Biogeography, changing climates, and niche

David B. Wakea,b,1, Elizabeth A. Hadlyc, and David D. Ackerlya,d aDepartment of Integrative , bMuseum of Vertebrate , and dJepson Herbarium, University of California, Berkeley, CA 94720; and cDepartment of Biology, Stanford University, Stanford, CA 94305

Edited by James Hemphill Brown, University of New Mexico, Albuquerque, NM, and approved September 29, 2009 (received for review September 25, 2009)

odern concepts central to future will have access to the original figure in the who current studies of biogeog- record of faunal conditions in Cali- wrote extensively about the relationships raphy, changing climates fornia and the west wherever we now of climate and . As a result of and evolution of ecological work. his studies of Volca´n Chimborazo in nichesM were born approximately a hun- Ecuador, von Humboldt appears to have These ideas were prophetic, and have dred years ago. In 1908, the Regents of been the first known scientist to a special poignancy at this time, when the University of California established discuss the zonation of vegetation along the impact of global climate change is the Museum of Vertebrate Zoology at an altitudinal transect and to develop a evident and when we realize how much Berkeley, in accordance with the wishes concept of zones (4). von Hum- we rely on records from the past, such of Annie M. Alexander (1867–1950). boldt’s work deeply influenced C. Hart as those meticulously kept by Grinnell, Alexander conceived the institution and Merriam who recalled, shortly before his his students, coworkers and successors. selected its first Director, Joseph Grin- , his father handing him a volume A century has now elapsed since the nell (1877–1939), a well known natural- of Humboldt’s ‘‘Views of ’’, Museum was founded, and we were ist who had received his Ph.D. at Stan- where he found early inspiration for his stimulated by Joseph Grinnell’s words to ford University and was then teaching at work on distributions (5). Merri- take stock of our current understandings the Throop Institute in Pasadena (later am’s classic study of the San Francisco of the relationships between , the California Institute of Technology). Mountains in Northern Arizona and his Grinnell, who founded the Museum in climate, and the distribution and ecolog- ical niche dimensions of in an biological survey of Mt. Shasta led to late 1908, meticulously adhered to the the development of his highly influential principles laid down by Alexander (1). ecological and evolutionary context, us- ing modern methods and approaches. life zone concept (6). Merriam recog- Alexander would provide the funding nized 12 life zones in the United States and inspiration and Grinnell would do In this issue contributions are pre- sented from an Arthur M. Sackler Col- and mapped them, noting that on altitu- the intellectual and practical work to dinal transects (e.g., from the Sonoran establish the institution and set it on a loquium of the National Academy of Sciences, held in Irvine, CA, December Desert to Humphrey’s Peak) one would trajectory. The Museum quickly became pass through as many as six life zones. known for its studies of terrestrial verte- 11–13, 2008, in celebration of the Cen- tennial of the Museum of Vertebrate Groups of species of plants and verte- brates, conducted in the framework of brates were associated with each zone, what we would recognize today as ecol- Zoology at the University of California at Berkeley and with the spirit of Grin- and thus the zone itself became predic- ogy and evolution. The founders were tive. Grinnell was strongly influenced by self-conscious of their roles from the nell’s contributions in mind. The collo- quium was focused on issues central to this approach, and it became a hallmark beginning. They had no illusions that of his subsequent research, especially the work they set out to do would be Grinnell and his colleagues one hundred years ago: , niche evolution evident in his famous studies of Yo- easy or soon accomplished, if ever. semite National Park (7), and through- Grinnell (2) set the course: and changing climates (or, more gener- ally, environments, for Grinnell focused out his life he made regular emenda- It will be observed, then, that our much attention on human-induced im- tions to his life zone map of California. efforts are not merely to accumulate pacts on the California environment). Although life zones became increasingly as great a mass of animal remains as Grinnell was a pioneer in studying geo- controversial through time, attempts to possible. On the contrary, we are graphic variation within and between adapt the life zone approach to modern expending even more time than species, in focusing on the relationships understandings were made by several would be required for the collection between geography, and the authors, notably Holdridge (8). Hold- of the specimens alone, in rendering distribution of