Brazilian Archives of Biology and Technology, v.42, n.2. p. 175-180, 1999

Changes in Abundance on Protected Versus Grazed Desert Scrub in Baja Sur,

Romero-Schrnidt Heidi L*.and Alfredo Ortega-Rubio Centro de Investigaciones Biologicas del Noroeste. Apartado Postal No 128, La Paz, 23000, Baja Califomia Sur, México

ABSTRACT

The changes in abundance of three of were detennined and compared between gr~edand ungrazed desert scmb near La PG, in the Cape Region. Baja California Sur, Mexico, from Apd 1992 to March 1993. A total of 54 censuses were takerf of these species over two transect systems, one inside and one outside livestock enclosure. nigricaudus were negatively aflected by the gmzing activities, but Uta stansburiona exhibited un apparently positive effect by such activities. Cnemidophom hyperythrus population appurently showed no eflect by the livestock grazing. The paper discusses the possible relationship between the microhabitat specificiq of each species ami their population number individuals response.

Kcy words: Baja California Sur, Lizard abundance, Livestock grazing, Mexico.

they play a multifaceted role in community svucture md function. Consequentiy, an Domestic livestock grazing are common over the understanding of the impact gming on whole Cape Region, Baja California Sur, peninsular sernidesex-t habitats and the associated Mexico. Although many studies have investigated Iizard fauna is of practical value. the influence of livestock grazing on vegetarion elsewhere (Anderson & Holte, 1981; Chew, 1982; West et al., 1984; Milchunas et al, 1988), MATERIAL AND METHODS few have investigated the inlpact of Iivestock grazing on the fauna such as (Janzen, The study was conducted in a 215 ha area, 1976; Bock et al., 1984, 1990; Romero-Schmidt owned by the Center of Biological Research of et al., 1994); rodent and lagomorphs (Linsdale, the Northwest (CIBNOR) at "E1 Comitan" in the 1946; Reynolds, 1950); and invertebrates (Heske northern part of the Cape Region in -k state of & Campbell, 1991). Baja Caiifornia Sur, Mexico. "El Comitan" is 17 km north of La Paz (24" 10' N; 110 O 30' W), Several authors have found that lizard population and it is a coasial lowland (10 above sea level) numbers were inversely related with grazing with mud-sandy soils (Alvarez et al., 1989). Its intensity (Bury & Busack, 1974; Jones, 1981). predominant flora is xerophytic scmb (Leon De However, most of the work has been done at other La Luz et al., 1998) and is cornposed mainly of desert and sernidesert habitats from North the following cacti: Pachycereus pringlei America but no previous work has been done on (Cardón), Stemcereus gummosus (pitaya dulce), such effects in the Baja California peninsula. and Stenocereus thurbeni (pitaya agria); trees: Prosopis articulara (mesquite) and Bursera The objective of this study was to examine how microphyila (torote), and shbs: Jatropha vegetative changes, associated with grazing, cinerea (Iomboy) and Fouqueria diguetti (palo affected lizard species population numbers. adán) (Alvarez et al., 1989). The weather of the Because lizards are both predators and prey, zone is BW(hl) hw (xf)(e) (Garcia, 1973). It is Brazilian Archives of Biology and Technology, v.42, n.2, p. 175-180, 1999

