Endangered Cacti in the Chihuahuan Desert: II. Biogeography and Conservation

Endangered Cacti in the Chihuahuan Desert: II. Biogeography and Conservation HI~CTOR M. HERN~NDEZ AND ROLANDO T. B~RCENAS Departamento de Bot~mica, Instituto de Biologia, UNAM, Apartado Postal 70-367, Ciudad Universitaria, 04510 MEXICO, D.F., email [email protected]

Abs t rac t : The d i s t r ibu t ions o f the m a j o r i t y o f the e n d a n g e r e d cacti in the C h i h u a h u a n Desert Reg ion are concen t ra ted in the sou theas t e rn a n d eastern segment s o f the area, where the p r e d o m i n a n c e o f n a r r o w en- d e m i s m is a r e m a r k a b l e phy togeograph ic p h e n o m e n o n . We used three cr i ter ia- -species richness, conserva- t ion value, a n d c o m p l e m e n t a r i t y - - t o eva lua te 3 7 cactus-rich area un i t s in the C h i h u a h u a n Desert. The e v a l u a t i o n o f these three q u a n t i t a t i v e p a r a m e t e r s together a l l owed us to d e t e r m i n e t ha t seven o f these areas (Huizache, Tol im~n, C i u d a d Victoria, Metz t i t ldn, Cuatro Ci~negas, J a u m a v e , a n d Xicht~) s h o u l d be considered conserva t ion pr ior i t ies because they ho ld the m o s t s ign i f i can t assemblage o f e n d a n g e r e d species, in t erms o f the ir n u m b e r s a n d the ir rarity. Conservat ion ac t ions in these seven areas w o u l d pro tec t 5 2 (55.9%) o f the 93 e n d a n g e r e d species s tud ied here, m o s t o f wh ich have ex t reme ly n a r r o w dis tr ibut ions. Geographi- cally, these crit ical areas are located in the Quere taroan-Hida lgoan a r id z o n e ( in the States o f Quer~taro, Hidalgo, a n d Guana jua to ) , in the J a u m a v e Valley (Tamaul ipas) , a n d in two d i s junc t areas (San Luis Potos i

a n d Coahui la) in the in ter ior o f the C h i h u a h u a n Desert.

Cactficuas Amenazadas en el Desierto Chihuahuense: II. Biogeografia y Conservaci6n

Resumen: Las dreas de d i s t r ibuc i6n de la g ran m a y o r i a de las especies a m e n a z a d a s en la Reg i6n del Desi- erto C h i h u a h u e n s e se concen t ran hac ia sus porc iones sureste y este, en d o n d e u n f e n 6 m e n o f i togeogrt i f ico no- table es la p r e d o m i n a n c i a de e n d e m i s m o s restringidos. En este es tudio e v a l u a m o s 3 7 dreas ricas en especies den t ro de la Regi6n del Desierto Chihuahuense , a trav~s del uso de tres criterios: r i queza de especies, valores de conservac i6n y complemen tar idad . La eva luac i6n de estos tres pardtmetros cuan t i t a t i vos de m a n e r a com- b i n a d a nos p e r m i t i 6 establecer que siete de estas dreas son pr ior i ta r ias en relacion con sus neces idades de conservac i6n (Huizache, Tol imdn, C i u d a d Victoria, Metz t i t ldn, Cuatro Ci~negas, J a u m a v e y Xichzg), deb ido a que, en t~rminos del nt~mero de especies y de su rareza, ~stas a lbergan la colecci6n m d s s igni f ica t iva de especies. La i m p l e m e n t a c i 6 n de acc iones de conservac i6n en estas Mete dreas g a r a n t i z a r i a n la pro tecc i6n de 5 2 (55.9%) de las 93 especies a m e n a z a d a s que se inc luyeron en este estudio, la m a y o r i a de las cuales t iene dreas de d i s t r ibuc i6n e x t r e m a d a m e n t e l imi tadas. Desde el p u n t o de vis ta geogrdfico, estas dreas crit icas se locali- z a n den t ro de la Z o n a Ar ida Quere tano-Hida lguense (en los estados de Quer#taro, Hidalgo y Guana jua to ) , en el VaUe de J a u m a v e (Tamau l ipas ) y en dos dreas d i s j un ta s (San Luis PotoM y Coahui la) den t ro del cuerpo

p r i n c i p a l de la Reg i6n del Desierto Chihuahuense .

Introduction

The Cac taceae family is one o f the mos t e n d a n g e r e d g roups in the p lan t k ingdom. More than one th i rd (563) o f the a p p r o x i m a t e l y 1500 spec ies in the family are dis- t r ibu ted in M~xico, and 197 (35%) of the Mexican spe-

Paper submitted March 9, 1995; revised manuscript accepted No- vember 14, 1995.

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cies are s o m e w h a t e n d a n g e r e d (Herngndez & Godinez 1994; HernAndez & Bhrcenas 1995). Most m e m b e r s o f this family are d i s t r ibu ted in arid and semiar id regions of. this count ry , and the r iches t assemblage of species , in- c lud ing the e n d a n g e r e d ones, is c e n t e r e d in the Chihua-

huan Deser t reg ion (CDR). In a p rev ious p a p e r (Hernfindez & Bhrcenas 1995) w e

analyzed the d is t r ibu t ion pa t t e rns o f 93 spec ies of en- • d a n g e r e d cact i f rom the CDR. The geograph ica l distr ibu-

Hermindez & Bdrcenas Biogeography and Conservation of Cacti 1201

t ions of all the endange red species were in tegrated in a grid map wi th grid squares measur ing 30 minu tes lati-

tude by 30 minu tes longi tude; species f requencies were calculated for each grid square. The great majori ty of the species-rich grid squares we re aggregated toward the southeas tern segment of the CDR, inc luding several dis- junc t f ragments located in isolated valleys in the Sierra Madre Oriental (e.g., Jaumave and Aramberri Valleys) and in the Queretaroan-Hidalgoan arid zone.

