No correlation between the diversity and productivity of assemblages: evidence from the phytophage and predator assemblages in various cotton agroecosystems

Abstract

Biodiversity research has shown that primary productivity increases with plant species number, especially in many experimental grassland systems. Here, we assessed the correlation between productivity and diversity of phytophages and natural enemy assemblages associated with planting date and intercropping in four cotton agroecosystems. Twenty-one pairs of data were used to determine Pearson correlations between species richness, total number of individuals, diversity indices and productivity for each assemblage every five days from 5 June to 15 September 2012. At the same trophic level, the productivity exhibited a significant positive correlation with species richness of the phytophage or predator assemblage. A significant correlation was found between productivity and total number of individuals in most cotton fields. However, no significant correlations were observed between productivity and diversity indices (including indices of energy flow diversity and numerical diversity) in most cotton fields for either the phytophage or the predator assemblages. Species richness of phytophage assemblage and total individual numbers were significantly correlated with primary productivity. Also, species richness of natural enemy assemblage and total number of individuals correlated with phytophage assemblage productivity. A negative but not significant correlation occurred between the indices of numerical diversity and energy flow diversity and lower trophic-level productivity in the cotton-phytophage and phytophage-predator assemblages for most intercropped cotton agroecosystems. Our results clearly showed that there were no correlations between diversity indices and productivity within the same or lower trophic levels within the phytophage and predator assemblages in cotton agroecosystems, and inter-cropped cotton fields had a stronger ability to support the natural enemy assemblage and potentially to reduce phytophages. correlation, productivity, diversity, cotton agroecosystem, insect assemblage

Moderate grazing promotes the root biomass in Kobresia meadow on the northern Qinghai–Tibet Plateau

“…The relationship between species richness and productivity has been a central but controversial issue in plant ecology for a decade. A growing number studies have documented the productivity–richness relationship (Bai, Han, Wu, Chen, & Li, ; Gao, Men, & Ge, ), mostly finding that a unimodal relationship at scales from local to landscape, although several studies have found no correlation between species richness and productivity (Fraser et al, ; Gao et al, ). Here, we found a positive relationship between species richness and AGB across both community and all the plant functional groups except for sedges (Figures and ).This is promoted to some degree by the greater gains in soil resources in more diverse plant communities (Fornara & Tilman, ).…”

Biomass allocation and productivity–richness relationship across four grassland types at the Qinghai Plateau

“…Nevertheless, no consensus has been obtained regarding the relationship between productivity and species richness along natural gradients (Tredennick et al, ). Three dominant views were put forth regarding the productivity–richness relationship in terrestrial ecosystems, that is, hump‐shaped or U shaped (Ni, Wang, Bai, & Li, ; Waide et al, ), positive relationship (Bai et al, ; Marquard et al, ), and no correlation (Gao, Men, & Ge, ). The hump‐shape indicated that plant diversity reach its highest value at intermediate levels of productivity owing to density limitation (Oksanen, ), dispersal limitation, and evolutionary history (Zobel & Pärtel, ).…”