Weed species, not mulching, affect web‐building spiders and their prey in organic fruit orchards in South Africa

Abstract

Citation: Arvidsson, F., P. Addison, M. Addison, C. R. Haddad, and K. Birkhofer. 2020. Weed species, not mulching, affect web-building spiders and their prey in organic fruit orchards in South Africa. Ecosphere 11(3):Abstract. Weed infestation affects economically relevant orchard properties, including tree performance, yield, and fruit quality negatively, and weeds are therefore often controlled by herbicide application in conventional farming. The addition of organic mulch below tree canopies has been proposed as an alternative reliable practice to suppress weeds and preserve soil moisture in organic farming. Mulching, however, may also affect arthropod pest and natural enemy populations, which highlights the need for simultaneously assessing weed, natural enemy, and animal pest communities in mulch experiments. This study addresses the limited knowledge about nonchemical ground cover management strategies for the control of plant and animal pests in orchards as a major constraint for organic growers. Here, we hypothesize that decisions about ground cover management practices in organic temperate fruit orchards affect the composition of web-building spider communities and their functional role as natural enemies of pest arthropods through effects on weed and insect pest communities. We studied weed, prey, and spider communities, as well as spider diet composition, in four temperate fruit types (apricot, peach, plum, and quince) on a single farm in the Western Cape, South Africa. We established experimental plots with and without addition of dead organic mulch under fruit tree canopies. Addition of organic mulch did not significantly affect weed cover under trees or the taxonomic composition of weed or spider communities over the eight-month study period. However, independent of mulching, the taxonomic composition of weed communities was significantly related to the composition of potential prey and spider communities. These relationships indirectly affected the prey composition of web-building spiders. These results suggest that the identity of weed species in the study orchards had a pronounced effect on the diet composition and functional role of web-building spiders. Future research should focus on the value of individual plant species for the promotion of pest control services provided by spiders across larger spatial scales and with higher levels of replication to allow for wider generalizations. The expected results would not only be relevant for weed control but could also be considered during the development of future flower strips in orchards.

Feeding habits and multifunctional classification of soil‐associated consumers from protists to vertebrates

“…Spiders also feed on Collembola (Roubinet et al, 2017), and in the tropics even attack and consume earthworms Nyffeler & Birkhofer, 2017). Most species are opportunistic predators, but the proportion of prey items in diets often does not reflect the local prey availability, particularly for very abundant prey which is often underrepresented (Kuusk & Ekbom, 2012;Diehl et al, 2013;Arvidsson et al, 2020). Several spider species have evolved prey preferences, for example by specialising on woodlice in Dysderidae (Pek ar, Spiders are excellent indicators of environmental change (Marc, Canard & Ysnel, 1999), as land-use intensification (Hanson et al, 2017;Birkhofer et al, 2017c), climate (Lensing, Todd & Wise, 2005;Wise & Lensing, 2019) or habitat heterogeneity (Sereda et al, 2012) alter their taxonomic and functional composition.…”

Molecular gut content analysis indicates the inter‐ and intra‐guild predation patterns of spiders in conventionally managed vegetable fields

“…Understanding trophic interactions among communities is essential to assess how ecosystems function and respond to environmental variations (Michalko et al., 2019; Symondson et al., 2002). Species relationships play a fundamental role in delivering ecosystem services, including the generalist and omnivore predators (Arvidsson et al., 2020; Brechtel et al., 2019; Thébault & Loreau, 2005), for which prey preferences and availability are key (Roubinet et al., 2018; Symondson, 2002). For example, the prey range of a predator depends on its capacity to capture and subdue a given prey type, the influence of competitors, handling time, and availability of alternative prey (Agustí et al., 2003; Friman et al., 2008; Kuusk & Ekbom, 2010; Michalko & Pekár, 2016).…”

“…Spiders are widely distributed in agroecosystems with diverse foraging behavior, so they are expected to be important predators (Arvidsson et al., 2020; Cuff et al., 2021; Mezőfi et al., 2020; Michalko et al., 2019), but the generalist nature of their diets makes it difficult to obtain precise information using conventional approaches, especially given that most spiders are fluid feeders. Further, many spiders are nocturnal hunters, ambush hunters, ground runners, and some hunt away from their webs (Mezőfi et al., 2020; Michalko & Pekár, 2016) making the direct observation of predation events even more difficult.…”

DNA metabarcoding of gut contents reveals key habitat and seasonal drivers of trophic networks involving generalist predators in agricultural landscapes

“…Plant species density was reported to be higher in organic fields (both inside the crop fields and adjacent non-crop areas) 54 than in conventional ones, which may provide plenty of resources, and thus contribute to the more diverse assemblages of arthropod prey. Conventional farms utilize more synthetic herbicides 55 to ensure weed control, resulting in lower plant species diversity (both within the crop fields and in adjacent areas), which ultimately has severe impacts on the diversity of inhabiting arthropod prey 22 . In addition, the availability of higher plant density and diversity outside the crop fields may provide alternative resources for several arthropod taxa to spill over into neighboring habitats 56–61 .…”