Journal of Coastal Research Fort Lauderdale, Florida

Vascular Diversity on Two Barrier Islands in Southwest Florida

Stanley R. Herwitz' and Richard P. Wunderlin'

"Graduate School of Geography 'Department of Biology Clark University University of South Florida Worcester, MA 01610, USA Tampa, FL 33620, USA ABSTRACT _

HERWITZ, S.R. and WUNDERLIN, R.P., 1990. species diversity on two barrier islands in southwest Florida. Journal cfCoaetal Research, 6(2), 311-322. Fort Lauderdale

The equilibrium theory of island biogeography was examined in relation to the indigenous vas­ cular floras of two barrier islands of different size and distance from the southwest Florida main­ land. On Cayo-Costa Island, which has a land area of 5.6 km 2 and is located 12.8 km from the mainland, 261 species were identified. On Sanibel Island, which has a land area of 43.6 km 2 and is located 3.2 km from the mainland, an inventory in the mid-1950's identified 266 species. The similar number of species, despite the differences in island area and distance from the main­ land, was attributed to the incompleteness of the inventory of Sanibel in the 1950's. An inven­ tory of Sanibel from 1965 to 1985 identified 432 native species. This almost two-fold difference in the number of species on Sanibel as compared with Cayo-Costa is more consistent with equi­ librium theory which predicts a significantly greater number of species on a larger island located closer to the mainland. However, comparison of the species-area relations ofCayo-Costa and Sanibel with other studies of island floras suggests that Sanibel should have had even more species. Urban development and the spread of alien plant species following the construction of a causeway linking Sanibel to the mainland in 1963 may have reduced the number of native plant species on Sanibel.

ADDITIONAL INDEX WORDS: Barrier islands, coastal , Cayo-Costa Island, equilib­ rium theory, Florida, native species, Sanibel Island, species composition.

INTRODUCTION (SOLEM, 1973), fish (SMITH, 1979), birds (DIAMOND, 1969; JOHNSON, 1975; ABBOTT The equilibrium theory of island biogeogra­ and GRANT, 1976), lizards (WILCOX, 1978) phy has stimulated much research since it was and mammals (LAWLOR, 1983). The theory first formulated by MACARTHUR and WIL­ also has been considered in relation to the vas­ SON (1963). According to the equilibrium the­ cular floras of high altitude paramo vegetation ory, species composition on islands is not fixed, in South America (SIMPSON, 1974), lake but rather changes over time due to on-going islands in Sweden (NILSSON and NILSSON, immigration and extinction. The balance 1978; RYDIN and BORGEGARD, 1988), very between these two processes is believed to small islands and offshore cays in Australia, result in a nearly constant equilibrium number , and (ABBOTT, 1977; of species. The theory also predicts that a large BUCKLEY, 1982; HEATWOLE and LEVINS, island located close to a mainland source area 1983; BURANDT and CAMPINS, 1986; FLOOD should have a higher equilibrium number of and HEATWOLE, 1986), the Galapagos Islands species than a smaller island located further (VAN DER WERFF, 1983), and the Gulf of Cal­ from the mainland. ifornia Islands (CODY et aZ., 1983). The studies The equilibrium theory has been tested for by VAN DER MAAREL (1982) and MENNEMA microorganisms (CAIRNS et al., 1969; HAVE, and WEEDA (1983) on the Frisian Islands 1987), fungi (ANDREWS et al., 1987), arthro­ along the coasts of the Netherlands and Ger­ pods (SIMBERLOFF and WILSON, 1970; many are among the few that have documented STRONG and REY, 1982), ants (GOLDSTEIN, plant species numbers on barrier islands of dif­ 1975; BOOMSMA et aZ., 1987), land snails ferent size and distance from the mainland,

89021 received 12 April 1989; accepted in revision 28 September Barrier islands differ geologically from 1989. oceanic islands (such as the Galapagos) and 312 Herwitz and Wunderlin

continental islands (such as those in the Gulf of and a mean annual precipitation of 1360 mm California) which originate by volcanic and tec­ (NATIONAL CLIMATIC CENTER, 1982). Flo­ tonic processes. Barrier islands, which com­ ristically, the islands are a mixture of southern prise roughly 10 to 13% of the world's continen­ temperate and tropical Caribbean species. tal coastline (SCHWARTZ, 1973), are <10" yr old and are composed of unconsolidated sedi­ METHODS ments lying offshore on gently sloping conti­ nental shelves. They are generally separated An inventory of vascular plant species on from the mainland by a shallow lagoon or bay, Cayo-Costa Island was made over the two-year and they rarely have elevations exceeding 10 m period from 1975 to 1977. The results from above sea level. Due to their depositional Cayo-Costa were compared with two invento­ nature and their limited topographic relief, ries made on Sanibel Island: (1) an inventory barrier islands are actively reworked by shore­ carried out in 1953 and 1954 (COOLEY, 1955), line processes and are vulnerable to storm over­ and (2) a more recent inventory carried out wash. The objective of our study was to consider from 1965 to 1985 (WUNDERLIN and HAN­ the equilibrium theory of island biogeography SEN, 1985). We assumed that the number of in relation to the indigenous floras of two bar­ plant species on Cayo-Costa did not change sig­ rier islands in southwest Florida. nificantly over the period 1977 to 1985. Our study consisted of comparing only the STUDY AREA native vascular plant species from the three inventories. Obsolescent nomenclature was The two barrier islands examined in this updated. Ruderal species, naturalized exotics, study are Cayo-Costa and Sanibel Islands. and ornamentals that had escaped from culti­ These islands are part of the Charlotte Harbor vation were excluded from the comparison. barrier island system located west of Fort To evaluate the predictions of the equilib­ Myers (latitude 26°45'N, longitude 82°10'W) rium theory, the number of species on each (Figure 1). The north end of Cayo-Costa is adja­ island was considered in relation to the land cent to Boca Grande Pass which is the major area of the island and its distance from the tidal inlet serving Charlotte Harbor and the mainland. The species-area relationship was discharge site of the Myakka and Peace Rivers. expressed in the standard form S = CA" where The south end of Sanibel Island is adjacent to S is the species number, A is the island area, C San Carlos Bay, the discharge site of the is a coefficient that relates to biogeographic Caloosahatchee River. region and is generally less in regions where Sanibel Island is the largest of the five there are fewer potential colonizing species in islands that comprise the chain. It has a land a given taxon, and z is an exponent that tends area of 4,362 hectares and recurves landward at to increase as a function of increasing island its southern end to a distance of 3.2 km from the isolation (MACARTHUR and WILSON, 1967). mainland. Cayo-Costa Island is located 14.9 km The best-fit equation was determined for Cayo­ to the north. It has a land area that is 13% of Costa and Sanibel Islands by plotting the two the land area of Sanibel, and it is 4 times fur­ data points on log-log graph paper and then fit­ ther from the mainland. ting a line through these points. Comparisons Both islands are composed mainly of calcar­ were made between the equation from our study eous biogenic marine sediments and some and those equations derived from other studies quartz sands derived from river discharge of plant species number and island area. (HUANG and GOODELL, 1967). The Gulf coast of Florida is periodically subject to hurricane RESULTS disturbances and storm overwash events. Accretionary beach ridges with the character­ The extent of land development on Sanibel at istic ridge and swale topography comprise the the time of COOLEY's inventory was compa­ Gulf side of both islands. The more protected rable to Cayo-Costa in the 1970's. Both islands bay side consists of tidal swamp deposits. were sparsely inhabited, and had essentially Southwest Florida has a moist subtropical cli­ the same habitat diversity consisting of beach mate with a mean annual temperature of 23°C strands, savannas, cabbage palm forests, slash

