BIOLOGICAL CONSERVATION

Biological Conservation 87 (1999) 341±347

Biological invasions and deletions: community change in south Florida

Elizabeth A. Forys a,*, Craig R. Allen b aEckerd College, Environmental Science, St Petersburg, FL 33711, USA bDepartment of Zoology, University of Florida, Gainesville, FL 32611, USA

Received 28 September 1995; received in revised form 27 May 1998; accepted 2 June 1998

Abstract This study used the endangered and exotic fauna of south Florida, USA, to test three non-exclusive hypotheses about community change. Over one third of the vertebrate fauna of south Florida is either endangered or exotic. We assumed that in the future, many of the currently endangered species will become extinct, while established exotics become more widespread and abundant. Using species' distributions, body mass data, and niche classi®cations, we compare the past (without exotics) and our predicted future (with exotics, without endangered species) vertebrate communities to determine if the future fauna would be on average smaller, more generalized feeders, or if there would be direct niche replacement. The results of the comparisons indicate that none of the hypotheses explained all of the expected changes in the vertebrate fauna of south Florida, and that the future vertebrate fauna of south Florida is likely to be very di€erent from that of the recent past. These changes are symptomatic of the profound ecosystem- level changes occurring here. Hypotheses generated by systemic-level investigations are more likely to increase our understanding of invasions and extinctions. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: South Florida; Endangered species; Exotic species; Invasive species; Community structure

1. Introduction exist in small, fragmented populations from which recovery is unlikely. The state of Florida ranks only after California in the Despite extinctions, the number of vertebrate species number of federally listed endangered and threatened in Florida has been increasing, due to the establishment vertebrate species present (United States Fish and of non-indigenous species. Florida presently has the Wildlife Service, 1991), the majority of these listed spe- largest number of breeding exotic vertebrate species in cies occur within the southern third of the state. This is the continental United States (Oce of Technology particularly signi®cant because of the relative paucity of Assessment, 1993). South Florida's seaports and air- native vertebrate species in this region. Vertebrate spe- ports handle large amounts of cargo and human immi- cies richness declines from north to south in Florida grants, and also a diversity of vertebrate species. Some with decreasing habitat diversity (Means and Simberl- of these animals are shipped purposely for pet-trade, o€, 1987; Forys, unpubl. data). Some of the listed spe- tourist attractions, or livestock; others are inadvertent cies (e.g. bald eagle Haliaeetus leucocephalus) may be imports (Loftus and Hernon, 1984). Most of these spe- capable of recovery and eventual delisting; others, such cies fail to reproduce in south Florida (Wilson and as the Carolina parakeet Conuropsis carolinensis are Porras, 1983), but some are able to establish breeding already extinct. The decline in the majority of endan- populations. Their chance for survival may be enhanced gered vertebrate species in south Florida is linked to by south Florida's subtropical climate; many estab- habitat destruction and fragmentation (Humphrey, lished exotic species may be from similar climates and 1992; Moler, 1992). Most currently endangered species may be `preadapted' to south Florida (Newsome and Noble, 1986). Some of these exotic species are having negative * Corresponding author. Tel.: +1-813-864-7880; fax: +1-813-864- impacts on native species. The feral cat Felis catus has 8382; e-mail: [email protected] increased predation pressure on many small mammals,