The ident if icat ion of areas wi th a high concen t r a t i on of endangered cacti in the CDR is a prerequis i te for the imp lemen ta t i on of act ions toward their conservat ion. But species r ichness itself c anno t be cons idered as the sole cr i ter ion for the select ion of conserva t ion areas. Several additional criteria, such as rarity, degree of threat, size, and naturalness, have b e e n used to select conserva- t ion areas (Margules & Usher 1981; Usher 1986). Never- theless, two of those easily quantif iable biological crite-

r i a - - spec ies r ichness and ra r i ty - -a re among the most c o m m o n l y used in site assessment (Margules & Usher 1981).

In the CDR endange red cacti differ in the ex ten t of their geographical ranges. Some species are restr icted to one or a few grid squares, whereas others occur in many (Hernfindez & B~trcenas 1995), and there is an inverse correlat ion b e t w e e n the geographical range of a species and its degree of vulnerabili ty. Thus, a grid square wi th a high p ropor t ion of geographical ly restr icted (s tenoen-

demic) species is of has greater conservat ion priori ty than ano ther wi th the same or even higher n u m b e r of widespread species. We scored endangered species according to the n u m b e r of grid squares in wh ich they oc- curred; the s t enoendemic species had the highest scores and the widespread ones the lowest scores. Conse- quent ly, the geographical information, expressed here as the n u m b e r of grids occup ied by each endangered

Table 1. Number of endangered species present, location, and conservation values of the grid squares having more than four species of endangered cacti in the Chihuahua Desert region.

No. o f endangered Conservation Grid square species Location value*

Tolimfin 13 20030'-21000 ' N, 99030'-100000 ' W 793.7 Huizache 14 22°30'-23°00 ' N, 100°00'-100°30' W 618.5 Ciudad Victoria 8 23030'-24000 ' N, 99000 '-99°30 ' W 602.8 Jaumave 7 23°00'-23°30' N, 99000'-99°30' W 441.7 Metztitlfin 8 20°30'-21000 ' N, 98°30'-99°00 ' W 431.5 Xicht] 9 21°00'-21°30' N, 100000'-100030' W 318.6 Ramos Arizpe 7 25°30'-26°00 ' N, 100°30'-101°00 ' W 301.7 Quer~taro 5 . 20°30'-21°00 ' N, 100°00'-100°30' W 294.2 Cinco de Mayo 6 25°00'-25°30' N, 101°30'-102°00 ' W 284.1 Cuatro Ci~negas 10 26°30'-27°00 ' N, 102°00'-102°30' W 278.0 San Miquel 5 20°30'-21°00 ' N, 100030'-101000 ' W 237.3 Rayones 4 25°00'-25030' N, 100°00'-100°30' W 237.2 Matehuala 10 23030'-24000 ' N, 100°30'-101°00' W 236.4 Aramberri 8 24000'-24030' N, 99°30'-100°00 ' W 233.1 San Luis Potosi 7 22000 '-22°30 ' N, 100030 ' - 101°00 ' W 224.0 Miquihuana 7 23030'-24°00 ' N, 99°30'-100000 ' W 223.9 Pefiamiller 4 21°00'-21°30' N, 99030'-100o00 , W 203.3 Tula 7 23000'-23030 ' N, 99030'-100000 , W 181.4 Marte 8 25o30'-26o00 , N, 101030'-102000 ' W 167.3 El Tepeyac 5 22°30'-23000 ' N, 99°30'-100°00 ' W 165.2 Doctor Arroyo 10 23030'-24000 ' N, 100°00'-100°30' W 160.7 Mier y Noriega 10 23000'-23030 ' N, 100°00'-100°30' W 154.9 Landa 4 21°00'-21°30' N, 99000'-99030 ' W 142.3 Hip61ito 6 25°30'-26°00 ' N, 101°00'-101°30' W 137.4 Viesca 6 25°00'-25°30' N, 102°30'-103°00 ' W 136.0 Saltillo 8 25000'-25°30' N, 100030'-101000 ' W 135.5 General Cepeda 8 25°00'-25030' N, 101°00'-101°30' W 132.8 Zimapfin 4 20030'-21000 , N, 99°00'-99°30' W 130.6 Pachuca 6 20°00'-20°30' N, 98°30'-99000 ' W 129.2 Galeana 7 24°30'-25000 ' N, 100°00'-100°30' W 116.4 San Pedro 6 25°30'-26°00 ' N, 102°30'-103°00 ' W 109.4 Parras 6 25°00'-25°30' N, 102°00'-102°30' W 99.0 Mexquitic 5 22°00'-22°30' N, 101°00'-101°30' W 73.2 Arista 6 22°30'-23°00 ' N, 100°30'-101°00 ' W 47.8 Villa de Guadalupe 5 23000'-23030 ' N, 100°30'-101°00 ' W 41.6 G6mez Palacio 4 25030'-26000 ' N, 103°30'-104°00 ' W 34.3 Big Bend 4 29000'-29030 ' N, 103030'-104000 , W 32.1

*Sum of index of rarity values for resident species.

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1202 Biogeography and Conservation of Cacti Herndndez & Bdrcenas

species, provides a quantitative index of rarity (IR) that reflects the conservation values of the analyzed area units.

