Threatened species, a re-evaluation of the statusof eight endemic plants of the GalaÂpagos

ANDREÂ MAUCHAMP*, IVAN ALDAZ, EDWIN ORTIZ andHUGO VALDEBENITO 

Charles Darwin Research Station, GalaÂpagos, Casilla 17-01 3891, Quito, Ecuador

Received 3 January 1996; revised and accepted 16 October 1996

Although still in relatively good condition, the Gala pagos Archipelago su�ers from increasing hu-

man pressures. Apart from direct actions like hunting and logging, endemic plants and animals arethreatened by introduced species, and in many cases the present status of the populations is notknown. The conservation status of eight plant species considered endangered was studied from

literature and ®eld surveys and the main threats were determined. Each of the eight species isendemic to only one island but in some cases is also present on nearby islets. Of these eight species,one is considered extinct, one critically endangered, and the others su�er various levels of threat. Asin all island systems of the world, the main threats are introduced organisms, both plants and

animals. The extinct species probably disappeared owing to invasion by Lantana camara, one of themost aggressively invasive plants of the islands, and the most endangered species is threatened bygoats. The remaining species seem to be regenerating well and we can expect positive results from

protection e�orts. Today, only one of the eight species bene®ts from a direct protection action.

Keywords: Island biology; introduced species; Gala pagos; conservation; endangered plants.

Introduction

The Gala pagos Islands are famous for the role they played in the genesis of Darwin'sOrigin of Species (1885) and for their striking examples of island evolutionary processes,radiations such as the Darwin ®nches (Grant, 1986), the giant tortoises, or the compositegenus Scalesia, endemic to the Gala pagos (Eliasson, 1974). When Darwin reached theGala pagos in 1835, the islands were still nearly pristine, although whalers and buccaneershad already had an impact on the ¯ora and fauna through the introduction of alien speciesand hunting of native animals. Goats were introduced to the Gala pagos with colonizationand are now destroying the ecosystems of the islands (Brockie et al., 1988). Cultivatedplants were introduced by the ®rst permanent resident about 1807, and a number of alienplants were already present by the time of Darwin's visit (Hooker, 1847).

The harsh conditions on the islands, scarce freshwater, isolation, distance from maincommercial routes, and absence of important resources delayed permanent human set-tlement and thus somewhat protected the islands. The Archipelago was named Ôa labo-ratory of evolution', emphasizing its natural and scienti®c assets, contrasting with therelatively low economic value. Conditions have now changed. Technology helped humansto settle more easily and a new resource appeared±tourism. Related impacts increased

*To whom correspondence should be addressed: Station Biologique de la Toor du Valat, Le Sanbuc. 13200 Arles,France Present address: Universidad San Francisco de Quito, Casilla 17-12 841, Quito, Ecuador

0960-3115 Ó 1998 Chapman & Hall

Biodiversity and Conservation 7, 97±107 (1998)

dramatically. In oceanic island systems, human impacts are strong and can be very rapid.Pimm (1987) underlines the fact that these island ecosystems are particularly fragile whenconfronted by biological invasions or human-made disturbances. This sensitivity is partlydue to structural characteristics of island communities (Pimm, 1987; Loope et al., 1988),such as the absence of large groups of species, and missing components like large herbi-vores or carnivores (Simberlo�, 1995). Communities are simple, often strongly dominatedby one or two species. There are few competitors and many predators are missing.Moreover, as the evolution and selection of species occurred without humans' presence,their arrival brings a series of related disturbances which are very disruptive.

The native ¯ora of Gala pagos is composed of 550 species, 32% of which are endemic.This level of endemism is comparable to rates for other oceanic islands such as La Re -union (33%; MacDonald et al., 1991) but is lower than rates for more isolated and mucholder islands such as Hawaii (89%; Wagner et al., 1990) or Juan Fernandez (60%; Stuessyet al., 1991). Since 1970, more than 10 plant species per year have been introduced to theislands accidentally or for agricultural or ornamental purposes, and alien plant speciesnow reach 45% of the total ¯ora. The proportion of naturalized species is 42% (Mau-champ, 1997). Some of these are very aggressive and have invaded extensive areas of theGala pagos National Park, thus threatening the native vegetation (Brockie et al., 1988;Scho®eld, 1989). As in other island systems, introduced animals are the other main threat(Stone and Stone, 1989; Parkes,1990).

