Biodiver.siq and Conservcltion 12: 13 2 1- 1334, 2003. O 2003 Klitwer Arademic Publishers. Prirzted in thr Netherlarzds.

Lizard assemblages in the Vizcaino Biosphere Reserve, Mexico

PATRICIA GALINA-TESSARO*, ARADIT CASTELLANOS-VERA, ENRIQUE TROYO D., GUSTAVO ARNAUD F. and ALFREDO ORTEGA- RUBIO Crrztro de Investigaciones Biológicas del Noroeste (CIBNOR), Mar Bermejo 195, Col. Playa Palo de Santa Rita, Ir1 Paz, Bqja California Sur 23090, Mexico; * ~ u t h o r for corrrspondence (e-rnail: p~alirza@cibizcr.mx; fax: +.52-612-125-3625)

Rcccivcd 22 August 2001; nccepted in revised forni 10 July 2002

Key words: Baja California Sur, Conservation, Lizard assemblages, Vizcaino Biosphere Reserve

Abstract. Lizzd assemblages were surveyed in eight selected habitats in the Vizcaino Biosphere Reserve in Baja California Sur, Mexico. We compared the species composition and relative abundance among habitats, consitiering hahitat characteristics, such as vegetation type, vegetation grouiid coverage, and soil types. Thirteeir lizard species were recorded. The most abundant species in almost al1 habitats was Uta stansburiana, accounting for 59% of al1 observations. Cnemiduphor~~s tigris was the second most abundant species, accounting for 12% of al1 observatioiis. The richest habitat was the rocky lower elevations of the Sierra de San Francisco (iiiiie species). Howcvcr, the habitat with the highest diversity value was Sc;immori's dunes. Implications of our findirigs for lizard conservation in this biosphere reserve are di,cussed.

Introduction

Vi~caino Biosphere Rcscrve (the reserve), in the northern part of the state of Baja California Sur, is the largest biosphere reserve in Mexico and represents an important example of the Sonoran Debert (Breceda et al. 1995). About 20 lizard species (1 7 diurnal) have been reported, six of which are endemic to the peninsula (Galina-Tessaro et al. 2002). Despite the ecological importance of reptiles in deber1 communities, as part of the food chain and as sensitive indicators of relative health and change of the ecosystem (Jones 1986; Grant et al. 1992; Fleet and Autrey 1999), and despitc thc importance of this reserve a\ a protected area, studies of this group in this area are scarce and limited to descriptive observations, distributions, systematic reports, and general biological information (Mosauer 1936; Wiggins 1969; Galina et al. 1991; (kismer et al. 1994). Biogeographical information can be obtained from Grismer et al. (1994) and peninsular works like Grismer and McGuire (1993), Grismer ( U 993, 1994a, b) and Murphy (1983, 1990). Al1 these works have been important to understand species distribution and ecology, but our study represents the first published quantitative survey of lizard assemblages in the reserve.

Structure and composition of herpetofaunal assamblages had been widely studied in differerit habitats (Pianka 1973; Bury 1982; Heatwole 1982; Fauth et al. 1989;

Gonziilez and Alvarez 1989; González et al. 1989), describing the variations among habitats (Pianka 1986; Stockwell and Hunter 1989; Gomez and Anthony 1996; Fitzgerald et al. 1999; Ross et al. 2000).

Effects of habitat, precipitation (James 1994). or cultural impact (Jones 1981) on the structure of some assemblages have been studied. The factor most commonly studied to describe spatial structure of reptile communities is vegetation (Pianka 1967: Germano and Hungerford 1981; Stockwell and Hunter 1989; Towns and Elliott 1996). Aspects of soil or ground surface have been considered in different works (James 1994; Jorgensen and Demarais 1998; Howard and Hailey 1999; Woinarski et al. 1999).

In deserts, the most important factor that has been related with the abundance of lizard species is the spatial heterogeneity of the environment, mainly vegetative heterogeneity or rock outcroppings (Pianka 1967; Heatwole 1982; Jones 1986; Szaro and Belfit 1986; Baltosser and Best 1990). However, Jorgensen and Demarais (1998) considered soil conditions as a critica1 habitat factor for herpetofauna in some areas, independent o€ vegetation.