In addition, we used the principle of complementarity to prioritize the conservation importance of the grid squares. As outlined by Williams et al. (1991), Humphries et al. (1991), and Pressey et al. (1993), this principle, when applied to specific areas, allows us to recognize and set priorities for the selection of area networks within particular regions in order to optimize the pro- tection of biodiversity. Thus, our analysis of the princi- pal centers of concentration of endangered cacti in the CDR was based on species richness, geographic range size, and complementarity.

Study Area and Methods

Data on the localization, limits, flora, climate, and other characteristics of the CDR are summarized in Hernfindez and B~rcenas (1995), which was based on published re- ports (Henrickson & Straw 1976; Schmidt 1979; Me- dellin-Leal 1982; Van Devender 1986, 1990). The 93 species included in this study are part of a larger list of Mexican endangered cacti compiled by Hern~ndez and Godinez (1994). To obtain an index of rarity for each of the endangered species of cacti from the CDR, the species were scored by dividing the total number of grid squares containing endangered species in the CDR (122) by the number of grid squares occupied by the species. Thus, the more geographically restricted species (e.g., Ariocarpus agavoides and A. bravoanus) that occur only in one grid square had the highest score, 122. On the other side of the spectrum, endangered species such as Echinocactus platyacanthus, which is distributed in 27 grid squares of the CDR, had a score of 4.5. Appendix 1 lists the IR values of the 93 endangered species studied by Hernfindez and Bfircenas (1995). The locality data for the calculation of the IR were taken exclusively from a database of herbarium collections from North and Cen- tral America (Hernfindez et al. 1993; Hermindez and Bfir- cenas 1995); this database contains over 9000 records from 32 Mexican, U.S. and European herbaria. To pro- vide a reasonable measure of the conservation value of each grid square, we added the IR values of all the endangered species found in a grid square. The conservation values of the grid squares with at least four endangered species are reported in Table 1. Information regarding species richness per grid square is that of Hernfindez and Bfircenas (1995), but the species richness figure in the Xichfl square is slightly modified in Table 1 to reflect recent findings in that part of the CDR (B/trcenas, personal communication).

The principle of complementarity (Humphries et al. 1991) was used as the third criterion to assess the conservation priorities of each of the grid squares. The prin-

ciple requires the subdivision of a region into smaller area units (grid squares in the present study). From these, the first-priority area--that containing the highest number of endangered speciesDis determined. The remaining areas are ordered according to their contribution of additional species not found in the first-priority area.

Based on floristic similarity indexes (Jaccard index of floristic similarity) among the grid squares (Hernfindez & Ruokolainen, personal communication), the CDR was divided into three subregions that we called Cuatro Ci6negas, Huizache, and Tolim~n (Fig. 1). For each of the subregions the complementarity values were calculated individually according to the following steps: (1) The grid square with the highest number of endangered species in each subregion was selected as first priority. Thus, the Cuatro Ci6negas, Huizache, and Tolim~n grid squares were considered first-priority areas in their re- spective subregions. (2) The complement, that is, the total number of endangered species in each subregion was calculated. (3) The residual complement was calculated as the difference between the complement and the

Figure 1. Approx imate phytogeographic units wi thin the Chihuahuan Desert region as suggested by similarity indexes o f cactus distributions. Only those 3 7 grid squares containing f o u r or more species are included.

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Herndndez & Bdrcenas Biogeography and Conservation of Cacti 1203

Table 2. Complementarity values of grid squares in the Chihuahuan Desert region.

Subregion Grid square Complement

Residual complement

Complementarity value

Cuatro Cienegas 28 18 Cuatro Ci6negas Ramos Arizpe General Cepeda Viesca Cinco de Mayo Hip61ito Parras Marte G6mez Palacio San Pedro Big Bend

Huizache 38 24 Huizache Jaumave Ciudad Victoria Miquihuana SaltiUo Aramberri Matehuala Doctor Arroyo Rayones Galeana Tula Mier y Noriega Villa de Guadalupe El Tepeyac Arista

Tolim~m 32 19 Tolim~n San Luis Potosi Metztitlfin Xichfi Mexquitic " San Miguel Quer~taro Pachuca Landa Zimaphn Pefiamiller

B

33.3 27.8 22.2 22.2 16.7 16.7 16.7 11.1 5.6 0.0

i

25.0 25.0 12.5 12.5 12.5 12.5 12.5 8.3 8.3 8.3 8.3 4.2 4.2 0.0

I

26.3 26.3 26.3 21.1 21.1 15.8 15.8 10.5 10.5 5.3

number of endangered species found in the first-priority grid square. (4) The complementarity value for each of the grid squares within their particular subregion was calculated by multiplying the number of unique endangered species (those not found in the first-priority square) by 100 and dividing the product by the residual complement. For instance, the G6mez Palacio grid square, which belongs to the Cuatro Ci6negas subregion, had a residual complement of 18 species and two unique species; thus, (2 x 100) / 18 = 11.1%. The resulting per- centage indicates the additional contribution from the residual complement to biodiversity in the first-priority square. The complementarity values of those 34 grid squares containing four or more endangered species are shown in Table 2.

