- Email: [email protected]
Reply from C.E. Lee and M.A. Bell
CORRESPONDENCE In the early 19th century, humans built canals to link the rivers of the Caspian Sea basin with tributaries of the Baltic Sea, and shipping traffic through this, and other, canals allowed zebra mussels to spread rapidly through central and western Europe2. Shipping activities subsequently brought zebra mussels to North America, where they now flourish. Thus, human activities allowed zebra mussels to move between freshwater drainage basins, but not to make the initial transition from saltwater to freshwater. Several other species, listed by Lee and Bell as examples of recent, human-caused invasions of fresh waters, probably also invaded fresh waters well before 1800 without human help. For instance, Cordylophora caspia, C. lacustris (probably a synonym of C. caspia), Corophium curvispinum and Echinogammarus ischnus were said by Lee and Bell to have entered freshwater between 1854 and 1931. However, by the early 1900s, these three species were reported to be common and widespread in lakes and rivers throughout the Black and Caspian Sea basins, from Turkey to the Urals7–9. It seems unlikely that this distribution could have been achieved if these species had entered freshwater only in the past 200 years as a result of recent human activities. Instead, these species probably have lived in freshwater ‘since ancient times’7. Undoubtedly, human activities have led to some important invasions of fresh waters by saltwater animals, but Lee and Bell overestimate the frequency of such human-caused invasions. This overestimate undermines parts of Lee and Bell’s conclusions, including their assertion that ‘many highly invasive and disruptive species in freshwater are recent immigrants from saline habitats’. Several of the most disruptive invaders (e.g. D. polymorpha, C. curvispinum, E. ischnus) entered fresh waters in prehistoric times without human intervention. Human activities have moved many freshwater pest species into new ranges, but this movement has been largely from one freshwater basin to another, not from salt waters to fresh waters.
David Strayer Institute of Ecosystem Studies, PO Box AB, Millbrook, NY 12545, USA ([email protected]) References 1 Lee, C.E. and Bell, M.A. (1999) Trends Ecol. Evol. 14, 284–288 2 Kinzelbach, R. (1992) in The Zebra Mussel Dreissena polymorpha (Neumann, D. and Jenner, H.A., eds), pp. 5–17, Gustav Fischer Verlag 3 Ehrmann, P. (1933) in Die Tierwelt Mitteleuropas. Mollusken (Weichtiere) (Brohmer, P. et al., eds), Verlag Von Quelle & Meyer 4 Strayer, D.L. and Smith, L.C. (1993) in Zebra Mussels: Biology, Impacts, and Control (Nalepa, T.F. and Schloesser, D.W., eds), pp. 715–727, Lewis Publishers 5 Kinzelbach, R. (1986) Zool. Middle East 1, 132–138 6 Bânârescu, P. (1990) Zoogeography of Fresh Waters (Vol. 1), AULA-Verlag 7 Mordukhai-Boltovskoi, P.D. (1964) Int. Rev. Ges. Hydrobiol. 49, 139–176 8 Mordukhai-Boltovskoi, P.D. (1979) Int. Rev. Ges. Hydrobiol. 64, 1–38 9 Hutchinson, G.E. (1967) A Treatise on Limnology, (Vol. 2), Wiley TREE vol. 14, no. 11 November 1999
Reply from C.E. Lee and M.A. Bell Strayer states that we erred in the dates we gave for the initial colonizations of fresh water1. However, our goal was not to document initial dates of freshwater invasions, but rather to discuss cases where there is evidence for recent habitat shifts by particular populations, independent of prior invasions by other populations. What we emphasize in our paper are the remarkable facts that (1) colonizations from salt water (brackish or marine) can occur on decadal rather than on millennial time scales, and (2) that recent immigrants from salt water can spread rapidly and persist in fresh water, through facilitation by humans. Table 1 of our perspective article1 lists examples for which timing and direction of invasions can be inferred from concrete evidence (the criteria for the examples we use are given in Box 1), rather than examples of first appearances in fresh water. For instance, for the copepod Eurytemora affinis, we list several dates, from the 1930s to the 1980s. These are not dates this species first entered fresh water but inferred dates of repeated and independent invasions from saltwater sources2. Strayer highlights the problem of using species distributions to infer pathways of freshwater invasions, especially when systematic relationships among populations are uncertain. For instance, in the case of the zebra mussel Dreissena polymorpha, the extent to which postglacial freshwater populations survived to the present day is inconclusive3. In addition, populations from southwestern Europe, such as those in Lakes Ohrid and Prespa, are thought to represent ancient invasions of fresh water, and are considered sibling species of populations from the Ponto-Caspian basin3,4, the likely source of recent invasions5,6. As stated in our paper, genetic markers would be required to determine pathways and frequency of invasions, and in the case of D. polymorpha, clarify systematic relationships among populations and sibling species. The impact of humans in the past 200 years should not be underestimated. The direct transfer of organisms (including those that Strayer mentions) from salt water to fresh water has occurred on massive scales, and many of these cases are documented1. For example, in Eastern Europe and Russia large-scale acclimatization of numerous Ponto-Caspian species into freshwater reservoirs was undertaken for aquaculture purposes7,8. In addition, impoundment of entire
bays and lagoons resulted in the large-scale trapping and acclimatization of populations9,10. Physiological studies indicate that these invaders are energetically less efficient in fresh water than more ancient freshwater species11,12. Yet, the creation of reservoirs (as havens for acclimation and as stepping stones) and transport vectors has extended their ranges7,8 and made invasions from saline habitats more likely and serious. The implication is that within the modern era we can expect many more independent invasions to occur from saline to freshwater habitats, especially from the Ponto-Caspian region. Human transport and habitat alteration have accelerated the pace of such invasions, and they have the potential for major impacts on aquatic ecosystems.
