Structure of past and present food webs from a semiarid wetland subjected to species invasion and environmental degradation
Species invasion and habitat degradation very often result in local species loss, which may result in a cascade of secondary extinctions that typically end up disrupting whole ecological netwroks. Herein, we used historical records and the natural abundance of stable isotopes (13C and 15N) of primary producers, aquatic animals and sediment/detritus to derive the past and present structure of food webs from the freshwater wetland "Las Tablas de Daimiel", in cen-tral Spain. Before the green
... tion and agricultural transformation of the area, this wet-land was characterised by a high biodiversity of basal species, including primary consumers such as bivalves and gastropods, which are currently absent or very scarce. Our results demonstrate that the increase of anthropogenic disturbances, exotic species and changes in primary productivity of this wetland is affecting the biodiversity at all trophic levels (mainly herbivorous fish) but not the length of the food chain, which we estimated between 3.9 and 4.4 trophic levels. Using the mixing models, we showed that macrophytes represent an im-portant contribution of matter and energy to higher trophic levels. Our model also suggested that a currently expanding, allochthonous halophytic tree (Tamarix canariensis) may be the main energy source for two species of commonly found butterflies (Pieris rapae and Rho-dometra sacraria) as well as for invertebrates, while the macrophyte Thypa dominguensis was the main diet source for the exotic crayfish Procambarus clarkii, which occupies the niche left by the native crayfish. Our work demonstrates the importance of taking a whole-systems ap-proach to characterize the magnitude of human impacts on the functioning of wetland ecosys-tems.