Results and Discussion

Geographic Ranges

The 93 species of endangered cacti from the CDR included in this study are listed in Appendix 1, together with the number of grid squares in which each one has been found and their calculated IRs. The range size of the endangered species varies enormously. Figure 2 is a graphic representation of the frequency distribution of the number of grid squares occupied by the species; it il- lustrates the pronounced stenoendemism among endangered cacti in Mexico. For instance, 35 endangered species, representing 37.6% of the total number of analyzed species, are restricted to a single grid square. In addi-

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V o l u m e 10, No . 4, A u g u s t 1 9 9 6


Figure 2. Frequency distribution o f the number o f endangered species o f cactus per grid square in the Chi- h u a h u a n Desert region.

tion, 21 species (22.6%) are found in only two, and nine (9.7%) are found in only three grid squares. This means that 69.9% of the endangered species we studied are restricted to three or fewer grid squares. In contrast, only 13 of the species are distributed in 10 or more grid squares. This supports previous suggestions (Hernhndez & Godinez 1994) that stenoendemism is a common phe- nomenon among Mexican Cactaceae. It is likely that the profusion of narrowly endemic species in the Cactaceae, as well as in several other plant families in the CDR, arose as a consequence of area contractions during the last Pleistocene glacial period (Van Devender & Burgess 1985; Van Devender 1986, 1990; Betancourt et al. 1990). It has been hypothesized (Van Devender '& Burgess 1985; Van Devender 1986; Hernfindez & B~ircenas 1995) that several areas within the CDR acted as refugia of desert floristic elements during these climatic changes.

Species Richness and Conservation Values

Table 1 shows the conservation values of 37 grid squares, that contain more than four endangered species. The high degree of variation in the conservation values among the grid squares (range -- 793.7-32.1) is only partially explained by differences in species richness. In fact, as a result of differences in species composition (IR differences), in a number of instances some grid squares have significantly higher conservation values than others with the same or even higher number of endangered species. For example, the conservation value of the Ciudad Victoria grid square with eight endangered species is more than four times higher than that of the Saltillo and General Cepeda grid squares, which have the same number of endangered species (Table 1).

In the first contribution of this series (Hernhndez & Bfircenas 1995), we determined that the endangered cacti of the CDR tend to be aggregated toward the

southeastern and eastern segments of this desert. Two areas were outstanding for their particularly high concentration of endangered cacti. The most important is located in central and northern San Luis Potosi, southern Nuevo Le6n, and southwestern Tamaulipas, particularly around the localities of Huizache, Matehuala, Doctor Ar- royo, and Mier y Noriega. The second in importance cor- responds to a smaller area found within the Quere- taroan-Hidalgoan arid zone, specifically in the southern portion of the Est6rax River basin in Quer6taro (see Fig. 3 in Hern~indez & B;ircenas 1995).

Based on species richness values alone, it is easy to as- sign priority among the grid squares. But when the conservation values of these area units are taken into consid- eration, based on specific geographic range sizes, the number of endangered species per grid square and their conservation values are not always correlated. Thus, com- bining these two criteria (Fig. 3) provides a more realistic approach to the evaluation of these areas. Five grid squares that have both high species numbers and conservation values have the highest conservation priority (Fig. 3). The most important of these are the Huizache (14 spp.) and the Tolimhn (13 spp.), which have conservation values of 618.5 and 793.7 respectively (Table 1 and Fig. 3). Located in northcentral San Luis Potosi, the Huizache grid square is well known for its diversity of cactus species, and it is the area with the highest concentration of endangered cacti in the entire CDR. The high conservation value in this area is determined by the abundance of stenoendemic species, such as Ariocarpus

Figure 3. Species richness and conservation value o f the grid squares with seven or more endangered cactus species within the Chihuahuan Desert region. Data taken f r o m Table 1: 1, Huizache; 2, Tolimdn; 3, Cuatro Cidnegas; 4, Matehuala; 5, Doctor Arroyo; 6, Mier y Noriega; 7, Xicha; 8, Ciudad Victoria; 9, Metztitl~n; 1 O, Aramberri; 11, Marte; 12, SaltiUo; 13, General Cepeda; 14,Jaumave; 15, Ramos Arizpe; 16, San Luis PotoM," 17, Miquihuana; 18, Tula; 19, Galeana.


Hern&Mez & Bdrcenas BiogeograptJy and Conservation of Cacti 1205

Table 3. Transformed (%) values of number of species, conservation value, and complementarity of grid squares in the Chihuahuan Desert region.

I II II I I III

Grid square No. of species Conservation vahte Complementarity Cumulative valtte

Tolim;m 0.9 1.0 1.0 2.9 Huizachc 1.0 0.8 1.0 2.8 Ciudad Victoria 0.6 0.8 1.0 2.4 Metztitlan 0.6 0.5 1.0 2.1 Cuatro Cidnegas 0.7 0.4 1.0 2.1 Jaumavc 0,5 0.6 1.0 2, I Xichu 0.6 0.4 1.0 2,0 Ramos Arizpe 0.5 0.4 1.0 t .9 San Luis Potosi 0.5 0.3 1.0 1.8 General Cepeda 0.6 0.2 0.8 1.6 Matehuala 0.7 0.3 0.5 1.5 San Miguel 0.4 0.3 0.8 1,5 Cinco de Mayo 0.4 0.4 0.7 1.5 l)octor Arroyo 0.7 0.2 0.5 1.4 Aramberri O.6 (}.3 0.5 1.4 Querdtaro OA 0.4 0.6 1.4 Miquihuana 0.5 0.3 0.5 1.3 Marte 0.6 0.2 0.5 1.3 Vicsca 0.4 0.2 0.7 1.3 Mexquitic O, 4 O. 1 0.8 1,3 Saltillo 0.6 0.2 0.5 1.3 Mier y N<)riega 0.7 0.2 (1.3 1.2 Pachuca 0.4 0.2 0.6 1.2 Hip61ito 0.4 0.2 0.5 1. l Tula 0.5 0.2 0.3 1.0 Parras 0.4 0. I 0.5 1,0 Galeana 0.5 0.2 0.3 1.0 Rayones 0.3 0.3 0.3 0:9 Landa 0.3 0.2 0.4 0,9 Zimap(m 0,3 0.2 0.4 0.9 Pefiamillcr O,3 0,3 0.2 0.8 El Tepeyac 0.4 0.2 0.2 0.8 San Pedro 0.4 0. I 0.2 0.7 Villa de Guadalupe 0.4 0.1 0.2 0.7 G6mez Palacio 0.3 0.0 0.3 0.6 Arista 0.4 0.1 0.0 0,5 Big Bend 0.3 0.O 0.0 0.3