During a workshop held in the islands in 1987, a list of 20 threatened plant taxa wasestablished for the Gala pagos, among which 12 were endemic (Lawesson et al., 1987;Lawesson, 1990). All were considered rare (Adsersen, 1989). For most species, the con-servation status was deduced from previous but incomplete ®eld work and it appearednecessary to complete the available data in order to implement conservation actions and todetermine whether these species were naturally rare or actually threatened by an externalfactor. Studies of the exact population status of eight of these species were performedbetween 1992 and 1995 on four islands: Scalesia atractyloides Arn. (2 subspecies) onSantiago, Lecocarpus darwinii Adsersen and Calandrinia galapagosa St. John on SanCristo bal, Alternanthera nesiotes Johnston, Psychotria angustata Anderss., Lippia salici-folia Anderss., and Linum cratericola Eliasson on Floreana, and Lecocarpus lecocarpoides(Robins. and Grenm.) Cronq. & Stuessy, on EspanÄ ola. Each of these species is endemic toa single major island.

Materials and methods

Sites and species

The Gala pagos Islands are in the Paci®c Ocean about 1000 km from the South Americancoast. The 13 main islands and numerous islets (a total of 121; Snell et al., 1996) cover atotal land area of 7850 km2 within a 45 000 km2 area of sea. Santiago, a central island, hasan area of 580 km2, and the highest point is 915 m. Floreana, the southernmost island ofthe Archipelago, measures 170 km2 and has a maximum elevation of 640 m. San Cristo bal,in the east of Gala pagos, covers 552 km2 and rises to 730 m, and ®nally EspanÄ ola, locatedbetween the last two, has a 58 km2 surface area and an elevation of 200 m.

Scalesia atractyloides Arn. vars. atractyloides and darwinii (Hook F.) Eliass. is anAsteraceae endemic to Santiago Island. The whole genus Scalesia is endemic to the Ar-chipelago, with 15 species (19 taxa including varieties and subspecies) (Eliasson, 1974;

98 Mauchamp et al.

Hamann and Wium-Andersen, 1984). Certain species, like S. pedunculata, have a widedistribution; others are restricted to very small areas (Adsersen, 1990). S. atractyloides waslast found in the wild by H. Adsersen in 1990 on cli�s of two old volcanoes on the westcoast of Santiago (personal communication), but specimens exist in the Botanical Gardenof Copenhagen (Hamann, personal communication). Lecocarpus, another endemic genusin the family Asteraceae, was revised by Adsersen (1980). Its three species are consideredvulnerable or endangered. Lecocarpus darwinii Adsersen is present only on San Cristo baland is endangered. Lecocarpus lecocarpoides (Robins. & Grenm.) Cronqu. & Stuessy isendemic to EspanÄ ola and was reported from islets in Gardner Bay. Its populations wereprobably strongly a�ected by goats, which were ®nally eradicated from EspanÄ ola in 1978(Hoeck, 1984). Calandrinia galapagosa St. John (Portulacaceae) was found in the arid andtransition zones of San Cristo bal. It is a shrub 1.5 m high, with succulent leaves and stems,which make it very attractive to goats. Alternanthera nesiotes Johnston (Amaranthaceae)from Floreana Island is a prostrate perennial plant found in the arid zone from the coastto 200 m. The genus Alternanthera includes 13 species (6 endemic) and 19 taxa, of which 12are endemic. Both Psychotria angustata Anderss. (Rubiaceae) and Lippia salicifoliaAnderss. (Verbenaceae) characterize the humid zone of Floreana, from 250 to 500 m. Theformer is a shrub 2±3 m high, the latter a tree 3±5 m high. Each genus has two endemicspecies in Gala pagos. Linum cratericola Eliasson (Linaceae) is a subshrub 50 cm high fromFloreana. It was described from only 2 sites in the center of the island, where the typespecimen originated (Eliasson, 1968). It had not been found for the last four years.