organisms, and especially ridge’s life zones, based on integration what we do obtain as permanently in the formulation of the ecological of biotemperatures, precipitation, and valuable as we know how, to the niche concept (3). These are all current potential evapotransporation, were used ecologist as well as the systematist. It issues in modern science, and recent by many researchers, especially in the is quite probable that the facts of years have witnessed the of distribution, life history, and eco- new scientific challenges, conceptual This paper serves as an introduction to the Arthur M. Sackler nomic status may finally prove to be frameworks, and analytic techniques, Colloquium of the National Academy of Sciences, ‘‘Bioge- of more far-reaching value, than what- all of which were on display at the ography, Changing Climates, and Niche Evolution’’ held ever information is obtainable exclu- colloquium. December 11–13, 2008, at the Arnold and Mabel Beckman sively from the specimens themselves. The colloquium took place at a propi- Center of the National Academies of Sciences and Engineer- ing in Irvine, CA. The complete program and audio files of At this point I wish to emphasize tious time, celebrating both the centen- most presentations are available on the NAS web site at what I believe will ultimately prove nial of the Museum of Vertebrate Zool- www.nasonline.org/Sackler࿝Biogeography. to be the greatest value of our mu- ogy and the sesquicentennial of the Author contributions: D.B.W., E.A.H., and D.D.A. wrote the seum. This value will not, however, publication of Darwin’s Origin of Spe- paper. be realized until the lapse of many cies on November 24, 1859 ( 1). The authors declare no conflict of interest. years, possibly a century, assuming Moreover, 2009 is also the 150th anni- This article is a PNAS Direct Submission. that our material is safely preserved. versary of the death of Alexander von 1To whom correspondence should be addressed. E-mail: And this is that the student of the Humboldt (1769–1859), a monumental [email protected]

www.pnas.org͞cgi͞doi͞10.1073͞pnas.0911097106 PNAS ͉ November 17, 2009 ͉ vol. 106 ͉ suppl. 2 ͉ 19631–19636 Downloaded by guest on September 29, 2021 Table 1. Early milestones and anniversaries related to the history of the niche concept marized the similarities and differences in biogeography, ecology, and evolution between the conceptualizations. Elton Year Milestone wanted to develop a coherent account of dynamics of interactions in communi- 1805 First publication of von Humboldt’s Volcan Chimborazo vegetation figure ties, such as chains, cycles of abun- 1859 May 6: Death of (1769–1859) dance, and the like; he was less con- Nov. 24: Publication of Darwin’s Origin of Species cerned with individual species than was 1908 Founding of UC Museum of Vertebrate Zoology (Grinnell and Alexander) Grinnell. Grinnell’s niche was seen as 1910 First published use of ЉnicheЉ in ecological context (11) more -oriented than Elton’s, 1917 Publication of Grinnell’s ЉThe niche-relationships of the California thrasherЉ which was seen as more -ori- 1927 Publication of Elton’s ЉAnimal EcologyЉ ented, but both saw the niche as a place 1936 Publication of Gause’s ЉThe Struggle for ExistenceЉ or role that a species occupies in the 1944 Publication of Simpson’s ЉTempo and Mode in EvolutionЉ environment rather than as a property 1957 Publication of G.E. Hutchinson’s ЉConcluding RemarksЉ of the species itself, a view more associ- ated with Hutchinson (ref. 20; see also refs. 21 and 22). The main difference New World and life zone maps Some insight into this conjecture is between Grinnell and Elton identified were produced for several countries derived from the field notes of Grin- by Griesemer is the issue of whether (e.g., refs. 9 and 10). nell’s graduate student Walter P. Taylor, more than one species can occupy a In parallel with his work on life zones, who was conducting field research in the niche, the difference stemming ulti- Grinnell pioneered the analysis of indi- Yosemite in early December, mately from Grinnell’s systematic per- vidual species distributions in relation to 1914 (notes on file, Museum of Verte- spective and Elton’s more functional their biotic and abiotic requirements in brate Zoology, University of California, one. In a concise and forceful overview, Udvardy (23) argued that there was no his 1917 article ‘‘The niche-relationships Berkeley, CA). Following routine obser- essential difference between Grinnell of the California thrasher’’ (3). Al- vations for December 11, 1914, Taylor and Elton in conceptualizing the niche, though the term ‘‘niche’’ had previously wrote a separate section headed ‘‘The but that Grinnell’s formulation was ear- appeared in print in its ecological con- .’’ These are musings, lier and broader. Furthermore, he cred- text (11), Grinnell’s article is appropri- obviously stimulated by time in the field its Grinnell with the concept of compet- ately credited with the introduction of with Grinnell since mid-November. Af- ter a brief introduction Taylor observes itive exclusion, which he calls the niche concept into general use in ‘‘Grinnell’s axiom.’’ Hardin (24) agreed ecology (12). Grinnell apparently first It seems to refer, as usage has it, to that Grinnell deserved credit, despite explicitly referred to niches in his 1913 different in the same local- the fact that competitive exclusion was doctoral dissertation, cited in a 1914 ity, as for instance, in the case of widely referred to as ‘‘Gause’s princi- monograph dealing with the Lower Col- , different states of foliage, or ple’’ by that time (1960); he proposed orado River region (13). Griesemer (14) different kinds of brush. the term ‘‘competitive exclusion princi- says that the term ‘‘niche’’ first ap- ple’’ to extricate the terminology from He continued for 4 pages, stating at one peared in Grinnell and Swarth (15), a its uncertain historical genesis. point: publication dealing with the vertebrate G. Evelyn Hutchinson, in his famous fauna of the San Jacinto Mountains. He But the ordinary sense in which the ‘‘Concluding Remarks’’ article (25), for- guesses that the term probably emerged term ecological niche is used refers malized the niche concept as a set of from discussions among active groups of to that critical something which is niche axes defining an ‘‘N-dimensional students at Stanford, who were attracted seized upon by one species, and by hypervolume’’ within which a species by David Starr Jordan and inspired by which it keeps its hold even in a lo- could maintain a viable . the life zone concept of Merriam. Grin- cality where related species are Hutchinson’s concept of the niche as an nell greatly admired Merriam, whose living. abstract set of environmental axes concepts were a significant influence on closely mirrors Grinnell’s original pre- the development of his work. Grinnell’s Taylor concludes: sentation, although he did not cite Grin- idea that each species occupies its own Put in another way, the continued nell’s article at this time. A critical dis- niche goes back to Darwin as a core existence of a species in a locality tinction is that Hutchinson redefined the concept, and Grinnell explicitly dealt where related species are living de- niche as a property of the species in re- with the issue of competitive exclusion pends upon the critical differences, lation to its environment (20). Hutchin- in 1904 (16). By 1917, when Grinnell slight or large, in the totality of re- son introduced the distinction between used the word ‘‘niche’’ in an article title quirements of each. the fundamental niche, reflecting the (3), the term was in wide informal use. abiotic requirements of a species, vs. the Grinnell concluded, ‘‘It is, of course, These notes, written a decade after realized niche, the set of conditions oc- axiomatic than no two species regularly Grinnell’s first formal conceptualization cupied in the presence of competitors. established in a single fauna have pre- of niches and competitive exclusion, al- Ellenberg, working independently on cisely the same niche relationships,’’ though without using those terms, sug- vegetation ecology in Central , which led Leibold (17, p. 288) to gest that ‘‘ecological niche’’ was a term had also considered how species distri- observe: already in circulation and a topic of de- butions along environmental gradients bate and discussion among graduate stu- shift in response to competitors (26). It Since that was one of the first uses of dents of the day. is not known (to us) how the work of the term niche and one of the first An apparently independently devel- Ellenberg and other European ecolo- statements of this principle, one won- oped concept of the ecological niche is gists, and that of the ‘‘American school’’ ders how much theoretical work was attributed to Elton (18), who either was of in the 50s and being developed outside of print by unaware of Grinnell or chose not to cite 60s, may have influenced each other. Grinnell and his collaborators. him (see ref. 19). Griesemer (14) sum- The subsequent history of the niche

19632 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0911097106 Wake et al. Downloaded by guest on September 29, 2021 concept, and its central yet at times re- inferring terrestrial paleoclimates and with respect to adaptive hypotheses. Al- viled role in ecology, has paleocommunities (35). In the case of though this view has generated consider- been discussed in some depth by several plants and mammals, the able debate, their work did represent a reviewers (refs. 12, 14, 19, 20, 27, and niches of species have been inferred to key step in the development of statisti- 28; see also refs. 21 and 22). remain ‘‘constant’’ over the time periods cal comparative methods in phylogenet- While ecologists were wrestling with studied (usually the last million years ics. Harvey and Pagel (44), in