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Home , Crotalus willardi, Natural History, Systematics

AMER. ZOOL., 34:48-56 (1994)

Systematics and , Foundations for Understanding and Conserving Biodiversity1

HARRY W. GREENE of Vertebrate and Department of Integrative , University of California, Berkeley, California 94720

SYNOPSIS. Enhanced by recent technical and conceptual advances, two classical endeavors in biology play vital roles in understanding, appre- ciating, and managing . Systematics defines the fundamental Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021 units and relationships among living things; natural history chronicles the lifestyles of in relation to environments. For example, analyses of evolutionary relationships emphasize the uniqueness of certain taxa, help prioritize groups of organisms for conservation, and enable us to estimate the biology of unstudied taxa. Radiotelemetry permits repeated location of and other stealthy , facilitating previously impossible behavioral studies and thus laying the groundwork for effective management. Natural history in a systematic and geographic context pro- vides a "rule-of-thumb" for predicting due to global climate change. Educators should emphasize the urgency of the biodiversity crisis, inform debates about priorities for funding and other conservation mat- ters, and teach about the goals, methods, and applications of systematics and natural history.

INTRODUCTION UNDERSTANDING AND APPRECIATING An environmental crisis is upon us, not BIODIVERSITY just looming on the horizon. More than six What are systematics and natural history? billion humans will burden the earth by the Systematics encompasses the character- end of the 20th Century, regardless of our istics, genetic status, and evolutionary his- best efforts, and extinction of many tories of organisms. Once devoted mainly and is underway now. In to describing obvious phenotypic variation addition to ameliorating the harmful effects and coining formal names, systematists now of growth and pollution, we must evaluate samples from throughout the geo- rapidly influence public opinion and save graphic distribution of living things with portions of the remaining biotas (Wilson, morphological, biochemical, multivariate 1992). Here I briefly review the broad goals statistical, and other sophisticated tech- and methods of modern systematics and niques. Phylogenetic systematics, in partic- natural history, then illustrate how these ular, strives to infer the evolutionary his- activities contribute to our understanding, tories of independent lineages (species and appreciation, and conservation of biodiver- higher taxa), and to determine relationships sity. I focus on the applications of phylo- between and the divergence of genetic analysis and on telemetry studies of organisms (Cracraft, 1994; O'Hara, 1994). stealthy vertebrates, illustrating how new techniques enhance traditional approaches. Natural history focuses on where - isms are and what they do in their environ- ments, including interactions with each other. The building blocks of natural history are descriptive and - detailed accounts of organismal biology in 1 From the symposium Science as a Way of Know- ing—Biodiversity presented at the Annual Meeting of natural settings—followed by experimental the American Society of Zoologists, 27-30 December studies of factors that affect distribution, 1992, at Vancouver, Canada. abundance, and interactions. 48 BASIC BIOLOGY AND BIODIVERSITY 49