.Iourrial of Coastal Research. Vol. G. No.2. 1990 Vascular Plants on Barrier Islands 313

CHARLOTTE HARBOR

cp,l\NUE t>"'ss \30cl\ ) FLORIDA 0 b fb~o <:Or? ~ Q ,

0 CAPTIVA PASS ~ PINE NORTH CAPTIV ISLAND ISLAND

SOUND

CAPTIVA ISLAND

GULF OF

SANIBEL 0 5 km 10 ISLAND I I -----l

Figure 1. Location of Cayo-Costa and Sanibel Islands in the Charlotte Harbor barrier island system of southwest Florida.

pine flatwoods, freshwater marshes, mangrove WITZ, 19771. In 1963, the construction of a swamps, salt marsh tidal flats, and tropical causeway linking Sanibel to the mainland led hardwood hammocks (COOLEY, 1955; HER- to urban development on parts of Sanibel dur-

Journal of Coastal Research, Vol. 6, No.2, 1990 :314 Herwitz and Wunderlin

ing the period of WUNDERLIN and HANSEN's DISCUSSION inventory. Sanibel continues to have the same habitat diversity as Cayo-Costa, but the areal On the basis of the land areas and distances extent of these habitats on Sanibel has been from the mainland of Cayo-Costa and Sanibel reduced. Islands, equilibrium theory predicts that Sani­ Table 1 shows the number of native vascular bel should have significantly more species than plant species and genera on the two islands. Cayo-Costa. Different-sized islands are The inventories of Sanibel reported by expected to have different species numbers due COOLEY (1955) and by WUNDERLIN and to the relationship between population size and HANSEN (1985) are shown separately in Table island area. The land area of Sanibel is more 1. than 7 times greater than Cayo-Costa. On Cayo-Costa, 261 species were found rep­ resenting 203 genera. Thirty-nine genera were Comparison Based on COOLEY Inventory represented by two or more species. COOLEY (1955) reported 266 native vascular plant spe­ The number of species identified on Sanibel cies representing 196 genera. Forty-five genera between 1953 and 1954 by COOLEY (1955) was were represented by two or more species. Non­ essentially the same number of species identi­ co-occurring species on islands having similar fied on Cayo-Costa. Some variance in species habitat diversity may be considered suggestive numbers would be expected due to turnover of species turnover (CODY et al., 1983). On the noise (DIAMOND, 1969), but this variance can­ basis of the COOLEY (1955) inventory, Sanibel not explain why the species numbers should be had 34% of its species and 25% of its genera not so similar. Four possible explanations may be co-occurring on Cayo-Costa, while Cayo-Costa presented. had 33% of its species and 27% of its genera not (1) Sanibel may have been in a nonequili­ co-occurring on Sanibel (Table 1). WUNDERLIN and HANSEN (1985) identi­ brium condition at the time of Cooley's inven­ fied > 1.6 times more species on Sanibel than tory. The physiography of the Charlotte Harbor COOLEY (1955). They found 432 species rep­ barrier island chain and radiometric dates from resenting 282 genera. Seventy-nine genera Sanibel suggest that Sanibel may be the young­ were represented by two or more species. On the est island in the chain, and may have had less basis of the WUNDERLIN and HANSEN (1985) time to establish the equilibrium species num­ inventory, Sanibel had 51 % of its species and ber. Barrier islands in many different geo­ 34% of its genera not co-occurring on Cayo­ graphic localities date from about 7000 yr BP Costa, while Cayo-Costa had only 15% of its (PETHICK, 1984); however, barrier islands species and 8% of its genera not co-occurring on that originate from elongating breached spits Sanibel (Table 1). Many of the non-eo-occurring (FISHER, 1968) would be expected to differ in species were represented by co-occurring gen­ age. The oldest beach ridges on Sanibel are only era. On Sanibel, 54% of the non-eo-occurring 4300 ± 50 yr old and the landward-recurving species were represented by co-occurring gen­ progradational lobe, which constitutes the bulk era on Cayo-Costa. On Cayo-Costa, 62% of the of Sanibel's land area (Figure 1), has been dated non-eo-occurring species were represented by at less than 2000 years (MISSIMER, 1973). The genera co-occurring on Sanibel. Charlotte Harbor barrier island chain may

Table 1. Comparison of n.umbern of native vascular plant species and genera.

Cayo-Costa Sanibelt Cayo-Costa Sanibel* 1975-77 195:3-54 1975-77 1965-85

Number of species 261 266 261 4:32 Co-occurring (r;{) 67.0 65.8 84.7 51.2 Not co-occurring (ric) :J:3.0 :J4.2 15.:J 48.8 Number of genera 20:J 196 20:J 282 Co-occurring (r,{) 72.9 75.5 91.6 66.0 Not co-occurring (%) 27.1 24.5 8.4 :34.0 t Based on Cooley (1955). " Based on Wunderlin and Hansen (19851.