an arid climate with the average annual Individual lizards belonging to the most temperature of 23.9"C, with a mean annual abundant species were seen mainly in the precipitation of 62 rnm, concentrated mostly following microhabitats: Urosaurus nigricaudus dunng the summer (August and September). (a Cape Region endemic species) on trees and small or mediurn mks; Cnemidophorus Livestock have been excluded from the CIBNOR hyperythrus hyperythms (a Cape Region property for about seven years. For the present endemic subspecies) on the ground. Uta study, we established a 2,500 m2 transect system stansburiana on fallen tree trunks. large mks, inside the enclosure (Site 1). In this system, we and rock wails. established ten, 50 m long transects, 10 m apart and marked by flagged wire stakes at 5 meter Table 1 shows the rnonthly abundance data for intervals. Outside the enclosure, in a grazed the lizards studied. For I.?. nigricaudus and U. boundary ranch, we established an identical system stansburiana, both inside and outside the of transects (Site 2). V. enclosure, the miullrnum abundance was during June. For both species. there was an abrupt Lizard abundance was estimated over a year decline from June to July. with further gradual period by counting the number of lizards decline until December. This was also true for observed per given time spent steadily looking for C. hyperythrus inside the enclosure with the them Lizards were detected by their movements. abundance peak in June. For the three species, Censuses were done during 50 minutes searches both inside and outside the enclosure, there was in each transect system two days each month. no activity from December to February. For each lizard observed, the date, time, species, and specific position inside the transect were Table 2 shows the average abundance, both recorded. Each census staRed from a different inside and outside the enclosure. There were location inside the transect system to try to avoid differences in lizard abundantes between both differences obtained by the lizard activities sites. Two significative differences were those associated to the time of the &y. related to the greater abundance of Urosaurus nigricaudus outside the enclosure (t = 2.260; p < 0.01), and Uta stansburiana inside (t = 4.141; p To determine vegetation structure and < 0.001). For Cnemidophow hyperythrus there microhabitat characteristics the following were no significant differences in either area (t = variables were recorded in a 1 m2 area around 1.520; p > 0.05). each flaggd wire stake: average height and cover of grasses, cacti, shrubs and trees (Moore Table 3 shows the microhabitat characteristics at & Chapman, 1986); Plant species richness and both the sites. There were remarkable density (Moore & Chapman. 1986), and percent differences in substrate availability related to of rmk, fallen tree tninks and bare soil cover, grass and herb cover (x2= 53.06; p < 0.001) and were visually estimated (Ortega et al., 1989). average height (x2= 16.33; p < 0.001), which was higher inside the enclosure. and those related to the proportion of exposed soil cover (xZ= 1008.20; p < 0.001) and falIen tree tninks RESULTS (xZ= 3.98; p < 0.05), which were significantly higher outside the enclosure. The lizard comrnunity was composed eleven species (Aivarez et al., 1989). The most For al1 the trees, shbs, and cactus abundant lizards on the study plot were: characteristics considered (Table 3), only a few Urosaurus nigricaudus, Cnemidophoms related to the structure, density, and diversity of hyperythrus and Uta stansburiana. Other the perenniai vegetation showed significant lizards present were Phrynosoma coronatum, differences between outside and inside. These Dipsosaurus dorsalis, Callisaums draconoides, were: tree density (higher inside), shbdensity BScelopow mnnserratensis, S. zosteromus, (higher outside), and percent of cactus species Ctenosaura hemilopha, Coleonyx variegatus and (higher outside). Phyllodactylus unctus. Brazilian Archives of Biology and Technology, v.42, n.2, p. 175-180, 1999 177

Table 1. Standardized data average (number of lizard individuals, found duing each census. rnultiplied by 100) of the individuals found monthly in the transects. Inside (1) and Outside (O) of the livestock enclosure area. Month Area No. Census Urosaurus Uta Cnemidophorus Total Apnl O 3 66.6 66.6 100 233.3 1 3 33.3 133.3 200 366.6 M~Y O 3 66.6 133.3 66.6 266.6 1 3 1O0 166.6 133.3 399.9 June O 3 400 233.3 133.3 766.6 1 3 266.6 400 266.6 933.3 Jul y O 3 266.6 100 166.6 533.3 1 3 100 366.6 133.3 599.9 August O 3 233.3 66.6 200 499.9 1 3 100 333.3 166.6 599.9 Sept. O 3" 200 33.3 166.6 399.9 1 3 66.6 266.6 200 533.3 Oct. O 3 200 66.6 133.3 399.9 1 3 100 266.6 166.6 533.3 Nov. O 3 133.3 66.6 100 299.9 1 3 33.3 166.6 133.3 333.3 Dec. O 1 san. O

Feb. O 1 March O 3 133.3 66.6 66.6 266.6

June is the month in which the rainy season Table 2. Average standardized individual began. Ortega & Hemández (1983) have shown numbers obselved outside and inside of that the availability of lizard prey was correlated livestock enclosure area . ( * = pc 0.05 ; ** = p < 0.01 ; *** = pc 0.001). with the increase of precipitation. June is the month when the newbom individuals, which Species Outside Inside t P were born in May, were recruited by the older age class. Urosaum 188.9 92.6 2.2 * Uta 92.6 251.8 4.1 *** Ortega et al., (1989) have suggested that the Cnemidophor 125.9 162.9 1.5 ns strong preferences shown by lizard species to specific kinds of microhabitats was the result of Total 407.4 507.3 responses evolved to cope with a complex combination of various selective pressures. DISCUSSION Lizards depend swngly on close substrate adaptation to thermoregulate efficiently, to mate Individual abundante changes during the year successfully, to defend tenitones, and to avoid could be explained both by changes in predators. environmental factors and by reproductive cycles of the three species. Brazilian Archives of Biology and Technology, v.42, n.2. p. 175-180, 1999