Conserving and appreciating The uncertain but potentially serious con- Systematics and natural history define the sequences of rapid climate change are a new boundaries and contours of biodiversity; challenge for conservation in the coming they elucidate the fundamental kinds of decades. Ideally, the predicted impact of organisms (species and higher taxa) as well temperature and moisture shifts (via organ- as their interactions with each other and ismal ) on population viability their environments. Areas are chosen for will be incorporated into management strat- conservation based on, among other crite- egies (Kareiva et al., 1992). Such detailed ria, the kinds and numbers of organisms knowledge requires years of research and is Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021 they encompass; effective captive breeding available for relatively few species, so indi- and reintroduction depend on knowledge of rect methods are potentially useful. For example, McDonald and Brown (1992) used a species' ecology and behavior; and pop- presence or absence of montane ular films and books translate research find- on isolated ranges of different sizes in the ings about nature into public education Great Basin to estimate minimum refuge (Greene and Losos, 1988). I will elaborate areas for each species. The resulting thresh- on two roles for systematics and natural his- olds for refuge area were then compared with tory, the first ubiquitous but widely unrec- estimates of shrinkage from climate ognized and the other relatively new. change to predict future . That If wild organisms and places are to be technique is limited to fairly large samples conserved, they must have value in human of habitat islands with well-documented societies. Interactions among and biotas; a less precise but more broadly appli- animals hold countless solutions to natural cable "rule-of-thumb" approach based on problems with analogues in human welfare; systematics and natural history is illustrated the skin toxins of dart-poison frogs and other later in this paper: Terrestrial species with natural products with pharmaceutical appli- fragmented geographic ranges and narrow cations are well known examples (e.g., Wil- elevational tolerances are especially at risk son, 1992). Equally important in the long under changing regimes of temperature and run, systematics and natural history also moisture. underlie esthetic evaluation, cultural accep- tance, and prioritization for management. STUDYING STEALTHY VERTEBRATES Beyond intrinsic cuteness, we regard the giant panda as special because of its con- The information on ecology and behavior troversial relationships with bears and rac- necessary for conservation, management, coons, strange thumblike dewclaws, and diet and nature appreciation are available for of bamboo. In the economic and political only a tiny fraction of species, generally those arenas of conservation, efforts to save rain- that are large, common, or otherwise rela- forests are based on their demonstrably tively easy to study (Greene, 1986). incomparable biodiversity, not just the Advances in telemetry during the past two emotional responses some of us have to decades, however, have greatly enhanced those places. Striking resemblances of unre- research on stealthy and otherwise cryptic lated organisms from distant, similar hab- animals. Early workers mostly localized itats are a common theme in exhibit labels radio signal coordinates on a map, but and other forms of environmental educa- recently have used telemetry to tion, yet without phylogenetic evidence that study undisturbed animals more directly in similar traits indeed were acquired inde- nature (e.g., Emmons, 1987, for rainforest pendently we could not marvel at conver- cats). Our research on pitvipers in gent (Luke, 1986). Systematics and illustrates the use of miniaturized, surgically natural history even facilitate the transfer implanted transmitters (Reinert, 1992) to and evaluation of knowledge about nature facilitate repeated encounters and behav- among human societies, since ioral . is based on their results (e.g., Patton et al, Since 1986 my colleagues and I have fol- 1982). lowed 17 blacktailed rattlesnakes ( molossus) in the Chiricahua Mountains, for HARRY W. GREENE Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021

FIG. 1. Vignettes from the natural history of blacktailed rattlesnakes (Crotalus molossus) in the Chiricahua Mountains, Cochise Co., Arizona. Courtship behavior in a juniper tree, 24 August 1991; telemetered male's head (#8, total length ca. 1 m) is pressed against the smaller female's neck (photograph by D. L. Hardy, ST.). periods of a few days to more than four or by following previously telemetered indi- years. Despite bright colors and a total length viduals, and during ca. seven months of of ca. 1 m, these snakes are indeed cryptic fieldwork at the site I encountered only one and difficult to locate. Most of our study blacktail by visual scanning in the habitat. animals were found as they crossed a road With telemetry, we have documented pat- BASIC BIOLOGY AND BIODIVERSITY 51 Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021

FIG. 2. Vignettes from the natural history of blacktailed rattlesnakes (Crotalus molossus) in the Chiricahua Mountains, Cochise Co., Arizona. Telemetered male (#6, total length ca. 80 cm) basking on a woodrat (Neotoma) nest, 29 September 1990; a suspiciously rat-sized bulge is visible on the left side of the . In each case observations commenced when the male was located initially by radiotelemetry. terns of daily and seasonal movements, Two SMALL RATTLESNAKES: SYSTEMATICS, ambush hunting tactics, late autumn feed- NATURAL HISTORY, AND DIVERGENT ing, courtship, copulation, shifts in retreat CONSERVATION PROSPECTS sites during the winter, and various main- Ridgenosed rattlesnakes (Crotalus wil- tenance behaviors in the field (Figs. 1, 2). lardi) inhabit the Sierra Madre Occidental In 1992 we extended radiotelemetry to a of and nearby mountains in the U.S. poorly known species with special conser- (Fig. 4). The ridgenosed rat- vation status, the ridgenosed rattlesnake tlesnake (C w. obscurus) is on the U.S. {Crotalus willardi, total length ca. 40 cm) in List and the Arizona the Huachuca Mountains. During the first ridgenosed rattlesnake (C. w. willardi) is state year's work with four telemetered C. wil- listed as threatened. The relatively well- lardi we have observed hunting, courtship, studied systematics of ridgenosed rattle- copulation, and winter activity (Fig. 3). Our snakes (Barker, 1992) provides important findings on mating patterns and seasonal insights for their conservation. First, infor- movements, among other factors, eventu- mation on the natural history of some taxa ally will help identify critical habitat for that can be used to estimate that of their unstud- species. ied or unstudiable relatives (Brooks et ai, HARRY W. GREENE