.Inurnal of Coastal Research. Vol. 6, No.2, 1990 Vascular Plants on Barrier Islands 315 have developed in a southerly direction with ent introduction of mainland species, a 62% Cayo-Costa being>1000 years older and there­ increase in the number of native species seems fore closer to the equilibrium condition. The unlikely. The unusually high proportions of weakness of this explanation is that 1000 years non-co-occurring species (>30%) on the two should be adequate time for a nearshore island islands, therefore, probably reflects the incom­ to achieve equilibrium (RYDIN and BORGE­ pleteness of COOLEY's inventory. GARD, 1988). (2) Prior to Cooley's inventory, Sanibel may Comparison Based on Wunderlin and have undergone an environmental perturba­ Hansen Inventory tion. For example, storm overwash, which can be extremely disruptive to the vegetation of According to the WUNDERLIN and HAN­ barrier islands (GODFREY and GODFREY, SEN (1985) inventory, Sanibel had 171 more 1976), may have resulted in a significant reduc­ native vascular plant species than Cayo-Costa. tion in species numbers on Sanibel. Sanibel This result is more consistent with equilibrium would be vulnerable to storm overwash from theory. Species-area curves of MACARTHUR the south and southwest because of the orien­ and WILSON (1967) predict a doubling in spe­ tation of its coastline. Cayo-Costa would be cies number with roughly a ten-fold increase in most vulnerable to storm overwash from the island area. west because of the north-south orientation of The species-area relationship for Cayo-Costa its coastline. Meteorological records for south­ and Sanibel Islands is best expressed by the 0 2 west Florida over the last 60 years indicate a equation S = 171A '. Figure 2 shows this rela­ relatively high frequency of storms from the tionship on log-log axes together with the best­ south and southwest (GENTRY, 1974) with at fit lines found for vascular plant species num­ least four hurricanes known to have been bers on the Galapagos Islands (VAN DER destructive to vegetation on Sanibel between WERFF, 1988), the Gulf of California Islands 1922 and 1953. The weakness of this explana­ (CODY et al., 1983), and the Frisian Islands tion is that, despite the different orientation of (MENNEMA and WEEDA, 1983). These studies Cayo-Costa's shoreline, it would be difficult to all found an exponential increase in species envisage Cayo-Costa being unaffected by these number with increasing island area; however, storm events. there were some marked differences in the C (3) Islands that have undergone a reduction and z values (Table 2). in land area, for example, as a result of shore­ As would be expected for oceanic islands line erosion, may initially support more species located >700 km from the mainland, the species than the equilibrium number (WILCOX, 1978). numbers on the Galapagos were lower than the The southern half of Cayo-Costa (Figure 1) has numbers on comparable-sized continental undergone significant shoreline erosion as evi­ islands (Figure 2). Both the Galapagos and the denced by the exposure of mangroves on the Gulf of California Islands had low C values pre­ Gulfside of the island. The number of plant spe­ sumably because they are located in relatively cies on Cayo-Costa, therefore, could represent a dry biogeographic regions with a smaller pool number that exceeds the equilibrium condition. of potential colonizing species. Higher C values This explanation is weakened by the fact that would be expected in the more favorable, mesic there has been a corresponding accretion of biogeographic regions of Florida and Europe. beach ridges on the northern half of Cayo­ The range of z values is generally between Costa, and no significant net reduction in land 0.20 and 0.35. According to MACARTHUR and area (HARVEY, 1979l. WILSON (1967), the values at the lower end of (4) The floristic inventory of Sanibel by this range correspond to islands located close to COOLEY (1955) may have been incomplete. If the mainland where there tends to be a higher we consider it complete, a total of 166 addi­ colonization rate of transient species. The z val­ tional species of native vascular plants would ues of 0.20 for the Gulfof California Islands and have had to colonize the island in the 30-year 0.25 for Cayo-Costa and Sanibel are consistent period from 1955 to 1985. While the construc­ with the prediction that the logarithm of spe­ tion of the causeway could have increased the cies number increases less rapidly on nearshore opportunities for both deliberate and inadvert- islands. The z value of 0.31 for the Galapagos

Journal of Coastal Research. Vol. 6. No.2. 1990 316 Hcrwitz and Wunderlin

1000 500 .--- en --- Sanibel (l) U IV _----- Cayo-Costa (l) 200 o, en III 0 100 W II~ .0 E 50 :::J Z

20

10 I! !! II ! 1 2 5 10 20 50 100 2 Island area (km )

Figure 2. Relationship between number of vascular plant species and island area shown for: 11) the Galapagos Islands (VAN DER WERFF, 1983), (1) the Gulf of California Islands (CODY et al., 19831, (IIII the Frisian Islands (MENNEMA and WEEDA, 19831, and (IV) Cayo-Costa and Sanibel Islands.

Table 2. Species-area slopes and coefficients [or different rier islands and their susceptibility to the influ­ island systems. ences of storm overwash, subsurface saltwater intrusion, and salt spray may limit the coloni­ Islands C n p zation rate of transient mainland species, thus Galapagos 30 0.31 18 0.89 0.001 increasing the z value. Gulf of California 55 0.20 :10 0.87 0.001 Frisian 133 0.37 17 0.90 0.001 The Frisian Islands are comparable to Cayo­ Cayo-Costa & Sanibel 171 025 2 NA NA Costa and Sanibel both in terms of their geo­ Species-area equation S CA'. morphogenesis, and their land area and dis­ n ~ number of islands. tance to the mainland. The Frisian Islands J 7 r = correlation coefficient. best-fit equation S = 133Ao: is based on spe­ p ~ significance probability. cies inventories of 17 islands and is highly sig­ NA ~ not applicable. nificant (r = 0.90; P < o.oon Ifthe high z value for the Frisian Islands is representative of bar­ Islands is at the higher end of the expected rier islands in general, the z value of 0.25 range as predicted for oceanic islands located obtained for Cayo-Costa and Sanibel may be far from a mainland source area. considered low. The z value of 0.37 for the Frisian Islands is Figure 2 shows how the number of species on greater than that found for the other island sys­ Cayo-Costa is almost directly on the Frisian tems including the Galapagos (Table 2). This species-area best-fit line, while the number of finding is contrary to the MACARTHUR-WIL­ species on Sanibel is well below the line. Add­ SON prediction that the logarithm of species ing those species on Cayo-Costa not co-occur­ number increases less rapidly on nearshore ring on Sanibel to the Sanibel species list yields islands. SCHOENER (1976), CONNOR and a sum of 472 species. This sum is still less than McCOY (1979), and WILLIAMSON (1988) have the number predicted using the Frisian Islands rejected the MACARTHUR-WILSON predic­ species-area equation. tion, and they have argued that the z values A lower-than-predicted number of plant spe­ tend to be lower for more distant and isolated cies on Sanibel would suggest that Sanibel may archipelagoes. In the case of nearshore barrier have been in a nonequilibrium condition at the islands such as Cayo-Costa, Sanibel, and the time of the Wunderlin and Hansen inventory. Frisian Islands, high z values perhaps could be This finding would be consistent with the fact expected. The characteristic narrowness of bar- that urban development on Sanibel has mark-

