Ecology, 63(6), 1982, pp. 1657-1664 © 1982 by the Ecological Society of America

EFFECTS OF LATITUDE, SEASON, ELEVATION, AND MICROHABITAT ON FIELD BODY TEMPERATURES OF NEOTROPICAL AND TEMPERATE ZONE SALAMANDERSl

MARTIN E. FEDER Department ofAnatomy and Committee on Evolutionary Biology, The University of Chicago, Chicago, Illinois 60637 USA, and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720 USA

AND

JAMES F. LYNCH Chesapeake Bay Center for Environmental Studies, Smithsonian Institution, P.O. Box 28, Edgewater, Maryland 21037 USA, and Museum of Vertebrate Zoology, University of California, Berkeley, California 94720 USA

Abstract. We analyzed field body temperatures of neotropical salamanders (Feder et al. 1982b) to examine existing generalizations about salamander thermal ecology, which have been based almost entirely upon data for temperate zone species. Our findings can be summarized as follows: 1) Behavioral thermoregulation in the field is evidently uncommon among the vast majority of tropical and temperate salamander species. Body temperatures of tropical salamanders closely parallel seasonal and altitudinal changes in the thermal environment. 2) Body temperatures of salamanders show a complex relationship with latitude. Temperate zone species experience lower minimum temperatures than neotropical salamanders, but there are no consistent latitudinal trends in maximum body temperatures. Tropical plethodontids and ambysto­ matids show similar rates of decline in mean body temperature with increasing elevation, but am­ bystomatid temperatures are significantly warmer than plethodontid temperatures at the same ele­ vation. 3) Variation in body temperature is greater seasonally for temperate salamanders than tropical salamanders. At a given time or locality, however, variation in field body temperature among members of a population is similar for tropical and temperate salamanders. 4) Interspecific thermal differences are not evident in sympatric species of tropical salamanders, and therefore may not serve as a means of niche segregation in tropical salamander communities. These latitudinal and phylogenetic differences in thermal ecology correspond to aspects of the morphology, life history, energetics, and physiological capacities of salamanders. Key words: Ambystomatidae; ectothermy; Plethodontidae; Temperate Zone; temperature; ther­ moregulation; tropical; variability.

INTRODUCTION The first of these generalizations is that salamanders In the Neotropical Region, salamanders exploit di­ in the field exert little behavioral control of their body verse habitats from lowland rain forest to montane temperatures, i.e., that salamanders are classical 'poi­ paramo (Wake and Lynch 1976). The neotropical sal­ kilotherms' (Bogert 1952, Brattstrom 1963, 1970a). One amanders include two families: the Plethodontidae, of several potential causes for such poikilothermy in which lack lungs, and the Ambystomatidae. The trop­ terrestrial salamanders from the temperate zone is that ical plethodontids are widely distributed and are ter­ microhabitats that might otherwise be selected to reg­ restrial or arboreal ~ the tropical ambystomatids have ulate body temperature are prohibitively dry (Feder restricted distributions in northern and central Mexico and Pough 1975, Tracy 1976, Brattstrom 1979). If lack and are primarily aquatic. The neotropical salaman­ of suitably moist microhabitats indeed limits behav­ ders are expected to differ from their temperate'zone ioral thermoregulation of temperate zone salamanders, counterparts in many aspects of their biology, partic­ then such thermoregulation might be expected to oc­ ularly in thermal relationships. Here we analyze field cur more frequently in the humid tropics. body temperatures of tropical salamanders to test the A second generalization is that salamanders, partic­ validity of previous generalizations about salamander ularly plethodontids, are physiologically restricted to thermal ecology. The latter have been based almost relatively cool temperatures. Abundant field data for entirely upon observations of temperate-zone species. temperate zone salamanders (Brattstrom 1963, Feder et al. 1982b) support this contention. Some investi­

