References1. Waddington, C.H. (1942). Canalization of

development and the inheritance ofacquired characters. Nature 150,563–565.

2. Ferrell, J.E., Jr. (2002). Self-perpetuatingstates in signal transduction: positivefeedback, double-negative feedback andbistability. Curr. Opin. Cell Biol. 14,140–148.

3. Freeman, M. (2000). Feedback control ofintercellular signalling in development.Nature 408, 313–319.

4. Stelling, J., Sauer, U., Szallasi, Z., Doyle,F.J., 3rd, and Doyle, J. (2004).Robustness of cellular functions. Cell118, 675–685.

5. Prill, R.J., Iglesias, P.A., and Levchenko,A. (2005). Dynamic properties of networkmotifs contribute to biological networkorganization. PLoS Biol. 3, e343.

6. Franceschini, N., Kirschfeld, K., andMinke, B. (1981). Fluorescence of

photoreceptor cells observed in vivo.Science 213, 1264–1267.

7. Mikeladze-Dvali, T., Wernet, M.F.,Pistillo, D., Mazzoni, E.O., Teleman, A.A.,Chen, Y.W., Cohen, S., and Desplan, C.(2005). The growth regulators warts/latsand melted interact in a bistable loop tospecify opposite fates in Drosophila R8photoreceptors. Cell 122, 775–787.

8. Chou, W.H., Huber, A., Bentrop, J.,Schulz, S., Schwab, K., Chadwell, L.V.,Paulsen, R., and Britt, S.G. (1999).Patterning of the R7 and R8photoreceptor cells of Drosophila:evidence for induced and default cell-fate specification. Development 126,607–616.

9. Wernet, M.F., and Desplan, C. (2004).Building a retinal mosaic: cell-fatedecision in the fly eye. Trends Cell Biol.14, 576–584.

10. Turenchalk, G.S., St John, M.A., Tao, W.,and Xu, T. (1999). The role of lats in cell

cycle regulation and tumorigenesis.Biochim. Biophys. Acta 1424, M9–M16.

11. Teleman, A.A., Chen, Y.W., and Cohen,S.M. (2005). Drosophila meltedmodulates FOXO and TOR activity. Dev.Cell 9, 271–281.

12. Monod, J., and Jacob, F. (1961).Teleonomic mechanisms in cellularmetabolism, growth, and differentiation.Cold Spring Harb. Symp. Quant. Biol. 26,389–401.

13. Waddington, C.H. (1957) The Strategy OfThe Genes. George Allen and Unwin,London.

MRC Laboratory of Molecular Biology,Hills Road, Cambridge CB2 2QH, UK.E-mail: MF1@mrc-lmb.cam.ac.uk

DOI: 10.1016/j.cub.2005.10.062

Current Biology Vol 15 No 22R926

Ecological Succession: Out of theAsh

A new study of plants recolonising the land devasted when Mount St.Helens erupted in 1980 is providing important new insights into theinteractions with herbivores that determine the pattern and outcome ofecological succession.

Tiffany M. Knight and Jonathan M. Chase

The volcanic eruption of Mount St.Helens in 1980 devastated humanlife and property, as well as plantand animal life across an area of 60km2. This catastrophic disturbancehas been intensively studied forthe past 25 years by ecologists,who have gained valuable insightson the successional dynamics thatlead to the rehabilitation of

terrestrial ecosystems [1].Nitrogen-fixing plants, such aslupines (Lupinus sp.), are critical toprimary succession, as thesespecies enrich the otherwiseintolerable soil and allow otherspecies to subsequently establish[2]. Thus, it is of critical interest tounderstand the factors that controlthe colonization of nitrogen-fixingplants in a successional series.

Although herbivores are knownoften to have important effects on

plant population dynamics [3],both classical [4] andcontemporary [5] views ofsuccession rarely considerherbivores as playing a major rolein successional pathways interrestrial ecosystems. A series ofstudies on the interactionsbetween herbivores and importantnitrogen-fixing plants on MountSt. Helens has been dispelling theview that herbivores play apassive, rather than active, role inthe processes of succession(Figure 1A). Bill Fagan, JohnBishop and their colleagues [6–8]have discovered that lupine-specific lepidopterans depressthe colonization and spread of thenitrogen-fixing lupine, Lupinuslepidus. Of particular importanceare caterpillars of moths in thegenus Filatima, which consume

Figure 1. The role of herbivores in ecological succession around a live volcano.

(A) Landscape view of Lupinus lepidus (plants with purple flowers) near the blast ridge of Mount St. Helens with Mount Adams in thebackground. (B) Close-up view of L. lepidus killed by stem-boring insects flanked by healthy plants. (Both photographs courtesy ofW. Fagan.)

Dispatch R927

Ido Pen and Gerald Kerth

For females, choosing the rightsexual partner can be crucial, asmate choice may strongly affecttheir fitness, even if males providenothing but genes [1]. A recentpaper reporting a long-term study

[2] of the colonial greaterhorseshoe bat Rhinolophusferrumequinum (Figure 1) providesa new twist to our understanding offemale mate choice in socialspecies. Combining data from 17years of fieldwork with detailedgenetic pedigree analyses, Rossiter

Mate Choice: Female RelativesShare Sexual Partners in Bats

Groups of female greater horseshoe bats share more than just caves.A long-term study has revealed that female relatives share males aswell, but the adaptive significance of this family-wide mate fidelityremains obscure.

lupine leaves, and cause plants tohave depressed growth and seedproduction (Figure 1B). Theherbivory by these insects is sointense that it greatly depressesthe rate at which lupines caninvade open habitat on Mount St.Helens [6].