their 1991 the niche concept and its implications, or so). monograph, coined the term ‘‘phyloge- paleontologists were tackling related The success of these applications de- netic niche conservatism’’, referring to problems, although not always using the pends on the relative constancy of niche the role of ecological sorting processes same language. George Gaylord Simp- relations over long periods of evolution- as factors that would promote stabilizing son presaged discussions of niche con- ary time. In its strongest formulation selection and minimize niche evolution. servatism by ecologists through his this constancy is manifest as evolution- They drew their concept from a brief consideration of the ‘‘realized environ- ary stasis, the prolonged persistence of passage by Grafen that outlined the mental hyperspace’’ (29). He viewed forms in the record with negligible same argument, acknowledging that it each point in ‘‘environmental hy- morphological change. The observation was ‘‘so natural that it cannot be origi- perspace’’ as a unique combination of of stasis, and its implications for evolu- nal’’ (ref. 45, p. 143). There has subse- environmental variables, and argued tionary biology, were the focus of quently been a lively debate regarding that individuals within , pop- Eldredge and Gould’s theory of punctu- the definition, significance and mecha- ulations within species, species within ated equilibria (36, 37). Punctuated nisms of niche conservatism, with no genera, and so on, will exhibit a slowly equilibria sparked a heated debate be- immediate resolution in sight (40, 46– decreasing measure of similarity in the tween population geneticists and paleon- 48). Currently, the integration of phylo- positions they occupy. Building on tologists, and contributed to the integra- genetic comparative methods and statis- Hutchinson’s formulations, Valentine tion of and tical niche models is opening up a new (30) wrote: evolution (‘‘evo-devo’’) (38). Less appre- era of insight into niche evolution and its ciated was the role of ecological dynam- relationship to diversification and bioge- The species niche is one of the more ics as a potential mechanism of stasis. ography (49–51). important concepts in . As Eldredge wrote later (ref. 39): In recent years, the niche concept has As employed here, the unqualified come full circle and returned to play an term niche subsumes the potential [S]pecies tend to change locale— important role in biogeography, particu- interactions of a species with all the rather than anatomical features–in larly in regards to the impacts of climate factors of the environment, physical response to environmental change. change (52–54). Geographical distribu- and biological. Since evolution is es- As long as suitable habitat can be tions of species in relation to underlying sentially an ecological process operat- found, a species will move rather climate gradients have received renewed ing with genetic machinery, a good than stay put and adapt to new envi- attention, particularly as the case can be made that the niche is ronmental regimes. for what are variously termed ‘‘species the most fundamental single unit of [W]e . . . have always emphasized distribution models’’, ‘‘climatic niche evolution. that it is habitat tracking—stabilizing models’’, or ‘‘statistical niche models’’ in the face of envi- (55). These models draw on a variety of For practical purposes, implicit use of ronmental change—that basically un- statistical methods to model species geo- niche concepts and niche conservatism derlies stasis. is the foundation of environmental re- graphic distributions in relation to large- constructions that rely on the fossil Habitat tracking, together with behav- scale climatic and topographic variables record. Key traits associated with the ioral and and the (56). Predictions of species responses to niche (distribution, morphology, relative dynamics of species interactions, offer a climate change are then derived by com- abundances, etc.) were assumed to be variety of ecological factors that may bining the models with outputs from conserved and the veracity of that as- help to resolve the observation of evolu- global circulation models that project sumption was upheld by practical results tionary stasis with the ubiquity of cli- changes in spatial patterns of tempera- that followed. As early as the 1960s, pa- mate change and environmental hetero- ture, precipitation, and associated cli- leontologists of the oil industry were geneity (40, 41). mate variables. A critical and unresolved essentially applying the concept in facies Researchers in , issue in the use of predictive models is reconstruction based on the assumption focused primarily on extant taxa, have the extent to which dispersal limitation that certain assemblages of fossil marine also had a long-standing interest in the will constrain short-term (i.e., century- organisms represented particular envi- similarities—and