I Manuscript received 13 October 1981; revised 23 Feb­ gators have suggested that the generally cool body ruary 1982; accepted 2 March 1982. temperatures of temperate zone plethodontids reflect 1658 MARTIN E. FEDER AND JAMES F. LYNCH Ecology, Vol. 63, No.6

physiological limitations, and that such limitations have Our data for tropical ambystomatids all refer to aquat­ constrained the geographic distribution, local abun­ ic forms. Water temperatures were taken 15 cm deep dance, behavior, reproductive tactics, and morpholog­ at arm's length from the water's edge, the general area ical diversification of salamanders (Whitford and where most salamanders were captured. Voucher Hutchison 1965, 1967, Bachman 1969, Beckenbach specimens have been deposited in the Museum ofVer­ 1975). Maximum field body temperatures of tropical tebrate Zoology, University of California, Berkeley, salamanders, especially plethodontids, are of special California. A complete listing of the primary data, in­ interest in this regard (Wake 1970, Feder 1976). cluding localities, habitat information, and collection A third generalization concerns thermal variability. dates, is available from the Herpetological Information Because tropical climates typically exhibit much lower Service, Smithsonian Institution, Washington, D.C., seasonal and daily thermal variability than temperate (Feder et al. 1982b). climates (Janzen 1967), the thermal regime of tropical We also reviewed the literature for records of body salamanders should be relatively stable. Latitudinal temperatures for temperate zone salamanders; a listing differences in climatic stability are thought to underlie of these data is likewise available (Feder et al. 1982b). both the finely partitioned altitudinal segregation of We have omitted unreliable records (e.g., measure­ tropical species (Schmidt 1936, Wake and Lynch 1976, ments of air temperature at collection sites) from this Huey 1978) and latitudinal variation in the physiolog­ compilation. ical responses of amphibians to thermal variation To analyze the effects of season, latitude, and ele­ (Snyder and Weathers 1975, Feder 1978, 1982a). How­ vation on body temperatures of tropical salamanders, ever, latitudinal differences in annual variation ofbody we performed stepwise multiple linear regression on temperature in individual species have not been doc­ the mean temperature for each sample of a tropical umented previously, and are examined here. species taken at a given place and date. We omitted Temperature is a potentially important niche dimen­ means for tropical plethodontids that represented rec­ sion along which species may segregate to lessen com­ ords for fewer than three conspecific individuals. This petitive overlap (Magnuson et al. 1979). However, protocol avoided undue weighting of large numbers of temperature appears to play little or no role in the local temperature records for a given species at one partic­ structuring of temperate zone salamander communi­ ular time and location; at the same time it eliminated ties, despite the restriction of some species to certain possibly misleading isolated temperature records for elevational or vegetational zones. At a given location, single individuals. Records for tropical species were sympatric salamander species have similar body tem­ pooled into two seasonal categories (Winter = N0­ peratures (Bogert 1952, Spotila 1972, Lynch 1974). vember-March; Summer = April-October), and two Differences in water relations and competition for space latitudinal zones (Northern tropical = Mexico north seem to be the major determinants of interspecific seg­ of Chiapas; Mid-tropical = Chiapas and Middle regation for terrestrial salamanders in the Temperate America). Season, latitude, and family (plethodontid Zone (e.g., Dumas 1956, Jaeger 1971a, 1971b, Spotila or ambystomatid) were entered into the regression 1972, Hairston 1980). In the present study we consider equation as dummy variables (Draper and Smith 1966), thermal differences as one potential means of niche with values either 0 or 1. segregation in tropical salamander communities. Up Tests of between-sample differences in central ten­ to 15 salamander species occur on a single tropical dency or variability used nonparametric statistical mountainside, and as many as 6 of these may be lo­ procedures as described by Siegel (1956). cally sympatric (Wake and Lynch 1976).