0006-3207/98/$Ðsee front matter # 1998 Elsevier Science Ltd. All rights reserved PII: S0006-3207(98)00073-1 342 E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347 birds, and reptiles (Churcher and Lawton, 1987). The comprised of proportionally more herbivorous and Cuban treefrog Osteopilus septentrionalis has been omnivorous species and fewer carnivorous species than linked with the decline of some native hylids (Wilson the historic community. and Porras, 1983). If habitat alteration continues, south Florida will 1.3. Niche replacement hypothesis experience more extinctions. Until dramatic changes in policy and enforcement occur, more exotics will become Some researchers have predicted that the exotic spe- established. The e€ect these changes will have on the cies that succeed are not necessarily the largest or most composition and structure of the future vertebrate generalized feeders, but are simply the ones that can use fauna in south Florida is not known. However, there the same resources as that of the extinct, or declining are a number of hypotheses concerning which native species (Lawton, 1984; Herbold and Moyle, 1986). species are most vulnerable to extinction, and which Because resources may be partitioned among species on exotic species make successful invaders. the basis of body size (Brown, 1975; Brown and For this paper, we assumed that in the future, many Maurer, 1987), they will be replacing species of similar of the currently endangered species will go extinct, while size, diet, and foraging strata. This hypothesis assumes the established exotics will become more widespread that most exotic species have become established after and abundant. We test three non-exclusive hypotheses the decline of the endangered native species or have about community change related to endangered and replaced natives through competitive exclusion. Thus, exotic fauna to predict how the future vertebrate fauna our third prediction is that individual exotic species will of south Florida (with exotics, without endangered spe- replace individual extinct or declining species in cies) will compare to the past fauna. resource use (diet and foraging strata) and body mass.

1.1. Body-mass di€erence hypothesis 2. Methods Species that are the largest members in their guilds (Leck, 1979; Willis, 1980; Pimm et al., 1989), or that We used three terrestrial vertebrate groups in our have high body mass in the community (Laurance, analysis: herpetofauna (reptiles and amphibians), birds 1991), are hypothesized to be extinction-prone because and mammals. Species' distributions were obtained they require large areas for foraging and are more likely from museum records (Allen, unpubl. data), published to be rare (Arita et al., 1990). Species that have smaller accounts, and the Florida Breeding Bird Atlas (Kale et body size may be more likely to be successful invaders al., in press). Only species that had established breeding because they are generally r-selected (Kitching, 1986; populations in at least some natural areas in south Lodge, 1993), more likely to be inadvertently intro- Florida were included in the analysis. We used the duced, and more likely to be human commensals boundaries of the Everglades sub-ecoregion (Bailey, (Myers, 1986; Newsome and Noble, 1986). The predic- 1983), that included the counties of Broward, Collier, tion, therefore is that the average body size of the future Dade, Hendry, Lee, Monroe, and Palm Beach. vertebrate communities of south Florida will be lower A species was considered to be an exotic either if it than the average body size of the historic past or the was introduced to south Florida by humans, or if it was present. a non-indigenous species that had invaded south Flor- ida since European colonization. A species was con- 1.2. Diet di€erence hypothesis sidered to be endangered if it was listed by the state of Florida as being extinct, endangered, threatened, or a Invading species that have the capacity to occupy a species of special concern (Florida Game and Fresh- wide potential niche are predicted to be more likely to water Fish Commission, 1994). A listed subspecies was succeed in their new environment (Arthington and included only if it was the sole subspecies of a species Mitchell, 1986; di Castri, 1990). Species that are highly present in the Everglades sub-ecoregion. specialized in their diet, foraging strategy, or behavior In most cases, vertebrate body masses were collected are more likely to face extinction when habitat is frag- from published accounts or unpublished ®eld data. For mented or altered (Faaborg, 1979; Ambuel and Temple, some herpetofauna, no published records of body mas- 1963). Carnivorous species generally require larger ses were available and body mass was determined by home ranges to meet their metabolic needs (McNab, weighing a sample of alcohol-preserved whole-animal 1983), and are more likely to be a€ected by pesticides museum specimens. Although some weight changes and other contaminants than herbivorous or omnivor- occur during the preservation process, these changes ous species (Douthwaite, 1992; Outridge and Scheu- tend to be <10% (Haighton, 1956; Mount, 1963). hammer, 1993). The second prediction, then, is that the In all cases, adult male and female weights were future vertebrate community of south Florida will be averaged. E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347 343

