Background Invasion-biology is largely based on non-experimental observation of larger organisms. Here, we apply an experimental approach to the subject. By using microbial-based microcosm-experiments, invasion-biology can be placed on firmer experimental, and hence, less anecdotal ground. A better understanding of the mechanisms that govern invasion-success of bacteria in soil communities will provide knowledge on the factors that hinder successful establishment of bacteria artificially inoculated into soil, e.g. for remediation purposes. Further, it will yield valuable information on general principles of invasion biology in other domains of life. Methodology/Principal Findings Here, we studied invasion and establishment success of GFP-tagged Pseudomonas fluorescens DSM 50090 in laboratory microcosms during a 42-day period. We used soil heating to create a disturbance gradient, and hypothesized that increased disturbance would facilitate invasion; our experiments confirmed this hypothesis. We suggest that the key factors associated with the heating disturbance that explain the enhanced invasion success are increased carbon substrate availability and reduced diversity, and thus, competition- and predation-release. In a second experiment we therefore separated the effects of increased carbon availability and decreased diversity. Here, we demonstrated that the effect of the indigenous soil community on bacterial invasion was stronger than that of resource availability. In particular, introduced bacteria established better in a long term perspective at lower diversity and predation pressure. Conclusion We propose increased use of microbial systems, for experimental study of invasion scenarios. They offer a simple and cost-efficient way to study and understand biological invasion. Consequently such systems can help us to better predict the mechanisms controlling changes in stability of communities and ecosystems. This is becoming increasingly relevant since anthropogenic disturbance causes increasing global change, which promotes invasion. Moreover, a thorough understanding of factors controlling invasion and establishment of artificially amended micro-organisms will mean a major step forward for soil-remediation microbiology.
References
[1]
Crawley MJ (1987) What makes a community invasible? In: Gray AJ, Crawley MJ, Edwards PJ, Editors. Colonization, Succession, and Stability. London: Blackwell Scientific publications. 429–453.
[2]
Levine JE (2000) Species diversity and biological invasions: relating local process to community pattern. Science 288: 852–854.
[3]
Vitousek PM, D'Antonio CM, Loop LD, Rejmánek M, Westbrooks R (1997) Introduced species: a significant component of human-caused global change. New Zeal J Ecol 21: 1–16.
[4]
Elton CS (1958) The ecology of invasions by animals and plants. London: Methuen 181 p.
[5]
Kneitel JM, Perrault D (2006) Disturbance-induced changes in community composition increase species invasion success. Community Ecol 7: 245–252.
[6]
Davis MA, Grime JP, Thompson K (2000) Fluctuating resources in plant communities: a general theory of invasibility. J Ecol 88: 528–534.
[7]
Eschtruth AK, Battles JJ (2009) Assessing the relative importance of disturbance, herbivory, diversity, and propagule pressure in exotic plant invasion. Ecol Monogr 79: 265–280.
[8]
Hobbs RJ, Huenneke LF (1992) Disturbance, diversity, and invasion-implications for conservations. Conserv Biol 6: 324–337.
[9]
Otfinowski R, Kenkel N (2010) Covariance between disturbance and soil resources dictates the invasibility of northern fescue prairies. Biol Invasions 12: 1349–1361.
[10]
Schooler SS, Cook T, Prichard G, Yeates AG (2010) Disturbance-mediated competition: the interacting roles of inundation regime and mechanical and herbicidal control in determining native and invasive plant abundance. Biol Invasions 12: 3289–3298.
[11]
van Elsas JD, Hill P, Chronakova A, Grekova M, Topalova Y, et al. (2007) Survival of genetically marked Escherichia coli O157: H7 in soil as affected by soil microbial community shifts. ISME J 1: 204–214.
[12]
Litchman E (2010) Invisible invaders: non-pathogenic invasive microbes in aquatic and terrestrial ecosystems. Ecol Lett 13: 1560–1572.