In summary, this report contrasts tropical and tem­ RESULTS perate zone salamanders with respect to: (1) behav­ ioral thermoregulation, (2) maximum and minimum field Body temperatures body temperatures, (3) spatial and temporal variability Elevation, season, and family each significantly in­ in field body temperatures, and (4) interspecific differ­ fluence mean body temperatures of neotropical sala­ ences in body temperature within local communities. manders (Table 1, Fig. 1). For tropical plethodontids, a simple regression of mean body temperature against MATERIALS AND METHODS elevation explains nearly two-thirds of the variance in We gathered body temperatures of tropical pletho­ mean body temperature [r 2 = Coefficient of Determi­ dontids by measuring the temperature of the substrate nation = .63]. Addition of season to the regression immediately beneath resting salamanders with either equation (step 2) increases r 2 to .75, but the inclusion a YSI Telethermometer (Yellow Springs Instrument oflatitude (step 3) has no significant effect. The regres­ Company, Antioch, Ohio) or a Schultheis quick-read­ sion equation for tropical plethodontids is thus: ing mercury thermometer. Bogert (1952) has shown Mean body that this method yields accurate approximations of sal­ temperature (OC) = 27.3 - 5. 1 Elevation (km) amander body temperatures. We shaded the temper­ - 3.2 Season '(1) ature sensor and carefully avoided changing the sub­ strate temperature inadvertently during measurements. where season is coded 1 for winter and 0 for summer. December 1982 SALAMANDER BODY TEMPERATURES 1659

TABLE 1. Summary of analysis of covariance for mean body A. PLETHOOONTIOS temperatures of tropical salamanders. ,-.... 30 U o + Mean '--"" 25 - Source of variation df square F p w ----;.--- + ~ 20 ---1tI-_C: + Constant 1 30102.48 3798.60 <.001 ~ ---- -+ -+- + + Elevation 1 1217.84 153.68 <.001 ~ 15 'l:t;-~- "'~ Season 1 279.88 35.32 <.001 w += SUMMER ----!?--ad?+-- Family 1 509.41 64.28 <.001 ~ 10 o = WINTER ~-~ ~:~--~ Elevation x season 1 3.85 0.49 .487 W Elevation x family 1 0.13 0.02 .900 r- 5 -+-----,------,,.----r-----.------.--_.__-----.------J..J-, Season x family 1 27.60 3.48 .065 400 800 1200 1600 2000 2400 2800 3200 3600 Elevation x season x family 1 4.91 0.62 .433 ,-.... B. AMBYSTOMATIOS Within + residual 110 7.92 U 0 30 '--"" + w 25 --- + ~ ~ ++ -----:t-j;- + => 20 --__ +0+0- -- __ + The relationship between mean temperature and el­ ~ ---~-~:#J- ~ 0------_ evation is similar for tropical ambystomatids: 15 w ~ + --- Q... !:iB"---D--_ ~ o - Mean body W 10 I- 400 800 temperature (OC) = 32.0 - 5.0 Elevation (km) 1200 1600 2000 2400 2800 3200 3600 ELEVATION (m) - 5.0 Season (2) FIG. 1. Effect of elevation and season on body temper­ However, temperatures for tropical ambystomatids atures of tropical plethodontid (above) and ambystomatid and tropical plethodontids differ in several ways. At (below) salamanders. Regression lines for winter and summer comparable seasons and elevations, mean tempera­ are plotted in each figure. tures for ambystomatids are greater, possibly more seasonal (P = .065, Table 1), and less well