bravoanus, Coryphantha odorata, Mammi l lar ia surculosa, and Turbinicarpus k n u t h i a n u s all of wh ich are restricted to the area. The Tolimfin grid square, on the o ther hand, is part of a dis junct por t ion of the CDR

k n o w n as the Queretaroan-Hidalgoan arid zone, and it is the area possessing tile highest conserva t ion value based on r~ange sizes. Four species of endange red cacti are restricted to this grid square: Eoginocactus grusonii, Echi- nocereus schmollii, Tbelocactus hastifer, and TurOinica- rpus pseudomacrochele. Four more species (Lophophora diffusa, Mammi l lar ia herrerae, M. parkinsoni i , Strom- bocactus discilbrmis) are found in this and one addi-

t ional grid square. Two addit ional grid squares, the Ciudad Victoria and

Jaumave, include together all of the Jaumave Valley and are also recognized individually for their high conserva-

t ion values (Fig. 3). The Jaumave Valley is a semiarid, geographical ly isolated f ragment of the CDR in wh ich

several species, inc luding the mono typ ic genus Obrego- nia, have b e e n repor ted as restricted to its limits. De- spite the fact that the species r ichness in these two grid

squares is comparat ively low (eight and seven endangered species respectivel)9, their conservat ion value is high because of the high f requency of s t enoendemic species. Likewise, the Metztitl'an square, wi th eight endangered species, which is also part of the Queretaroan- Hidalgoan arid zone, has a relatively high conservat ion value (C.V. = 4 3 1 . 5 ) b e c a u s e of the occur rence of three s t enoendemic species: Cephalocereus senilis, Mammil l - aria humboMti i , and Turbinicarpus horripilus. It is likely that the high f requency of s t enoendemic cacti in

the Queretaroan-Hidalgoan arid zone (Tolimfin and Metz- tiff-an grid squares) and in the Jaumave Valley ( laumave and Ciudad Victoria grid squares) is a c o n s e q u e n c e of geographic and climatic isolation, wh ich has s t imulated speciat ion in these disjunct pockets of the CDR.

(:OI1SC fvatioll Biology


A contrasting situation is illustrated by the Cuatro Ci6negas (C.V. -- 278), Matehuala (C.V. = 236.4), Doc- tor Arroyo (C.V. = 160.7), and Mier y Noriega (C.V. = 154.9) grid squares, all of which are relatively rich in cactus species (10 endangered species each), but their conservation values are very low (Fig. 3). A possible ex- planation for this pattern is that all of these grid squares are located within the main body of the CDR and the species included in them have low IRs, as they extend into adjacent grid squares. This situation is also true for all the grid squares with low conservation values within the CDR (Fig. 3).

The Principle of Complementarity

Figure 1 is a graphic representation of the phytogeographic units within the CDR, based on similarity-index data of endangered cactus distributions. Three primary phytogeographic areas (subregions) were established according to a preliminary analysis (Hermindez & Ruoko- lainen, personal communication): Cuatro Ci6negas, Huizache, and Tolim~n. To assess the conservation importance of the grid squares, their complementarity values were calculated individually by subregion. Data on total number of endangered species per subregion (complement), residual complement, and complementarity values are presented in Table 2.

In the Cuatro Ci6negas subregion (complement = 28 spp.), the Ramos Arizpe grid square was the second-priority choice, with a complementarity value (COV) of 33.3%. This square is followed by the General Cepeda (COV = 27.8%), the Viesca, Cinco de Mayo (COV = 22.2%), the Hip61ito, Parras, and Marte grid squares (COV -- 16.7%) (Table 2). In the Huizache subregion (complement -- 38 spp.), the Jaumave and Ciudad Victo- ria grid squares, both within the Jaumave Valley, are the obvious second choice (COV = 25%). These are followed by five grid squares (third choice) with an equal number of unique species (COV = 12.5%): Miquihuana, Saltillo, Aramberri, Matehuala, and Doctor Arroyo. In the Tolimfin subregion (complement = 32 spp.), three grid squares are second-priority choices (Table 2): San Luis Potosi, Metztitl~.n, and Xichti (COV = 26.3%). The third- and fourth-priority grid squares in this subregion were Mexquitic, San Miguel (COY = 21%), Quer6taro, and Pa- chuca (COV -- 15.8%). These grid squares, those with the highest complementarity values within each subregion, add the greatest biodiversity to the first-priority grid squares (Cuatro Ci6negas, Huizache, and Tolimfin); thus, they are of highest conservation priority. There are several areas with few additional species (those not found in the first-priority area) that are of low conservation priority. Two grid squares, Big Bend and Arista, have zero complementarity value.

Conclusion

We used three criteria to evaluate the conservation priorities of 37 cactus-rich area units within the CDR. Each criterion provides insight for the selection of conservation areas. When all three are combined, however, a more realistic picture emerges. With the purpose of making them comparable, the data presented in Tables 1 and 2 (species richness, conservation value, and complementarity) are given as percentages in Table 3, and these results are shown graphically in Fig. 4.