To test the body-mass di€erence hypothesis, we used Table 1 Number and percentage of non-endangered native, endangered native, median values rather than means because the data was and exotic vertebrate species in south Florida and the average body not normally distributed. Using a Mann-Whitney-U mass and standard error of each group test, we ®rst compared endangered species with native, non-endangered species for each vertebrate group and Taxonomic group N Percentage Median body SE of species mass (g) then exotic species with native species for each group. The diet di€erences and species replacement hypoth- Bird eses both concerned niche use. Niche classi®cation was Non-endangered 98 65 351.1 72.6 Endangered 21 14 890.9 316.8 based on diet and foraging strata based on Eisenberg Exotic 32 21 395.9 166.1 (1981, Appendix 1) for mammals and herpetofauna and Herpetofauna Ehrlich et al. (1988) for birds. Diet was divided into the Non-endangered 43 61 63.9 21.5 same three categories for all three groups, name carni- Endangered 7 10 468.8 365.9 vore, omnivore and herbivore (granivores and frugi- Exotic 21 29 291.6 220.5 Mammal vores). Foraging in mammals was divided into semi- Non-endangered 24 53 6273.7 3627.6 aquatic, terrestrial, and volant; for herpetofauna it was Endangered 10 22 20 208.2 13 138.8 divided into fossorial, terrestrial, and arboreal; and in Exotic 11 25 15 064.9 12 796.3 birds four groups were used, i.e. ground foragers, foli- age foragers, arboreal (soaring) foragers, and aquatic (non-soaring) foragers. Table 2 For each taxonomic group, we compared the pro- Comparisons among the body mass distributions of the vertebrates of portion of herbivores/omnivores and carnivores for the south Florida endangered species with that of the exotic species. We Taxomonic group Median body mass (g) U p used a Fisher's exact test if >20% of the cells in the comparison were <5; otherwise a chi-square goodness- Bird Non-endangered 86.6 of-®t test was used. 1593.0 0.02 The replacement hypothesis was tested by classifying Endangered 355.25 each endangered and invasive species by a diet and Native 109.0 foraging/habitat niche, and then comparing niches 2540.5 0.62 between each invasive species and the endangered species Exotic 131.5 Herpetofauna closest in size, within each vertebrate group. Each exotic Non-endangered 11.1 species was scored as either replacing an endangered 212.0 0.36 species, or not replacing one. More than one exotic spe- Endangered 51.0 cies was allowed to replace a single endangered species. Native 11.1 The proportion of exotic species that replaced endan- 760.0 0.97 Exotic 8.9 gered species was compared to the proportion that did Mammal not replace endangered species among all three taxo- Non-endangered 344.5 nomic groups using a chi-square goodness-of-®t test. 244.0 0.47 Endangered 291.0 Native 267.0 248.5 0.25 3. Results Exotic 3900.0

At least one third of all vertebrate species in south Mann-Whitney U statistic (U) and probability (p) are given for com- Florida are either endangered or exotic (Appendix 1; parisons between the non-endangered natives and the endangered species (upper U and p) and the native species (non-endangered and Table 1). Comparisons suggest that endangered native endangered) and the exotic species (lower U and p). species may have a higher body mass than non-endan- gered ones, although only in the birds was the result signi®cant (p<0.05, Table 2). Exotic species were not parrots, parakeets, and macaws in the exotic faunal found to be signi®cantly smaller than native (endan- components. The results of the mammal and herpeto- gered and non-endangered) species in any of the taxo- fauna comparisons do not support the diet di€erence nomic groups; among mammals they were noticeably hypothesis. Nearly all of the native and exotic herpeto- larger. fauna were classi®ed as carnivorous; few species were The diet di€erence hypothesis was only supported for omnivorous or herbivorous. An equal proportion of the birds. The diet of the exotic avifauna is di€erent endangered and exotic mammals were carnivorous. from the endangered avifauna (Table 3), the majority of The niche replacement hypothesis also was not the latter being carnivorous while most of the exotic birds supported. The majority of the exotic species did not are herbivores. This is mainly due to high proportion of occupy similar niches as the endangered species. 344 E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347

Table 3 Mediterranean gecko Hemidactylis turcicus, black rat The number of carnivorous, omnivorous, and herbivorous endangered Rattus rattus). and exotic species In general, commonly invoked hypotheses explaining Taxonomic Carnivorous Omnivorous Herbivorous 2 d.f. p species' deletions and invasions that are based on body group size and niche were not supported. A similar conclusion