,Journal of Coastal Research. Vol. 6. No.2, 1990 Vascular Plants on Barrier Islands 317 edly increased following the construction of the Celtis pallida Torr. causeway linking Sanibel to the mainland in Cenehrus i ncert.us M.A. Curtis Ccntrosema virginianum (1..) Benth. 1963. The reduction in the area of native hab­ Cereus gracilis Mill. itats as a result of human disturbance would be Charnaocrist.a fasciculata rMichx.: Greene expected to decrease species numbers. In addi­ Chamaecrista nietitans (1...) Moench tion, HEATWOLE and WALKER (1989) Chamaesycc blodgettii (Engelm. ex Hitchc.1 Small Chamaesyce hypericifolia IL.l Millsp. recently noted that the spread of alien plant Chamaesycc hyssopifolia IL.I Small species on islands may reduce the number of Chamaesyce mcsembryanthcmifolia (.Iacq.) Dugand native plant species. Chiococca alba IL.) Hitchc. Barrier islands often are desirable shoreline Chrysobalanus icaco L. localities vulnerable to human activity. Estab­ Cirsium horridulum Michx. Cladium jamaiccnse Crantz lishment and maintenance of an equilibrium Cnidoscolus st.irnulosus IMichx.1 Englem. & Gray condition may be less commonly achieved on Coccoloba uvifcra IL.I L. readily accessible barrier islands such as San­ Commclina crecta L. ibel Island. We conclude that human distur­ Conocarpus ercctus L. Conyza canadensis IL.I Cronq. bance of native habitats and the spread of alien Coreopsis leavcnworthii Torr. & Gray plant species into undisturbed native habitats Crinum amcricanum L. may have caused a significant reduction in the Crotalaria rotundifolia rWalt.I Gmel. number of native plant species on Sanibel. Croton glandulosus L. Croton punctatus J acq. Appendix I. Native Vascular Plant Species Cynanchum angustifolium Pet-s. Cynanchum scoparium Nutt. on Cayo-Costa and Sanibel Islands Cyperus cornpressus L. Cyperus ligularis L. Acrostichum danaeifolium Langsd. & Fisch. Cyperus planifolius L. Rich. Agal inis maritima lRafl Raf. Cyperus polystachyos Rottb. Agave decipiens Baker Dalbergia ecastophyllum IL.I Taub. Alternanthera flavesccns Kunth Dichanthelium dichotomum IL.) Gould Amaranthus australis IA. Gray) Sauer Dichanthelium portoricense iDefv. ex Ham.I B. F. Hansen & Amaranthus ftoridanus IS. Wats.1 Sauer Wunderlin Ambrosia arternisiifol i a L. Dichanthelium strigosurn IMuh!. ex El l.: Freckmann Ambrosia hispida Pursh Digitaria villosa IWalt.1 Pers. Ammannia latifolia L. Distichlis spicata (L.I Greene Andropogon glomeratus tWa lt.) BSP. Dodonaea vi scosa (1...) Jacq. Andropogon virginicus L. Ericycli a tampensis (Li nd l.) Small Ardisia escallonioides Schlecht. & Cham. Eragrost.is ciliaris IL.l R. Br. Aristida patula Chapm. ex Nash Erechtites hieracifolia IL.) Raf. Aristida purpurascens Pair. Erigeron quercifolius Lam. Aster subulatus Michx. Ernodea littoralis Sw. Atriplex pentandra IJaeq.1 Standl. Erythrina herbacea L. Avicennia germinans (1..) L. Eugenia axf llar-is (Sw.: Willd. Baccharis angustifolia Michx. Eugenia foetida Pet-s. Baccharis halimifolia L. Eupatorium mi kanioidcs Chapm. Bacopa monnieri IL.I Pennell Eustachys petraea (Sw.} Desv. Batis maritima L. Evolvulus alsinoides L. Bidens alba (L.I DC. Ficus aurea Nutt. Blechnum serrulatum L. Rich. Fimbristylis caroliniana (l.am.l Fern. Blutaparon vermiculare IL.) Mears Boerhavia diffusa L. Fimbristylis castanea IMichx.1 Vahl Borrichia ftutescens IL.) DC Pimbristylis spathacea Roth Bouteloua hirsuta Lag. Flaveria li ne ari s Lag. Buchnera americana L. Forestiera segrcgata IJacq.l Krug & Urban Bumelia celastrina Kunth Galium hispidulum Michx. Bursera simaruba IL.) Sarg. Gaura angustifolia Michx. Caesalpinia bonduc IL.) Roxb. Genipa clusiifolia (.Iacq.l Gr-iseb. Cakile lanceolata (Wil ld.l O. Schulz Gnaphalium obtusifolium L. Callicarpa americana L. Hedyotis nigricans t Larn.l Fosberg Canavalia rosea (L.I DC. Hedyot.is procumbens IJ.F. Gmcl.) Fosber-g Capparis cynophallophora L. Hedyotis uniftora (L.I Lam. Capsicum frutcscens L. Heliotropium angiospermum Murr. Cassytha filiformis L. Heliotropium curassavicum L.