To achieve the adequate management and conservation of any taxonomic group, it is mandatory to define species assemblages in different habitats (Morrison et al. 1992; Jorgensen and Demarais 1998). The quantification of the distribution and relative abundance of wildlife provides valuable baseline data for future monitoring (Morrison et al. 1995). This information is necessary to construct predictive models of the effects of management practices on species, understanding the ecology of particular areas, and aid land managers and planners in making decisions for conservation or anticipating human activities (Clawson et al. 1984: Towns and Elliott 1996; Fleet and Autrey 1999).

Because of the importante both o€ this unique area and of uriderstanding the role of spatial variability on species richness and distribution for conservation planning (Meliadou and Troumbis 1997), we compare the occurrence and relative abundance of 1:zard assemblages associated with eight habitats in the reserve, considering habitat characteristics, such as vegetation type, vegetation coverage, and soil.

Methods

Stutly ureu

The Vizcaino Biosphere Reserve is located in the center oí" the Baja California Peninsula, between 26'30' and 28'00' N, 115'15' and 112'14' W (Figure 1). It conlprises 2546800 ha under protection, including islands and marine zones (Ortega and Arriaga 1991). The greatest area within the rcserve comprises the southern part of the Vizcaino Desert. The vegetation types were grouped into four principal types: xerophilous scrub (XS) (including Sarcocracicaule and Sarcocaule); halophyte vegetation (HV); microphyllous vegetation (MV); and vegetation of sandy desert (DV) (INEGI 1991). Zoning in the reserve includes two core areas

designed to protect pronghorn (Antilocapra americana) in the west and bighorn sheep (Ovis canadensis) in the east (Figure 1).

On the plains of the reserve, most soils are light-colored and coarse and poorly developed. ln the eastern sierras, the soils are heavy-textured, with bare rock and volcanic outcrops (Maya and Troyo-Dieguez 1991). Activities in the reserve are agriculture, fishery, salt extraction, livestock ranching, and tourism.

Methodology

We selecteo eight sites (Figure 1), representing the four vegetation types (XS, HV, MV, and DV) and three different soil types (coarse sandy, rocky, and fine sandy). The eight study sites or habitats are described in Table 1. Habitats with halophyte vegetation are the least diverse and the sites with xerophilous vegetation are the most diverse.

During April, June, and September 1998, we spent 2 days at each site, performing time-constrained surveys by two teams composed of two persons. Forty-eight surveys were perfonned. The surveys were conducted between mid-morning

Figure l. S-udy locations and zoning in the Vizcaino Biosphere Reserve, Baja California Siir, Mexico. Habitat abb.eviations are as l'ollows: SAF: San Angel Flatlands (plains), Sí ' : Santa Teresita Rancli,VF: Vizcaino Fiatlands (plains), SID: San Ignacio's dunes, T: El Tecolote, SR: San Ramón Ranch, SD: Scammon's dunes, SF: San Francisco.

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Uta

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55 (2

Qa

4.4

(18)

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45 (1

4)

3.15

(13)

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2.38

(10)

1.

95 (

8)

0.08

(<O

S)

989

58.9

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mid

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rus

rigr

is

0.85

(16

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78 (

15)

0.95

(18)

0.

68 (1

3)

0.28

(5)

0.

6 (1

2)

0.48

19)

0.

63 (

12)

209

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ness

(1')

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0.

48

0.42

0.

61

0.49

0.

73

0.78

0.

54

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pson

(II

D)

1.33

1.

73

1.79

2.

59

2.04

3.

21

3.9 1

2.

24

"Num

bers

in

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(09.00-11.00 A.M.) and mid-afternoon (16.00-18.00 P.M.) by each team walking parallel paths about 100 m apart. Five meters separated members of each team, recording al1 lizards observed. Al1 surveys were conducted by the same four persons, walking at the same slow pace to avoid bias in observation skills. At 5 m separation, it is equally likely to detect a lizard in any of the habitats studied and in any o? the seasons. For each observed lizard, we recorded the species, time, and substrate at the first sighting.

The same effort was made at each of the eight sites. The abundance of each species was calculated as the number of observationslpersonlhour and species richness as the total number of species observed in this study (Magurran 1988).

In each habitat, vegetation composition and cover were estimated by the line- intercspt method (Mueller-Dombois and Ellenberg 1974; Etchberger and Krausman 1997). We sampled the habitat only one time during the study because there had been no rain and the vegetation did not change. The percent of rocky soil was estim~ted visually by consensus, taking into account the percentage of bare soil coverid with rocks in 10 1-m2 quadrants.

