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The effect of habitat complexity on interactions within a terrestrial food web.
Harvey, Chad*,1, 2, Eubanks, Micky1, 1 Auburn University, Auburn, AL2 University of Wisconsin-Madison, Madison, WI
ABSTRACT- Habitat complexity and species diversity have long been believed to affect interactions within food webs. It has even longer been believed that species diversity and the strength and number of interactions among species are related. Although appealing to many ecologists, and highly significant to biological control, there are few studies that have experimentally tested these ideas in conjunction. The focus of this study was to experimentally determine the effect of habitat complexity on the number and strength of natural enemy (NE)- herbivore interactions, the number of interactions among NE, and the effect of interactions among NE on herbivore suppression in collards (Brassica oleracea). Based on interaction models for the 11 most abundant herbivore, we found that habitat complexity did not affect the number of NE-herbivore interactions, nor did it affect the strength of NE-herbivore interactions (paired t = 2.31, df = 10; p > 0.05). Furthermore, there was no relationship between the number of NE attacking a herbivore and the mean strength of NE-herbivore interactions (top-down control) (R = 0.41, df = 10, p > 0.05). Habitat complexity significantly affected the number of interactions among NE associated with two herbivores, however, there was no correlation between the number of interactions among NE and the strength of NE-herbivore interactions (R = 0.29, df = 10, p > 0.05, simple habitat; R = -0.53, df = 10, p > 0.05, complex habitat). The results of this study suggest that interactions among NE and herbivores and interactions among NE do not respond to changes in habitat complexity as predicted by classical community ecology theory. This study highlights that the basis of our knowledge of interactions within food webs is highly theoretical and more empirical studies need to be performed before we can identify the ecosystem characteristics affecting NE assemblages and top-down control.
Key words: species diversity, top-down control, intraguild interactions, interaction strength