1992). Although only C. w. obscurus is offi- cially "endangered," systematics provides strong support for Arizona's strict protec- tion of C. w. willardi; three alternative phy- logenies and two ranking methods agree that the latter is evolutionarily more distinctive than the former (Fig. 5). Massasauga rattlesnakes (Sistrurus cate- natus) inhabit seasonally wet grasslands,

bogs, and adjacent forests from Arizona and Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021 northern Mexico to New York and southern Canada, a distribution indicative of post- Pleistocene expansion of prairie into north- eastern North America (Schmidt, 1936). In contrast to Crotalus willardi, geographic variation in S. catenatus is so incompletely studied that we lack a basis for prioritizing any particular segment of the range in terms of phylogenetic significance; three subspe- cies are based on vaguely defined clinal vari- ation in coloration and a few scale counts, and relationships among are unknown (Gloyd, 1955). Most massasauga populations are isolated by land conversion for agriculture, and the species is threatened or endangered throughout much of its range (Seigel, 1986). The status ofS. catenatus in the southwestern U.S. is especially precar- FIG. 3. Courting ridgenosed rattlesnakes (Crotalus ious; there are no recent records from west willardi) in the Huachuca Mountains, Cochise Co., Ari- of the Pecos River in Texas or from south- zona, 21 July 1992. The snakes are coiled and the western New Mexico. A few small popula- telemetered male (# 1, total length ca. 60 cm) is tapping the female's back (#7) with his chin (photograph by F. tions remain in Arizona, where massasau- Wilson); this species is difficult to locate in its typical gas are seen above ground only during the microhabitat of oak leaves and bunch grass (note dia- late summer rainy season and their persis- gram). tence might be dependent on the stable high humidity in kangaroo rat burrows (Kay and Whitford, 1978). 1992). Four subspecies of C. willardi feed Systematics and natural history enhance on and as juveniles and appreciation for these small pitvipers and on rodents (rarely ) as adults, but only suggest divergent prospects for conserva- one natural prey item (a warbler) is known tion. Neither species constitutes a threat to for the New Mexico race (Greene et ah, human welfare and both are regarded as unpublished). Lacking direct information, attractive by naturalists (some Native management can precede on the conser- Americans called massasaugas "pictures of vative assumption that C. w. obscurus has the sun," alluding to the large, silver-edged not diverged in diet from other ridgenosed dorsal blotches). Both are living icons for rattlesnakes. Second, all members of a group landscape history, ridgenosed rattlesnakes {e.g., species in a genus) usually have been for fragmentation of ancient mountain valued equally, thus ignoring their differ- ranges and massasaugas for more recent ential evolutionary significance if particular vagaries of grassland . Biogeog- taxa must be slighted when funds, person- raphy, based on systematics and natural his- nel, and other resources are scarce (Vane- tory, suggests that these two species would Wright et al, 1991; Greene and Campbell, respond differently to anthropogenic cli- BASIC BIOLOGY AND BIODIVERSITY 53

Desert Grassland Encinal Pine-Oak Woodland

Coniferous Forest Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021

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willardi Peloncillo Mts. PhobscUrus Douglas/ /_;J; xd.?. j Agua Prieta

