Progress in Physical Geography 32(2) (2008) pp. 115–138 Macroecology: more than the division of food and space among species on continents Felisa A. Smith,1* S. Kathleen Lyons,2 S.K. Morgan Ernest3 and James H. Brown1 1Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA 2National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA 3Department of Biology, Utah State University, Logan, UT 84322, USA Abstract: Macroecology is a big-picture, statistical approach to the study of ecology. By focusing on broadly occurring patterns and processes operating at large spatial and temporal scales and ignoring localized and fi ne-scaled details, macroecology aims to uncover general mechanisms operating at organism, population and ecosystem levels of organization. Although such an approach is evident in writings dating from the mid- to late 1800s, not until 1989 was the domain of macroecology clearly articulated. Since then there has been an exponential growth in publications employing a macroecological perspective. Here we (1) briefl y review the history of macroecology, with emphasis on cultural, scientifi c and technological innovations that made this approach possible, (2) highlight current developments in the fi eld, including its increasing linkages with biogeography and other disciplines, and (3) point to likely future directions. We also touch upon methodological, statistical and institutional challenges faced by this and other highly interdisciplinary approaches. Our review of macroecology is especially timely, since it has been 20 years since the term was coined and the seminal paper published. Key words: biogeography, body size, metabolic theory, palaeoecology, range size, species abundance, species diversity. I Introduction dynamics and structure of ecological systems Ecological systems typically contain many are almost always highly complex. Such different kinds of organisms interacting in complexity is a challenge for modern science. a myriad of ways with each other and their While traditional ecology has made great abiotic environment. Consequently, the strides in understanding various kinds of *Author for correspondence. Email: [email protected] © 2008 SAGE Publications DOI: 10.1177/0309133308094425 Downloaded from http://ppg.sagepub.com at Utah State University on September 30, 2008 116 Progress in Physical Geography 32(2) ecological interactions, it has been less suc- integrates divergent scientifi c methodologies, cessful at understanding the many connec- perspectives and disciplines (Brown and tions between individuals, populations, Maurer, 1989; Brown, 1995; 1999; Blackburn communities and ecosystems and the emer- and Gaston, 2002). Moreover, while the main gent structures and dynamics generated aims of biogeography are in understanding by these interactions. Yet, understanding and describing patterns of biodiversity across these linkages and their evolutionary history space and time, macroecological approaches is imperative to solving emerging challenges often focus on population or even individual posed by rapid rates of habitat fragment- level processes (eg, Damuth, 1981; West ation, loss of biodiversity and global climate et al., 1997; Enquist et al., 1998; Belgrano change. In response, approaches that focus on et al., 2002; Ernest et al., 2003; Defeo and broad patterns and seek to elucidate general Cardoso, 2004). Because of the emphasis on processes in space and/or time are increas- identifying broad-based emergent patterns ingly infl uential in ecology, evolution, syste- and processes, macroecologists necessarily matics and palaeoecology (ie, Brown and ‘stand back and take a sufficiently distant Maurer, 1989; Blackburn and Gaston, 1994; view so that the idiosyncratic details disappear Brown, 1995; Smith et al., 1995; Gaston and and only the big, important features remain’ Blackburn, 1996a; 1996b; 2000; Jablonski, (Brown, 1995: 20). This is not an approach that 1997; Alroy, 1998; Enquist et al., 1998; Roy et lends itself to replicated experimental studies al., 1998; Harvey and Rambaut, 2000; Erwin, or standard statistical methodologies. 