differences—among scale) range shifts (57). However this ronments that were associated with oil- close relatives. Dating back to Darwin problem is resolved, the models still of- bearing strata. Transfer functions, devel- (42), comparisons between close rela- fer one of the most powerful approaches oped in detail for foraminiferal tives have played a critical role both to to project potential impacts of climate assemblages (31) and used for tree elucidate patterns of evolutionary change on . rings, pollen and , are empiri- change, and in mechanistic studies to In this Sackler Colloquium, we sought cally derived equations used to calculate ‘‘control’’ for the many features shared a wide array of perspectives on the quantitative estimates of paleoclimate, by relatives and isolate the importance niche concept, and its role in ecology, which are then tested against calibration of traits of interest. Clutton-Brock and evolution, and climate change biology. datasets (32). Modern plant distribu- Harvey (43), studying behavioral organi- We intentionally intermixed topics, jux- tions and their associated abiotic envi- zation in primates, recognized that the taposing with conserva- ronments are fundamental for hindcast- similarities of close relatives also pose a tion, and conceptual reviews with case ing the climates of the past (33, 34), and statistical problem for the analysis of studies. Most of the talks from the col- associations of the environment with comparative data, as closely related and loquium are represented by papers in present mammalian geographic distribu- phenotypically similar species may not this Special Issue. The result, we hope, tions have been used as a technique for represent ‘‘independent data points’’ is an intellectually diverse yet inter-

Wake et al. PNAS ͉ November 17, 2009 ͉ vol. 106 ͉ suppl. 2 ͉ 19633 Downloaded by guest on September 29, 2021 twined series of papers that will illumi- that his duality (niche vs. biotope) estab- events. Diversity is inferred to have nate current advances at the intersection lished many elements of the modern ap- dropped thoughout the . Okie of ecology, evolution and biogeography. proach to classifying and mapping envi- and Brown propose that unique mam- The Colloquium opened with a contri- ronments, modeling species distributions malian traits, including body size and bution from the ‘‘Grinnell Project,’’ a se- under different climate models, and in niche characteristics such as habitat ries of studies by personnel associated general contributed greatly to broader and food requirements, played a role with the Museum of Vertebrate Zoology dimensions of modern studies of niches. in probability. to resurvey original study sites laid out by Holt (55) follows with an investigation of Jackson et al. (64) apply niche con- Grinnell in the early part of the last cen- the demographic basis of the Hutchinso- cepts to long-term ecological dynamics, tury. The ambitious project is stimulated nian niche, emphasizing that under cer- emphasizing some simple yet surprising by Grinnell’s prediction that the value of tain circumstances, possibly more wide- implications of climate variability nested his team’s research might not be fully ap- spread than currently recognized, across temporal scales. They illustrate preciated for a century. The first publica- conditions allowing population growth that contrasting conditions for establish- tion from the project focused on mam- from low density can differ from the con- ment and persistence can generate an mals (58), and showed that although some ditions under which an established popu- ‘‘ecological ratchet,’’ with episodic dy- species in the Sierra Nevada (Yosemite lation can maintain itself. Holt’s work also namics of range expansion and contrac- National Park) had similar elevational provides an important link between mi- tion (see related discussion in ref. 55). distributional patterns as in the past, oth- croevolutionary processes and larger mac- They further discuss several sources of ers had undergone major shifts in distri- roevolutionary patterns. uncertainty in the application of correla- bution. Tingley et al. (59) found that Few workers use physical principles to tive niche models to the problem of fu- many species of birds have also experi- model persistence in environments. Porter ture climate change, including the com- enced changes in distributional patterns. and Kearney (60) apply an ecophysiologi- plex dynamics of climate change, the were studied along four cal approach to explicitly model the ther- importance of the regeneration niche, elevational gradients in the Sierra Nevada, mal niche of a endothermic ellipsoid or- and historical contingencies that can including 82 species and 53 separate local- ganism. From first principles of physics, alter dynamic response of ecological ities. Species tracked changes in the geo- they quantify how shape, size and body systems. graphical