correlated with elevation and season (r2 for Eq. 2 = .47) than are plethodontids than for plethodontids, both at tropical equivalent values for plethodontids. and temperate latitudes (Table 2). Most instances in For most tropical species, samples are too few or which maximum temperatures for nonplethodontids elevational ranges too narrow to allow a meaningful exceed 25° involve either aquatic larvae (e.g., Ambys­ test for elevation-body temperature correlations with­ toma spp., Taricha rivularis) or adults of species that in species. However, for 12 tropical populations of the inhabit still water (e.g., Siren spp.). The only com­ ambystomatid Ambystoma tigrinum, the body tem­ parably high value for a temperate plethodontid in­ perature, elevation, and season are related as follows: volves Eurycea [Manculus] quadridigitatus (maxi­ mum temperature = 26.3°), a swamp-dwelling form Mean body (Feder et al. 1982b). temperature (OC) = 29.7 - 3.7 Elevation (km) Temperate species experience lower minimum tem­ - 5.4 Season (3) peratures than tropical species (Table 2). In addition, Elevation accounts for 33% of the variance in body tropical plethodontids have lower minima than tropical temperature, and season accounts for an additional ambystomatids. 28%. Of the three species of tropical plethodontids (Bolitoglossa franklini, Chiropterotriton chiropterus, Variation in body temperature and Pseudoeurycea leprosa) for which at least four Each sample of body temperatures (all records for samples are available throughout a substantial eleva­ a given species taken at a single locality on the same tional span, only P. leprosa (n = 4 samples) showed day) reflects thermal variation experienced by a pop­ a significant correlation between mean body temper­ ulation under prevailing climatic conditions. We quan­ ature and elevation (Spearman's r = -1.0; P < .05). tified this variation by calculating the range and stan­ However, values of r", for the remaining two species dard deviation for each sample. Few previous reports have the predicted negative sign, and we suspect that have included both of these statistics, so we have ana­ larger samples would reveal significant altitudinal trends lyzed them separately. within all tropical salamander species that have sig­ Both range (Fig. 3) and standard deviation of tem­ nificant elevational distributions. peratures within a sample show the same pattern. No Fig. 2 depicts maximum and minimum temperatures differences in within-sample variability are evident be­ for both tropical and temperate salamander species. tween tropical and temperate plethodontids or be­ In species with records for only one season, winter .tween temperate plethodontids and nonplethodontids temperatures were omitted from analysis of maximum (P > .05; Kruskal-Wallis test for difference in central temperature and summer temperatures were omitted tendency and Kolmogorov-Smirnov test for shape of from analysis of minimum temperature. distributions). Maximum body temperatures are greater for non- For tropical plethodontids, the standard deviation 1660 MARTIN E. FEDER AND JAMES F. LYNCH Ecology, Vol. 63, No.6

