01956nas a2200265   4500008004100000020001400041245008600055210006900141260001200210300001600222490000700238520123500245653001201480653001201492653001401504653002101518653002601539653001701565653003101582653001301613653001401626653000901640100001701649856002401666       2007                        eng d  a0012-965800aDefining and measuring the impact of dynamic traits on interspecific interactions0 aDefining and measuring the impact of dynamic traits on interspec  c2007///  a2555 - 25620 v883 aTrait- and density-mediated indirect effects describe different pathways by which indirect interactions in food webs are propagated from one species to another, through changes in intermediate species. A series of articles in Ecology has progressively altered the original definitions of "trait-mediated’’ to the point where understanding is being impeded. The most recent of these articles are two meta-analyses that use "trait-mediated’’ to describe the demographic costs to a prey species of employing anti-predator defenses. These same articles introduce a companion term, "density-mediated interaction,’’ apparently to describe direct and indirect interactions that only involve changes in population density due to consumption by predators. This new terminology has many disadvantages, including ( 1) using a general term for a relatively narrow group of processes; ( 2) using "mediated’’ in a manner inconsistent with existing terminology; ( 3) confusing the accepted definitions of different types of indirect effects; and ( 4) providing a highly incomplete measure of the impact of behavior on the predator - prey interaction. Solutions to these problems and the meaning of the meta-analyses are discussed10adefense10aecology10afood webs10aindirect effects10aindirect interactions10ainteractions10aINTERSPECIFIC INTERACTIONS10aPREDATOR10apredators10aPREY1 aAbrams, P.A.  uISI:00025071420001602585nas a2200229   4500008004100000020001400041245009500055210006900150260001200219300001600231490000700247520197100254653001302225653001702238653001402255653001302269653001402282653000902296653000902305100001702314856002402331       2008                        eng d  a0012-965800aMeasuring the impact of dynamic antipredator traits on predator-prey-resource interactions0 aMeasuring the impact of dynamic antipredator traits on predatorp  c2008///  a1640 - 16490 v893 aThis article analyzes the limitations of the most widely used method for quantifying the impact of dynamic antipredator traits on food chain dynamics and discusses alternative approaches. The standard method for a predator-prey-resource chain estimates the effects of the prey’s defensive behavior by comparing population densities or fitness measures in a ’’predator cue’’ treatment to those in a no-predator treatment. This design has been interpreted as providing a measure of the ’’nonconsumptive effect’’ of the predator on the prey and the ’’trait-mediated indirect effect’’ of the predator on the resource. Other approaches involve measurements of the impact of the behavior in the presence of functional predators. The questions addressed here are: (1) How consistent are the results of different approaches? (2) How time-dependent are their results? (3) How well do they correspond to theoretical measures of effect size? (4) How useful are the measurements in understanding system dynamics? A model of a tritrophic system in which the prey species adjusts a defensive trait adaptively is used to evaluate the experimental designs. Measures of changes in prey fitness or population density in a cue treatment generally include offsetting effects of the cost of the behavior and the benefit of more resources. This means that the sign of the effect, as well as its magnitude, may change depending on when the experiment is terminated. Because predation is not present in the cue treatment, few conclusions can be drawn about the impact of the behavior on population densities or fitness of the prey in a natural setting with predators. Cue experiments often do not accurately separate trait-mediated from density-mediated effects on the resource. Most scalar measures of effects are sensitive to experimental duration and initial densities. Use of a wider range of experimental designs to measure trait-related effects is called for10aDYNAMICS10ainteractions10apredation10aPREDATOR10apredators10aPREY10aSIZE1 aAbrams, P.A.  uISI:000256540300017