distribution of their climatic insulation (e.g., mammalian fur) affect Several papers address aspects of niches through time. These results suggest in variable environments and niche evolution, from small scale popu- that climatic niche modeling may prove test this against field and laboratory data. lation level dynamics at range edges, to useful in predicting the distribution of Their data show the power of biophysical macroevolutionary patterns evident in birds under different models of climate models for combining functional traits comparative data and the fossil record. change. with environmental data to recapitulate Processes operating at the margin of the Several authors addressed issues related observed gradients in body size and sug- geographic ranges will attract increasing to conceptualization of niches and some gest this as a fruitful area of further re- attention as the magnitude of climate historical perspectives. An advantage of search. For example, recent exciting re- change becomes more evident to biolo- the flurry of activity in discussions of search combines ecophysiological models gists. Angert (65) conducted field stud- niche conservatism is the multiple per- with (see ref. 61). ies of the demography of two species of spectives afforded by workers from many From the outset, niche theory has closely related monkey-flowers (Mimu- fields. The disadvantage is that concepts played a central role in community lus) in the Sierra Nevada of California, of the niche may not always align, which ecology. The mechanisms underlying focusing especially on populations at the confuses the discussion. Sobero´n and Na- community composition and phyloge- margins of geographic ranges. Central kamura (22) focus specifically on discrimi- netic diversity are the subject of the and marginal populations showed strik- nating between fundamental, potential, study by Graham et al. (62) comparing ing differences within species but there and realized niches to clarify exactly what 189 hummingbird communities in Ec- were also differences between species. is conserved. The distinctions between the uador. A robust phylogenetic hypothe- One species had less productive popula- Hutchinsonian ‘‘response niche’’ and the sis is used to assess how species and tions at lower elevational marginal re- Grinnellian ‘‘impact niche’’ are timely be- phylogenetic lineages change along en- gions whereas both displayed higher fe- cause they have received relatively little vironmental (e.g., elevational) gradi- cundity and population growth in the attention and figure prominently in ents and biogeographic barriers. At upper elevational marginal . Re- whether we view niches as conserved or lower elevations there is less phyloge- cent climate changes are thought to not. Using a mathematical approach, So- netic clustering than at higher eleva- have shifted climatic envelopes in the bero´n and Nakamura also examine the tions, in accord with ideas that compe- direction of higher elevations. fundamental differences in niche model- tition is more important in the The study of niche evolution is an ing algorithms that use presence data ver- lowlands and environmental filtering in important focus of comparative biology, sus those that also rely on absence data. the uplands, where coexistence of close integrating ecological diversity and phy- They conclude that clearly defined termi- relatives is found. Their study provides logenetic history. Ackerly (48) presents nology and explicit treatment of the un- insight into the pattern of faunal a simple extension of the theory of inde- derlying variables in niche conservatism buildup in a biotically rich and com- pendent contrasts to measure rates of will do much to integrate this field. Col- plex region. Community assemblage is trait diversification, focusing on plant well and Rangel (21) explore how also the focus of Okie and Brown (63), traits that are associated with growth Hutchinson’s niche concept differed from who examine the effects of rising sea and regeneration strategies. Compari- earlier conceptions. Whereas Grinnell and level and concomitant creation of is- sons among reveal Ͼ100-fold dif- Elton saw niches as elements of environ- lands in the region. They ferences in rates of trait diversification, ments, Hutchinson attributed them to spe- show how the original mammal fauna with higher rates on Hawaiian cies. They identify Hutchinson’s term of this region has been disassembled clades compared with continental clades biotope with a formal separation of physi- on islands of differing size and com- from California and the North Temper- cal place from environment and argue plexity following the late Pleistocene ate flora. This approach could be ap-