14 A. TROP ICAL PLETHOOONTIOS 14 A. TROP ICAL PLETHOOONTIOS

12 12 10 10 8 8 6 6 4 4 2 2 o o -1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33

TROP I CAL AM8YSTOMATIOS 4 8. TROP ICAL AM8YSTOMATIOS ~ ~j IS. r,' ~" n~j" r ,I fV1 ~ ~ ~ -1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 a w 8: 10 C. TEMPERATE PLETHODONTI DS 10 C. TEMPERATE PLETHOOONTIOS 8 6 4 i~~nni 2 o -1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 ~l TH~D~NT:DSn ~l r , :TE:E ,NO

-1 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 MINIMUM TEMPERATURE COC) MAXIMUM TEMPERATURE COC) FIG. 2. Minimum and maximum body temperatures of salamanders. Unshaded bars represent species for which only summer records were available for minimum temperature or species for which only winter records were available for max­ imum temperature.

of series temperatures is unrelated either to elevation The above generalizations fail to encompass some or to the number of temperature records in a series temperate and tropical species. Notable exceptions (P > .05; Kendall's tau). However, the range of tem­ (Feder et al. 1982b) include temperate species that live peratures is proportional to the number oftemperature in forested, thermally equable streams (e.g., Dicamp­ records in a series; the partial correlation coefficient todon, Rhyacotriton), caves, or cave outflows (e.g., between range and sample size (with elevation held Eurycea multiplicata). These taxa resemble tropical constant) is .52 (P < .001). species in encountering only modest seasonal temper­ Detailed seasonal records of temperatures are lack­ ature fluctuations. ing for most species, but sufficient data are available for 48 populations (Feder et al. 1982b) to allow some Species differences generalizations. Tropical and temperate salamanders Body temperatures are available for 11 pairs of neo­ differ markedly in seasonal variability in temperature. tropical salamander species collected in sympatry With values for plethodontids and nonplethodontids (Feder et al. 1982b). None of the members of these pooled, annual variation is 16.8 ± 1.1 0 (mean ± stan­ species pairs differs significantly in temperature, and dard error) for temperate species (n = 2g) but only the largest measured temperature difference between 0 0 7.6 ± 0.7 for tropical species (n = 20). These differ­ any two species at a given site is only 1.1 • Thus, ences in variation are highly significant (Table 2). Thus, thermal segregation seems uncommon as a mechanism temperate salamanders experience more than twice the for subdividing habitat space among locally sympatric annual thermal variation oftheir tropical counterparts. neotropical plethodontids. Indeed, the figures presented here undoubtedly un­ derstate the true latitudinal differential, as many tem­ DISCUSSION perate species must experience near-freezing temper­ It is important to recognize the implicit assumptions atures in their winter retreats, where they are in using single measurements from different individu­ inaccessible to collectors. Except for a few high mon­ als to estimate the range of thermal conditions en­ tane forms, tropical salamanders are rarely or never countered by a salamander population as a whole. subjected to temperatures this low. Many terrestrial salamanders alternate between sur- December 1982 SALAMANDER BODY TEMPERATURES 1661

TABLE 2. Mean temperature records and mean annual vari­ 16 A. TROP I CAL PLETHOOONTIOS ation for tropical and temperate salamanders. We per­ formed all possible pairwise Mann-Whitney V tests among 14 groups within columns. Superscript letters indicate results 12 of tests with Bonferroni's inequality. Groups are consid­ 10 ered significantly different when P of V < (.05/number of pairwise tests). Means with common superscript letters do not differ significantly.

Body temperature o 1 2 3 4 5 6 7 8 9 10 11 12 13 Mini- Maxi- Annual Group mum mum range >- ~ 12 B. TEMPERATE PLETHOOONTIOS d a w Tropical nonplethodontids 14.6 23.2 7.9 ~ 10 e a a Tropical plethodontids 9.7 17.4 7.3 w 8 Temperate nonplethodontids 5.6b 21.8 d 17.5c 0::: u... 6 Temperate plethodontids 3.3 b 17.ge 16.1 c