Journal of Coastal Research, Vo!. 6, No.2, 1990 318 Herwitz and Wunderlin

Heliotropium polyphyllurn Lehm. Portulaca rubricaulis HBK. Herissantia crispa (L.) Briz. Psilotum nudum (1,.) Beauv. Heterotheca subaxillaris (Lam.) Britt. & Rusby Psychotria ncrvosa Sw. Hydrocotyle umbellata L. Pteridium aquilinum IL.) Kuhn latifolia IMil1.J Roem. Pterocaulon pycnostachyum (Michx.I Ell. Ipomoea alba L. Ptilimnium capillaceum IMichx.1 Raf. Ipomoea indica (Burm. f. 1 Merrill Quercus virginiana Mill. Ipomoea pes-caprae 11,.1 R. Br. Randia aculeata 1,. Ipomoea sagittata Pair. Rapanca punctata (Larn.) Lundell Ipomoea violacea L. Rhizophora mangle L. diffusa Humb. & Bonpl. ex Willd. Rhynchospora colorata IL.) Pfeiffer Iva frutescens L. Ri vi n a humilis 1... Iva imbricata Walt. Sabal palmetto IWalt.) Lodd. ex Schult. J acquinia keyensis Mez Salicornia virginica L. Kosteletzkya virginica 11,.) Presl ex A. Gray Salix caroliniana Michx. Laguncularia racernosa (L.) Gaertn. f. Samolus ebracteatus Kunth Lantana involucrata L. Samolus valerandi L. Lasiacis divaricata IL.) Hitchc. Sarcostemma clausum t.Iacq.I Roem. & Schult. Lcpidium virginicum L. Scaevola plumieri (L.J Vahl Leucaena leucocephala tLam.l de Wit Scoparia dulcis L. Licania michauxii Prance Serenoa repcns (Bartr.) Small Limonium carolinianurn (Walt.: Britt. Sesuvium portulacastrum L. Ludwigia microcarpa Michx. Setaria geniculata (Larn.J Beauv. Ludwigia repens Forst. Setaria macrospcrma IScribn. & Merrill I Schum. carolinianum Walt. Sida acuta Burm. f. Malvastrum corchorifolium (Dear} Britt. Smilax auriculata Walt. Mastichodendron foetidissimum (.Jacq.J H.J. Lam americanum Solidago gigantea Ait. Maytenus phyllanthoides Benth. Solidago scmpcrvircns L. Melanthera nivea IL.) Small Sophora tomentosa L. Melothria pendula 1,. Spartina bakeri Merr. Merremia dissecta IJ acq.1 Hall. f. Spartina patens t Ait.) Muhl. Mikania scandens (L.l Willd. Spermacoce prostrata Aubl. Monarda punctata L. Sporobolus virginicus (1...) Kunth Muhlenbergia capillaris (Lam.) Trin. Stenotaphrum secundatum rWa lt..l Kuntze Myrica cerifera L. Suaeda linear-is (El l.l Moq. Oenothera humifusa Nutt. Suriana maritima L. Opuntia humifusa iRaf.) Raf. Tbelypteris kunthii rDesv.I Morton Opuntia stricta Haw. ba lbisiana Schult. Panicum amarum Ell. Tillandsia flexuosa Sw. Panicum virgatum L. Tillandsia paucifolia Baker Parietaria floridana N utt. Tillandsia recurvata (L.) L. Parthenocissus quinquefolia IL.) Planch. Tillandsia setacea Sw. Paspalum distichum L. Tillandsia usneoides (L.) L. Passiflora suberosa L. Tillandsia utriculata L. Pectis glaucescens tCass.) Keil Toxicodendron radicans (L.) Kuntze Pedilanthus tithymaloides IL.) Poit. Trichostema dichotomum L. Pet.iveria alliacea L. Triplasis purpurea tWalt.! Chapm. Phlebodium aureum (L.l Sm. Typha domingensis Pers. Phyla nodiflora IL.l Greene Uniola paniculata L. Verbesina virginica L. Phyllanthus abnormis Baill. Vicia acutifolia Ell. Phytolacca americana L. Vigna luteola IJacq.l Benth. Engelm. Vitis munsoniana Simpson Pisonia aculeata L. Vittaria lincata (1,.1 Smith Pithecellobium unguis-cati IL.l Benth. Waltheria indica L. Pluchea odorata IL.l Cass. Zanthoxylum clava-herculi s L. Pluchca rosea Godfrey Zanthoxylum fagara IL.) Sarg. Poinsettia cyathophora (Murr.) KI. & Gke. Polygala boykinii Nutt. Polygala grandiflora Walt. Appendix 2. Native Vascular Plant Species Polygala incarnata L. on Cayo-Costa Island But Not on Sanibel Polygonum hydropiperoides Michx. Island Polypodium polypodioides 11,.1 Watt Polypremum procumbens L. Agal in is filifol ia IN utt.l Raf. Portulaca pilosa L. Apium leptophyllum (Pors.) F. Muell.

Journal of Coastal Research, Vol. 6, No.2, 1990 Vascular Plants on Barrier Islands 319