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CHIHUAHUA silus

50 miles

FIG. 4. Distribution of three subspecies of the ridgenosed rattlesnake (Crotalus w. willardi, C. w. obscurus, and C. w. silus) in the northern Sierra Madre Occidental and outlying ranges of Mexico, Arizona, and New Mexico; two Mexican subspecies are not shown (based on Marshall, 1957; Barker, 1992; Thirkhill and Starrett, 1992). Ridgenosed rattlesnakes occur in evergreen oak woodland ("encinal"), pine-oak woodland, and coniferous forest. mate change during the coming decades. related populations are separated by unsuit- Crotalus willardrs wide attitudinal range (ca. able habitat {e.g., grassland between the 1,475-2,770 m, Lowe et ai, 1986) spans Huachucas and Sierra de Cananea for C. w. several major vegetation belts; closely willardi, Fig. 4), suggesting that their wood- 54 HARRY W. GREENE

B U R, amabilis 1 .125 6 1 .143 a. meridionalis 1 .125 6 1 .143 obscurus 1 .125 6 1 .143 silus 1 .125 6 1 .143 Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021 willardi 4 .50 2 3 .429 2 .25 4 1.5 .231 b. amabilis meridionalis 2 .25 4 1.5 .231 obscurus 1 .125 6 1 .154 silus 1 .125 6 1 .154 willardi 2 .25 4 1.5 .231 1 1 c. amabilis .17 5 .176 meridionalis 1 .17 5 1 .176 obscurus 1 .17 5 1 .176 silus 1 .17 5 1 .176 willardi 2 .33 3 1.67 .295 FIG. 5. Three alternative hypotheses of evolutionary relationships (based on Barker, 1992) and two phylogenetic methods for assessing conservation priorities (May, 1990; Vane-Wright et ai, 1991) for five subspecies of the ridgenosed rattlesnake (Crotalus willardi). A simple method weights "sister taxa" (e.g., amabilis and meridionalis) equally and converts their scores (C) to proportions (P,). A second method totals for each the number of branches from each node between the taxon and the tree's origin (B), takes the inverse of B as a measure of phylogenetic distinctiveness (U), and converts scores for U into proportions (P2). For example, phylogeny (a) indicates that C. w. willardi represents one half of the initial divergence event in this species by P, and about 43% of overall phylogenetic distinctiveness by P2; phylogeny (b) suggests that C. w. willardi should be prioritized only at values of 25% and about 23%, respectively. Larger groups would not always yield identical rank orders of importance by P, and P2, and more refined approaches are possible with some data sets (e.g., Crozier, 1992; Faith, 1992). land repeatedly have contracted ment, the massasauga might survive only upward and expanded downward in the past in moister, eastern segments of its distri- {cf. Van Devender and Spaulding, 1979). bution. Southwestern populations would dry Under moderate global warming ridge- up like water drops on a griddle. nosed rattlesnakes probably will persist at higher elevations in several mountain BIOLOGY, CONSERVATION, AND ranges, as they have during previous glacial EDUCATION cycles. Sistrurus catenatus has a narrow ele- Unfortunately, despite the irrevocable, vational range and populations have been imminent realities of extinction, support for separated by human impact over the past systematics and natural history continues to two centuries rather than by natural, long- dwindle. Current levels of funding imply term habitat shifts. Subjected to moderate that understanding and conserving biodi- climate change and without heroic manage- versity are far less important than space BASIC BIOLOGY AND BIODIVERSITY 55 travel, sequencing the human genome, and should take every opportunity to teach about other multi-billion dollar activities (e.g., ca. modern systematics and natural history, 10 million dollars/year for systematic biol- especially their implications for appreciat- ogy at the National Science Foundation, vs. ing and managing nature. Complexities of 30 million dollars for a single toilet on the the biodiversity crisis and roles for science Space Shuttle). Underlying such disparities in conservation are appropriate topics for are our failure to comprehend the urgency discussion in every high school and under- of the biodiversity crisis, the view prevalent graduate biology course.