Species diversity was calculated by Shannon's index (H' = --Ep, ln p,, where p, is the proportion of individuals found in the ith species) and evenness by Shannon's evenness index (E = H'lln S, where S is the total number of species). Lizard evenness is constrained between O and 1.0, the last representing a situation in which al1 species are equally abundant. Dominance or abundance of the commonest specizs, as a diversity measure, was calculated by the reciprocal of Simpson's index (N, =. 1 ID, where D = c ~ , ' ) (Magurran 1988). We use differerit indices, consider- ing that the first is more sensitive to changes in number of spccies and the last is more sensitive to changes in equitability. We used the non-parametric Kruskal- Wallis analysis of variance to compare the diversity and abundance of species among habitats. To quantify the similarities of lizard assemblages between habitats, the Pianka overlap index (Pianka 1973) was calculated for each of the 28 possible pairs of habitats:

w h e ~ e p,, and p,, are the proportions of the ith lizard species. For grouping the habitats, we applied single linkage cluster analysis to standardized data, using Euclidian distance (Pielou 1984) employing Statistica software (Statistica 1994). The higher the Euclidian distance value, the higher is the dissimilarity of habitats.

Results

Gen;ral species composition nnd species diversi9

During the field surveys, 1680 lizards belonging to 13 species were sighted within

Table 3. Piank.3 index (Ojk) of similarity values for tiie frequency of individuals recorded for each pair of species in the eight selected habitats (for habitat identifications see Figure 1) .

-

VF SAI' SD ST S F SR T SID

VF SAF SD ST SF SR 7' SID

Boldface indicates high overlapping vaIues

the eight smdy areas. By habitat, the number of species ranged from six to nine. Species richness was greatest in the San Francisco habitat. and lowest in the San Angel plain and Santa Teresita with six different species (Table 2).

Three 1ii:ards made up 78% of the sample and were recorded in al1 habitats: Uta staasburia~za (59% of al1 observations), followed by Cnemidophorus tigris (12%), and Sceloporus zosteromus (7%). Callisaur~is draconoides made up about 8% of the individuals observed, but it was abundant only in Scammons's dune and San Ignacio's dunes. The abundance of species varied significantly between habitats (Kruskal-Wallis one-way analysis of v'ariance H = 41.59, df = 9, P < 0.001).

Uta stur~sburiana was the most abundant in al1 areas except in San Francisco, where Uri~saurus nigricaudus was the most abundant (63%). U. nigricuudus represents only 4% of al1 observations, yet it was found only in San Francisco. Cnemidop/zorus labialis, Sceloporus orcutti, Sauromalus ater, and Petrosaur~is repens were other species that were exclusive to one habitat. The first was found in Scammon's dunes arid the other three in the San Francisco habitat.

Dipsoscturus dorsalis and Phryno.~oma coronatum were found in seven habitats, but they were low in number, except in the San Ramon habitat. Cnemidophorus hyperythrlds was low in number in five habitats, but was more aburidant in the El Tecolote Iiabitat (26% of the observations in this habitat). Gambelia copei was scarce in habitats with coarse and sandy soils, but absent in Santa Teresita.

Diversiiy values and evenness are shown in Table 2. The values among habitats were similar (H = 7, df = 7, P > 0.05). In most habitats, there are only one or two common species. Scammon's dunes had the highest values, followed by San Ramon. The San Angel 'Flatland' (plain) had the lowest values. In Scammon's dunes, a high Simpson diversity value reflects the similar abundance of four species, in contraat to San Angel Flatlands, where only one species was dominant (Uta stansburiuna) (Table 2).

Lizard as~emblage by hubitat

San Angel Flatland (SAF) - In this habitat, the most abundant species was Uta stansburitlna with 86% of the observations. This species could be seen more

VF

SAF

ST

SR

T

SD

SID

SF

Figure 2. Tree diagram from cluster analysis, illustratiiig similarities in hahitat types. Habitat abbrevia- tions are the same as in Figure 1.

Table 4. Euclidean distance (A) and amalgamation schedule (B) between hzibitats from the cluster analysis (for habitat identifications see Figure 1).

