode. Diagonal represents equalitybetween members of each pair.



FIG. 5. The number of regions occupied by each species plottedagainst the latitudinal midpoint of each species range (for Acacia;Β, bird dispersed,Χ, ant dispersed,Ε, unassisted: for Eucalyptusspecies; Α, wind dispersed; Μ, unassisted).

comparisons were made between species from differentgenera, families or higher level taxa. It seems likely thatthis was not just a matter of taxonomic remoteness. Allsix contrasts between species from different families werecontrasts of different dispersal models. Four of these werealso contrasts between different growth forms. LikeOakwood et al. (1993), we found that when growth formwas similar, vertebrate dispersed species typically occurredin a larger number of regions than species utilizing otherdispersal modes. Comparisons among other dispersalmodes, within growth form, showed few differences in thenumber of regions occupied. Unlike Oakwood et al. (1993),we found that when dispersal modes were similar but growthforms different, larger seed mass (associated with tallergrowth form) was associated with wider range series.

Similarly on contrasts within the genera Acacia andEucalyptus, with growth form and seed mass held constant,geographic range was associated with dispersal mode.Species making the greater investment in dispersal structureFIG. 4. Pairwise comparisons of the product of latitudinal

spread×longitudinal spread for congeners having similar reserve (bird adapted versus other and wind adapted versusmass but of different dispersal modes. Fig. 4a shows comparisons unassisted) tended to have wider geographic range.of bird-dispersed with anti-dispersed or with unassisted Acacia These results are consistent with natural selection withinspecies. Fig. 4b shows comparisons of wind-dispersed with genera being shaped mainly by the proximal processesunassisted dispersal syndromes in Eucalyptus species.

of locating establishment opportunities within the currentrange of the population (Hamilton & May, 1977; Harper,1977; Motro, 1982). In contrasts between genera, familiesor higher level classifications, larger seed size was sometimesseed reserve mass, a significant overall tendency was found

for larger-seeded species to have wider geographic ranges. associated with wider geographic range, but these effectswere nearly always associated with a divergence in dispersalThe four within-genus PICs, however, showed little range-

size difference, consistent with the absence of any mode or growth form or both, suggesting that widergeographic range is somehow caused by these attributesrelationship for the within-genus geographic-range-contrast

PICs. The overall significant difference in range size rather than by larger size directly. This was supported bythe demonstration of wider geographic range sizes whereassociated with seed size differences was generated when



TABLE 3. The number of regions, latitudinal and longitudinal spread, latitudinal midpoint and product of latitudinal and longitudinalspread (range) size for five pairs of species from the genera Acacia and Eucalyptus. Species are similar seed mass and growth form anddiffer only in dispersal modes (for Acacia spp. (∗)=bird dispersed, (+)=ant dispersed, (‡)=unassisted; Eucalyptus spp. (∗)=wind dispersed,( )=unassisted).

Genus Species Number of Longitudinal Latitudinal Latitudinal Rangeregions spread spread midpoint

Acaciatetragonophylla∗ 28 38 18 34.50 684.00longifolia+ 13 20 10 33.00 200.00

oswaldii∗ 41 38 19.5 27.25 741.00ramulosa‡ 35 11.5 12.5 26.75 143.75

coriacea∗ 22 38 17 23.50 646.00harpophylla‡ 15 15 19 26.50 285.00

salicina∗ 39 24.5 20 27.00 490.00penninervis+ 17 9.5 16.5 28.75 156.75

melanoxylon∗ 41 15.5 27.5 24.25 426.25verticillata+ 17 13 9 34.50 117.00

Eucalyptusintermedia∗ 16 12 18.5 19.75 222.00nortonii 10 11 10.5 33.75 115.5

polycarpa∗ 24 39.5 21.5 21.25 849.25gummifera 8 4.5 13 31.00 58.50

terminalis∗ 26 39.5 21.5 21.25 849.25eximia 2 3 5.5 35.25 16.50

tessellaris∗ 16 15.5 22.5 21.75 348.75beyeri 3 5.5 6.5 34.75 35.75

incrassata∗ 25 32.5 8.5 32.75 276.25dendromorpha 4 4 5.5 35.25 22.00

Wales. University of New England Printery, Armidale, N.S.W.congeners have diverged in dispersal mode without seedBeadle, N.C.W., Evans, O.D., Carolin, R.C. & Tinsdale, M.D.(reserve) mass changes.

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Reserve mass and dispersal investment in relation to geographic range of plant species: phylogenetically independent contrasts