There are seven grid squares that have cumulative values above 2 (Fig. 4), and these should be considered as top priority for conservation of endangered cacti in the CDR. These seven grid squares hold 52 endangered species, representing 55.9% of the endangered species included in this study; the remaining 41 endangered species are distributed among the other 30 grid squares. The most important of the seven grid squares are the Tolim~in and Huizache, both of which have cumulative values approaching the maximum of 3; conservation ac- tions in these two areas are extremely urgent. Geograph-

3

2.S

llllllnl;lltlll;ll i l.S

: lllDllllili , . i . . . . . i I

a 7 ~l 9 10111213t41516171B19202122232425262728293031323334353637 Gdd squane

[mNoSpec~s DConservationvalu. mCornplerne~arity]

Figure 4. Cumulative values of number of endangered cactus species, conservation value, and complementarity of the 3 7 cactus-rich grid squares in the Chihua- huan Desert region. The size of the bars reflect conservation priority. Data taken from Table 3: 1, Tolimdn; 2, Huizache; 3, Ciudad Victoria; 4, Metztitl~n; 5, Cua- tro Ci~negas; 6, Jaumave; 7, Xich6; 8, Ramos Arizpe; 9, San Luis Potosi," 10, General Cepeda; 11, Matehuala; 12, San Miguel; 13, Cinco de Mayo; 14, Doctor Arroyo; 15, Aramberri; 16, Quer~taro; 17, Miquihuana; 18, Marte; 19, Viesca; 20, Mexquitic; 21, Saltillo; 22, Mier y Noriega; 23, Pachuca; 24, Hip61ito; 25, Tula; 26, Par- ras; 27, Galeana; 28, Rayones; 29, Landa; 30, Zi- mapdtn; 31, Pe~amiller; 32, El Tepeyac; 33, San Pedro; 34, Villa de Guadalupe; 35, G6mez Palacio; 36, Arista; and 37, Big Bend.

Conservation Bio|ogy Volume 10, No. 4, August 1996

Herndndez & Bdrcenas Biogeography and Conservation of Cacti 1207

ically, t h r e e o f t h e m o s t i m p o r t a n t g r id s q u a r e s (Tolimfin,

Metz t id f in , a n d Xicht~) b e l o n g to t h e Q u e r e t a r o a n - H i d a l -

g o a n a r i d z o n e , w h e r e a s t h e C i u d a d V i c t o r i a a n d Jau-

m a v e c o r r e s p o n d t o t h e i s o l a t e d Va l l ey o f J a u m a v e , a n d

t h e H u i z a c h e a n d C u a t r o C i ~ n e g a s a r e l o c a t e d w i t h i n

t h e m a i n b o d y o f t h e CDR. T h e m a j o r i t y ( 2 0 o u t o f 3 7 )

o f t h e g r i d s q u a r e s ( g r i d s q u a r e s 8 - 2 7 ; Fig. 4) h a v e m o d -

e r a t e c u m u l a t i v e v a l u e s r a n g i n g f r o m 1 t o 1.9, a n d 10

h a v e v a l u e s b e l o w 1 ( r a n g e -- 0 . 3 - 0 . 9 ) . T h e i n f o r m a t i o n

in Fig. 4 s e t s t h e bas i s f o r t h e s e l e c t i o n o f a n a r e a ne t -

w o r k fo r t h e c o n s e r v a t i o n o f e n d a n g e r e d c a c t i i n t h e

CDR. It m u s t b e e m p h a s i z e d t h a t t h e g r id s q u a r e s w i t h

r e l a t i v e l y l o w c u m u l a t i v e v a l u e s s h o u l d n o t a u t o m a t i -

ca l ly b e e x c l u d e d f r o m t h e n e t w o r k . M o s t o f t h e g r id

s q u a r e s w i t h v e r y l o w c u m u l a t i v e v a l u e s h o l d s t e n o e n -

d e m i c c a c t u s s p e c i e s , g i v i n g s o m e c o n s e r v a t i o n a n d

c o m p l e m e n t a r i t y v a l u e s t o t h e a reas .

T h e i n f o r m a t i o n p r o v i d e d h e r e , t o g e t h e r w i t h t h a t in

t h e f i r s t c o n t r i b u t i o n ( H e r n f i n d e z & Bf i rcenas 1995) , is a

s t a r t i n g p o i n t f o r u n d e r s t a n d i n g t h e g e o g r a p h i c r e l a t i o n s

o f t h e e n d a n g e r e d c a c t i i n t h e C h i h u a h u a n D e s e r t re-

g ion . H o w e v e r , w e n e e d to b r i n g o u r k n o w l e d g e o f t h e

d i s t r i b u t i o n p a t t e r n s o f t h e s e p l a n t s t o a h i g h e r l eve l o f

r e s o l u t i o n . W e h o p e t h a t t h e s e d a t a a n d i d e a s wi l l s t imu-

l a t e f u r t h e r s t u d i e s t h a t wi l l t e s t t h e b i o g e o g r a p h i c c o n -

g r u e n c e o f e n d a n g e r e d c a c t i w i t h o t h e r p l a n t g r o u p s

(e .g. , A g a v a c e a e , N y c t a g i n a c e a e ) a n d a n i m a l g r o u p s

(e .g. , Rep t i l i a ) t h a t a r e r e p u t e d t o h a v e h i g h d e g r e e s o f

e n d e m i s m in t h e area . U n f o r t u n a t e l y , b a s i c i n f o r m a t i o n

o n e n d a n g e r e d c a c t i a t t h e p o p u l a t i o n l eve l a re sti l l lack-

ing . It is p a r t i c u l a r l y i m p o r t a n t to d i r e c t s c i e n t i f i c re-

s e a r c h t o w a r d a n u n d e r s t a n d i n g o f t h e i r d e m o g r a p h y ,

g e n e t i c s t r u c t u r e , a n d r e p r o d u c t i v e b io logy , i n c l u d i n g

p o l l i n a t i o n b i o l o g y , b r e e d i n g s y s t e m s , a n d s e e d - d i s p e r s a l

m e c h a n i s m s .