Carol Eunmi Lee Marine Biology Research Division 0202, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA ([email protected])
Michael A. Bell Dept of Ecology and Evolution, State University of New York, Stony Brook, NY 11794-5245, USA ([email protected]) References 1 Lee, C.E. and Bell, M.A. (1999) Trends Ecol. Evol. 14, 284–288 2 Lee, C.E. Evolution (in press) 3 Kinzelbach, R. (1992) in The Zebra Mussel Dreissena polymorpha (Neumann, D. and Jenner, H.A., eds), pp. 5–17, Gustav Fischer Verlag 4 Kinzelbach, R. (1986) Zool. Middle East 1, 132–138 5 De Martonne, E. (1927) Trait de Geographie Physique, Librairie Armand Colin 6 Rosenberg, G. and Ludyanskiy, M.L. (1994) Can. J. Fish. Aquat. Sci. 51, 1474–1484 7 Mordukhai-Boltovskoi, P.D. (1979) Int. Rev. Gesamten Hydrobiol. 64, 1–38 8 Jazdzewski, K. (1980) Crustaceana (Suppl.) 6, 84–107 9 De Beaufort, L.F. (1954) Veranderingen in de Flora en Fauna van de Zuiderzee (thans IJsselmeer) na de Afsluiting in 1932, C. de Boer, Jr 10 Miller, R.C. (1958) J. Mar. Res. 17, 375–382 11 Taylor, P.M. and Harris, R.R. (1986) J. Comp. Physiol. 156, 323–329 12 McMahon, R.F. (1996) Am. Zool. 36, 339–363
Corrigendum Luikart, G. and England, P.R. Trends Ecol. Evol. 14, 253–256 (July 1999) In Table 1, the correct source of the CERVUS program for assigning paternity and inferring parentage should be:
http://helios.bto.ed.ac.uk/evolgen
0169-5347/99/$ – see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0169-5347(99)01739-5
449
David Strayer Institute of Ecosystem Studies, PO Box AB, Millbrook, NY 12545, USA ([email protected]) References 1 Lee, C.E. and Bell, M.A. (1999) Trends Ecol. Evol. 14, 284–288 2 Kinzelbach, R. (1992) in The Zebra Mussel Dreissena polymorpha (Neumann, D. and Jenner, H.A., eds), pp. 5–17, Gustav Fischer Verlag 3 Ehrmann, P. (1933) in Die Tierwelt Mitteleuropas. Mollusken (Weichtiere) (Brohmer, P. et al., eds), Verlag Von Quelle & Meyer 4 Strayer, D.L. and Smith, L.C. (1993) in Zebra Mussels: Biology, Impacts, and Control (Nalepa, T.F. and Schloesser, D.W., eds), pp. 715–727, Lewis Publishers 5 Kinzelbach, R. (1986) Zool. Middle East 1, 132–138 6 Bânârescu, P. (1990) Zoogeography of Fresh Waters (Vol. 1), AULA-Verlag 7 Mordukhai-Boltovskoi, P.D. (1964) Int. Rev. Ges. Hydrobiol. 49, 139–176 8 Mordukhai-Boltovskoi, P.D. (1979) Int. Rev. Ges. Hydrobiol. 64, 1–38 9 Hutchinson, G.E. (1967) A Treatise on Limnology, (Vol. 2), Wiley TREE vol. 14, no. 11 November 1999
Reply from C.E. Lee and M.A. Bell Strayer states that we erred in the dates we gave for the initial colonizations of fresh water1. However, our goal was not to document initial dates of freshwater invasions, but rather to discuss cases where there is evidence for recent habitat shifts by particular populations, independent of prior invasions by other populations. What we emphasize in our paper are the remarkable facts that (1) colonizations from salt water (brackish or marine) can occur on decadal rather than on millennial time scales, and (2) that recent immigrants from salt water can spread rapidly and persist in fresh water, through facilitation by humans. Table 1 of our perspective article1 lists examples for which timing and direction of invasions can be inferred from concrete evidence (the criteria for the examples we use are given in Box 1), rather than examples of first appearances in fresh water. For instance, for the copepod Eurytemora affinis, we list several dates, from the 1930s to the 1980s. These are not dates this species first entered fresh water but inferred dates of repeated and independent invasions