in some circles that those branches of biol- Downloaded from https://academic.oup.com/icb/article/34/1/48/111738 by guest on 30 September 2021 ogy are outmoded, and a widespread belief ACKNOWLEDGMENTS among lay people that knowledge is already I thank D. L. Hardy, Sr., C. W. Painter, available or can be gained easily. C. J. Schneider, T. A. Snell, B. R. Tomber- The realities are straightforward. Behind lin, and F. Wilson for their collaboration on all the facts, interpretations, and impres- research projects discussed herein; the Ari- sions in nature programs and field guides zona and New Mexico game and depart- are thousands of biologists: collecting and ments for encouraging our studies; U. C. curating specimens, weighing nestling eagles, Berkeley Committee on Research for finan- sketching fern leaves, and recording the cial support; K. Klitz for preparing the fig- behavior of ants. Practical applications of ures; and an anonymous, grizzled reviewer those and countless other seemingly esoteric for helpful criticisms of the manuscript. tasks range from developing new pharma- ceuticals to designing wildlife refuges and REFERENCES detecting pesticides in eggshells. Neverthe- Barker, D. G. 1992. Variation, infraspacific relation- less, we are surprisingly ignorant of on ships, and of the ridgenose rattle- snake, Crotalus willardi. In J. A. Campbell and E. earth. Scientists have learned how many D. Brodie, Jr. (eds.), Biology of the pitvipers, pp. are in a and how many cra- 89-105. Selva, Tyler, Texas. ters are on the moon, but not how many Brooks, D. R., R. L. Mayden, and D. A. McLennan. species of birds, butterflies, or trees live in 1992. Phytogeny and biodiversity: Conserving our Brazil. A new species of amphibian or rep- evolutionary legacy. TREE 7:55-59. Cracraft, J. 1994. Species diversity, biogeography, tile is found about every other year in Cal- and the evolution of biotas. Amer. Zool. 34:000- ifornia (Greene and Losos, 1988), one of the 000. world's best explored places, and only two Crozier, R. H. 1992. and the agony of 69 species of snakes in the western U.S. of choice. Biol. Conserv. 61:11-15. have been analyzed phylogenetically (Bar- Emmons, L H. 1987. Comparative feeding ecology of felids in a neotropical rainforest. Behav. Ecol. ker, 1992; Grismer, 1990). The biotas of Sociobiol. 20:271-283. tropical regions are even more incompletely Faith, D. P. 1992. Conservation evaluation and phy- studied, and newly discovered organisms logenetic diversity. Biol. Conserv. 61:1-10. there are literally disappearing faster than Gloyd, H. K. 1955. A review of the massasauga, they can be described. Sistrurus catenatus, of the southwestern United States (Serpentes: Crotalidae). Bull. Chicago Acad. Artists, teachers, politicians, journalists, Sci. 10:83-98. citizen activists, and scientists all have vital Greene, H. W. 1986. Natural history and evolution- ary biology. In M. E. Feder and G. V. Lauder roles to play in saving biodiversity. Of fore- (eds.), Predator-prey relationships: Perspectives and most importance is convincing everyone approaches from the study of lower vertebrates, pp. that a crisis is underway now, that solutions 99-108. Univ. Chicago Press, Chicago. must be found soon. With that recognition, Greene, H. W. and J. A. Campbell. 1992. The future we need to provoke and inform debates of pitvipers. In J. A. Campbell and E. D. Brodie, Jr. (eds.), Biology of the pitvipers, pp. 421-427. about priorities at all levels of government, Selva, Tyler, Texas. for in a monetary sense conservation com- Greene, H. W. and J. B. Losos. 1988. Systematics, petes with other scientific endeavors as well natural history, and conservation. BioScience 38: as broader societal needs. Systematists and 458^62. natural historians must refine their own goals Grismer, L. L. 1990. A new long-nosed snake (Rhino- cheilus lecontei) from Isla Cerralvo, Baja Califor- and techniques, as well, for solving these nia Sur, Mexico. Proc. San Diego Soc. Nat. Hist. urgent problems (Soule, 1990). Finally, we 4:1-7. 56 HARRY W. GREENE

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