Bird about exotic species was reached by Williamson (1996) Endangered 17 2 3 for a variety of taxonomic groups and habitats. The lit- 20.4 1 0.0001 erature is full of generalizations concerning which spe- Exotic 4 1 27 cies are likely to become endangered and which are Herpeto- likely to invade, but these generalizations are based on fauna Endangered 6 0 1 limited samples and pairwise or generic comparisons. ± ± 1.0000 We suggest that the ratio of native to exotic species may Exotic 17 4 0 be used as a bioassay of community integrity and that Mammals the processes of biological invasion and species dele- Endangered 4 1 7 ± ± 0.6590 tions may be more related to changes in community Exotic 3 5 3 structure than to inherent characteristics of the species involved. We believe that community-level investiga- Chi-square and Fisher's exact tests compared the carnivores to the tions and those that occur at multiple scales (see Ver- herbivores and the omnivores combined. Yates correction of con- tinuity was used in the Chi-square test. Fisher's exact test is an exact meiji, 1996), are more likely to increase our knowledge probability test, without degrees of freedom. of biological invasions and deletions than small-scale taxonomically limited studies. In a thorough study of avian extinctions and inva- Signi®cantly more of the exotic species occupied di€er- sions world-wide, Case (1996) found that the number of ent niches than occupied the same niche as the endan- successful invasions was highly correlated with the gered species ( 2=5.97, d.f.=2, p=0.045). Thirty exotic number of native species extinctions. However, this birds, 17 reptiles and amphibians, and six of the exotic probably indicates, that in areas with abundant human mammals di€ered in niche from the species closest to activity and related landscape change, both extinctions them in body mass. Only four exotic birds, four exotic and invasions are expected. As global change accel- herpetofauna, and ®ve exotic mammals directly erates, we can expect more invasions and extinctions. replaced similar-sized animals in niche. Until we have a better understanding of the phenomena of species invasions and deletions that transcends single species traits and incorporates community and ecosys- 4. Discussion tem level understanding, we should concentrate on managing for intact ecosystems. It is likely that there will be many changes in the future vertebrate fauna of south Florida, but few of the potential changes in the fauna are predictable using the body mass and diet-based hypotheses tested. Extinct Acknowledgements and declining species will not be replaced by ecologically similar species, nor will they be replaced only by small This research was supported in part by a NASA/EOS herbivores and omnivores. grant, number NAGW 2524, a part of the Inter- Some of the results may be explained by habitat a- disciplinary Scienti®c Investigations of the Earth nity. Species that inhabit only a few habitats in a limited Observing System Program, and a NASA grant, num- range (i.e. endemics) are likely to become endangered if ber NAGW 3698, a part of the Terrestrial Ecology their habitat is destroyed (e.g. white-crowned pigeons Program. We thank David Auth and Ken Dodd for Columba leucocephala, Florida Keys mole skink Eume- generously providing their time, data, and assistance in ces egregius, Florida mouse, Podomys ¯oridanus), obtaining weights for the herpetofauna. Doria Gordon, regardless of size or niche. Exotic species that succeed Stephen Humphrey, Michael Moulton, Peter Moyle, may be those that do best in disturbed, urban, or agri- and an anonymous reviewer provided constructive cultural environments (e.g. rock dove Columba livia, comments. E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347 345

Appendix

Table A1 Diet and foraging strata classi®cation and body mass of exotic and endangered vertebrate species in south Florida in order of body mass