[13]
Fleming GM, Diffendorfer JE, Zedler PH (2009) The relative importance of disturbance and exotic-plant abundance in California coastal sage scrub. Ecol Appl 19: 2210–2227.
[14]
Wolters V, Silver WL, Bignell DE, Coleman DC, Lavelle P, et al. (2000) Effects of global changes on above- and belowground biodiversity in terrestrial ecosystems: Implications for ecosystem functioning. BioScience 50: 1089–1098.
[15]
Chantigny MH, Curtin D, Beare MH, Greenfield LG (2010) Influence of temperature on water-extractable organic matter and ammonium production in mineral soils. Soil Sci Soc Am J 74: 517–524.
[16]
Griffiths BS, Kuan HL, Ritz K, Glover LA, McCaig AE, et al. (2004) The relationship between microbial community structure and functional stability, tested experimentally in an upland pasture soil. Microbial Ecol 47: 104–113.
[17]
Adair EC, Burke IC, Lauenroth WK (2008) Contrasting effects of resource availability and plant mortality on plant community invasion by Bromus tectorum L. Plant Soil. 304: 103–115.
[18]
Davis MA, Pelsor M (2001) Experimental support for a resource-based mechanistic model of invasibility. Ecol Lett 4: 421–428.
[19]
Matos A, Kerkhof L, Garland JL (2005) Effects of microbial community diversity on the survival of Pseudomonas aeruginosa in the wheat rhizosphere. Microbial Ecol 49: 257–264.
[20]
Clark GF, Johnston EL (2009) Propagule pressure and disturbance interact to overcome biotic resistance of marine invertebrate communities. Oikos 118: 1679–1686.
[21]
Ekelund F, R？nn R (1994) Notes on protozoa in agricultural soil, with emphasis on heterotrophic flagellates and naked amoebae and their ecology. FEMS Microbiol Rev 15: 321–353.
[22]
Hooper DU, Dukes JS (2010) Functional composition controls invasion success in a California serpentine grassland. J Ecol 98: 764–777.
[23]
Wardle DA, Yeates GW (1993) The dual importance of competition and predation as regulatory forces in terrestrial ecosystems: evidence from decomposer food-webs. Oecologia 93: 303–306.
[24]
Fridley JD (2002) Resource availability dominates and alters the relationship between species diversity and ecosystem productivity in experimental plant communities. Oecologia 132: 271–277.
[25]
Romanuk TN, Kolasa J (2005) Resource limitation, biodiversity, and competitive effects interact to determine the invasibility of rock pool microcosms. Biol Invasions 7: 711–722.
[26]
Maron J, Marler M (2007) Native plant diversity resists invasion at both low and high resource levels. Ecology 88: 2651–2661.
[27]
Roscher C, Bessler H, Oelmann Y, Engels C, Wilcke W, et al. (2009) Resources, recruitment limitation and invader species identity determine pattern of spontaneous invasion in experimental grasslands. J Ecol 97: 32–47.
[28]
Pedersen AL, Nybroe O, Winding A, Ekelund F, Bj？rnlund L (2009) Bacterial feeders, the nematode Caenorhabditis elegans and the flagellate Cercomonas longicauda, have different effects on outcome of competition among the Pseudomonas biocontrol strains CHA0 and DSS73. Microb Ecol 57: 501–509.
[29]
Page FC (1988) A New Key to Freshwater and Soil Amoebae. Ambleside: Freshwater Biological Association, Scientific Publication.
[30]
Thirup L, Ekelund F, Johnsen K, Jacobsen CS (2000) Population dynamics of the fast-growing sub-populations of Pseudomonas and total bacteria, and their protozoan grazers, revealed by fenpropimorph treatment. Soil Biol. Biochem. 32: 1615–1623.
[31]
R？nn R, Ekelund F, Christensen S (1995) Optimizing soil extract and broth media for MPN-enumeration of naked amoebae and heterotrophic flagellates in soil. Pedobiologia 39: 10–19.