Acknowledgments

W e t h a n k o u r c o l l e a g u e s F. C h i a n g a n d H. Ar i ta f o r t h e i r

v a l u a b l e c o m m e n t s o n t h e m a n u s c r i p t . T h e C h i h u a h u a n

D e s e r t p r o j e c t h a s b e e n s u p p o r t e d b y t h e N a t i o n a l Geo -

g r a p h i c S o c i e t y ( 4 3 8 7 - 9 0 ) , t h e R e d L a t i n o a m e r i c a n a d e

Bo t f in ica (91 DATAB 10), t h e B i o d i v e r s i t y S u p p o r t Pro-

g r a m ( 7 5 6 8 ) , a n d t h e C o n s e j o N a c i o n a l d e C i e n c i a y Tec -

n o l o g i a , M ~ x i c o ( 5 3 8 N ) .

U ~ C ~ d

Betancourt, J., T. Van Devender, and P. Martin, editors. 1990. Packrat middens. The last 40,000 years of biotic change. The University of Arizona Press, Tucson.

Henrickson, J., and R. Straw. 1976. A gazetteer of the Chihuahuan Desert Region. A supplement to the Chihuahuan Desert flora. Cali- fornia State University, Los Angeles.

Hernfindez, H. M., and R. T. B~ircenas. 1995. Endangered cacti in the Chihuahuan Desert. I. Distribution patterns. Conservation Biology 9:1176-1190.

Hernfindez, H. M., and H. Godinez. 1994. Contribuci6n al cono- cimiento de las cactficeas mexicanas amenazadas. Acta Botfinica Mexicana 26:33-52.

Hernfindez, H. M., V. Alvarado, and R. Ibarra. 1993. Base de datos de colecciones de cact:iceas de Norte y Centroam6rica. Anales dei In- stituto de Biologia, Universidad Nacional Aut6noma de M6xico, Se- rie Botfinica 64:87-94.

Humphries, C., D. Vane-Wrigth, and P. Williams. 1991. Biodiversity re- serves: Setting new priorities for the conservation of wildlife. Parks 2(2):34-38.

Margules, C., and M. B. Usher. 1981. Criteria used in assessing wildlife conservation potential. Biological Conservation 21:79-109.

Medellin-Leal, F. 1982. The Chihuahuan Desert. Pages 321-372 in G. L. Bender, editor. Reference handbook on the deserts of North Amer- ica. Greenwood Press, Westport, Connecticut.

Pressey, R., C. Humphries, C. Margules, R. Vane-Wright, and P. Will- iams. 1993. Beyond opportunism: key principles for systematic re- serve selection. Trends in Ecology and Evolution 8:124-128.

Schmidt, R. H. 1979. A climatic delineation of the "real" Chihuahuan Desert. Journal of Arid Environments 2:243-250.

Usher, M. B. 1986. Wildlife conservation evaluation: attributes, criteria and values. Pages 3-44 in M. B. Usher, editor. Wildlife conservation evaluation. Chapman and Hall, London.

Van Devender, T. 1986. Pleistocene climates and endemism in the Chi- huahuan Desert flora. Pages 1-19 inJ. Barlow, A. M. Powell, and B. Timmermann, editors. Second symposium on the resources of the Chihuahuan Degert Region. Chihuahuan Desert Research Institute, Alpine, Texas.

Van Devender, T. 1990. Late Quaternary vegetation and climate of the Chihuahuan Desert, United States and Mexico. Pages 104-133 in J. Bctancourt, T. Van Devender, and P. Martin, editors. Packrat middens. The last 40,000 years of biotic change. The University of Ari- zona Press, Tucson.

Van Devender, T., and T. Burgess. 1985. Late Pleistocene woodlands in the Bolson de Mapimi: a refugia for the Chihuahuan Desert biota? Quaternary Research 24:346-353.

Williams, P., C. Humphries, and R. Vane-Wright. 1991. Measuring biodiversity: taxonomic relatedness for conservation priorities. Australian Systematic Botany 4:665-679.


1208 Biogeography and Conservation of Cacti

Appendix 1 Index of rarity of endangered species of cacti from the Chihuahuan Desert region and marginal areas.

Taxon No. o f grids

Herndndez & Bdrcenas

Index o f rarity

Ariocarpus agavoides (Castafieda) Anderson A. bravoanus Hernfindez et Anderson A. f i ssuratus (Engelmann) Schumann

