‘Carabidologists do it all’ (Niemelä 1996a) is a phrase with which most European carabidologists are familiar. Indeed, during the last half a c

Summary: Carabids and other epigeal arthropods make important contributions to biodiversity, food webs and biocontrol of invertebrate pests and weeds. Pitfall trapping is widely used for sampling carabid populations, but this technique yields biased estimates of abundance (‘activity‐density’) because individual activity – which is affected by climatic factors – affects the rate of catch. To date, the impact of temperature on pitfall catches, while suspected to be large, has not been quantified, and no method is available to account for it. This lack of knowledge and the unavailability of a method for bias correction affect the confidence that can be placed on results of ecological field studies based on pitfall data. Here, we develop a simple model for the effect of temperature, assuming a constant proportional change in the rate of catch per °C change in temperature,r, consistent with an exponential Q₁₀response to temperature. We fit this model to 38 time series of pitfall catches and accompanying temperature records from the literature, using first differences and other detrending methods to account for seasonality. We use meta‐analysis to assess consistency of the estimated parameterramong studies. The mean rate of increase in total catch across data sets was 0·0863 ± 0·0058 per °C of maximum temperature and 0·0497 ± 0·0107 per °C of minimum temperature. Multiple regression analyses of 19 data sets showed that temperature is the key climatic variable affecting total catch. Relationships between temperature and catch were also identified at species level. Correction for temperature bias had substantial effects on seasonal trends of carabid catches. Synthesis and Applications. The effect of temperature on pitfall catches is shown here to be substantial and worthy of consideration when interpreting results of pitfall trapping. The exponential model can be used both for effect estimation and for bias correction of observed data. Correcting for temperature‐related trapping bias is straightforward and enables population estimates to be more comparable. It may thus improve data interpretation in ecological, conservation and monitoring studies, and assist in better management and conservation of habitats and ecosystem services. Nevertheless, field ecologists should remain vigilant for other sources of bias.

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 annuaandStellaria 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.

Summary: The importance of predation in determining the fate of post‐dispersal dandelion (Taraxacum officinale) seed was investigated. Flowering, seed dispersal, seedling establishment, seed predation and seed predator abundance were recorded in 2002 and 2003, at two sites. Number of flowers were counted in 1‐m²plots, wind‐borne seeds were collected in water traps, invertebrate seed predation was estimated from the rate of removal of dandelion seeds exposed on the ground and invertebrate activity density was determined by using pitfall traps. The censuses were made at 2‐ to 3‐day intervals. Seed dispersal occurred 10 days after flowering. Although some seeds were blown away, 3.7–24.2 × 10³seeds m⁻²fell to the ground. Four weeks after the peak in seed dispersal 0.7–3.1% of these seeds germinated. Three weeks later only 11–13% of the dispersed seed remained on the ground and most of these were damaged, the remainder presumably having been removed by predators. Predation of exposed seeds was low before seed dispersal but increased after its onset, in parallel with increases in the number of seeds present on the ground and in the activity density of adults of a seed‐consuming carabid,Amara montivaga. In cafeteria experiments in which the seeds of 28 perennial and annual herbs were providedA. montivagaconsumed the most dandelion seeds, followed by nine otherAmaraspecies. In no‐choice experiments, under field conditions,A. montivagaconsumed six seeds day⁻¹. Post‐dispersal predation, mainly due to aggregation of a single ground beetle species, was more important than that which occurred prior to dispersal. Although predators destroyedc. 97% of the seeds, the effect on dandelion population biology is likely to be small. Post‐dispersal seed predation may nevertheless be important in other species, as aggregates of large invertebrate predators can consume large quantities of seed.