Spatial and temporal patterns of carabid activity-density in cereals do not explain levels of predation on weed seeds

Abstract

Seed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris > P. annua > S. media > L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a field.

Effects of Carbaryl-Bran Bait on Trap Catch and Seed Predation by Ground Beetles (Coleoptera: Carabidae)

“…Mauchline et al (2005) determined there was a signiÞcant correlation between seed predation and activity-density of two genera of carabids that were primarily granivorous (Amara and Harpalus) but not with total carabid density-activity. Saska et al (2008) also measured only weak correlations between activity-density of carabids and levels of seed predation.…”

A synthesis of feeding habits and reproduction rhythm in Italian seed-feeding ground beetles (Coleoptera: Carabidae)

“…Harpalus, Ophonus, Pseudophonus) and Zabrini (Amara, Zabrus) (Zetto Brandmayr, 1990), with a few belonging to the Trechini, Platynini and Pterostichini (Goldschmidt & Toft, 1997;Honek et al, 2003) (Appendix 1). Exceptions include the Scaritine, Clivina fossor, a single Trechine species, Trechus quadristriatus, scattered taxa in the Pterostichinae, such as Molopina (Abax parallelepipedus), Poecilina (Poecilus cupreus), Pterostichina (Pterostichus melanarius) and some Platyninae (Calathus fuscipes and Agonum mülleri) (Johnson & Cameron, 1969;Larochelle, 1990;Goldscmidt & Toft, 1997;Honek & Martinkova, 2001;Toft & Bilde, 2002;Honek et al, 2003Honek et al, , 2007Honek et al, , 2009Mauchline et al, 2005;Saska et al, 2008;Lundgren et al, 2009). The latter two species are often "reluctant" to accept seeds in no choice experiments or accept the soft seeds of Capsella bursa pastoris in large quantities (Calathus ambiguus, T. quadristriatus).…”

“…Accepts fresh meat if offered with lettuce seeds, Triticum, Avena, Hordeum, Secale a seed mixture Gersdorf, 1937in Thiele, 1977Zhavoronkova, 1969;Honek et al, 2005Honek et al, , 2007Pierce, 1971;Bassett, 1978 Briggs, 1965;Larochelle, 1990;Jørgensen & Toft, 1997b;Honek et al, 2003Honek et al, , 2005Martinkova et al, 2006;Saska et al, 2008Saska et al, , 2010 Brandmayr & Zetto Brandmayr, 1974, 1987Brandmayr, 1974;Brandmayr et al, 1994;Zetto Brandmayr, 1990;Zetto Brandmayr et al, 1994 D. (S.) Saska et al, 2008 …”

Comparing methods of weed seed exposure to predators

“…The seeds of three species of annual weeds that are frequently consumed by seed predators Saska et al, 2008;Saska, 2008) were used. The species differ in taxonomic affiliation, shape and size: Stellaria media (L.) Vill.…”