- - -

A VF SAF SD ST SF SR T SID

VF SAF SD ST SF SR T SID

Obj. 1 S AF VF VF VF SID VF VF

Obj. 2 ST SAF SAF SAF SD SAF S AF

Obj. 3 Obj. 4 Obj. 5 Ohj. 6 Obj. 7 Obj. 8

SID SID SF

frequently on sniall stones (<50 cm) and near holes in the afternoon or early in the morning. The second more abundant species was Cnernidophorus tigris (1 1%), whicli was seen active between shrubs. The other four species were seen in low numhers (Table 2).

Sarita Teresita (ST) - Here Uta stansburiana was the most abundant (74%),

followed by Cnemidophorus tigris (13%) and Sceloporus zosteromus (9%). Al1 were seen under shrubs, but U. stansburiana was the only species found on shrubs (<50 cm high) during the hot hours. Sceloporus zosteromus was associated to woodrat nests. Dipsosaurus dorsalis was common in Santa Teresita in open areas (especially on roads) or under shrubs.

Vizcaino flatlands (VF) - Uta stansburiana represented 72% of the observations followed hy Cnemidophorus tigris with 20% of observations. Phrynosoma coronatum was seen slightly more abundant than in the other habitats (3%).

San Ignacio's dunes (SID) - Uta stansburiana was the most abundant (54%). Callisauru.~ draconoides represented 28%, over Cnemidophorus tigris 12%. C. draconoides was seen mainly on dunes (fine sandy soils) and in open spaces, whereas U. stansburiana was mainly under shmbs.

El Tecolate (T) - This area is located near a mountain of Santa Clara Mountains. Uta stansb,nriana represented 65% of the observations followed by Crzemidophorus hyperythrus with 26% of observations and was more abundant than in the other habitats. Cnemidophorus tigris accounted for just 6% of observations.

San Ramon (SR) - It is near San Ramon ranch in the Sierra of Santa Clara. It is a xerophilous vegetation but with coarse-sandy soils. Here there are big trees of torote (Bursera), mezquites (Prosopis) and many Yucca trees. The most abundant species were Uta sransburiana (48%), Sceloporus zosteromus (23%), Cnemidophorus tigris (12%) and Dipsosaurus dorsalis (10%). Most of the observations of Sceloporus zosteromur were on the Yucca trees (until 4 m high).

Scammon's dunes (SD) - The area is located south of the Scammon's Lagoon. Uta stansburiana and Callisaurus draconoides had almost the same number of observations (34 and 32%, respectively), followed by Sceloporus zosteromus (13%) and Cizemidophorus tigris (8%). In this habitat we found in low numbers CnemidopEaorus labialis (lo%), a pensinsular endemic lizard. Sceloporus zos- teromus was associated to woodrat nests under shmbs. C. dracorzoides was observed in open areas on dunes.

San Francisco (SP) - Here many saxicolous species are present: Urosaurus rzigricaudzu, Petrosaurus repens, Sauromalus ater and Sceloporus orcutti. The first was the most abundant species in this habitat (63%), but the others were observed in low numbcrs (Table 2). U. rzigricaudus was observed on different cacti (about 4 m high), or on the ground. P. repens, Sauromalus ater and Sceloporus orcutti were seen on big rocks (about 4 m). The second most abundant species was Cnemidophorus tigris with 22%. The observations of Uta stansuriana were scarse (3%), conipared with the other habitats.

Habitat comparison

The composition of species, according to the frequency overlap values, seems to be similar aniong habitats, except in the San Francisco habitat. Similarity values were high between most of the habitats (0.80-0.99), but San Francisco showed the lowest values (0.08-0.12) (Table 3). Scammon's dunes also showed low values of similarity with the other habitats (0.65-0.73), except with San Ignacio's dunes, where it liad its higher value (0.92).

Single linkage cluster analysis of the relative abundance of lizards (Figure 2) allowed us to distinguish three groups of habitats at the Euclidian distance of 1.69 (Table 4). These groups seem to be more similar in soil types than in vegetation type: habitat with rocky soil (San Francisco), fine, sandy soils (Scammon's dunes and San Ignacio's dunes) and coarse, sandy soils (the other five habitats). The Euclidian distance values obtained by cluster analyses are shown in Table 4, where the higher values represent the sites with higher dissimilarity. These habitats are San Francisco and Scaminoii' S dunes.