Methods

A systematic review of all the available information on the eight species under study wasdone to orient ®eld work. The literature, unpublished Charles Darwin Research Station(CDRS) reports of ®eld surveys, and CDRS Herbarium specimens were used to rebuildmaps of the former distribution of each species. On each of the three islands, sites wherethe species had been found were visited. We also surveyed other areas that had similar soilconditions, exposure, or vegetation types, and that were potential sites for the species. Foreach population found, we made inventories of the vegetation of the area. Total surfacearea and number of plants were measured for small populations. In larger ones, weestimated these ®gures using randomly set quadrants, 25 to 100 of 4 to 64 m2 according tothe density. All the individuals found were classi®ed as seedlings or adults according to sizecriteria: less than 15 cm total diameter for individuals of A. nesiotes, less than 1 m high forL. salicifolia, 0.8 m high for Psychotria angustata, less than 1 cm basal diameter forC. galapagosa and L. darwinii, and less than 5 mm basal diameter for L. lecocarpoides wereconsidered seedlings; none of these individuals had ¯owered. For C. galapagosa andL. lecocarpoides, we measured the basal diameter and height of all the plants from themain populations. Finally, in all the sites visited, we described the possible threats for thevegetation, sought for animal damage, and evaluated the cover of alien plant species.

If not speci®cally mentioned, nomenclature follows Lawesson et al. (1987). For eachspecies other than the eight species under study, N, E or I indicate whether they are Native(de®ned as naturally present on the islands and found in other places), Endemic to theGala pagos or Introduced by humans.

GalaÂpagos threatened plants 99

Results

The current status of the populations of the eight endemic species is presented in Table 1and Fig. 1. For three species, C. galapagosa, S. atractyloides, and L. cratericola, there wereimportant reductions of the number of populations during the last 10 years (Table 2).Only two C. galapagosa populations could be found (plus a few individuals on cli�s on theislet Leo n dormido, north of San Cristo bal), only ®ve plants of S. atractyloides wererecently found by park wardens, and none of L. cratericola (Fig. 1a, b and c). For the ®rsttwo species, goats are the threat. Santiago has a population of 60 000 to 80 000 goats(unpublished analysis by W. Pittro� based on data by L. CalvopinÄ a), which have stronglya�ected vegetation cover in arid coastal areas and totally destroyed it in the moisterhighlands. The succulent character of C. galapagosa makes it particularly attractive togoats. One large population of this species (Fig. 1b) was protected by a fence in 1993,including about 500 plants in a 3500 m2 area. During this study, we tagged and measured466 plants in the exclosure; the others, growing on cli�s, were not accessible. The sizedistribution (Fig. 2a) shows a slow regeneration; plants less than 1 cm diameter consti-tuted a third of the population. During this survey, we also found small populationsrestricted to inaccessible crater walls in the northeast of the island. These had a total ofabout 250 adult plants and were probably the remnants of a single former population.They were almost inaccessible to goats and thus naturally protected. The other mainspecies found in the site were L. darwinii, Psidium galapageium (E), Croton scouleri (E),and Zanthoxylum fagara (N). The sites where Scalesia atractyloides had been found pre-viously are small scoriaceous craters that show clear signs of goat damage to the plants,and erosion (Fig. 1a). The ®ve plants found by the park wardens are located on cli�s in-accessible to goats in a crater of reddish scoriaceous lava similar to the other two sites. Thescarce vegetation was dominated by Bursera graveolens (N), Erythrina velutina (N), Sar-costemma angustissima (E) and a few plants of Galvezia leucantha ssp. pubescens (E)restricted to cli�s. The site where L. cratericola had previously been described (Fig. 1c) isnow completely covered by the invasive Lantana camara (cover >80%) and we could not®nd any L. cratericola remaining.

