PARENT SESSION
Contributed Oral Session 160: Biodiversity: Communities
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Biodiversity as both a cause and consequence of resource abundance.
Cardinale, Bradley*,1, 2, Weis, Jerome1, 2, Tilmon, Kelley2, Forbes, Andy2, Ives, Anthony2, 1 University of California-Santa Barbara, Santa Barbara, CA, 931062 University of Wisconsin-Madison, Madison, WI, 53706
ABSTRACT- It has long been recognized that the diversity of species in a community is closely tied to the availability of biologically limiting resources such as water, light, nutrients, or prey. Studies have tried to understand this relationship by focusing either on how diversity responds to resource abundance, or alternatively, how resource abundance responds to consumer diversity. These contrasting perspectives have led to debate over whether diversity is the cause or the consequence of resource availability. Here we explore one potential resolution of this debate with an experiment that examines how causal relationships between consumer diversity and prey resource abundance can change as a function of spatial scale. Using a split-plot experimental design, we manipulated the abundance of prey (aphids) in discrete habitat patches (alfalfa) within field enclosures to asses how variation in prey abundance affects the number of co-occurring predator species (ladybird beetles). At the same time, we manipulated predator species richness within enclosures to examine how consumer diversity impacts system-wide prey abundance. At the smaller scale of habitat patches, consumer diversity was an increasing function of resource abundance because aggregation of predators in patches of high prey density led to more predator species being observed in any fixed sampling effort. In contrast, at the larger scale of whole enclosures prey abundance was a function of consumer diversity because predator species in the colonist pool exhibited a non-additive, antagonistic interaction when together in the same system. These results demonstrate that it is possible for species diversity and resource abundance to exhibit reciprocal causality at the same time in the same system. Because the mechanisms operating in our study are well known, we suggest that a better understanding of observed relationships between biodiversity and community-level properties may be possible by considering the scale-dependent nature of causal associations.
Key words: species richness, ecosystem functioning, predator-prey dynamics, spatial scale