Discussion

Thc Vizcaíno Biosphere Reserve encompasses the southem part of the Vizcaíno Desert, which is considered the most floristically depauperate and vegetationally scant area within Vizcaíno Region (Grismcr ct al. 1994), although the number of species and diversity in these assemblages is comparable with other lizard assem- blages in desert habitats (Pianka 1967, 1986; Bury 1982; González et al. 1989; Baltosser and Best 1990). There are 17 diurna1 lizard species reported (Galina- Tessaro et al. 2002), but in the eight selected sites, we recorded 13 species. The species not observcd dunng the censuses were Eurnec~s lagunensis, Elgaria nov sp., Crotczphytus vestigium, and Xantusia vigilis, which have restricted distributions and secretive habits.

In general, the habitats studied which have more diverse vegetation (Pianka 1967; Jones 1986), such as xerophilous and vegetation of sandy desert;, were more diverse in lizard species than halophyte.

Lizard assemblages among these habitats were similar, sharing most of the specjes, except in the San Francisco and Scammon's dune areas, where the presence of some species makes them different. The abundance of some species, such as Cnernidophorus hyperythrus, varied between habitats. In fact, somc species show substrate specificities like Callisaurus draconoides (fine sandy soil), Sauromalus ater? Petrosaurus repens, and Sceloporus orcutti (rocky soils with big rocks), as other authors reported (Mosauer 1936; González et al. 1989; (3rismer et al. 1994).

The presence of species unique to the San Francisco or Scammon's dunes habitats could be explained by the biogeographical history of the area (see Grismer 1994a, b; Grismer et al. 1994). For example, Urosaurus nigricaudus is found only in areas with rocky soil in the eastem part of the Reserve, even though it uses diffcrcnt habitats elsewhere in the Peninsula (see Alvarez et al. 1989).

There were some differences in the overlapping values, especially with Scam- mon's dunes and San Francisco. In the case of San Francisco, the differences could be attributed to the presence of many saxicolous species and the lower number of Uta stansburiana (quite abundant in the other habitats). Scammon's dunes and San 1gn;acio's dunes show great overlapping value, sharing al1 species except Cntmidophorus labialis and Dipsosaurus dorsalis, respectively. Both habitats had a great number of Callisaurus draconoides.

LVe can distinguish with overlapping values and Euclidian distance that the area

of San Francisco is quite different. This area differs in number and species of lizards and soil characteristics (rocky with big rocks, crevice, and cliffs). The area of Scammon's dunes is different by the presence of the endemic Baja whiptail Cnemidophorus labialis. even though San Ignacio's dunes is a similar habitat. Euclidian distances confirm that the San Francisco habitat is the most dissimilar habitat, followed by Scammon's dunes. These differences may be related to the preference of some species to particular substrates and the relative abundance of competing species, but more rebearch is needed.

The Vizciilino Biosphere Reserve was created in 1988 and incorporated into UNESCO's Man and the Biosphere Program (MAB) in 1993 (Gómez-Pompa and Dirzo 1995). Core zoning was created to protect the habitat of species of concern (pronghorn antelope and bighom sheep). The Reserve (Instituto Nacional de Ecología 2000) now includes three world heritage sites (Scammon's Lagoon, San Ignacio Lagoon, and Sierra de San Francisco). The management focus oi the reserve is on sites where the two large mammals and the sea mammals live, leaving other wildlife populations with few management and protection guidelines.

Lizard assemblages in this area include many rare species; some of them are endemic to the Baja California Peninsula and listed in the Mexican Official Norm (NOM-ECOL-059-94) as rare or threatened (Cnemidophorus labialis, Urosaurus nigricau~lus, Sauromalus ater, Callisaurus draconoides, Sceloporus zosteromus, Petrosaurus repens or P. thalassinus, and Gambelia copei or G. wislizeni) and in CITES (1999) (Cnemidophorus hyperythrus and Phrynosoma coronatum).

Cattle and goat ranching are an extensive and poorly regulated activity in the Reserve. Currently, there is evidence of goat overgrazing in some areas, particularly in the Sizrra de San Francisco. Considering that lizard populations are rare and some species sensitive to overgrazing (Busack and Bury 1974; Jones 1979), this may represent a threat for local lizard populations, especially endemic ones. Al1 these facts miist be taken into account in order to protect, restore, or enhance the habitat features for these lizard species inside the Reserve.