On Floreana, the total population of A. nesiotes was estimated to be 4500 individuals(Table 1). The habitat of the species was the arid zone on cones of brown basaltic scoria(McBirney and Williams, 1969) abundant in Floreana and very susceptible to erosion after

Table 1. Current status of the populations of the species under study. No population of Linum

cratericola could be found. It is considered extinct

Island

Number of

populations

Estimated

area (m2)

Adult

number

Seedlingsto adult

proportion

Adults ofthe largest

population

Scalesia atractyloides Santiago 1 100 5 ± 5Alternanthera nesiotes Floreana 5 12000 4500 0.6/1 3000Psychotria angustata Floreana 3 2000 250 1/1 200

Lippia salicifolia Floreana 10 55000 2600 0.5/1 950Lecocarpus darwinii S. Cristo bal 6 24000 26500 0.4/1 8400Calandrinia galapagosa S. Cristo bal 3 15000 450 0.5/1 300

Lecocarpus lecocarpoides EspanÄ ola 4 1000 150 2.3/1 100

100 Mauchamp et al.

goats removed the vegetation cover. All the populations are equally threatened by thiscombination of factors. The species was found in open areas characterized by prostrate orherbaceous species such as Tiquilia galapagoa (E), Boerhaavia caribaea (N), and Aristidasubspicata (E), a few trees with goat damage to the trunks (Bursera graveolens and Acaciamacracantha both native), and the endemic shrub Lantana peduncularis.

Figure 1. Distribution of the eight studied species: (a) 1 Scalesia atractyloides on Santiago, (b) 2Calandrinia galapagosa and 3 Lecocarpus darwinii on San Cristo bal where the underlined population

was protected by a fence, (c) 4 Linum cratericola and 5 Lippia salicifolia, (d) 6 Alternanthera nesiotesand 7 Psychotria angustata on Floreana and (e) 8 Lecocarpus lecocarpoides on EspanÄ ola. The circlesindicate previously described but now locally extinct populations. Scales are 50 km for the general

map, 5 km for the others, 100 m contour lines are shown.

GalaÂpagos threatened plants 101

Table2.Conservationstatusandmain

factorsofthreatforeightendem

icplantsin

Gala pagos

Species

Island

Reductionof

populations

Origin

ofthreat

Regeneration

IUCN

Red

Data

Bookcategories:

new

status

Linum

cratericola

Floreana

Number

Lantanacamara

None

EX,Extinct

Scalesiaatractyloides

Santiago

Number

Goats

None

CR,CriticallyEndangered

Alternantheranesiotes

Floreana

Size

Goatsanderosion

Good

EN,Endangered

Psychotria

angustata

Floreana

Size

PigsandLantanacamara

Good

EN,Endangered

Lecocarpuslecocarpoides

Espan Äola

Number

andsize

Goats

Good

VU,Vulnerable

Lippia

salicifolia

Floreana

Size

P.guajava

andL.camara

Medium

VU,Vulnerable

Calandrinia

galapagosa

SanCristoÂbal

Number

Goats

Medium

LR,cd,Lower

risk,

conservationdependent

Lecocarpusdarwinii

SanCristoÂbal

Possiblysize

Erosionandgoats

Good

LR,nt,Lower

risk,near

threatened

102 Mauchamp et al.

We found 10 populations of L. salicifolia, and 65% of the plants were in one bigpopulation in good condition, on the Cerro de Pampe Bola. In this area, we found a fewadult trees of the introduced guava, Psidium guajava, which are a serious threat for thefuture. Among the other nine populations, four were threatened by Lantana camara (I),and in two cases the trees were in poor condition. On average, the recruitment of seedlingswas high (Table 1). In all the sites, the vegetation was dominated by Croton scouleri (E),Zanthoxylum fagara (N), Macraea laricifolia (E) and Cordia leucophlyctis (E). For threesites, the endemic tree Scalesia pedunculata was also abundant.

P. angustata was a very rare species. The biggest population we could ®nd had about200 adult plants and was located in the crater of the Cerro Pajas, an area carefullyprotected by the Gala pagos National Park Service, who eliminated all the invasiveLantana camara (I) plants in 1995. The Psychotria population was in a good condition.The second largest population was much smaller and clearly su�ered damage by feral pigs.We observed many adult and small plants destroyed by these animals. This populationprobably su�ered a recent reduction in size and is very vulnerable. A third and smallerpopulation was inaccessible to animals and in good condition. The sites were dominatedby Croton scouleri (E), Zanthoxylum fagara (N), Cordia leucophlyctis (E), Macraea la-ricifolia (E), and Ctenitis sloanei (N) except for the Cerro Pajas, which is a Scalesiapedunculata (E) woodland.

