Abundance of weeds and seeds but not of arthropods differs between arable habitats in an extensive Mediterranean farming system

Abstract

Agricultural intensification has profoundly affected European farmlands in the last decades, and their associated biodiversity has undergone a widespread decline. Although largely considered by farmers to be a threat to crop productivity, weeds and arthropods are key factors in farmland ecosystems and provide multiple ecosystem services. We analyze variations between three arable habitats—cereals, plowed and fallow fields—in the biomass of weeds, seeds and arthropods in an extensive rotation system of Central Spain. We also investigate the effect of the vegetation structure in the overall biomass of arthropods and that of the most abundant orders found, Coleoptera and Orthoptera, which constitute key resources for many declining farmland birds. Our results show that fallows had the greatest biomass of weeds and seeds, whereas no differences were found between cereal and plowed fields. Although vegetation structure was related to the biomass of total arthropods, as well as that of coleopterans and orthopterans of a large size, arthropod biomass did not vary between the three arable habitats. Overall, higher weed cover and denser vegetation favored higher biomass of arthropods. Our results suggest a process of ecological homogenization, where arthropod populations may be suffering a widespread decline across habitat types, likely due to high tillage frequency or agrochemical use, despite the extensive rotation system and the mosaic landscape of our study site. Short‐ and mid‐term fallows might function as a source habitat for weeds and arthropods, although this role might be compromised by their progressive disappearance and isolation within the landscape.

Functional habitat suitability and urban encroachment explain temporal and spatial variations in abundance of a declining farmland bird, the Little Bustard Tetrax tetrax

“…We acknowledge that estimating availability of food resources based mainly on potential effects of management practices is a simplification, which should be re-assessed with information from future studies. For example, accumulated effects of agricultural intensification over the years may result in the homogenization of specific food resources across land uses (Tarjuelo et al 2019). Regardless of this limitation, we showed that habitat suitability calculated with three simple variables (vegetation height, cover, and food abundance) allows for the production of habitat suitability indices that have biological meaning and explain variations in abundance of Little Bustards.…”

Metabarcoding insights into the diet and trophic diversity of six declining farmland birds

“…Pin-tailed sandgrouse and black-bellied sandgrouse are mainly granivorous species 20 , so they rely on the availability of seeds and seed banks. Seed availability is highly variable between habitats and among seasons, being also strongly influenced by agricultural intensification 18 , 50 . Within arable land, natural and semi-natural vegetation growing in grassy field boundaries and fallow land provides an important stock of seeds, being thus important habitat elements for these species 50 .…”

Can current farmland landscapes feed declining steppe birds? Evaluating arthropod abundance for the endangered little bustard (Tetrax tetrax) in cereal farmland during the chick‐rearing period: Variations between habitats and localities

“…Biomass was calculated using the equations developed by Hódar (1996), which require the average length of each group. For this purpose, the length of 30 individuals per order was measured, except when the sample for a particular order was <30, in which case the mean was obtained from all the sampled individuals (see Tarjuelo et al., 2019 for similar procedures). Total and per‐order values were estimated.…”