Because the Sierra de San Francisco and Scammon's dunes are the habitats showing more endemics and protected lizard species, we suggest that current management plans should be reconsidered to incorporate specific territorial and operational guidelines to protect these species and their habitats. Additionally, the Sierra de San Francisco is considered a biological corridor for reptiles (mainly mesic and saxicolous species) and an important area of endemism (Grismer 1993; Grismer et al. 1994; Galina-Tessaro et al. 2002).

In the San Francisco area, the impact of goat overgrazing on lizard populations and habitat conditions must be evaluated in more detail. Specific recommendations concerning the number of goats and bounded grazing areas must be based on further fieldwork to protect this sensitive habitat and its lizard assemblage.

Acknowledgements

Appreciation is acknowledged to A. Cota, 1. Tobar, 1. Guerrero, A. Valencia, and B. Bareño for providing valuable field assistance and company. Thanks to an anony- mous reviewer for the time and effort devoted to improve an earlier version of our manuscript. CONACYT, SEP, and CIBNOR provided financia1 support. Director V. Sanchez of the Vizcaíno Biosphere Reserve provided help and support and the authcrities of SEMARNAP provided permits for this research. We thank the local people and ranchers who gave us their friendship and hospitality. Thanks to 1. Fogel for editing the text.

Refeaences

Alvariz S., Galina P. and Ortega-Rubio A. 1989. Structure and composition of two lizard communities of thr Cape Kegion Baja California Sur, México. Bulletin of the Maryland Herpetological Society 25: 41-48.

Baltosser W. and Best T.L. 1990. Seasonal occurrence and habitat utilization by lizards iri southwestcrn New Mexico. The Southwesterii Naturalist 35: 3777384.

Brecrda A,, Castellanos A,, Arriaga L. and Ortega A. 1995. Nature conservation in Baja California Sur, México: protected areas. Natural Areas Journal 15: 267-273.

Bury R.B. 1982. Structure and compositiori o i Mojavc Dcsert reptile communities determined with a rc:moval method. In: Scott N.J. Jr (ed.), Herpetological Communities: A Symposium for the Society for the study of amphibians and the Herpetologists League, August 1977. Fish and Wildlife Service, Wildlife Research Report 13, Washington, DC, pp. 135-142. .

Busack S.D. and Bury R.B. 1974. Some effects of off-road vehicles and sheep grazing of lizard populations in the Mojave Desert. Biological Conservation 6: 179-183.

CITES 1999. Appendices 1,II and 111 to the Convention on Inlerrialional Tradc in Endangered Species of \Vild Fauna aiid Flora. International Affairs, US Fish and Wildlife Service.

Clawson M.E., Baskett T.S. and Armbruster M.J. 1984. An approach to habitat modeling for her- petofauna. Wildlife Society Bulletin 12: 61-69.

Etchberger R.C. aiid Krausmun P.R. 1997. Evaluation of five methods for measuring desert vegetation. Wildlife Society Bulletin 25: 604-609.

Fauih J.E., Crother B.I. and Slowinski J.B. 1989. Elevational patterns of species richness, cvenness. and :lbundance of the Costa Rican Icaf-litter herpetofauna. Biotropica 21: 178-185.

Fitzgerald L.A., Cruz F.B. and Perotti G. 1999. Phenology of a lizard assemblage in the dry Chaco of Argentina. Journal of Herpetology 33: 526-535.

Flect R.R. and Autrey B.C. 1999. Herpetofaunal assemblages of four forest types from the Caddo Lake area of northeastern Texas. Texas Journal of Science 51: 297-308.

Galina P., Alvarez-Cárdenas S., González-Romero A. and Gallina S. 1991. Aspectos generales sobre la fauna de vertebrados. In: Ortega A. arid Arriaga L. (eds), La Reserva de la Biosfera El Vizcaino en la Peninsula de Baja California. Publ. no. 4. Centro de Investigaciones Biológicas de Baja California Sur, Baja California Sur, Mexico, pp. 177-209.

Ga'ina-Tessaro P., Grismer L.L., Hollingswordi B. and Ortega-Rubio A. 2002. Distribution and conservation of lizards in the Vizcaíno Biosphere Reserve, Baja California Sur, México. The Southwestern Naturalist 47: 40-55.

Gerinano D.J. and Hungerford C.R. 1981. Reptile population changcs with manipulation of Sonoran Desert shrub. Great Basin Natiiralist 41: 129-138.