vat. f i ssuratus var. hintoni i Stuppy et Taylor var. lloydii (Rose) Marshall

A. kotschoubeyanus (Lemaire) Schumann A. retusus Scheidweiler A. scaphirostris B6deker A. trigonus Schumann Astrophytum asterias (Zuccarini) Lemaire A. capricorne (Dietrich) Britton et Rose A. myriost igma Lemaire A. o r n a t u m (De Candolle) Weber ex Britton et Rose A z t e k i u m hintoni i Glass et Fitz A. ritteri (B6deker) B6deker ex Berger Cephalocereus senilis Haworth Coryphantha odorata B6deker C. poselgeriana (Dietrich) Britton et Rose C. pseudoechinus B6deker C. werdermani i B6deker Echinocactus grusoni i Hildmann E. parry i Engelmann E. p la tyacanthus Link et Otto Echinocereus delaetii (Guerke) Guerke E. knippel ianus Liebner E. longisetus (Engelmann) Ruempler E. nivosus Glass et Foster E. pa lmer i Britton et Rose E. pulchellus (Martius) Schumann E. schmoUii (Weingart) Taylor Escobaria aguirreana (Glass et Foster)? E. laredoi (Glass et Foster) Taylor E. roseana (B6deker) Marshall Ferocactus latispinus (Haworth) Britton et Rose

var. latispinus ~: macrodiscus (Martius) Britton et Rose

vat. septentrionalis Meyrfin F. pi losus (Galeotti) Werdermann Geohintonia mex icana Glass et Fitz Hamatocac tus crassihamatus (Weber) Buxbaum Leuchtenbergia principis Hooker Lophophora diffusa (Croizat) Bravo Mammi l lar ia a lbicoma B6deker M. aurei lanata Backeberg M. aur ihamata B6deker M. b a u m i i B6deker M. carmenae Castafieda M. grusoni i Ruenge M. hahn iana Werdermann M. herrerae Werdermann M. humbold t i i Ehrenberg M. klissingiana B6deker M. lenta K. Brandegee M. l o n g i m a m m a De Candolle M. mathi ldae Kraehenbuehl et krainz M. melaleuca Karwinsky ex Salm-Dyck M. moelleriana B6deker M. nana Backeberg

1 1

20

11 19

1 4 2 9

10 6 1 2 2 1

12 3 4 1 3

27 2 3 2 1 1 5 1 1 1 2

22

2 14

1 2

11 2 1 1 1 1 1 2 2 2 1 1 2 6 1 1 2 5

122.0 122.0

6.1

11.1 6.4

122.0 30.5 61.0 13.6 12.2 20.3

122.0 61.0 61.0

122.0 10.2 40.7 3O.5

122.0 40.7

4.5 61.0 40.7 61.0

122.0 122.0

24.4 122.0 122.0 122.0 61.0

5.5

61.0 8.7

122.0 61.0 I I . I 61.0

122.0 122.0 122.0 122.0 122.0 61.0 61.0 61.0

122.0 122.0 61.0 20.3

122.0 122.0 61.0 24.4


Hemdndez & Bdrcenas Biogeography and Conservation of Cacti 1209

Appendix 1. Continued

Taxon No. o f grids Index o f rarity

M. painteri Rose M. parkinsonii Ehrenberg M. pennispinosa Krainz

var. nazarensis Glass et Foster var. pennispinosa

M. pilispina Purpus M. plumosa W e b e r M. rettigiana B6deker M. schiedeana Ehrenberg M. surculosa B6deker M. theresae Cutak M. weingartiana B6deker M. zephyranthoides Scheidwei ler Neobuxbaumia euphorbioides (Hawor th) Buxbaum N. polylopha (De Candolle) Backeberg Obregonia denegrii Fric Opuntia rufida Engelmann Pelecyphora aselliformis Ehrenberg P. strobiliformis (Wer de r m ann) Fric et Scheelle Peniocereus greggii (Engelmann) Briton et Rose

var. greggii Sclerocactus intertextus (Engelmann) Taylor S. mariposensis (Hester) Taylor S. uncinatus (Galeott i) Taylor S. unguispinus (Engelmann) Taylor Stenocactus coptonogonus (Lemaire) Berger Strombocactus disciformis (De Candolle) Bri t ton et Rose Thelocactus hastifer ( Wer de r m ann et B6deker) Knut T. macdowellii (Reb. ex Quehl ) Bri t ton et Rose T. tulensis (Poselger) Bri t ton et Rose

var. tulensis var. buekii var. matudae

Turbinicarpus gautii Benson T. gielsdorfianus (Wer de r m ann) J o h n et Riha T. horripilus (Lemaire) J o h n et Riha T. knuthianus (Bfdeker ) J o h n et Riha T. laui Glass et Foster T. pseudomacrochele (Backeberg) Buxbaum et Backeberg T. pseudopectinatus (Backeberg) Glass et Foster T. saueri (B6deker) J o h n et Riha T. schmiedickeanus (B6deker) Buxbaum et Backeberg

var. dickisoniae Glass et Foster var.flaviflorus (Frank et Lau) Glass et Foster vat. gracilis (Glass et Foster) Glass et Foster var. klinkerianus (Backeberg et Jacobsen) Glass et Foster var. macrochele (Werde rmann) Glass et Foster var. schmiedickeanus var. schwarzii (Schurly) Glass et Foster

T. subterraneus var. subterraneus var. zaragozae

T. valdezianus (Moeller) Glass et Foster T. viereckii (Werde r m ann) J o h n et Riha

var. major (Glass et Foster) J o h n et Riha var. viereckii

3 2 1 3 1 1 1 5 3 3 2

16 2 3

17 6 9

25 10

9 2 1 1 9

1.22.0 61.0 61.0

40.7 61.0

122.0 40.7

122.0 122.0 122.0

24.4 40.7 40.7 61.0

7.6 61.0 40.7

7.2 20.3 13.5

4.9 12.2 13.5 61.0

122.0 122.0

13.5

17.4 122.0 122.0 122.0 122.0 122.0

15.2 122.0

17.4

122.0

40.7 61.0


Endangered Cacti in the Chihuahuan Desert: II. Biogeography and Conservation

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