Abstract
Species of carabid (ground) beetles are among the most important postdispersal weed seed predators in temperate arable lands. Field studies have shown that carabid beetles can remove upwards of 65%–90% of specific weed seeds shed in arable fields each year. Such data do not explain how and why carabid predators go after weed seeds, however. It remains to be proven that weed seed predation by carabids is a genuine ecological interaction driven by certain ecological factors or functional traits that determine interaction strength and power predation dynamics, bringing about therefore a natural regulation of weed populations. Along these lines, this review ties together the lines of evidence around weed seed predation by carabid predators. Chemoperception rather than vision seems to be the primary sensory mechanism guiding seed detection and seed selection decisions in carabid weed seed predators. Selection of weed seeds by carabid seed predators appears directed rather than random. Yet, the nature of the chemical cues mediating detection of different seed species and identification of the suitable seed type among them remains unknown. Selection of certain types of weed seeds cannot be predicted based on seed chemistry per se in all cases, however. Rather, seed selection decisions are ruled by sophisticated behavioral mechanisms comprising the assessment of both chemical and physical characteristics of the seed. The ultimate selection of certain weed seed types is determined by how the chemical and physical properties of the seed match with the functional traits of the predator in terms of seed handling ability. Seed density, in addition to chemical and physical seed traits, is also an important factor that is likely to shape seed selection decisions in carabid weed seed predators. Carabid responses to seed density are rather complex as they are influenced not only by seed numbers but also by trait‐based suitability ranks of the different seed types available in the environment.
Highlights
Predation is one of the fates many weed seeds succumb to either on the mother plant or after seed dispersal (Crawley, 2000)
Studies on annual weeds revealed that larvae of the specialized micro-lepidopterans Coleophora lineapuvella (Chambers) and Scrobipalpa atriplicella (Fischer von Röslerstamm) could destroy large numbers of the seed heads of Amaranthus retroflexus L. and Chenopodium album L., respectively, in corn and soybean fields in Eastern Canada (Nurse et al, 2003)
The seed- destructive effects of those predispersal predators were sporadic and remained rather low throughout the season and showed high variability across locations and years (DeSousa & Swanton, 2003; Nurse et al, 2003). These findings led the authors to suggest that predispersal weed seed predation alone is unlikely to bring about significant suppression of annual weeds in arable fields
Summary
Predation is one of the fates many weed seeds succumb to either on the mother plant or after seed dispersal (Crawley, 2000). The seed- destructive effects of those predispersal predators were sporadic and remained rather low throughout the season and showed high variability across locations and years (DeSousa & Swanton, 2003; Nurse et al, 2003). The presence of the gall midge Clinodiplosis cilicrus (Kieffer) larvae in the flower heads of Centaurea cyanus L. in a field study in France was found to be associated with a four-fold reduction in seed numbers, and about 40% drop in seed viability. This suggests C. cilicrus larvae can potentially depress populations of C. cyanus in the field (Koprdova et al, 2015). The effect cannot be attributed to genuine seed predation but to fertilization disruption by consuming resources necessary for successful fertilization or repelling pollinators (Koprdova et al, 2015)
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