Altitudinal Distribution of Birds in the Sierra Madre Del Dur, Guerrero
Total Page：16
File Type：pdf, Size：1020Kb
The Condor94~29-39 0 The Cooper Ornithological Society 1992 ALTITUDINAL DISTRIBUTION OF BIRDS IN THE SIERRA MADRE DEL SUR, GUERRERO, MEXICO’ ADOLFO G. NAVARRO S. Muse0 de Zoologia “Alfonso L. Herrera,” Department0 de Biologia, Facultad de Ciencias, UniversidadNational Autbnoma de Mexico, Apartado Postal 70-399, Mt?xicoD.F. 04510, Mxico Abstract. Altitudinal patterns of distribution, diversity, and speciesturnover in the avi- fauna of the Sierra de Atoyac, Sierra Madre de1Sur, Guerrero, Mexico, were studied along a transectfrom the tropical coastalplain to high-altitude coniferousforests. Species richness is highest at low elevations and declines with increasing altitude. Richness is relatively uniform within habitat types,but high levels of speciesturnover are found at habitat ecotones. Altitudinal rangesof congenerspecies pairs overlap more frequently than predicted by null models, suggestingthat competition may not have played a dominant role in structuring the community. Patterns of diversity, endemism, and habitat destruction are discussedin terms of conservation priorities. Key words: Altitudinal distribution;Guerrero; Mkxico; speciesturnover; competition; con- servation. Resumen. Se estudiaron 10spatrones de distribution altitudinal, diversidad y recambio de especiesde la avifauna residente en la Sierra de Atoyac, Guerrero, Mexico, a lo largo de un transect0 altitudinal que abarca todos 10stipos de vegetation presentes,desde la vege- tacion costerahasta 10sbosques altos de coniferas. La riqueza de especieses mayor en las partesbajas, decreciendo conforme aumenta la altitud. La riqueza es notablementeconstante dentro de 10s habitats, pero altos niveles de recambio de especies se encuentran en 10s ecotonos. Los intervalos altitudinales que ocupan pares y trios de especiescongenericas muestranun mayor solapamientoque el predicho por modelosestadisticos nulos, sugiriendo que la competencia no ha jugado un papel dominante en la estructuracionde las comuni- dades. Los patronesde diversidad, endemism0 y 10sefectos de la destruction de 10shabitats son discutidos en ttrminos de prioridades de conservation. Palabras clave: Distribucih altitudinal; Guerrero;Mgxico; recambiode especies;com- petencia;conservacidn. INTRODUCTION tudinal patterns in the avifauna of the Sierra Ma- Analysis of altitudinal changes in diversity, dre de1 Sur, Guerrero, Mexico, in an attempt to abundance, and species composition of biotas understand the relative importance of thesethree can provide important information on such phe- factorsin structuring the community. The degree nomena as aspectsof the environment limiting to which habitat boundaries and competition in- the distribution of organisms, factorsinfluencing troduce structure into the community is statis- the structure of communities, and aspectsof bio- tically analyzed and variation not explained by geography.A theoretical framework by which to those two factorsis attributed to gradual changes understand altitudinal distributions of commu- in environmental parameters (Terborgh 197 1). nities was described by Terborgh (1971, 1977) Although the avifauna of the Sierra Madre de1 and Terborgh and Weske (1975). These authors Sur of Guerrero has been studied since the late arguedthat the three principal factorsinfluencing nineteenth century (Salvin and Godman 1879- altitudinal structuring of communities are abrupt 1904; Nelson 1903; Griscom 1934,1937; Martin changesin habitats, gradual changesin environ- de1 Campo 1948; Blake 1950; Goldman 195 l), mental parameters, and competition. little is known about the composition of the avi- The purpose of this study is to analyze alti- fauna of the humid coastal slope. Moreover, no information exists on altitudinal patterns of avi- an distribution for the region as a whole. Hence, ’ Received 22 January 1991. Accepted 9 October a secondpurpose of this study is to provide base- 1991. line data on the distribution and ecologicalchar- 1291 30 ADOLF0 G. NAVARRO S. TLACOTEPEC . PUERTO EL GALL0 0 CHILPANCMGO . TIERRA COLORADA dirt roads I m I paved roads 1 FIGURE 1. Geographiclocation of the studyarea: (a) Stateof Guerrero;(b) Sierrade Atoyac. acteristics of the avifauna of the Sierra Madre Ocean. Thus, the Pacific slopesare generally hu- de1 Sur. mid, whereas the interior slopes are xeric. This study was conducted along an altitudinal transect STUDY AREA AND METHODS between the city of Atoyac de Alvarez and the The Sierra de Atoyac lies at the southwestern peak of the highestmountain in the Sierra Madre end of the Sierra Madre de1 Sur, which extends de1 Sur, Cerro Teotepec (Fig. 1). (The higher lo- from western Guerrero east to south-central Oa- calities on this transect have been often referred