Table 3. Microhabitat characteristics inside and The results of this work for Urosaurus outside the exclusion area. X (* = p< 0.05 ; ** = p nigricaudus, which was more abunáant in the < 0.01 ; *** = p< 0,001). grazed site, are in accordance with Vitt & Characterisucs Outsi Inside x 2 P Ohmart (1974). who demonstrated a relationship Exposed soil cover % 76 5 100 ** between the number of downed Iimbs and branches of mesquite tres and the number of Grass & herb cover % 24 95 !3? **$* M Sceloporus magister, Urosaums ontatus, and Grass & herb height cm 4.22 24 16. ** Urosaurus graciosus populations. They found 33 * that adult S. magister used both trees and Stones cover % 24 20 1.2 N 51 S downed litter while juveniles pnmarily used Fallen tmnk cover % 6.2 2.9 3.9 * downed litter. 86 Trees They hypothesized that adults were able to Density 44 80 16. ** forage on both large and srnall prey, but 3 * Species % 20.8 17.3 b.0 N juveniles only on small prey. By using primarily downed litter, juvenile S. magister Height- 2.15 2.7 O!; N were able to reduce prey size competition with Cover adults and U. ornatus and U. graciosus , al1 of which foraged on small prey items but spent a majonty of their time in trees. Thus, the Densi ty 360 307 9.1 ** reduction in prey competition created by A0 * Species % 41.6 58.6 2.2 N increased numbers of downed tree limbs at 61 S grazed sites rnight account for the greater Height 1.42 1.81 0.0 N abundance of U, nigricaudus found in the Cover current study .

Cacti The greatest effect of grazing was on the Density 369 347 1.3 N abundance of the sit- and- wait type lizard '34 S species predating in soils, such as Uta Species % 29.2 20.7 3.4 ** 9 stansburiana. Their lower abundance at grazing Height 1.51 1.63 0.0 N sites would seem to be related to losses in low Cover 1.06 1.58 vegetative cover, particularly perenniai grass. 7'1 r, Perennial grass tended to moderate conditions of surface and near suface microenvironrnental regimes (increased water retention and cooler Jones (1981), in a study made in five different temperatures) (Jones, 1981). The lack of comrnunity types, demonstrated that grazing perennial grass at grazed sites created xenc reduced overail lizard abundance and species microenvironmental conditions at or near the diversity when associated with changes in suface, resulting in unfavorable conditions for species that foraged ovea twge areas, like Uta structural composition. SPP.

Conversely, comrnunities not affected Losses in perennial grass reduced the abundance smcturally by grazing showed little or any of certain invertebrate species and thus the food difference in lizard abundance or diversity. available to some species of lizards. This was particularly disadvantageous to lizards that spent Although the vegetation at "El Comitan" study a great deal of time and energy actively seeking area showed differences in cover and density prey (Vitt & Ohmart, 1974; Tubbs, 1977). between the grazed and ungrazed, in our study site at both system transects the vegetation Cnemidophorus hyperythms was a widely foraging species and therefore was not affected taxonomic composition was similar. by the changes in cover and density in %&bs because it was in continuous movement. Braziliun Archives of Biology and Technology, v.42. n.2, p. 175-180, 1999

