Synergistic effects of propagule pressure and trophic subsidies overcome biotic resistance to a non-native fish
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A central question in invasion ecology is how non-native species develop sustainable populations from small numbers of introduced founders. As biotic resistance, propagule pressure and trophic subsidises affect the outcomes of introductions of non-native fish, their individual and combined effects were tested in experimental mesocosms using the model species Pseudorasbora parva, a highly invasive fish in Europe. Their effects were measured as the number of 0+ P. parva present per treatment at the end of one reproductive season. The control started with 8 mature individuals (equal sex ratio). There were seven treatments, comprising propagule pressure (16 individuals), biotic resistance (presence of a coexisting fish) and trophic subsidies (daily release of fishmeal pellets), and their combinations. Compared to the control, biotic resistance resulted in significantly reduced 0+ fish numbers, with stable isotope analysis (δ13C, δ15N; SIA) suggesting this was due to facultative piscivory by the coexisting fish. There were significantly elevated 0+ fish numbers in the trophic subsidy, with SIA suggesting the diet of co-existing fish now primary comprised the subsidy. There was no significant difference in 0+ fish number between the control and propagule pressure treatment. Whilst the effect of biotic resistance on 0+ fish number was reduced slightly with propagule pressure and also when the trophic subsidy was available, there were significantly increased numbers of 0+ fish present in the treatment where they acted in combination. Thus, their effects appeared synergistic, overcoming the biotic resistance and enabling greater numbers of 0+ P. parva to survive until the end of the reproductive season.
KeywordsInvasion Global change Pseudorasbora parva Propagule pressure
ARN and JRB were supported by the ‘RINSE’ project (Interreg IVA 2 Seas Programme); TNQT was supported by TECHNO, an EU Erasmus Mundus programme.
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