xaca. The Sierra Madre de1 Sur consists largely to as “Mount Teotepec” or just “Teotepec” in of igneous and metamorphic rocks and appar- the literature.) Eleven stations were established ently arose in the Precambrian independently in primary habitats, each separated by approx- from other mountain massesto the north (Lopez- imately 200 m of altitude (from 620 to 3,100 m; Ramos 1983). Climatically, the region is largely Table 1). These stations span the range of hab- influenced by weather systems from the Pacific itats along the transect (Fig. 2), including semi- ALTITUDINAL DISTRIBUTION OF BIRDS 3 1 altitude (m ) FIR FOREST -------__-- --_----_-----_________ PINE-OAK FOREST 2500 2000 1500 1200 -__----- -----__-----_---__-_-- 1000 SEMIDECIDUOUS TROPICAL FOREST 60C FIGURE 2. Vegetation profile of the humid slopeof the Sierra de Atoyac. Broken lines indicate the approximate location of the ecotones. deciduous tropical forest, cloud forest, pine-oak site, with field time distributed in ten of the forest and high-altitude fir forest (see descrip- months of the year. At each site, lines of mist- tions in Table 1). nets were set in each habitat, and experienced A total of 90 days was spent working along the observers made additional observations. Vouch- study transect between March 1983 and May er specimens were obtained for as many species 1985, supplemented by occasional visits during as possible, using both mist-nets and a shotgun. 1989. Between 4 and 16 days were spent at each These are deposited in the Museo de Zoologia, TABLE 1. Sampling stations along the altitudinal gradient in the Sierra de Atoyac, Guerrero. Locality Altitude (m) Habitat 1. Rio Santiago, 14 km SW Paraiso 680 SemideciduousTropical Forest 2. Puente Lugardo, 3.5 km W Paraiso 820 SemideciduousTropical Forest 3. El Faisanal, 7.5 km NNE Paraiso 1,200 Ecotone Cloud-SemideciduousForest 4. Nueva Delhi, 8.5 km NNE Paraiso 1,400 Cloud Forest 5. Retrocesos,5.5 km S Puerto El Gallo 1,600 Cloud Forest 6. La Golondrina, 13 km NNE Paraiso 1,800 Cloud Forest 7. El Descanso, 2 km SW Puerto El Gallo 2,000 Cloud Forest 8. El Iris, 3 km NE Puerto El Gallo 2,200 Cloud-Pine-Oak Forest 9. Puerto El Gallo, 15.5 km NNE Paraiso 2,500 Pine-Oak-Cloud Forest 10. Toro Muerto, 10 km NW Puerto El Gallo 2,600 Pine-Oak Forest 11. Teotepec, 4 km E Puerto El Gallo 3,100 Fir Forest 32 ADOLF0 G. NAVARRO S. 60 ; RS PL EF ND RE LG BL El PG TM TE statbns ~ linear regression FIGURE 3. Resident speciesrichness along the altitudinal transect. Facultad de Ciencias, Universidad National Au- titudinal distributions were assumed to be con- tonoma de Mexico. tinuous, with gapsfilled as describedabove, and, Cumulative plots of resident speciesvs. field for the purposes of this test, altitudinal range days were inspected to assurethat field effort at width was assumed to be insensitive of the pres- each site was sufficient to understand the com- ence of other species(see Discussion). Two def- position of the avifauna of that site. Eight of 11 initions of “non-overlap” were used: (1) com- of these plots were asymptotic by the final day pletely exclusive distributions, in which the of field work, indicating that few species re- congener speciespair never occurred at the same mained undiscovered. When gaps were present station, and (2) adjacent distributions, in which in a species’ altitudinal distribution, we assumed overlap at one station that constitutes an alti- that these representedinadequate sampling, and tudinal limit for both specieswas counted as non- not actual gaps, and thus used adjusted species overlap. Under both overlap definitions, prob- lists for each locality in the analyses that follow. abilities of distributional overlap were calculated In addition, these analysesdo not include highly for all possible combinations of altitudinal range aerial species (e.g., Apodidae, certain Falconi- widths of two species(i.e., one to eleven stations) formes) and speciesof uncertain seasonal status of speciespairs. For the eight congenerpairs and in the area (e.g., Selasphorusplatycercus, Pheuc- six congener trios resident in the Sierra de Ato- ticus melanocephalus, Caprimulgus vociferus). yac, predicted overlap frequencies were calcu- Because it was difficult to distinguish seasonal lated as the weighted mean probability of overlap movements from actual residency of several un- over all possible congener species-pairs.Overlap common species, altitudinal ranges may have probabilities were weighted by devaluing prob- been overestimated for some species.(Complete abilities from congener trios so that each genus avifaunal information is given in Navarro [ 19861 contributed equally to the overall mean. Actual and Navarro et al. [in prep.].) Altitudinal pat- overlap frequencies(also a mean weighted so that terns of species turnover were summarized in each