Diversity in Mediterranean farm ponds: trade‐offs and synergies between irrigation modernisation and biodiversity conservation

1. Agricultural intensification has caused dramatic biodiversity loss in many agricultural landscapes over the last century. Here, we investigated whether new types of farm ponds (made of artificial substrata) in intensive systems and natural‐substratum ponds in traditional farming systems differ in their value for aquatic biodiversity conservation. 2. We analysed the main patterns of environmental variation, compared α‐, β‐ and γ‐diversity of macroinvertebrates between ponds types and evaluated the role of submerged aquatic vegetation (SAV). Generalised additive models (GAM) were used to analyse the relationships of α‐ and β‐diversity with environmental predictors, and variation partitioning to separate the effect of environmental and spatial characteristics on the variation in macroinvertebrate assemblages. Moran’s eigenvector maps (MEMs) were used to define spatial variables. 3. A principal coordinate analysis (PCoA) detected a primary environmental gradient that separated nutrient‐rich ponds from those dominated by SAV; a secondary morphometric gradient distinguished natural‐substratum ponds, with large surface area and structural complexity, from artificial‐substratum ponds with steeper slopes. Natural‐substratum ponds had almost twice the α‐ and γ‐diversity of artificial‐substratum ponds, and diversity significantly increased when SAV was present, particularly in artificial‐substratum ponds. Total phosphorus (TP) strongly contributed to explain the patterns in diversity, while SAV was a significant predictor of assemblage composition and diversity. GAMs revealed optima of both α‐diversity at intermediate SAV covers and β‐diversity at intermediate–high TP concentrations. 4. These findings have important implications for conservation planning. Adaptation of artificial‐substratum ponds by adding natural substratum and smoothing the gradient of pond margins would improve their conservation value. Development of SAV with occasional harvests and certain cautionary measures to control nutrient levels may also improve both the agronomical and environmental function of ponds.     

Pre- and postzygotic isolation and Haldane rule effects in reciprocal crosses of Danaus erippus and Danaus plexippus (Lepidoptera: Danainae), supported by differentiation of cuticular hydrocarbons, establish their status as separate species

Hybridization experiments and cuticular hydrocarbon analyses were performed to determine the extent of the reproductive isolation present to clarify the taxonomic status of Danaus erippus (Cramer, 1775), which has often been classified as a subspecies of Danaus plexippus (Linnaeus, 1758) . The results of crosses between D. erippus and Danaus plexippus nigrippus (Haensch, 1909) showed pre- and postzygotic isolation. Pupal inviability, and Haldane rule effects (male hybrids only, the homogametic sex in butterflies) were observed after the crosses. These results reinforce the hypothesis that D. plexippus and D. erippus are separate, reproductively isolated species. However, we have also investigated the cuticular hydrocarbons in D. erippus and D. p. nigrippus with temperature-programmed gas chromatography. The chromatographic profiles of peaks were similar in both taxa, with retention indices in the range 2100–3797. The profiles were characterized by the presence of 15 peaks whose retention indices were in the range 2501–3772. Although no major qualitative differences between the two species were observed, we did find some quantitative differences. A principal component analysis showed a clear separation between members of D. erippus and D. p. nigrippus , suggesting that semiochemical differences might have become differentiated after isolation, perhaps in response to different physiological pressures.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 91 , 445–453.