Comparing methods of weed seed exposure to predators

Abstract

Several methods of seed exposure are used in seed predation studies, but how these methods influence the results remains poorly studied. In this article, two commonly used methods of seed exposure -seed cards and plasticine trays -were compared in the field and in the laboratory using three species of weed seeds. In the field, cards or trays with seeds were exposed either with or without cages to keep vertebrates out and either with or without impermeable roofs to provide protection from the weather. The overall seed retrieval from the control stands varied significantly between the methods of seed exposure, roof treatment and the species of seeds, and the scatter in the seed retrieval increased or decreased monotonically with the temperature or precipitation for some species of seeds. This indicates that the controls were more or less relevant depending on the weather conditions and species. The seed removal from cards varied between the species of seeds. The effect of exclosure cages indicated that invertebrates were the dominant seed predators of Capsella bursa-pastoris, while in Poa annua and Stellaria media both vertebrates and invertebrates were important. Higher seed removal from plasticine trays compared to seed cards was found for all three species of seeds, and placing roofs over the seeds affected seed removal in C. bursa-pastoris and P. annua. In the laboratory, seed consumption varied with the method of exposure in 10 out of 12 combinations of seed species and predator (two species of carabids and two species of isopods). The overall tendency was the opposite of the field observations: seed consumption was higher for seeds on filter paper and cards compared to seeds on tin trays. We conclude that seed cards are more convenient for short term studies in the field, while tin trays are useful in laboratory multi-choice experiments. To measure the realistic consumption of invertebrate predators in the laboratory, filter paper seems to be the best option as it does not present an obstacle to predators eating the seed. Using roofs introduced further bias regarding the estimates of seed removal in the field and thus should be avoided.

Factors that influence the level of weed seed predation: A review

“…Besides, seasonal population fluctuations (Honek et al 2006), phenological changes in predators life cycle (e.g., overwintering stages, breeding season, dispersal etc. ), biotic factors such as high-level trophic interactions (Davis & Raghu 2010), the presence of alternative food sources (Frank et al 2010(Frank et al , 2011, abiotic factors such as temperature , seed distribution patterns on the soil surface (Noroozi et al 2012), and the method of seed exposure in the field (Shuler et al 2008;Saska et al 2014) can be attributed to levels of weed seed predation in the field.…”

The role of invertebrates in seedling establishment in a heterocarpic plant, Atriplex sagittata

“…Each year we placed five pitfall traps in a linear transect that was parallel to the nearest A. sagittata stand at a distance of approximately 25 m, traps were c . 10‐m apart (Saska et al ., ). The traps used were plastic cups (7 cm in diameter, orifice area: 38.5 cm 2 , depth: 8 cm) and contained no bait.…”

“…The experiments were conducted in glass dishes (6 cm in diameter, 6 cm high), each containing one predator. Fifty seeds were exposed to predators on a moist filter paper (Saska et al, ). The experiments continued for 3 days with 20 replicates for arthropods and 5 for slugs.…”

“…In multi‐choice experiments we tested the consumption of A. sagittata seed in the presence of another 23 species of seeds selected based on the co‐occurrence with A. sagittata (Appendix). The seeds were stuck on plasticine baits, by 30 per a small tin tray (Saska et al, ). Trays containing individual seed species were arranged in a Petri dish (diameter: 20 cm) in two concentric circles, in a randomised order (Honek et al, ).…”

Burial-induced changes in the seed preferences of carabid beetles (Coleoptera: Carabidae)

“…Petri dishes measuring 25 cm in diameter with a 0.8-cm deep layer of sieved soil at the bottom served as experimental arenas. The seeds were mounted on a tin tray fi lled with white modelling clay (Plasticina JOVI®, Barcelona) and pressed into the layer of soil so that the clay surface was fl ush with the soil surface (Honek et al, 2003;Saska et al, 2014). Trays fi lled each with thirty fresh or thirty buried seeds of a particular species were placed in a Petri dish and arranged in two concentric circles.…”