Resistance and re-organization of an ecosystem in response to biological invasion: Some hypotheses

Using a dynamic model of Lake Chozas developed by Marchi et al. (2011), we tested three hypotheses about recovery of the indigenous community and water quality after radical changes caused by introduction of an invasive allochthonous crayfish, Procambarus clarkii: 1. Can the lake resist the pressure of an invasive species, like P. clarkii, by adaptation? 2. Can the ecosystem recover when all the crayfish are removed and low phosphorus concentrations persist in inflow water? 3. Does the simulated recovery of submerged vegetation occur at a total phosphorus concentration below 100 mg TP m(-3), as estimated by Scheffer et al. (1993), Scheffer (1997), Jeppesen etal, (1998) and Zhang et al. (2003)? We obtained the following answers: 1. Lake Chozas can at least partly resist by adaptation. A combination of possible parameter changes could lead to a significant increase in eco-exergy. 2. Removal of the phosphorus represented by crayfish (by harvesting) implies complete recovery of the lake and its eco-exergy, albeit not necessarily with the same organisms having the same properties. 3. The expected hysteresis created by introduction and harvesting of crayfish is observed under the following conditions: phytoplankton dominance at total phosphorus >= about 200-250 mgTP m(-3) and submerged vegetation returns at total phosphorus <100 mg TP m(-3). (C) 2011 Elsevier BM. All rights reserved.