In San Cristo bal, the populations of L. darwinii were large and regenerating well. Thegoats seemed to debilitate the plants, which are shallow-rooted and thus sensitive to erosion,though this problem does not seem to threaten this species greatly. The most important

Figure 2. Basal diameter frequencies of (a) the largest population of Calandrinia galapagosa in San

Cristo bal island (466 plants in an exclosure) and (b) Lecocarpus lecocarpoides on Osborne, an isletnorth of EspanÄ ola (290 plants). The upper limit of the classes (mm) is given. The plants less than 10mm basal diameter were considered seedlings.

GalaÂpagos threatened plants 103

species in the studied sites were Croton scouleri (E), Bursera graveolens (N), Psidium gala-pageium (E), and Alternanthera ®lifolia (E).

Lecocarpus lecocarpoides was found at a single site on the north of EspanÄ ola calledPuerto manzanillo, where it had been previously described, and on three islets in GardnerBay (Osborne, Gardner and West islet, Fig. 1e). On the main island, 11 ¯owering plantswere found, ranging in size from 6 to 16 mm diameter, and from 20 to 40 cm high, as wellas 140 seedlings. The largest population was on Osborne islet, with 85 adult plants and205 seedlings. The largest plant we could ®nd was 1.5 m high and 50 mm diameter, onGardner islet.

Discussion and conclusions

This study led to some changes in the classi®cation of status of the species according to thecategories approved by the 40th Meeting of the IUCN Council (1994). Of the eight speciesstudied, all initially classi®ed as endangered, one can be considered extinct, one criticallyendangered (and present in a botanical garden), and one at only low risk (Table 2). Apartfrom L. darwinii (and the extinct Linum cratericola), all these species can be consideredrare, although some of them might not have always been rare. A. nesiotes, L. salicifolia,and C. galapagosa were probably much more common before the presence of humans onthe islands and are rare on the basis of conservation criteria. Others, like S. atractyloides,L. cratericola or P. angustata, have probably always had small populations and are rare onthe basis of geographical and biological criteria (Batiano� and Burgess, 1993). These rarespecies are not necessarily more prone to extinction than others and it can be argued thatthey were selected for `rareness' (e.g. not su�ering from inbreeding). Thus the size of theminimum viable populations may be rather small and extremely dependent on the species(Soule , 1987). None of the species under study is an obvious keystone species for thecommunity where it is found and although information is lacking on speci®c relations withpossible host invertebrates, their extinction would probably have no major ecologicalimpact on the ecosystems. For example, A. nesiotes is a creeping plant that protects the soilfrom erosion, but it does not play a more important role than any other low herbaceousplant of the sites. However, an endemic of the Gala pagos present on only one island is animportant contribution to global biodiversity. The small populations are fundamentalevolutionary elements that may be the basis for the founder e�ect and allopatric specia-tion, evolutionary processes that give birth to new species, and this justi®es e�orts for theirprotection.

The introduced shrub Lantana camara is possibly the direct cause of the extinction ofL. cratericola, although we could not determine whether it was through competition forlight or nutrients, or allelopathy. S. atractyloides became extremely rare in the wild be-cause of goats. Fortunately, the species is present in the Botanical Garden in Copenhagen(Denmark), represented by eight individuals from the same mother plant (Hamann, per-sonal communication). Moreover, seeds were collected from the ®ve adult plants and aproject for reintroduction is being developed. This gives the Gala pagos up to three speciesextinct in situ ± Blutaparon rigidum from Santiago, Sicyos villosa and L. cratericola fromFloreana. This is still less than 1% of the native and endemic ¯ora. However, otherendangered species must be studied and the recent increase of goats in some areas such asDarwin and Alcedo Volcanoes on Isabela Island, or on Santiago, may lead to furtherextinctions. Five species are endemic only to Santiago, one has been long extinct (Bluta-

104 Mauchamp et al.

paron rigidum), only ®ve plants of Scalesia atractyloides are left, and the current status ofthe other three (Mollugo crockeri, Chrysanthellum fagerlindii and Verbena sedula var.darwinii) is not known. In fact, most of the endemic ¯ora of Santiago could be considered`threatened'.