o o 1 2 3 4 5 6 7 8 9 10 11 12 13 face and subterranean microhabitats, and 90-10Qt% of a given population may be underground at any given time, even when surface activity is feasible (Anderson ~l JaN~P:D:TIDS 1960, Heatwole 1962, Burton and Likens 1975, V. Maiorana, personal communication). Because deep soil temperatures are stable and moderate (Geiger 1965), o 1 2 3 4 5 6 7 8 9 10 11 12 13 measurement of surface temperature alone is likely to SAMPLE RANGE cOe) overestimate the thermal variability of the population FIG. 3. Range ofbody temperatures for salamanders. Each as a whole. In addition, salamanders often are highly range is for a sample of conspecific salamanders taken at the same site on a given day. Only samples for which n > 3 are sedentary, with home ranges of only a few square included. metres (Maiorana 1974). Hence no individual animal may encounter the full range of temperatures mea­ sured from a series of salamanders at a given locality. In the extreme case, one individual may experience temperate zone counterparts (Maximum == 30°C; Fig. consistently warm temperatures throughout the activ­ 2). Nevertheless, the overall lack of latitudinal differ­ ity season, while another individual in a shady spot a ences in maximum temperature is not entirely unex­ few metres away might experience cooler but equally pected, for maximum warm-season temperatures are stable temperatures. Yet a series of single temperature similar in many temperate and tropical areas readings representing many individuals might suggest (Mac Arthur 1972). that individual salamanders are subjected to a variable In general, tropical plethodontids experience the thermal environment. Continuous records of individ­ same moderate maximum body temperatures as their ual salamanders or appropriate microhabitats may be temperate zone counterparts. We speculate that a ma­ necessary to resolve such ambiguities, but repeated jor factor underlying this similarity is the interaction disturbance of cover objects is likely to disrupt both between lunglessness and the temperature of suitable the animals themselves and their microclimate. Pend­ microhabitats. Except in the moist tropical lowlands, ing the availability of data from highly miniaturized warm terrestrial microhabitats tend to be too dry to thermal telemeters, the admittedly imperfect data we be suitable retreats for salamanders (Feder and Pough present here are as realistic as can be obtained in the 1975). Because they lack lungs, plethodontids may have field. difficulty in exploiting warm but oxygen-deficient A surprising outcome of our tropical-temperate aquatic microhabitats (Ultsch 197M, Feder 1977). comparison is that tropical plethodontids do not ex­ Oxygen exchange in submerged plethodontids is high­ perience maximum temperatures greater than those of ly susceptible to hypoxic limitation (Beckenbach 1975, temperate salamanders. This result may in part reflect Ultsch 1976b), and plethodontids cannot compensate our unintentional bias in favor of montane tropical for aquatic hypoxia by inspiring air at the surface, a species; only II% of our 97 temperature series are common practice in many aquatic vertebrates (Randall from populations living below 1500 m elevation. This et al. 1981). The fact that most records of body tem­ underrepresents the tropical lowland plethodontids, peratures ~25° involve aquatic nonplethodontid sala- which constitute 2Qt% (30 species) of all tropical pleth­ . manders, both in the tropics and the temperate zone, odontids (Wake and Lynch 1976, Feder et al. 1982a). supports this speculation. Body temperatures of lowland tropical plethodontids Our data provide no evidence for behavioral ther­ occasionally are as warm or warmer than those oftheir moregulation in either temperate or tropical salaman- 1662 MARTIN E. FEDER AND JAMES F. LYNCH Ecology, Vol. 63, No.6

