PARENT SESSION
Poster Session 19: Biodiversity
Wednesday, August 10, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of detrital subsidy on abundance and diversity of ground-dwelling spiders and insects.

Riem, Jennifer^*,1, Buddle, Chris², Rypstra, Ann³, ¹ Miami University, Oxford, OH, USA² McGill University, Ste. Anne de Bellevue, Quebec, Canada³ Miami University, Hamilton, OH, USA

ABSTRACT- Productivity has been shown to have a strong effect on species diversity in some ecosystems. Within the framework of competition theory, productivity can be defined as the flow of energy into resources for which competition is occurring. Soybean fields are cyclical ephemeral ecosystems in which an interaction between the annual recolonization by spiders and competition for prey may drive spider abundance and diversity. The purpose of our study was to investigate the species diversity and community composition of ground-dwelling spiders in response to an experimentally imposed range of prey densities. Spiders are generalist arthropod predators that are food-limited, and previous studies have established that a bottom-up linkage exists between detrital food webs and spider assemblages. We conducted our study in a no-till soy agroecosystem where we manipulated densities of spider prey through detrital additions. We added detritus at four levels (control, low, medium, high) at early and mid-season. We sampled insects and spiders at early, mid-, and late season. Insects were collected on sticky traps, and using Berlese funnels to extract insects from litter. Spiders were collected by destructive sampling of litter and soil. Preliminary results suggest that insect abundance did not respond to detrital subsidies. Regression with data from sticky traps suggests that overall spider abundance, and wolf spiders (Lycosidae) in particular, responded weakly to prey availability mid-season. ANOVA results show that time of sampling affected overall spider abundance while productivity did not. There was similarly no effect of time on prey abundance. Results of non-metric multidimensional scaling analysis at the family level suggest that community structure was also influenced by sampling time but not prey. Our results suggest that time since planting, which is indistinguishable from seasonal shifts, had a stronger influence on spider abundance and community structure than productivity.

Key words: biodiversity, productivity, spiders, insects