Over a decade of research on thedevastating effects of herbivory onlupine population dynamics hasjust come to fruition with a recentpaper in the American Naturalist[9]. For this work, empirical andtheoretical ecologists teamed up tocreate a mathematical model that isable to project the spread oflupines across the volcanic area.Their model included 18 empiricallymeasured parameters whichdescribe the ecology of the lupinesand their enemies, including lupineseed dispersal distances and thespatial location of herbivory.

Lupine seeds can move longdistances as a result of dispersalby small mammals, winter runoffand wind. The first lupine plantwas found on Mount St. Helens in1981, and to get there the seeddispersed over 2 km [10].However, long-distance seeddispersal is a relatively rare eventin these lupines. In contrast, theirlepidopteran enemies are capableof frequent, long distancedispersal [9]. Lepidopteranherbivores preferentially consumelupines that are isolates, orindividuals located on the edge ofa cluster of plants [6–8]. This mayresult from the higher quality ofnutrients they obtain for plantsgrowing at low density [8], orbecause arthropod predators aremore prevalent in large clusters ofplants [10]. However, becausethese isolated individualsotherwise have the potential tocontribute disproportionately tothe spread of the population [11],lepidopteran herbivory greatlystunts the rate of lupine invasion.

The results of the model [9]show that, under the bestestimates for all parameters, thelupine population is expected tospread by approximately 25 minper year. However, smallperturbations in any of theparameter values can cause thespread of lupines to come to a halt.For example, a slight increase (5%)in the fertility rates of herbivores

would cause the lupine populationto contract rather than expand.Their results also highlight theimportance of chance events, suchas the timing in which herbivoresinvade [9]. If lupines are able tocolonize and establish 9 years ormore before herbivores arrive, thenherbivores will be able to slow, butnot stop the spread of lupines. Butif herbivores arrive earlier, they candrive the lupine population extinct.At Mount St. Helens, the first lupinearrived in 1981, and by 1991 over 1million plants were present. It wasnot until after 1991 thatlepidopteran herbivoresestablished in strong numbers onthe front of the lupine invasion.

The implications of these newresults [9] extend well beyond howlupines and other lifeforms reassertthemselves after a volcaniceruption. This researchdemonstrates that speciesinteractions, such as interactionsbetween plants and herbivores, willinfluence the recovery ofvegetation after natural andanthropogenic disturbances.Further, the results are alsoapplicable to the invasion of non-native pests. A take home messagefrom these results is that biologicalcontrol and other types ofmanagement will have the highestlikelihood of success early on inthe invasion process.

References1. Dale, V.H., Swanson, F.J., and Crisafulli,

C.M. eds (2005). Ecological Responsesto the 1980 Eruption of Mount St.Helens. (Springer).

2. Halvorson, J.J., Franz, E.H., Smith, J.L.,and Black, R.A. (1992). Nitrogenaseactivity, nitrogen-fixation, and nitrogeninputs by lupines at Mount St. Helens.Ecology 73, 87-98.

3. Knight, T.M. (2004). The effects ofherbivory and pollen limitation on adeclining population of Trilliumgrandiflorum. Ecol. Appl. 14, 915–928.

4. Connell, J.H., and Slatyer, R.O. (1977).Mechanisms of succession in naturalcommunities and their role in communitystability and organization. Am. Nat. 111,1119–1144.

5. Walker, L.R., and del Moral, R. (2003).Primary Succession and EcosystemRehabilitation (Cambridge: CambridgeUniversity Press).

6. Fagan, W.F., and Bishop, J.G. (2000).Trophic interactions during primarysuccession: herbivores slow a plantreinvasion at Mount St. Helens. Am. Nat.155, 238-251.

7. Bishop, J.B. (2002). Early primarysucession on Mount St. Helens: impactof insect herbivores on colonizinglupines. Ecology 83, 191–202.

8. Fagan, W.F., Bishop, J.G., and Schade,J.D. (2004). Spatially structured herbivoryand primary sucession at Mount St.Helens: Field surveys and experimentalgrowth studies suggest a role fornutrients. Ecol. Entomol. 29, 398–409.

9. Fagan, W.F., Lewis, M., Neubert, M.G.,Aumann, C., Apple, J.L., and Bishop,J.G. (2005). When can herbivores slow orreverse the spread of an invading plant?A test case from Mount St. Helens. Am.Nat., in press.

10. Bishop, J., Fagan, C. Crisafulli, and J. S.Schade. 2005. Causes andconsequences of herbivory on prairielupine (Lupinus lepidus) in early primarysuccession. pp151-162. In EcologicalResponses to the 1980 Eruption ofMount St. Helens. V.H. Dale, F.J.Swanson, and C.M. Crisafulli, eds.Springer-Verlag.

11. Neubert, M.G., and Caswell, H. (2000).Demography and dispersal: calculationand sensitivity analysis of invasion speedfor structured populations. Ecology 81,1613–1628.

Department of Biology, WashingtonUniversity in St. Louis, One BrookingsDrive, Box 1229, St. Louis, Missouri63130, USA.

DOI: 10.1016/j.cub.2005.10.056