Asclepias verticillata L. Cardamine hirsuta L. Bulbostylis barbata (Rottb.) Clarke Cardiospcrmum microcarpum Kunth Cenchrus gracillimus Nash. Carex albolutcsccns Schwcin. Chamaesyce cumulicola Small nitida Vahl Chrysopis scabrella Torr. & Gray Celtis iguanaea (Jacq.l Sarg. Dalea feayi (Chapm.) Barneby Cenchrus echinatus L. Desmodium marilandicum (L.I DC. Centella asiatica (L.l Urban Eupatorium leptophyllurn DC. Cephalanthus occidentalis L. Galactia parvifolia A. Rich. Cereus pentagonus (L.I Haw. Gnaphalium purpureum L. Chamaesyce bombensis (.Iacq.t Dugand 'iratiola virginiana L. Chamaesyce hirta (L.l Millsp. lelianthemum corymbosum Michx. Chamaesyce maculata (L.I Small Iieracium megacephalon Nash. Chamaesyce ophthalmica tPcrs.I Burch Lantana depressa Small Chamaesyce thymifolia (L.I Millsp. Launaea intybacea (Jacq.1 Beauv. Chenopodium ambroaioides L. Lechea sessiliflora Raf. Chromolaena odorata (L.I King & Robins. Mecardonia acuminata (Walt.) Small Cissus trifoliata L. Nephrolcpis cordifolia (L. 1 Presl Cissus verticillata (L.I Nicols. & Jarvis Panicum anccps Michx. Commelina diffusa Burm. f. Persea borbonia (L. I Spreng. Commelina elegans Kunth Physalis walteria Nutt. Cuscuta pentagona Engelm. Rhynchosia reniformis DC. Cypcrus brcvifolius (Rot.tb. I Hassk. Rhynchospora grayi Kunth Cypcrus g lobulosus Aubl. Rhynchospora microcarpa Baldw. ex A. Gray Cyperus odoratus L. Sagittaria lancifolia L. Cypcrus retrorsus Chapm. Salvia coccinca Buchoz ex Epling Cyperus suri namcnsis Rottb. Scleria triglomerata Michx. Cyperus tetragonus Ell. Setaria corrugata (Ell. I Schult. Desmodium incanum DC. Sisyrinchium mi arnicnse Bickn. Dcsmodium scorpiurus t Sw.! Desv. Sonchus asper (L. I Hill Desmodium tortuosum tSw.I DC. Sonchus oleruceus L. Dichanthelium aciculare (Desv. ex Poir.) Gould & Clark Sporobolus jacquemontii Kunth Dichanthelium commutatum (Schult.I Gould Thelypteris palustris Schott Dichondra caroli nensis Michx. Vitis acstivalis Michx. Dicliptera assurgens (1..) Juss. Woodwardia virginica (L.) Smith Digitaria ciliaris (Retz.I Koel. Ximenia americana L. Digitaria longiflora (Ret.z.) Pers. Xyris elliottii Chapm. Diodia teres Walt. Zamia pumila L. Diodia virginiana L. Diospyros virginiana L. Appendix 3. Native Vascular Plant Species Drymaria cordata (L.l Willd. ex Roem. & Schult. on Sanibel Island But Not on Cayo-Costa Duranta rcpcns L. Echinochloa colonum (L.I Link Island Echinocbloa paludigena Weig. Echinochloa walteri t Pursh l Heller Acacia pinetorum (Smalll I!erm. Eclipta prostrata (L.I L. Aeschynomene americana L. Eleocharis albida Torr. Agalinis fasciculata (Ell. I Raf. Eleocharis atropurpurea tRetz.J Kunth Amaranthus hybridus L. Elcocharis flavcscens (Poi r.) Urban Amaranthus spinosus L. Eleocharis geniculata (L.I Roem. & Schult. Amaranthus viridus L. Eleocharis montevidensi s Kunth Ampelopsis arborea (L. I Kohne Emilia fosbergii Nicols. Amphicarpum muhlenbergianum (Schult.) Hitchc. Anagallis minima (L.I Krause Eragrostis elliottii F. Wats. Annona glabra L. Eragrostis speetabilis (Purshl Steud. Argemone mexicana L. Eragrostis tracyi Hitchc. Asplenium abscissurn Willd. Erianthus giganteus (Walt. I Muhl. Aster bracei Britt. ex Small Eriochloa michauxii (Poir.l Hitchc. Aster simmondsii Small Eryngiurn baldwinii Spreng. Axonopus furcatus (Fluegge) Hitchc. Eugenia confusa DC. Baccharis glomeruliflora Pers. Eupatorium capillifolium (Lam.) Small Berlandiera subacaulis (Nutt.) Nutt. Eupatorium serotinum Michx. Boerhavia erecta L. Euphorbia inundata Torr. ex Chapm. Bothriochloa pertusa (L.l A. Camus Eustachys glauca Chapm. Capraria biflora L. Eustoma exaltatum (L.) Griseb. Capsicum annuum L. Eutharnia tenuifolia (Pursh l Greene

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Evolvulus sericcus Sw. Panicum rigidulum Bose ex Nees Fimbristylis autumnalis (L.) Roem. & Schult. Parietaria practcrmissa Hinton Fl avcria floridana J.R. Johnston Paspalum blodgettii Chapm. Flaveria trinervia (Spreng.: Mohr Paspalum boscianum Fluegge Froelichia floridana (Nutt.) Moq. Paspalum caespitosum Fluegge Fuirena breviscta (Cov.l COy. Paspalurn floridanum Michx. Fuirena pumila (Torr.) Spreng. Paspalum sctaccum Michx. Fuirena scirpoidea Michx. Pedis linearifolia Urban Gaillardia pulchella Foug. Pectis prostrata Cav. Galactia striata (Jacq.1 Urban Physalis angulata L. Galactia volubilis (L.) Britt. Physalis angustifolia Nutt. Galium tinctorium L. Physalis pubcscens L. Geranium carolinianum L. Pi lea her-ni ar-ioides tSw.t Lindl. Gnaphalium falcatum Lam. Pilea microphylla (L.I Liebm. Gnaphalium pensylvanicum Willd. Piriqueta caroliniana (Walt.! Urban Gossypiurn hirsutum L. Piscidia piscipula (L.I Sarg. Habenaria odontopetala Reichb. f. Plantago virginica L. Hamelia patens Jacq. Plumbago scandens L. Haplopappus phyllocephalus DC. Poinsettia heterophylla (L.) KI. & Gke. Hedyotis corymbosa (L.) Lam. Polygonum setaceum Baldw. ex Ell. Helenium amarum (Raf.) H. Rock Pyrrhopappus carolinianus (Walt.) DC. Hemicarpha micrantha (Vahl ) Pax Reimarochloa oligostachya (Munro) Hitchc. Hexalectris spicata (Walt.] Barnh.. Hydrocotyle verticillata Thunb. Rhabdadenia biflora (-Iacq.t Muell.-Arg. Hypcxis juncea Smith Rhus copallina L. Ipomoea triloba L. Rhvnchoaia m ichauxi i Vail Juncus marginatus Rostk. Rhynchosia minima (L.I DC. Juncus megacephalus M.A. Curtis Rudbeckia hirta L. Lantana camara L. Rumex pulcher L. Lemna obscura (AustinI Daubs Rumex verticillatus L. Leptochloa dubia (Kunthi Nccs Ruppia maritima L. Leptochloa fascicularis (Lam.) A. Gray Sabatia stellaris Pursh Linaria canadensis (L.) Dun. Sagittaria graminea Michx. Lindernia crustacea (L.) F. Muell. Salvia riparia Kunth Linum medium tPlanch.I Britt. Sambucus canadensis L. Lipocarpha maculata tMichx! Torr. Scirpus robustus Pursh Lobelia feayana A. Gray Scirpus validus Vahl Ludwigia curtissii Chapm. Scleria rcticularis Michx. Ludwigia erecta (L.) Hara Scleria verticillata Muhl. ex Willd. Ludwigia octovalvis t.lacq.) Raven Senecio glabellus Poir. Ludwigia paluatris (L.) Ell. Senna occidentalis (L.I Link Ludwigia peruviana (L.) Hara Sesbania emerus (Aubl.) Urban Lythrum alatum Pursh Sesbania vesicaria t.l acq.I Ell. Malvastrum americanum (L.l Torr. Sesuvium maritimum r Walt.: BSP. Melochia villosa (Mi ll.) Fawc. & Rendle Setaria magna Griseb. Mentzelia floridana Nutt. Sida rhombifolia L. Micranthemum glomeratum (Chapm.) Shinners Sisyrinchium atlanticum Bickn. Mitreola petiolata (J.F. (Imel.I Torr. & Gray Spar-tina alterniflora Loisel. Mollugo ver-t.ici llata L. Spermacoce assurgens Ruiz & Pavon Morinda royoc L. Najas guadalupensis (Spreng.t Magnus Spirantbes vernalis Englem. & Gray Najas marina L. Sporobolus domingcnsis rI'ri n.! Kunth Nephrolepis biserrata (Sw.I Schott Sporobolus junceus tMichx.: Kunth Neptunia pubescens Benth. Stillingia sylvat.ica L. Nymphaca mexicana Zucco Stylosanthes hamata (1,.1 Taub. Oenothera laciniata Hill Tb al assia tcstudinum Banks & Solander ex Koenig Opizia stolonifera Presl Thelypteris interrupta (Wi lld.) Iwatsuki Oxalis corniculata L. Tillandsia fasciculata Sw. Oxalis florida Salisb. Tribulus tcrrcstr-is L. Panicum adspcrsum Trin. Triglochin striata Ruiz & Pavon Panicum chapmanii Vasey Tripsacum dactyloides (1,.1 L. Panicum dichotomiflorum Michx. Typha latifolia L. Panicum hians Ell. Urena lobata L. Panicum rcpens L. Verbena scabra Vahl