P. angustata is a very rare species, but we found one additional population not pre-viously reported (Lawesson, 1990). Feral pigs are an important threat for the species andthey have to be controlled to avoid local extinctions. Moreover, pigs cause importantdamage to other species, plants or animals (Harris, 1984; Hoeck, 1984), and a�ect thesoils. L. salicifolia was previously used by the inhabitants of Floreana for construction(Lawesson, 1990), which could have led to reduction of its populations. Lawesson men-tions a `maximum of 50 adult trees' found in 1987, whereas we found 10 populations andabout 2600 adult trees. Most populations had not been included in the former evaluation.The numerous seedlings we observed show that the population status is improving. Themain threat is now the risk of invasion by the alien species Psidium guajava (I). Thepopulations of L. darwinii are extensive and regenerating well; moreover, the goat pressureon San Cristo bal has decreased during recent years owing to hunting by the local popu-lation and the recent accidental introduction of a porcine fever. This species is vulnerablebut not directly threatened. In most cases, we observed that this species is regeneratingwell. When the threat is diminished, there is recuperation of the populations, althoughsometimes it is very slow. Adsersen (1980) mentions that the EspanÄ ola population ofL. lecocarpoides had three plants in 1974, six in 1977, and we found, in 1995, 11 repro-ductive individuals and 140 seedlings. This increase probably results from the eradicationof goats (started in the late 1970s and ®nished in 1978; Hoeck, 1984). However, thereseems to be a bottleneck between the seedling and adult stages and the recovery of thepopulation may be very slow, making the small EspanÄ ola population still very vulnerable.These observations are consistent with studies made on other small islands after theeradication of feral animals (Hamann, 1979), where there is good regeneration, althoughsome species that had reached very low levels had further di�culties. This was also ob-served on Santiago Island in permanent exclosures established in 1975 and 1993. Thisobservation supports the hypothesis of the pioneer characteristics of the island ¯ora, andparticularly the capacity of its species to form viable populations from reduced numbers ofindividuals (®rst observed by Darwin; Porter, 1976). The observation that most Gala pagosplant species are self-compatible (McMullen, 1987) also supports this hypothesis.

These eight threatened and vulnerable plant species clearly illustrate the range of im-pacts caused by human presence on islands. The extinct and critically endangered specieswe recorded here were previously rare, known from only one or two sites, and we cannotexclude the possibility that other rare species may have become extinct in the Islands. Inparticular, islands that have or had dense goat and pig populations, such as Santiago orCerro Azul volcano on Isabela, are candidates for high rates of endangered species, andwork is needed to update the endangered species lists. In many cases, it is not too late,although the decrease in population size may have dramatically reduced the genetic di-versity within the species, and it is di�cult to evaluate the long term consequences of sucha loss. Conservation e�orts must be made immediately, if there is to be eventual ecologicalrestoration (Towns et al., 1990; North et al., 1994). C. galapagosa is so far the onlyendangered species that was speci®cally protected with an exclosure, and the result wasvery encouraging. In a protected area as large as the Gala pagos, the objective is not theconservation of the species per se. The maintenance of the ecological and evolutionary

GalaÂpagos threatened plants 105

processes is at least as important and the spatial distribution of the populations, also apart of the biodiversity, determines future evolution. The small populations of the speciesstudied here have to be protected for the Gala pagos National Park to ful®l its objectives.

Acknowledgements

Special thanks are due to the sta� of theGala pagos National Park Service and the CDRS, aswell as to all the persons who provided information about the species under study. G. Davis,O. Hamann, C. Blanton, H. Van derWer�made useful comments on early drafts.We thankM. Arsiniegas for helping complete the data for one of the species, TAME for providingreduced air fares to Gala pagos, and Monsanto for support for conservation of the ¯ora inGala pagos. The study was supported by the USAID grant 518-0107-G 112700 and Euro-pean Community B7-5040/91/037. This is contribution number 551 of the Charles DarwinFoundation for the Gala pagos Islands.

Addendum

Since the ®nalization of this work, about 25 individuals of Linum cratericola were found byA. Tye, presently resident botanist at the CDRS (Tye 1997). A fence was estabilishedaround the site and further conservation actions will be taken in the near future. Thespecies hence actually escaped from extinction but is still Critically Endangered.

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