19634 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.0911097106 Wake et al. Downloaded by guest on September 29, 2021 plied widely across other groups, as The final set of papers examines ap- et al. (69) investigate the relative size of comparative data and time-calibrated plications of niche theory in climate the niche. Counter to prevailing wisdom phylogenies become available. change and . Zim- (70), they find that narrowly distributed Hadly and colleagues (41) examine merman and colleagues (66) consider species confined to the rainforest have patterns in the range size of mammal the importance of climatic extremes in high local abundances. They posit that genera in from the late shaping distributions of tree species persistence of restricted species is possi- Pleistocene through the late Holocene, along climate gradients in Switzerland. ble when intrinsic demographic traits comparing distributions in the fossil Incorporation of climatic extremes permit high local . Their re- and modern record. They find remark- (i.e., interannual variability) offers a sults challenge the paradigm that geo- able stability in range size within gen- modest but significant improvement in graphically restricted species have a era through time, despite the glacial- fitting distributions to climate data, greater extinction probability than do deglacial transition, extinction of and especially helps to correct mar- widely distributed species. species within the or how many ginal areas where over and under-pre- In the following pages, a rich array of species are included in the genus. They diction problems arise. Given the clear contributions to our modern under- suggest that different processes may physiological impacts of of climate ex- standing of the relationship between influence niche conservatism at higher tremes, they suggest several reasons organisms and species, their ecological taxonomic levels, positing that intrinsic why niche models based on climate niches, and biogeography is presented. traits are more important at higher lev- averages may perform as well as they Although the integration of these topics els and environmental controls may do. Wiens et al. (67) implement two has been a century-long goal, we have a models on a fine play more of a role at the species level. sense of rapid progress during the last geographic scale to predict the future Using range size as a proxy for the re- decade, and especially at the present distribution of bird species in Califor- alized niche, they propose a ‘‘genus time. In this era of rapid climate nia by 2070 (also see 68). Of the 60 niche’’ and underscore the importance change, new ways of thinking are essen- species they model, a majority show a of maintaining a genus pool for con- tial as we confront the reality of impacts reduction in geographic distribution on organisms and their distribution servation of North American mamma- within California. As a practical exer- lian communities. through space and time. If even a frac- cise, Wiens et al. compare and contrast tion of the projected changes are real- Across the broadest spatiotmporal these models and discuss implications ized, the changes we face are truly perspective, Vieites et al. (51) apply an to managers of the differences between frightening and the world of 2100 may innovative use of the niche to explore them. They are mindful of the uncer- be drastically transformed from its how environmental tolerances of tainties and assumptions inherent in present state. salamanders, which are thought to be species distribution models and future prime examples of organisms with phy- projections, but stress the urgency of logenetically conserved niches, have ACKNOWLEDGMENTS. We thank the colloquium action despite them. The world is presenters and authors of the accompanying pa- evolved since mid-Tertiary times. They changing at a pace perhaps faster than pers for their thoughtful and insightful contribu- calculate the environmental niche space our ability to model biotic response tions; S. Marty and her staff at the Beckman Cen- of species in the family Salamandridae with our traditional standards of statis- ter for hosting the colloquium; J. Patton, who in the northern hemisphere and use found the Walter Taylor field notes and brought tical rigor. them to our attention; A. Prinzing for pointing these data to propose the environmental Niche theory has a variety of applica- out Ellenberg’s early contributions; G. Clausing niches of the lineage. The study exam- tions in conservation and restoration for assistance with translation; J. H. Brown on the ines methods and shows the promise of biology, beyond the current focus on Proceedings of the National Academy of Sci- current approaches while at the same ences Editorial Board; and D. Stopak and K. Du- climate change. Using patterns of abun- gan in the Proceedings of the National Academy time indicates some of the daunting dance and distribution in Australian of Sciences office for their guidance and over- problems remaining. Wet Tropic vertebrate species, Williams sight of the editorial process for this special issue.

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