Daniel A. Soluk

Estimating the prevalence and strength of non-independent predator effects

Understanding whether multiple predator species have independent effects on shared prey is critical for understanding community dynamics. We describe the prevalence and strength of non-independence between predators by quantifying the prey’s risk of predation and the degree to which it deviates from the risk predicted from a null model of independent predator effects. Specifically, we document how frequently non-independent effects occur among ten different multiple predator combinations with mayfly larvae as prey. These predator combinations vary both predator density and predator species richness. Overall, the predator effects were non-independent and translated to an average of 27% fewer prey being consumed compared to independent predator effects. Non-independence of this magnitude is likely to have population level consequences for the prey and influence the distribution or prey preference of predators. Closer inspection shows that much of the risk reduction in this system is weak, to the point of being indistinguishable from independent predator effects, while few effects are strong. This pattern of many weak interactions and few strong ones parallels the pattern of interaction strengths documented previously in intertidal communities. Consequently, understanding strong interactors in multiple predator systems may help us understand the importance of a species.

Nonlethal Tissue Sampling Techniques and Microsatellite Markers Used for First Report of Genetic Diversity in Two Populations of the Endangered Somatochlora hineana (Odonata: Corduliidae)

ABSTRACT Techniques for obtaining DNA noninvasively or nonlethally are highly desirable in molecular genetic studies of protected species, and several advances have been made in these types of sampling and extraction techniques. Insects present a unique set of difficulties in this regard that are not present when working with most vertebrates. This study evaluated the effectiveness of several nonlethal sampling techniques for larval and adults of the federally listed endangered dragonfly Somatochlora hineana (Williamson) (Odonata: Corduliidae). Fecal pellets and shed exuviae from captive S. hineana larvae did not provide high enough quality DNA for microsatellite analyses. Invasive, but nonlethal, wing clips from adults and tarsi from larvae provided high-quality DNA that amplified 10 microsatellite markers for this species. Ten loci were polymorphic in 94 specimens with four to 14 alleles per locus. Two populations in WI had average observed heterozygosity of 0.47, which is within the range reported for other odonates. Our sampling techniques and these new microsatellite markers provide an essential tool for determining the genetic structure of S. hineana populations throughout its range.