Consumer assemblages are strongly affected by the availability of food resources. In recent years, more and more studies have shown that, in addition to background resource fluctuations, pulsed resources are also ubiquitous in ecosystems and could potentially have profound ecological consequences in consumer-resource dynamics. Depending on the trophic origin of the food resources, however, a resource pulse may affect the same consumer assemblages differently. In this study, we examined how beetle (Coleoptera) assemblages responded to artificially simulated seed and carrion pulses in second growth, oak-hickory woodlots in a highly fragmented landscape. Millet seeds (seeds of Panicum miliaceum) and mealworms (larvae of beetles in the family of Tenebrionidae) were used in a field experiment to simulate seed and carrion pulses. In order to contrast the differences between food resources from different trophic levels (seeds are basal resources and mealworms are from higher trophic levels), mixtures of millet seeds and mealworms at equal proportion were used as the control treatment. Beetles were sampled with pitfall traps in the three treatment plots (seeds, mealworms, mix) across two different woodlot sites.
Results/Conclusions
The results showed that the relative abundance of ground beetles (Coleoptera: Carabidae), a group composed of several seed-eating species, increased in response to seed pulses whereas the relative abundance of predatory rove beetles (Coleoptera: Staphylinidae) decreased in response to seed pulses. In addition, stable carbon isotope data showed evidence that ground beetles, but not rove beetles, utilized millet seeds during the period of the experiment. We found that the increase of ground beetles in response to seed pulses might also have driven down the overall evenness of beetle assemblages. However, these results are not consistent between the two woodlot sites included in the study, possibly because of the differences in their successional stages and vegetation structures. We concluded that more field experiments are needed to understand the ecological consequences of pulsed resources from different trophic levels in different types of habitats.