Common name Latin name Mass (g) Class Diet a Strata b

AVIFAUNA Grasshopper sparrow Ammodramus savannarum 17.0 Endangered Carn. Ground Cave swallow Hirundo fulva 20.0 Exotic Carn. Arboreal Bachman's sparrow Aimophila aestivalis 20.2 Endangered Herb. Ground House ®nch Carpodacus mexicanus 21.4 Exotic Herb. Ground Seaside sparrow Ammodramus maritimus 23.3 Endangered Carn. Ground Red-whiskered bulbul Pycnonotus jocosus 27.0 Exotic Herb. Foliage House sparrow Passer domesticus 27.7 Exotic Herb. Ground Budgerigar Melopsittacus undulatus 29.0 Exotic Herb. Ground Shiny cowbird Molothrus bonariensis 35.5 Exotic Herb. Ground Spot-breasted oriole Icterus pectoralis 36.0 Exotic Herb. Foliage Red-cockaded woodpecker Picoides borealis 43.6 Endangered Carn. Foliage Brown-headed cowbird Molothrus ater 43.9 Exotic Carn. Ground Loggerhead shrike Lanius ludovicianus 47.4 Endangered Carn. Arboreal Red-crested cardinal Paroaria coronata 48.0 Exotic Herb. Foliage Canary-winged parakeet Brotogeris versicolurus 60.3 Exotic Herb. Foliage Scrub jay Aphelocoma coerulescens 70.0 Endangered Omniv. Ground European starling Sturnus vulgaris 82.3 Exotic Carn. Ground Monk parakeet Myiopsitta monachus 101.0 Exotic Herb. Foliage Dusky-headed parakeet Aratinga weddellii 108.0 Exotic Herb. Foliage Carolina parakeet Conuropsis carolinensis 109.0 Endangered Herb. Foliage Common myna Acridotheres tristis 110.0 Exotic Omniv. Ground American kestrel Falco sparverius 115.5 Endangered Carn. Arboreal Rose-ringed parakeet Psittacula krameri 125.0 Exotic Herb. Foliage Black-hooded parakeet Nandayus nenday 128.0 Exotic Herb. Foliage Eurasian collared-dove Streptopelia decaoto 135.0 Exotic Herb. Ground Ringed rurtle-dove Streptopelia risoria 136.0 Exotic Herb. Ground Red-masked parakeet Aratinga erythrogenys 140.0 Exotic Herb. Foliage White-winged dove Zenaida asiatica 145.0 Exotic Herb. Ground Blue-crowned parakeet Aratinga acuticaudata 152.0 Exotic Herb. Foliage Hill myna Gracula religiosa 192.0 Exotic Herb. Foliage Tricolored heron Egretta tricolor 264.0 Endangered Carn. Arboreal White-crowned pigeon Columba leucocephala 290.0 Endangered Herb. Foliage Orange-winged parrot Amazona amazonica 293.0 Exotic Herb. Foliage Red-crowned parrot Amazona viridigenalis 294.0 Exotic Herb. Foliage Cattle egret Bubulcus ibis 338.0 Exotic Carn. Ground Little blue heron Egretta caerulea 339.5 Endangered Carn. Arboreal Chestnut-fronted macaw Ara severa 353.5 Exotic Herb. Foliage Rock dove Columba livia 354.0 Exotic Herb. Ground Snowy egret Egretta thula 371.0 Endangered Carn. Arboreal Snail kite Rostrhamus sociabilis 371.5 Endangered Carn. Arboreal Yellow-headed parrot Amazona oratrix 426.0 Exotic Herb. Foliage Reddish egret Egretta rufescens 450.0 Endangered Carn. Water Black francolin Francolinus francolinus 450.0 Exotic Herb. Ground Ivory-billed woodpecker Campephilus principalis 511.0 Endangered Carn. Foliage Fulvous whisting-Duck Dendrocygna bicolor 721.0 Exotic Herb. Water White Ibis Eudocimus albus 900.0 Endangered Carn. Water Crested caracara Polyborus plancus 931.0 Endangered Carn. Ground Limpkin Aramus guarauna 1080.0 Endangered Carn. Water Roseate spoonbill Ajaia ajaja 1507.0 Endangered Carn. Water Wood stork Mycteria americana 2376.0 Endangered Carn. Water Muscovy duck Cairina moschata 2685.0 Exotic Herb. Water Bald eagle Haliaeetus leucocephalus 4683.5 Endangered Carn. Arboreal Common peafowl Pavo cristatus 4850.0 Exotic Herb. Ground Sandhill crane Grus canadensis 5089.0 Endangered Omniv. Water