2007). One of these approaches, macro- The past two decades have witnessed ecology, explores the domain where ecology, rapid expansion of macroecological research biogeography, palaeobiology, and evolution programmes, as demonstrated by an expo- overlap, and so it has the potential to forge nential increase in the number of published synthetic links among these disciplines. papers (Figure 1). Currently, macroecological A macroecological approach to biology publications are increasing by 34% per year, emphasizes describing and explaining pro- signifi cantly higher than either the 14.6% for cesses that operate at regional to global those in biogeography, or the 2.5% for scien- spatial scales and decadal to millennial (or tifi c papers across all disciplines. Presumably longer) temporal scales (Brown, 1995). The this disproportionate increase in macro- prefi x ‘macro’ refers to both the broad and ecological research reflects the growing synthetic extent of the questions tackled as realization that many complex biological well as the fact that the approach derives problems are best tackled by adopting a new much of its power from focusing on the approach and using a different toolkit than emergent statistical properties of large employed in more traditional reductionist numbers of ecological ‘particles’ (Brown, experimental science. Scientists involved in 1995). Statistical patterns that appear to global change research, for example, have be invariant across large scales suggest been particularly proactive in employing a universal casual mechanisms operating at macroecological perspective (eg, Kuhn et al., organism, population and ecosystem levels 2008, and references therein). This led in 2006 of organization (Brown and Maurer, 1989; to an international conference on the use Brown, 1995; Maurer, 1999; Gaston and of macroecology in global change research Blackburn, 2000). headed up by the recently established German While macroecology is closely allied with Virtual Institute of Macroecology (www. biogeography, there are clear distinctions macroecology.org). Similarly, the field of between the two. Most importantly, macro- physical geography has embraced this ecology is an approach towards biology, approach to the extent that the flagship rather than a discipline itself, so it necessarily journal on macroecology (Global Ecology and Downloaded from http://ppg.sagepub.com at Utah State University on September 30, 2008 Felisa A. Smith et al.: Macroecology 117 Biogeography: A Journal of Macroecology) insects to past, ongoing and predicted future has become the most infl uential in terms of environmental fl uctuations (Figure 2; Lyons, ranking and impact factors (eg, Kent, 2007). 2003; Hunt and Roy, 2006; Smith and The breadth of macroecological work has Betancourt, 2006; Kerr et al., 2007; Willis also grown tremendously; recent studies et al., 2007; Kuhn et al., 2008; Sekercioglu relate the temporal and spatial organization et al., 2008). of numerous morphological, physiological, Here, we describe the development of behavioural, ecological, evolutionary, pheno- macroecology from earlier antecedents, logical and phylogenetic traits among taxa as briefl y touch upon the importance of scien- diverse as plants, birds, fi sh, mammals and tifi c and technological innovations that have 6 4.10 100 80 6 2.10 60 SciSearch ArticlesSciSearch 40 or Macroecology Biogeography (x 20) Biogeography 20 0 0 1989 1993 1997 2001 2005 Year of Publication Figure 1 Rise in the number of published papers using macroecology (open circles with dots) or biogeography (fi lled circles) in the title, abstract or key words over the 20 years from 1988 to 2007. The term ‘macroecology’ was fi rst coined by Brown and Maurer (1989). Data are taken from a search of over 21M records using ‘Search Plus v2.4’ – a comprehensive scientifi c search engine housed at Los Alamos National Laboratory. Shown also is the background rate of all papers indexed by this search engine over the same time period (grey bars). Although there has been a rise in all published works over the last 20 years, there have been signifi cantly higher increases in papers containing biogeography and/or macroecology in their title, abstract or key words. Equations (log transformed): all SciSearch, y = –14.84 + 0.011x, r2 = 0.947; all Biogeography, y = –115.05 + 0.59x, r2 = 0.92; all macroecology, y = –253.6 + 0.12x, r2 = 0.93; the 95% confi dence intervals do not overlap for any of the equations. Note that, while both biogeography and macroecology have seen signifi cant growth in publications, the slope for macroecology is signifi cantly steeper and is best approximated by an exponential function (although a log transformed linear fi t is used here for ease of comparison) Downloaded from http://ppg.sagepub.com at Utah State University on September 30, 2008 118 Progress in Physical Geography 32(2) Macroecology Papers by Subject Area 350 300 250 200 150 100 Number of Papers 50 0 Ecology Zoology Forestry Fisheries Biology Ornithology Entomology Paleontology Microbiology Plant Sciences Oceanography Geography, Physical Geography, Evolutionary Biology Genetics & Heredity Environmental Sciences Environmental Multidisciplinary Sciences Biodiversity Conservation Biodiversity Marine & Freshwater Biology Marine & Freshwater Geosciences, Multidisciplinary Geosciences, Biochemistry & Molecular Biology Subject Area Figure 2 Subject areas