ders. The mean decrease in salamander body temper­ cated on the well-established difference in thermal ature with increasing elevation (5.1°/km) is similar to variability between tropical- and temperate-zone cli­ the adiabatic lapse rate for moist air, 6.5°/km (Miller mates (Janzen 1967). However, none of these studies and Thompson 1975). Tropical salamanders act as es­ has measured thermal variation experienced by indi­ sentially passive indicators of the prevailing surface vidual organisms; instead, gross climatic characteris­ temperature, and show little tendency to depart from tics have been used as an index of probable variation 'average' conditions expected for a given site. The few in animal body temperature. This approach can lead known instances of thermoregulation in the field by to erroneous results for at least two reasons. First, tropical plethodontids (Feder 1982b) are clearly ex­ microclimate often differs markedly from the macro­ ceptional. These involve extremely diminutive sala­ climate measured by weather stations (Swan 1952, manders (Thorius) that seek out warm temperatures Bartholomew 1958, Geiger 1965). In addition, a ther­ in the space beneath loose bark on logs exposed to the moregulating animal may experience a thermal envi­ sun. The larger size ofmost other tropical salamanders ronment that is very different from the 'climatic' tem­ denies them access to this moist thermal gradient. perature, however the latter is measured (Pearson The data (Feder 1982b, Feder et al. 1982b, and ref­ 1954). Thus, our field data are significant in that they erences cited therein) suggest only that thermoregu­ are the first documentation of major latitudinal differ­ lation is infrequent among salamanders, and not that ences in variability of body temperatures of related temperature is unimportant to salamanders. Temper­ animals. ature has profound effects on the energetics, growth, Possible ecological consequences of the observed and reproduction of salamanders (see below). Our data latitudinal differences in thermal ecology include dif­ also do not rule out the possibility that salamanders ferences in feeding and assimilation rates (Merchant engage in activities such as courtship and foraging only 1970, Bobka et al. 1981), reproductive periodicity within limited temperature ranges, and thereby effec­ (Houck 1977), growth and differentiation (Houck 1977, tively 'maintain' stable body temperatures during ac­ Hanken 1979), and other fundamental aspects of life tivity. Both energetic costs and the potential vapor history (Hanken et al. 1980). Tropical plethodontids pressure gradient are proportional to temperature; sal­ have lower temperature-specific rates of oxygen con­ amanders may be restricted to nocturnal foraging within sumption than temperate salamanders (Feder 1976, a narrow range of temperatures even though the tem­ 1977). Also, tropical plethodontids are less able than perature per se does not limit foraging (Spotila 1972). temperate species to undergo thermal acclimation of No conclusive data are available to substantiate these oxygen consumption (Feder 1978). These differences possibilities; however, circumstantial evidence sug­ may reflect an historical loss ofancestral physiological gests that foraging activity in terrestrial salamanders capacities by neotropical plethodontids, perhaps in re­ is primarily a function of their water relations and not sponse to the reduced thermal variability of their en­ of temperature per se (Rosenthal 1957, Spotila 1972, vironments. Jaeger 1978), and that tropical plethodontids court and Physiological ecology has advanced considerably oviposit without regard to seasonal thermal variation beyond the classical dichotomous characterization of (Houck 1977). organisms as 'poikilotherms' and 'homeotherms.' Re­ The apparent rarity of behavioral thermoregulation cent research has documented the diverse means by in tropical salamanders may be due in part to the low which organisms exert behavioral and physiological thermal heterogeneity in moist tropical forests, partic­ control oftheir thermal environment (Brattstrom 1979, ularly in the cloud forest inhabited by many species Regal and Gans 1980). Accordingly, it is somewhat (Wake and Lynch 1976). Records for contiguous moist ironic to conclude from our field studies that most sal­ microsites within individual bromeliads (Tillandsia amanders, particularly plethodontids, functionally em­ spp.) and banana plants (Musa sp.) yield temperature body the classical definition of poikilothermy. How­ ranges of 2.0° and 3.7°, respectively (Feder 1982b). ever, this is less than surprising given that Given this modest thermal gradient, salamanders can thermoregulatory strategies evolve only within the exert little behavioral control of their body tempera­ constraints ofthe physical environment (Spotila 1980). tures, and clearcut interspecific differentiation cannot occur within a local habitat. Moreover, we are unable ACKNOWLEDGMENTS to document any consistent thermal differences asso­ We thank L. Houck, H. Pough, J. Spotila, T. Taigen, D. ciated with particular microhabitats, other than their Wake, and R. Wassersug for constructive criticism of the manuscript; A. Bennett, J. Feder, J. Hanken, L. Houck, T. elevation. Thus, little distinguishes the thermal envi­ Papenfuss, M. Wake, and D. Wake for assistance in gathering ronment of terrestrial vs. arboreal sites, or leaf litter thermal data; and M. Haber, A. Farber, S. Underhill, and B. vs. rocks or logs as cover objects. J. Bialowski for aid in data analysis. Collecting permits were Many studies that have contrasted thermal special­ provided to D. Wake by Mexican (Direcci6n General de la izations of temperate and tropical organisms (e.g., Fauna Silvestre) and Guatemalan (lnstituto Nacional Fores­ tal) authorities. Research was supported by the following: Brattstrom 1968, 1970b, Levins 1969, Snyder and National Science Foundation Grant DEB 78-23896, Uriiver­ Weathers 1975, Feder 1978, 1982a) have been predi- sity of California Chancellor's Patent Fund, The Andrew December 1982 SALAMANDER BODY TEMPERATURES 1663

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