(continued) 346 E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347

Table A1Ðcontd

Common name Latin name Mass (g) Class Diet a Strata b

HERPETOFAUNA Greenhouse frog Eleutherodactylus planirostris 0.6 Exotic Carn. Terrest. Brahminy blind snake Ramphotyphlops braminus 0.9 Exotic Carn. Fossor. Oscellated gecko Sphaerodactylus argus 1.0 Exotic Carn. Arboreal Florida Keys mole skink Eumeces egregius 1.3 Endangered Carn. Terrest. Ashy gecko Sphaerodactylus elegans 1.3 Exotic Carn. Arboreal Rim rock crowned snake Tantilla oolitica 1.3 Endangered Carn. Fossor. Yellowhead gecko Gonatodes albogulari 2.0 Exotic Carn. Arboreal Bark anole Anolis distichus 2.6 Exotic Carn. Arboreal Indo-paci®c gecko Hemidactylis garnotii 2.7 Exotic Carn. Arboreal Mediterranean gecko Hemidactylis turcicus 3.4 Exotic Carn. Arboreal Florida scrub lizard Sceloporus woodi 4.1 Endangered Carn. Terrest. Brown anole Anolis sagrei 5.2 Exotic Carn. Terrest. Puerto Rican coqui Eleutherodactylus coqui 5.3 Exotic Carn. Terrest. Crested anole Anolis cristatellus 8.9 Exotic Omniv. Arboreal Rainbow whiptail Cnemidophorus lemniscatus 13.3 Exotic Carn. Terrest. Cuban treefrog Osteopilus septentrionalis 20.0 Exotic Carn. Arboreal Jamaican giant anole Anolis garmani 27.8 Exotic Omniv. Arboreal North curlytail lizard Leiocephalus carinatus 31.7 Exotic Carn. Arboreal Gopher frog Rana capito 51.0 Endangered Carn. Fossor. Knight anole Anolis equestris 82.1 Exotic Carn. Arboreal Brown basilisk Basiliscus vittatus 99.9 Exotic Carn. Terrest. Giant ameiva Ameiva ameiva 108.9 Exotic Carn. Terrest. Giant toad Bufo marinus 126.0 Exotic Carn. Terrest. Pine snake Pituophis melanoleucus 140.0 Endangered Carn. Fossor. Indigo snake Drymarchon corais 450.0 Endangered Carn. Terrest. Spinytail iguana Ctenosaura pectinata 975.0 Exotic Omniv. Arboreal Gopher tortoise Gopherus polyphemus 2633.9 Endangered Herb. Fossor. Green iguana Iguana iguana 4605.0 Exotic Omniv. Arboreal MAMMALS House mouse Mus musculus 17 Exotic Herb. Terrest. Yellow bat Lasiurus intermedius 17 Endangered Carn. Volant Florida mouse Podomys ¯oridanus 37 Endangered Omniv. Terrest. Masti€ bat Eumops glaucinus 38 Endangered Herb. Volant Long-tailed weasel Mustela frenata 205 Endangered Carn. Terrest. Black rat Rattus rattus 213 Exotic Omniv. Terrest. Norway rat Rattus norvegicus 242 Exotic Omniv. Terrest. Roundtailed muskrat Neo®ber alleni 243 Endangered Herb. Terrest. Eastern woodrat Neotoma ¯oridana 291 Endangered Herb. Terrest. Red-bellied squirrel Sciurus aureogaster 556 Exotic Herb. Terrest. Mink Mustela vison 925 Endangered Carn. Aquatic Fox squirrel Sciurus niger 953 Endangered Herb. Terrest. Black-tailed jack rabbit Lepus californicus 2200 Exotic Herb. Terrest. Domestic cat Felis catus 3900 Exotic Carn. Terrest. Red fox Vulpes vulpes 5600 Exotic Carn. Terrest. Armadillo Dasypus novemcinctus 5600 Exotic Omniv. Terrest. Domestic dog Canis familiaris 6000 Exotic Omniv. Terrest. Coyote Canis latrans 15 500 Exotic Carn. Terrest. Red wolf Canis niger 24 750 Endangered Carn. Terrest. Florida panther Felis concolor 6300 Endangered Carn. Terrest. Hog Sus scrofa 117 256 Exotic Omniv. Terrest. Black bear Ursus americanus 152 000 Endangered Omniv. Terrest.

a Carn.=carnivore, Omniv.=omnivore, Herb.=herbivore. b Fossor.=fossorial, Terrest.=terrestrial. E.A. Forys, C.R. Allen/Biological Conservation 87 (1999) 341±347 347

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