Asymmetric interactions and their consequences for vital rates and dynamics: the smaller tea tortrix as a model system.

Asymmetric interactions among conspecifics can have diverse effects on population dynamics including stabilization, generation of cycles, and induction of chaotic fluctuations. A difficult challenge, however, is establishing the link between the impact of asymmetric interactions on life history and the consequences for population dynamics. The smaller tea tortrix, Adoxophyes honmai, is a good example. Larval instars differ dramatically in size and have a tendency for cannibalism, which suggests the potential for strong asymmetric interactions among instars. Yet whether these asymmetries have any role in generating the distinct single-generation cycles observed in the field and laboratory is unclear. Here we report on the development of a new experimental approach to characterize the impact of asymmetric interactions on life history that can be directly embedded into stage-structured population models. The experiments use donor-replacement protocols in which focal individuals are challenged to complete their life cycles in competitive environments where the instar and density of the competitors are held constant. The experimentally derived interaction surface contains all the information about stage-specific interactions and provides a straightforward framework for evaluating alternative ways of abstracting the interactions into traditional models of asymmetric competition. Working with the smaller tea tortrix, we found strong evidence of asymmetric interactions and identified critical "tipping points" in the competitive environment that strongly affected survival but not development. We incorporated the experimentally derived interaction surface into a stage-structured population model and found that despite the strong impact that asymmetric interactions have on tea tortrix life history, they do not scale-up to impact the predicted asymptotic population dynamics. Comparing these dynamics with two abstracted models of stage-structured interactions revealed that while the quantitative details of the emergent dynamics depends on the shape of the interaction surface, the qualitative features, such as the emergence of single-generation cycles and rapid synchronization of development among individuals, are pleasingly robust.

Alzheimer's disease and eyeblink conditioning: 750 ms trace vs. 400 ms delay paradigm.

Patients with probable Alzheimer's disease (AD) and hippocampal disruption are severely impaired in eyeblink classical conditioning (EBCC) in the 400 ms delay paradigm. Hippocampectomized rabbits are not impaired in the delay paradigm but perform poorly in the trace paradigm. It was anticipated that probable AD patients would be severely impaired in the 750 ms trace paradigm. In Study 1, probable AD patients were significantly impaired in the trace EBCC paradigm, but the sensitivity of the test was poorer than for the delay paradigm. In Study 2, probable AD patients tested in trace were tested in the delay paradigm 4 months later. Sensitivity for AD was also better for the delay paradigm. Rabbits and humans show behavioral parallels in the 400 ms delay paradigm but not in the 750 ms trace paradigm. The 400 ms delay EBCC paradigm was superior to the 750 ms trace paradigm for the detection of AD.