Gcmez D.M. and Anthony R.G. 1996. Amphibian and reptile abundance in riparian and upslope areas of five forest types in western Oregon. Northwest Science 70: 109-119.

GGmez-Poinpa A. and Dirzo R. 1995. Reservas de la Biosfera y otras áreas naturales protegidas de

México. Secrztaría dc Medio Ambiente, Recursos Naturales y Pesca, Instituto Nacional de Ecología, Comisión Nacional para el Conocimiento y 1Jso de la Biodiversidad, México.

González A. and Alvarez S. 1989. Hevetofauna de la regióti del Pinacate Sonora, México: un iiiventario. The Southwestern Katuralist 34: 5 19-526.

Gonzále~ A,, Ortega A. and Barbault R. 1989. Habitar partitioning and spatial organizatioii in a lizard community of the Sonorari desert, México. Amphibia-Keptilia 10: 1-1 1.

Grant B.W., Tucker A.D., Lovich J.E., Mills A.M., Dixon P.M. and Ciihhons J.W. 1992. The use of cover hoards in estimating patterris of repiile and amphibian diversity. In: McCulloug D.R. and Barrett R.H. (eds), Wildlife 2001: Populations. Elsevier Applicd Science Puhlications, London, pp. 379-403.

Grisrner L.L. 1993. Ecogeography of the peninsular heigetohuna of Baja California, México and its utility in historical biogeography. In: Wright J.W. and Brown P. (eds). Herpetology of the North Arnerican Deserts. Soutliwestcrn Herpetological Society, Van Nuys, Califuriiia, pp. 89- 126.

Grismer L.L. 1994a. The evolutionaiy and ecological biogeography of the herpetofauna of Baja Cülifornia 2nd the Sea of Cortés, Ph.D. Thesis, Loma Linda University, Loma Linda, California.

Grisrnei- L.L. 1994b. The origin and evolution of the peninsular hcrpetofauna of Raja California, México. Herpetological Natural History 2: 51-106.

Grismer L.L. and McGuire J.A. 1993. The oases of central Baja California, México. Part 1. A preliminary account of the relict mesophilic herpetofauna and the status of the oases. Bulletin u[ ihe Southern California Academy of Science 92: 2-24.

Grisirier L.L., McGuire J.A. and Hollingsworth B.D. 1994. A report on the herperofauna of thevizcaino Peninsula, Baja California, Mexico with a discussion on its biugwgraphic and taxonomic iniplica- tions. Bulletin of the Southern California Academy of Science 93: 45-80.

Heatwole H. 1982. A review of slructuring in herpetofaunal assemhlages. In: Scu~t N.J. Jr (ed.), Herpetolcgical Conimunities: A Symposiurn for the Society fnr the study of aniphibians and the Herpctologists League, August 1977. Fish and Wildlifc Service, Wildlife Research Report 13, Washingloii, DC, pp. 1-19.

Howard K. and Hailey A. 1999. Microhabitat separation anioug diurna1 saxicoluus lizards in Zimhabwe. Journal nf Tropical Ecology 15: 367-378.

Instituto Nacional de Ecología 2000. Programa de Manejo Reserva <le la Biosfera El Vizcaíno, Mixico. Instituto Nacional de Ecología, SEMARNAP, México D.F., México.

INEGI 199'. Carta de Uso del Siielo. Instituto Nacional de Estadística, Geografía e Informática, Aquascalientes, México.

James C.D. 1994. Spatial and teinporal variation in structure of diverse lizard asseiriblagc in arid Australia. In: Vitt L.J. and Pianka E.R. (eds), Lizard Ecology. Historical and Experimental Perspec- tives. Princeton University Press. Princeton, New Jersey, pp. 287-317.

Jones K.B. 1979. Effects of overgraziiig on the lizards of five upper and lower Sonoran habitat types. Cal-Neva Wildlife 1979: 88 -101.

Jones K.B 1981. Effects of grazing on lizard ahundance and diversity in westeril Arizona. The Southaestern Naruralist 26: 107- 115.

Joiies K.B 1986. Amphibians aiid reptiles. In: Cooperrider A.Y., Boyd R.J. and Stuart H.R. (eds). Inventciry of Wildlife Hahitat. 1JS Department of the Interior, Bureau of Land Mariagemeiit Service Center Uenver, Cvlorado, pp. 267-290.