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ACKNOWLEDGEMENTS FLOOD, P.G. and HEATWOLE, H., 1986. Coral cay instability and species-turnover of plants at Swain We thank George Avery, William Brumbach, Reefs, Southern Great Barrier Reef, Australia. Journal of Coastal Research, 2, 479-496. John Morrill, Ken Alvarez, and Oliver Hewitt GENTRY, R.C., 1974. Hurricanes in South Florida. for their help. This study was funded in part by In: P.J. Gleason (Ed.), Environments ofSouth Flor­ a grant from the Jessie Smith Noyes Founda­ ida: Present and Past. Memoir 2, Miami Geological tion to the New College Environmental Studies Society, Miami, Florida. Program, and by the Ecological Confederation GODFREY, P.J. and GODFREY, M.M., 1976. Barrier island ecology of Cape Lookout National Seashore of Southwest Florida. Reference specimens rep­ and Vicinity, North Carolina. National Park Service resenting vascular plant species from Cayo­ Scientific Monograph Series No.9, Washington, Costa and Sanibel Islands have been deposited D.C. in the herbarium at the University of South GOLDSTEIN, E.L., 1975. Island biogeography of ants. Florida in Tampa, the herbarium at New Col­ Evolution, 29, 750-762. HARVEY, J., 1979. Beach processes and inlet dynam­ lege of the University of South Florida in Sar­ ics in a barrier island chain, southwest Florida. New asota, and the Gray Herbarium at Harvard College Environmental Studies Publication No. 22, University in Massachusetts. Sarasota, Florida, pp. 1-75. HAVE, A., 1987. Experimental island biogeography: LITERATURE CITED immigration and extinction of ciliates in micro­ cosms. Oikos, 50, 218-224. ABBOTT, I., 1977. Species richness, turnover and HEATWOLE, H. and LEVINS, R., 1973. Biogeogra­ equilibrium in insular floras near Perth, Western phy of the Puerto Rican Bank: species turnover on Australia. Australian Journal of Botany, 25, 193­ a small cay, Cayo Ahogado. Ecology, 54, 1042-1055. 208. HEATWOLE, H. and WALKER, T.A., 1989. Dispersal ABBOTT, I. and GRANT, P.R., 1976. Nonequilibrial of alien plants to coral cays. Ecology, 70, 787-790. bird faunas on islands. American Naturalist, 110, HERWITZ, S., 1977. The natural history of Cayo­ 507-528. Costa Island. New College Environmental Studies ANDREWS, J.H.; KINKEL, L.L.; BERBEE, F.M. and Publication No. 14, Sarasota, Florida, pp. 1-118. NORDHEIM, E.V., 1987. Fungi, leaves, and the the­ HUANG, T.C. and GOODELL, N.G., 1967. Sediments ory of island biogeography.Microbial Ecology, 14, of Charlotte Harbor, southwestern Florida. Journal 277-290. of Sedimentary Petrology, 37, 449-474. BOOMSMA, J.J.; MABELIS, A.A.; VERBEEK, JOHNSON, N.K., 1975. Controls of number of bird M.G.M. and LOS, E.C., 1987. Insular biogeography species on montane islands in the Great Basin. Evo­ and distribution ecology of ants on the Frisian lution, 29, 545-567. islands. Journal of Biogeography, 14, 21-37. LAWLOR, T.E., 1983. The mammals. In: T.J. Case BUCKLEY, R., 1982. The habitat-unit model of island and M.L. Cody, (Eds.I, Island Biogeography in the biogeography. Journal ofBiogeography, 9, 339-344. Sea of Cortez. Berkeley: University of California BURANDT, C.L., Jr. and CAMPINS, R.D., 1986. Col­ Press, pp. 265-289. onization, extinction and species numbers of vas­ MACARTHUR, R.H. and WILSON, E.O., 1963. An cular plants for the island Gran Roque, Venezuela. equilibrium theory of insular zoogeography. Evo­ Journal ofBiogeography, 13, 541-546. lution, 17,373-387. CAIRNS, J., Jr.; DAHLBERG, M.L.; DICKSON, K.L.; MACARTHUR, R.H. and WILSON, E.O., 1967. The SMITH, N. and WALLER, W.T., 1969. The relation­ theory of island biogeography. Monographs in Pop­ ship of freshwater protozoan communities to the ulation Biology No.1, Princeton University Press, MacArthur-Wilson equilibrium model. American NJ. Naturalist, 103, 439-454. MENNEMA, J. and WEEDA, E.J., 1983. Vascular CODY, M.L.; MORAN, R. and THOMPSON, H., 1983. The plants. In: T.J. Case and M.L. Cody (Eds.), plants. In: K.S. Dijkema and W.J. Wolff, (Eds.) , Island Biogeography in the Sea ofCortez. Berkeley: Flora and vegetation of the Wadden Sea islands and University of California Press, pp. 49-97. coastal areas. Rotterdam: A.A. Balkema, pp. 38-50. CONNOR, E.F. and McCOY, E.D., 1979. The statistics MISSIMER, T.M., 1973. The depositional history of and biology of the species-area relationship. Amer­ Sanibel Island, Florida. M.Sc. Thesis, Florida State ican Naturalist, 113,791-833. U ni versity, Tallahassee. COOLEY, G.R., 1955. The vegetation of Sanibel NATIONAL CLIMATE CENTER, 1982. Monthly nor­ Island, Lee County, Florida. Rhodora, 57, 269-289. mals of temperature, precipitation, and heating and DIAMOND, J.M., 1969. Avifaunal equilibria and spe­ cooling degree days 1951-1980 Florida. Climatol­ cies turnover rates on the Channel Islands of Cali­ ogy of the United States No. 81, NOAA, Asheville, fornia. Proceedings of the National Academy ofSci­ North Carolina. ences USA, 64, 57 -63. NILSSON, S.G. and NILLSON, LN., 1978. Species FISHER, J.J., 1968. Barrier island formation: discus­ richness and dispersal of vascular plants to islands sion. Geological Society of America Bulletin, 79, in Lake Mockel n , southern Sweden. Ecology, 59, 1421-1426. 473-480.