from saltwater sources2. Strayer highlights the problem of using species distributions to infer pathways of freshwater invasions, especially when systematic relationships among populations are uncertain. For instance, in the case of the zebra mussel Dreissena polymorpha, the extent to which postglacial freshwater populations survived to the present day is inconclusive3. In addition, populations from southwestern Europe, such as those in Lakes Ohrid and Prespa, are thought to represent ancient invasions of fresh water, and are considered sibling species of populations from the Ponto-Caspian basin3,4, the likely source of recent invasions5,6. As stated in our paper, genetic markers would be required to determine pathways and frequency of invasions, and in the case of D. polymorpha, clarify systematic relationships among populations and sibling species. The impact of humans in the past 200 years should not be underestimated. The direct transfer of organisms (including those that Strayer mentions) from salt water to fresh water has occurred on massive scales, and many of these cases are documented1. For example, in Eastern Europe and Russia large-scale acclimatization of numerous Ponto-Caspian species into freshwater reservoirs was undertaken for aquaculture purposes7,8. In addition, impoundment of entire
bays and lagoons resulted in the large-scale trapping and acclimatization of populations9,10. Physiological studies indicate that these invaders are energetically less efficient in fresh water than more ancient freshwater species11,12. Yet, the creation of reservoirs (as havens for acclimation and as stepping stones) and transport vectors has extended their ranges7,8 and made invasions from saline habitats more likely and serious. The implication is that within the modern era we can expect many more independent invasions to occur from saline to freshwater habitats, especially from the Ponto-Caspian region. Human transport and habitat alteration have accelerated the pace of such invasions, and they have the potential for major impacts on aquatic ecosystems.
Carol Eunmi Lee Marine Biology Research Division 0202, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA ([email protected])
Michael A. Bell Dept of Ecology and Evolution, State University of New York, Stony Brook, NY 11794-5245, USA ([email protected]) References 1 Lee, C.E. and Bell, M.A. (1999) Trends Ecol. Evol. 14, 284–288 2 Lee, C.E. Evolution (in press) 3 Kinzelbach, R. (1992) in The Zebra Mussel Dreissena polymorpha (Neumann, D. and Jenner, H.A., eds), pp. 5–17, Gustav Fischer Verlag 4 Kinzelbach, R. (1986) Zool. Middle East 1, 132–138 5 De Martonne, E. (1927) Trait de Geographie Physique, Librairie Armand Colin 6 Rosenberg, G. and Ludyanskiy, M.L. (1994) Can. J. Fish. Aquat. Sci. 51, 1474–1484 7 Mordukhai-Boltovskoi, P.D. (1979) Int. Rev. Gesamten Hydrobiol. 64, 1–38 8 Jazdzewski, K. (1980) Crustaceana (Suppl.) 6, 84–107 9 De Beaufort, L.F. (1954) Veranderingen in de Flora en Fauna van de Zuiderzee (thans IJsselmeer) na de Afsluiting in 1932, C. de Boer, Jr 10 Miller, R.C. (1958) J. Mar. Res. 17, 375–382 11 Taylor, P.M. and Harris, R.R. (1986) J. Comp. Physiol. 156, 323–329 12 McMahon, R.F. (1996) Am. Zool. 36, 339–363
Corrigendum Luikart, G. and England, P.R. Trends Ecol. Evol. 14, 253–256 (July 1999) In Table 1, the correct source of the CERVUS program for assigning paternity and inferring parentage should be:
http://helios.bto.ed.ac.uk/evolgen
0169-5347/99/$ – see front matter © 1999 Elsevier Science Ltd. All rights reserved.
PII: S0169-5347(99)01739-5
449