Low‐intensity management benefits solitary bees in olive groves

Abstract

One of the current challenges for applied ecologists is to understand how to manage/restore agroecosystems in a sustainable and cost‐effective way. The intermediate landscape complexity hypothesis (ILCH) predicts that the effectiveness of agri‐environmental measures (AES) on biodiversity and ecosystem services recovery is often largest in landscapes of intermediate complexity. This hypothesis has rarely been tested in savanna‐like permanent agroecosystems. Focusing on pollinators, we test the ILCH at the regional scale in Mediterranean olive orchards, one of the most important permanent agroecosystems in the world. We inferred abundance of cavity‐nesting pollinators in 40 paired olive orchards (extensively vs. intensively managed herbaceous cover) in 20 localities selected across a landscape complexity gradient. We also studied how different magnitudes in local management switches may affect pollinators by considering organic and intensive fields as management extremes in olive orchards. We used 208 trap nests for solitary bees to measure colonization rates. Additionally, we conducted pollinator surveys to ascertain that colonization rate was a representative proxy for pollinator activity. Our results showed that (a) changes in colonization rates due to local herb cover management peaked at intermediate landscape complexity, with extensively managed fields rendering higher colonization rates. (b) Organic fields had higher colonization rates than their control farms regardless of landscape complexity. (c) There was a highly significant correlation between nest colonization rates and density of pollinators foraging on flowers, which suggests that colonization rate is a good estimator of pollinator activity. Policy implications. The maintenance of ground herb cover (main agri‐environmental measure in olive orchards) is a cost‐effective investment allowing recuperation of pollinators when targeting olive farms located in landscapes of intermediate complexity. Additionally, fostering organic farming (still minority in olive groves) for the conservation of solitary bees should be a priority for policymakers since its effects are beneficial in any landscape.

Agricultural intensification erodes taxonomic and functional diversity in Mediterranean olive groves by filtering out rare species

“…Martínez‐Núñez et al. (2019) found in the same study plots that agricultural intensification resulted in a decrease and spatial homogenization of cavity‐nesting bee diversity. This is congruent with the impoverishment of insect‐pollinated plants compared to wind‐pollinated ones by agriculture intensification and landscape simplification (see Table 1).…”

“…Prominently, in the past decades, the use of herbicides and recurrent tillage has diminished the diversity of plants and contributed to taxonomic and functional filtering of their communities. The decrease in herb diversity has generated cascading effects on arthropods (Lichtenberg et al, 2017;Marshall et al, 2003;Martínez-Núñez et al, 2019) and farmland birds (Marshall et al, 2003). Thus, ecosystem services such as crop pollination by insects (Martínez-Núñez et al, 2020) or pest control by birds have been compromised (Nave et al, 2017).…”

Interacting effects of landscape and management on plant–solitary bee networks in olive orchards

“…We used 96 bee trap nests to sample plant–solitary bee communities. Bee trap nests were chosen because they (a) target a bioindicator group (solitary bees that nest in cavities above‐ground) that is highly dependent on environmental heterogeneity, (b) provide an easy and reliable method to detect and sample interactions, and (c) represent a fully standardized sampling method (Staab et al, ) previously proven to be applicable in our study system (Martínez‐Núñez et al, ). On each pair of farms, we placed four or six bee trap nests depending on field size: small (<25 ha but frequently <10 ha) or big (>50 ha but frequently >100 ha), respectively.…”

Reviewing the use of bee trap nests for the study of interaction networks in agroecosystems: insights from its use in olive farms

“…Encontramos sólo 13 especies de abejas solitarias pertenecientes a 5 géneros de la Familia Megachilidae utilizando 96 nidales en 18 olivares de Andalucía y casi 100 especies realizando censos mediante observación y mangueo en los mismos olivares. Aumentando el esfuerzo de muestreo a 40 olivares y 204 nidales, registramos 17 especies de 6 géneros (Martínez-Núñez et al 2019a). No obstante, en nuestro sistema, la tasa de colonización de los nidales estuvo positivamente correlacionada con la densidad de polinizadores que forrajeaban en parches florales de especies arvenses (Martínez-Núñez et al, 2019a) indicando que, pese a que los nidales ofrecen estimas de riqueza muy sesgadas a un grupo concreto, este es un grupo bioindicador.…”

“…Por ejemplo, no se conoce cómo afecta la capacidad de detección de los nidales y la escasez de cavidades naturales a su tasa de colonización. Algunos resultados parecen indicar que la preferencia de uso y la capacidad de detección podrían jugar un papel importante amortiguando las diferencias observadas entre sitios (Martínez-Núñez et al 2019a).…”