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PETHICK, J., 1984. An Introduction to Coastal Geo­ STRONG, D.R., Jr. and REY, J.R., 1982. Testing for morphology. London: Edward Arnold. MacArthur-Wilson equilibrium with the arthropods RYDIN, H. and BORGEGARD, S., 1988. Plant species of the miniature Spartina archipelago at Oyster richness on islands over a century of primary Bay, Florida. American Zoologist, 22, 355-360. succession: Lake Hjalrnaren. Ecology, 69, 916-927. VAN DER MAAREL, E., 1988. Vegetation dynamics: SCHOENER, T.W., 1976. The species-area relation patterns in time and space. Vegetatio, 77, 7-19. within archipelagoes: models and evidence from VAN DER WERFF, H., 1983. Species number, area island land birds. Proceedings of the 16th Interna­ and habitat diversity in the Galapagos Islands. tional Ornithological Congress, pp. 629-642. Vegetatio, 54,167-175. SCHWARTZ, M.L., 1973. Barrier Islands. Strouds­ WILCOX, B.A., 1978. Supersaturated island faunas: a burg, Pennsylvania: Dowden, Hutchinson and Ross. species-age relationship for lizards on post-Pleisto­ SIMBERLOFF, D.S. and WILSON, E.O., 1970. Exper­ cene land-bridge islands. Science, 199, 996-998. imental zoogeography of islands: a two-year record WILLIAMSON, M., 1988. Relationship of species of colonization. Ecology, 51, 934-937. number to area, distance and other variables. In: SIMPSON, B.B., 1974. Glacial migrations of plants: A.A. Myers and P.S. Giller, (Eds.l, Analytical Bio­ island biogeographical evidence. Science, 185,698­ geography, London: Chapman and Hall, pp. 91-115. 700. SMITH, G.B., 1979. Relationship of eastern Gulf of WUNDERLIN, R.P. and HANSEN, B.F., 1985. Native Mexico reef-fish communities to the species equilib­ and Naturalized Vascular Plants of Sanibel and rium theory of insular biogeography. Journal or Captiva Islands. Sanibel-Captiva Conservation Biogeography, 6, 49-61. Foundation Barrier Island Publication, Sanibel, SOLEM, A., 1973. Island size and species diversity in Florida, 52p. Pacific land snails. Malacogia, 14,397-400.

lJ RESUME [1 Examine, en fanction des flares indigenes vasculaircs, une theorie de l'equi librc biogeographique de deux iles barrierc, differerites par leur taille et par leur eloignement du SW de la Floride. Sur Cayo-Costa (5.6km' de surface et Iocalisee a 12.8 km de la terrel, 261 especes ont ete ident.ifiecs. Sur Sanibel 143,6km' de surface et situcc a3,2km de la terreI un inventaire des annees 50 a identifie 266 especes, ce dernier et.ant incomplet par rapport a celui de Cayo-Costa. Un inventaire a indent.ifie de 1965 a 1985 432 especes indigenes sur Sanibel. Cotto difference doublant presque Ie nombre d'especes a Sanibel par rapport a Cayro-Costa est cohercnte par rapport a une theor-ie de I'equilibre qui predit significativement un nombre plus grand d'especes sur une ile plus vaste et plus proche de Ia Terre. Comparee ad'autres etudes de flore insulaire, Sanibel a pu avoir davantage d'especes. Le devcloppernent urbain et I'eparpillement d'especes al logeries qui resulta de la creation d'unc chaussce reliant Sanibel a la terre en 1963 a pu y reduirc Ie nombre de plantes autochtones.-Catherine Bressolier (Ueomorphologie EPliE, Montrouge, France).

n ZUSAMMENFASSUNG Die Gleichgewichtstheorie in Arbeiten zur Biogeographie von Inseln wurde untersucht bei der Aufnahme der einheimischen Gefaflpflanzcnflcrn von zwic Barriercinscln untcrschicdlichcr Gr6J3e und unterschiedlicher Entfernung vom Fest.land Sudwest­ Floridas. Auf der Insel Cayo-Costa, die 5,6 km' fro/3 und 12,8 km vom Fest.land entfernt ist, konnten 261 Arten gefunden werden. Auf der Insel Sanibel, die 43,6 km' fro/3 ist und in 3,2 km Entfernung vom Festland liegt, konnten in eincr Aufnahme in den 50er Johren 266 Arten identifiziert werden. Die vergleichbare Anzahl von Arten, ungeachtet der Unterschiede in Entfernung zum Festland und GroBe der Inscln, wurde auf die Unvollstandigkeit der Florenaufnahme in den 50er Jahren auf Sanibel zuriickge­ fuhrt. Eine Aufnahme, die zwischen 1965 and 1985 durchgefiihrt wurde, erbrachte ein Vorhandensein von 432 einheimischen Arten. Die fast doppelt so groBe Anzahl von Arten auf Sanibel im Gegensatz zu Cave-Costa stimmt mehr mit der Gleichgewicht­ stheorie uberein, die cine signifikant groflerc Anzahl von Artcn auf der frolleren und naher zum Festland gelegenen Insel vor­ aussagt. Vergleicht man die Arten-Gebiets-Relationen von Sanibel und Cayo-Costa mit anderen Studien zur Florenausstattung von Inseln, mii/3te Sanibel eigentlich eine noch gro/3ere Anzahl von Arten aufweisen. Wahrscheinlich hat aber die Stadtentwick­ lung und die Verbrcitung von nicht einbcimischen Arten i m Zugc des Darnmbaus zwischen Sanibel und dem Festland die Anzahl einheimischcr Arten auf Sanibel reduziert.-Ulrich Radtke, Geogrnphisches l netitut. Universitdt Dusseldorf, FB.G.

Journal of Coastal Research, Vol. 6, No.2, 1990