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Copenhagen1990 Minireviewsprovides an opportunityto summarizeexisting knowledge of selected MINI- ecologicalareas, with specialemphasis on currenttopics where rapidand significant advancesare occurring.Reviews should be concise and not too wide-ranging.All key REVIEW referencesshould be cited. A summaryis required. Phylogenetic approaches in ecology Hans-Erik Wanntorp, Daniel R. Brooks, Thomas Nilsson, Soren Nylin, Fredrik Ronquist, Stephen C. Stearns and Nina Wedell Wanntorp,H.-E., Brooks, D. R., Nilsson,T., Nylin, S., Ronquist,F., Stearns,S. C. and Wedell, N. 1990. Phylogeneticapproaches in ecology. - Oikos 57: 119-132. This paperargues that manyecological studies could benefit greatly from a phylogen- etic approach.For this purpose, cladisticsis an appropriatemethod to reconstruct phylogeny.Case studies from seven researchtopics in ecology are reviewed. In all studies, historicalexplanations have played a centralrole, and mostly, cladograms have been used. Connectionsto statisticalmethods for estimatingquantitative vari- ation amongtaxa are discussed.A phylogeneticbase would greatlystrengthen both problemformulation and analysis.This is true for populationstudies as well as for all areas where adaptationalexplanations are invoked;single species studies as well as comparativestudies or coevolution studies. Three cladistic proceduresuseful in ecologicalresearch are brieflydescribed. Ecology and systematicshave much to offer each other and it is a challengeto bringthe two fields together. H.-E. Wanntorp and T. Nilsson, Dept of Botany, Univ. of Stockholm, S-10691 Stockholm, Sweden. - D. R. Brooks, Dept of Zoology, Univ. of Toronto, Toronto, - Ontario, Canada M5S 1A1. S. Nylin and N. Wedell, Dept of Zoology, Univ. of Stockholm, S-10691 Stockholm, Sweden. - F Ronquist, Dept of Zoology, Uppsala Univ., Box 561, S-75122 Uppsala, Sweden. - S. C. Stearns, Dept of Zoology, Univ. Basel, Rheinsprung 9, CH-4051 Basel, Switzerland. But a still more important consideration is that the chief part of the organisation of every living creature is due to inheritance; and consequently, though each being assuredly is well fitted for its place in nature, many structures have now no very close and direct relations to present habits of life. (Darwin 1859) Introduction more quickly than would be possible with a single hy- pothesis (Chamberlain 1897). In 1897, William Chamberlain, the President of the Ecology and population biology have been dom- American Society of Geologists, spoke convincingly on inated by explanations rooted in processes observable the role of alternative explanation in science. By help- today. Evolution has often been seen as rapidly bringing ing one to resist the temptation to confirm one's favou- populations into equilibrium with local conditions, an rite hypothesis, the comparison of alternative explana- equilibrium in which the existence of certain genotypes tions maintains objectivity, demonstrates error earlier and phenotypes is explained through their having been in an investigation, and leads one closer to the truth the best available. In community ecology, the historical Accepted 13 September1989 © OIKOS OIKOS 57:1 (1990) 119 0 A B siomorphies) are identified by using outgroup compari- son - any trait found in at least one member of the group being studied that is also found in species outside the group is most parsimoniously interpreted to have evolved prior to the origin of the common ancestor of the group, and is hence plesiomorphic. The correspond- la ing traits not present in the outgroup are then relatively derived (apomorphies). Once a collection of apomor- phies has been assembled for a group, cladistic analysis groups the species according to their shared apomor- phies (synapomorphies) (Fig. 1). Due to parallel and convergent evolution, not all apomorphies will conform to a single pattern, however. Contemporary cladistics Fig. 1. Cladogramof three species, A, B and C. The traitslb, uses a variety of numerical methods and computer- 2b, 3b and 4b are interpretedas primitivebecause they occur assisted programs for discerning the pattern of syn- also in the outgroup,0. la and 2a are commonspecializations apomorphies that best fits the data at hand (Wiley 1981, B a in C. unitingspecies and C. 3a is uniquespecialization Trait Fink 1986, Platnick 1989). The pattern that results is a 4a is homoplasticand has arisenindependently in A and C as a convergence. hypothesis of cladistic relationship, a cladogram, which can be interpreted as a phylogenetic tree to support historical explanations in biology. Cladograms are atemporal representations of relationship. They say approach to hypothesis formation has been, until re- nothing about the process of evolution. In contrast, cently, equally negligible. Only in the biogeographical phylogenetic trees are historical interpretations of cla- and geobotanical traditions has historical explanation dograms. The relationship represented in one clado- continued to play a central role. gram is compatible with more than one phylogeny (Nel- While ecology has been maturing as an experimental son and Platnick 1981). Wiley (1981) is a useful hand- and theoretical science, cladistics has increased the rigor book for those further interested in cladistic analysis. of historical explanations. This rigor has made the ex- Cladistics is, thus, a method that uses traits to in- planations based on phylogenies more reliable and vestigate the systematic relationship of organisms. more testable than they had previously been. At the Comparative biology, on the other hand, uses clado- same time, their own results have led ecologists to re- grams to investigate the systematic or temporal distribu- evaluate the role of adaptation, and they have begun to tion of traits. The idea of using the comparative ap- analyze comparative data with the aim of identifying proach to historical explanations in ecology was wide- historical constraints. spread in the 19th century and has continued as a Community ecology and evolutionary ecology have central theme in the European geobotanical tradition been suffused with experimental and theoretical ap- and in comparative morphology (Riedl 1978, Lauder proaches in the last quarter century, and some of them 1982). It has become increasingly prominent in ecology. have been making rapid progress on adaptationist as- The historical approach complements the current adap- sumptions. Because this progress has uncovered some tationist approach to evolutionary ecology. The main patterns not readily explained by adaptation, attention difference is the use of indirect estimates of history and has turned to techniques that can partition the effects of the emphasis on adaptation in evolutionary ecology and adaptation and constraint (reviewed by Pagel and Har- the use of direct estimates of history (through phyloge- vey 1988). netic trees) and the emphasis on constraint in historical The use of cladistics in comparative biology has be- ecology. Historical ecology is best suited to asking ques- come more widespread only during the last few years. tions about the origins and diversification of ecological Cladistics is a method of analysis, also known as phylo- phenomena, ranging from life history traits to commu- genetic systematics, that was first developed by the Ger- nity structure. As a form of comparative biology, it is a man entomologist Willi Hennig (Hennig 1950, 1966). method for suggesting patterns and locating possible Hennig devised it as an empirical method for discov- adaptations. It is a method for discovery and descriptive ering and justifying phylogenetic relationship. All spe- explanation but it can also, indirectly, discriminate cies are mosaics of primitive and derived traits, and the among causal explanations (O'Hara 1988), e.g. through phylogenetic relationships in a group of species can be statements about the sequence of origination