Data presented in this paper indicated that not al1 lizards were adversely affected by livestock grazing. Land management managed vegetation Alvarez, S., P. Galina & Ortega-Rubio, A. and not individual species. By understanding (1989). Structure and composition of two relationships between various foraging groups lizard communities of the Cape Region, Baja and vegetative structure, and how grazing California Sur, México. Bull. Maryland affected such structures, grazing system and Herpetol. Soc., 25,4048 habitat management plans could be developed Anderson, J. E. & Holte, R.E. (1981), that would allow for the most diverse and Vegetation development over 25 years abundant fauna in any given vegetative without grazing on sagebrush dominated community. rangeland in southeastem Idaho. J. Range Manag., 34,25- 29 Bock, C. E., J. H. Bock, W. R. Kenney & ACKNOWLEDGEMENTS Hawthome, V.M. (1984). Responses of birds, rodents, and vegetation to livestock This work was supported by the Centro de exclosure in a semidesert grassland site. J. Investigaciones Biologicas del Noroeste, The Rnnge Manag., 37, 239-242 Secretaría de Educación Pública, and the Bock, C. E., H. M. Smith & J. H. Bock. (2990), Consejo Nacional de Ciencia y Tecnología of The effect of livestock grazing upon México. We would like to thank M. Acevedo B. abundance of the lizard SceIopoms scalaris, F. Cota, S. Arguelles M., R. Dornínguez C., and in southeastem . J. Herperol., 24; P. Galina T., for their help during the field 445 -446 work. Thanks also to two anonymous reviewers Bury, R. R. & Busack, S. D. (1974), Some who improved an early version of this effects of off-road vehicles and sheep manuscript and to Ellis Glazier, for editing the grazing on lizard populations in Mohave English language text, and Dolores Vázquez Desert. Biol. Conservation. 6,179-183 who typed the manuscript. Chew, R. M. (1982). Changes in herbaceous and sufmtescent perennials in grazed desertifíed gassland in southeastem Arizona, 1958- 1978. Amer. Midland Nat., 108, 159-169 García, E. (1973). Modificnciones al Sistema de Os cambios na reproduo de 3 especies de Ch~jicaciónClirnática de Koeppen. 2a. Ed. lagartixas forarn definidos e tem sido Instituto de Geografía. UNAM. México, comparados em dois sitios de matos deserticos: D.F. pp 246 um de pastoreado e o outro no, localizados nos Heske, E. J. & Campbell., M. C. (1991), arrededores Cidade & La Paz, na Regio del Effects of an 11 year livestock exclosure on Cabo na Baja California Sur no Mexico, no rodent and ant numbers in the Chihuahuan lapso de abril de 1992 ao maro de 1993. desert, Southeastern Arizona. Southwest. Nat,. 36, 89-93 Foram desenv~ividosum totai de 54 censos para Janzen, D. H. (1976). The depression of as tres espcles com base ao sistema de " dois biomass by large herbivores. Amer. Nat., transectosV-quer dizer: um dentro e o outro fora 110, 371-400 da excluso de gado. O resultado foi: urna Jones, K. B. (1981), Effects of mngon lizard lagartixa foi negativamente afectada pelas abundance and diversity in Westem Arizona. actividades de pastoreo. Uma oum mostr um Southwest. Nat., 26, 107-1 15 aparente efecto positivo pelas mesmas condies e León De La Luz, J. L., Coria, R., Cmz, M. & a terceira, no mostm altera0 nehuma pelo Dornínguez, R. (1996). Patrones fenológico- pastoreo. Este artgo pe em causa, as posiveis reproductivos de una comunidad árido- relaes entre a especificidade do microhabitat de tropical en Baja Califomia Sur. Acta Bot. cada uma das espcies e a sua resposta de Mex. 35.45-64 abundncia no numero de indiv4u 0,s. Brazilian Archives of Biology and Technology, v.42. n.2. p. 175-180, 1999

Linsdale, J. M. (1946), The California ground Romero-Schmidt, H., Ortega-Rubio, A., squirrel. University California Press. Arguelles-Mendez, C., Coria-Benet, R. & Berkeley. pp. 475 Solís-Malín, F. (1994), Effect of Livestock Milchunas, D. G., Sala, O. E. & Laureroth, W. Grazing hclosure upon abundance of lizard K. (1988), A generalized model of the cornmunity in Baja California Sur, México. effects of gazing by large herbivores on Bull. Chicago Herpetol. Soc., 29, 245-248 gassland cornmunity structure. Arner. Nar., Tubbs, A. A. (1997). Effects of artificial 132, 87-106 crowding on behavior, growth and survival Moore, P. D. & Chapman, S. B. (1986). of juvenile spiny lizards. Copeia, 820-823 Methods in Plant Ecology. Blackwell Vin, L. J. & Ohmart, R. D. (1974), Scientific Publications. Oxford, pp. 275 Reproduction and ecology of a Colorado Ortega-Rubio A., Alvarez-Cárdenas, S. & River population of Scelopom magister. Galina-Tessaro, P. (1989), Possiblegffects of Herpetol., 30,4 10-417 nicrohabitat avaibility. on lizard diversity West, N. E., Provenza, F. D., Johnson, P. S. & and density at Baja California Sur. Miscel. Owens, M. K. (1984), Vegetation changes Zool., 13, 133-139 after 13 years of livestock grazing exciusion Ortega, R. A. & Hernández., L. (1983), on sagebrush semidesert in west central Utah. Abundancia relativa de insectos en un medio J. Range Manag., 37,262-264 estacional: su influencia en la historia de vida de dos ig~anidossimpamcos. Fol. Entomi. Mex., 55, 129-144 Reccived: June 06,1998; Revisal: June 22 1998; Reynolds, H. G. (1950). Relation of memam Accepted: March 12,1999. kangaroo rats to range vegetation in southem Arizona. Ecology, 31, 456-463