Jorgensen E.E. and Demarais S. 1998. Hcrpetofaunal associated with arroyos and uplarids in foothills of the Ctihiiahuan desert. The Southwestern Naturalist 43: 441 -448.

Magurran A.E. 1988. Ecological Diversity and its Measuremcnt. Princeton IJniversity Press, Princeton, New Jersey.

Maya Y. and Troyo-Dieguez E. 1991. Edafología. In: Ortega A. and Arriaga L. (cds), La Reserva de la Biosfcra El Vizcaino en la peninsula de Baja California. Publ. no. 4. Centro de lnvcstigaciones Biol6:icas de Baja California Sur, Baja California Sur, México, pp. 117-130.

Meliadou A. and Troumbis A.Y. 1997. Aspects of Iieterugcncity in the distrihution of diversity of the Europeari herpctofauna. Acta Ecologica 18: 393-412.

Morrisor M.L., Marcot B.G. and Mannan R.W. 1992. Wildlife-Habital Relatioriships, Concepts and Applucations. The University of Wisconsin Press. Madison, Wisconsin.

Morrisoii M.L., Block W.M., Hall L.S. arid Stone H.S. 1995. Habitat characterislics and monitoring of

iamphibians and reptiles in the Huachuca Mountains. Arizona. The Southwestern Naturalist 40: (85- 192.

Moaauer W. 1936. The reptilian fauna of sand dunes areas of the Vizcaino Ilesert and of northwestern Lower California. Occasional Paper of the Museum of Zoology University of Michigan 329: 1-21.

Mueller-Dombois D. and Ellenberg H. 1974. Aims and methods of vegetation ecology. John Wiley and Sons, New York.

Murphy R. 1983. Paleobiogeography and genetic differentiation of the Baja California herpetofauna. Occasional Paper of the Museum of Zoology University of Michigan 137: 1-48.

Murphy R. 1990. Plate tectonics, peninsular effects and the borderlands: herpetofauna of Western North mer ica . In: Ganster P. and Walter H. (eds), Environmental Hazards and Bioresource Management in the United States-Mexico Borderlands. Latin American Center Publications, University of Califor- nia, Los Angeles, California, pp. 433-457.

Ortega A. and Arriaga L. (eds) 1991. La Reserva de la Biosfera 'El Vizcaíno' en la Península de Baja California. Publ. no. 4. Centro de Investigaciones Biológicas de Baja California Sur, Baja California Sur, México.

Piarika E.R. 1967. On lizard species diversity: North American flatland deserts. Ecology 48: 333-351. Piaiika E.R. 1973. The structure of lizard communities. Annual Review of Ecology and Systematics 4:

53-74. Piaiika E.R. 1986. Ecology and Natural History of Desert Lizards. Princeton University Press, Princeton,

h'ew Jersey. Pielou E.C. 1984. The lnterpretation of Ecological Data, a Primer on Classification and Ordination. John

Wiley and Sons, New York. ROSS B., Fredericksen T., Ross E., Hoffman W., Morrison M.L., Beyea J. et al. 2000. Relative abundance

and species richness of herpetofauna in forest stands in Pennsylvania. Forest Science 46: 139-146. Staiistica 1994. Statistica for Windows. StatSoft, Inc., Tulsa, Oklahoma. Stockwell S.S. and Hunter M.L. Jr 1989. Relative abundance of herpetofauna among eight types of Maine

peatland vegetation. Journal of Herpetology 23: 409-414. Szaro R.C. and Belfit S.C. 1986. Herpetofaunal use of a desert riparian island and its adjacent scrub

habitat. Journal of Wildlife Management 50: 752-761. Towns D.R. and Elliott G.P. 1996. Effects of habitat structure on distribution and abundance of lizards at

Pukerua Bay, Wellington, New Zealand. New Zealand Journal of Ecology 20: 191-206. Wiggins I.L. 1969. Observations on the Vizcaíno Desert and its biota. Proceedings of the California

Academy of Science 4th Series 36: 317-346. Woinarski J.C.Z., Fisher A. and Milne D. 1999. Distribution patterns of vertebrates in relation to an

extensive rainfall gradient and variation in soil texture in the tropical savannas of the Northem Territory, Australia. Joiirnal of Tropical Ecology 15: 381-398.