Crayfish and Trophic Cascade

Crayfish and Trophic Cascade - Biological Invasions (2005)...

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Loss of diversity and degradation of wetlands as a result of introducing exotic crayFsh C.F. Rodrı ´guez 1, * ,E .Be ´ cares 2 , M. Ferna ´ ndez-Ala ´ ez 2 & C. Ferna ´ ndez-Ala ´ ez 2 1 Instituto de Medio Ambiente, Universidad de Leo ´n, La Serna 56, 24071 Leo ´n, Spain; 2 Departamento de Ecologı´a, Facultad de Biologı´a, Universidad de Leo ´n, Campus de Vegazana, 24071 Leo ´n, Spain; *Author for correspondence (e-mail: [email protected]; fax: +34-987-291501) Received 4 June 2003; accepted in revised form 30 March 2004 Key words: alien species, aquatic birds, biodiversity, cray±sh, ecosystem, lake, macrophytes, wetland Abstract The introduction of the alocthonous Louisiana red swamp cray±sh ( Procambarus clarkii ) in Chozas (a small shallow lake situated in Leo ´ n (North-West Spain)) in 1996 switched the clear water conditions that harboured an abundant and a quite high richness of plants, invertebrates, amphibians and birds to a turbid one followed by strong losses in abundance and richness in the aforementioned groups. Cray±sh exclusion experiments done in Chozas previous to this work con±rmed the role of cray±sh herbivorism on macrophyte destruction that had a trophic cascade e²ect on the wetland ecosystem. Direct and indi- rect e²ects of cray±sh introduction on Chozas lake communities have been evaluated and compared with previous conditions before 1996 or with other related lakes in which cray±sh were no present. Cray±sh had a main role in submerged plant destruction and a potential e²ect on amphibia and macroinverte- brate population decrease. Plant destruction (99 % plant coverage reduction) was directly related to invertebrates (71 % losses in macroinvertebrate genera), amphibia (83 % reductions in species), and water- fowls (52 % reduction). Plant-eating birds were negatively a²ected (75 % losses in ducks species); never- theless, ±sh and cray±sh eating birds increased their presence since the introduction. Introduction of cray±sh in shallow plant-dominated lakes in Spain is a main risk for richness maintenance in these endangered ecosystems. Introduction Many studies include the fundamental role of aquatic vegetation in maintaining the ecological integrity of wetlands (e.g. Jeppessen et al. 1990; Moss 1990; Sche²er 1990). Submerged macro- phytes participate in a series of feedback mecha- nisms so that various physical and chemical variables remain within the limits appropriate to their development in the presence of aquatic veg- etation. This submerged vegetation also supports a complex trophic chain, completely di²erent from and much more diverse than those present in wetlands without vegetation (Carpenter and Lodge 1986). Shallow lakes can change abruptly from a situ- ation characterised by abundant submerged vege- tation and transparent waters to another characterised by the absence of vegetation and very turbid conditions due to the dominance of phytoplankton. These two extreme situations are considered alternative stable states related to the nutrient load received by the lake (Sche²er 1990).
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This note was uploaded on 04/21/2011 for the course BIO 105 taught by Professor Staff during the Winter '08 term at Grand Valley State University.

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Crayfish and Trophic Cascade - Biological Invasions (2005)...

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